The technology of forming composite materials is the basis and condition for the development of the composite materials industry. With the expansion of the field of application of composite materials, the composite material industry has developed rapidly, some molding processes have been improved day by day, new molding methods have appeared. At present, there are more than 20 molding methods for polymer materials. composite materials, and they are successfully used in the industry.Productions such as:(1) hand molding process - wet molding method;(2) injection molding process;( 3) resin transfer molding technology (RTM technology); (4) pressure bag molding (pressure bag method);(5) vacuum bag molding;(6) autoclave molding technology;( 7) hydraulic molding technology (8) Thermal expansion molding technology;(9) Sandwich molding technology;(10) Molding material production process;(11) ZMC molding material. injection molding technology; >(12) pressing process;(13) laminate production technology;(14) coil tube forming technology;(15) fiber winding forming technology;< br> (16) Continuous plate manufacturing process;(17) Casting molding technology;(18) Pultruding molding process;(19) Continuous winding tube manufacturing process;(20) Woven fabric production composite materials. (21) Thermoplastic molding compound production technology and cold forming process;(22) Injection molding process;(23) Extrusion molding process;(24) Centrifugal casting Pipe molding process;< br>(25) other molding methods.
Depending on the selected polymer matrix material, the above methods are applicable to the production of thermoset and thermoplastic composite materials, and some processes are applicable to both. Features of the composite material molding process: Compared with other material processing processes, the composite material molding process has the following characteristics: (1) Material production and product molding are performed simultaneously. The composite materials process is also a product forming process. The characteristics of the material must be designed according to the requirements for the use of the product, so in the selection of material, the development of the ratio, the determination of the fiber stacking and the forming method, the physical and chemical properties, the structural form and the quality requirements of the appearance. the product must be satisfied. (2) Product molding is relatively simple. The resin matrix of conventional thermosetting composite materials is a flowing liquid before molding, and the reinforcing material is soft fiber or fabric. Therefore, the production of composite products with these materials requires moreMore procedures and equipment than other materials. The material is much simpler, and for some products only one set of molds is required.
1. Contact low pressure casting process
The low-pressure contact molding process is characterized by manual placement of reinforcement, soaking of resin, or simple placement of reinforcement and resin with tools. Another feature of the low-pressure contact molding process is that the molding process does not apply molding pressure (contact molding), or only low molding pressure is applied (pressure of 0.01-0.7 MPa is applied after contact molding, and the maximum pressure does not exceed 2.0 MPa).
The low pressure contact molding process is to first form the material into a desired shape on a female, male or counter mold, then heat or cure at room temperature, and then undergo post demoulding post-mould processing to obtain a product. Such molding processes include hand molding, injection molding, press bag molding, resin transfer molding, autoclave molding, and thermal expansion molding (low pressure molding). The first two of them are contact molding.
Among the low pressure contact molding processes, the hand molding process is the first invention in the production of polymer-based composite materials and has the widest scope. Other methods are the development and improvement of the hand laying process. The biggest advantage of the contact molding process is simple equipment, wide adaptability, less investment and quick results. According to recent statistics, the low pressure contact molding process still occupies a large share in the industrial production of composite materials in various countries, for example, 35% in the United States, 25% in Western Europe, 42% in Japan, and 75% in China. This demonstrates the importance and indispensability of the low pressure contact molding process in the industrial production of composite materials, and it is a technological method that will never fall into disrepair. But its biggest disadvantage is low production efficiency, high labor intensity and poor product repeatability.
1. Raw Materials Raw materials undergoing low pressure casting include reinforcing materials, resins and auxiliary materials. (1) Reinforcing materials Requirements for contact molding of reinforcing materials: ①Reinforcing materials are easily impregnated with resin; ②Have sufficient deformability to meet the requirements of molding complex shapes; Meet the physical and chemical performance requirements of the product use conditions, ⑤ reasonable price (as cheap as possible), abundant sources. To the reinforced materials used for contact fformations include fiberglass and fabric from it, carbon fiber and fabric from it, aramid fiber and fabric from it, etc.
(2) Main material
Low-pressure contact molding requirements for matrix materials: ① The fiber-reinforced material is easy to impregnate under the condition of hand laying, easy to remove air bubbles, and has strong adhesion to the fiber; ② It can gel and harden at room temperature and needs to shrink Small, less volatile substance; ③Suitable viscosity: usually 0.2-0.5 Pa·s, no adhesive flow; ④ Non-toxic or low toxicity; ⑤Reasonable price, guaranteed source. Resins commonly used in manufacturing include: unsaturated polyester resins, epoxy resins, phenolic resins, bismaleimide resins, polyimide resins, etc.
Performance requirements for several resin contact molding processes:
Resin performance requirements for molding methodsGelcoat production
1. Does not flow during molding, easy to defoam2. Uniform color tone, non-floating color3. Fast curing, no wrinkling, good adhesion to laminated resin
1. Good impregnation, easy fiber absorption and easy removal of air bubbles2. Fast curing after laying, less heat generation and low shrinkage3. Less volatile matter and the surface of the product is not sticky >4. Good adhesion between coats
1. Ensure compliance with hand molding requirements.2. Thixotropy recovers earlier.3. Temperature has little effect on resin viscosity.4. The resin has a long reservoir. life time. After adding the accelerator, the viscosity should not increase
1. Good wettability, easy fiber absorption and easy removal of air bubbles2. Fast curing, less heat during curing3. Poor adhesive flow, strong interlayer adhesion
(3) Auxiliary Materials Auxiliary materials in the contact molding process mainly belong to fillers and colorants, while hardeners, thinners, hardeners, etc. belong to the resin matrix system.
2. Mold and release agent (1) Mold The mold is the main equipment in various contact molding processes. The quality of the mold directly affects the quality and cost of the product, so it must be carefully designed and manufactured.
When designing a mold, the following requirements must be fully considered:
①Meet the product design precision requirements, the mold size is accurate and the surface is smooth;
②There must be sufficient strength and rigidity;
④Sufficient thermal stability;
⑤Light weight, sufficient materials and low costb. Mould structure Contact casting molds are divided into three types: mold, mold and counter mold. No matter which mold, it can be designed as a whole or assembled mold according to the size and molding requirements.
Mold material When turning out the mold material, the following requirements must be observed:
①It can meet the requirements for dimensional accuracy, appearance and service life of the product;
②The material of the mold must have sufficient strength and rigidity so that the mold cannot be easily deformed and damaged during use;
③The resin does not corrode or affect the curing of the resin;
④Good heat resistance, when the product is cured and cured by heating, the mold is not deformed;
⑤Easy to manufacture and dismantle;
⑥Reducing mold weight and simplifying production;
⑦The price is cheap and the materials are easy to get. Materials that can be used as hand molds include: wood, metal, gypsum, cement, low melting metals, rigid foam and fiberglass reinforced plastics, etc.
Basic requirements for a release agent:
1. Does not cause corrosion of the mold, does not affect the curing of the resin, and the adhesion to the resin is less than 0.01MPa;
②Short film forming time, uniform thickness and smooth surface;
③It is safe to use and has no toxic effect;
④Heat resistance, can be heat cured;
⑤Easy to operate and cheap.
Lubricants for the contact molding process mainly include film release agents, liquid release agents, ointments and wax release agents.
Manual laying process
The manual laying procedure is as follows:
(1) Preparing for production The size of the hand laying area should be determined according to the product size and daily output. The area should be clean, dry and well ventilated. The air temperature should be maintained at 15-35° C. In between, the post-treatment and repair area should be equipped with ventilation, dust removal and water spraying facilities.
Preparation of the mold Preparation includes cleaning, assembly and application of a release agent.
When preparing resin adhesive, two points should be paid attention to: ① prevent air bubbles from entering the adhesive; ② The amount of glue should not be too large, and each dose should be used up before the resin turns into a gel. Reinforcing material preparation The types and characteristics of reinforcing materials are selected according to the design requirements.
(2) Sticking and curing Layering paste system There are two types of manual layering paste system: wet method and dry method:
①Dry laying uses pre-impregnated fabric as raw material. First, the pre-examined material (fabric) is cut into bad material according to the pattern, heated and softened when laying a layer, and then attached to mold layer by layer, and reverse attention to getting rid of interlayer air bubbles to make it tight. This method is mainly used for autoclave pressing and bag pressing.
②Wet lamination. Dip the reinforcing material directly into the mould, stick it to the mould, layer by layer, and remove air bubbles to make it tight. Typically, the manual laying process uses this method to lay layers. Wet laying is divided into gelcoat layer paste system and structural layer paste system.
Hand tools for forming Hand tools for forming are of great importance to ensure product quality. There are wool rollers, bristle rollers, spiral rollers, electric saws, electric drills, grinders and polishers, etc. The curing of the cured products is divided into two stages: curing and aging: it usually takes 24 hours from gel to triangularization, and the curing rate at this time reaches 50-70% (Bacol hardness 15), and it can be demoulded. Curing under natural environmental conditions for 1-2 weeks can give the product mechanical strength, which is called curing, and its cure rate can reach more than 85%. Heating can speed up the curing process. For polyester FRP, heat at 80°C for 3 hours. For epoxy FRP, the post-curing temperature can be controlled within 150°C. There are many heating and curing methods: small and medium-sized products can be heated and cured in a curing oven, and large-sized products can be heated using in-mould heating or infrared heating.
(3) demolding and trimming demoulding and demoulding to make sure the product is not damaged. There are several demoulding methods as follows: ① Demoulding Pre-insert the ejector into the mould, and turn the screw to eject the product during demolding. ②Pressure demoulding The mold has an inlet for compressed air or water. When demolding, press compressed air or water (0.2MPa) between the mold and the product, and simultaneously tap with a wooden and rubber mallet to separate the product from the mold . ③Demolition of large items (such as boats) can be done using tools such as jacks, cranes, and hardwood wedges. ④ Complicated products can be manually dismantled by sticking two or three layers of FRP on the mold, peeling them off the mold after curing, and then placing them in the mold to continue gluing to the specified thickness.After curing, they are easy to remove from the mold. mold down. Cropping There are two types of cropping: dimension cropping and defect correction. ①Cut to size After forming the product, cut off the excess part according to the design size; ②Removal of defects includes repairing perforations, air bubbles, repairing cracks, reinforcing holes, etc.
Injection molding technology
Injection molding technology is an improvement of manual molding with a semi-mechanized degree. Injection molding technology accounts for a relatively large share of composite casting processes, such as 9.1% in the US, 11.3% in Western Europe and 21% in Japan. At present, the injection molding machines used in China are mainly imported from the United States.
(1) Principle, advantages and disadvantages of the injection molding process In the injection molding process, two kinds of polyester mixed with initiator and accelerator are sprayed on both sides of the spray gun respectively and simultaneously. , the chopped fiberglass roving is formed by spraying from the center of the spray gun to evenly mix it with the resin and apply to the mold. When it is applied to a certain thickness, it will be roller compacted to make the fiber impregnated with resin, remove air bubbles, and after curing, form a finished product.
Advantages of spray molding: ① using glass roving instead of fabric, which can reduce material costs; ② production efficiency is 2 to 4 times higher than manual molding; ③ product integrity is good, no seams, interlayer cutting High cutting strength, high resin content, good corrosion resistance and leakage resistance; ④ It can reduce the consumption of flash, cutting cloth and residual adhesive; ⑤The size and shape of the product is not limited.
Its disadvantages: ① high resin content, low product strength; ② the product can only be smooth on one side; ③ pollute the environment and harm the health of workers. The injection molding capacity is up to 15 kg/min, so it is suitable for making large size cases. It is widely used for processing bathtubs, car lids, toilet bowls, car body components and large-sized embossed products, etc.
(2) Preparation of production Site In addition to fulfilling the requirements of the manual laying process, special attention should be paid to the ventilation of the environment in the injection molding site. Depending on the size of the product, the operating room can be built into a closed type to save energy. Material preparation The raw materials are mainly resin (mainly unsaturated polyester resin) and untwisted glass fiber roving. Preparing the mold Preparing includes cleaning, assembling and applying a release agent.
Equipment for injection molding Machines for injection moldingIt is divided into two types: with pressure tank and with pump: ① In the pump type adhesive injection molding machine, the resin initiator and the accelerator are respectively pumped into the static mixer. After complete mixing, it is sprayed from a spray gun, which in the gun is called a mixed type. Its components are pneumatic control system, resin pump, additive pump, mixer, spray gun, fiber cutting injector, etc. The resin pump and the auxiliary pump are rigidly connected by the rocker arm, and adjusting the position of the auxiliary pump on the rocker arm can ensure the proportion ingredients. Under the action of an air compressor, the resin and additives are evenly mixed in the mixer, and through the atomizer they form drops that are continuously sprayed onto the surface of the mold with chopped fibers. This inkjet machine only has one glue gun, which is simple in structure, light in weight and less initiator waste, however, due to the internal agitation of the system, it must be cleaned immediately after use to prevent clogging of the jet. ②Pressure tank glue supply machine is designed to supply the resin glue solution into the pressure tank respectively, and depends on the pressure of the gas entering the tank, so that the glue solution enters the atomizer and sprays continuously. The plant consists of two resin tanks, pipes, valves, nozzles, fiber cutting injectors, carts and supports. During operation, turn on the compressed air source, so that the compressed air enters the resin tank, fiberglass cutter and spray gun through the gas-water separator, so that the resin and fiberglass are continuously sprayed from the spray gun, the resin is sprayed, and the fiberglass is dispersed, well mixed and poured into shapes. This type of sprayer is that the resin is mixed outside the spray gun, so it is not easy to clog the nozzle of the spray gun.
(3) Injection molding process control Selection of injection molding process parameters: ①Resin content In injection molded products, the resin content is controlled at about 60%. ② Atomization pressure When the resin viscosity is 0.2 Pa·s and the pressure in the resin tank is 0.05-0.15 MPa, the atomization pressure is 0.3-0.55 MPa to ensure that the components are evenly mixed. ③Attachment angle of the sprayer Mixed resin sprayed at different angles has different crossing distances. Generally, the adjoining angle is 20°, and the distance between the sprayer and the mold is 350-400mm. To change the distance, the included angle of the high-speed gun is necessary to ensure that the components cross and mix close to the surface of the mold so that the adhesive does not fly away.
Injection molding precautions: ①The ambient temperature must be kept atnot (25±5)℃, if it is too high, it will easily cause the spray gun to clog; if it is too low, mixing will be difficult. uneven and curing will be slow; ②The injection system must not have moisture, otherwise it will affect the quality of the product; ③Before molding, first spray a layer of resin on the mold, and then spray a mixed layer of resin fiber; ④Adjust the air pressure before injection molding to control the resin and glass fiber content; ⑤The sprayer must be uniform. Move to prevent skipping spray, do not follow the arcs, the overlap between two rows is less than 1/3, and make sure the coating is even and the thickness is uniform; ⑥After applying one layer, immediately compact it with rollers, paying attention to edges, corners and unevenness. On the surface, make sure that each layer is smooth and air bubbles are removed to prevent burrs on the fibers; ⑦After each layer is sprayed, it must be checked, and the next layer must be sprayed after passing the passage; ⑧The last layer should be sprayed thinner to make the surface smooth; ⑨ Clean the atomizer immediately after use to prevent curing and damage to resin equipment.
Resin transfer molding
Resin transfer casting is called RTM (resin transfer casting). RTM began in the 1950s and is a closed-mould molding technology enhanced by a hand-stacked molding process that allows products to be produced on both sides. There are also Resin Injection technology and Pressure Infection technology, which belong to this category of processes in foreign countries. The basic principle of TM is to place fiberglass reinforced material in a closed mold cavity, inject resin adhesive into the mold cavity under pressure, impregnate the fiberglass reinforced material, and then solidify and release the molded article. In the previous level of research, the research and development direction of RTM technology will include microcomputer-controlled injection unit, reinforced material pre-molding technology, low-cost mold, fast resin curing system, process stability and adaptability, etc.
RTM molding technology features: ①Can produce products with two cardinal directions; ②High molding efficiency, suitable for medium batch production of fiberglass products (within 20,000 pieces per year); ③RTM is a closed-mould operation, which does not pollute the environment without harming the health of workers; ④Reinforcement materials can be placed in any direction, and are easy to lay according to the strength state of the product; ⑤Low consumption of raw materials and energy;
RTM technology has a wide range of applications and is widely used inconstruction, transport, telecommunications, healthcare, aerospace and other industries. Designed products include: automotive body and components, recreational vehicle components, propellers, 8.5m wind turbine blades, fairings, machine covers, bathtubs, showers, pool boards, seats, water tanks, telephone booths , cables, small yachts. , etc.
(1) RTM process and equipment The whole production process of RTM molding process is divided into 11 processes. The operators, tools and equipment of each process are fixed in place, and the mold is transported on a trolley, and it goes through each process in turn, to implement the stream operation. The assembly line mold cycle time mainly reflects the production cycle of the product. Small products usually only need ten minutes, while the production cycle of large products can be controlled within 1 hour. Molding Equipment RTM's molding equipment is mainly resin casting machines and molds.
① Village Resin Injection Machine Village resin injection machine consists of resin pump and injection gun. The resin pump is a set of reciprocating piston pumps with an air pump on top. When the compressed air makes the piston of the air pump move up and down, the resin pump quantitatively pumps the resin from the cylinder to the resin storage through the flow regulator and filter, and the side arm moves the catalyst pump to quantitatively supply the catalyst. in storage. Compressed air fills two reservoirs, creating a buffer force against pump pressure to ensure a constant flow of resin and catalyst to the injection tip. Behind the injection gun, there is a static turbulent mixer, which can evenly mix the resin and catalyst in an airless state, and then inject the mold through the gun. Behind the mixer, there is a cleaning agent inlet, which is connected with a solvent. with a pressure of 0.28Mpa. The tank is connected, when the machine is used up, turn on the switch, the solvent will be sprayed automatically, and the injection gun will be cleaned.
②Mold RTM is divided into three types: FRP mold, FRP surface coated metal mold and metal mold. FRP molds are easy to make and relatively cheap. Polyester FRP molds can be used 2000 times, while epoxy FRP molds can be used 4000 times. The metallized FRP mold can be used over 10,000 times. Metal molds are rarely used in the RTM process. Generally speaking, the cost of an RTM mold is only 2% to 16% of the cost of an SMC.
(2) RTM Raw Material Raw materials used in RTM include resin system, reinforcing material and filler. Resin system The resin used in the RTM process is mainly unsaturated polyester resin. Reinforcing material As a rule, arthe reflective material RTM is mainly glass fiber, and its content is from 25% to 45% (weight ratio); commonly used reinforcing materials are fiberglass continuous mat, composite mat and square cloth. Fillers Fillers are very important to the RTM process, not only to reduce costs and increase productivity, but also to absorb heat during the exothermic stage of resin curing. Commonly used fillers are aluminum hydroxide, glass beads, calcium carbonate, mica, etc. Its dosage is from 20% to 40%.
Bag pressure method, autoclaving method, hydraulic boiler method and
Bag pressure method, autoclaving method, hydraulic kettle method and thermal expansion method are collectively referred to as low pressure molding process. The molding process consists of hand-laying reinforcing material and resin (including prepreg material) on the mold layer by layer according to the design direction and order. receive products. The difference between the four methods and the hand lay-up process is only the pressure curing process. Therefore, these are just improvements to the hand lay-up process to increase the compactness and strength of the product interlayer bond. Using high-strength fiberglass, carbon fiber, boron fiber, aramid fiber and epoxy resin as raw materials, high-performance low-pressure injection molded composite products have found wide application in aircraft, rocket, satellite and spacecraft. . Such as aircraft doors, fairings, side fairings, brackets, wings, tails, bulkheads, wall panels and stealth aircraft, etc.
(1) Bag pressing method Bag pressing is an uncured product that is placed by hand, and gas or liquid pressure is applied to it through a rubber bag or other elastic material to make its product tight under pressure. Advantages of bag pressing method: ① Both sides of the product are smooth; ② Can be adapted for polyester, epoxy and phenolic resin; ③ The weight of the product is higher than hand molding. . Bag compression molding is divided into two types: pressure bag method and vacuum bag method: ① Pressure bag method Pressure bag method is to put the uncured hand molded product into the rubber bag, fix the lid and then pass through compressed air or steam (0.25 ~ 0.5 MPa) to make the product harden under hot pressing conditions. ②Vacuum bag method This method is to make an uncured product by hand and cover it with a layer of rubber film. The product is placed between the rubber film and the mold, and the periphery is sealed, and the vacuum (0.05 -0.07MPa) andIt is used to form air bubbles in the product and exclude volatile substances. The vacuum bag forming method is only used for wet forming polyester and epoxy composite products due to the low vacuum pressure.
(2) Autoclaving and hydraulic boiler method
Both autoclave and hydraulic autoclave methods are a process in which hand-laid, uncured items are heated and pressurized with a compressed gas or liquid in a metal container to cause them to harden and form. Autoclave Method The autoclave is a horizontal metal pressure vessel, hand-packed uncured product is added to a sealed plastic bag, vacuumed, and then together with the mold with a cart and steam (pressure 1.5-2.5Mpa), and also vacuumed, pressurize and heat the product, release air bubbles and cause it to solidify under hot pressing conditions. It combines the advantages of the pressure bag method and the vacuum bag method with a short production cycle and high product quality. The autoclave method can produce high-quality, high-performance composite products of large sizes and complex shapes. Product size is limited by autoclave. At present, the largest autoclave in China has a diameter of 2.5 m and a length of 18 m. The products developed and applied include wings, tail, satellite reflectors, missile return parts, airborne sandwich structure fairing, etc. d. The biggest disadvantages of this method are high equipment costs, high weight, complex design and high cost. Hydraulic Boiler The hydraulic boiler is a closed pressure vessel with a smaller volume than an autoclave. It is positioned vertically. During production, pressurized hot water is supplied to heat and pressurize uncured hand laid products to harden them. The pressure of the hydraulic boiler can reach 2 MPa or more, and the temperature can reach 80-100°C. Oil carrier, heat up to 200°C. The products produced by this method are dense and the cycle is short. The disadvantage of the hydraulic boiler method is that the equipment investment is large.
(3) Thermal expansion molding Thermal expansion molding is a process used to produce high-performance hollow thin-walled composite materials. Its working principle is to use molding materials with different expansion ratios and use the extrusion force generated by different thermal volumetric expansion to apply pressure to the product. The thermal expansion male mold is a high expansion silicone rubber, and the female mold is a small metal material.by their coefficient of expansion. The uncured product, placed by hand, is placed between the male and female molds. Due to the different coefficients of expansion of male and female molds when heated, there is a huge difference in deformation, so the product hardens under hot pressure.
2. Manufacturing technology of sandwich structures
Laminated structures are typically composite materials made up of three layers of material. The top and bottom layers of multi-layer composite materials are high-strength, high-modulus materials, and the middle layer is thicker lightweight materials. FRP sandwich structure is actually a recombination of composite materials and other lightweight materials. The sandwich structure is used to improve the efficiency of materials and reduce the weight of the structure. In the case of a beam-and-slab element, during operation, it must firstly meet the requirements of strength, and secondly, must meet the requirements of rigidity FRP material characteristics - high strength Low module. Therefore, when the beam and slab are made of the same FRP material, the deflection is often large when the strength requirement is met. If the calculation is made according to the allowable deflection, the strength will be greatly exceeded, resulting in waste. This contradiction can only reasonably be resolved by adopting the sandwich structure design. This is also the main reason for the development of multilayer structures.
With high strength, light weight, high rigidity, corrosion resistance, electrical insulation and microwave transmission, FRP sandwich structure is widely used in the aviation industry. And aerospace aircraft, rockets, spacecraft and models, roof panels can greatly reduce the weight of buildings and improve the use of features. The transparent fiberglass sandwich panel is widely used for roof lighting of industrial plants, large public buildings and greenhouses in cold regions. In the field of shipbuilding and transportation, FRP sandwich structures are widely used in many components of FRP submarines, minesweepers and yachts. Street crossing pedestrian bridges, road bridges, automobiles and train insulation products designed and manufactured in my country use FRP sandwich structures to meet the multi-functional requirements of light weight, high strength, high rigidity, heat insulation and heat preservation. In the lightning protection coating that requires microwave transmission, FRP sandwich structure has become a special material that cannot be compared with other materials.
1. Types and characteristics of FRP sandwich structure According to the different types and shapes of the main materials used in sandwich structures, FRP sandwich structures are divided into: foam sandwich structure, sandwich structure with honeycomb coresand, a trapezoidal plate. sandwich structure, rectangular sandwich structure and round sandwich structure.
(1) Foamed Resin Sandwich Structure Foamed plastic sandwich structure uses glass fiber reinforced plastic sheet as the cladding (panel) and foamed plastic as the sandwich layer. and foam sandwich parts with strong layer bonding, low stresses and high thermal insulation requirements, such as aircraft tails, thermal insulation and ventilation ducts and templates, etc.
(2) Honeycomb Sandwich Structure Honeycomb sandwich structure uses fiberglass reinforced plastic sheet as shell and honeycomb material (fiberglass honeycomb, paper honeycomb or other cotton cloth and aluminum honeycomb, etc.) as sandwich. layer. The honeycomb sandwich structure has light weight, high strength and high rigidity. It is mainly used for structural members with large structural dimensions and high strength requirements, such as fiberglass bridge carrier plate, spherical roof structure, fairing. , reflective surface, refrigerator floor and body. Wait.
(3) Trapezoidal and rectangular structure of the leading working layer The panel (shell) of this leading working layer structure is a thin glass fiber reinforced plastic plate, and the sandwich layer is a trapezoidal glass fiber reinforced plastic plate or a rectangular plate. This type of sandwich structure has a strong directionality and is only suitable for high-strength flat plates, not for curved products.
(4) Round Sandwich Structure The FRP sheet is used as the skin, and the FRP ring is used as the sandwich layer. This type of sandwich structure is characterized by less base material consumption, relatively high strength, and no direction of force on the plate. It is most suitable for transparent FRP sandwich panels for illumination, with the characteristics of less shading and high light transmission.
2. Manufacturing technology of honeycomb sandwich structure(1) Honeycomb type The strength of honeycomb depends on the choice of raw materials and the geometric shape of honeycomb. According to the geometric shape of the projection plane, honeycomb sandwich material can be divided into hexagonal, diamond-shaped, rectangular, sinusoidal and hexagonal reinforced, etc. Among these multilayer honeycomb materials, hexagonal reinforced strip has the highest strength, followed by square honeycomb. Since ordinary hexagonal honeycombs are easy to manufacture, save materials and have high strength, they are most widely used.
(2) There are many types of cladding and core materials for sandwich structure raw materials. If aluminum and titanium alloys are used as cladding and core materials, it is called metal sandwich structure.glass fiber reinforced. plastic sheets, wood plywood and inorganic. The board is made of composite material as the skin, and the sandwich material is made of fiberglass honeycomb, paper honeycomb and foam, which is called non-metal sandwich structure. At present, the most widely used sandwich structure with FRP sheet as skin and FRP honeycomb core and foam as core material.
①Glass Fiber (Reinforcing Material) The glass fabric used to produce the FRP sandwich structure is divided into surface fabric and honeycomb fabric with a thickness of ~0.2mm. To increase the viscosity between the shell and the honeycomb, a layer of chopped fiberglass mat is often added between them. Using waxed fiberglass as a honeycomb material can prevent the resin from being absorbed into the back of the fiberglass, reduce the adhesion between the layers of the honeycomb block, and make the honeycomb hole easier to stretch.
②Paper The production of honeycomb paper requires good resin wettability and sufficient tensile strength.
③Glue (Resin) The resin used to make the multi-layer honeycomb structure is divided into skin resin, honeycomb resin, and honeycomb-skin bonding resin. Epoxy resin, unsaturated polyester resin, phenolic resin, silicone resin and dipropylene phthalate can be selected according to the operating conditions of the sandwich structure. In the manufacture of honeycomb strips, epoxy resin, modified phenolic resin, polyvinyl acetate and polyvinyl butyral glue are usually used. Among these adhesives, epoxy resin has high adhesive strength, and modified phenolic resin has low price, so it is widely used. Polyvinyl acetate glue is non-toxic, cheap, and can be cured at room temperature, but bee strips made from this glue cannot be immersed in polyester glue, because the styrene in polyester resin can dissolve polyvinylaldehyde acid, causing the bee strips to peel off, destroy.
(3) Production of multilayer honeycomb core In the production of glass fiber sandwich material, the main method is color gluing and stretching. The process is to first apply the adhesive strips to the fiberglass fabric for making honeycomb materials, and then overlap and glue them into honeycomb stacks. After curing, cut into honeycomb strips according to the required honeycomb height, stretch and preform, and finally immerse in glue and cure, shaping the honeycomb core. The method of gluing the adhesive tape for the manufacture of honeycomb sandwich stacks can be manual or mechanized.
(4) Production of honeycomb sandwich structure The production technology of glass fiber honeycomb sandwich structure is divided into wet method and dry method.
①Dry Forming This method is to first produce a honeycomb corespruce and panel of sandwich panels, and then glue them into a sandwich structure. To ensure a strong bond between the base material and the panel, a layer of thin felt (impregnated with adhesive) is often placed on the panel and the honeycomb is spread, heated, and pressed to harden into one piece. In a sandwich structure made by this method, the bonding strength of the honeycomb core and the panel can be increased to more than 3 MPa. The advantages of dry forming are mainly that the surface of the product is smooth and flat, and every process in the production process can be checked in time, and the quality of the product is easy to guarantee, while the disadvantage is a long production cycle.
②Wet molding This method is that both the panel and the honeycomb sandwich are in the uncured state, bonded and formed on the mold at the same time. In the production process, the top and bottom panels are first made on a mold, and then the honeycomb strips are dipped in glue, placed between the top and bottom panels, subjected to pressure (0.01-0.08MPa), cured and cut into products after being removed from forms. The advantage of wet forming is that the adhesive strength between the honeycomb and the panel is high and the production cycle is short, which is most suitable for the production of special-shaped products such as spherical surfaces and shells. The disadvantage is that the surface quality of the product is poor and the manufacturing process is difficult to control.
Technology for the manufacture of multilayer foam structures
(1) Raw Materials The raw materials for sandwich foam structure are divided into panel materials, sandwich materials and adhesives.
①Panel Material It is mainly fiberglass and resin thin plate, which is the same as the material used for sandwich honeycomb panel.
②Adhesive The adhesive for panels and sandwich materials mainly depends on the type of foam, such as Styrofoam, which cannot be glued with unsaturated polyester resin.
③There are many types of foam sandwich materials, and there are two classification methods: one is based on the resin matrix, which can be divided into: polystyrene foam, polystyrene foam, polyethylene foam, thermoset foams such as polyurethane foam, phenolic, epoxy and unsaturated polyester, etc. e. The other is almost hard, which can be divided into three types: hard, semi-hard and soft. The biggest advantages of foam core sandwich construction are cold protection, heat insulation, good sound insulation performance, light weight, large mask bonding surface, uniform load transfer and good impact resistance.
(2) Foam production technology There are many foaming methods for foam production, including mechanical foaming method, decompression foaming method mixed with inert gas,foaming with evaporation of a liquid with a low boiling point, decomposition of the foaming agent and degassing. raw materials components react with each other and are blown away by foaming, etc.
①Mechanical foaming method Under strong mechanical agitation, gas is mixed with a polymer solution, emulsion or suspension to form a foam, which then solidifies to form a foam.
②The inert gas-mixed decompression foaming method uses the principle that inert gas (such as nitrogen, carbon dioxide, etc.) is colorless, odorless, and difficult to combine with other chemical elements and is pressed into the polymer under high pressure. The pressure decreases, the gas expands and foams.
③ Low-boiling Liquid Evaporation and Foaming Method Press the low-boiling liquid into the resin, and then heat the resin. When the resin softens and the liquid reaches the boiling point, the resin is foamed by the vapor pressure generated by the evaporation of the liquid into foam.
④The chemical blowing agent foaming method uses the gas produced when the blowing agent decomposes under heat to expand the volume of the polymer to form foams.
⑤ Raw material chemical reaction foaming method This method uses raw material components that can be foamed to react with each other to release carbon dioxide or nitrogen, etc., so that the polymer expands and foams into foam.
(3) Manufacture of Sandwich Structures from Styrofoam Sandwich Foam Sandwich The production methods of sandwich structure are: prefabricated bonding method, monolithic molding method and continuous mechanical molding method.
①Assembled Bonding Method The skin and foam core are made separately and then glued together. The advantage of the prefabrication method is that it can be applied to a variety of foams, the process is simple and does not require complex mechanical equipment. Its disadvantage is that the production efficiency is low and the quality is difficult to guarantee.
②In the integral pour molding method, first the shell of the sandwich structure is made, then the evenly mixed foam slurry is poured into the shell, and after the foam is molded and cured, the foam fills the cavity and combines with the shell to form the overall structure.
③The continuous molding method is suitable for the production of styrofoam sandwich panels.
3. Pressing process
Compression molding is the oldest and endlessly dynamic molding method in the production of composite materials. This is a method where a certain amount of premix or prepreg is added to a metal vapor mold and cured by heat and pressure.
The main advantages of the compression molding process:
①High production efficiency, easy to implement cnspecialized and automatic production; ②High dimensional accuracy and good repeatability; ③Smooth surface, no need for secondary modification; ④ Can form products of complex structure at one time; ⑤Due to mass production, the price is relatively low. The disadvantage of compression molding is that mold making is complicated, the investment is large, and it is limited by the press, so it is most suitable for mass production of small and medium-sized composite products. With the continuous improvement and development of metal processing technology, press production level and synthetic resin production process performance, the press tonnage and table size are increased, and the molding temperature and molding material pressure are relatively reduced, making the size of the molded product gradually. With large-scale development, now it can produce large-scale auto parts, bathtubs and general toilet components.
The spinning process can be divided into the following types according to the physical state of the reinforcing material and the type of molding material: ①The fiber spinning method is to apply pre-mixed or pre-impregnated fiber molding material. into a metal form. The method of molding products from composite materials at a certain temperature and pressure. The method is simple and easy to implement and has a wide range of applications. Depending on the specific operation, there are methods for molding premixes and prepregs. ② Fine fabric forming method Cut the remnants of fiberglass fabric or other fabric impregnated with resin adhesive, such as linen, organic fiber fabric, asbestos fabric or cotton fabric, into pieces, and then heat and press in a metal mold to form composite products. materials. . ③Fabric molding method: 2D or 3D fabric pre-woven into the desired shape, impregnated with resin adhesive, and then placed in a metal mold for heating and pressing to form a composite product. ④Lamination method. Cut fiberglass fabric or other fabrics pre-impregnated with resin adhesive into the desired shape, and then heat or press into a metal mold to form composite products. ⑤ Winding forming method Continuous fiber or fabric (tape) pre-impregnated with polymer adhesive is wound on a mandrel with a certain tension and temperature provided by a special winding machine, and then put into a mold for heating and pressing to form composite materials. products. ⑥ Plastic Sheet Molding Method (SMC) Cut the SMC sheet according to the size, shape, thickness and other requirements of the product, and then stack the multi-layer sheets and put them into a metal mold for heating and pressing to form the product. ⑦ Molding method preformedof these blanks First, the chopped fiber is converted into a preformed blank of a similar shape and size, which is placed in a metal mold, and then the prepared binder (resin mixture) is injected into the mold. pressure.
There are many types of molding materials, which can be prepregs, premixes or blanks. The types of molding materials currently used mainly include: prepreg, fiber premix, BMC, DMC, HMC, SMC, XMC, TMC and ZMC and other varieties.
1. Raw Material (1) Synthetic resin The molding material used in composite molding requires the synthetic resin to have:
① It has good wetting properties on the reinforcing material, forming a good bond at the interface between the synthetic resin and the reinforcing material;
②With appropriate viscosity and good fluidity, it can evenly fill the entire mold cavity together with the reinforcing material under pressing conditions;
③Under the pressing conditions, it has a suitable curing speed, and no by-products or by-products are generated in the curing process, and the volume shrinkage is small;
④It can meet the specific performance requirements of molded products. According to the above material selection requirements, the commonly used synthetic resins are: unsaturated polyester resin, epoxy resin, phenolic resin, vinyl resin, furan resin, silicone resin, polybutadiene resin, allyl ether, melamine resin, polyimide resin, etc. In order for the molded product to achieve a certain performance index, after selecting the type and grade of resin, the appropriate auxiliary materials, fillers and pigments should also be selected.
(2) Reinforcing materials Reinforcing materials commonly used in molding materials mainly include fiberglass knife wire, non-twisted roving, twisted roving, fiberglass continuous bundles, fiberglass cloth, fiberglass mat, etc. also a small number of special products use asbestos felt, asbestos cloth (fabric) and asbestos paper, and high silica fiber, carbon fiber, organic fiber (such as aramid fiber, nylon fiber, etc.) cloth, etc. .) and other varieties. Sometimes mixtures of two or more fibers are used as reinforcing materials.
(3) Auxiliary materials generally include auxiliary materials such as hardener (initiator), accelerator, thinner, surface treatment agent, low shrinkage additive, mold release agent, dye (pigment) and filler.
2. Preparing the molding material Using the resin-impregnated glass fiber (or fiberglass) molding material as an example, the manufacturing process can be divided intopremixing and prepreg method. (1) Pre-mixing method First, cut the fiberglass into 30-50mm chopped fiber, after beating, fully knead the resin glue in the mixer until the resin is completely impregnated into the fiberglass, and then dry (air dry) until appropriate viscosity. Its characteristics are that the fibers are loose and non-oriented, and the production volume is large. The molding material obtained by this method has a large specific volume and good fluidity, but the fiber strength loss during the preparation process is relatively large.
(2) Prepreg method The fiber prepreg method is achieved by dipping, drying and cutting a whole bundle of continuous glass fibers (or cloth). It is characterized by the fact that the fibers are bundled and relatively compact, and the loss of strength of the fibers during the preparation of the molding composition is small, but the fluidity of the molding composition and the compatibility between the tows is somewhat poor. SMC, BMC, HMC, XMC, TMC and ZMC production technologies
Sheet molding material (SMC) is a kind of sheet molding material made of resin paste impregnated fiber or chopped fiber mat coated on both sides with polyethylene film, which belongs to the prepregmat field. It is one of the most widely used molding materials in the world.
SMC is mixed with an unsaturated polyester resin, a thickener, an initiator, a crosslinker, a low shrinkage additive, a filler, an internal mold release, and a dye to form a resin paste impregnated with chopped fiber roving or sheet molding. a compound formed by a glass fiber coating with a polyethylene or polypropylene film on both sides. As a new type of molding material with rapid development, SMC has many characteristics: ① Good reproducibility, independent of operators and external conditions; ② Easy to operate and handle; ③ The working environment is clean and hygienic, which improves working conditions; ④ Fluidity Good flexibility, can form special shapes; ⑤ The molding process does not require high temperature and pressure, and the range of variables is large, which can greatly reduce the cost of equipment and molds; ⑥ Fiber length 40-50mm, good quality uniformity, suitable for cross pressing -Section change Small and large thin-walled products; ⑦High purity of the surface of the obtained products, and the surface quality becomes more ideal after the use of low shrinkage additives; ⑧High production efficiency, short molding cycle, easy to implement fully automatic mechanized operation, and relatively low production cost.
As a new type of material, SMC has developed a number of new varieties according to various specific applications and requirements, such as BMC, TMC, HNC, XMCetc.
①Bulk Molding Compound (BMC) Its composition is very similar to SMC, and it is an improved premixed bulk molding compound that can be used for molding and extrusion. The difference between them is only in the shape of the material and the manufacturing process. The fiber content of BMC is low, the fiber length is short, about 6-18mm, and the filler content is relatively large, so the strength of BMC products is lower than that of SMC products. BMC is more suitable for pressing small products, while SMC is suitable for large thin-walled products. products.
②Thick molding compound (TMC) Its composition and production is similar to SMC, thickness up to 50mm. Due to the large thickness of TMC, the glass fibers can be randomly distributed, which improves the impregnation of the glass fiber with resin.sex. In addition, the material can also be injection molded and transfer molded.
③Hight Molding Compound (HMC) and XMC high strength sheet molding compound are mainly used in the automotive parts industry. HMC does not add filler or less filler is added, chopped glass fiber is used, the fiber content is about 65%, the glass fiber has a directional distribution, it has excellent fluidity and molding surface, and its strength is about 3 times higher than that of SMC product. . XMC uses 70% to 80% oriented continuous fiber without filler.
④ZMC ZMC is an injection molding technology. The three letters ZMC do not have an actual meaning, but include three meanings: injection mix, injection machine, and mold. ZMC products not only maintain a high strength index, but also have excellent appearance and high production efficiency. The advantages of SMC and BMC have been integrated, and rapid development has been achieved.
1. Raw material for SMCThe raw material for SMC consists of three categories: synthetic resin, reinforcing material and auxiliary material. (1) Synthetic resin Synthetic resin is an unsaturated polyester resin, and various unsaturated resins directly affect the thickening effect, process performance, product performance, shrinkage rate and surface condition of the resin paste. SMC has the following requirements for unsaturated polyester resin: ① low viscosity, good glass fiber impregnation performance; ② sufficient reactivity with thickener to meet thickening requirements; ③ fast curing, short production cycle and high efficiency; ④ the cured product has sufficient thermal strength, which is convenient for thermal demolding of the product; ⑤The cured product has sufficient strength, and the product does not crack under some deformation; ⑥Low shrinkage.
(2) Reinforcing material Reinforcing material representsThis is a chopped roving or fiberglass strand. In the unsaturated polyester resin molding compound, the reinforcement material used for SMC is currently only chopped glass fiber mat, while the reinforcement material used for premix includes chopped glass fiber, asbestos fiber, hemp and other kinds of organic fibers. . In SMC, the glass fiber content can be adjusted from 5% to 50%.
(3) Auxiliary Materials Auxiliary materials include hardeners (initiators), surface treatments, thickeners, low shrinkage additives, release agents, colorants, fillers and crosslinkers.
2. SMC preparation process The SMC production process mainly includes resin paste preparation, gluing operation, fiber cutting and impregnation, resin thickening and other processes. The flow diagram is as follows:< / p> p>
(1) Resin paste preparation and bonding process There are two methods of resin paste preparation, batch and continuous. The batch method procedure looks like this:
①Pour unsaturated polyester resin and styrene into the dosing pot and mix evenly;
②Pour the initiator into the dosing pot and mix it with resin and styrene;
③Add thickener and release agent while mixing;
④Add filler and low shrinkage additive while mixing at low speed;
⑤ When the components listed in the formula are dispersed, stop mixing and let stand for use. The continuous method is to separate the resin paste in the SMC formula into two parts, that is, thickener, release agent, some fillers and styrene as one part, and other components as another part, which are measured and mixed separately. , and then sent to the SMC unit In the corresponding storage container installed above, if necessary, dosed by the piping dosing pump, and then enter the static mixer. After even mixing, it is transported to the paste area of the SMC unit, and then onto the plastic film.
(2) The impregnated and compacted bottom carrier film coated with resin paste enters the chopped glass fiber deposition chamber under the draft of the machine, and the chopped chopped glass fibers are evenly deposited on the resin paste to achieve the required deposition. measuring, exits the sump with a transfer device and is applied to the upper carrier film coated with resin paste, and then enters a row of staggered roller rows. Under the action of tension and rollers, the lower and upper carrier films, resin paste and chopped glass fiber, are tightly pressed against each other. friend, and after repeated repetitions, the chopped fiberglass is impregnated with resin and air bubbles are distilled off in it with the formation of a dense andhomogeneous continuous sheet of QMS.
Composite molding materials can generally be divided into two types: fast prototyping process and slow prototyping process depending on the length of the molding cycle. The rapid prototyping process is suitable for pressing small thin-walled composite products, and the slow prototyping process is suitable for pressing large thick-walled composite products.
Fourthly, the process of laminating and forming rolls
1. Lamination Process Lamination consists of cutting and laying prepregs to the shape and size of the product, placing them between two polished metal moulds, heating and pressing them to form composite products. It is an earlier and more mature molding method in the composite molding process. This process is mainly used for the production of electrical insulating boards and printed circuit boards. At present, printed circuit boards are widely used in all kinds of radios, televisions, telephones and mobile phones, computer products, various control circuits and other products that require planar integrated circuits. The laminating process is mainly used to produce composite material panels with different characteristics, which have the characteristics of mechanization, high degree of automation, stable product quality, etc., but the one-time investment is relatively large, suitable for mass production. production and can only produce panels, and the specifications are limited by the device. The laminating process usually includes: prepreg tape preparation, tape cutting and laminating, hot pressing, cooling, demoulding, processing, post-processing and other processes.
2. Pipe winding process Pipe winding is a composite molding method in which a pre-impregnated rubber fabric is hot rolled on a pipe winding machine. The basic principle is to use a hot roller on the pipe. winding machine, soften the tape to melt the resin on the tape. Under a certain tension, when the roller is running, with the help of friction between the roller and the mandrel, the adhesive tape is continuously wound on the core tube until the required thickness is reached, after which it is cooled and formed using a chill roller. Remove it from the machine and send it to the curing oven. After the pipe has cured, the mandrel is removed to obtain a composite coiled pipe.
Roll pipe forming can be divided into two types: manual laying method and continuous mechanical method according to different laying methods. Main process: clean each roller first, then heat the hot roller to the set temperature, and adjust the tension of the adhesive tape. When the pressure roller is not applying pressure, wrap the guide cloth over the shape of the eraser.the cloth coated with release agent about 1 turn, then lower the pressure roller, stick the guide fabric on the hot roller and wrap the adhesive tape at the same time. The length of the guide cloth is about 800-1200mm, depending on the diameter of the pipe, the overlap length of the guide cloth and tape is usually 150-250mm. When rolling thick-walled pipes, the rotation speed of the mandrel can be properly accelerated after the rolling operation is normal, and then slowed down when the wall thickness is close to the design, and the tape should be cut when the thickness reaches the thickness of the structure. Then, maintaining the pressure of the roller, continue to rotate the mandrel for 1-2 turns. Finally, the pinch roller is raised to measure the outside diameter of the tube blank. After passing the test, the tube blank is taken out of the tube rolling machine and sent to the curing oven for vulcanization and shaping.
3. Prepreg tape preparation process
Prepregs are semi-finished products for the production of composite laminates, rolls and tape wraps. (1) Raw materials The main raw materials needed for the production of prepregs are reinforcing materials (such as fiberglass cloth, asbestos cloth, synthetic fiber cloth, glass fiber felt, asbestos felt, carbon fiber, aramid fiber, asbestos paper, kraft paper etc.) and synthetic resins (such as phenolic resins, amino resins, epoxy resins, unsaturated polyester resins, silicone resins, etc.).
(2) Prepreg Adhesive Fabric Preparation Process The preparation of prepreg adhesive fabric is to use heat-treated or chemically treated glass fabric, impregnate resin glue through the dipping tank, and control the movement of the adhesive fabric through the scraper and traction device. a certain temperature after a certain period of time, the resin will be transferred from stage A to stage B in order to obtain the required prepreg. This process is commonly referred to as glass dipping.
5. Winding molding process
The winding molding process consists of winding a continuous fiber (or fabric tape, prepreg yarn) impregnated with resin adhesive onto a mandrel according to certain rules, and then solidifying and demoulding to obtain a finished product. According to the physical and chemical state of the polymer matrix during the formation of fiber winding, it can be divided into three types: dry winding, wet winding and semi-dry winding.
(1) Dry winding Dry winding is the use of prepreg-treated yarn or tape, which is heated and softened to a viscous liquid on a winding machine, and then wound onto a mandrel. Since the prepreg yarn (or tape) is professionally produced, the resin content (accurate to 2%) and the quality of the prepregwarp yarn can be strictly controlled. Thus, dry winding allows precise control of product quality. The biggest feature of dry winding process is high production efficiency, winding speed can reach 100-200m/min, winding machine cleanliness, good occupational health conditions and high product quality. The disadvantage is that the winding equipment is expensive and prepreg yarn needs to be added. Production equipment, so the investment is large. In addition, the interlaminar shear strength of dry winding products is low.
(2) Wet winding Wet winding consists in winding a bundle of fibers (belt yarn) directly onto a mandrel under tension control after dipping into the adhesive. Advantages of wet winding: ①40% lower cost than dry winding; ②The product has good airtightness, as winding tension causes excess resin glue to extrude bubbles and fill the gap; ③Good fiber parallelism ④During wet winding, polymer adhesive on fiber can reduce fiber abrasion ⑤High productivity (up to 200m/min). Disadvantages of wet winding: ①Resin waste is large and the working environment is poor; ②It is not easy to control the amount of glue and the quality of the finished product; ③ Fewer resin types are available for wet winding.
(3) Semi-dry winding Semi-dry winding consists of adding a set of drying equipment along the winding path to the mandrel after dipping the fiber to remove the solvent from the dipped filament and drying. winding Compared with this method, the pre-treatment process and equipment are saved, compared to the wet method, the content of air bubbles in the product can be reduced.
Among the three winding methods, wet winding is the most common application; dry winding is used only in high-performance and high-precision advanced technical fields.
Advantage of filament winding formation ①The winding law can be designed according to the strength conditions of the product, so that the strength of the fiber can be fully utilized; ②High specific strength: generally speaking, the fiber wound pressure vessel is comparable to steel with the same volume and pressure. Compared with containers, the weight can be reduced by 40-60% ③High reliability: filament winding products are easy to realize mechanized and automated production .After determining the process conditions, the winding quality, the products are stable and accurate; The production requires fewer operators and high winding speed (240m/min), so the labor productivity is high; ⑤ Low cost: for the same product, multiple materials (including resin, fiber and inner lining) can be reasonably selected to make it a reusable compound to achieve the best technical and economic effect.
Disadvantages of winding molding ① Winding molding has low workability and cannotcan wrap products of any structural shape, especially products with concave surfaces, since the fibers cannot stick to the surface of the mandrel and be overhead during winding; ② Winding molding requires winding machines, mandrels, curing ovens, stripping machines and skilled technical personnel require large capital investment and high technical requirements, so only mass production can reduce production costs and obtain relatively high technical and economic advantages.
1. Raw materials The raw materials for winding molding are mainly fiber reinforced materials, resins and fillers. (1) Reinforcing materials Reinforcing materials used to form the winding are mainly various fiber filaments, such as alkali-free glass fiber yarns, medium alkaline glass fiber yarns, carbon fiber yarns, high tenacity glass fiber yarns, aramid fibers. yarn and rug surface Wait.
(2) Resin matrix Resin matrix refers to an adhesive system consisting of resin and hardener. The heat resistance, chemical corrosion resistance and natural aging resistance of winding products mainly depend on the properties of the resin, and also have a great influence on the workability and mechanical properties. Commonly used winding molding resins are mainly unsaturated polyester resins, and sometimes epoxy resins and bismaleimide resins. For general civil products such as pipes, tanks, etc., unsaturated polyester resins are mainly used. Epoxy can be used to wind products requiring high mechanical properties such as compressive strength and interlaminar shear strength. Aerospace products mainly use bismaleimide resin with high fracture toughness and good moisture resistance.
(3) Filler There are many types of fillers that, when added, can improve certain functions of the polymer matrix, such as improving wear resistance, improving fire resistance, and reducing shrinkage. The addition of hollow glass microspheres to the adhesive makes it possible to increase the rigidity of the product, reduce the density and reduce the cost. In the production of underground pipelines of large diameter, 30% quartz sand is often added to increase the rigidity of the product and reduce the cost. To increase the bonding strength between the filler and the resin, the filler must be cleaned and treated with surfactants.
2. Core mold The inner mold for forming hollow products is called core mold. Typically, after the winding product has cured, the mandrel separates from the product. Basic requirements for mandrel design
①It must have sufficient strength and rigidity to withstand various loads applied to the mandrel during product molding, such asnatural weight, product weight, winding tension, curing stress, cutting force during secondary processing, etc. ;
②It can meet the requirements of product shape and dimensional accuracy, such as shape size, concentricity, ellipticality, taper (release), surface finish and flatness, etc.
③Ensure that the product can be separated from the product smoothly after curing;④Easy to produce, cheap to produce, and convenient to obtain materials.
Mandrel Materials There are two types of mandrel materials for winding molding: meltable materials, soluble materials and prefabricated materials. Meltable and soluble materials include paraffin wax, water-soluble foundry sand based on polyvinyl alcohol, fusible metals, etc. These materials can be made by casting into hollow or solid core molds. high-pressure steam is introduced from the hole, which dissolves and melts, flows out of the product, and the leaked molten solution is reused after cooling. The assembled core shape materials are commonly used in aluminum, steel, sandwich structure, wood and plaster. In addition, there are lining materials. The lining material is an integral part of the product. After curing, it is not removed from the product. The function of the backing material is mainly corrosion protection and sealing. Of course, it can also play the role of a core mold. Some of these materials are rubber, plastic, stainless steel and aluminum alloy, etc.
3. Winding machine
The winding machine is the main equipment for carrying out the winding forming process. Winding machine requirements: ①It can realize the winding law of product design and accurate yarn positioning ②Easy operation ③High production efficiency; ④Low equipment cost.
The winding machine mainly consists of two parts: mandrel drive and wire winding nozzle drive. In order to avoid loosening of the fiber during the reverse movement of the winding nozzle, keep the tension stable and accurately position the ribbons of yarn on the head or tapered winding products, and realize the winding with a small winding angle (0°~15°), vertical core. developed on a winding machine. Axial feed mechanism (hand extension). To prevent the yarn from twisting when the winding nozzle moves in the opposite direction, a mechanism is provided on the outrigger that can turn the winding nozzle.
My country successfully developed the chain winding machine in the 1960s. In the 1970s, he introduced the German WE-250 CNC winding machine. international market.
Types of mechanical winding machine (1) The winding arm type flat winding machine is characterized bythat the winding arm (equipped with a wire winding nozzle) rotates uniformly around the mandrel and the mandrel rotates uniformly around the mandrel. its own axis. Rotation at a slow speed, each time the winding arm (that is, the winding nozzle) is rotated once, the mandrel rotates a small angle. This small angle matches the width of the yarn sheet on the winding container, ensuring that the yarn sheets tightly cover the surface of the container one by one on the mandrel. When the mandrel rotates rapidly, the winding nozzle moves slowly up and down along the vertical direction of the ground. At this time, circular winding can be realized. The advantages of using this winding machine are that the mandrel is evenly loaded, the mechanism runs smoothly, and the wires are evenly arranged. It is used for dry winding of small and medium short and thick cylindrical containers.
(2) Roll Type Winding Machine The core form of this winding machine is supported by two beams. When winding, the core form itself rotates around its own axis, and the two arms rotate synchronously to form the core form. rolled in a circle. The width of the sheet is adapted to the angle, while the fibrous yarn is fed by a fixed outrigger to realize flat winding, and the ring winding is carried out by an additional device. Since the rolling mechanism should not be too large, this type of winding machine is only suitable for small products and is not widely used.
(3) Horizontal winding machine This type of winding machine is driven by a chain so that the trolley (winding nozzle) reciprocates, and there is a momentary stop at the head end, and the mandrel rotates at a constant speed. around its axis. By adjusting the speed of both, flat winding, ring winding and spiral winding can be realized. This type of winding machine has a simple structure and a wide range of applications, and is suitable for winding thin pipes and containers.
(4) Orbital winder There are two types of orbital winder: vertical and horizontal. Bundles of yarn, glue grooves and winding nozzles are installed on the trolley. When the trolley goes around the mandrel in a circle along a circular path, the mandrel itself rotates by the width of the yarn sheet. The angle between the axis of the mandrel and the horizontal plane is the winding angle of the plane α. Thus, by forming a flat winding type, by adjusting the speed of the mandrel and the trolley, it is possible to realize the circular and spiral winding. Orbital winding machine is suitable for the production of large products.
(5) Planetary winding machine The mandrel and the horizontal plane are inclined at an angle α (that is, the winding angle). When forming the winding, the core mold makes two rotation and rotation movements, and the winding nozzle is fixed. By adjusting the rotation speed and rotation speed of the mandrel, flat,ring and spiral winding. The turn of the mandrel is the main motion, and the rotation is the feed motion. This winding machine is suitable for the production of small items.
(6) Spherical winding machine The spherical winding machine has 4 axes of movement, the winding head of the spherical winding machine rotates, the mandrel and the mandrel rotate. is to use the winding nozzle step by step to realize the winding of the yarn sheet, reduce the accumulation of fibers outside the pole hole, and improve uniformity. container sleeve thickness. The mandrel and winding nozzle rotate to make the fiber cover the surface of the sphere. The deflection movement of the mandrel shaft can change the size of the winding pole hole and adjust the winding angle according to the product strength requirement.
(7) Longitudinal Circular Cable Winding Machine The longitudinal circular cable winding machine is suitable for the production of cylindrical containers without heads and various pipes. The swivel with a bundle of longitudinal threads rotates synchronously with the mandrel and can reciprocate along the axis of the mandrel to complete the laying of the longitudinal thread. The wedding thread is installed on carts on both sides of the swivel. Depending on the stress of the pipeline, the ratio of the number of longitudinal annular threads can be adjusted arbitrarily.
(8) New Type Pipe Winding Machine The difference between the new type pipe winding machine and the existing pipe winding machine is that it is based on the rotation of the pipe core and can reciprocate along the length of the pipe. at the same time to complete the winding process. The advantage of this new type of winding machine is that the winding mouth is fixed, which is very convenient for workers when dealing with broken ends, wool and care; multi-channel feeding can ensure large capacity winding, high winding speed, uniform fabric. , It is beneficial to increase product weight and performance.
6. Continuous molding process
The continuous molding process of composite materials refers to the entire process from raw material supply, dipping, molding, curing, demoulding, cutting, etc. to the final finished product, which is carried out continuously. According to the product, the continuous molding process is divided into three types: continuous pultrusion molding process, continuous winding molding process and continuous plate manufacturing process. The continuous winding forming process is mainly used for the production of glass steel pipes and tank shells of various diameters. Characteristics of the continuous winding machine: high production efficiency, stable qualityproduct quality, low labor intensity, saving raw materials, reducing the number of mandrels, etc., but this process has high technical content, large investment in equipment, and difficult diameter change. . Another process is the combination of plastic pipe extrusion technology with fiber winding technology, glass steel pipe with plastic lining, and the extruded plastic pipe plays the role of mandrel and anti-corrosion lining at the same time. The pultrusion molding process is mainly used to produce various FRP profiles, such as FRP rods, I-shaped, angle, grooved, square, quick release and special profiles. At present, the largest pultrusion molding machine can produce 800mm×800mm quick release FRP profiles. New pultrusion molding technologies are constantly emerging, such as RIM pultruding machine, curved profile pultruding process, etc. The continuous board production process mainly uses fiberglass felt and cloth as reinforcing materials to continuously produce various specifications of flat boards , corrugated boards and sandwich construction boards. General characteristics of the continuous molding process: ①The production process is fully automated, and the production efficiency is high; ②The production process is continuous, and the length of the product is not limited; ③The product does not require post-processing, and there is less waste in the production process, saving raw materials and energy; ④ stable product quality, good reproducibility, high productivity; ⑤ easy operation, labor saving, good working conditions; ⑥ low cost.
The pultrusion molding process consists in forming and curing continuous strands of fiberglass, ribbons or fabric impregnated with polymer adhesive through extrusion dies under the action of traction and in the continuous production of FRP profiles of unlimited length. This process is most suitable for the production of GRP profiles of various cross-sectional shapes, such as rods, pipes, solid profiles (I-beam, trough-shaped, square profiles) and hollow profiles (door and window profiles, curtains, etc.). .).
Pultrusion molding is a special molding process for composite materials, the advantages of which are: ①The production process is fully automated and controlled, and the production efficiency is high ②The fiber content of pultruded products can reach as high as 80%. least play the role of reinforcing materials, and the product has high strength; ③Longitudinal and transverse strength of the product can be adjusted arbitrarily, which can meet the requirements of using products with different mechanical properties; ④ There is no corner waste in the production process, and the product does not need to be constantlyprocessing, so it saves labor, raw materials and energy consumption compared to other processes; ⑤The quality of the product is stable, the repeatability is good, and the length can be cut at will.
The disadvantage of the pultrusion process is the uniformity of the shape of the product, the possibility of manufacturing only shaped profiles, and low transverse strength.
(1) Raw material for pultrusion process ① Resin matrix in pultrusion process, the most widely used is unsaturated polyester resin, which accounts for more than 90% of the resin used in this process. epoxy resin, vinyl resin, thermosetting methacrylic resin, modified phenol resin, flame retardant resin, etc. continuous fiber and so on. To meet the special performance requirements of the product, aramid fiber, carbon fiber and metal fiber can be selected. Whatever fiber is used in the pultrusion process, its surface must be treated so that it can adhere well to the resin matrix. ③Auxiliary Materials Auxiliary materials of the pultrusion process mainly include release agents and fillers.
(2) Pultrusion mold The mold is an important tool in pultrusion technology and usually consists of two parts: a pre-molding mold and a molding mold.
①In the process of pultrusion of the preform mold, after impregnating the reinforcing material with resin (or during impregnation), before entering the mold, it must pass through the preform, consisting of a group of elements guiding the yarn, preforming The role of the reinforced material after dipping is to gradually form the preform, which approaches the shape and size of the mold according to the profile section configuration, and then enters the mold, so that the yarn content in the product can be guaranteed that the cross section of the product will be homogeneous.
②Mould The ratio of the cross-sectional area of the mold to the cross-sectional area of the product should generally be greater than or equal to 10 to ensure that the mold is strong enough and rigid, and the heat distribution is uniform and stable after heating. The length of the pultrusion head is determined according to the drawing speed and the curing speed of the resin gel during the molding process, to ensure that the product reaches the demolding and curing rate when it is taken out. In general, the steel is chromium plated, and the surface of the mold cavity should be smooth and wear-resistant in order to reduce the frictional resistance of pultrusion and increase the life of the mold.
(3) Pu processPultruded Molding The pultrusion molding process consists of yarn feeding, dipping, preforming, curing and stacking, drawing, cutting and other processes. After the roving is pulled out of the creel, it enters the dipping tank through the yarn discharge device to impregnate the resin adhesive, and then enters the pre-molding mold to remove excess resin and air bubbles, and then enters the molding mold to gel and affirmations. . The cured product is continuously pulled out of the mold by a tractor and finally cut to length by a cutting machine. In the forming process, each process can have different methods: for example, in the yarn feeding process, continuous fiber felt, ring wound yarn or three-sided fabric can be added to improve the cross-strength of the product; pulling force. the process may be a crawler tractor or manipulators may be used; the curing method may be mold curing or heating oven curing; heating method can be high frequency electric heating or molten metal (metal with low melting point), etc.
(4) Other pultrusion processes In addition to vertical and horizontal installations, there are also bent pultrusion processes, jet injection and filler pultrusion processes, extrusion process, etc.</p >
Continuous pipe wrapping process
Compared with fixed length glass steel pipe, the continuous winding process has the following characteristics: ① continuous production, easy to realize automatic control and fast curing, and high production efficiency; ② less auxiliary equipment is required, especially the amount of mold required Less investment in product replacement; ③The length of the product can be arbitrarily cut, and using this length (12m or 15m) can reduce the number of pipe joints and reduce the cost of the project; ④The production process is automated, process parameters are centrally controlled, and product quality is easy to guarantee. Another continuous pipe manufacturing process uses the combined process of plastic pipe and fiberglass reinforced plastic, that is, the EPF method. Composite pipes made by this method have better anti-corrosion and impermeability than ordinary fiberglass steel pipes.
(1) Raw materials for continuous wound pipes The raw materials for continuous wound pipes must meet both the product usage requirements and the manufacturing process requirements. ①Reinforcing material According to the requirement of fiberglass pipe and PVC/GRP composite pipe production, the types of reinforcing materials include surface mat, chopped fiberglass mat or needle-punched composite mat combinedwith surface mat and roving. ② Resin Matrix The resin used for continuous winding is mainly unsaturated polyester resin. The requirements of the continuous winding process for the resin are: appropriate viscosity, easy wicking into fiber, long gel time, short curing time, low curing exotherm, and little curing shrinkage. ③Auxiliary materials To increase the rigidity of the pipe, quartz sand is often added, the amount of which can reach 30% (maximum). Polyester film is used as a release agent and the film is cut into strips twice the width of the steel strip and 1/2 overlap is wound.
(2) Continuous winding process Continuous winding is made from pre-impregnated fiberglass. Yarn or tape (or dipped in place) is wound on the mandrel according to the developed winding rule and formed by external and internal heating and solidification. tape on the mandrel, it is continuously advanced, demolded, and then passed through two cuts along the length after secondary curing. When changing the pipe diameter, only the mandrel of the pipe machine needs to be replaced.
Continuous plate making process
The continuous panel manufacturing process began in an era when the FRP industry was converted from military to civilian after World War II. My country began studying it at the beginning of 1965. The first successful research was the production of corrugated PVC panel reinforced with steel wire, and the products were horizontal corrugated tiles. Longitudinal wave polyester FRP production line was developed in Shanghai in the 1970s. Three continuous sheet production lines were introduced in the 1980s, and their production technology is internationally advanced. Corrugated FRP sheet is the most widely used product in the construction industry. It is mainly used for temporary construction projects, roof lighting of industrial buildings and agricultural greenhouses. Compared with traditional asbestos tiles, it has the characteristics of light weight, high strength, impact resistance, light transmission, beauty and durability. FRP corrugated plate is divided into longitudinal wave plate and transverse wave plate. Concerning the corrugation shape, there are standard continuous arcuate waves, special-shaped continuous corrugations, and special-shaped discontinuous corrugations. The process of continuous production of thick plates at home and abroad is approximately the same, but there are slight differences in mlocal structure of equipment and technological measures.
7. The molding process of thermoplastic composites
Thermoplastic composite is a general term for various thermoplastic resins reinforced with glass fiber, carbon fiber, aramid fiber, etc. Abroad, it is called FRTP (Fiber Rinforced Thermo Plastics). Due to different types of thermoplastic resins and reinforcing materials, the production process and characteristics of composite materials vary greatly.
In terms of production technology, plastic composite materials are divided into two categories: short fiber reinforced composite materials and continuous fiber reinforced composite materials: (1) short fiber reinforced composite materials ① injection molding process, ② injection molding process under pressure; ③ spin molding process. (2) Composite materials reinforced with continuous fiber and long fiber ① Prepreg compression molding; ② Punching molding compound; ③ Vacuum forming sheet sand; ④ Winding prepreg yarn; ⑤ Pultruded.
The special properties of thermoplastic composite materials are as follows: (1) Low density and high strength.The density of thermoplastic composite materials is 1.1-1.6g/cm3, which is only 1/5-1/7 . steel, which is higher than thermoset FRP Light 1/3～1/4. It can obtain higher mechanical strength with lower specific gravity. Generally speaking, whether it is general purpose plastics or engineering plastics, after glass fiber reinforcement, a higher reinforcement effect will be obtained, and the strength grade will be improved.
(2) High degree of freedom in designing characteristics The physical, chemical and mechanical properties of thermoplastic composite materials are achieved through a reasonable selection of raw materials types, proportions, processing methods, fiber content and layering methods. Since there are many more types of matrix materials for thermoplastic composites than for thermoset composites, there is much more freedom in material and design choice.
(3) Thermal properties The operating temperature of common plastics is 50-100°C, and it can be raised up to 100°C after glass fiber reinforcement. The heat distortion temperature of nylon 6 is 65°C, and after being reinforced with 30% fiberglass, the heat distortion temperature can be increased to 190°C. The temperature resistance of the polyetherketone resin reaches 220°C. After reinforcing 30% glass fiber, the service temperature can be increased to 310°C. Such a high temperature resistance cannot be achieved with thermosetting composite materials. The coefficient of linear expansion of thermoplastic composite materials is 1/4-1/2 lower than that of non-reinforced plastics, which reduces the shrinkage rate in the molding process and improves accuracy.l sizes of products. Its thermal conductivity is 0.3~0.36W(㎡·K), which is similar to the thermal conductivity of thermoset composite materials.
(4) Chemical corrosion resistance The chemical corrosion resistance of composite materials is mainly determined by the properties of the matrix material. There are many types of thermoplastic resins, and each resin has its own anti-corrosion performance. use the environment and the average conditions of the material, and the optimization of the matrix resin as a whole can meet the requirements of the use. Thermoplastic composites have better water resistance than thermoset composites.
(5) Electrical properties As a rule, thermoplastic composite materials have good dielectric properties, do not reflect radio waves and transmit microwaves well. Because the water absorption rate of thermoplastic composites is lower than thermoset FRP, its electrical properties are better than the latter. By adding conductive materials to thermoplastic composite materials, their electrical conductivity can be improved and static electricity can be prevented.
(6) Waste can be recycled. Thermoplastic composite materials can be recycled and molded many times, and waste and leftover materials can be recycled without causing environmental pollution.
Because thermoplastic composite materials have many special properties superior to those of thermoset FRP, they can be used in a wide variety of fields. From the analysis of foreign applications, thermoplastic composite materials are mainly used in automotive, electromechanical industry, chemical anti-corrosion and building machinery others
1. Injection Molding Process Injection molding is the main production method of thermoplastic composite materials with a long history and the most widely used. Its advantages are: short molding cycle, minimal energy consumption, high product accuracy, the ability to simultaneously mold complex switches and products with inserts, the ability to produce several products in one mold, high production efficiency. The disadvantage is that it cannot produce fibre-reinforced composite products and has high demands on the quality of molds. According to the current state of technology development, the largest injection molding product is 5kg, and the smallest is 1g. This method is mainly used for the production of various mechanical parts, building products, household appliance housings, electrical materials and car accessories.
2. Extrusion molding process Extrusion molding is one of the most widely used processes in the production of thermoplastic composite products. Its main features are continuousth production process, high production efficiency, simple equipment, easy to learn technology and so on. The extrusion molding process is mainly used to produce products such as pipes, rods, plates, and special-shaped cross sections. Reinforced plastic pipes and special-shaped fiberglass reinforced profiles for doors and windows have a large market in our country.
3. Winding molding process The principle of winding molding process of thermoplastic composite materials is the same as winding equipment and thermosetting glass, the difference is that the reinforcement material of thermoplastic composite winding products is not glass fiber roving, but impregnated (thermoplastic resin) Prepreg yarn. Therefore, it is necessary to add a prepreg preheater and a heat and pressure roller on the winder. During the formation of the winding, the prepreg yarn is first heated to the softening point, then the contact with the mandrel is heated, and the pressure roller is pressed so that it is welded together.
4. Pultrusion molding of thermoplastic composite materials The process of pultrusion molding of thermoplastic composite materials is basically the same as that of thermoset FRP. If the dipping method before mold entry is changed, thermoset FRP production equipment can be used. There are two kinds of reinforcing materials for the production of thermoplastic composite pultrusion products: one is impregnated prepreg yarn or prepreg tape, and the other is unimpregnated fiber or fibrous tape.
5. Layer Welding Method This method uses the weldability of thermoplastic composite materials to produce sheets of composite materials. The method is as follows: first put a layer of prepreg (usually 500mm wide) on the workbench, and when laying the second layer of prepreg, start the pressure roller welding machine, so that the prepreg gets under the pressure roller, and the welder makes the top and bottom Two layers of prepreg are heated and melted at the same time within a few seconds. When the machine moves forward, the prepreg is glued together under the pressure of the pressure roller (0.3 MPa). By repeating this process, sheets of any thickness can be produced.
6. The process of stamping thermoplastic sheet products Stamping of thermoplastic sheet products is different from SMC thermosetting.
7. Joining Technology of Thermoplastic Composite Materials There are many ways to join thermoplastic composite materials, namely:rod. During construction, the rivet is preheated to a temperature at which it can be deformed under pressure, while the rivet and hole diameter must exactly match each other, neither large nor small. You can also use metal bolts. The advantages of riveting include good impact resistance, absence of electrochemical corrosion and low price. ②Welding The welding process of thermoplastic composite materials is to heat the welding surface of the materials to be joined to a molten state, and then overlap and press them to integrate. The principle of welding composite materials is similar to welding plastics, but it should be noted that the effect of fiber reinforcement in the weld cannot be greatly reduced. ③ Butt welding of tube fittings There are two methods of butt welding of thermoplastic composite pipes: direct butt welding and reinforced butt welding. The advantage of this connection method is that the process is simple, can be constructed on site, does not require machining of the pipe, has high connection strength, and is not easy to break. The disadvantages are high cost, stringent process requirements and the need for careful sizing. ④ Wrapping and Welding Use prepreg tape to manually or mechanically wrap along the weld seam, and use a flame spray gun to heat and melt the contact point so that it can be firmly adhered to the connected parts. When choosing a prepreg tape, pay attention to the direction and content of the fibers. This method is more practical and the materials to be joined may retain better characteristics, but it is prone to uneven heating. ⑤ Ultrasonic welding of thin sheets. This method uses ultrasonic waves to heat and weld joints, and generally results in higher joint strengths.
8. Other molding processes
Other resin-based composite molding processes mainly refer to spin molding process, injection molding process, elastomeric storage resin (ERM) molding process, enhanced reaction injection molding (RRIM) process, etc.</p >
1. Spin Molding Process Spin molding process is mainly used to make pipes (buried pipes) in the production of composite products. It is mixing resin, glass fiber and filler in a certain proportion and method. Added to the rotating mold cavity, relying on the centrifugal force generated by high-speed rotation, the material is tightly extruded and solidified in the mold.
Centrifugal glass steel pipes are divided into pressure and non-pressure, and the working pressure is 0-18 MPa. The diameter of this type of tubes is usually φ400～φ2500mm, and the maximum diameter can be up to 5m.diameter φ1200mm or more. The length of the centrifuge tube is 2～12m, usually 6m.
Centrifugal glass steel pipe has many advantages. Compared with ordinary glass steel pipe and concrete pipe, it has high strength, light weight, anti-corrosion resistance, wear resistance (5-10 times higher than that of asbestos cement pipe) , Energy saving and durable (more than 50 years), and the comprehensive design costs are low, especially for large diameter pipes; Compared with sandblasted glass steel pipe winding, its biggest feature is high rigidity, low cost, and the pipe wall can be designed into a multi-layer structure according to its function. The quality of the centrifugal pipe is stable, the loss of raw materials is small, and its total cost is lower than that of steel pipe. Centrifugal glass steel pipes can be buried up to 15 m deep, they can withstand vacuum and external pressure. The disadvantage is that the inner surface is not smooth enough and the hydraulic properties are relatively poor.
The application prospects of centrifugal glass steel pipes are very wide. Its main applications include: main water supply and drainage pipes, oil field water injection pipes, sewage pipes, chemical anti-corrosion pipes, etc. < /p>
(1) Raw materials The raw materials for the production of centrifuge tubes include resin, glass fiber and filler (powder and granular filler). Resin The most widely used is unsaturated polyester resin, resin grade and hardener can be selected according to usage conditions and process requirements. Reinforcing material The main work is fiberglass and products from it. Fiberglass products include continuous fiber mat, lattice fabric, unidirectional fabric, etc. In the production of special-shaped cross-section products, glass fiber can be first formed into a blank and then placed into a mold. Filler The role of the filler is to increase the rigidity and thickness of the product and reduce the cost. The type of filler should be selected according to the requirements of use. Generally, it is quartz sand, quartz powder, diabase powder, etc.
(2) Technological process The manufacturing process of centrifugal tubes is as follows:The feeding method of manufacturing centrifugal tubes is different from the winding method. device for resin, fiber and filler.Uniform installation on a reciprocating trolley.
(3) Mold The centrifugal glass steel pipe mold is mainly a steel mold. The mold is divided into two types: integral type and assembly type: smaller pipe mold. than φ800mm is one-piece, and the pipe mold is larger than φ800mmand may be collected. The design of the mold must provide sufficient strength and rigidity to prevent deformation during rotation and vibration. The mold consists of a pipe body, a head and a support wheel hoop. The pipe body is rolled and welded from steel sheet, and the small diameter pipe body can be made from seamless steel pipe. The function of the head is to increase the strength of the end of the pipe shape and prevent material from flowing out. The role of the support ring is to support the mold, transmit rotational force, and make the mold rotate at high speed on the centrifuge. The inside surface of the mold tube body should be flat and smooth, and generally should be machined. and polished to ensure smooth demoulding.
2. Injection molding process Injection molding is mainly used for the production of composite products without fiber reinforcement, such as artificial marble, buttons, embedded animal and plant specimens, handicrafts, fixing aids for anchors , ornaments, etc. board, etc. Mold casting is relatively easy, but high quality products require skilled work techniques.
(1) Production Process of Buttons Buttons embedded with polyester resin have the advantages of high hardness, good gloss, wear resistance, scalding resistance, dry cleaning resistance, variety of colors and low price. it has mainly replaced plexiglass buttons at home and abroad, which account for more than 80% of the button market. The raw materials for the production of buttons are mainly unsaturated polyester resin, hardener (methyl ethyl ketone peroxide is used as an initiator) and auxiliary materials (including color paste, pearl powder, thixotropic agent, etc.). Polyester buttons are produced by rod centrifugal casting: first they are made into plates or rods, then they are cut into plates and rods to make buttons, then they undergo heat treatment, surface scraping, bottom scraping, groove milling, drilling. , polishing and other processes for making buttons.
(2) Artificial stone production process Artificial stone is made from unsaturated polyester resin and filler. Due to the different fillers used, the produced artificial stone is divided into artificial marble, artificial agate, artificial granite and polyester concrete.
Raw materials for the production of artificial stone are unsaturated polyester resins, fillers and pigments:
①ResinThe resin used to produce artificial stone is divided into a surface layer and a structural layer. The surface decorative resin layer requires low shrinkage, toughness, good hardness, heat resistance, wear resistance, water resistance, etc. be easy to painttsya. Octanyl glycol phthalic resin is used for artificial stone, and octanyl glycol isophthalic resin is used for sanitary ware. Curing system, commonly used methyl ethyl ketone peroxide, cobalt naphthenate solution.
② Filler There are many fillers for producing artificial stone. The fillers for producing artificial marble are marble powder, quartz powder, dolomite powder, calcium carbonate powder, etc. The fillers for producing artificial granite are classified with granular materials. the color of the granules, and the filler for the production of agate must have a certain transparency. Hydroxide or aluminum oxide is mainly used. ③Pigments The production of artificial stone requires a variety of pigments. For example, for bathtubs made of artificial marble or artificial agate, heat-resistant and waterproof color pastes should be selected.
Mold materials used for the production of artificial marble and granite slabs include fiberglass, stainless steel, plastic, glass, etc. Formwork for the production of artificial stone slabs requires smooth glossy surfaces, sufficient strength and rigidity, withstand thermal loads, withstand loads and collisions during the production process.
3. Elastomeric resin storage molding Elastomer resin storage molding (Elastic Reservir Molding, ERM) is a new technology that emerged in Europe and the United States in the 1980s. cellular polyurethane foam) as the main material and impregnated with resin paste. This resin-bonded foam remains in the middle of the formed ERM material. The foam reduces the density of the ERM-made product and improves toughness and rigidity, so it can be called a sandwich molded product. ERM, like SMC, refers to a sheet molding composition for compression molding, but since ERM has a sandwich structure, it has advantages over SMC: (1) Light weight: ERM is lighter than felt and SMC. more than 30% lighter; (2) The specific rigidity of ERM products is better than that of SMC, aluminum and steel products; (3) High impact strength: With the same reinforcing material content, ERM is more resistant than SMC The impact strength is much higher; (4) High physical and mechanical properties: With the same reinforcing material content, the physical and mechanical properties of ERM products are better than those of SMC products; (5) Low investment cost: ERM molding blocks are simpler than SMC blocks and ERM products. The molding pressure is about 10 times lower than that of SMC products, so low-tonnage presses and low-strength material molds can be used in the production of ERM products, which reduces construction investment.
Process aboutThe production of ERM products is divided into two processes: the production of ERM and the molding of ERM products:
(1) ERM production process The raw material for ERM production is open-cell polyurethane foam, various fiber products (such as glass fiber, carbon fiber, chopped strand aramid fiber, continuous fiber mat, knitted mat, etc.) and various thermosetting resins A. The production process is as follows: first, impregnate the adjusted resin paste into the open-pore polyurethane foam in the ERM machine, apply the resin paste to the foam with a scraper, press the resin paste into the pores of the foam with pressure. roller, and then two layers of foam rubber, gather them together, and finally put fiberglass felt or other fiber products on the upper and lower sides to make ERM interlayers, cut them into appropriate sizes, and use for pressing or storage.
(2) Production process of ERM products Compared with other thermoset molding materials (glass fiber cloth or felt prepreg, SMC, etc.), the production process of ERM products requires curing under hot pressing conditions, but molding pressure Much less than SMC, about 1/10 of the molding pressure of SMC, 0.5-0.7 MPa.
ERM technology is currently used mainly in the automotive and lightweight building composites industries. Since ERM has the characteristics of sandwich structure materials, it is suitable for the production of combined parts of large structures, various light slabs, mobile homes, radar domes, doors, etc. Automotive products include luggage cart trailers, covers, dashboards, bumpers, doors, floor plates, etc.
4. Reinforced Reaction Injection Molding TechnologyReinforced Reaction Injection Molding (RRIM) uses high pressure to mix two monomeric materials and short fiber reinforcing materials. mold cavity and undergoes a rapid curing reaction to form an injection molded product. If reinforcing material is not used, this is called reactive injection molding (ReactionInjectionMoling, RIM). When continuous fiber reinforcement is used, this is referred to as structure reaction injection molding (SRIM).
The raw materials for RRIM are divided into two types: resin system and reinforcing material(1) The resin system for producing RRIM resin must meet the following requirements: ① It must be composed of two or more monomers; ② Monomer can be used at room temperature Keep stable; ③Suitable viscosity, easy to pump; ④Fast curing after mixing the monomer; ⑤The curing reaction does not produce by-products. The most widely used polyurethane resin, unsaturated polyester resin and epoxsolid resin.
(2) Reinforcing Materials Commonly used reinforcing materials are glass fiber powder, glass fiber and glass microspheres. In order to increase the adhesive strength between the reinforcing material and the resin, all of the aforementioned reinforcing materials are treated with a reinforcing bonding agent.
Characteristics of the RRIM process: ①Great product design freedom, and large-sized parts can be produced; ② Low molding pressure (0.35-0.7MPa), no molding stress during reaction molding, and the product generates less heat in the mold; ③ The shrinkage rate of the product is low and the dimensional stability is good. Due to the addition of a large number of fillers and reinforcing materials, the shrinkage of the resin during curing is reduced; ④ Inlay process The product is simple; Abrasiveness and heat resistance; ⑥ Simple production equipment, low mold cost, short molding cycle and low production cost.
The largest consumer of RRIM products is the automotive industry, which can be used as automotive bumpers and dashboards, while RRIM's high-strength products can be used as structural and load-bearing materials for vehicles. Due to its short molding cycle and design characteristics, it can be used instead of engineering plastics and polymer alloys in the electrical insulating, anti-corrosion and instrumentation industries.