Brazing is to use a metal with a lower melting point than the weld metal (base metal) as solder (filler material), heating the weld and solder to a temperature above the solder temperature and below the melting point of welding, and use liquid soldering . This is a method in which the material wets the weld metal, fills the gap in the joint, and interdiffusions with the base metal to achieve the weld joint.

The soldering deformation is small, the joint is smooth and beautiful, suitable for precision welding, complex parts and components composed of various materials, such as honeycomb plates, turbine blades, carbide tools and circuit boards. Before soldering, the workpiece must be carefully machined and strictly cleaned of oil stains and excessively thick oxide films in order to ensure the mounting clearance of the interface. The gap should normally be between 0.01 and 0.1 mm.

Compared to fusion welding, the base metal does not melt during soldering, only the solder melts;

Compared to pressure welding, no pressure is applied to the welded joint during soldering.

A weld formed by soldering is called a brazed joint.

The filler metal used for soldering is called hard solder.

Brazing process: Cleaned parts are overlapped together and solder is placed next to the seam gap or between the seam gaps. When the workpiece and solder are heated to a temperature slightly above the melting point of the solder, the solder melts (the workpiece does not melt), but is sucked in and filled into the gap between the solid workpiece due to capillary action and the liquid solder and the metal of the part diffuse and dissolve, after condensation a brazed seam is formed .

When the melting temperature of solder is lower than 450℃, it is called soldering;

Soldering is called soldering when the melting temperature of the solder exceeds 450°C. Southern Club HVAC

Soldering classification:

According to the different heat sources used, soldering can be divided into: (as shown in the figure below) flame soldering, induction soldering, soldering iron soldering, resistance soldering, furnace soldering, etc.

Soldering principle:

Soldering is a welding method that uses liquid solder to fill the gap between the metal surfaces of the solder to form a strong joint. This process must meet two basic conditions.

a) liquid solder can wet the solder and fill all gaps tightly;

b) Liquid solder and brazing solder enter into the necessary physical and chemical reactions to achieve a good intermetallic bond.

1. The principle of pouring with liquid solder

During soldering, liquid solder flows between solder joints by capillary action, and the ability of this liquid solder to penetrate and adhere to the base metal is called wettability. Southern Club HVAC

The better the wettability of the liquid solder by the solder, the stronger the capillary action and hence the more adequate gap filling. solder always flows towards the hot spot, not down;

2. Interaction between solder and weld metal

The interaction between the solder and the weld metal has two parts:

a) The weld metal is dissolved in the liquid solder;

b) Diffusion of liquid solder into the weld metal.

During the solder diffusion process on the surface of the base metal, the diffusion of the solder is easily affected by external factors such as: insufficient heating temperature, uneven heating, presence of oxides on the surface, etc. The solder should not reach the diffusion surface of the base metal, as shown in the figure below.

Design of the main soldering equipment, safe operation and maintenance:

Torch (torch):

1. What is a welding torch?

The combustible gas and oxygen are evenly mixed in the welding torch according to the required ratio, and ejected from the welding nozzle with a certain opening to burn, forming a stable welding flame with a certain energy output and properties.

2. Torch classification:

According to the different ways that the combustible gas enters the mixing chamber, it can be divided into two types: jet suction type and equal pressure type. The most commonly used jet-suction torch (used for welding refrigerators), as shown in the figure below.

Structural drawing of a jet-suction welding torch

1-welding nozzle; 2-welding nozzle connection; 3-tube gas mixture; 10 flywheel oxygen adjustment; 11-nut flywheel oxygen adjustment; 12-hose fitting; 13-tube oxygen, acetylene; 14-handle; 15-handle screw (female), 16-acetylene handwheel, 17-acetylene stem

The working principle of an isobaric welding torch is shown in the figure below. Oxygen and gaseous acetylene with the same pressure simultaneously enter the mixing chamber. After natural mixing, they are ejected from the nozzle and ignite, forming a flame. Since the pressure of acetylene is similar to that of oxygen, the mixture is homogeneous, the flame is stable and does not depend on the temperature of the burner, and since the pressure of acetylene is higher, the possibility of tempering is less than that of a jet-vacuum torch. But it must use medium pressure acetylene, so it is also called medium pressure welding torch.

3. Meaning of the welding torch code:

4. Working principle of jet-suction welding torch:

Oxygen is rapidly expelled from the nozzle after the oxygen control valve is opened and causes suction around the nozzle. When the acetylene control valve is opened, acetylene gas accumulates around the oxygen nozzle. Due to the suction of the oxygen jet, it accumulates at the periphery of the nozzle. Gaseous acetylene is quickly sucked off by oxygen, mixed with oxygen in a certain proportion and ejected from the welding nozzle through the gas mixing nozzle of the discharge nozzle.

The advantage of the jet suction welding torch is that since the combustible gas enters the welding torch by oxygen jet suction, it can work normally regardless of using low pressure combustible gas or medium pressure combustible gas. The disadvantage is that during the welding process, the temperature of the torch rises, which increases the temperature and pressure of the gas mixture in the mixing tube, which reduces the vacuum around the nozzle, reduces the consumption of combustible gas, causes mixing of oxygen and combustible gas. The ratio increases, the flame becomes oxidizing, which reduces welding quality. Therefore, after the torch has been running for a while, it is necessary to adjust the flame or immerse the welding tip and mixing tube in water to cool them down.

Backfire safety device (called a backfire valve):

The quench guard is called the quench valve for short. Its main function is to prevent the return of the flame and the explosion of the pipeline during the quenching of the burner. Its design is shown in the figure below:</ p>

The tempering valve basically plays the role of one-way circulation. If it is reversed during installation, acetylene gas will not flow. Impurities in the acetylene gas stick to the flame arrester valve, thereby blocking the small hole on the fire stop pipe pipe, resulting in a decrease in the consumption of acetylene gas. replace every six months.

The cleaning method of the thermostatic valve is to soak in hot water at about 70°C and dry. Air leak.

Welding tip:

Acetylene, oxygen cylinder, pressure reducing valve, auxiliary tools:

1. Acetylene bottle:

The outer surface of the acetylene cylinder is painted white, and the words "acetylene" and "keep away from fire" are written on the surface of the cylinder, the total volume of the acetylene cylinder is 40l;

2. Oxygen tank:

The outer surface of the oxygen cylinder is painted sky blue, and the word "oxygen" is written in black on the surface of the cylinder; Usually the bottle is designed for 40 litersoxygen;

3. Pressure reducing valve:

The pressure reducing valve is a control device that reduces high pressure decompressed gas to low pressure gas. The working pressure required for gas welding is less. For example, the working pressure of oxygen is usually 0.1-0.4MPa, and the pressure of acetylene is lower, up to 0.15MPa, so it is necessary to use a pressure reducer to reduce the high pressure gas stored in the cylinder to low pressure gas before supplying to welding torch used inside. Southern Club HVAC

Pressure stabilization function: When gas is consumed, the gas pressure in the gas bottle gradually decreases, that is, the gas pressure in the gas bottle is constantly changing during gas welding, and this change will affect the smooth running of the gas welding process. Therefore, it is necessary to use a pressure reducer so that the pressure and flow of the outgoing gas do not depend on the pressure difference of the gas in the cylinder, so that the working pressure remains stable from start to finish.

4. Auxiliary tools:

Hose: According to GB/T9448-1999 standard, oxygen hose is black with 8mm ID and acetylene hose is red with 10mm ID. These two hoses are not interchangeable, let alone replaceable. other hoses.

Safety glasses: mainly to protect the welder's eyes from the bright light of the flame, and secondly, to observe the flow of solder.

Adjustable wrench, thru-needle, sandpaper and file are mainly used to clean the welding tip.

5. Throttle valve

Main functions: saving oxygen and acetylene, when installing, pay attention to the direction of gas flow, and avoid incorrect connection of the inlet and outlet pipes (as shown in the figure below). In between work, constant lighting and welding, the torch should be turned off, the distance between two refrigerators on the line body should reach 3 m. The welder must turn off the welding torch if it is more than one meter above the refrigerator, and when the refrigerator reaches the welding station, re-ignite the welding torch. welding torch with constant light for welding.

Safe operation and maintenance:

1. Safe use of the welding torch:

(1) Check the welding tip and each air valve for leaks before use. The method is: close the air valves tightly, insert the burner into the water, and then pass oxygen and acetylene respectively. If there are no bubbles in the water, this proves that the air tightness is good.

(2) The gas passages of the burner must not be contaminated with grease to prevent ignition and explosion of oxygen upon contact with the grease. At the same time, the mating surface of the welding tip must not be damaged, so that air leakage does not affect the use.

(3) Fire can only be lit byafter passing the test. When ignited, first turn on the acetylene handwheel, and then immediately turn on the handwheel of the oxygen control valve to adjust the flame when acetylene ignites.

(4) When stopping use, turn off the acetylene flywheel first, and then turn off the oxygen flywheel to prevent flames from igniting and black smoke from being generated. If the welder finds that the pressure or flow of acetylene and oxygen changes during work and cannot meet the requirements of the work and needs to be adjusted, he must stop welding, extinguish the flame and re-ignite after processing. It is forbidden to adjust by flame to prevent hardening caused by alternator pressure and flow fluctuations.

(5) After stopping use, the welding torch should be hung in an appropriate place or the rubber hose removed and the torch put away in the tool box. The source is always connected.

2. Common problems with jet-suction welding torches:

The most common main malfunction of the welding torch is blockage. The reason for the blockage is mainly due to water in oxygen and acetylene, particles and particles such as rust caused by long-term use of the inner wall of the main pipe. After the flow of oxygen and acetylene, finally it is introduced into the welding torch, and the oxygen and acetylene control valves are all needle valves, and the inner hole is very small, resulting in reduced capacity injection and suction, or even blockage. Southern Club HVAC

3. Method for checking the suction capacity of a jet-suction burner:

Connect the oxygen connector on the torch to the oxygen hose (the acetylene connector on the torch is not connected), then fully open the oxygen valve and the acetylene valve, put your finger on the acetylene connector, if you feel strong suction means the torch can work normally, and if suction is small, this indicates the presence of deposits on the inner wall of the torch;

4. If a bad suction power of the torch is found, it can be soaked or scalded with water at a temperature of about 70°C, and then blown with compressed air at high pressure (the contents during blowing also need to be blown through the torch (completely remove water) in order to completely remove particles from the welding torch and restore the supply and suction capabilities of the welding torch.

5. The length of the rubber tube should generally be at least 5m. If the workplace is far away from the gas source, the two rubber tubes can be connected with a pipe connection according to the actual situation, but they must be tied tightly. If a frozen leather tube is found, it should be thawed with warm water; it is forbidden to bake on an open fire;

6. If quenching occurs during use, the acetylene control valve must be quickly closed and the valveThe oxygen control valve must be closed at the same time. After the hardening is extinguished, the oxygen control valve must be opened to allow residues in the welding torch and connecting piping. Remove the residual flame and soot and place the front of the torch handle in water to cool. In addition, during use, if you find an air leak, you should immediately stop using it, and you can use it after the air leak is fixed.

7. Do not put a burning welding torch on the workpiece or the ground; when changing or stopping welding, the oxygen and acetylene valves must be closed; when leaving the post, it is forbidden to put a burning welding torch on the operating table;</p >

8. In the case of acetylene quenching, the acetylene valve and oxygen valve must be closed immediately to find out the cause of quenching. After quenching, check the pipeline and replace the quench preventer to prevent the quencher from being damaged.

Protective equipment:

1. The welding temperature will emit harmful light. Working with the naked eye for a long time will cause damage to the eyes, so safety glasses must be worn.

2. Wear clean work clothes and gloves to avoid burns.

Preparation before soldering:

Tube end processing shape and intubation assembly process requirements:

1. A brief introduction to the pipe end processing mold:

Secondly, the requirements for the cannula assembly process:

Brazed joints include butt joints, lap joints, T-joints, crimps, and socket joints. In the refrigeration system of refrigerators, socket connections are used. The soldering machine must provide an adequate and uniform soldering gap with one side from 0.05 mm to 0.15 mm.

If the gap is too large, the capillary effect will be broken, which will affect the even distribution of the solder in the solder joint and cause the weld to break, appearing to be half or completely blocked under pressure or vibration. ;

If the gap is too small, it will prevent the flow of solder liquid, so that the solder cannot fill the entire solder joint and reduce the strength of the joint;

An uneven solder gap will prevent the liquid solder from being evenly distributed in the solder, which affect the quality of soldering. Southern Club HVAC

For flare solder joints, it is very important to select the appropriate flare length. Generally, the flare length of copper tube is 5-15mm and the flare length of capillary tube is 10-15mm. to fatigue performance and low temperature performance) is insufficient, and more importantly, it is prone to welding jamming.

After the piping connections are in place, check if the solder joints are deformed or damaged and if the length of the flare is correct (as shown in the figure below),

If there is a bad connection, it should be removedpour and reinstall before welding.

Shaping the pipeline before welding:

1. Importance of shaping the pipeline before welding

Before welding, connect the refrigerant piping such as evaporator, condenser, compressor, dry filter, capillary tube and connecting pipe according to the refrigerant flow sequence to form a piping before welding.

Because the forming operation before welding is directly related to the installation gap between the pipes, the insertion depth and deformation of the pipes after forming, as well as the bending of the pipe, the forming of the pipes before welding plays a vital role. as welding.

2. Pipeline forming method before welding

When forming the piping before welding, each piping must be connected together in the correct refrigerant flow direction. Specific operation sequence: pull out the rubber plug of the refrigeration unit (Fig. 1.1) → bend the condenser (Fig. 1.2) → bend the evaporator (Fig. 1.3) → install the dry filter (Fig. 1.4) and fill with nitrogen for protection.

3. Factors affecting the formation of the pipeline before welding

There are many factors that affect the quality of pipeline forming before welding. Before forming, each influencing factor must be checked to ensure good performance and efficiency of subsequent welding. Factors influencing the formation of the pipeline before welding, roughly include the following categories: the correct model of the refrigeration unit, the tightness of the piping of the refrigeration unit, the cleanliness of the surface of the refrigeration unit, the flexibility of the pipeline material, shaping. method and time of system opening.

Correctly match the type of refrigeration parts: before welding and forming operations, check the drawings and actual piping to avoid confusion of materials with similar shapes, welding directions and positions, etc. The operator must check whether the cooling parts are used correctly. Making sure in the correct compressor model, two device models and dry filter, the cooling system will be efficient and the pre-welding operation can be performed. If there is a wrong model, the correct material must be replaced; if it cannot be replaced on site, the product must be turned off for repair or appropriate processing.

Pipe tightness: Before shaping, the operator checks the appearance and tightness of each refrigeration line. There are no damages or breaks in each pipeline. Pull the plug on the fitting and you should hear nitrogen rushing out of the line. nozzle. If the cooling parts are damaged, the tube is broken or there is no nitrogen pressure, the material should be placed in the unqualified material setting area and not used, and the system without airtight pipelines cannot work normally; after the road is qualifiedis set, the operator can perform the normal shaping operation. Southern Club HVAC

Cleaning the surface of the refrigerator parts: Before starting work, you must carefully check that the surface of the refrigerator parts is clean. Contaminants such as oxides and oil stains on the surface will prevent contact between the solder and the metal of the part, causing liquid solder to collect in balls and difficult to spread; if present, it must be removed before use. Method for removing oil stains, oxides, burrs and other impurities on the surface of the weld and joints: oil stains on the surface can be cleaned with environmentally friendly organic solutions such as acetone, alcohol, gasoline, etc. In addition, hot alkaline solutions can also give good results in removing oil stains. Ultrasonic cleaning can be used for small and complex parts or a large number of parts, and after cleaning, they must be dried. Note. Chemicals containing chlorine must not be used to clean refrigeration equipment (eg hydrochloric acid).

The flexibility of the pipeline material. When an operator performs pipeline shaping operations, the flexibility of the piping material directly affects the shaping effect and work efficiency. Provided that the flexibility of the pipeline material is suitable, the operator can easily perform the forming operation before welding in accordance with the quality requirements, and the operation will not be too difficult; if the flexibility of the pipeline material exceeds the required range, it will lead to operational difficulties, pipeline damage and other adverse effects. For example, the pipeline material is too hard, and it is difficult for the operator to bend the pipeline during plastic surgery. Excessive force can easily cause pipeline damage, pipe breakage, and at the same time, work efficiency will decrease. be reduced in comparison. Therefore, external inspection is more important to check the flexibility of the pipeline material. When the pipeline material is hard and difficult to shape during production, it is necessary to evaluate the flexibility of the pipeline material in a timely manner.

Forming method: After the forming operation before welding, most defects such as pipeline rupture and damage caused by the product are related to the forming method, so the rationality of the forming method before welding is especially important. The key to the pre-weld forming operation is that the bending and cutting angle of the pipeline should not be less than 90 degrees, and the twisting angle of the pipeline should not exceed 15 degrees to ensure that the pipeline does not deform. and pipe bending.

System opening time: Before welding, all pipe plugs must be pulled out, because after the plugs of each pipe are pulled out, oxygen, moisture and impurities in the air will quickly enter the compressor and refrigerationoh pipe. Oxygen oxidizes the piping, especially during welding. Once moisture and impurities enter the system, it affects the normal flow of the refrigerant, causing cooling defects such as dirty blockage and ice blockage. Therefore, after molding is completed, how long to weld will directly affect the operation of the entire refrigeration system. Currently, our refrigeration system completes welding within 5 minutes of being opened. If the work is stalled for special reasons, all products of the open system must be stopped after welding or sealing.

Pressure requirements for oxygen, acetylene, nitrogen:

When filling with nitrogen during welding, it is most reasonable to keep the nitrogen pressure between 0.02 MPa and 0.03 MPa. The nitrogen pre-filling method is used at the site before welding, so the nitrogen loss factor after nitrogen filling should be taken into account. The pressure requirement for nitrogen pre-filling is higher than welding during nitrogen filling. At present, the pressure requirement for nitrogen filling before welding is 0.3 MPa~0.5MPa, nitrogen filling time is guaranteed to be 3~5s.

Classification of solder and flux, grade value and main application:

1. Solder classification:

The melting point of solder below 450°C is called solder. The melting temperature of solder over 450°C is called hard solder.

In the process of soldering components of systems and pipelines, solders are mainly used. Due to the different components of solders, when soldering, three basic rules must be observed when choosing solders: the physical properties of solders, the melting characteristics of the solder, the shape of the solder. Based on the analysis of the melting temperature of copper and the main regularities of soldering, it was concluded that when soldering copper tubes and Bundy pipes for soldering, it is necessary to choose solders with a melting point of 600°C-850°C. There are basically two types of soldering solder: copper-based solder, silver-based solder, because there are various brazed pipe joints in the refrigerator refrigeration system, so there are many types of use. the following four types are mainly used:

Secondly, the meaning and main function of the solder brand:

Silver-based solder: Mainly based on silver-copper and silver-copper-zinc alloys, and elements such as tin, manganese, nickel and lithium can also be added to meet different requirements of the soldering process. widely used solder. Because the melting point is not very high, it can wet many metals and has good strength, ductility, thermal conductivity and corrosion resistance. It is widely used for brazing mild steel, stainless steel, copper and copper alloys, Kovar alloy, refractories. Metal

Etc.

P (phosphorus) is the main element that reduces the melting point of solder, increases the hardness of solder joints, and increases the crystallization temperature, improving wettability and spreadability, as well as improving fluidity.

Third, the melting point of copper pipe, Bangdi pipe and solder:

Fourth, flux type, degree value and main function:

The main function of the flux is to remove oxides from the surface of the solder and the base metal, protect the weld and solder liquid from oxidation during the soldering process, and improve the wettability of the liquid solder by the weld. .

Basic steps and highlights of manual flame soldering:

Flame types and how to set them up:

1. Flame types and characteristics:

There are three types of flames for gas flame soldering, as shown in the figure below (three different flame shapes):

1. Neutral flame

Characteristics: When the ratio of acetylene to oxygen is 1:1.2, the resulting flame is called a neutral flame. It consists of a core flame, an inner flame and an outer flame. The core of the flame near the welding tip is white and bright, the second is the inner flame. It is blue-violet in color and has the highest temperature, about 3150°C, at a distance of 2-4 mm from the front end of the core of the flame. Used to heat the workpiece and solder during welding. The outermost layer is the outer flame, and the orange-red core of the flame is about 3-5 cm long. Compared with the oxidation flame and carbonization flame, the sound is more moderate, and the flame temperature is more suitable for copper pipe soldering, so it is also called normal flame. .

2. Oxidizing flame

Features: the flame and the core of the flame are short, the core of the flame is conical, the inner flame almost disappears, there is a strong "sisi" sound is relatively sharp and noisy, the acetylene and oxygen ratio is not balanced, the oxygen content is too high, the oxygen ratio of the flame greater than 1.2 (the standard ratio should be 1 to 1.2), so the temperature is relatively high and concentrated. Copper pipe (Bundy pipe) is easy to overheat during the welding process.

3. Flame of carbonization

Features: the flame and the core of the flame are long, the sound is very delicate, the ratio of acetylene and oxygen is not balanced, there is too much acetylene, and the ratio of acetylene in the flame is more than 1, the standard ratio should be 1 to 1.2). The whole flame is longer than the neutral flame and the temperature is also lower.

Note: In the process of welding Bangdi pipe, the flame of the torch should use a weak neutral flame, prolong the preheating time, and there should not be local burnout of the steel pipe.

2. How to adjust the flame:

Step 1: Before adjusting the flame, make sure that the welding torch (as shown in the figure below) has been used before. If it has not been used for more than 1 hour, the acetylene and oxygen manual valves must be opened and emptied (after a certain period of time). If it is not used, the air will mix between the burner from the valve with the handle to weldingtip, and if the mixed gas in the burner is not emptied before ignition, this can lead to detonation, reverse explosion).

The emptying sequence is as follows: open the oxygen handle valve (turn one turn) to remove air and close it for 5-10 seconds, then open the acetylene handle valve to open (turn one turn) to remove air and close it for 5-10 seconds. 10 Seconds.

Note. When the oxygen and acetylene handle valves on the welding torch are open, the method is to open counterclockwise and close clockwise.

Step 2: Open the acetylene valve with a quarter turn handle, use a lighter or igniter to ignite (the hand should be behind or below the welding tip when igniting with a lighter), slowly open the oxygen valve to adjust the flame size. If the phenomenon shown in Figure 1 occurs when the acetylene valve is opened, it means that the acetylene is opened too much and the acetylene is not completely burned. At this time, the acetylene must be reduced. If it is not reduced, the flame will be blown by oxygen when the oxygen is turned on.

3. Pipeline welding method under special conditions:

1. Due to the short distance between the pipeline and the tank, it is easy to cause the tank to be scalded when welding the pipeline, so the nitrogen shield should be purged when welding (as shown in the figure below);

2. When welding refrigerator-freezer piping, asbestos gaskets should be placed behind the welding points so that the flame does not burn through the inner tank (as shown in the figure below);

3. For solder joints, asbestos gaskets should be placed next to the compressor terminals behind the solder joints so that the flame does not burn the terminals (as shown in the figure below);

Basic steps for soldering copper pipes and Bangdi pipes:

1. Welding method:

According to the actual design of the cooling system piping, there are three welding modes: vertical welding, horizontal welding and inverted welding (as shown in the figure below).

Three welding methods are shown in the figure above. When heated, the welding tip is within 10-20mm of the weld. To ensure uniform heating of the joint, the flame travels along the length of the copper pipe. during welding, make sure that the cup-shaped neck and the surrounding 10mm range are evenly heated inside, but when welding upside down, the lower end should not heat up too much, if the temperature of the copper tube at the lower end is too high, the liquid solder will be lost due to gravity and flow.

Notes:

1. If possible, avoid direct heating of the capillary when welding the capillary;

2. With different pipe wall thicknesses, one should focus on heating the thick wall;

3. First, heat the copper tube inserted into the connection to transfer heat to the insideconnections.

2. Soldering steps:

The flame heating step is very important in flame brazing copper pipes. If the heating position is incorrect, it will lead to safety violations such as corrosion of the copper pipe wall surface, welding torch backfire explosion, and pipe wall burn. through, as well as poor-quality welding. Therefore, it is necessary to ensure the correctness and accuracy of the heating position during the welding process. The heating position of the flame is determined by the size of the flame. According to research on the characteristics of the flame, if the flame is set to neutral, the most ideal position is to use 5-10mm of the flame tip to heat (because the temperature is about 1000 ° C, closer to the melting point of copper pipe).

First step: heating the top of the nozzle (as shown in the figure below, the correct preheating position and the best swing method)

Note: When starting heating, the flame must be heated at the center of the copper tube, otherwise it will cause uneven heating of the tube wall. When the heating state becomes reddish, the flame must fluctuate evenly around the initial heating position (forward and backward movement) Heating to dark red colors (the flame cannot completely leave the copper tube when swinging (moving)) before proceeding to the next step, as shown in the figure below.

Second step: solder addition method (as shown in the figure below, correct feeding position, lower feeding position, too close to the flame, incorrect feeding position)

Note. When the temperature reaches a temperature through which the solder can penetrate (when the base metal turns light red), apply solder from the side opposite to the direction of the flame. The solder flows in the direction of the high temperature, so it must be supplied from the opposite side of the flame.

Note. When adding solder, the nozzle should be used as a guide and the back of the solder should be turned up about 45° so that the flame does not burn your hands. the brazing addition position should also be about 2mm higher than the nozzle. If placed at a lower position, welding bulges will appear, and the soldering addition position must also be guaranteed immediately after the flame heating, in order to prevent the solder from being directly burned by the flame. Because the temperature in the position The flame heating position is higher than the temperature of the back of the flame heating position, so if the solder is added to the flame heating position, the flame will directly burn the filler metal soldering, producing welding bumps and spatter, as shown in the figure, welding defects caused by the incorrect solder filling position, therefore, it is necessary to ensure the correct position of adding solder. surface of the tube gap (it should not be too full, it can completely cover the entire assembly gap), and then remove the solder before proceeding to withnext step;

Third step: Heat up part of the outlet (as shown below)

Note: After making sure the second step is complete, turn the flame down in a "Z" shape and heat evenly until the solder added for the first time has completely penetrated the weld.

During the soldering process, if the flare part is not heated to melt completely and penetrate the solder, it will lead to virtual welding and the phenomenon that the solder and the pipe wall will not fuse. cause the phenomenon of micro-leakage. Therefore, when soldering, it is necessary to ensure the fusion and diffusion of the solder and the base metal. This diffusion phenomenon must be promoted under heating conditions. When the temperature reaches the state of complete melting of the solder, the liquid solder will penetrate into the non-precious metal instant noodle welding phenomenon is called diffusion!

Fourth Step: Thermally Preserve Solder Joints (as shown below)

Note. After the completion of the third step, the flame will follow a Z-shaped path and move evenly to the top of the heating nozzle (heat the position heated in the first step and slowly raise the flame). (avoid pipe wall corrosion), the flame removal rate is about 1 cm per second, while heating the top of the nozzle, solder should also be added until it is uniform and complete. the flame must be slowly drawn back to the tip of the flame core by 3-5 cm, you must stay for about 2-3 seconds to warm the solder joint, and then remove the flame to complete the entire welding stage.

Importance of heat preservation: Although cooling and heat preservation of solder joints is carried out after soldering, the cooling rate also has a great influence on the quality of the joints. If the cooling rate is too low, it may cause grain growth of the base metal and increase the interaction time between the solder and the base metal, which will cause the base metal to dissolve too much in the solder, resulting in dissolution defects; acceleration of the cooling rate helps to refine the structure of the brazed seam, thereby increasing the strength of the joint;

However, if the cooling rate is too high, solder joints may crack due to excessive internal stress, or pores may form due to the fast solidification of the solder joint, so that the gas does not have time to escape. So isolating solder joints to cool them slowly is an important step!

3. Matters Needing Attention During Soldering

In the soldering process, it is necessary to strictly control the flame size, heating time, etc., otherwise it will be difficult to guarantee the internal quality and the appearance quality of welding. soldering steps, the soldering process can be divided into 6 parts (hereinafter referred to as the six main confirmations), as shown in the figure below:

Four. Criteria for evaluating the quality of the appearance of conventional soldered joints of pipeline componentsa

1. Criteria for evaluating the quality of the appearance of single-point flare brazes (cup mouth)

Explanation: Appearance The total height of the solder should be 1-1.5mm above the nozzle, and the surface of the tube wall should be free from corrosion, concave tubes, uneven distribution of solder, and incomplete fusion of the solder to the nozzle (virtual welding) 1. Surface solder on the weld surface must be free of solder joint defects such as pores, and the internal solder penetration must completely fill the rounded bottom corner (see solder joint defects comparison table for details).

The amount of solder added during soldering is also of great importance for the quality of the weld. If less solder is added, it will cause defects such as solder joint leakage and reduced solder joint working load capacity. , Adding more will cause pores, Generation of virtual welding defects, as shown in the figure below, pores inside the solder on the weld surface.

When the solder accumulates on the nozzle, the molten solder mixes with the gas, which prevents the gas from escaping from the solder. does not promote solder wetting, spreading, so the amount of added solder should have a certain limit when soldering.

2. Process Pipe Sealing Weld Appearance Quality Evaluation Standard

Explanation: The appearance of solder filling should be 0.5mm above the nozzle and below 1.0mm. There should be no solder joint defects such as pores on the surface of the solder on top, and the internal solder should penetrate into the gap clamped by the clamp .

4. Criteria for evaluating the appearance of solder joints

The welder evaluates the presence of leakage in the solder joint in the direction of flow and solder consumption during the welding process. If there is uncertainty, a small mirror should be used to check the quality of the appearance of the solder. soldered connection.

Basic steps for soldering various refrigerator pipes:

1. Spot welding of galvanized steel pipe with copper pipe:

Note: When welding galvanized steel pipes, the flame of the torch must be tilted so that the flame does not burn the galvanized pipes, damage the galvanized layer, and cause rust.

Second, spot welding galvanized steel pipe to galvanized steel pipe:

Note: In the process of welding galvanized steel pipe, the flame of the welding torch should be a weak neutral flame, which will increase the preheating time, and there should not be local burnout of the steel pipe.

3. Capillary welding:

Step 1. Heat the copper tube until dark red

Step 2. Add the required amount of solder to the weld

Fourthly, the method of sealing and welding

1. Adjusting the welding flame

In the previous chapter 3, on basic knowledge and method of adjusting the soldering flame, it was stated that the flameRefrigerator soldering should use a neutral flame, and seal welding flame should also use a neutral flame.

2. Sealing and welding method

Sequence of sealing and welding operations:

Adjust the neutral flame (Figure 2.1)→clamp the sealing pliers (Figure 2.2)→pull out the quick connector (Figure 2.3)→sealant welding (Figure 2.4)→forming (Figure 2.5).

3. Factors affecting sealing and welding

Sealing and welding is the last welding process in the production of refrigerators. The quality of sealing and welding directly affects the rate of refrigerant leakage and the cooling efficiency of the entire refrigerator. Therefore, we must work hard to improve our own sealing and welding level and quality level. Factors affecting the quality of sealing and welding can be roughly divided into the following categories: clamping and sealing welding gun operation, sealing and welding operation, and forming.

Clamp welding gun: The position of the clamp welding gun directly affects the welding operation. If the position deviation is too large, it is easy to cause deformation and leakage of process pipe brazed joints, deformation and leakage of nozzles in quick couplings, etc., which will affect refrigerator cooling system. When clamping and sealing the welding tongs, use sealing tongs to clamp at a distance of 20-30 mm from the lower end of the quick connector (as shown in the figure below) Clamp at a distance of ~5 mm.

Sealing and welding operation: after adjusting the torch to neutral flame, heat the process pipe nozzle until the copper pipe on the nozzle turns orange, heat and melt solder to seal and weld the place while feeding. process The solder and the end of the process pipe must be heated at the same time.

Shape change: After the sealing and welding operation is completed, the process pipe must be changed and inserted into the engine room so that the process pipe does not go beyond the vertical plane of the engine room and touch the packing box or cause shock and leakage. . If the shaping operation is not performed properly, it may cause the tube to break or the solder joint to leak. When forming, hold the seal welding pliers, and then push the process pipe into the mechanical room (bottom) along the pipeline extension plane. During operation, prevent the welding joint from leaking due to the pipeline twisting force, and make sure that the process pipe does not go beyond the vertical direction mechanical room.

Solder cleaning, rust protection:

1. Soldered joints are cleaned at high temperature:

When the solder joint is in a state of high temperature (200℃～300℃), it can be cooled down and removed with clean water:

Flux removal: cools quicklye solder joint of copper pipe and galvanized steel pipe with a damp cotton cloth under high temperature conditions of the solder joint and rub back and forth for 2-3 seconds to form a hard flux on the surface. weld due to thermal expansion of the pipeline shrink and fall off.

Cleaning Rags: Clean the rags in clean water after cleaning 5 refrigerators. Remove the flux solution from the rag.

Secondly, solder joints stay clean at room temperature:

When solder joints are at room temperature, you can use a copper wire brush to clean and remove slag; use a copper wire brush to remove welding slag on copper-to-steel and steel-to-steel solder joints. one at a time, if necessary, use citric acid for auxiliary cleaning.

3. Forming after welding

1. The Importance of Post-Weld Treatment

In the second chapter on preparation for soldering, we introduced the meaning, operation method and influencing factors of pre-weld forming, and here we also introduced the whole content of post-weld forming.

The main purpose of pre-weld forming is to connect the refrigerant piping correctly and at the same time facilitate welding and ensure welding quality. Raised joints in solder joints can lead to solder joint leakage and safety accidents. We also need to reprofil the piping in the mechanical room of the product, so post-weld reprofiling operations are necessary.

2. Post-weld forming method

The sequence of operations for shaping the pipeline after welding:

Condenser line formation (Figure 3.1) → Filter drier formation (Figure 3.2) → Filter drier piping → (Figure 3.3).

3. Factors affecting the formation after welding

The quality of forming after welding is directly related to the performance and safety of product testing, so we must pay attention to various influencing factors. Factors that directly or indirectly affect the quality of shaping after welding can be divided into: methods, pipeline materials and the location of dry filters. Tighten the lock and save it. Southern Club HVAC

Shape reshaping method: Just like pipe reshaping before welding, after the reshaping operation after welding, most defects such as pipeline rupture and damage caused by the product are due to the reshaping method. Therefore, the rationality of the pre-welding method is especially important . The key to the pre-weld forming operation is that the bending and cutting angle of the pipeline should not be less than 90 degrees, and the twisting angle of the pipeline should not exceed 15 degrees to ensure that the pipeline does not deform. and folding the tube. Help hold the filter drier and perform the shaping operation with your right hand (as shown in Fig.See below) and change the shape of the filter drier to a fixed position. In the process of reshaping, the capacitor is mainly used to prevent the interaction force between the filter drier and the capacitor from causing leakage of solder joints.

Pipe material. When an operator performs pipeline shaping operations, the flexibility of the piping material directly affects the shaping effect and work efficiency.

As long as the flexibility of the pipeline material is suitable, the operator can easily perform the forming operation before welding in accordance with the quality requirements, and the operation will not be too complicated; if the flexibility of the pipeline material exceeds the required range, it will lead to adverse effects such as difficult operation and damage to the pipeline.

For example: The piping material is too hard. During plastic surgery, it is difficult for the operator to bend the pipeline. Excessive force can easily damage the pipeline, break the pipeline, and work efficiency will be reduced. reduced in comparison. Therefore, external inspection is more important to check the flexibility of the pipeline material. When the pipeline material is hard and difficult to shape during production, it is necessary to evaluate the flexibility of the pipeline material in a timely manner.

Dry filter position: The position of the dry filter greatly affects the transport and use of the refrigerator. If the dry filter is irregularly shaped, it may lead to defects such as capillary leakage, difficulty in packing the refrigerator. box and pipeline damage during transportation. The dry filter re-forming position should be located behind the corner of the machine room (as shown in the figure below), without going beyond the vertical plane of the machine room, to prevent scratching fingers and leakage when the lock is tightened. shock during transport and use.

A caveat for the puff lock: Because the puff lock must ensure that the dry filter is fixed after binding, to prevent the filter drier from slipping and at the same time prevent the puff lock from falling off, so cut and pull after tightening the lock When tightening the lock, leave 2 to 3 teeth to keep the lock from falling out (as shown in the picture below).

Fourthly, paint the solder points to prevent rust:

After cleaning the solder joints, apply a black quick-drying anti-corrosion paint with a brush to the solder joints. The solder points must be in place and there must be no loose parts around the solder points.

Note:

1. In addition to solder joints in freezer and cold rooms, copper-to-copper, copper-to-steel and steel-to-steel solder joints in the mechanical room must be painted.

2. With the exception of the solder joints of the dry filter, the remaining solder joints must be smeared more than 3 cm from the solderconnections.

3. Place the brush in thinner when using to keep the brush from drying out and hardening (as shown in the picture below).

Description of the classification of various solder joints:

1. Description of solder joints:

The welding point between the evaporator return air pipe and the connection pipe is 1, the welding point of the compressor return air pipe is 2;

The welding points of the condensation pipe on the side of the exhaust pipe of the engine room and the anti-condensation pipe are located in series inside 3 and outside 16;

The solder joints of the condenser and connecting pipe on the other side of the mechanical room are inner 9 and outer 17 respectively;

There are 4 solder joints between the compressor outlet and the condenser; 5 soldering process pipe press;

Brazed joints of the compressor exhaust pipe - 6; solder joints dry filter capacitor - 7;

Welding point of the sealing pipe of the process pipe with two dryer pumps - 8; welding point of the sealing technological pipe of the press - 18;

10 solder between dry filter and capillary tube; 12 solder capillary tubes inside the box;

The capillary connections in the foam are numbered 19 and 20, the copper tubing connections in the box are numbered 11 and 21;

13, 14, 15 and 26 temperature controlled capillary solder joints in mechanical room;

Two points on the jaws of the jaws of the process pipe of the compressor - 22 and 23 (the point near the press is 22, and the point near the sealing weld is 23;);

The pinch points of the tongs on the double suction drier filter are 24 and 25 (the point near the dryer is 24 and the point near the sealing solder joint is 25;);

2. Classification of brazed joints of various pipes:

1. Soldering galvanized pipe-copper pipe: 3, 4, 7, 9, 16, 17, 30;

2. Copper tube soldering - copper tube: 1, 2, 5, 6, 11, 21;

3. Capillary solders: 10, 12, 13, 14, 15, 19, 20, 26;

4. Seal welding point: 18, 8 (process pipe sealing point on the filter drier);

5. Places for sealing tongs: 22, 23, 24, 25;

Answers to frequently asked questions about soldering various refrigerator pipes:

Comparison table of common welding defects:

Technical requirements for repair welding:

Repair welding is a measure to eliminate defects in solder joints, but not all joints with quality defects can be used this method.

1. A few joints that cannot be repaired:

A． Burnt joints. B. The copper pipe at the joint is corroded. C. Joint cracking phenomenon is severe (generally more than 2mm). D． Joint that was repaired once. E. The copper tube at the joint is very thin.

2. A few connections that can be repaired:

A． The joint space is not partially filled. B. Brazing material is embossed on one side only, roundednot completed and the surface of the brazed joint is rough. C. There are impurities in the solder joint (digest after removing the solder joint). D. There are leaks (weld not repaired) E. There are pores in the weld F. The butt and wall of the outer shell are too large (more than 2 mm) and must be heated with an external flame and the direction must be shifted towards the weld.

Issues to pay attention to when using solder in the maintenance team: The maintenance team should use BAg34CuZnSn solder for maintenance.

It is not allowed to add solder with hard flux when welding ordinary copper pipes; a small amount of hard flux can be used when welding Bondy pipes, and a small amount of hard flux can be added when repairing refrigerators, but the solder joints must be cleaned.

Frequently asked questions

1. Is hand flame soldering the same as gas welding?

Answer: Not the same. Gas welding refers to fusion welding, so gas welders must melt the base metal and filler material during operation to form a strong joint or weld. In the manual flame soldering process, the heating temperature must be strictly controlled to avoid melting the base metal during the soldering process. As long as the heating exceeds the melting temperature of the solder, solder joints or welds may be damaged. achieved without melting the base material.

This operational difference is especially important when switching from gas welders to soldering irons.

Secondly, is it possible not to fill them with nitrogen when soldering copper pipes?

Answer: No, when brazing copper pipes, it is necessary to introduce nitrogen gas to prevent dirt and metal oxides from clogging the internal piping of the refrigerator during welding. When we weld, the copper tube is oxidized by atmospheric oxygen at high temperature and forms a layer of oxide film on the surface of the copper or galvanized tube. The system is not cooled, and such a phenomenon is quite harmful. The welder must fill the shield with nitrogen during welding to prevent this kind of phenomenon from occurring.

Third, what is distribution?

Answer: Diffusion itself is a material transfer process, a material macroflow phenomenon. For example, by dropping a drop of ink into a glass of water, we can clearly see that the ink gradually spreads in water, and over time, the spreading area becomes larger and the color lighter, i.e., the concentration becomes smaller. It is not difficult to detect this phenomenon: the ink diffuses from a place of high concentration to a place of low concentration.

4. What is solder wetting and spreading?

Answer: As shown in the figure below (left): the whole process of wetting and spreading when soldering. There are many examples of this in nature. For example, if you drop a drop of water on a clean glass plate, then the drop of water will completely spread over the glass plate, as shown in Fig.at this time, it can be said that the water completely wets the glass plate if, when a drop of oil falls, the drop of oil forms a semicircle and spreads of course, as shown in the figure below. At this time, it can be said that a drop of oil can wet the glass plate; if you drop mercury, the mercury forms a spherical body on the glass. Roll over the plate as shown in the figure below, at this time, it means that the mercury has not hit the glass.

5. What are the advantages of brazing copper pipes? What are the disadvantages?

Answer: Advantages of brazed copper pipes:

⑴The heating temperature is low, and the structure and properties of the base metal change little;

⑵The connection ensures accurate assembly, the deformation after welding is small, and the structural size is easy to ensure;

⑶ For assembly structures such as flare joints, lap joints, butt joints, soldering can be used to connect;

⑷ Soldering can be used to connect copper pipes with different wall thicknesses and diameters

⑸ High production efficiency, easy automatic production welding.

Disadvantages of soldering copper pipes:

⑴ The bond strength is relatively low and the heat resistance is low;

⑵The use of joints such as sockets, butt joints, lap joints, etc., which increases the consumption of the base metal and the weight of the structure;

⑶ There are various degrees of electrochemical corrosion between the joint and the base metal.

6. What factors affect solder wetting?

Answer: Solder wettability is influenced by many factors, mainly in the following aspects:

⑴Influence of composition of solder and base metal;

⑵Influence of soldering temperature;

(3) Influence of non-ferrous metal oxides;

⑷Flow influence;

7. Does solder wettability change at high heating temperatures?

Answer: Yes, the heating temperature affects the wettability, the higher the heating temperature, the smaller the contact angle θ, which improves the wettability, but the higher the heating, the better. If the temperature is too high, the wettability of the solder is too high, which will cause the solder to flow to places other than the solder joints, resulting in uneven welding. If the temperature is too high, it will also cause corrosion and other phenomena.

8. Does solder wettability change at low heating temperatures?

Answer: Yes, the soldering temperature is too low, the soldering viscosity increases, the fluidity becomes poor, and the wettability is too weak, resulting in insufficient filling and solder penetration, making it difficult to fill the joint gap, thus forming poor solder joints.

9. How does uneven heating affect solder wettability?

Answer: In the case of socket soldering of copper pipes, uneven heating is common. On the side close to the flame, the temperature tends to rise, and on the otherside the temperature is low. With this uneven heating phenomenon, the solder on the high temperature side melts first, wets and fills the seams, while the solder on the low temperature side has not yet melted or is in a liquid-solid mixing state. the wettability of the solder at this time is poor. When the solder on this side reaches normal wetting, the higher temperature side loses solder, evenly fills the gap, and melts the copper pipe nozzle. corrosion defects.

10. Does the oxide on copper tube surfaces affect solder wetting?

Answer: The presence of oxides on the surface of copper tubes will seriously affect the wettability of the solder liquid of the copper tube surface. Direct contact between the material and the surface of the copper tube will cause the liquid solder to agglomerate into an agglomerate. spherical shape, that is, a non-wetting state is formed. The solder joints will also oxidize after soldering, so it will be difficult for the solder to spread over the solder joints when resoldering.

eleven, Is it possible not to keep warm when soldering copper pipes?

Answer: No, although solder joints are cooled and kept warm after soldering, the cooling rate also has a big impact on joint quality. If the cooling rate is too low, it may cause the growth of wood grains and the interaction time between the solder and the base metal, which will cause the base metal to dissolve too much in the solder, resulting in corrosion defects; acceleration cooling rate is favorable for finishing The structure of the solder joint can improve the strength of the joint, but the cooling rate is too high, which may cause cracks in the solder joints due to the generation of excessive internal stress, and pores may also form due to the rapid solidification of the solder joint, so that the gas can't get out. So isolating solder joints to cool them slowly is an important step!

12. Can oxygen burn?

Answer: No, oxygen itself does not burn, but it is an extremely active gas that supports combustion. Oxygen on contact with flammable materials will burn violently and cause an explosion. Therefore, it is forbidden to contaminate all equipment and tools of oxygen pipelines or gas cylinders with flammable materials such as grease.

13. Is it possible not to install a tempering stop valve?

Answer: No, the working principle of the release shut-off valve is very simple, it basically plays the role of one-way conduction. When the welding torch has a backfire, it can effectively prevent the flame from entering the inside of the pipeline and avoid accidents.

14. When the flame heats up the copper pipe, is the welding tip closer to the wall of the copper pipe?

Answer: No. Currently, the welding torches used by our company are unified as jet-suction weldingtorches. After seeing the working principle of jet-suction welding torches, it is not difficult to understand that when the welding tip is too close to the copper pipe wall, it will cause hardening, explosion, and the flame is too close to the copper pipe wall will cause corrosion of the pipe wall, which will cause hidden dangers. for welding quality.

Fifteen, why use flow?

Answer: Most metals oxidize in the atmosphere, and their surface is covered with an oxide film. When soldering copper tubes, if there is an oxide film on the surface, it cannot be wetted by liquid solder, just as if liquid solder is wrapped with an oxide film, it cannot spread on the wall of the copper tube. Therefore, in order to complete the soldering process and obtain quality joints, it is very important to completely remove the oxide film from the surface of the copper tube and the surface of the solder.

Sixteen, what are the functions of the stream?

Answer: In technical terms, flux is called "flux". There are many different flux states, such as flux powder, liquid flux, etc., but they all play the same role in the soldering process. ⑴, remove the oxide film on the surface of the base metal and the surface of the solder; ⑵, prevent the re-oxidation of the base metal during the heating process; 3, improve the wettability of the solder.

17. Why is it difficult for the solder to stick to the copper tube after soldering when it is being redone again?

Answer: There are several common metals that do not oxidize in air. During soldering, because the copper tube is oxidized when heated at high temperature, an oxide layer is formed on the surface of the copper tube. Therefore, it is necessary to carry out secondary repairs. The solder is difficult to dissolve with oxides when welding.

18. What is the heating procedure for soldering copper pipes with the same wall thickness?

Answer: The heating steps are very specific when welding copper pipes. Heating method for the same pipe wall: first swing up and down within 20mm of the pipe mouth to preheat. When observing the dark red state of the pipe mouth, the flame should heat the position of the top of the nozzle by 3mm-5mm, and then add solder, and then heat the bottom of the nozzle after filling with solder, so that the solder can completely penetrate the weld (when welding one and the same pipe wall, the top of the nozzle heating time is about 2 seconds longer than the top of the nozzle).

19. How is soldering copper pipes with different wall thicknesses?

Answer: When welding copper pipes with uneven walls, if the upper part of the nozzle has a thinner pipe wall and the lower part is thicker, the heating steps are as follows: first, heat within 6 mm below the nozzle. the nozzle is dark red, the flame swings up and down within 10mm of the heating nozzle, and then heats the bottom of the nozzle after filling with solder, so that the solder can completely penetrate the inside of the weld (pipe walls are different. In the case of weldingki the heating time of the lower part of the nozzle is longer than the upper part of the nozzle (about 2 seconds).

Soldering operation "ten without welding":

1. Welding is prohibited if there is air leakage on each connecting part of the welding machine;

Secondly, if you are not a welder, you will not weld;

Third, do not weld if the piping assembly is not installed;

Fourthly, do not weld if there is water and oil in the pipe;

5. Do not weld unless labor insurance products are completely worn out;

6. Welding without nitrogen filling is prohibited;

7. Welding is prohibited if the welding torch is not equipped with a release shut-off valve;

8. Welding is prohibited if the solder joints of the cooling evaporator are not protected;

9. Do not weld if the solder grade does not match;

10. The corroded pipe wall is not replaced or welded.

Welders must strictly observe the "Ten Welding Prohibitions" rules regarding welding soldering operations!

Cases of poor soldering quality:

A case of severe corrosion of solder joints:

Cause analysis: after investigation, the operator of this process has little sense of responsibility and does not apply Vaseline to solder joints in strict accordance with the requirements of the process; at the same time, the advanced management personnel of the workshop and the quality department did not carry out sufficient inspection and monitoring and did not work on this process. Effective quality control is the main cause of quality related accidents.

A case of cracking and leaking filter solder spots:

Analysis of the reasons: after analyzing the actual object, the solder material between the two pipes of the two-point filter has insufficient penetration and is pulled out in the process of forming the pipe, filling with fluorine and sealing, resulting in brittle solder joints, internal solder leaked around the walls of the tube on both sides, but the solder does not penetrate or penetrate the middle (as shown in the figure below).

Filter metallographic analysis

Corrective action: formulate welding technology requirements for two-point filters to ensure the consistency and correctness of welding methods, conduct whole pipe welding training, fluorine filling, etc., so that they can understand the characteristics of solder. joints.

Condenser outlet tube burnout case:

Event Description: When leaks were detected, two 46W capacitors were found to have raised an alarm. After unpacking, it was found that both of them were caused by severe tube wall erosion (commonly known as: burnout) and repair welding (one of the condenser outlet tube is burned out, one of them is the condenser connecting pipe is burned out), there is a hidden danger of great quality.

Cause analysis: after investigation, it was found that the corroded pipe wall was covered with solder, so it can be concluded thato The team did not replace the burnt copper pipe in order to save money, resulting in a leak!

The corroded wall of the pipe is coated with solder.

Compressor return duct overheating case:

Event Description: Compressor air return pipe overheated within 20 minutes of welding.

Brazed area of ​​return air pipe overheated

Evaporator welding body:

Event Description: Evaporator

When the parts are used, when the collection staff recovers the helium gas, the equipment will sound an alarm and the red indicator will light up, which is considered a substandard product. The reason is that there is no helium in the inlet pipe of the evaporator. After inspection, it was found that one of the welds of the tee had burned through.

Cause Analysis: After investigation, it was confirmed that the tee was welded and clogged. Upon further inspection, it was discovered that one of the welds on the tee had burned through, the reason being that the welder repaired the tee. The mouth of the flare was burned and the long U-tube was not immediately removed to replace it, and solder was added directly to the burnt mouth of the flare, blocking the weld.

Attachments:

Gas flow and generator:

Gas flow

1. Gas flow introduction:

The flux is a colorless liquid (slightly yellowish) consisting of borides (trimethyl borate) and alcohols. It is used to prevent welding oxidation during welding, and forms an anti-corrosion layer on the surface of the weld to improve the corrosion resistance of the weld. The flux readily decomposes into borides and methanol upon contact with water or moist air. When the boride in the flux burns, it easily decomposes and forms a white mist when it comes into contact with moist air. If the air pressure is low, the air is humid, or the environment is poorly ventilated, it is easily adsorbed to the surface of a wet object to form a white powder or white flakes.

Secondly, how it works:

The flux evaporates in the welding generator and mixes uniformly with the gas (natural gas) before being fed into the welding torch. When burning, it can quickly form a protective layer on the metal surface, and can reduce metal oxides, preventing the formation of oxides and improving welding quality. After welding the workpiece, the weld has an orange or natural color. An anti-corrosion layer is formed on the surface of the weld, which increases the corrosion resistance of the weld. It can improve the structure of the weld (to prevent burnout) and improve the ductility and strength of the joint. It can reduce and eliminate defects such as air holes, sand holes, cracks, etc. in the weld.

Gas Fluxing Agents, more precipitation falls during use, and it is easy to block LPG pipelines and valves. The main reason for this phenomenon after analysis: trimethylborate is decomposed by water.

SoSo the white powder should be B2O3 and H3BO3.

Gas flow generator:

As the most important equipment of gas flux flame brazing technology, the flux generator is a kind of gas flux (called flux) that can be added to gas (acetylene, LPG, propane, etc.) into the form of steam. Modern equipment eliminates the problem of manually adding borax to the flame soldering process in the past, which greatly simplifies the soldering process. Since the flux addition form in this process is uniform and continuous addition, the flux can completely cover the welding part in the burning torch flame, which not only increases the wettability and fluidity of the solder, but also reduces pore formation and improves welding quality, prevents oxidation and blackening of the surface of the welded area, after welding, pickling is not required.