This is a successful case of vacuum brazing Si3N4 ceramic material and Q235 mild steel.

First, the composition of the glow plug

The glow plug is mainly composed of a heating element and a shell. The heating element is made of Si3N4 ceramics, and the shell is made of Q235 steel. They are connected and assembled as shown in Figure 1. Using Ag-30Cu-1.5Ti as solder, the method vacuum soldering is used to realize the connection between them.

Second, preparation before soldering

1. Polish with sandpaper to make the solder and the two bare metal electrodes on Si3N4 shiny, and then clean with acetone or carbon tetroxide. The 235 steel outer set is cleaned using the normal rust removal and metal degreasing process.

2. Insert a sheet of material with a thickness of 0.05-0.15mm between the SiN4 heating element and the steel sheath, and then wrap a 1.5mm diameter solder wire around the steel sheath. Put the solder sheet into the steel cap, then attach it to the heating element and place it on the bottom support according to the picture.

Third, the soldering process

Put the assembled components together with the bottom bracket into the soldering oven. Soldering parameters used: vacuum degree 6×10-3Pa, soldering temperature 30~100℃ higher than soldering melting point, holding time 5~10min. , the heating rate is limited to ensure the degree of vacuum, and the cooling rate is less than 10°C/min. Take it out after it has cooled down and carry out a general assembly and inspection