Welding process for new energy relays

New energy relay technology, vacuum brazing of arc extinguishing cover (static point joint component)

New energy relays require electrical performance requirements such as high voltage, high current carrying capacity, and long lifespan. The product must ensure long-term contact voltage drop and insulation strength, and the moving and stationary points must be sealed in a vacuum or inert gas environment without oxidation. High alumina ceramics, due to their excellent electrical properties such as low dielectric loss, high volume resistivity, high strength, high hardness, low coefficient of linear expansion, wear resistance, and good heat resistance and impact resistance, are metalized and welded together with the stationary point and kovar gas tight to form arc extinguishing cover components with high mechanical strength and vacuum density.

The welding of the arc extinguishing cover involves positioning the parts to be brazed in a vacuum brazing furnace through a brazing fixture for brazing. Vacuum brazing is achieved in a closed furnace to approximate a vacuum state, preventing reactions between the workpiece and oxygen and other active gases in the air during the high-temperature brazing process. Gas residual welding strength is high under high vacuum. A welding method that uses a metal material with a lower melting point than the base material as the brazing material to heat and insulate the structural components and brazing material, melting the brazing material at an appropriate temperature (lower than the melting point of the base material) and time range. The liquid brazing material is fully immersed, dissolved, diffused, and welded with the solid metal under capillary force, thereby achieving the welding purpose.

The high vacuum brazing furnace of the molecular pump system (including bedroom and vertical) can achieve almost enclosed vacuum brazing, reduce the content of oxidizing gases, and control the generation of metal oxides.

The "turbo molecular pump system" obtained by high vacuum in the furnace has obvious advantages over the mainstream "oil diffusion pump system":

1. Clean, oil-free steam backflow, relatively simple system (no need for any traps);

2. The vacuum degree of the molecular pump can reach 10-7Pa level, while that of the diffusion pump is 10-5Pa level;

3. The inlet pressure range of the molecular pump is wide: 13.33Pa to 133.3mPa. And such a wide range will make the operation of the diffusion pump (1Pa~100mPa) unstable;

4. The time for the molecular pump to reach normal operating speed is short (a few minutes) and it can be immediately shut down, with low power consumption during operation. The diffusion pump needs to heat the silicone oil at around 240 ℃ to achieve normal pumping speed.

The entire heating process is automatically controlled. In a vacuum brazing furnace, the workpiece is mainly heated by thermal radiation. The vacuum brazing temperature directly affects the brazing quality. When the brazing temperature is low, the brazing material has not yet reached the necessary temperature, and the fluidity and wettability of the brazing material are poor. It is easy to produce defects such as internal pores, discontinuous brazing joints, and virtual welding, which reduce the strength of the brazing joint, fail to meet the pressure bearing capacity, and cause leakage. In severe cases, it may even tear; When the temperature is high, the brazing material completely melts and has excessive fluidity, which can easily cause oxidation of the brazing material to form pores and reduce the capillary force on the weld seam, resulting in defects such as brazing material loss, melting corrosion, and product bending. Liquid solder has good wetting and flowability to the welded metal, can fill the brazing gap well under capillary force, and can produce good alloying effect with the welded metal, forming high-strength joints.

The automatically controlled temperature rise fully ensures the quality of brazing. The high brazing (horizontal furnace) of the molecular pump system also comes with a forced rapid cooling system, which can quickly cool down below 70 ℃ under high temperature conditions, meeting process requirements.

Brazing operation process for welding components such as arc extinguishing hood: Load the parts into a dedicated brazing fixture and stabilize the furnace → Close the furnace door and various inlet valves → sequentially open the front stage pump → Open the pre extraction valve → Close the pre extraction valve → Open the front stage valve → Open the molecular pump → Open the main valve → Start the temperature control program (heating, insulation, heating, visualization, insulation, cooling with the furnace) after reaching the vacuum degree → Close the main valve, molecular pump, front stage valve, and front stage pump in sequence → Open the high-purity nitrogen inflation valve in sequence below 400 ℃ → Close the nitrogen inflation valve in sequence (with a forced rapid cooling system that can be started) → Cool down below 70 ℃ (after closing the rapid cooling system) → Open each inlet valve → Open the furnace door and exit Furnace.

In all processes, only temperature control (curve) programs are developed and adjusted based on actual welding results (differences in brazing product quantity, specifications, brazing materials, etc.). All other processes must be operated according to the operating procedures and usage steps, and the operation of each pump and valve before cooling can also operate automatically according to the settings.

Compared to the brazing method of gas shielded welding, vacuum brazing has significant advantages:

1. No flux required. Significantly improved the corrosion resistance of the product, exempted various types of pollution, pollution-free treatment equipment costs, and provided good safety production conditions.

2. Vacuum brazing not only saves a large amount of expensive metal brazing flux, but also does not require complex flux cleaning processes, reducing production costs.

3. The wettability and flowability of vacuum brazing filler metal are good, and the welding of complex and narrow channel devices improves the yield of products, achieving a sturdy and clean working surface.

4. Compared with other welding methods, the internal structure and fixtures of vacuum furnaces have a longer lifespan and can reduce maintenance costs.

5. There are many materials suitable for vacuum brazing, which can connect different metals and achieve complex structures while welding. The welded joint is smooth, dense, with small deformation and excellent mechanical and corrosion resistance properties.

At present, vacuum brazing technology has been widely used in the electronic industry for brazing copper and stainless steel, aviation engines, engineering machinery, vehicles and ships, air separation equipment, petrochemical industry, and other fields such as air conditioning units and various electric heaters for heat exchange core strips. Of course, it is also gradually being applied in the new energy relay industry.