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Vacuum Brazing Furnace

Research on Vacuum Brazing Technology of Ceramic and Metal

Ceramics in the welding of ceramics and metals basically refer to new ceramics that are artificially synthesized from various metals, oxygen, nitrogen, carbon, etc. It has high strength, high temperature resistance, wear resistance, corrosion resistance, super hardness and other characteristics, and has been widely used; commonly used are alumina, silicon nitride, zirconia ceramics and so on. Advanced ceramic materials have attracted widespread attention due to their unique mechanical and functional properties. Ceramics and metals are connected to form composite components, which can give full play to the respective advantages of ceramics and metals, and are widely used in microwave devices, vacuum switches, electronic packaging, high temperature and high pressure sensors, mechanical seals, nuclear energy, solar energy, aerospace and other fields.

Difficulties in welding ceramics and metals

1.The coefficient of linear expansion of ceramics is small, while the coefficient of linear expansion of metals is relatively large, resulting in easy cracking. Generally, the thermal stress problem of the metal interlayer should be well handled.

2.Ceramics have low thermal conductivity and weak thermal shock resistance. During welding, the temperature gradient of the welding part and its surroundings should be reduced as much as possible, and the cooling rate should be controlled after welding.

3.Most ceramics have poor conductivity, or even no conductivity, so it is difficult to use electric welding. Special technological measures are required for this purpose.

4.Due to the stable electronic coordination of ceramic materials, metal-ceramic connections are unlikely. Ceramic metallization or active solder brazing is required.

5.Since ceramic materials are mostly covalent crystals, they are not easy to deform, and brittle fracture often occurs. At present, the intermediate layer is mostly used to reduce the welding temperature, and the indirect diffusion method is used for welding.

6.The structural design of ceramic and metal welding is different from ordinary welding. It is usually divided into flat sealing structure, sleeve sealing structure, needle sealing structure and opposite sealing structure. The sleeve sealing structure has the best effect, and the production requirements of these joint structures are very stricthigh.

The advantages of vacuum brazing

1.Vacuum brazing is carried out in a vacuum atmosphere, which significantly improves the corrosion resistance of the product, avoids various pollution, pollution-free processing equipment costs, and has good safety production conditions.

2.Vacuum brazing solder has good wettability and fluidity, and can weld more complex and narrow-channel devices. Vacuum brazing improves the yield of products and obtains a strong and clean working surface.

3.Compared with other methods, the internal structure and fixtures of the furnace have a long service life, which can reduce the maintenance cost of the furnace. Moreover, the uniformity of the furnace temperature is high, and the production is automated, so that high-quality welding parts can be obtained.

4.There are many materials suitable for vacuum brazing, such as: aluminum, aluminum alloy, copper, copper alloy, stainless steel, alloy steel, low carbon steel, titanium, nickel, Inconel, etc. can be brazed in a vacuum electric furnace For welding, the designer determines the required material according to the use of the brazing device, among which aluminum and aluminum alloys are the most widely used.

Ceramic and metal welding process

1.Cleaning: The surface of metal and solder must be cleaned, and ceramics are usually cleaned with ultrasonic cleaning agent.

2.Paste: The paste is mostly composed of pure metal powder and appropriate metal oxide powder, and the particle size is mostly between 1 and 5um. It is made into a paste with a certain viscosity with an organic binder. Then use a painting tool to evenly coat the paste on the ceramic surface to be metallized, and the thickness of the coating is generally 30~60um.

3.Mounting: Assemble the processed metal parts and ceramic parts with stainless steel, graphite and ceramic molds, and install brazing at the joints; the parts to be welded should be kept clean during the entire operation process, and bare parts should not be usedhand touch.

4.Vacuum brazing: Brazing is carried out in a vacuum furnace. The temperature selection and heating speed selection should be determined according to the characteristics of the brazing material used. Special attention should be paid to the cooling speed not being too fast to prevent the ceramic parts from being damaged due to temperature stresscracking.

5.Post-welding inspection: After ceramics and metals are welded, firstly inspect them with naked eyes, and then carry out necessary inspections according to the requirements of technical documents.

Process technology must be matched with excellent equipment to play a role, and the brazing furnace selected in vacuum brazing is very important. The RHVB vacuum high-temperature brazing furnace produced by SIMUWU is an excellent product for handling such processes. With its excellent temperature control accuracy and temperature uniformity, it can realize the brazing of workpieces evenly, so as to achieve high-level brazing standards, reduce scrap rate, increase production efficiency and reduce costs.