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Vacuum Brazing Furnace

Vacuum Brazing of Hydrogen Generator Components

Nitrogen generator is a set of equipment that can extract nitrogen. Its main application fields are: aerospace, nuclear power nuclear energy, food and medicine, petrochemical industry, electronics industry, material industry, national defense and military industry, and scientific experiments.

The cell body is an extremely critical part of the ultra-pure hydrogen gas generator. After the hydrogen is separated by it, the purity can reach more than 99.999%. It is brazed by a palladium alloy tube with a grade of PdAg20 and a specification of φ3×0.08 and a pure nickel flange. In the past, oxyacetylene flame brazing was used, and the solder was silver-copper alloy. Due to the poor corrosion resistance of the brazing seam, pure silver is used instead of silver-copper solder, but the brazing process performance is very poor, and it is difficult to ensure the quality of the brazing seam. The advanced vacuum brazing process not only can obtain excellent brazed joints, but also eliminates the tedious cleaning work after flame brazing.

Vacuum Brazing Process

1.Cleaning before welding

Degrease with gasoline or carbon tetrachloride, polish with emery cloth, scrub with alcohol, and clean the nickel flange. After pickling, rinse with cold and hot water, scrub with alcohol, and blow dry. To clean the palladium alloy tube and silver wire, wipe with alcohol to remove oil and then blow dry.

2.Positioning and assembly of weldments

In order to prevent the surface of the cleaned weldment from being polluted, absorbent cotton gloves should be worn during assembly and positioning of the weldment. According to the structural characteristics of the brazing parts, using the burr positioning method, 3 burrs are evenly punched around each small hole in the lower part of the nickel flange to prevent the pipe from leaking. After the silver-based solder ring is placed, the tube bundle is fixed with a heat-resistant alloy grid to control the instability and deformation of the tube bundle at high temperature.

3.Determination of vacuum brazing process parameters

Process parameters include vacuum degree (cold vacuum degree and hot state vacuum degree), heating rate, brazing temperature, holding time, cooling rate and exit temperature. Here, brazing temperature and holding time are important process parameters.

The melting point of silver is 961.93°C. Brazing is a process in which solder fills the joint gap under the action of capillary force to form a joint. The selection of brazing temperature should not only consider melting the solder, but also make the fluidity and wettability of the solder out of the best state. The brazing temperature should not be too high, and the holding time should not be too long. When the temperature is about 975°C and the holding time is 3 to 5 minutes, the brazing quality is the best.

4.Post-weld inspection

After the palladium alloy and the nickel pool body are vacuum brazed, they must withstand the air tightness test of 1MPa pressure.

The vacuum brazing process solves the welding problem of the palladium alloy and the nickel pool body. By strictly controlling the maximum heating temperature and holding time, excellent brazed joints can be obtained, and the first pass rate of air tightness inspection is 100%. Compared with the flame brazing of the old process, the vacuum brazing of palladium alloy and nickel pool body can avoid the tedious post-welding cleaning work, improve the corrosion resistance of the brazing seam, and prolong the service life of the instrument.

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.