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stainless steel vacuum brazing furnace
Vacuum brazing is a kind of brazing method without brazing flux under vacuum condition. Mainly used for brazing materials with dense oxide film, such as stainless steel, aluminum alloy, superalloy.
Characteristics of stainless steel vacuum brazing furnace:
(a) During the whole brazing process, the brazed parts will not be oxidized, polluted and deteriorated under the vacuum condition, and the cleanliness and strength of the welded joints are higher.
B) When brazing, the whole part is heated uniformly and the thermal stress is small, so the deformation can be controlled to a minimum, which is especially suitable for brazing of precision products.
C) Because no brazing flux is used, there will be no defects such as pore and inclusion. The process of cleaning residual flux after brazing can be omitted and the efficiency can be improved.
D) It can eliminate all volatile gases and impurities released at brazing temperature and improve joint performance.
Stainless steel brazing operation in vacuum brazing furnace mainly includes the following steps:
1) Assemble the workpiece and add brazing material;
2) Place the assembled workpiece in the brazing furnace;
3) Close the furnace and vacuum it to meet the corresponding technical requirements.
4) To ascend and descend the temperature according to the set temperature curve;
5) Product Discharge
The two key parameters of stainless steel vacuum brazing are vacuum (pressure rise and fall) and temperature curve of brazing furnace. Generally, when heating, the vacuum pump needs to be opened all the time, which has reached the technical requirements of vacuum degree.
Vacuum brazing process, like ordinary brazing process, needs to control the gap of workpiece joints. When brazing, the filler metal fills the gap by capillary action. Correct selection of joint clearance greatly affects the compactness and strength of the brazing seam. Different solders have different requirements for joint clearance.
Common defects of stainless steel vacuum brazing furnace:
1. Surface oxidation of parts
Cause: Oxygen partial pressure in the furnace is high, with air or water entering.
Causes: high leakage rate of equipment or faulty parts of the pumping system, or fixture is water, oil pollution is contaminated furnace.
2. no penetration.
Joint clearance is not partially or totally filled with filler metal, or the filler metal and base metal are not fully fused.
Causes: insufficient vacuum, the oxide on the surface of parts has not been thoroughly removed; the surface of parts is not clean; the gap between joints is too large.
3. deformation:
Cause: The local internal stress caused by temperature, placement of filler metal and performance of base metal exceeds the yield point of component material.
Main factors affecting the quality of stainless steel vacuum brazing furnace
1. Process parameters of vacuum brazing;
2. Leakage rate of equipment;
3. Surface cleanliness of parts and tooling;
4. Assembly clearance and product placement status;
The selection of brazing material (filler metal) for stainless steel vacuum brazing furnace depends on the material characteristics of the workpiece being welded and the service environment of the workpiece after welding. Because stainless steel is mainly used for workpieces to see its excellent corrosion resistance, so according to this use, the best cost-effective is nickel-based solder, usually BNi-2, BNi-5. The amount of solder also needs to be based on the actual situation. The principle is to ensure that the weld seam is full and avoid excessive solder flow to other parts of the workpiece. Nickel-based solders require joint clearance of 0.02-0.10 mm. Compared with other solders, this solder requires small joint clearance, which should be paid enough attention to.
In the vacuum brazing process of stainless steel, the selection of brazing materials should avoid low boiling point (high vapor pressure) elements, such as zinc, manganese, phosphorus and so on. This element volatilizes in vacuum, resulting in changes in the melting point of solder and contamination of equipment.
Vacuum brazing of stainless steel includes vacuum high frequency induction brazing and high temperature vacuum brazing besides brazing in vacuum furnace.
Product parameters of stainless steel vacuum brazing furnace: