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Stainless steel oil filter vacuum brazing

All kinds of stainless steel oil filters on the aircraft are brazed with silver-based solder, high-frequency heating or flame heating. When brazing with silver-based solder at high frequency or flame heating. The traditional brazing method needs to add a large amount of flux, and the flux residue after brazing must be cleaned by ultrasonic waves, otherwise it will cause corrosion. In addition, the high-frequency magnetic field is harmful to the human body, the flame heating temperature is difficult to control, and the working conditions are very harsh. For this reason, vacuum brazing using a vacuum brazing furnace is the best choice.

Because vacuum furnace brazing has a series of advantages such as accurate temperature control, small deformation of the workpiece to be welded, high productivity, easy operation, and good working conditions. Therefore, the stainless steel oil filter brazing process filled with shielding gas in the vacuum brazing furnace is widely used.

Stainless steel oil filter technical requirements

The brazing structure of the stainless steel oil filter is to insert the two ends (or one end) of the multi-layer (several layers of mesh together by diffusion welding) or single-layer wire mesh (some with steel skeleton) into the steel base Brazed. The technical requirements of the product are: the brazing filler metal is not allowed to block the mesh, the brazing filler metal is not allowed to turbulently flow to the thread surface of the part, the welded parts are oxidized and blackened, and the deformation is out of tolerance, and the brazing filler metal is not allowed to erode the mesh wire. In addition, the brazing joint should be dense, smooth, filled and free of slag inclusions. The following introduces the method of brazing stainless steel oil filter in combination of vacuum furnace and argon gas.

In order to be able to braze in a protective gas, the following technological measures are usually adopted:

1.Use suitable flux.

2.Nickel plating on the steel surface.

3.Pre-oxidize the steel surface in wet hydrogen, then pickle to remove oxides (especially titanium oxide) on the steel surface.

In the first method, the flux residue should be completely removed after brazing, otherwise it will cause corrosion. When the second and third methods are actually applied in production, in addition to consuming a lot of preparation time, the brazing quality is not stable. When some low-priced manganese-based and copper-based solders are used, because they contain many volatile elements, it is not only easy to cause the volatilization of some elements in the brazing seam, but also to cause condensate in the vacuum system. Therefore, the method of filling with argon is not suitable for all vacuum brazing.

The advantages of filling with protective gas are:

1.Filling with protective gas can achieve high vacuum effect.

2.Brazed containers are not easily crushed by atmospheric pressure (especially at high temperatures).

3.The air is exhausted quickly, and the air adsorbed on the inner wall of the brazing container and the surface of the workpiece to be brazed can be easily exhausted with a vacuum pump at a temperature below 150°C.

4.Using argon flow to transfer heat can accelerate the heating or cooling speed.

Process flow:

1.Assembly

Before brazing, all parts are cleaned and degreased with acetone, and the stamping parts (base) are also pickled. Make the cleaned brazing wire or brazing sheet into a ring shape, and fit it in the machined groove of the base or on the outer diameter of the wire mesh. Use a portable capacitor energy storage point to spot weld the solder on the steel base. Then, apply solder stopper where necessary to prevent turbulent flow of solder. After applying the flux stopper, place the assembled oil filter assembly in an oven to dry.

2.Solder stopper

During oil filter brazing, it often occurs that the brazing material blocks the mesh. This will seriously affect the normal working performance of the oil filter. Therefore, solder stopper must be used to prevent solder from plugging holes. Solder stoppers are formulated from coatings and adhesives. In addition to having a good anti-welding effect, the anti-soldering agent should be easy to remove after brazing. The general coating is mica powder, and the binder is an alcohol solution of polyvinyl alcohol.

3.Vacuum brazing

In the past, it was brazed under the protection of pure argon, but it was found that the machined steel base always had an oxidation color. Therefore, a high-vacuum high-temperature brazing furnace is used for brazing. Vacuum brazing is carried out at 880 degrees Celsius with silver-copper solder, and a small amount of argon gas is introduced into the brazing. The brazing process is smooth and the brazed joints are good, meeting the quality requirements.

Vacuum brazing furnace selection: Process technology must be matched with excellent equipment to play a role, among which the vacuum 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 the workpiece evenly and evenly, so as to achieve a high level of brazing level, reduce the scrap rate, increase the efficiency of production and reduce the cost.