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Vacuum Brazing of Stainless Steel Mixer Parts

Vacuum brazing refers to the brazing process in which the workpiece is placed in a vacuum furnace and heated by vacuum atmosphere and radiation. It is mainly used for welding products with high quality requirements and easily oxidized materials. It is widely used in brazing stainless steel, aluminum alloy and other materials.

Advantages of vacuum brazing:

The greatest advantage of vacuum brazing is that the brazing process is carried out in a vacuum atmosphere, completely eliminating product corrosion. The closed vacuum furnace eliminates all kinds of pollution in traditional welding, which is environmentally friendly and pollution-free. The whole process of brazing is automatically controlled, providing safe and comfortable production conditions. In terms of product quality, vacuum brazing filler metal has good wettability and fluidity, can weld more complex and narrow channel devices, improve the yield of products, and obtain a solid and clean working surface. Compared with other methods, the internal structure and fixture of vacuum brazing furnace have long service life and low maintenance cost.

Vacuum brazing of stainless steel mixer:

A stainless steel static mixer is widely used in chemical fiber manufacturing equipment. The main function of the mixer is to mechanically mix different kinds of material pulps. The structure and size of the mixer vary with the type of materials to be mixed, and it is composed of an internal rotary vane group and an external conduit. During the manufacturing process, it is required that the rotary vane group and the conduit are reliably connected to bear the force of self mixing slurry under working condition. Due to the complex shape of the spinner set and the spiral outline of the outer edge, the conventional brazing cannot meet the requirements. According to this requirement, the brazing method is appropriate for the connection of the spinner set and the conduit.

The module adopts nickel base filler metal and vacuum brazing method, which is a mature technology for vacuum brazing stainless steel. In the brazing production of static mixer, the primary problem encountered is how to place the solder. When facing the brazing of such parts, adhesive tape solder shall be selected. Like ordinary tape, this tape solder can be well adhered to the outer edge of each rotary vane of the rotary vane group, and when the rotary vane is assembled into the conduit, it will not fall off due to friction.

Technological process:

(1) Degrease the brazing surface of all conduits and rotary vane groups, stick the adhesive tape solder to the rotary vane along the outer edge of each rotary vane of the rotary vane group, carefully install the rotary vane group with the solder into the conduit, and position itself with a slightly tight fit. Follow this procedure to assemble all the spinners and guides into the static mixer assembly to be welded.

(2) Place all assembled components on the brazing frame with multiple worktops in the furnace in a horizontal direction. In order to heat the components evenly, only one layer shall be placed on each table top, and certain space shall be reserved between the tables after the components are placed.

(3) Carry out vacuum brazing as per the process curve shown in the figure. Brazing heating can only be carried out when the vacuum degree in the furnace reaches 10-2 Pa. As the radiation heating method is adopted, the radiation degree of components on different worktops will be different during the heating process, so it is advisable to adopt a slower heating rate to minimize the temperature difference between components. Two insulation sections are set on the brazing process curve. The low section insulation is to reduce the influence of the gas released by the adhesive strip solder on the vacuum, and the high section insulation is to ensure that all components have a lower temperature before the solder is about to melt.

(4) When the holding time of brazing temperature is reached, furnace cooling or forced cooling with inert gas can be used to reduce the cooling time and improve production efficiency. The tapping temperature can be selected according to the needs. Higher tapping temperature can reduce the cooling time and improve the production efficiency. However, it should not be too high, so as not to affect the brazing quality.

The brazing furnace selected in vacuum brazing is the key to complete the process. Only excellent vacuum furnace products can complete the brazing process with high efficiency and quality. The RHVB vacuum high temperature brazing furnace produced by SIMUWU is an excellent product for handling this kind of process. With its excellent temperature control accuracy and temperature uniformity, the brazing of workpieces can be carried out smoothly and evenly, so as to achieve a high-level brazing level, reduce scrap rate, increase production efficiency and reduce costs.