The Process of Stainless Steel Vacuum Brazing – Part One

1. braze welding head design.
Design brazing welding head, consideration should be given the strength of the joint, assembly method, the position of the solder placed, joint clearance, and many other factors
1.1 braze welding head connection mode:
Brazing welding head butt and lap in two ways. The butt joint, as a result of the strength of the solder and brazing seam is generally lower than the parent metal, and butt joint cannot ensure joint with the bearing capacity of the parent metal is equal, so brazing welding head are mostly in the form of lap joint. By changing the strength of the lap length increase braze welding head. For high strength copper, nickel-based brazing filler metals of the lap joint, lap length usually take for thin wall thickness of 2 ~ 3 times. Because of the shape of the work-piece is different, the specific shape of the lap joint are different. For the thin-walled, often adopts over-lock form of lap joint method, improve the strength of the braze welding head.
1.2 joint positioning:
Assembly location is one of the important factors affecting brazing quality. Positioning methods mainly depend on the weight, the orientation of tight fit, burr, spot welding, location (argon arc welding) up mouth, fixture positioning, etc. Shell and tube type EGR cooler will use up the orientation of the mouth, spot welding, welding displacement device such as a variety of positioning method
1.3 the solder placed:
Solder implantation is the principle of gravity and brazing seam should as far as possible use of filler metals of capillary used to promote solder fill the gap. EGR cooler will use nickel-based brazing filler metals of paste and two kinds of amorphous thin belt. Paste filler metals shall be coated directly on the brazing seam, and amorphous thin tape solder standard include the different thickness of 0.0254 mm to 0.0381 mm. According to the requirements of the work-piece is processed into different shapes, placed in the brazing joints. Anyhow nickel-based solder the use of reasonable for us to do a lot of work, such as solder coating method of surface treatment, paste, solder dosage and so on many aspects, further perfect according to the actual requirement.
1.4 joint clearance:
Depend on capillary action when brazing solder to fill gaps. Correctly choose joint gap largely affect the density of brazing seam and intensity. Different solder joint clearance requirements is also different. Nickel-based solder joint gap to 0.02 ~ 0.10 mm, compared than other solder, the solder for the characteristics of small joint gap should cause enough attention.
Due to BNi2 nickel-based solder containing boron (3.2%), silicon (4.5%) of brittle phase can be formed elements, in order to guarantee the performance of the joint, should try to make these elements within the brazing seam through the diffusion effect and reduce to a minimum.
Hours when clearance, the number of elements, less brittle phase to the parent metal diffusion distance is short, can be spread through lower the concentration of these elements in the brazing seam. To avoid brittle phase and improve the strength of the brazing. Instead of the brittle phase elements will be stranded in the brazing seam formation of brittle phase,.
Data show that when the gap is “zero” clearance, 0.05 mm and 0.1 mm. Brittle phase as the change of clearance increases. Clearance in 0.1 mm, the brittle phase not only increased, and formed distinct successive layers. The strength of the brazing seam severely reduces, great harm. So the best clearance brazing seam should be controlled less than < 0.08 mm.