Tin welding is a kind of welding process that melts the solder material by heating, which mainly plays the role of connecting the surface of the welded part. Its melting point is 232 ° C. The melting point of stainless steel is much higher, generally above 1400 ° C. This means that at high temperatures, there is a significant temperature difference between tin and stainless steel. This is also the reason why most models of stainless steel on the market cannot be welded with tin, and laser tin welding also can not be operated. Because the characteristics, melting limits and strength of the base metal and the welding material are different.
Stainless steel is an alloy whose main components include iron, chromium, nickel, manganese and so on. On the surface of stainless steel, there is usually a very thin layer of chromium oxide, its thickness is only a few nanometers. This layer of oxidation layer is the main protective layer of stainless steel, which can protect the surface of stainless steel from oxidation corrosion. At the same time, the hardness of the chromium oxide layer is extremely high, which can prevent chemical reactions between external substances and stainless steel. In addition, the chemical properties of tin and stainless steel are also different. Tin is an acidic substance that produces a chemical reaction when it comes into contact with acid and acidic substances. Stainless steel has good acid resistance, even if it is in contact with acid, there will be no obvious chemical reaction.
Therefore, the principle of stainless steel non-stick tin is that the protective layer on the surface of stainless steel can effectively protect the surface of stainless steel from oxidation corrosion and prevent the chemical reaction between external substances and stainless steel, and the difference in physical and chemical properties of tin and stainless steel will cause a large lack of adhesion between the two, resulting in non-adhesion. These are also the main reasons why most stainless steel can not be welded with tin.
1. How can stainless steel be welded with tin?
(1) Welding range of tin welding. Only a part of the metal has good weldability, which can be connected with tin welding. Generally, copper and its alloys, gold, silver, zinc, nickel and so on have good weldability, while aluminum, stainless steel, cast iron and so on are very poor, and generally need to use special flux methods to weld.
(2) Welding stainless steel has strict requirements for tin solder. Solder composition is not standard or impurities exceeding the standard will affect the quality of solder, especially the content of some impurities, such as zinc, aluminum, cadmium, etc. Even 0.001% content will significantly affect the solder wettability and fluidity, and reduce the quality of welding.
(3) For the welding of stainless steel, it is generally necessary to use special fluxes and methods to weld.
Stainless steel soldering can only play a protective effect such as sealing, and can not achieve solid welding. Stainless steel welding is still laser welding. Different from laser tin welding, stainless steel laser welding is a connection method that uses a pulsed laser beam to locally heat the workpiece to high temperature, so that the surface metal vaporizes to form a metallurgical bond layer, and the temperature can reach more than 1400℃. Its characteristics are: non-contact heating mode, no thermal deformation; Temperature and time can be controlled to improve product quality; Reduce production costs; It is suitable for connection or repair between parts of different materials (such as carbon steel, alloy steel, etc.). Guosheng stainless steel laser welding machine is widely used in the automotive industry, aerospace field and mechanical parts repair and other fields.
2. What should pay attention to stainless steel welding?
(1) Because the welding characteristics of stainless steel is thermal conductivity, hot melt, and large linear expansion coefficient, so the welding technic is more troublesome, and must take the corresponding welding techniques to ensure good quality.
(2) The residue splash will occur during welding, so we must take appropriate protective measures, such as wearing an eye mask and helmet, so as to ensure our safety.
(3) The splash should be handled well when welding. These items are very easy to attach to the outer layer of stainless steel, which will lead to a shorter use time of stainless steel, and it is necessary to apply an anti-splash agent on the welding mouth before welding.
(4) When welding, if the operation is not appropriate, it is very easy to leave a defect on the outer layer, such as the protective film is damaged, so the welding needs to lead the arc in the welding path and integrate the trace into the gap.
From the above we can see that laser tin welding is not able to weld stainless steel, although some special types of sheet stainless steel can be used, but only in the sealing protection of stainless steel. It is necessary to choose a welding machine that can reach the cladding metal parts, and choose a stainless steel automatic laser welding machine, which can reduce the loss caused by manual improper operation and avoid the trouble of recruiting workers.