First of all, let's take a look at the production process of solid solution (annealing): although the welding process of stainless steel is very mature, the heating and cooling of the welding process are in a very small local range and are completed in an instant at an extremely fast speed. Therefore, it is unavoidable to generate strong and concentrated material internal stress or local burns at the weld. Therefore, the bellows must be subjected to a solution (annealing) process after welding. After years of research and development and transformation, the current solid solution (annealing) process is already a dedicated automatic assembly line production operation. On-line solid-melting (annealing) is to heat the stainless steel bellows in a solid-melting (annealing) equipment to a constant temperature of 1100 °C in an inert protective gas. After a certain period of time in a constant temperature environment of 1100 °C, it is slowly cooled at the specified speed, and the entire assembly line is more than 40 meters. The main purpose is to completely eliminate the internal stress concentrated in the weld, so that the weld hardening and welding softening and material unevenness at the weld can be homogenized. At the same time, the internal stress generated by the cold rolling process of the steel strip and the internal stress generated by the extrusion forming process are eliminated in the high temperature environment of 1100 °C, so that the stainless steel molecules are rearranged evenly. As a result, the corrugated pipe is not easy to crack, more flexible, easier to bend and shape during installation and use, and has better stability. In this process, the stable flame temperature, heating speed and temperature, and cooling speed (cooling water temperature and flow rate) are mainly adjusted. Solid solution (annealing) plays a key role in the quality of stainless steel bellows!
Stainless steel bellows solution (annealing)
For stainless steel bellows to have good elastic properties, solution (annealing) is an indispensable process.
The solution (annealing) of the bellows can eliminate work hardening during the manufacturing process, restore the plasticity of the stainless steel bellows, and at the same time strengthen the material and obtain elasticity.
The solution (annealing) treatment of bellows has its quality requirements inside and outside.
The internal requirement is to obtain certain microstructure, grain size and mechanical properties of the product after heat treatment;
The external quality is mainly the degree of surface oxidation after solution (annealing) treatment.
Solid solution (annealing) has another effect: it is the surface smooth treatment of stainless steel bellows
The surface smoothness treatment process of stainless steel bellows mainly includes processes such as degreasing, loosening oxide scale and cleaning, so that the surface of stainless steel bellows products is smooth and clean.
How to distinguish whether the stainless steel bellows has solid melting (annealing)?
1) The surface of the solid-melting (annealed) bellows is fresh and clean, and it is the natural color of stainless steel.
If there is no solid-melting, the surface is black and dark. Look carefully at the surface is not clean! There is no solid melting (no annealing) because the oxide layer on the surface of the welded stainless steel pipe needs to be treated, and it must be electrolyzed, polished or pickled.
2) The stainless steel corrugated pipe is welded into a steel pipe by stainless steel strip, and then corrugated to become a corrugated pipe. In the process of welding the stainless steel pipe, two light yellow oxides will be left on the inside and outside of the welding seam layer. If you look carefully at the inside of the bellows welding seam, there are light-colored light yellow lines, this kind of bellows is a bellows without solid fusion (no annealing)!
3) Take a section of 30 cm long and short corrugated pipe, bend it quickly, and it will crack at about 10 times. This corrugated pipe has not been solidified (annealed).
