Metal bellows are manufactured from the selection of raw materials, through the main technological links of tube blank manufacturing, bellows forming, shaping, heat treatment, surface treatment, quality inspection, etc., to produce bellows that meet the design requirements.

Bellows are thin shell elements with complex shape and high performance requirements. It has many manufacturing processes and complex technology. Therefore, in the manufacture of bellows, the correct process design and implementation is very important.

Manufacturing technology of bellows billet

Metal bellows are divided into seamless billets and seamless billets.

The manufacture of seamless tube blanks should be based on different raw materials and different process methods. Material plus factory can provide long stainless steel thin-walled seamless pipe with wall thickness of 0.1-0.3 mm and outer diameter of 10-60 mm. This kind of seamless pipe has a high surface finish, but its wall thickness tolerance is large (+/-0.03mm). It is generally used to manufacture spiral bellows and annular bellows with low performance requirements. Metal bellows manufacturer can use 0.8-1 mm thick metal sheet (strip) or 0.5-1 mm thick standard thin-walled tube, after several deep drawing or spinning deep drawing process to manufacture various specifications of bellows billet. This process can produce billets with high surface finish, small wall thickness tolerance (<=+/-0.005mm) and short length, which can be used to manufacture bellows with higher requirements.

The manufacture of seamed tube blanks is usually made of plates or strips of the required thickness and butt welded by special welding after the drum. The quality of seamed tube blank directly depends on the quality of plate (strip) material and welding quality. Generally speaking, the wall thickness tolerance is easy to control.

1. Manufacturing Technology of Multiple Thinning and Deep Drawing

The multi-thinning and deep drawing process is suitable for the manufacture of bellows with the length of billet less than 300 mm. The process mainly includes blanking, multi-drawing, multi-heat treatment and multi-thinning and deep drawing.

2. Manufacturing Technology and Equipment of Steel Ball Spinning Thinning and Drawing

Rotary thinning and deep drawing of steel balls is a process in which the billet is rolled between punch, die and steel balls at high speed. The high-speed rotation of the punch (or die) drives the ball itself to rotate and rotates along the circumference of the blank. When the blank is fed axially on the punch, the material is deformed by the action of positive force and tangential force.

3. Manufacturing Technology of Welded Tube Billet

Using welding method to manufacture bellows billet is a process with high production efficiency, low cost, easy wall thickness control and strong adaptability. At present, it is mostly used to manufacture large diameter bellows for expansion joints and tube blanks for hoses. At present, gas shielded direct current argon arc welding, micro arc plasma welding and laser welding are the main welding methods for bellows billet. The welding thickness is 0.1mm~1mm, and the materials are 1Cr18Ni9Ti, 0Cr18Ni9, 00Cr17Ni14Mo2 and GH169.

4. Manufacture of Multilayer Bellows

Multilayer bellows have higher pressure resistance, smaller stiffness and larger displacement. They are often used to manufacture metal expansion joints and bellows for leak-free valves.

Multilayer bellows are used for expansion joints. The inner diameter of the bellows is usually more than 80mm. Most of the billets of the bellows are welded with the clearance of the casing reserved. After the billets of the corresponding layers are welded separately, the sequential casing can be used.

Most of the inner diameters of multi-layer bellows used for valves are less than 60 mm. The multi-layer bellows are damaged and have different manufacturing methods. One is to use rolling or spinning process to manufacture corresponding layer billets according to reserved casing clearance, and sequentially to form multi-layer billets. Another method is to select a basic tube blank, and then use the shrinkage or expansion process to make the corresponding layer of tube blank, and then sequentially casing into multi-layer tube blank. Because the precision of diameter tolerance is lower than that of rolling and spinning tubes, the reserved casing clearance is slightly larger.

According to the different requirements of corrugated pipe products for the quality of interstitial layers, the two methods of hard casing and soft casing can be used in the casing of multilayer billet. After cleaning the inner and outer surfaces of the manufactured rigid billet, the tube is directly bushed and then treated by solid solution or annealing. This method is difficult to ensure smooth surface and no redundancy between layers because of heat treatment and pickling after casing. Hard billet is first treated by heat treatment and pickling. After obtaining smooth surface quality, then soft casing can ensure the quality of bellows product layers reliably.