There are two main types of metal bellows: hydroforming and welding. Hydroformed bellows improve pressure resistance by increasing the number of layers and have good pressure resistance performance. Multi-wave one-time molding or single-wave continuous molding, short production cycle, low price, high rigidity, and small allowable displacement (single-wave displacement is 15% to 20% of the wave distance). The raw materials are seamless tube blanks or seamed tube blanks. The production process of extremely thin-walled seamless tubes is complex, and the seamed tubes have higher requirements for welding equipment. The domestic production process of small-diameter seamed tubes is immature. The hydraulic bellows have a high degree of standardization and serialization, and users can select models according to the samples of professional manufacturers. Welded bellows are generally single-layer or double-layer, and the pressure resistance is limited. The number of welds is proportional to the wave number, the production cycle is long, the price is high, the stiffness is small, and the allowable displacement is large (the compression rate is 40% to 60%). The raw materials are sheets or strips, which are relatively easy to obtain, and materials with poor plasticity and good elastic properties can be selected, and the degree of standardization and serialization is poor.
The working conditions of bellows valves are becoming more and more severe, which puts forward higher requirements on the material of bellows. In the selection process of special material bellows for valves, appropriate materials and bellows forming methods should be selected according to the specific working conditions of the valve. Due to the characteristics of high-pressure resistance, high-temperature resistance, corrosion resistance, and long life, the special material bellows for valves will definitely become the development trend of valve bellows.