Bellow

Bellows is a tubular elastic sensitive element made of foldable wrinkled sheets connected in the direction of folding and expansion. Bellows are widely used in instrumentation, the main use is as a pressure measuring instrument measuring element, the pressure is converted into displacement or force. The bellows has a thin wall and high sensitivity, with a measuring range of tens of Pa to tens of MPa. It has a fixed open end and a free sealing end, and uses an auxiliary coil spring or reed to increase elasticity. When working under the action of internal pressure along the length of the tube elongation, so that the active end of the pressure into a relationship with the displacement. The active end drives a pointer that directly indicates the size of the pressure. Bellows are often combined with displacement sensors to form a pressure sensor with an electrical output, and are sometimes used as an isolation element. Because bellows stretch requires a large volume change, its response speed is lower than that of bourdon tube. Bellows are suitable for measuring low pressure.

Bellows: A pressure measuring elastic element in pressure measuring instruments. It is a cylindrical thin-walled folded shell with a number of transverse corrugations, bellows has elasticity, in the pressure, axial force, transverse force or bending moment can produce displacement. Bellows are widely used in instrumentation, the main use is as a pressure measuring instrument measurement element, the pressure is converted into displacement or force. Bellows have a thin wall, high sensitivity, and a measurement range of tens of Pa to tens of MPa. In addition, bellows can also be used as a sealing and isolation element to separate two media or to prevent fluids from entering the measuring part of the device. It can also be used as a compensating element to compensate for temperature errors in the instrument by taking advantage of the variability of its volume. Sometimes also used as two parts of the elastic coupling joint. Bellows according to the composition of the material can be divided into metal bellows, non-metallic bellows two; according to the structure can be divided into single-layer and multi-layer. Single-layer bellows is used more. Multi-layer bellows, good sex, small stress, used in important measurements. Bellows material is generally bronze, brass, stainless steel, monel alloy and inconel alloy.

Design

The theoretical basis for the design of metal bellows is plate and shell theory, mechanics of materials, computational mathematics and so on. There are more parameters for bellows design, and because of the different uses of bellows in the system, their design calculations are not the same. For example, the bellows used for force balance element, the requirement of the bellows in the working range of its area is unchanged or change is very small, used for measuring elements, the requirement of the elastic properties of the bellows is linear; used for vacuum switching pipe for vacuum seals, the requirement of the bellows of the vacuum sealing, the amount of axial displacement and fatigue life; used for valves for seals, the requirement of the bellows should have the pressure resistance, etching, temperature resistance, work displacement and fatigue life. According to the structural characteristics of the bellows, the bellows can be treated as a circular shell, flat cone shell or circular plate. The design and calculation of bellows is also the design and calculation of circular shell, flat cone shell or doughnut ring plate.

The calculated parameters are stiffness, stress, area, instability, permissible displacement, pressure resistance and service life.