The outer diameter is one of its two main geometric parameters, which requires strict control

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This post was last edited by ztj1118 on 2012-12-15 at 17:45. As the inner and outer diameters of the butterfly valves used with welded bellows decrease, their wall thickness also has to decrease accordingly. Overall, this increases the difficulty of manufacturing them. In addition to the aforementioned changes in the process route, there are also specific process measures. For example, there are stricter requirements in areas such as fixture design and gas protection accessory design. Determination of the initial inner and outer diameters of the stamped diaphragm: The inner and outer diameters of a welded bellows are its two main geometric parameters, which need to be strictly controlled in order to ensure the performance of the bellows as well as to prevent it from coming into contact with the casing and shaft during operation. Since the vast majority of welded bellows use end-connected joints, the edges of the diaphragm are welded by the melting of the base material itself to form a weld without the use of filler metal; as a result, the outer diameter of the final welded bellows is slightly smaller than the initial outer diameter of the diaphragm. The inner diameter of the final gate valve finished product is slightly larger than the initial inner diameter of the diaphragm. If the product drawings specify the inner and outer diameters of the bellows, then the first issue that arises when designing the diaphragm is determining the initial inner and outer diameters for diaphragm blanking – in other words, how much weld sink allowance needs to be reserved at the edges of the diaphragm to ensure that the final inner and outer diameters of the product meet the requirements specified in the drawings. The diaphragm profile design for welded bellows is not complex. The diaphragm profiles of Type I and Type II welded bellows are essentially straight lines, while the design method for the diaphragm profile of Type III welded bellows is basically the same as that used for diaphragm membranes. For these three types of bellows, both the upper and lower diaphragms use diaphragms of the same shape; simply reverse their order when welding. The profiles of the upper and lower diaphragms in a laminated welded bellows are generally different, but their waveforms are conjugate; when compressed by axial forces, the upper and lower diaphragms can overlap each other. The diaphragm surface is formed by several arcs connected to each other; the arcs near the inner hole and the outer circle each extend a short tangent segment that serves as the flat edge portion, allowing it to be clamped with fixtures during welding.