Analysis of pre-tensioned disc springs in solving bolt tightening problems

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This post was last edited by yuchenchf on 2017-8-5 at 16:11. The consequences of bolts being subjected to periodic impact vibrations differ significantly from those resulting from changes in temperature and pressure; the former tends to cause the bolts to loosen, and this loosening is closely related to the magnitude of the impact forces and the frequency of these changes. The greater the impact force, the more energy is generated that leads to vibration, and thus the bolts become more prone to loosening. The more frequently they are subjected to impacts, the shorter their vibration period becomes, and the faster the preload is lost. The latter generally manifests as a gradual relaxation of the bolt preload, thereby causing leaks at the pipe flanges and the flanges of pressure vessels such as heat exchangers. Based on the actual usage conditions on site, the following two solutions were adopted: 1) Solving the issue by installing split spring washers on the bolts. Effect: There is virtually no improvement in the problem of frequent loosening of the device’s bolts; upon disassembly, it was found that the spring washers had been flattened, losing their original function of providing tension compensation. 　　2) Bolt fastening technology is employed—pre-tensioned disc springs of size M64, which are manufactured using advanced processing techniques and are also easy to install. 　　Effect: The problem of loose bolts in the device was satisfactorily resolved; the original average loosening period increased from 3 days to 2 months. The decrease in free height after disassembly was within only 10%, which is acceptable in the design and use of tensioning disc springs, allowing the device to continue to be used. 　　The technical requirements for bolt tightening specify different torque values for various bolt specifications and materials, thereby providing the necessary effective pre-tightening compensation for different applications of bolts. For specific applications, there is a specific “effective compensation window”. Even disc springs of the same size can have completely different deformation curves due to differences in heat treatment processes. 　　As an advanced fastening technology, the pre-tensioned disc spring possesses unique characteristics.