The failure forms of mechanical seal of ordinary bellows are mainly caused by the bellows mechanical seal and its auxiliary system.
1. The seal failure caused by the loss or fracture of the bellows. During the use of the bellows, the mechanical seal or elasticity of the stiffness of the pump will gradually decrease, which is usually called the loss of elasticity. The experiment and practical application show that when the loss of the bellows is more than 18% to 20% of the initial compression of the design, the mechanical seal of the bellows will leak. The metal bellows mechanical seal at a temperature below 200 DEG C when the loss is not obvious, but at high temperature (above 300 DEG C) use, after driving pump soon leak, will remove the use of mechanical seal mechanical seal test Netzsch volume found metal bellows assembly is installed before the average height decreased from 2 to 3mm. The loss of the bellows is mainly due to the permanent deformation or the mechanical seal relaxation of the stress multistage pump. There is another case that the working medium is crystallized or precipitated or solidified in the gap of the bellows, so that the deformation capacity of the bellows is reduced or the deformation capacity is lost. Therefore, the high temperature and load are the main causes of the failure of the bellows, . In addition, when the temperature and bellows compression or contact pressure are large, the bellows will fracture. The higher the temperature and the larger the load, the higher the probability of fracture.
2. The sealing failure caused by the excessive wear of the graphite ring in the pairs of pairs of friction pairs. Usually, it is found that the graphite seal ring is seriously worn out by the failure inspection. Through analysis and test, it is found that the end face of the metal bellows is influenced by the effective diameter of the bellows, and the effective diameter changes with the pressure. As the pressure is too large, the friction pair has a serious friction, and the excessive wear of the graphite ring causes the leakage.
3. The seal failure caused by the surface heat crack of the cemented carbide ring in the pair friction pair. The inspection found that the hard alloy sealing friction pair ring many thickness by hard divergence center outward in a radial crack, which is caused by thermal sealing failure. The main causes of thermal cracking is high local heat stress, the hard alloy ring and the ring seat coefficient difference of two kinds of material line expansion, the use of welding structure and overall structure, seal cooling system flushing fluid type, washing mode and the size of the flow is appropriate may cause seals to hot cracking.
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