Why bolt looseness, what reason is caused by loose?

Bolt is the preferred fasteners in multiple industries and application, choose the bolt is a simple reason, is because of the bolt is easy to remove. However, this also makes them easy to loosen and lose by preloading. The composition of chemical pumps, pipe flange connection requires bolts, bolts loose after is very troublesome, bolt looseness caused a series of problem is often, so what reason is loose, according to the bolt loosening bolts in the use of some of the effects. In is a loose bolts may make the whole factory to a standstill and make the company loss, etc. , in loose bolt is also the safety of the factory. So, what is the main cause of bolt looseness that? Bolt from broad sense, there are two main reasons: loose loose spontaneous, automatic relaxation, fatigue, etc. One, the harm of bolt looseness 1, 2, fan rotor flange leak separated from engine room off 3 falls off, Marine engine vibration connecting bolts, Marine engine vibration connecting bolts fall off, and with the ship rolling, causing further damage of the equipment. In the bolt connection and tighten nut can actually make the bolt elongation, like pull the spring. This kind of tension, or tension, will have the opposite clamping force, two parts will be fitting tightly together. 4, if the bolt looseness, clamping force will be weakened. Looseness of the bolt is not only a headache problem. If joint not to tighten rapidly, could start to leak liquid or gas, bolt may rupture, may damage the equipment, or may be catastrophic accidents. Second, the main reason for the bolt looseness: 1, embedded design and development engineers are allowed a bolt tension period, produce certain loss of prestressing force, in the meantime, bolt tightness will appear slack. The relaxation is due to the bolt head and/or nut, screw, and by embedded between the fitting surface, and can be in soft material ( Such as composite materials) And hard polished metal. If a joint design, improper, or in tension at the beginning of the bolt did not reach regulation, the joint of the embedded may result in loss of clamping force and reach the required clamping force. Joint surface between the micro uneven, after tighten bolt pre-tightening force under the action of will generate convex point crushing, permanent plastic deformation, thus bolt clamping length decreases, resulting in a decline in the pre-tightening force of the bolt. 2 many bolts, gasket, creep and thermal expansion joint between bolt head and joint surface consists of a thin and soft gasket, seal joint, to prevent the gas or liquid leakage. Washer itself also have the effect of spring, rebound under the bolt and the joint surface pressure. As time goes on, especially close to high temperatures or corrosive chemicals, gasket may & other; Creep & throughout; , which means it lose elasticity, leading to loss of clamping force. If the joint bolts and material is different, due to the rapidly changing environment or industrial cycle caused by temperature difference is too big, can lead to bolt material rapid expansion or contraction, may make the bolt is loose. 3, insufficient tighten tighten or false tighten bolt pre-tightening force is insufficient, if again to loosen, joint there isn't enough clamping force to the parts together. This can lead to lateral sliding between two parts, bolt is unnecessary and shear stress may lead to the bolt fracture. 4, impact shock - Large impact load exceeds the bolt pre-tightening friction, sliding. From machinery, generators, wind turbines and other dynamic or alternating load leads to mechanical shock & ndash; — On the impact of the bolt or joint & ndash; — Lead to relative sliding bolt. Like vibration, this slide will result in bolt looseness. Even impact is often in the design of joint connection has not been given such a big load. 5, vibration of bolt connection under vibration test showed that many small & other; Transverse & throughout; Lead to connect the two parts of the mutual movement, the bolt head or nut with the fitting at the same time also can produce movement. These repeated games offset friction between bolt and fittings. Vibration will lead to the bolt threads & other; Rotary loosening & throughout; Loss of clamping force, joint. 3, what is the preload? With a variety of the meaning of the term in the engineering. A are produced by the fastener in early tight tension ( Load) 。 When bolt stretch parts compression between bolt and nut, thereby increasing the clamping load, until the end of the fastening process.
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