The quality of the thread connection is to ensure the quality of equipment and equipment, the normal operation of the foundation, the vast majority of threads in the connection should be preloaded, the purpose is to enhance the connection of the rigidity, precision, anti-loose and anti-skid. The proper control of the preload is the key to ensuring the quality of the thread connection, but if the preload is not appropriate, it will cause problems such as slipping of the coupling, separation or fastening of the fastener.

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    For normal bolts that are subjected to lateral loads, the preload forces create positive pressure between the joints and rely on friction to resist the external load, so the size of the preload determines its affordability. If the preload is insufficient, the coupling will slip, causing the connector to be misaligned, skewed, wrinkled, and even the fastener is cut short.

    For the bolts connected by axial load, the preload force causes the clamping surface to produce the pressing force, and the residual pretension force after the external load is the pressing force when the working surface is engaged. Insufficient preload will cause the contact surface to leak, such as pressure pipe leakage, engine leakage, and even lead to separation by the coupling. The lack of preload will also cause a strong lateral vibration, resulting in nuts loose.