After a car has been driven for a period of time or tens of thousands of kilometers, some fasteners (bolts and nuts) are always loose, and some key chassis parts, once the bolts and nuts are loose, may cause very serious consequences. The cause of the loosening of automobile fasteners Need to explore. Based on the experience of working in an automobile factory over the years, the investigation results of various fastener looseness encountered, the reasons for the fastener looseness are summarized for your reference.
If the tightening torque is too small, the bolts are not pre-tightened enough and are easy to loosen.
If the tightening torque is too large, the bolt is subjected to excessive force, plastic deformation occurs, the length becomes longer, the thread diameter becomes smaller, and the thread engagement surface becomes smaller, making it easy to loosen.
The contact surface of the fastened part and the bolt or nut is too small or point or line contact. During the running of the vehicle, the contact surface of the part and the fastener rubs against each other, and a gap gradually appears between the two, and the thread pre-tightening force becomes smaller. Loose.
If the contact surfaces between multiple fastened parts are too small or point or line contact, the contact surfaces rub against each other during the driving process of the vehicle, a gap gradually appears between the two, and the thread pre-tightening force becomes smaller and loose.
Parts that are elastic or prone to plastic deformation will cause insufficient pre-tightening force of the fasteners and looseness after a period of tightening.
The lack of a loosening effect or a self-locking function of the bolt is also one of the reasons why the bolt is easy to loosen.
The design fastener does not match the strength of the part. If the strength of the part is too low, the bolt will deform the contact surface with the collar during the movement, and then loosen.