How to use double nuts to prevent loosening?

How to use double nuts to prevent loosening?

Everyone only needs to prevent loosening of bolts and nuts. Many people even know various methods of preventing loosening of nuts. Among them, double nuts are also very common. But did you know that many people use double nuts to prevent loosening?

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The principle of double nut anti-loosening

Double nut locking principle: To make the nut not loose, it is necessary to increase the friction resistance to stabilize the nut. After the two nuts are tightened, the axial force generated between the nuts increases the friction between the nut teeth and the bolt teeth. Large and prevent the nut from loosening automatically.

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Common forms of double nut relaxation

There are generally three types of double nut locking. As shown below. The first type of thin nut is matched with a thick nut, the thick nut is at the bottom, and the thin nut is at the top, the second type of thin nut is matched with the thick nut, the thin nut is at the bottom, the thick nut is at the top, and the third type is matched with two thick nuts. The matching of thin nuts on the top is unreasonable.

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Why is the matching of thin nuts unreasonable?

Why is the matching form of thin nuts on the top unreasonable? We need to analyze from the perspective of the force of the bolt. First, the bolt needs to be pre-tightened. When double nuts are used to prevent loosening, there is an axial tightening force between the two nuts. When the connecting part bears an external load, the force transmitted by the bolt is still To increase, thin nuts have fewer threads and can bear less load than thick nuts.

If the load is too large, the stress on the thread section will be very large, and there may be a risk of tripping, which is what we usually call a sliding buckle. Therefore, the thick nut must be placed on the double nut to prevent loosening.

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The tightening method is also very important when the double nut is anti-loosing

If there is a requirement for pre-tightening of the double nut when tightening the first nut, the designed tightening torque must be reached, because if the first nut is not tightened, no matter how much torque is used, the designed pre-tightening cannot be achieved. force.

When screwing the second nut, the first nut must be fixed with a wrench. This is to prevent the first nut from rotating with the second nut at the same time when the second nut is screwed, so that there will be no axial alignment between the two nuts. There will be no additional frictional resistance, and thus will not play a role in preventing loosening.

Sometimes, because of the easy fixation of the following nuts, two thick nuts will be selected, and the choice of one thin nut and one thick nut is considered from an economic point of view.