CBIES AUTOMOTIVE|What's The Difference Between Screwing A Bolt And Screwing A Nut?

In automobile assembly, three thread fastening methods are commonly used: torque, torque plus angle, and yield point.

In conventional fastener rotation methods, the nut is the main tightening object to fix the bolt head. However, some particular fastening parts are limited by space, and the tightening equipment cannot be inserted, and the fastening can only be achieved by clamping the nut and rotating the bolt.

CBIES CBIES AUTOMOTIVE is committed to creating more energy-saving, safe, and lightweight products in terms of fastener products. Products include bolts, nuts, rivets, screws, and other products. Today, under the same assembly environment, CBIES conducts experimental comparative research on the difference in torque required to tighten nuts and bolts to ensure the same clamping force.

Usually, people also generally think that there is a difference in the stress state between screwing bolts and nuts. They think that screwing bolts may cause greater stress. What is the actual situation?

For welding nuts, riveting nuts, welding bolts, riveting bolts, internally threaded holes, and similar places, everyone will not be entangled in whether to screw the bolt or the nut.

Because only one part can be screwed in this kind of similar place: bolt or nut (combination of double-headed stud and nut), the other part has already been fixed and cannot be tightened. Only the bolt can be tightened, so it does not exist. The difference between screwing a bolt and screwing a nut is shown in the figure.

The stud connection on the right can only be screwed with nuts.

The place where there is a dispute about screwing bolts or nuts is the bolt-nut connection. In this case, both bolts and nuts can be screwed, which will involve the problem of screwing bolts or screwing nuts, and it will also involve screwing bolts Or the difference in screwing the nuts.

A. Regarding whether to tighten bolts or nuts, after searching for relevant standards and analysis, there is currently no standard that specifies whether to tighten bolts or nuts.

 

That is to say, both methods of screwing bolts and screwing nuts are in principle all possible. Of course, conventionally speaking, bolts and nuts are connected by screwing the nuts.

B. In terms of force, both screwing bolts and screwing nuts are subject to torsional shear stress imposed by tensile stress and thread torque. Therefore, in theory, the force of screwing bolts and screwing nuts is the same.

Of course, some people will say that the stress may be greater when the bolts are screwed. Whether screwing a bolt or a nut, it will be subject to the tensile stress generated by the bolt pre-tightening force, as well as the torsional shear stress applied to the bolt by the friction torque generated by the thread torque. As long as the friction coefficient and the diameter of the supporting surface are the same, theoretically, there should be no difference in the comprehensive stress.

C. From the analysis of the friction coefficient, the friction coefficient of the bolt and the nut may be inconsistent, which will also cause a difference between screwing the bolt or screwing the nut.

D. The size of bolts and nuts may also be different. If you don’t pay attention when designing, for example, flange bolts and flange nuts are also used. The flange surface bolts of GB/T 6177.1 are used, because the diameters of the supporting surfaces of the two are different, so there will be differences in the equivalent friction diameters of the two when tightening

E. From the perspective of tightening the sleeve, when the bolt is tightened, the sleeve can be very short. If you tighten the nut, you need to consider the exposed length of the bolt. At the same time, some bolts have a certain guiding function, and the extension length will be very long. The sleeve needs to choose a long sleeve, which will increase the cost and even reduce the rigidity of the sleeve

Of course, the long sleeve at the other end is also used in the design of the anti-rotation tooling, so the selection of the sleeve is the same.