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Why there is no screw mark on the new car

After the car leaves the factory, will the screws leave traces as long as they are repaired?

No!!!!!!! sometimes the screws will not leave traces after twisting.

More than 20 years ago, I found that some home appliance maintenance personnel would not leave any marks when removing the screws (returning to the factory). The specific method is to wrap the screwdriver head with silk, so that the removal of the screws would not leave any marks.

The repair garage also has a way to remove the screws without leaving any traces. Of course, this depends on the value of the vehicle to be repaired and the needs of the owner (used car dealer). There are many ways to remove the screws without leaving traces. The simplest way is to use special tools. For example, a screw sleeve membrane is used:

Before removing the screw, just buckle the sleeve onto the removed screw/nut. The force bearing part of the sleeve is borne by the sleeve, so that no trace will be left when removing the screw.

Therefore, it is not completely reliable to judge whether the repair has been carried out by observing the screw twisting trace. For example, the key parts such as the engine fulcrum screws are equipped with traceless removal tools. Even if the engine has been repaired, it may not be obvious. This is also true for other parts. There is also traceless removal and repair driven by interests.

New car screws have also been twisted. After all, every screw on the car needs to be twisted. Theoretically, as long as you use a wrench to twist the screws, you will leave traces, but when the traces are small enough, it is not easy to see them with the naked eye. If you observe carefully, you will find that the twisting marks on the screws of some new domestic vehicles are more obvious when they leave the factory, and the twisting marks on the screws of some joint venture vehicles are smaller.

However, some painted screws may not be able to find any traces of twisting, nor can they be seen by the magnifying glass, because these screws are painted after assembly, and no traces of twisting can be seen on the surface. For example, the screws at the hood, fender, tailgate and door are painted again after assembly:

However, those screws with no paint on the surface can not see the traces of twisting, which is related to the requirements of tools and processes. Part of the reason why we left traces when we tightened the screws is that the sleeves of the screws were worn. After the wear, the contact between the sleeves and screws changed from surface to point contact, or the point contact was reduced by half. The screw/nut would leave traces when the point force was applied, but more serious traces would be left when the screws were tightened with a solid wrench. Only two surfaces of the screws were stressed, and the deviation of the solid wrench was large, which caused serious wear in use, More obvious marks will be left after screwing.

Whether there is any mark left by screwing is related to the assembly tool. A sleeve with high precision contacts the nut more closely. When a high-quality sleeve is sleeved on a standard nut, you will find that there is no excess clearance between the sleeve and the nut. At this time, the nut is stressed evenly, and the contact area between the nut and the sleeve is large, so the wear marks will naturally be smaller.

The force is not controlled well during the screw twisting process. When the torque of the screw is too large, it is not only easy to slide and break the wire, but also the traces left on the nut surface will be more obvious.

Therefore, when the screws are tightened with high-precision sleeve tools and standard torque, the traces on the screw surface will become invisible. Of course, the torque setting is related to the screw parameters. The higher the hardness level, the higher the strength, and the surface is not easy to leave traces of twisting.

Post time: Nov-22-2022