Are spring washers really anti-loose?

Recently, an engineer asked HJ.Tech, do you still use a flat washer after using a spring washer? Instead of answering his question directly, I told him not to use a spring washer, not much use.
So let's talk today about whether the spring washer is really loose.
Spring washers are also standard parts often used in bolted connections, and are often used as a measure to prevent loosening. However, as engineers deepen their understanding of bolted connections, they are more and more skeptical about the anti-loosening effect of spring washers. And spring washers are rarely used in high-strength bolted and high-vibration equipment.

1. The role of the spring washer

The basic function of the spring washer is to give a force to the nut after the nut is tightened, increasing the friction between the nut and the bolt! That is to say, a protective measure is added to prevent the loosening of the fastening bolts caused by the vibration of the equipment in operation.

2. Anti-loose principle of spring washer

The anti-loosening principle of the spring washer is that after the spring washer is flattened, the spring washer will generate a continuous elastic force, so that a frictional force is continuously maintained in the threaded connection pair of the nut and the bolt, and a resistance torque is generated, thereby preventing the nut from loosening. At the same time, the sharp corners at the opening of the spring washer are respectively embedded in the surface of the bolt and the connected part, thereby preventing the bolt from rotating relative to the connected part.

3. The relaxation effect of the spring washer is poor

However, practice has proved that the spring washer can only provide a spring force of 10 N/m, and the spring force of 10 N/m is negligible for the bolt pre-tightening torque of tens of Nm and hundreds of Nm. Secondly, such a small force is not enough to make the sharp corners of the spring washer cut into the surface of the bolt and the connected part. After disassembly, there is no obvious indentation on the surface of the bolt and the connected parts. Therefore, the anti-loosening effect of the spring washer on the bolt can be ignored.

The anti-loose function and schematic diagram of the spring washer are also attached:

At the same time, judging from the appearance of the disassembled spring washer, after a period of use, the spring washer rarely returns to its original size, which means that the spring washer can no longer provide continuous elastic force, and the spring washer loses elasticity. , the part of the preload that was originally occupied is also useless, so bolts that use spring washers are more likely to loosen.
From the point of view of the function and principle of the spring washer, using the spring washer to prevent loosening is not a good way to prevent loosening, and it is still time to find an ideal loosening method.
Therefore, Machinery Finance recommends that spring washers should not be used in bolt connections above M10; spring washers should not be used on high-vibration equipment; spring washers should not be used on equipment with gentle vibration if the hardness of the connected parts is high. ; Do not use spring washers in high-strength bolted connections.