Talking about the use of spring washers
Among all kinds of mechanical connectors, the anti-loose of high-strength bolts is an important part. There are many ways to lock the bolts, including the use of spring washers to prevent loosening. Let's share with you some of the problems with the use of spring washers:
Principle: The spring washer's anti-loose principle is that after the spring washer is flattened, the spring washer produces a constant spring force. Keep the frictional force between the nut and the threaded connection of the bolt, and generate a resistance torque to prevent the nut from loosening.
Use case: The sharp corners at the opening of the spring washer are respectively embedded in the bolt and the surface of the connected member, thereby preventing the bolt from rotating relative to the connected member. For the commercial heavy-duty axle part, the spring washer is widely used, and about 50% of the bolts are spring washers to prevent loosening.
Practical case: Take the 10.6 M16 bolt as an example. The connection between the axle final reducer and the axle housing is 10.9 M16X100 bolts. The tightening torque is 280+20 Nm and tightened with a high-precision electric tightening machine. The change of the torque with the rotation angle during the tightening of the bolt is detected in the state of the spring washer and the spring washer. Comparing the torque angle curve, it is found that there is always a pre-tightening torque of about 10 Nm in the case of a spring washer; and in the absence of a spring washer, the torque is in a state of 0 Nm before the torque rises significantly.
Verification: It is inferred that the spring washer can be completely flattened with a bolt pre-tightening torque of approximately 10 Nm. Then, by using a digital torque wrench, it was found that the bolt torque has not reached 20 Nm, and the spring washer has been completely flattened, which verifies the correctness of the above inference.
Analysis: Analysis of the above two points, the spring washer can only provide 10 Nm elastic force, and the 10 Nm elastic force can be ignored for the 280 Nm bolt pre-tightening torque. Secondly, such a small force is not sufficient to allow the sharp corners of the spring washer incision to be embedded in the bolt and the surface of the member to be joined. After the disassembly, the bolts and the surface of the connected parts have no obvious inlays. Therefore, the spring washer has a negligible effect on the bolt. In addition, adding a washer between the bolt and the connected piece, if the quality of the washer is problematic, it is equivalent to adding a safety hazard to the bolt connection.
Conclusion: In summary, when the bolt torque is large (greater than 200 Nm), the use of spring washers to loosen the bolts is more harmful than good. Therefore, under the action of impact, vibration and load change, the pre-tightening force may disappear at a certain moment, and the connection may be loosened.
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