The anti loosening of bolts is a very important aspect in various types of mechanical connectors. There are many ways to prevent bolts from loosening in daily life, including using spring washers to prevent loosening. Spring washers are often referred to as spring washers in the screw industry. So why is it frequently used? This depends on the function and principle of spring washers.
1、 The function of spring washers:
The basic function of spring washers is to apply force to the nut after tightening, increasing the friction between the nut and the bolt! This is an added protective measure to prevent loosening of fastening bolts caused by equipment vibration during operation.
2、 The anti loosening principle of spring washers:
The anti loosening principle of spring washers is that after pressing the spring washers flat, the spring washers will generate a continuous elastic force, which will maintain a frictional force between the threaded connection pair of the nut and the bolt, generating a resistance torque to prevent the nut from loosening. At the same time, the sharp corners at the opening of the spring washer are embedded into the surface of the bolt and the connected part respectively, thereby preventing the bolt from rotating relative to the connected part.
However, practice has shown that spring washers can only provide a spring force of 10 N/m, which can be ignored for bolt pre tightening torque of 280 N/m. Secondly, such a small force is not enough to embed the sharp corners at the notch of the spring washer into the surface of the bolt and the connected part. After disassembly, there are no obvious embedded marks on the surface of the bolts and the connected parts. Therefore, the anti loosening effect of spring washers on bolts can be ignored.
Also attached is the anti loosening effect and schematic diagram of the spring washer:
From the perspective of the function and principle of spring washers, using spring washers to prevent loosening is not a good method. It is still necessary to find an ideal method of preventing loosening by increasing the friction resistance moment.
Case study on anti loosening of spring washers
The connection between the axle main reducer and the axle housing uses 10.9 grade M16X100 bolts, with a tightening torque of 280+20 N.m, and is tightened using a high-precision electric tightening machine. Detect the variation of torque with rotation angle during bolt tightening process in two states: with and without spring washers. Comparing the torque angle curve, it was found that there was a pre tightening torque of approximately 10 N.m in the presence of a spring washer; In the absence of spring washers, the bolt is in a state of 0 N.m before the torque significantly increases.
Based on this, it can be inferred that a pre tightening torque of approximately 10 N.m of the bolt can completely flatten the spring washer. Through testing with a digital torque wrench, it was found that the bolt torque had not yet reached 20 N.m and the spring washer had been completely flattened, verifying the correctness of the above inference.
The analysis of the above two points indicates that spring washers can only provide 10 N.m of elasticity, which can be ignored for the pre tightening torque of 280 N.m bolts. Secondly, such a small force is not enough to embed the sharp corners at the cut of the spring washer into the surface of the bolt and the connected parts. After disassembly, there are no obvious embedded marks on the surface of the bolts and the connected parts. Therefore, the anti loosening effect of spring washers on bolts can be ignored.
In addition, adding a washer between the bolt and the connected part adds another safety hazard to the bolt connection if there is a quality issue with the washer.
In summary, when the bolt torque is high (greater than 200 N.m), using spring washers to prevent the bolt from loosening has more disadvantages than advantages. Therefore, under the effects of impact, vibration, and variable load, the preload may disappear at a certain moment, and the connection may become loose. On the premise of improving the fatigue strength of bolt connections, one of the measures to reduce fatigue failure is to use thread locking adhesive anti loosening technology, and apply anti loosening locking adhesive to the threaded parts. It is a bonding and anti loosening technology that involves filling the thread locking adhesive into the gap of the thread connection pair and bonding (curing) the internal and external threads together to achieve anti loosening requirements.