The main connection method of heavy trucks is bolt connection, and there are many types of fasteners and matching methods. Through the lateral vibration test, the fastener matching optimization suggestions are proposed after comparative analysis.
At present, the main connection between the truck assemblies and components is still bolted, because the standard, versatility and interchangeability of bolted joints make bolting applications widely available and cost-effective.
At the same time, however, there are many problems of matching varieties, which result in different fastening characteristics and anti-loose performance between different matches, which leads to loose bolts and connection failure.
The reasons for loose bolts are complicated. In addition to the manufacturing, heat treatment and coating processes, they are also closely related to the damping speed and amplitude of the clamping force between the joints. Therefore, it is necessary to study the matching characteristics of bolts and nuts and use reasonable matching to improve the thread pair. Anti-loose performance and reduced fastener varieties.
High-strength bolts commonly used in heavy trucks have hexagonal and flanged faces (with or without teeth). Common nuts are non-metallic inserts (nylon) locknuts, elastic rings (reeds), lock nuts, flange faces Nuts and squirrel (tooth type) nuts, etc.
In order to verify and verify the anti-loosening performance of various matching combinations, the international common and national standard recommended thread pair lateral vibration tester is used for test comparison and analysis test data.
1. Test overview
1.1 M18 bolts match different nuts
Take the M18×2 hexagonal head galvanized bolt as an example, and respectively perform the vibration test after matching with the Schmidt nut, the reed lock nut and the nylon lock nut.
According to the standard requirements and test plan, after the nut is tightened according to the set clamping force, the instrument will record the initial clamping force and the remaining clamping force at the end of the vibration in real time during the vibration process, and determine the percentage of the remaining and initial clamping force. The difference in the anti-loosening performance of the test piece.
Figure 1 Fastener lateral vibration tester (GB/T 10431-2008)
The test presets the same clamping force, and each nut performs two sets of tests under the same clamping force. Data are as follows:
Figure 2 M18 bolts with different lock nuts
It can be seen from the table that the nylon clamping nut has the least attenuation of the clamping force at the end of the vibration under the same clamping force.
Table 1 Test data of different types of lock nuts
1.2 Different coated wheel bolts match the wheel nuts
The wheel bolts are M22×1.5-10.9. In order to verify the influence of different surface coatings on the bolts, the phosphating and galvanizing bolts and nuts are prepared and the vibration tests are carried out respectively to obtain the comparison data.
Figure 3 Test wheel bolts and nuts
The following are two sets of test data for phosphating and galvanizing:
Table 2 Different surface treatment matching tests
It can be seen from the data in the table that the clamping force of the phosphating bolt nut is attenuated more under the same clamping force.
1.3 Spring washers, wedge washers and bolts match
Figure 4 Spring washer and lock washer
Use M18×1.5-10.9 hex head bolts and M18×1.5-10 hex head nuts, and tighten the nut at the end of the nut. The following are the data obtained by lateral vibration:
Table 3 Different gasket matching test data
As can be seen from the data in the table, the clamping force of the wedge washer is less attenuated at the same clamping force.
2, analysis and summary
The test is carried out in accordance with the requirements of the national standard. The test equipment is used to tighten the nut, and the vibration is automatically stopped after 1500 vibrations. Based on the test data, the test is summarized as follows:
2.1 too many types of fasteners
Not conducive to procurement management, production organization, quality control and after-sales service, should reduce varieties. For example, in parts that are not frequently disassembled, hex head bolts and self-locking nuts can be used to match and improve the anti-off ability.
In the frequently disassembled parts, the hexagonal head bolts can be matched with the Schemen nuts, and the axial force can be quickly attenuated by increasing the locking force and friction between the thread pairs.
2.2 Wedge washer because the wedge angle is larger than the thread helix angle
When the nut has a tendency to loosen, the washer will compensate for the gap and ensure that the axial force will not be greatly attenuated, and the structure is anti-loose rather than frictional.
Therefore, after the wedge-shaped lock washer is used, the ordinary nut can be used. Although the washer is added, the variety of the bolt and nut is reduced.
2.3 Test certificate
Due to the large axial clamping force of the high-strength bolt, the spring washer has been completely flattened into a flat washer during installation, and the elastic anti-loose performance cannot be realized.
2.4 test found
When the phosphating high-strength bolt and nut are connected in the lateral vibration, the clamping force is attenuated greatly, and the reason for the analysis may be caused by the low friction coefficient of the phosphating surface.
3, the conclusion
In high-strength bolted connections, it is not necessary to use a spring washer to prevent loosening above the diameter M14 or above 200Nm.
Phosphating bolts will be oiled and rustproof in actual use, so it is not conducive to loosening. High-strength bolts and nuts are not recommended for phosphating surface treatment.
Matching fasteners in key parts, not only to prevent loosening, but also to increase the anti-off function. Therefore, the research and promotion of structural anti-loose mode should be done to reduce the adverse effects of large friction coefficient difference.
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