Using the proper torque is an important part of a reliable bolted joint. Insufficient torque can lead to the fastener being loosened by vibrations while excessive torque can cause stretching and breaking of bolts. Once the proper torque has been determined for a joint, it is a good practice to perform periodic audits to ensure you are reaching your targets.
There are three general methods of testing to ensure that the proper torque has been applied.
First Movement Test
This particular method requires the use of a torque measuring tool, and is best used to determine residual torque. Residual torque is the amount of tension leftover in a joint after fastening a threaded fastener.
First, mark the tightened fastener and surrounding application. Slowly apply force to the tool, in the same direction used to tighten it, until the first movement in the fastener is noted. The reading recorded should provide you with an idea of the original torque applied to the joint.
This method is similar to the first, with one fundamental difference. Instead of tightening the fastener, this test applies the torque in the direction that loosens the fastener. Should you choose this method, you’ll record a torque reading once the fastener breaks loose, and that should give you an accurate indication of the approximate torque applied to the joint.
For the third and final testing method, mark the surface of the tightened fastener and continue that mark onto the surface that is being clamped. Then, loosen the fastener and retighten until the marks are aligned. This allows you to measure the torque required to return the fastener to its original location, and thus the original torque applied.
Knowing how to properly utilize each method is equally important to understanding the importance of such tests. To learn more about torque and methods for measuring it, contact Bossard at ProvenProductivity@bossard.com.
Methods for Torque Testing by Bossard