While tools like Kolver's electric screwdrivers with torque & angle control ensure that the correct torque is applied during assembly, companies may still have a need to audit existing joints at a later date, perhaps as part of their ongoing quality control process.
This is generally referred to as a “torque audit” and aims at measuring the residual torque.
REASONS FOR AUDITING TORQUE
After all, a precision screwdriver can guarantee that the joint has been tightened in accordance with specifications, but there remains a question of what happens to the joint after tightening is complete, as a range of factors can influence the residual torque and, consequently, the joint's integrity and reliability over time.
A common scenario, for instance, is that there may be some joint relaxation.
A degree of joint relaxation is common, though often so small that it is negligible, and when it's expected to be more significant, it is often taken into account by those providing the fastening specifications in the first place.
Another scenario is added-friction to the tightening process; this friction contributes to the total torque applied to the fastener, yet does not directly affect the clamping force to it. In other words, the residual torque will end up being lower than the applied torque by the amount of torque needed to overcome that friction. Luckily, Kolver's K-DUCER has features that allow you to automatically compensate for this variable and still reach the desired torque.
Finally, environmental conditions such as excessive heat or vibrations, could impact the residual torque found in a joint.
Therefore, as with any situation concerning a certain degree of uncertainty, further testing is recommended, at least occasionally, and residual torque testing can provide the peace of mind needed - especially in critical applications where the product's safety, reliability, or performance depends on the integrity of the joints.
HOW TO PERFORM A TORQUE AUDIT
While there is no single standard way to perform a torque audit, the most widely used technique, the breakaway method, is to perform a 5-degree tightening of the bolt, an angle wide enough to ensure the residual torque is overcome and the bolt is rotated, but small enough to usually avoid over-tightening the joint. The torque reading during this small tightening operation will correspond to the residual torque.
Note that this kind of torque audits always runs a small risk of over-tightening beyond the maximum torque specified for the application.
However, since the product being audited is generally intended for customer use, the small additional tightening performed during the torque audit tends to compensate for joint relaxation rather than causing dangerous over-tightening.
Other techniques include:
* loosen/tighten, which consists slight loosening of the fastener followed by a re-tightening and measuring the final torque; any K-DUCER screwdriver can be used for this purpose;
* using a click-wrench on the existing bolt to ensure a certain torque threshold was reached; this method is usually not favored as it does not provide an actual reading of the residual torque;
* untightening the joint by a few degrees of angle using a digital torque wrench or a K-DUCER screwdriver, carefully noting the peak loosening torque value recorded. It is always recommended to follow this with a re-tightening of the joint by the same amount of rotation in order to compensate for the inevitable loss of residual torque during the loosening process.
In general, if torque audits are necessary, Kolver recommends utilizing a torque tester with a rotatory transducer (like Kolver's K-TESTER) or a digital torque wrench specifically designed for the measurement of residual torque. We also always recommend involving the engineer who determined the torque specifications for the joint being analyzed.
Need help with your torque testing needs? Don't hesitate to contact us.
This is generally referred to as a “torque audit” and aims at measuring the residual torque.
REASONS FOR AUDITING TORQUE
After all, a precision screwdriver can guarantee that the joint has been tightened in accordance with specifications, but there remains a question of what happens to the joint after tightening is complete, as a range of factors can influence the residual torque and, consequently, the joint's integrity and reliability over time.
A common scenario, for instance, is that there may be some joint relaxation.
A degree of joint relaxation is common, though often so small that it is negligible, and when it's expected to be more significant, it is often taken into account by those providing the fastening specifications in the first place.
Another scenario is added-friction to the tightening process; this friction contributes to the total torque applied to the fastener, yet does not directly affect the clamping force to it. In other words, the residual torque will end up being lower than the applied torque by the amount of torque needed to overcome that friction. Luckily, Kolver's K-DUCER has features that allow you to automatically compensate for this variable and still reach the desired torque.
Finally, environmental conditions such as excessive heat or vibrations, could impact the residual torque found in a joint.
Therefore, as with any situation concerning a certain degree of uncertainty, further testing is recommended, at least occasionally, and residual torque testing can provide the peace of mind needed - especially in critical applications where the product's safety, reliability, or performance depends on the integrity of the joints.
HOW TO PERFORM A TORQUE AUDIT
While there is no single standard way to perform a torque audit, the most widely used technique, the breakaway method, is to perform a 5-degree tightening of the bolt, an angle wide enough to ensure the residual torque is overcome and the bolt is rotated, but small enough to usually avoid over-tightening the joint. The torque reading during this small tightening operation will correspond to the residual torque.
Note that this kind of torque audits always runs a small risk of over-tightening beyond the maximum torque specified for the application.
However, since the product being audited is generally intended for customer use, the small additional tightening performed during the torque audit tends to compensate for joint relaxation rather than causing dangerous over-tightening.
Other techniques include:
* loosen/tighten, which consists slight loosening of the fastener followed by a re-tightening and measuring the final torque; any K-DUCER screwdriver can be used for this purpose;
* using a click-wrench on the existing bolt to ensure a certain torque threshold was reached; this method is usually not favored as it does not provide an actual reading of the residual torque;
* untightening the joint by a few degrees of angle using a digital torque wrench or a K-DUCER screwdriver, carefully noting the peak loosening torque value recorded. It is always recommended to follow this with a re-tightening of the joint by the same amount of rotation in order to compensate for the inevitable loss of residual torque during the loosening process.
In general, if torque audits are necessary, Kolver recommends utilizing a torque tester with a rotatory transducer (like Kolver's K-TESTER) or a digital torque wrench specifically designed for the measurement of residual torque. We also always recommend involving the engineer who determined the torque specifications for the joint being analyzed.
Need help with your torque testing needs? Don't hesitate to contact us.