Fastening Torque Testing
Threaded fixings and fasteners are frequently secured to a prescribed number of turns, or to a specified torque, to achieve a required clamping force. In many applications this is safety critical. The fastener must not vibrate loose, nor, through over-tightening, damage the threads. Adding additional fasteners to, or around, a joint may result in joint relaxation and loosening, so torque verification after complete assembly of parts is required. The torque tools themselves also must therefore be reliable, so regular calibration is important.
Crucially, whatever prescribed torque is applied to a fastener, what matters is the residual torque, or the tension remaining in the joint after fastening. To test or verify this, a number of features matter:
- what does it take to tighten the fastener more? (test with applied incremental torque in the direction of tightening). Sometimes called first movement, or crack-on, test.
- what is the loosening torque? (test with applied incremental torque against the direction of tightening). Sometimes called loosening, or crack-off, test.
- what is the retightening torque? (test by loosening and retightening a fastener from and back to a marked position). Sometimes called the marking test.
Torque verification or torque auditing, is also important because the rundown friction in tightening is not the same as the static friction of the fastened head.
Mecmesin supplies a versatile digital torque wrench calibrator, torque screwdrivers, and bench-top fully-programmable torque testers, including precision testing down to a few mN.m for the very smallest fasteners.
Related test types
Fastening torque test standards
A number of standards for torque testing have been developed. For example:
- ASTM D5649 : torque strength of adhesives used on threaded fasteners
- ASTM F543-13e1 : standard specification and test methods for metallic medical bone screws
- BS EN ISO 11608-2 : Needle-based injection systems for medical use. Requirements and test methods. Needles
- IFI 143 : test for evaluating the torque-tension relationship on both externally and internally threaded fasteners
- IFI 543 : test for evaluating the torque-tension relationship on both external and internal metric threaded fasteners
- ISO 10964 : adhesives - determination of torque strength of anaerobic adhesives on threaded fasteners
- ISO 16047 : fasteners - torque/clamp force testing
- SAE AIR 1471A : torque tightening threaded fasteners
- SAE AS1310B : fastener torque for threaded applications, definitions of
- SAE J1701 : torque-tension tightening for inch series fasteners
- SAE J1701M : torque-tension tightening for metric series fasteners
- SAE J174 : torque-tension test procedure for steel threaded fasteners, inch series
- SAE J174M : torque-tension test procedure for steel threaded fasteners - metric series
