Why Torque and What Are We Trying to Achieve?

Let’s delve deeper into what’s going on when we tighten a bolt down and what we can do to ensure consistent results.

Put very basically we are wanting to stretch the bolt or stud, also known as elongation, so that fastener stays tight, too much stretch and the bolt can become weak and prone to breaking, too little stretch and the fastener may become loose. In our game both situations can equal downtime, non-compliance, or more importantly injury to ourselves or others.

The number one thing stopping us from obtaining the perfect amount of stretch every time is friction. With this in mind, we must always begin our procedure with checking and cleaning the bolts, studs, nuts, and surfaces. As simple as it sounds this step is often overlooked, especially on the side of the road changing a tyre while it’s hosing down with rain.

After we have cleaned our threads and surfaces ready for assembly, we should be referring to the manufacturers specifications as to exactly how much torque we need, usually this in a Nm or Ft lbs measurement, also note any other special precautions needed. Some of these precautions may be the order in which we tighten each bolt down on a flange, the use of a torque setting plus an angle, or the use of special lubricants. The bottom line is that every bolt is different, and we should avoid using generic settings/procedures.

The final comment we want to touch on for today, the re-checking of tensioned bolts after a suitable amount of time or use is highly important. In applications where critical nuts and bolts are subjected to vibration and/or high heat fluctuations, consideration should be made towards periodic re-tightening i.e., truck wheels are often retightened 100Km after a tyre repair.

HTC Ltd is New Zealand’s leading supplier of torque wrench tools and calibration, servicing, and repair services. To book a calibration service for your torque tools, visit htc.co.nz/calibration-and-testing/ and scroll down to the booking form. To contact the team directly, call 0800 48 2000.

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