We’ve been fastening things together with bolts and nuts for well over a century and apart from better materials, there has been little in the way of improvements to this system. Fact is, the bolted joint remains a superior fastening method — that is, when fasteners are properly installed…
That’s where the challenge comes in…for many decades, the accepted practice has been to measure torque to determine the tightness or clamp force in a bolted joint. Installers and inspectors lug around heavy torque wrenches, taking readings, and referring to “standard” bolt/fastener torque settings charts (like the example on the right) in order to determine a joint’s tightness.
Unfortunately, checking with a torque wrench only provides a measurement of torque which can be greatly affected by friction factors — even cross threading. That’s why on torque settings charts you’ll typically see two different settings, one for ‘dry’ bolts and one for ‘oiled’ bolts. You’ll even see some sort of disclaimer or warning on fastener torque settings charts, like the statements at the bottom of the sample chart. Below is another disclaimer we saw on anther chart:
“The above recommended assembly torques are offered as a guide only. Torque specifications, especially for critical joints, should be determined under actual assembly conditions due to the many variables involved which are difficult to predict and do affect the torque-tension relationship.”
Given the complexities and variances involved with even properly interpreting a torque settings chart, it’s not surprising that achieving proper design tension using torque measurements is like shooting at a moving target. It’s far too common for installers to make errors or to even be fooled into thinking they have successfully installed a properly tensioned bolted joint, when in fact, the joint may be loose or even over-tightened due to torque readings affected by undetermined friction factors.
This is why reliance on torque values alone should no longer be an acceptable practice, especially when proper installation and maintenance of design tension is critical for safety concerns or when joint failures can result in costly down times. This is when there can be no room for errors associated with misleading torque readings. To learn more read Why Tension, Not Torque.
SmartBolts are a Superior Method to Assure Joint Tension
The BEST way to accurately determine tension in a bolted joint is by measuring actual fastener elongation under load. In other words, the true way to measure the force exerted on the fastener shank, that holds the joint together, is to monitor how much the bolt has been stretched.
Only DTI SmartBolts® use fastener elongation to visually indicate whether a bolted joint is within design tension (within +/-10%).
DTI SmartBolts indicate whether a bolted joint is loose or tight with a clear, visible indicator that gradually darkens from bright red to black as the fastener is tightened.
DTI SmartBolts Features Include:
>> Easy to use – visual indication – no contact with the fastener required
>> Measures tension, a more accurate measure of “tightness” than torque
>> Accurate to +/- 10% of design tension
>> Reusable
>> No special tools or training required
>> Long service life
>> Design Tension customizable in design phase
Learn More or to Order DTI SmartBolts
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