We often hear questions about breakaway torque. More importantly, when discussing torque measurement, we encounter a lot of misinformation about breakaway torque.
We've been making torque tools for more than 90 years. We only make torque application tools and testers. Torque application is not a sideline with us. It is our total and only focus. So, we live torque every day.
When you are thinking about breakaway torque, you really want to know, how much clamping force, or how tight is this already tightened fastener? Another term for breakaway torque is Residual Torque. We have tools that measure Residual Torque. What is breakaway torque or as others call it, Residual Torque?
Once torque has been applied to a joint, an audit function measures exactly how tight that fastener was torqued. Please note, due to surface conditions, joints can relax. So, there can be changes in the clamping force between the time the torque was applied and the time that the torque value audit is conducted.
While a good tool with residual mode will provide an accurate assessment of the clamping force, there is no way to tell if the joint relaxed, or by what percentage it relaxed.
After being tightened, and torque is applied, there is a point when the fastener begins to move again. That point of movement is "breakaway torque." We tend to look at movement at about 3 degrees of rotation. That means the tool you will be using must have both torque and angle functionality. And it must have Residual Torque capabilities.
It starts with selecting the appropriate torque wrench. Our tools with Residual Torque functionality include:
- DTC - Digital Torque and Angle Wrench - Five wrenches covering 1 ft-pound up to 250 ft-pounds.
- 1250 Series Exacta 2, Digital Torque and Angle Wrench - Twelve wrenches covering 5 ft-pounds up to 600 ft-pounds.
- 1350 Series Exacta 2, Digital Torque and Angle Wrench - Five wrenches covering 1 ft-pound up to 250 ft-pounds.
- 1350 Series TD, Digital Torque and Angle Screw Driver - Two drivers covering 5 Inch-ounces to 80 inch-pounds
When auditing previously tightened fasteners, using the appropriate torque wrench is imperative. You'll want to use the most accurate wrench you can find. The wrenches we have listed above are all +/- 1% of the indicated value or +/-2% of the indicated value. Even the 1350 TD is accurate to +/- 2% of the indicated value.
Sturtevant Richmont digital torque and angle wrenches come equipped with a radio and there are models without an embedded radio. In the tools that come radio-equipped, the radio transmits the torque and angle values to the controller. The data is stored in the controller or sent to a data repository. The DTC does not have a radio. It comes with a mini-USB port and you simply connect the DTC to a computer and use the DTC CONNECT freeware to download the date/time-stamped results from the wrench.
Digital torque wrenches with a radio are designed to communicate with the Global 400 and Global 400mp torque controllers. To find more information about those wrenches look for our 1250 Series Exacta 2, 1350 Series Exacta 2, 1350 Series TD digital torque and angle wrenches.
We also make suitable audit tools without a radio. Those wrenches are the DTC digital torque and angle wrenches.
Once you have the appropriate wrench selected, the process is the next point of focus.
Mode of Operation is important.
Just as there are different modes of operation for different tools in torque application, there is a specific mode of operation for establishing the value of breakaway torque. That mode of operation is called "Residual Mode." It is called residual mode because breakaway torque is often referred to as residual torque.
So far, everything has been straightforward. That means this is where it gets messy.
In which direction should you apply force to create the movement needed to establish breakaway torque?
Despite the laws of physics and the application of common sense, some still come to the wrong conclusion.
For this example, consider a fastener that is turned clockwise to tighten and is turned counterclockwise to loosen.
Which direction should the fastener be turned to establish "breakaway torque"? The direction in which the fastener was originally tightened. While most of those will be clockwise, there are fasteners that have left-handed threads, so they are tightened in the counter-clockwise direction.
Remember that breakaway torque is that moment in time when the previously torqued fastener begins to move again. Once that movement happens, it cannot be created or captured again.
If you loosen the fastener, you've just changed the joint that someone worked so hard to create.
Given reaction times, we've seen too many cases where someone trying to establish breakaway torque simply loosens the fastener to the point where the joint is no longer in the condition it was when the fastener was tightened.
That is a problem. You were just trying to solve for the established torque value of a previously tightened fastener, and now you are creating the problem of a joint that is no longer in the condition it once was.
If you tighten the fastener, catching the moment of movement is easier. More importantly, you will get a more accurate breakaway torque reading.
Most importantly, in your audit to validate accuracy, you won't destroy the joint that you are auditing.
To learn more about how Sturtevant Richmont tools with Residual Torque functionality can solve your auditing challenges, contact your local Sturtevant Richmont Torque Strategist.