What Is Torque?

Torque, or the measure of how much a force acting on an object causes that object to rotate, is an important concept in equipment maintenance. When buying, repairing or maintaining bolt fastening equipment, it’s important to know what torque is, how it pertains to certain tasks and what equipment is best suited to those tasks.

How Torque Works

You generate torque any time you apply force using a wrench. In most cases, you use torque to tighten nuts or other fasteners to bind two materials or objects tightly together. When you apply force to the handle of a wrench, you create torque that turns the nut and secures the bolt.

How Torque Applies to Bolt Tension

In simple terms, you need torque to create tension in a bolt. You use torque to turn a nut onto a bolt and then to stretch the bolt, making it a solid spring that then clamps the two materials together. The bolted materials cannot come apart if the clamp load remains more than the tensile load (the ability of a material to withstand a pulling force).

The Importance of Torque Control

Though it may seem that more torque is always better when it comes to bolt tension, that‘s not the case. It’s possible to use too much or too little torque. If too little torque is used, a bolt can become deformed and will not provide enough clamping force. If too much torque is used, the bolt can break. Using the right tools and having the right training are both keys to applying the right amount of torque for a particular task.

What Is Torque Tensioning?

Torque tensioning refers to the stretching or elongation of a bolt that is needed to clamp two materials together. For a bolt to hold two materials together securely, a certain amount of preload tension is required. Preload refers to the amount of tension that needs to be applied to a bolt with a torque wrench to secure it in place before the load it needs to support is added. When the load is placed on a bolt, the load amount is normally limited to what the bolt itself can handle without failing. When the bolt is tightened against a material, however, the bolt can then distribute the amount of the load throughout that material and it can hold much greater loads when the right amount of preload is applied.

How to Determine Torque Preload

Applying the right amount of preload to a bolt involves a bit of science. To indirectly control a bolt’s preload, you use torque. To calculate the amount of preload needed, you must know the specific bolt material and grade, the amount of load it needs to carry, the loss of torque due to friction and numerous other aspects of the load. Preload is specified as a percentage of the bolt material’s tensile yield strength. You calculate it using either an equation or an online bolt torque calculator. When you don’t meet preload conditions, the two materials will not stay fastened.

How a Torque Wrench Works

To be effective, a torque wrench needs three things: torque to stretch the bolt, torque to overcome friction at the bolt threads, and torque to overcome friction at the nut spot face. Let’s dive a little deeper into each action:

Torque to stretch the bolt

When you apply proper torque, you stretch the bolt just short of its yield point. To get this right, you need to accurately determine both the amount of torque to stretch the bolt and the amount to overcome friction. In most cases, only 10 to 15% of the torque used actually stretches the bolt.

Torque to overcome friction at the bolts threads

Approximately half of the tightening torque overcomes friction. You need 30% of this to overcome friction in the threads.

Torque to overcome friction at the nut spot face

You need the rest of the torque to overcome friction under the nut face. Approximately 50 to 55% of torque dissipates under the nut face.

Aztec: Your Supplier for the Best Torque Wrench for Your Job

Using the right tools is half the battle when it comes to applying the right amount of torque for the job, and that’s where Aztec shines. We sell and rent only the most durable torque wrenches and tensioning tools from brands such as Enerpac, Norbar, Skidmore-Wilhelm, and others to increase the life of your equipment. We also provide in-house and mobile services to repair and calibrate torquing and tensioning tools and train your team on how to use our products to get the job done correctly. We utilize the latest bolting technology to serve petrochemical, oil and gas, wind generation, construction, maintenance and power generation leaders. Ready to experience unmatched customer service and the highest quality bolting tools in the industry? Contact the pros at Aztec today.