Why Do We Torque Bolts & Why Bolt Tensioning Safety is Critical

Why do we torque bolts, with high attention to detail? Consider that on August 20th, 2011 the US military investigated the crash of a Global Hawk aircraft drone outside of Kandahar Afghanistan. The subsequent report concluded that the cause of the crash was an improperly torqued fastener. In total it cost the military 73 million dollars. [1]

This example illustrates why bolt tensioning safety is crucial to manufacturers.

What is Torque?

Torque is a twisting force measuring force multiplied by distance – foot or inch pounds in the US and Newton-Metres in Europe. Usually distance would be the length of the wrench (say 2 feet) and your hand would apply force (2-foot wrench, 10 pounds of pressure equals 20 foot-pounds). [2]

How Does this Apply to Bolt Tension?t-con-bolt-tensioning

Torque is used to create tension. Bolts are used to affix two components so that they can resist tensile (pulling apart) and shearing (sliding apart) forces. After the nut has been turned onto the bolt, additional torque causes the nut to turn and stretch the bolt.

When the bolt stretches it becomes a solid spring that clamps the components together. As long as the clamp load is not exceeded by the tensile load, the components won’t be pulled apart. Under shear loads, the increased friction prevents relative motion of the components, preventing material failure.[3]

Proper Torque Value

Determining how much torque is needed depends on two related questions:

  • The material properties of the bolt (i.e. what metal are they made from)
  • Their purpose.

In short, you need the right materials for the right job.

The Importance of Proper Torque

You can both over, and under torque a bolt. According to the US military’s report, their drone had screw caps 18-22 inch-pounds above prevailing torque, allowing the cap screws to loosen in flight. [4]

Typically, an under torqued bolt will deform and be unable to provide as much clamping force as needed. An over torqued bolt will break.

The Tools You Need and How to Care for Them 

Torque wrenches will measure the amount of torque being applied in either analog or digital formats. To function reliably they must be treated with care. Unlike a hammer, or a screwdriver, a torque wrench is a precision instrument and must be handled to avoid costly recalibration.

Torque Tools from Ultra Torqstahlwille-angle-controlled-713r

Whether you’re creating a multi-million-dollar drone, or an everyday item, attention to bolt tension safety is crucial to proper functionality.

Achieving precise results requires a precision tool. Our selection of torque wrenches will allow you to measure and apply the proper torque for the results you need.

If you have questions about why you should torque bolts with more precision, contact us at Ultra Torq.

[1] Rosenberg, Zach. Loose wire caused Afghanistan Global Hawk crash. Flight Global. March 7, 2012. Available online: https://www.flightglobal.com/news/articles/loose-wire-caused-afghanistan-global-hawk-crash-369238/
[2] The Importance of Using Proper Torque Values for Nuts and Bolts. BimmerTips. August 3, 2016. Available online: https://bimmertips.com/importance-using-proper-torque-values/
[3] Mohan, Sankar. What is the purpose of torquing bolts? Quora. January 6, 2018. Available online: https://www.quora.com/What-is-the-purpose-of-torquing-bolts
[4] Improper Torque & Loose Screws Cause Critical & Costly Issues Mountz. August 14, 2013. Available online: https://www.mountztorque.com/blog/apply/improper-torque-loose-screws-cause-critical-costly-issues/