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Comparing Bolt Tightening Methods: Torquing, Hydraulic and Mechanical Tensioning

factory worker

Which method of bolt tightening is right for you? Find out how they compare below.

Torque Tightening

Most people have only ever seen a bolt torqued, usually by a mechanic who is working on their car. By turning the nut, the mechanic tightens the bolt or stud. Torquing is, of course, used in many other applications.

Wherever it is used, torquing achieves a high useful bolt load, at about 70 percent of the bolt’s yield strength. The other 30 percent is lost by torsional stresses. This is a higher yield strength than hydraulic tensioning normally achieves but lower than mechanical tensioning.

It is also an inexpensive and simple method of bolt tightening. Your torquing tool is small, easily portable, and easy to train people to use. Pneumatic torque tools may also offer you speed. However, torque tightening is less precise than other methods of bolt tensioning.

Hydraulic Tensioning

You can use a hydraulic bolting tool to stretch the bolt, instead of turning it. The tool provides a high degree of accuracy, which is necessary in many applications. Or if you’re simply using a very large bolt, torquing may not be feasible, in which case you need to turn to hydraulic tensioning.

Hydraulic tensioning doesn’t achieve the same yield strength as torquing. While the bolt is stretched to 90 percent of its yield strength, the bolt springs back after the hydraulic pressure is relieved. This causes additional stress to the assembly.

The bolt only maintains 66 percent of its yield strength, unless you’re using a longer tie rod, in which case it may maintain up to 80 percent of its yield strength.

Hydraulic tensioning is fast and accurate, but much more complex and challenging than torque tightening.

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Mechanical Tensioning 

Mechanical tensioning is similar to hydraulic tensioning in that it is highly accurate and complex. However, it achieves a higher bolt load than hydraulic tensioning.

It does this by acting on the bolt directly, so there is no springing back or torsional stress as in the other bolt tightening methods. This allows mechanical tensioning to achieve 90 percent bolt yield strength.

Mechanical tensioning is best used in applications where a high bolt yield and high accuracy are both top priorities.

Which Tensioning Method is Best for You?

If you’re not sure which tensioning method can deliver you the best results considering your application needs and budget, reach out to us at Ultra Torq. We can find the best solution for your application.

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