Fasteners and Fixings: Methods of Tightening Threaded Bolts

When dealing with fasteners and fixings, such as threaded bolts, you may have found that you have a hard time when you are preloading. This is to be expected, especially if you don’t understand how to tighten the bolts correctly. The problem is, if you don’t tighten the threaded bolts the right way, you end up with a lot of scatter and a failed bolt. So how do you avoid these problems?

Tightening Your Threaded Bolts

If you want to prevent bolt failure and reduce scatter, you must understand how to correctly tighten the bolts. There are six popular methods for doing so, and each one can be used to control the preload.

Torque Control Tightening- With this method, the torque that is needed to tighten the bolt is either calculated or pre-determined with a chart. Torque control tightening overcomes the friction that is normally associated with bolt tightening and calculating the amount of pressure that will be placed on the threads.

Angle Control Tightening-This method involves the use of pre-determined angles that are used to tighten bolts.

Yield Control Tightening-Unlike other types of tightening for fasteners and fixings, this method is generally determined by feeling. You feel where the yield point is while you are tightening the bolt, which allows you to reduce the amount of friction and reduce scatter. Electronic methods have been developed to assimilate this process, and they involve sensors which determine the yield point.

Bolt Stretch Method-The bolt stretch method involves the use a hydraulic device that causes an extension of the threaded bolt. If the pressure on the hydraulic device accurately controlled, the preload of the bolt will be controlled.

Heat Tightening-With this method, the bolt is heated slowly either under fired,Lag screw  with the use of carbon elements, or with the use of a heating coil so it will expand. The nuts is placed using angle control, and as the bolt cools, it is forced to remain extended.

Tension Indicating Method-To correctly tighten threaded bolts, a number of different tension indicating methods can be used. In general, though, this method of tightening relies on the measurement of the extension of a bolt and bolts and washers that indicate how they should be loaded.
Taking the Bad with the Good

Accurately tightening your fasteners and fixing will help you with preloading, but each method will have its ups and downs. Some of the disadvantages for these methods include:

The need to correctly place the bolt the first time. Threaded bolts can only survive a few attempts before they will not be of any use anymore.
Some methods are very time consuming, like the heat tightening method.
You may have experiment a few times before you understand how to correctly tighten the bolt.
Some of the methods may make it hard to remove the nuts from the bolts because of corrosion.
With any method you choose, there will be a little bit of scatter, but this is normal. The advantages of these methods for tightening fasteners and fixings will far outweigh the disadvantages. Try one of these methods today to see if you have an easier time with preloading.




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