The Loosening Of Prevailing Torque Nuts

Whether you are working professionally on commercial buildings or you are creating your latest home project there is nothing more annoying than the uncertainty that one of your prevailing torque nuts might come loose with time. While you might think that by this point in time a better system would have been put in place that protects the nuts from loosening, the reality is that the most common bolt and nuts designs might still come loose over time.

What causes loose nuts?

The reasons for the loosening of nuts have been commonly studied, and it is now known that for the most part, any transverse joint movement might lead to your nuts loosening if they are not locked in place. This is because the relative motion occurring causes friction between the two surfaces, which might lead to the nuts coming loose. Put simply, the little motion of the bolt and nuts leads the bolt to start traveling down the spiral design of the bolt. While sufficiently tightening the nut can at times be the key, it is not always easy to lock the mechanism in place just by tightening it. This is why locking devices are often added to the bolts in order to stop them from coming loose.

Interesting facts about loosening nuts

Research has shown that the nuts resistance to becoming loose will often depend on the prevailing torque. Those of higher value will often be less likely to loosen up, however, there is a downside to this, as the torsional stress could potentially lead to premature yielding.

It is also worth noting that there have been cases previously where prevailing torque nuts have gone completely loose and even fallen off the bolts. This could have incredibly negative results in the construction that these bolts were used. Usually, in these cases, the self-loosening is caused by vibrations. Transverse vibration could potentially cause prevailing torque-type nuts to loosen. This is because while these types of nuts are less likely to go loose, the reality is that they are not truly "lock nuts". As such, there is always some space for friction to enter the situation and cause the nuts to come loose. Still, it is important to note that under a standard transverse vibration test it has been shown that with prevailing torque nuts it is more likely for them to loosen than it is for them to drop completely. This is because they usually manage to keep a certain amount of preload. Finally, it was been shown that the loosening of prevailing torque nuts is widely dependent on the magnitude of the bolt preload. In essence the higher the preload the more likely the loosening will be.

Research in conjunction with the Jost Institute of Tribotechnology at the University of Central Lancashire also posed an interesting hypothesis into the role of axial loading in transverse movement in the loosening of prevailing torque nuts. In order for this hypothesis to be further investigated and proven alterations to the Junker, a machine was necessary. This modification would essentially allow both axial and transverse loading to be felt by a joint. The results of the research showed clearly that the combination of these two was far more likely to cause the loosening of prevailing torque nuts.

One of the things that the testing process showed was that in cases of the axial load exceeding the preload on the nut, then the nut would often detach from the bolt. This is important information to hold, as it can limit the usage of prevailing torque nuts, and it can mean that they should not be used in certain construction projects. Whether prevailing torque nuts are a good fit for any particular project will widely depend on what type of stress it is expected that the join will be put under.

How are prevailing torque nuts different?

Prevailing torque nuts, or stiff nuts, are commonly employed by those who want to ensure that their nuts don't self-loosen. These types of nuts began appearing in the 1860s as a way of providing resistance that would stop the nuts from loosening. The way that this is done is through a locking feature which can be found in most nuts of this type. These lock nuts will often have filled centers that stop the nut from naturally unwinding on the bolt. This filling, which is usually made up of the same material as the rest of the bold, is a natural locking mechanism that secures the fastening of the nuts.

Are there any standards for prevailing torque nuts?

Prevailing torque nuts need to abide by the standard test code ISO 2230. Nuts that can pass through this certification are ensured to be able to meet the minimum performance standard. These include ensuring that the first prevailing torque in the tightening direction does not exceed the value set and that the fifth prevailing torque in the untightening direction never drops below the minimum value.

Are there varieties of prevailing torque nuts?

There are two popular varieties of prevailing torque nuts. These are the all-metal designs and the non-metallic insert designs. These two often have slightly different looks as they have two different designs that allow them to secure the bolt in place. For the all-metal nut, there is usually a distortion at the top part of the nut which allows the top threads to create an elliptical, rather than a completely circular shape. With non-metallic insert nuts on the other hand there is usually a polymer ring that is placed on the top part of the nut. This is what will keep the bold tight with time.

Metal Lock Nuts

Prevailing Torque Type Nut

Nylon Insert Hex Lock Nut

How to fasten Prevailing Torque nuts?

To avoid loosening prevailing torque nuts, one of the most important things to take care of is to fasten them properly. This includes avoiding certain common mistakes as well as following the best possible practices for these types of nuts.

1. Consider temperatures

When you are deciding what type of locknuts you should use, you should think about the temperatures that the nuts you are using will have to experience. For higher temperatures, it is best to buy nuts made of high-quality stainless steel. These might also be the best choice for environments with high corrosion.

2. Lubrication

If you know that your nuts are bound to face either corrosion or galling then using lubrication can allow you to create an additional layer that will improve the strength of your nut. Lubrication might also vary based on the material that the nuts you are using are made of. This will help prevent it from loosening regardless of the vibrations that might take place.

3. Follow the instruction manual

While you may feel like there is no reason to read through the manufacturer's manual for your bolts and nuts, you will be surprised at the amount of useful information that you might actually be able to find within it. Often the information will include the size of the screwdriver you should use, both the minimum and maximum torque to be applied, and even suggestions on how to proceed with the installation. It is also usually suggested that you tighten the locks slower as this can help bring down the chances of galling.

4. Overtightening and tightening the nuts too fast

One of the most common mistakes made during the installation process is overtightening the nuts. This is very common as you might be applying more torque than what the nut can actually withstand. The ideal torque to use is normally defined by the minimum and maximum torque that the nut can withstand. This is information that you will be able to find in the instruction or manufacturer's manual. Another important point to remember when tightening the nuts is that you don't want to proceed with tightening them too fast. This is because the friction between the two sections can lead to the surfaces becoming more abrasive. This could cause galling, which during any periods of vibration would lead to the nuts loosening.

Conclusion

The loosening of nuts is a common problem that many will face when dealing with construction, manufacturing, or even home projects. The use of prevailing torque nuts is often suggested as one of the solutions to this problem, as for the most part, these nuts can help ensure that there will be less loosening occurring. This is because of the lock mechanism that they employ. However, despite their design, these nuts are not full-proof, and depending on the type of vibrations you are expecting the joint to experience you might be better off choosing a different nut type. Regardless of the construction or handy work you are taking on it is clear that the most important things are proper installation and good-quality nuts. This is where AYA FASTENERS can be a valuable ally in your work as their high-quality nuts can often remain fastened even in adverse conditions.

AYA FASTENERS is one of the most reputable leading fasteners manufacturers and suppliers in China, we focus on assembly and fastening materials, supplying global customers with high-quality screws, bolts, washers, and nuts products over 20 years.

AYA has been deeply involved in the Fastener industry with a single-minded and dedicated attitude, devoted itself to providing our customers with more industry-specific, professional, standardized, and precise Fastener solutions. If you want more information, please contact AYA FASTENERS for the details.