If you intend to use fasteners such as Inconel hex lag bolts or alloy 20 hex tap bolts, one of the issues you might come across is how to improve the performance of the bolts. Of course, general measures such as making sure that you buy high quality bolts and that they are made of […]

If you intend to use fasteners such as Inconel hex lag bolts or alloy 20 hex tap bolts, one of the issues you might come across is how to improve the performance of the bolts. Of course, general measures such as making sure that you buy high quality bolts and that they are made of the right material are all important.
bolt preloand graph
However, there are other things you can do to further improve the performance of any bolt even after doing all these. For instance, you could turn your attention to the issue of preloading the bolts. It has been found that when done properly, doing a bolt preload can go a long way in ensuring that it lasts longer and provides the performance that you are interested in.

What is bolt preload?
When a bolt is tightened, there is a stretching force known as tension that is created within it. This force is then transmitted to the joint that is being held together by the bolt. The force keeping the joint together usually corresponds to the amount of preload that the bolt has.
This means that when you are tightening the joint, you need to ensure that you place the right amount of preload on the bolt, otherwise it is likely to fail.

 
Factors that determine the amount of preload you can subject a bolt to
Not all types of bolts are tightened to the same degree. There are some factors that influence how tight it can be. These include the material in which the bolt is made of, as well as the physical size of the bolt.
Another factor that will influence the degree of preload you should subject the bolt to is the application. For instance, if you want to keep two surfaces in contact with each other as tight as possible, you would need high degrees of preload to do this. If the joint is going to be subjected to huge forces (such as use in great depths under water), then the preload has to be even higher. In such cases, you would need to get bolt types that are designed to withstand these degrees of preload without breaking.
How do you ensure that the bolts have the right amount of preload?
To ensure that a bolt is tightened correctly, you will first need to find out what its limits are. This can be found by consulting the manufacturer. You will then need to use a torque wrench to put the bolts in place. This is particularly important if you want the bolt to be as tight as it can bear, without exceeding its limits. Doing it without taking note of the actual torque readings can lead you to overdoing it.
What are the risks of not using the right preload?
The commonest problem you will face if you use a bolt without preloading it properly include loosening. The threads can also become abraded particularly if the bolt is subjected to a lot of vibration, such as when fastening a moving machine.

About the Author

Larry Melone
By Larry Melone
President

Started my career in the fastener world in 1969 at, Parker Kalon Corp. a NJ based screw manufacturer located in Clifton, NJ working in inventory control, scheduling secondary production and concluding there in purchasing. In 1971 I accepted a sales position at Star Stainless Screw Co., Totowa, NJ working in inside sales and later as an outside salesman, having a successful career at Star I had the desire with a friend to start our own fastener distribution company in 1980 named: Divspec, Kenilworth, NJ. This was a successful adventure but ended in 1985 with me starting Melfast in August 1985 and have stayed competitive and successful to date. Melfast serves the OEM market with approximately 400 accounts nationally.

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