Bolts are one of the most common forms of threaded fasteners. They are used to fix materials together, usually along with a Nut, to form a secure bolted joint.
They are excellent for a variety of applications across several industries, including construction, automotive, marine and aerospace. This is down to bolts being extremely versatile and easily installed, removed or adjusted.
As a non permanent fastening, Bolts are also susceptible to loss of preload and self loosening, particularly when subjected to harsh vibrations. In this article, we take a look at some of the main reasons why bolts and other threaded fasteners become loose and what you can do to prevent it.
What Causes Bolts To Loosen?
Bolted joints are vital for the safe operation of many different types of equipment in a wide variety of applications, ranging from car engines right the way through to chemical reactors.
It is important that loose bolts are addressed. If a bolt is not re-tightened the joint might fail which could lead to a leak, equipment becoming damage or even an accident.
After assembly, fasteners can loosen for a variety of reasons. These range from human error to environmental conditions. When fasteners are exposed to vibration, shock, or thermal expansion, loosening frequently occurs. Some of the most common causes are as follows:
Vibrations
When fasteners are subjected to continuous vibrations they can gradually loosen due to minor movements and load changes which cause the nut or bolt to unwind.
Thermal Expansion
Metal bolts can expand when subjected to heat and contract when they are cool. Fast changes in temperature due to environmental changes or from industrial processes can cause metal fasteners to loosen.
Under-Tightening
For the bolt to work, it must be suitably tightened. This is so that the preload applied can act as a clamping force by passing through the fastener. If the bolt’s preload is insufficient, the absence of clamping force will cause the fastener to rotate and become free.
When used in tension applications, a loose bolt can cause one of the attached surfaces to move, putting shear stress on the bolt and possibly leading to its failure.
Over-Tightening
During installation, it’s crucial to follow the torque recommendations because overtightening nuts and bolts might damage the threads, which will impair the fastener’s function.
Damaged Fasteners
The performance of a fastener will be compromised if it has been damaged. This can be the result of a manufacture defect, an installation error, or the reuse of old fasteners. Any damage could result in an incorrect torque reading, making the fastener looser or tighter than required, which would result in the issues listed above.
How To Stop Bolts From Loosening?
If your nuts and bolts are coming loose, it can be a real headache. Fortunately, there are several methods you can use to keep your fasteners in place. These include the following:
Use Locking Nuts
Locking nuts are designed to prevent bolts from self loosening. Two of the most common types of vibration resistant locking nuts, which are inexpensive, are made from nylon and metal.
Use Washers
Washers have a wide surface area, which can help to increase the friction that holds a bolt to the mating thread adding extra ‘clamp force’. There are several types of washers, like conical, cup-shaped, wedge-lock that can all provide extra friction and help prevent bolt loosening.
Adhesives
Bolts have been successfully secured in some applications using liquid adhesives, hot thermoplastic coatings, or solid adhesive patches. The issue is that they make it more difficult to later disassemble the joint.
Double Nuts
Using two nuts, a thick one and a thinner one (often referred to as a jammer nut), is a common method used to help prevent bolts from self loosening.
Maintenance
Regular maintenance and checks of equipment is the best way to ensure that bolts do not loosen to a point that they fail. Whenever you notice a loose bolt, tighten it, replace it with a new fastener or implement one of the methods mentioned above so it does not become loose again.
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So there you have it, some of the most common causes of self loosening bolts and how you can prevent it from occurring. If you need high-quality, reliable bolts for your next project, be sure to source them from Leyton Fasteners.
No matter your requirements, we can provide you with the right fastener for your needs. With a comprehensive range of nuts, bolts, fasteners and fixings we’re confident that we have the right products for your application.
To find out more about our range of fasteners or to get a quote for an order, don’t hesitate to get in touch with our team today on 0151 355 8045. Alternatively, you can place an order for your fasteners using our new online shop.
