In both commercial and industrial operations it is critical to ensure nuts and bolts remain tightened. A slip can range from a minor inconvenience to an operational failure that could threaten machinery and life together. This is why selecting the proper lock nut is a vital process to ensure the job does not risk failure in the future. There are dozens of varieties of lock nut to use depending on your unique scenario, it is important to find the lock nut to match your needs. In determining the correct lock nut it is also important to understand how lock nuts are tested and what standards are most relevant.
One of the most common types of lock nut is the Nyloc nut. This nut operates with a piece of nylon at the end of the threading to prevent the nut from unscrewing. While many claim these nuts can be reused it is not guaranteed they will operate as well after multiple uses. A critical drawback of Nyloc nuts is their inability to function over 250 degrees Fahrenheit. Another downside is that the Nyloc nut is often used as a one way nut, which means even if the Nyloc nut can be reused it is generally not intended to be removed.
For situations where a lower profile setup is optimal, a wedge lock washer may be the solution. A commonly known type would be the Nord-Lock wedge lock washer. This setup includes two washers that are positioned in front of the bolt. These washers have teeth between them that prevent them from loosening, along with ridges on the outsides of the washers to hold them in place with the bolt. Instead of using friction the wedge lock uses tension created between the two washers to keep the bolt held tight. In a setup where aesthetics or profile are important the wedge lock is optimal. The downsides of the washer lock are in the higher cost and the requirement that bolts be tightened to the point of engraving the bottom of the nut in the washer. This may be prohibitive to certain uses where lower tension is desired.
Slip-On Lock Nut
In some scenarios it is optimal to be able to insert a locking device after tightening the nut. For these situations the Slip-On lock nut would be optimal. The Slip-On lock nut is able to be easily positioned anywhere on the bolt at any time, it is best used for situations where disassembly of the bolt mechanism would be costly or time-consuming. While the Slip-On lock nut is very effective it may not be appropriate for all scenarios, such as set-ups with very short bolts. The bulky size of the Slip-On lock nut may not be appropriate for low profile scenarios.
Flex Lock nut
The Flex Lock nut is another all metal lock nut that operate through friction between the lock nut and the bolt to maintain the nut in its position. While these nuts are sturdy, it is important to note that there will be friction in attaching the bolt, as this is the same friction used to hold the bolt in place. Much like the Nyloc bolt, the Flex Lock nut is another one way nut and is generally not intended to be removed on the regular.
A new arrival to the lock nut market is the Coilock. The Coilock is a strong coil based lock nut that is robust and able to resist massive amounts of vibration using its coil based design. The Coilock brings intense holding power at an economical price point that exceeds. The Coilock is able to be reversed and easily removed depending on the job. A vigorously tested design, the Coilock is able to to withstand severe vibrations and exceeds even the highest standards.
In determining the correct lock nut for your need it is critical that you research the testing data for your candidates. Depending on your intended use different tests may carry more weight, but all give an accurate picture of the versatility of the lock nut.
The Junker Test
The Junker Test, originally known as DIN 65151, is the most severe test for bolted joints. It is a popular test used to determine the resistance of the lock nut to vibrations. These tests are conducted on Junker Test rig and put through a number of different vibration frequencies to determine strength. Regardless of your need, it is always critical that lock nuts hold under vibration and the Junker Test is optimal. The test will output a result that shows how much of the clamp load remains based on the time under vibration. Without a lock nut the nut will become loose in a second. Many good lock nuts will prevent the nut from becoming loose for up to about 10 seconds. The top of the line lock nuts will prevent the nut from becoming loose indefinitely. For example, when the Coilock was tested it lost very little clamp load and maintained performance beyond the duration of the test.
Another incredibly critical set of tests are those of the United States Military, known as NAS 3350, NAS 3354, and NASM 1312-7. These are a set of standards that test the ability of lock nuts to withstand severe vibration and maintain their hold, critical elements to the US Military. While the testing data is not readily available for most lock nuts, the Coilock met and exceeded the standards of all three tests. This demonstrates the ability of the Coilock to maintain powerful holding ability under stress without excessive loosening.
While your specific lock nut needs may vary, it is always critical that the proper lock nut is used for the stress the bolt will be subject to. Make sure you seriously research your options and use the bolt best for the job.