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Why Your Fastener is Loose and How to Fix It

Do you have a fastened joint that keeps coming loose? Before proposing a solution, we first need to understand why it’s coming loose.

Reasons for a Fastened Joint Being Loose

  1. Is there visible damage to the surfaces under the head of the bolt or nut? If so, you may have an embedment issue where the surface of the clamped material is not hard enough to support the load of the joint. The best way to address this is to increase the surface area of the fastener by using hardened washers or flanged hardware.
  2. If embedment is not your issue, but you have loose hardware, then rotational loosening is occurring. Some things to check for:
  • What is the clamping length of your joint? 5 times the diameter of the bolt is recommended to ensure proper bolt stretch.
  • Is the proper clamp load being applied? See your hardware supplier to help with bolted joint calculations or a joint study to determine the proper torque to achieve your desired clamp load.

Fixing the Loose Fastened Joint

 Sometimes it is not possible to employ the 5 times the diameter rule, and we still have loosening. Several strategies may be used to help combat this issue.

  1. Thread locking
    • Thread forming screws
    • Pre-applied locking adhesive
    • Liquid thread lockers applied during assembly
    • Lock nuts
  2. Locking at the bearing surface
    • Serrated hardware – make sure to use serrated nuts AND bolts
    • Locking washers
      • Rip-Lock™ – good for up to and including 8.8 property class
      • Ribbed lock washers – good for 10.9
      • Nord-Lock® – good for up to and including 12.9 property class

For more information on keeping joints tight, check out www.bossard.com or contact our engineering department at ProvenProductivity@bossard.com.

Doug Jones
Applications Engineer
Email: djones@bossard.com

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May 04, 2018

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