Bolts & nuts joints are the most economical, serviceable and easiest to install of all fastening systems. Vibration, shock, temperature variations, chemical surrounding and other factors which occur during the life of the joint, case loss of clamping load, which occur during the life of the joint, cause results in the fastened joint failure, owing to fatigue. Fastener fatigue is best avoided by not allowing the fastener to become loose.
Thread locking methods, both mechanical & chemical have been developed as a mean of locking the fastener in place and resist loosening. Some methods are aimed at the male fastener (bolts) whilst others are targeted at the female fastener (nuts).
The four main methods used for achieving locking achieving locking of fasteners are:
(all the products are effective in achieving the desired of fastener locking result to a lesser or greater extent and the choice is dependent on factors such as application, cost, reusability, installation technique etc.)
With various inbuilt design features, fall within the mechanical category and are the most common type of mechanical thread locking products available in the market today.
Serrated flange-type: The increased bearing surface are of the serrated flange resists loosening.
Hex lock nuts with attached lock washer : have a spring, split, toothed, serrated, conical, serrated flange or similar type of washer attached directly onto the nut which provides increased breakaway torque and decreases the likelihood of the nut loosening.
Jam Nuts: the jam nut is a thin nut (about 2/3rd standard nut thickness) which is used under a full nut to develop locking action. This assembly is designed to avoid compression of the part being fastened and at the same time lock it in place and allow it to rotate freely. Jam nuts are sometimes used for leveling purposes as well. When a jam nut is to be used, it should always be placed as shown:
The use of a thin jam nut is based on the fact that a thin nut exerts less overall force than a fully torqued thicker nut. The jam nut should always be assembled in the bolt first and pulled up snug (or as required) but not tightened up, so as to put high tension on the bolt. The standard nut is then assembled over the jam nut, and is tightened to a snug fit against the jam nut.
The jam nut should be now be held firm against rotation, whilst the thicker standard nut is tightened to full tension. This causes the threads under the standard nut to be deformed upwards whilst the thread under the thin jam nut are deformed downwards. Thus, the two nuts are bearing in opposite directions on the threads and are jammed against each other (hence the name jam nut), with the full standard nut exerting a greater force on the thin jam nut and holding it in place, locked-in against the assembly face.
Rely on the bonding of mating threads through the use of a chemical adhesive. Nuts/bolts are manufactured with dry-to-touch adhesive coating pre-applied via a micro-encapsulation process or two parts mix. When the locknut or bolt is assembled and rotated around the mating parts of the fastener, the micro capsules rupture, releasing the anaerobic chemicals or two part mix, in and around the thread flanks, which then cures and forms the locking bond. This method of chemical locking is very economical and is used for both male and female fasteners.
On the other hand are liquid , gel or semi-solid anaerobic adhesives that are applied to the fastener joint either before or after the joint has been torqued. The anaerobic fluid flows to the gaps in the mating threads and as the name implies, cures in the absence of air. Anaerobic lockers come in a variety of strengths and viscosities depending on the application and whether a permanent or semi-permanent joint is required. The correct choice of viscosity of the anaerobic threadlocker is important in joints that have been torqued to enable the fluid to flow into the thread cavities.
Incorporate a pair of washers that have cam faces on one side with the cam angle greater than the thread pitch. In addition, there are radial teeth on the opposite sides. The pre-assembled washers are installed in pairs, cam face to cam face. When the bolt and /or nut is tightened, the teeth of the washers, grip and lock the mating surfaces, allowing movement only across the cam faces. Any rotation of the bolt/nut is restricted by the wedge effect of the cams.