The importance of threadlocker as an adhesive for fasteners
Different improvements have been made on fasteners through the years but they still fail. One of the reasons for failure is tension relaxation caused by temperature changes and involves the contraction and expansion of bolts and substrate materials. This tends to reduce bolt tension and clamping force in the assembly. Another reason for fastener failure is self loosening due to the lateral sliding motion between the fastener and contact surfaces. Different methods have been developed to prevent uncontrolled loosening of fasteners but they only added substantial cost to the assembly. A threadlocker is an adhesive that is inexpensive but can permanently prevent fastener failure. This anaerobic cure mechanism will flow and settle evenly on the grooves of the threaded fasteners without curing prematurely. Whatever excess threadlocker that overflows from the application will remain liquid and can be simply wiped off.
How to choose the right threadlocker
There are different factors that have to be taken into account when selecting the right threadlocker for the application. Sometimes, the bolts must be removed and reused for ongoing maintenance and repair and the threadlocker must have low strength for ease of disassembly using hand tools. Medium strength threadlocker is also designed to be removable with hand tools on the ¼” to ¾” fasteners. Contrary to popular belief, bolts that have been applied with the adhesive can be reused by simply removing the old adhesive and applying a new one prior to reassembly. High strength threadlocker is designed for highest holding abilities but they can also be removed using hand tools after direct exposure to temperature at 450oF.
Size of the fastener
The strength and viscosity of the adhesive should be related to the size of the fastener used. For example, low strength is ideal for screws that are ¼” in diameter like adjustment and calibration screws while the medium strength adhesive can be used for ¼” to ¾” fasteners that are used in machine tools and presses, pumps and compressors. The high strength adhesive is used on fasteners with 1-inch diameter like those found in permanent assembly applications for heavy equipment.
The operating conditions at the end user’s environment is also critical to the performance of the adhesive because if the fastener is made from two inactive metals like stainless steel, zinc, magnesium, black oxide, cadmium, anodized aluminum or passivated titanium, a primer is needed to facilitate the cure.
During the application of threadlocker, it is important to take note that the pre-applied adhesive can be applied beforehand on bolts that are waiting to be assembled while the pre-assembly adhesive is designed to be applied at the moment that parts will be assembled. Post assembly adhesive is applied on parts that have been assembled.