Written by Simla Ay | Technical Marketing Writer
Mechanical fasteners — such as split washers, double or nylon nuts, or toothed-flanged bolts — are often used to lock threaded assemblies into place. Although these components are typically effective, they can add weight to an application and are more challenging to apply on an industrial scale or at high-speed in an assembly line.
Sometimes mechanical locking mechanisms also require a special order or additional inventory spaces. Over time, they can rust and damage the appearance or functionality of an application. However, chemical threadlockers offer an alternative that prevents fasteners from loosening.
They are anaerobic adhesives formulated to seal and lock threaded fasteners into place after tightening.
Threadlockers are recommended for use anytime a threaded fastener will be exposed to vibration, repeated impacts, or when it’s imperative to maintain a product’s structure and function.
How they work
Threadlockers fill the gap between the threads of a nut and bolt. Typically, there’s a range of about 15% metal-to-metal contact between the two (and this is where friction occurs), but the remaining 85% of the threads are not in contact. Threadlockers work by filling this gap and increasing the area of friction between the mated surfaces.
Only a small amount — typically just a drop — of threadlocker is required for most applications. The threadlocker is applied near the end of the male threads and away from the bolt head.
As a bolt is screwed into a nut or retaining piece, the adhesive will coat the female threads. Once the fastener is fully tightened, the threads will bear down on one another, leaving a small amount of liquid threadlocker as oxygen is pushed out. This anaerobic environment, or the absence of free oxygen, triggers threadlocker curing and the threaded assemblies will lock into place.
Threadlockers are available in a variety of strengths, colors, and grades, and there are several important factors to consider when choosing this type of adhesive.
For example, the strength is generally denoted by color:
• Low-strength (purple): these low-strength bonds can be disassembled using hand tools. This is important when disassembly is routine.
• Medium-strength (blue): these medium- strength assemblies require power tools for disassembly. They’re used for critical joints that may only rarely need disassembly.
• High-strength (red): only used for permanent bonds. Disassembly is not easy and usually requires a combination of high heat and power tools.
Fastener size is another important consideration when choosing the ideal strength and viscosity of the adhesive required. For example, high-strength threadlockers are most often used on fasteners between three-quarters of an inch, up to one inch in diameter — and usually used with heavy equipment. Screws that are less than one-quarter-inch in diameter, such as calibration screws or gauges, are typically locked by low-strength formulations.
The application method is also important to consider when selecting a threadlocker. If applied during the assembly of a part, any grade can be used based on the requirements. However, for parts that are already assembled, consider a wicking grade.
A wicking threadlocker is a low-viscosity liquid for penetrating and locking pre-assembled parts. This type of threadlocker lets the parts remain complete and requires no disassembly or reassembly of the fasteners to work properly. Wicking can also be used to retrofit threadlockers into already-assembled fasteners, where disassembly is next-to-impossible. This means it’s a valuable option for overcoming certain challenges in the manufacturing process.
This adhesive moves between fastened threads using a capillary action, so it can flow through narrow spaces without any assistance.
Wicking is associated with the color green to differentiate it from the other threadlocker types. It is important to note that localized heating and hand tools are required for disassembly when wicking is selected.