Anaerobic Threadlocking Adhesives

Threaded fasteners set and hold tolerances on assemblies ranging from light duty equipment to heavy machinery. In many cases fasteners that self-loosen during equipment operation may contribute to wear and fatigue, and result in poor operating tolerances, misalignment, and sometimes catastrophic equipment failures that cost millions of dollars in unscheduled downtime each year. Various types of differential stresses such as vibration and shock, thermal expansion and contraction, and micro-movement reduce clamping force on the assembly and ultimately cause machine failure. Case after case, anaerobic threadlocking adhesive technology has proven to be more reliable and cost efficient to prevent the loosening of threaded fasteners and leakage in a variety of applications versus mechanical fasteners such as spring washers, wire retainers and nylock nuts.

Liquid threadlockers have become one of the most reliable and inexpensive ways to ensure that a threaded assembly will remain locked and leak proof for its entire service life. Applied drop-wise to fastener threads, liquid anaerobic adhesives fill the grooves of the threads and cure to a hard thermo-set plastic when exposed to active metal ions in the absence of air. Anaerobic adhesives lock the threaded parts together, ensuring that mating parts will ultimately act as one conjoined part that resists failure and delivers the greatest possible reliability.

Mechanical devices such as spring washers, wire retainers and nylock nuts are costly and are ineffective in preventing loosening of threaded fasteners caused by side sliding motion. They also do not seal or prevent corrosion within the fastener assembly and must be sized appropriately for the specific fastener, resulting in large and costly parts inventories.

Most assemblies held together by threaded fasteners will at some time be dismantled for repairs, maintenance or adjustment. For this purpose, industrial anaerobic adhesives are available in differing grades: low strength threadlockers for easy removal, medium strength threadlockers that can be removed using common hand tools and high strength or “permanent” threadlockers suitable for very demanding assemblies with minimal service requirements. Even the high strength threadlockers can be removed with standard hand tools following direct exposure to 232 – 260°C (450-500°F) high temperatures for about five minutes.

Using Anaerobic Adhesives Reduce Cost and Increase Reliability for Industries

Several case studies from various industries manufacturing and maintenance applications show that anaerobic threadlocking adhesives increase the reliability of threaded fasteners and reduce the cost associated with downtime and unscheduled callbacks.

In one case study with hydropulpers – machines designed to agitate a mixture of paper pulp and water to prevent dewatering until this mix can be used in the papermaking process extreme vibration incurred by the machine resulted in problems with keeping the mounting bolts for the gearbox tight. Even with proper torquing procedures, the bolts needed to be retightened every two weeks – requiring additional labor costs and downtime. Unplanned loosening caused misalignment problems and equipment failure resulting in severe productivity loss and maintenance costs. Once anaerobic thread locking adhesives were introduced to all the mounting studs and nuts during a recent downtime, loose bolts were no longer causing problems and held the hydropulper gearbox tight until the next scheduled annual preventive maintenance.

In another case, a pump manufacturer had problems with gland studs and adjustment nuts that either broke during assembly or loosened during adjustment. Gland studs were made to Class 5 interference fit tolerance of 0.0254 – 0.213mm (0.001″ to 0.0084″) To achieve this, special oversized studs with 0.0762mm (0.003″) tolerance pitch diameter were used with a Class 2 tapped hole. Stud drivers were used with a capability of driving M12 (½”) studs up to 111.6 kg/m (75 lbs/ft) and M20 (¾”) studs up to 282.7 kg/m (190 lbs/ft). Any deviation from tolerance resulted either in broken studs during assembly or loosened studs during gland adjustment with the retaining nut. If studs loosened, the whole pump needed to be disassembled for repair. The heavy interference fits caused high flange stresses which warped the end plates and gland box causing power loss, excess wear, and shortened pump life. The manufacture utilized threadlocking adhesives to solve this problem.

When threadlockers were applied during assembly to Standard Class 2 studs up to and including M12 (½”), over M12 and stud nuts, cost savings were immediately achieved because the manufacture of studs now requires only standard tolerance and standard gauges, while assembly is easily done by hand. The locking ability of the threadlockers exceeds the interference fit strength by about 20% and adjustments of the gland nuts are easy and precise because the studs are never loose. Finally, all housings are now stress and warp free.

A traffic infrastructure tunneling solutions manufacturer, uses threadlocking adhesives to lock all the screws, hydraulic motors, hoses and fittings in their tunnel boring machines, which have to withstand enormous pressure while eating its way through rocks underground. In this case, threaded fittings have to resist up to 350 bar oil pressure. “An insane piece of engineering” is how the Discovery Channel describes the machine that drilled a 5.4 and a 3.9-kilometer tunnel in Kuala Lumpur in 2006. The 82-meter tunnel boring machine is as tall as a high rise building with 20 floors lying on its side. Imagine this machine moving through the ground, encountering a variety of soil types and loading conditions, hard rock or loose rock, working under tremendous pressures, high stresses, torques, rotating and twisting forces. Threadlocking adhesives are able to resist the extremely high oil pressure and provide reliable locking, sealing and long-term vibration resistance.

Liquid threadlockers were also applied at a hydraulic lift manufacturer for forestry, mining and construction use. M16 structural bolts on the base turn table of the lift, which holds the boom & bucket loosened when subjected to severe vibrations, impacts & shear loads. Previously nyloc nuts were used to prevent vibrational loosening of these bolts but they failed to retain clamp load over long periods. Bolts also had to be retorqued frequently. After threadlockers were used, the bolts retained clamp load under severe conditions without any loosening while protecting threads from rust and corrosion. Re-torquing of bolts was no longer needed and safety and equipment reliability were improved.

New Innovations in Anaerobic Threadlocking Technology

New technological advances in anaerobic threadlocking adhesives have also provided many advantages previously unavailable including surface insensitive, high temperature, and chemically resistant materials, as well as formulations engineered to withstand extreme vibrations. Semi-solid threadlocking formulations in a stick format that complement their liquid counterparts have also been developed to work well in overhead or hard to reach applications where liquids might be too messy or potential migration might be a concern.

Since its invention in 1953, liquid anaerobic threadlocking adhesives and thread sealants have become the most reliable and cost efficient methods for sealing and securing threaded fasteners and pipefittings in a variety of assemblies in many different industries. Many case studies have demonstrated that these innovative anaerobic adhesives and sealants are better able to withstand various types of differential stresses such as vibration and shock, wide range of temperatures and micro-movements that reduce clamping forces than traditional mechanical threadlockers to reduce downtime, unscheduled maintenance and costs.