How to Eliminate Threaded Fastener Failure in Industrial Equipment
Loosening of fasteners is one of the major causes of industrial equipment failure, resulting in millions of dollars of unscheduled downtime costs each year.
In many cases, fasteners that self-loosen during equipment operation may contribute to wear and fatigue, and result in poor operating tolerances and misalignment. Various types of differential stresses such as vibration and shock, thermal expansion and contraction, and micro-movement reduce clamping force on threaded assemblies and ultimately cause machine failure. So, how do you avoid it?
Maintaining Clamp Load to Prevent Loosening
Two very different maintenance strategies can counteract self-loosening – mechanical locking methods and chemical threadlocking systems, also called machinery adhesives. But one method is much less costly and more reliable than the other.
Mechanical locking devices include spring, star and tab washers; nuts with nylon inserts; castellated and lock nuts; tooth flanged bolts; and ramp washers. Some devices are more effective than others at resisting loosening, but no common mechanical locking device is also capable of sealing threads. These devices always leave assemblies vulnerable to rust and corrosion.
On top of that, mechanical fasteners with locking devices cannot reliably prevent self-loosening caused by side-sliding motion and must be sized appropriately for the specific fastener, resulting in large and costly parts inventories.
Threadlocking (or machinery adhesives) 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. These single-component anaerobic adhesives are applied to the threads of a bolt as a liquid, gel or stick. The adhesive fills the grooves of the threads and cures to a hard thermoset plastic when exposed to active metal ions in the absence of air. Machinery adhesives lock the threaded parts together, ensuring that mating parts will ultimately act as one conjoined unit that resists failure and delivers the greatest possible reliability.
The approximate metal-to-metal contact within a bolted system without threadlocking adhesives is just 15 percent. Threadlockers fill voids 100 percent to lock the threads and maintain consistent clamp load over time. Prior to cure, these adhesives also lubricate the assembly to reduce both friction and torque load during fastener tightening. Post-cure, threadlockers seal the assembly to prevent corrosion and seizure, and ensure that disassembly is consistent and predictable.
The Threadlocking Myth
Contrary to common belief, threadlockers are not permanent and can be removed when required for disassembly. This is critical as most equipment at some point must be dismantled for repairs, maintenance or adjustment. Even the highest strength threadlockers can be removed with standard hand tools following direct exposure to 450-500°F temperatures for about five minutes.
Choosing the Right Threadlocker
The strength and viscosity of the threadlocker required for an application are directly related to the size of the fastener used:
Low strength threadlockers are used on screws up to ¼-inch in diameter, such as calibration screws, meters, gauges, and other fasteners that will need ongoing adjustment.
Medium strength materials work well on fasteners up to ¾ inch in diameter used in machine tools and presses, pumps, compressors, and as mounting bolts.
High strength threadlockers are best used on fasteners up to one inch in diameter found in permanent assembly applications such as heavy equipment and a variety of mounts.
Low viscosity penetrating threadlocking formulations are also available that easily wick into pre-assembled fasteners up to ½ inch in diameter.
Advances in Threadlocking Technology
The operating conditions of the end-use environment can also dictate the threadlocking formulation needed. The newest threadlocking technologies offer many advantages formerly unavailable, including surface insensitive, high temperature and chemically resistant formulations, as well as formulations engineered to withstand extreme vibration.
Threadlockers also come in more than just liquid formulations. Need to use a threadlocker in an overhead or hard-to-see application? Semi-solid threadlocking sticks work well in applications like this where liquids might be too messy or may potentially migrate out of the desired location.
Tape formulations are another option. They remain on the fastener without running or wiping off, and can be used for immediate assembly or carried in a toolbox and assembled days later. Regardless of the delay between application and assembly, tapes provide consistent strength and reliability.
Over to You
With more than 300 billion fasteners used in the US every year, it is critical that assemblies relying upon them never fail in service. The latest threadlocking adhesives defy the root causes of fastener failure and are the most reliable and cost effective products available, designed to ensure that threaded fasteners remain secure and sealed for their entire service life.
Do you have any questions related to your application? Leave us a comment, or reach out to us on Twitter (@Loctite_NA).