Thread sealants are single component adhesives applied to fastener threads. Thread lockers are applied to the threads of screws, bolts, and other fasteners to prevent loosening, leakage, and corrosion. Fastener failure tends to occur for one of two reasons:
· Tension relaxation caused by expansion and contraction due to temperature changes
· Self-loosening caused by lateral motion between fastener contact surfaces
Thread lockers are designed to fill every tiny space in a fastener thread as they cure, achieving 100 percent contact between parts as opposed to the 15-25% contact of metal-on-metal fasteners.
Thread lockers are a type of thixotropic fluid, meaning that the compound remains thick and viscous until it is shaken or otherwise disturbed. Therefore, after an adhesive is shaken and applied to a screw thread, it cures enough to withstand brief periods stress caused by vibration or shock.
Typical thread lockers cure anaerobically and are sold as small containers of fluid, but some manufacturers produce the adhesives as sticks or tapes. Adhesives that use anaerobic curing harden and toughen when isolated from oxygen; this is ideal in thread lockers, since oxygen isolation typically occurs when the compound is sealed between a threaded screw and bolt. Thread locking adhesives are manufactured with a variety of strength and toughness characteristics ranging from easily reversible to semi-permanent when cured, but no thread locking compound is truly permanent, and fasteners secured with even the strongest adhesive can be removed using high heat (> 450° F) and tools.