Thread-locking compound

Thread-locking compound was developed by American professor Vernon K. Krieble in 1953. His company, American Sealants, founded the Loctite brand. An early version of the compound was patented in 1960. == Properties ==

Typically, thread-locking compounds are methacrylate-based, and cure anaerobically when exposed to clean metals. Thread-locking compound is often a thixotropic fluid: under shear stress, it exhibits a time-dependent decrease in viscosity to allow it to be squeezed into place but not flow too quickly on its own. Thread-locking fluid is typically sold in small containers, in amounts from 5 millilitres (about one teaspoon) to . Thread-locking compound is also sold as paste in sticks and in tape form, similar to teflon tape. == Application and care ==

Thread-locking compound may be applied before or after assembly, depending on the type. Thread-locking compounds are available in varieties of "permanent", "removable", and "low-strength" formulas. Many brands color-code the container and the compound itself to indicate the degree of permanency. The low-strength types prevent loosening under vibration, but may still be readily disassembled. Removable types resist higher amounts of vibration, but may still be disassembled with hand or power tools. The strongest permanent thread-locking compounds are rated at in shear strength. The applied torque required to loosen a fastener with permanent compound may exceed the yield strength of the fastener itself, such that attempting disassembly by force may twist off the stem of the fastener. However, high-strength permanent thread-locking compounds become potentially removable by heating the assembly, typically to . Working temperatures for fasteners with thread-locking compound are typically limited to , which is below the softening point of the methacrylate polymer. Above this temperature, the material softens and strength reduces. Lock washers, locknuts, jam nuts, and safety wire may be used in conjunction with thread-locking compound to prevent loosening of bolted joints. Surface interaction and curing Thread-locking compounds typically rely on the electrochemical activity of a metal substrate to form a bond; surfaces must be clean to develop the full bonding strength. In the case of less electrochemically active metals such as the normally oxidised surface of aluminium, an additional step of priming is required for full strength results. Surface-insensitive thread-locking compounds do not require activation by metal ions, and can be used with non-reactive, oxidized or soiled surfaces. Because electrochemical activity is one of the two triggers that cause polymerization of the thread-locking compound, care must be taken to avoid contaminating the container with any thread-locking compound that has had contact with metal, or the material in the container may polymerize. == References ==