Thread-locking fluid or threadlocker is a single-component adhesive, applied to the threads of fasteners such as screws and bolts to prevent loosening, leakage, and

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

. Most thread-locking formulas are methacrylate-based and rely on the

electrochemical Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference and identifiable chemical change. These reactions involve electrons moving via an electronically conducting phase (typi ...

activity of a metal substrate to cause

polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...

of the fluid. Thread-locking fluid is thixotropic, which allows it to flow well over time, yet still resist shocks and vibrations. It can be permanent or removable; in the latter case, it may be removable merely by force or may also require heating, for example. Typically, brands are color-coded to indicate strength and whether they can be removed easily or require heat for removal.

History

Thread-locking fluid 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 fluids are methacrylate-based, and

cure A cure is a substance or procedure that resolves a medical condition. This may include a medication, a surgery, surgical operation, a lifestyle change, or even a philosophical shift that alleviates a person's suffering or achieves a state of heali ...

anaerobically. Thread-locking fluid is often a thixotropic fluid: under

shear stress Shear stress (often denoted by , Greek alphabet, Greek: tau) is the component of stress (physics), stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross secti ...

, it exhibits a time-dependent decrease in

viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

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 . Threadlocker is also sold in sticks and in tape form, similar to teflon tape.

Application and care

Thread-locking fluid may be applied before or after assembly, depending on the type. Threadlockers are available in varieties of "permanent", "removable", and "low-strength" formulas. Many brands color-code the container and the fluid 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 threadlockers are rated at in shear strength. The applied torque required to loosen a permanently threadlocked fastener may exceed the

yield strength In materials science and engineering, the yield point is the point on a stress–strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and w ...

of the fastener itself, such that attempting disassembly by force may twist off the stem of the fastener. However, high-strength permanent threadlockers become potentially removable by heating the assembly, typically to . Working temperatures for threadlocked fasteners are typically limited to , which is below the softening point of the methacrylate polymer. Above this temperature, the material softens and strength reduces. Because thread locking adhesives 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. Lock washers, locknuts, jam nuts, and safety wire may be used in conjunction with thread-locking fluid to prevent loosening of bolted joints. Because electrochemical activity is one of the two triggers that cause

of the threadlocker fluid, care must be taken to avoid contaminating the entire threadlocker container with threadlocker that has had contact with metal, or the material in the container may polymerize.

References

External links

* {{ cite web , last = Allen , first = Mike , title = How to Secure Bolts Using Threadlocker: Auto Clinic , work = Popular Mechanics , date = September 2009 , url = http://www.popularmechanics.com/cars/how-to/a1172/4208687/ Adhesives Acrylate polymers Non-Newtonian fluids Screws