Thread-locking fluid or threadlocker is a single-component

adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...

, applied to the threads of

fastener A fastener (US English) or fastening (UK English) is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or disman ...

s 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 Methacrylates are derivatives of methacrylic acid. * Methyl methacrylate * Ethyl methacrylate * Butyl methacrylate * Hydroxyethyl methacrylate * Glycidyl methacrylate Glycidyl methacrylate (GMA) is an ester of methacrylic acid and glycidol. Co ...

-based and rely on the electrochemical activity of a metal substrate to cause

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

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 can be removed with heat, for example. Typically, brands are color-coded to indicate strength and whether they can be removed easily or if they 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 Loctite is an American brand of adhesives, sealants, surface treatments, and other industrial chemicals that include acrylic, anaerobic, cyanoacrylate, epoxy, hot melt, silicone, urethane, and UV/light curing technologies. Loctite products ar ...

brand. An early version of the compound was patented in 1960.

Properties

Typically, thread-locking fluids are

-based, and

cure A cure is a substance or procedure that ends a medical condition, such as a medication, a surgical operation, a change in lifestyle or even a philosophical mindset that helps end a person's sufferings; or the state of being healed, or cured. The ...

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

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

, it exhibits a time-dependent decrease in

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inte ...

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

stick Stick or the stick may refer to: Thin elongated objects * Twig * The weapon used in stick fighting * Walking stick, a device to facilitate balancing while walking * Shepherd's crook * Swagger stick * Digging stick * Swizzle stick, used to stir d ...

s 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 Shear may refer to: Textile production *Animal shearing, the collection of wool from various species **Sheep shearing *The removal of nap during wool cloth production Science and technology Engineering *Shear strength (soil), the shear strength ...

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 wi ...

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 230°C (450°F). Working temperatures for threadlocked fasteners are typically limited to 150°C (300°F), 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 washer A washer is a thin plate (typically disk-shaped, but sometimes square) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener, such as a bolt or nut. Other uses are as a spacer, spring (Bellevil ...

locknut A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut,. stiff nut or elastic stop nut, is a nut that resists loosening under vibrations and torque. Prevailing torque nuts have some portion of the nut that def ...

jam nut A jam nut is a low profile type of nut, typically half as tall as a standard nut. It is commonly used as a type of locknut, where it is "jammed" up against a standard nut to lock the two in place. It is also used in situations where a standard nut ...

s, and

safety wire Safety wire or locking-wire is a type of '' positive locking device'' that prevents fasteners from falling out due to vibration and other forces. The presence of safety wiring may also serve to indicate that the fasteners have been properly tigh ...

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/
Current Loctite Threadlockers

Adhesives Acrylate polymers Non-Newtonian fluids Screws