Thread-locking fluid or threadlocker is a single-component adhesive, 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 engi ...

. 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, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outc ...

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 Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick or viscous under static conditions will flow (become thinner, less viscous) over time when shaken, agitated, shear-stressed, or otherwise stressed ( ...

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

Properties

Typically, thread-locking fluids are methacrylate-based, and cure anaerobically. Thread-locking fluid is often a

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 ...

, 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 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 ...

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 Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...

surface of aluminium, an additional step of priming is required for full strength results. Lock washers, locknuts,

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 may be used in conjunction with thread-locking fluid to prevent loosening of

bolted joint A bolted joint is one of the most common elements in construction and machine design. It consists of a male threaded fastener (e. g., a bolt) that captures and joins other parts, secured with a matching female screw thread. There are two main ...

s. 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