Thread-locking fluid
Encyclopedia
Thread-locking fluid is a thin
, single-component adhesive
, applied to the threads
of fastener
s such as screws and bolts to prevent loosening, leakage, and corrosion
. Typically, thread-locking fluids are methacrylate
-based, and cure anaerobically. Thread-locking fluid is a thixotropic
fluid, meaning that under shear stress, it exhibits a time-dependent decrease in viscosity. This allows it to flow well over time, yet still resist short-duration shearing, as in vibration or shock
.
Thread-locking fluid may be applied either before or after assembly, depending on the type. Threadlockers are available in "permanent" and "removable" formulas, with heavy-duty permanent threadlockers rated to withstand as much as 3000 psi (20.7 MPa) in shear
. Some threadlockers are removable with the application of heat. Because thread locking adhesives typically rely on the electrochemical activity of a metal substrate in order to form a bond, substrates often require thorough cleaning, and, in the case of less electrochemically active metals such as aluminum, priming.
Because electrochemical activity is one of the two triggers that cause polymerization
of the threadlocker fluid, care must be taken to avoid contaminating the entire container of threadlocker with threadlocker that has had contact with metal, otherwise the material in the container may polymerize.
Thread-locking fluid is typically sold in small containers, in amounts from 5 millilitres (about one teaspoon) to 250 mL, and are often color-coded to indicate their strength. Threadlocker is also sold in stick
s, and in tape form, similar to Teflon tape.
Lock washer
s, locknut
s, and safety wire
s may be used in conjunction with thread-locking fluid to prevent loosening bolts.
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
, single-component adhesive
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...
, applied to the threads
Screw thread
A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...
of fastener
Fastener
A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...
s such as screws and bolts to prevent loosening, leakage, and corrosion
Corrosion
Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
. Typically, thread-locking fluids are methacrylate
Methacrylate
Methacrylates are the salts or esters of methacrylic acid.Methacrylates contain methyl-vinyl groups, that is, two carbon atoms double bonded to each other, directly attached to the carbonyl carbon, and wherein the vinyl group is substituted with a non-terminal methyl group.Methacrylates are common...
-based, and cure anaerobically. Thread-locking fluid is a thixotropic
Thixotropy
Thixotropy is the property of certain gels or fluids that are thick under normal conditions, but flow over time when shaken, agitated, or otherwise stressed...
fluid, meaning that under shear stress, it exhibits a time-dependent decrease in viscosity. This allows it to flow well over time, yet still resist short-duration shearing, as in vibration or shock
Shock (mechanics)
A mechanical or physical shock is a sudden acceleration or deceleration caused, for example, by impact, drop, kick, earthquake, or explosion. Shock is a transient physical excitation....
.
Thread-locking fluid may be applied either before or after assembly, depending on the type. Threadlockers are available in "permanent" and "removable" formulas, with heavy-duty permanent threadlockers rated to withstand as much as 3000 psi (20.7 MPa) in shear
Shear stress
A shear stress, denoted \tau\, , is defined as the component of stress coplanar with a material cross section. Shear stress arises from the force vector component parallel to the cross section...
. Some threadlockers are removable with the application of heat. Because thread locking adhesives typically rely on the electrochemical activity of a metal substrate in order to form a bond, substrates often require thorough cleaning, and, in the case of less electrochemically active metals such as aluminum, priming.
Because electrochemical activity is one of the two triggers that cause polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
of the threadlocker fluid, care must be taken to avoid contaminating the entire container of threadlocker with threadlocker that has had contact with metal, otherwise the material in the container may polymerize.
Thread-locking fluid is typically sold in small containers, in amounts from 5 millilitres (about one teaspoon) to 250 mL, and are often color-coded to indicate their strength. Threadlocker is also sold in stick
Glue stick
Glue sticks are solid adhesives in twist or push-up tubes. The user can apply glue by holding the open tube, thus keeping their fingers clean...
s, and in tape form, similar to Teflon tape.
Lock washer
Washer (hardware)
A washer is a thin plate with a hole that is normally used to distribute the load of a threaded fastener, such as a screw or nut. Other uses are as a spacer, spring , wear pad, preload indicating device, locking device, and to reduce vibration...
s, locknut
Locknut
A locknut, also known as a lock nut, locking nut, prevailing torque nut, stiff nut or elastic stop nut, is a nut that resists loosening under vibrations and torque. Elastic stop nuts and prevailing torque nuts are of the particular type where some portion of the nut deforms elastically to provide a...
s, and safety wire
Safety wire
Safety wire or lockwire is common in the aircraft and racing industries as an extra precaution to keep vital fasteners from unintentionally loosening and parts from falling off due to vibration or other forces. The use of safety wire is a type of positive locking device. It also allows rapid and...
s may be used in conjunction with thread-locking fluid to prevent loosening bolts.
| Type | Typical color-code | Torque to break free | Torque to continue turning | Temperature range |
|---|---|---|---|---|
| Low strength | purple | 62 in-lb (7 N-m) | 27 in-lb (3 N-m) | −54 to 149 °C |
| Medium strength | blue | 115 in-lb (12 N-m) | 53 in-lb (6 N-m) | −54 to 149 °C |
| Medium strength surface insensitive | blue | 180 in-lb (20 N-m) | 62 in-lb (7 N-m) | −54 to 149 °C |
| High strength | red | 230 in-lb (25 N-m) | 225 in-lb (25 N-m) | −54 to 149 °C |
| High temperature | red | 180 in-lb (20 N-m) | 270 in-lb (30 N-m) | −54 to 232 °C |
| Penetrating | green | 90 in-lb (10 N-m) | 310 in-lb (35 N-m) | −54 to 149 °C |