Thread lockers such as Loctite brand thread lockers are adhesive in nature. Their use of is beneficial for installation of threaded fasteners, especially where fatigue may occur or where it is impractical to torque a fastener in such a way that it will not loosen. An additional benefit is corrosion protection in a threaded joint because the threads would be sealed.
The thread lockers discussed here are anaerobic. Anaerobic thread lockers work on the principle of "active metal" presence and absence of oxygen. When these conditions are met together, the thread locker cures by chemical reaction. Anaerobic thread lockers do not dry. In fact, storage in the presence of oxygen maintains the thread locker in a liquid state. It is important to realize that anaerobic thread lockers and sealants will not cure in the presence of all metals. Most metals such as copper, aluminum and steel are not a problem. For metals that do not react, a primer must be used, such as copper spray, which is available as an aerosol.
Loctite brand (and others), thread lockers are available in a variety of types designed for specific uses. These uses go far beyond threaded fasteners and include products for gasket making, pipe thread sealing, bearing retaining, shaft retaining and worn parts assembly. This article is limited to the basic types of thread lockers, generally available in at least three basic strength types. These types include the following:
The low and medium strength thread lockers are easily removed with hand tools. Medium strength has a much stronger bond than low strength thread locker. High strength thread lockers are very strong and most often require the use of heat to break the adhesive bond. These three types are intended to be applied to threads prior to assembly. Loctite does make a medium strength thread locker (green) that is a penetrating thread locker that can be applied to fasteners after assembly. This type of thread locker is noticeably thinner than other types and will "wick" into the threaded joint.
The use of thread lockers is an excellent practice in machine assembly, enhancing an assemblies' ability to remain intact during use. Caution should be heeded when using them, however. For example, getting a thread locker in a bearing surface could lock or restrict a rotating joint, possibly causing damage or hindering motion, albeit unlikely. Another concern is the use in the presence of plastics. There are thread lockers designed for plastics, but those being discussed here are designed for metal and can chemically attack and destroy certain plastics.
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Loctite Threadlocker Blue 242 is designed for the locking and sealing of threaded fasteners which require normal disassembly with standard hand tools. The product cures when confined in the absence of air between close fitting metal surfaces. It protects threads from rust and corrosion and prevents loosening from shock and vibration. Loctite Threadlocker Blue 242 is particularly well-suited for applications on less active substrates such as stainless steel and plated surfaces, where disassembly is required for servicing.
Note: NOT recommended for use in pure oxygen and/or oxygen-rich systems and should not be selected as a sealant for chlorine or other strong oxidizing materials. NOT recommended for use on plastic parts, particularly thermoplastic materials, where stress cracking of the plastic could result.
Loctite Threadlocker Red 262 is a high-strength product that is applied to fasteners up to 3/4" (20 mm) in size before assembly. Localized heat and hand tools are required to separate parts. Solvents will not weaken the adhesive bond.