Anaerobic adhesives

Acrylates or anaerobic adhesives

Based on synthetic acrylic resins, anaerobic adhesives cure when in contact with metal, and the air is excluded, e.g. when a bolt is home in a thread.
They are often known as "locking compounds", being used to secure, seal and retain turned, threaded, or similarly close fitting parts.

Sources/Properties:
Anaerobic adhesives are derived from methacrylates, a monomer related to acrylic or more commonly known as Plexiglas. The word anaerobic really applies to microbes that become active or live in the absence of oxygen. While anaerobic sealants do not contain microbes, they become active and cure or polymerize in the absence of oxygen. These adhesives were developed by Professor Vernon Krieble, the founder of American Sealants Company which is now known as Loctite Corporation.

The basic ingredient in anaerobic adhesives is a monomer from the acrylic family, a special liquid of small molecules which can combine chemically to form a polymer or group of molecules. The molecules of an anaerobic monomer contain two carbon atoms that are double bonded to each other. The "active" ingredient in this monomer is called a free radical. This is a molecule that has an affinity for carbon, but prefers to react with oxygen. As this free radical reacts with oxygen molecules, it forms a stable liquid like the original monomer.

A special ingredient in this chemical composition continually produces free radicals as they react with the oxygen and are used up. As you can see, there is an unlimited supply of catalyst being produced.

If no oxygen is present, the free radical then reacts with the carbon of the double bonded atom of the monomer molecule. A reaction is caused which makes that molecule react with another molecule and begin a chain reaction which produces a solid polymer chain

Some of you may already know that metal has a place in this reaction process. The presence of metal speeds the polymerization process by causing the production of free radical catalysts to increase greatly. The increased amount of catalyst in the monomer causes polymerization to occur more quickly.

This anaerobic reaction has been stated in a fairly simple maner, but it is really a very complex chemical reaction using certain ingredients in a parts per million basis. Other reactions can take place at the same time as curing is occurring, such as crosslinking of the polymer chains which makes the resultant solid resin insoluble in a solvent or by the use of heat.

Common Uses:
Anaerobic adhesives are very versatile and are used in a wide variety of applications.
Adhesive used to keep nuts tight on bolts, such as those within ATMs and heavy machinery
They are used to seal pipe fittings, retain bearings, pulleys, and gears to shafts as well as sealing flanged surfaces to replacing cut gaskets.
The major users are the automotive, truck, construction and farming equipment companies.
The actual market for these adhesives is anywhere that fasteners, gaskets, bearings or any mechanical device that needs to be secured or sealed are used in both OEM or MRO areas.