How does anaerobic glue work? Types, properties and application

What are anaerobic adhesives? How they cure and where they are used

Anaerobic (oxygen-free) compounds were developed in the USA in the 1950s. Thanks to the unique advantages of this chemistry, they quickly gained popularity and were adopted in many countries. Initially, they were created as an alternative to traditional anti-loosening methods for fasteners (e.g., mechanical locking elements). Anaerobics were designed to prevent spontaneous loosening of bolts, nuts and other fasteners. Early applications in Poland were connected with the development of the automotive and aerospace industries. Today, they are used not only for locking but also for sealing in a wide range of technological processes. Special anaerobic products are used, among other things, for bonding cylindrical parts, sealing pipe threads, sealing weld defects (impregnation), threadlocking, retaining bearings and sealing flanges.

Key takeaways

✅ Anaerobic adhesives are typically one-component products

✅ They cure at room temperature after oxygen is excluded from the joint gap

✅ Curing is strongly supported by contact with metal (catalytic effect)

✅ Common applications include: threadlocking, thread sealing, flange sealing, retaining coaxial fits and porosity impregnation

Video: anaerobic adhesives – applications and selection

This playlist includes materials on threadlocking, sealing and typical selection/application mistakes related to anaerobic products.

How do anaerobic adhesives work?

Anaerobic adhesives are one-component materials that cure at room temperature when contact with oxygen is eliminated. The curing component does not activate as long as it remains in contact with atmospheric oxygen. When the adhesive is deprived of oxygen—for example, by assembling the parts—curing can occur quickly, especially when the adhesive is simultaneously in contact with metal.

The curing mechanism can be described as follows: when the supply of atmospheric oxygen is cut off, metal ions (Cu, Fe) promote the formation of free radicals, which initiate polymerization. The liquid adhesive can completely fill the joint and penetrate even very small gaps due to capillary action. Then the cured adhesive fills micro-roughness on the joined parts and “anchors” into it, which increases static friction and prevents spontaneous loosening of fasteners. Curing is also stimulated by contact with metal surfaces that act as a catalyst.

Types of anaerobic products

1) Threadlockers

Threadlockers include anaerobic compounds whose main purpose is to prevent spontaneous loosening and unfastening of threaded fasteners due to vibration, mechanical loads or thermal expansion. Most often, this is a thixotropic (non-dripping on inclined and vertical surfaces) one-component liquid that completely fills microscopic spaces between threads and contact surfaces. Although initially designed mainly for threaded joints, the application range of these products turned out to be broader.

2) Pipe thread sealants

Pipe thread sealants are anaerobic materials that seal and fill all free spaces in a thread, providing full sealing. Proper selection of adhesive/sealant prevents relative movement in the joint, eliminating one of the main causes of leakage, regardless of pressure and tightening force.

3) FIP flange sealants (Formed-In-Place)

These products allow formation of the required gasket in a short time and have a wide application range thanks to high sealing quality. Their key advantages include durability, the ability to seal any flange shape and heat resistance. This type of sealing is used on rigid flanges. In vehicles, examples include:

• gearbox housing,
• crankcase to block,
• water pump to engine housing,
• timing cover to cylinder head.

4) Retaining compounds for coaxial fits

Thanks to the curing mechanism, they are suitable for metal parts exposed to high loads in demanding environmental conditions. This is one method of joining coaxial parts, used for example in:

• bearing installation in housings or on shafts,
• mounting rotors, gears, sprockets, pulleys on shafts,
• bonding bushings,
• sealing casting plugs in engine blocks,
• eliminating keyways in favour of cross pins,
• reducing deformation of precision tools,
• mounting guides in drilling devices,
• fixing dipstick sleeves for oil level control,
• correcting tolerances of worn parts.

5) Anaerobic porosity sealing (impregnation)

This is one method of sealing micro-porosity created by physical phenomena occurring during solidification of molten metal: crystallization and shrinkage, as well as gas absorption. Cast parts are impregnated mainly to prevent leaks. Examples of components subjected to impregnation include:

• steering gear and automotive pump parts,
• fuel supply system pumps,
• regulators,
• cylinder heads,
• hydraulic pumps,
• gearbox housings,
• sealed housings for aerospace instruments and avionics,
• pneumatic brake components.

Application areas

Anaerobic adhesives are valued in technical and engineering environments due to their clear benefits. The most important include:

• gap filling and preventing joint weakening due to vibration,
• forming a seal between threads, preventing leaks and corrosion,
• excellent fit to surfaces,
• an alternative to mechanical locking solutions (e.g., locking pins, special wire, locking washers),
• reduction of material and technical costs as well as production costs,
• one-component products (ready to use, no mixing required),
• ease of use and cleaner workstations.

Due to these benefits, anaerobic products are increasingly used across many industries, such as:

• automotive manufacturing,
• mining,
• power generation/energy sector,
• aerospace,
• defence industry,
• railway,
• manufacturing of agricultural, construction and mining machinery.

See also

For a practical guide focused on threadlocking selection by material and threaded joint specifics (to avoid duplicating content here), see:

➡️ Anaerobic adhesives vs material type – threadlocking

FAQ – anaerobic adhesives

What makes anaerobic adhesives different from general-purpose assembly adhesives?

Anaerobic adhesives cure after oxygen is excluded from the joint gap and when in contact with metal. They are primarily designed for metal-to-metal joints (threads, flanges, coaxial fits).

Why are anaerobic products effective under vibration?

After curing, they fill micro-gaps and micro-roughness, increasing static friction and limiting spontaneous loosening.

What are anaerobic pipe thread sealants used for?

They fill free space in the thread and help achieve sealing—regardless of pressure and tightening force.

What does porosity sealing (impregnation) mean in practice?

It is a method of sealing micro-porosity in castings, used mainly to prevent leaks.

Author

Marcin Filipczyk – long-time specialist in adhesive bonding.

*Materials referenced: Henkel Company “Worldwide design handbook”, 2nd edition