What are anaerobic adhesives?

Anaerobic (non-oxygen) plastic was developed in the USA in the 1950s. Due to the unique advantages of this chemical mixture, it quickly gained popularity and began to be used in many countries in a short time. Initially, it was created as an alternative to traditional protection against spontaneous unscrewing of fasteners, such as a flat washer or a toothed washer. Anaerobes were intended to prevent spontaneous loosening of bolts, nuts and other fasteners. The first applications of anaerobic adhesives in Poland were related to the development of the automotive industry and aviation technology. Now they are used not only for fixing, but also for sealing in various technological processes. Special adhesives of this type are used, among others, for joining cylindrical parts, sealing pipe threads, filling welding defects (impregnation), securing threads, embedding bearings or sealing flanges.

Anaerobic adhesives are one-component materials that cure at room temperature while eliminating contact with oxygen. The curing component does not activate as long as it is in contact with atmospheric oxygen. When the adhesive is deprived of oxygen, e.g. by assembling parts, it cures very quickly, especially when in contact with metal. The hardening process can be imagined as follows: when the supply of atmospheric oxygen is turned off, free radicals are formed under the influence of metal ions (Cu, Fe), which initiate the polymerization process. The liquid adhesive is able to completely fill the joint and penetrate into even the smallest gaps due to its capillary properties. Then, the cured adhesive thoroughly fills the micro-irregularities of the glued parts and "anchors" in them, which causes a very large increase in static friction and prevents spontaneous loosening of the elements. The curing process is also stimulated by the contact of the adhesive with metal surfaces, which acts as a catalyst.

Types of anaerobics

• Threadlock adhesives include anaerobic compounds whose primary purpose is to prevent spontaneous loosening and unscrewing of fasteners under the influence of vibration, mechanical stress or thermal expansion. Most often it is a thixotropic (i.e. non-sagging when applied to sloping and vertical surfaces) liquid one-component adhesive that completely fills the microscopic spaces between threads and surfaces. Designed in the initial phase primarily for fastening threaded connections. However, it soon turned out that the spectrum of application of these adhesives is much wider.
• Pipe thread sealants are anaerobic materials that seal and completely fill all free spaces of the thread, ensuring its complete sealing. Proper selection of the adhesive / sealant excludes possible relative movements in the joint, thus eliminating the main cause of most leaks, regardless of the pressure and tightening force of the joint.
• FIP (Formed-In-Place) sealants for flat surfaces. They allow you to create the necessary seal in a short time and have a wide range of applications due to the provision of a high-quality seal. Their main advantages are durability, the ability to seal any surface shape and heat resistance. This type of seal is used when connecting rigid flanges. In vehicles, these may be:
• gearbox housing
• crankcase with block
• water pump for engine body
• the timing cover to the cylinder head
• Adhesives for belt joints. Using a hardening mechanism, they are suitable for use on metal components that are subjected to high loads in harsh environmental conditions. This is one of the methods of joining coaxial parts used, for example, in:
• assembly of bearings in housings or on shafts
• mounting on shafts of rotors, gears, chain wheels, pulleys
• inserting sleeves
• sealing of casting plugs in engine housings
• eliminating cross pin grooves
• exclusion of deformation of precision tools
• assembling guides for drilling equipment
• fixing the dipstick sleeves for checking the oil level
• adjusting the accuracy of worn parts
• Anaerobic porosity sealing is one of the methods of sealing microporosity resulting from two physical phenomena that occur during the solidification of molten metal, i.e. crystallization and shrinkage as well as gas absorption. Cast parts are impregnated mainly to prevent leakage. Examples of impregnated elements include:
• parts of steering gears and car pumps
• feed system pumps
• regulators
• cylinder heads
• hydraulic pumps
• gear bodies
• hermetic enclosures for avionics and avionics
• air brake parts

Areas of application

Anaerobic adhesives have been appreciated in technical and engineering environments due to their undoubted advantages. Among the most important are:

• filling gaps, preventing weakening of joints due to vibration;
• creating a seal in the space between the threads, which prevents leakage and corrosion;
• perfect surface fit;
• an excellent alternative to mechanical devices, such as: cotter pins, cup nuts, lock washers, special wire, etc.;
• reduction of material and technical costs as well as production costs;
• single-component products (the material is immediately ready to use, no need to mix);
• easy to use, the ability to keep the workplace clean.

Anaerobic adhesives, due to the benefits listed above, are increasingly used in many industries, such as:

• production of motor vehicles (automotive)
• mining
• energy
• aviation
• arms industry
• railways
• production of agricultural, construction and mining machinery

*materials from Henkel Company "Worldwide design handbook" second edition