Full definition
Anaerobic adhesives are advanced engineering materials designed for specific applications where traditional bonding methods may be insufficient. These single-component liquid adhesives are unique because they cure when confined between close-fitting metal surfaces in the absence of air, a process known as anaerobic curing. The curing mechanism is catalyzed by metal ions, particularly from iron, copper, and their alloys, which initiate a reaction in the acrylic-based formulation. This characteristic makes anaerobic adhesives particularly useful in environments where mechanical fasteners are subject to vibration and movement, as they provide a robust, reliable bond that enhances the integrity of the assembly.
There are three primary application categories for anaerobic adhesives. The first is threadlocking, where these adhesives prevent the loosening of bolts and screws due to vibrations. They come in various grades: low (purple), which is hand-removable; medium (blue), which allows for wrench-removal; and high (red), which requires heat for disassembly. The choice of threadlocker is critical depending on the application and the required strength of fastening.
The second application is flange sealing, where anaerobic adhesives serve as a superior alternative to cut gaskets on machined metal flanges. They effectively fill gaps up to 0.25 mm and are resistant to various fluids, including oil, coolant, and gas, making them ideal for automotive and industrial applications where leakage prevention is paramount.
Lastly, anaerobic adhesives are used as retaining compounds to secure bearings, bushings, and cylindrical assemblies within housings. They can fill gaps up to 0.15 mm and cure to provide structural adhesive strength, typically achieving shear strengths of 15-35 MPa on steel substrates. The operational temperature range for most anaerobic adhesives is between -55 to +150°C, with some high-temperature grades capable of withstanding temperatures up to +230°C. The curing speed varies, with fixture times of 5-30 minutes and a full cure time of 24 hours at room temperature. Accelerators can be used to enhance curing on inactive surfaces such as stainless steel, zinc, and aluminum, ensuring a versatile application spectrum.
Compliance with industry standards such as MIL-S-46163 further ensures the reliability and performance of these adhesives in critical applications. Major brands known for their anaerobic adhesives include Loctite (Henkel), which is recognized as the market leader, along with competitors like Permatex, 3M, and Hernon.