Why do threaded fastening adhesives come in different colors such as red, blue, green, etc.? What are the differences between them?

Thread adhesive, also known as anaerobic adhesive, is a one-component sealing and bonding agent made using the principle of oxygen inhibiting the polymerization of free radicals; it can be used both for bonding and for sealing. When the coated surface is isolated from air and under catalytic conditions, it can polymerize and cure rapidly at room temperature. The composition of thread adhesives is relatively complex; unsaturated monomers are the main components, along with aromatic amines, phenols, aromatic hydrazines, peroxides, and others. The formulations of external thread adhesives are constantly being improved and refined, earning them favor in the machinery industry. Thread adhesive (anaerobe) is also known as anaerobic adhesive, anaerobically curing adhesive, or mechanical adhesive. It does not solidify when in contact with oxygen or air, but once isolated from air, it rapidly polymerizes to form a cross-linked solid polymer. The so-called “anaerobic” refers to the fact that this adhesive does not require oxygen when in use.

Due to its unique curing property under oxygen-deficient conditions, thread adhesive can be used for locking, sealing, holding, bonding, and leak sealing. Thread sealant has become an essential liquid tool in the machinery industry. It has a wide range of applications in industries such as aerospace, military, automotive, machinery, electronics, and electrical engineering. (1) Locking to prevent loosening. Metal screws can easily become loose or come unfastened under the effects of impact and vibration. Traditional mechanical locking methods are not ideal, whereas chemical locking methods are inexpensive and effective. If the screw is coated with anaerobic adhesive before assembly, a strong and plastic adhesive film is formed in the thread gaps after curing, ensuring that the screw remains secured and does not loosen. There is a pre-coated type (B-204) of thread adhesive that is applied to the screws in advance and kept ready for use (with a shelf life of four years); simply tightening the screws will achieve the desired anti-loosening effect. (2) Airtight and leak-proof. No two planes can be in perfect tight contact; leakage prevention through sealing is necessary. Traditional methods involve using gaskets made of rubber, asbestos, metal, etc., but these will leak quickly due to aging or corrosion. By using thread adhesive in place of solid gaskets, tight contact can be achieved after curing, resulting in more durable sealing. Thread sealant is used for sealing threaded pipe fittings and threaded plugs, as well as for sealing the mating surfaces of flanges and the joints of mechanical enclosures, providing excellent leak prevention effects. (3) Fixation and positioning. Cylindrical components, such as bearing-to-shaft, pulley-to-shaft, gear-to-shaft, bearing-to-housing bore, bushing-to-hole, and other shaft-and-hole assemblies, have without exception always been reassembled using methods of dimensional interference such as hot fitting or cold pressing, supplemented by keys and pins. This fixing method requires high precision in processing, and due to different coefficients of thermal expansion, wear and corrosion occur, making it easy for the connection to become loose. Using thread sealant can fill the fit gap; once cured, it is strong and durable, offering stability and reliability. Using anaerobic adhesives reduces the requirements for machining precision, simplifies assembly operations, increases production efficiency, and saves energy consumption and processing costs. Fill and seal leaks. For castings, die-cast parts, powder metallurgy components, and welded parts that have micropores, a low-viscosity anaerobic adhesive (B-290) can be applied to the defective areas; this allows the adhesive to penetrate into the micropores. Curing takes place at room temperature in an oxygen-free environment, filling the pores and thus providing a sealing effect. If vacuum impregnation is used, the success rate is higher, and it has become a new technology in the casting industry.

Thread adhesives are composed of various components, with monomers in particular being highly diverse; changes in any of these components can result in new properties. As a result, there are many types of anaerobic adhesives, and their classification methods are not standardized. Generally, it can be classified by the structure of the monomer, the type and strength of the monomer, as well as its viscosity; it can also be classified by its application. A more common classification method is one based on the structure and application of the monomers; specifically, they can be divided into four categories according to their structure. (1) The ether type features a structure represented by trimethacrylate of tetraethylene glycol. (2) Common alkyd esters include polyethylene glycol dimethacrylate ； Hydroxyethyl or hydroxypropyl methacrylate. (3) Epoxy esters are products resulting from the reaction of epoxy resins with various structures and methacrylic acid. Common ones include bisphenol A epoxies (such as the domestically produced Y-150, GY-340, etc., which are mixtures of epoxies and polyethylene glycol esters). (4) Polyurethane is the product of the reaction between isocyanate, hydroxyalkylphenyl methacrylate, and polyols. In fact, many anaerobic adhesive products are mixtures or complex compositions, making it difficult to classify them simply. Classification basis: Based on application, it can be divided into fastener locking and sealing, sealing of flange surfaces and pipe joints, adhesive bonding and holding, as well as impregnation for leak sealing. This classification method is simple and clear, easy to remember and use, and is particularly easy for users to accept. Although adhesives have various uses, there is always a primary use that can serve as the basis for classification.

That’s because they have different uses and different components, which is why their colors vary.