6.6 Anaerobic Adhesives

Anaerobic adhesives were made commercially viable in 1953 by a chemist in Connecticut called Professor Vernon K. Krieble; whose single component curing formula started a new era of bonding possibilities. Initially developed as threadlockers, anaerobic formulations resulted in a new era of mechanical reliability by preventing vibrational loosening of mechanical fasteners; however, new solutions and applications were developed on this technology including thread sealants, gasketing and retaining compounds and several structural bonders.

6.6.1 Threadlockers

Threadlockers are 1C liquid adhesives that completely fill the gaps between interfacing threads on nuts-and-bolts assemblies; the liquid resin changes its liquid state into solid by the contact of metal and the absence of air (anaerobic), creating an interfacial connection to prevent any loosening of the threads. It is essential that the effective length of the thread is wetted and that there is no surface contamination in the curing of the adhesive.

Figure 186 Threadlocker between the interfacing threads of a nut and bolt

Different formulas for threadlocker adhesives are available and these are classified by the torque value: removable, semi-permanent, permanent and some special characteristics like wicking grade, semi-solid formulations or pre-applied (dry film adhesive coating) for overhead applications. Recent developments are threadlockers that contain no declarable carcinogens, mutagens or reproductive toxins and thus carry no hazard symbols, risk or safety phrases.

Anaerobic threadlocker adhesieves are covered in detail in the book How to Increase Reliability and Prevent Threaded Assembly Failure (Henkel Corporation, 2020).

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