Anaerobic adhesives normal applications

Although there is, as might be expected, a grey area between structural and mechanical applications of adhesives, it helps understanding to consider them separately. Generally, structural adhesives are used in some form of overlap joint, as distinct from the co-axial joints formed from turned parts, where anaerobic adhesives (see Chapter 3 and Section 5.1.2) are normally employed. However, structural adhesives may be used in co-axial configurations when maximum performance is required. 

Anaerobic adhesives are one-component, solventless, acrylic based liquids and pastes which cure at room temperature in the absence of air — a process which is catalytically speeded by a metallic surface. Secondary curing techniques are sometimes (though not often) required and these would normally comprise the use of an activator or the application of heat. 

In the Automotive industry there is a trend towards complete automation of production lines. In the application of adhesives/sealants for gasketing, the principles of dispensing have normally been to use a pressure-time system, or alternatively a cartridge system with a robotic head. However, a faster system is to screen print an anaerobic on to the surface of a component. 

Joint sealing and retention of co-axial components - often both in the same application - are prime examples. Components can be threaded (screws or pipes), or splined or smooth (eg bearings). Special versions of these adhesives (often not truly anaerobic - in that primers may have to be used) give much higher levels of effective adhesion than the normal materials and so may be used in lap joints. Other versions are formulated as gasketting media. 

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