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The Relationship Between Air, Metal and Anaerobic Adhesive

Anaerobic adhesives remain liquid until isolated from oxygen in the presence of metal ions, such as iron or copper.   These adhesives are used in a variety of applications including threadlocking, retaining, pipe sealing, and gasketing and are often referred to as sealants instead of adhesives.

The relationship between the amount of air, metal and adhesive/sealant is significant in the manufacturing, packaging, and use of these products.   Manufacturing – Air is introduced in manufacturing to ensure stability.  Packaging – Products are packaged in containers that permit sufficient air permeation.   Use – During use, the type of metal and the gap and between the two surfaces are the main contributors to the speed of cure. Metal ions on the surface of the substrate are generally sufficient.  In the event no metal is present, or a less reactive metal is used.  Surface conditioners may be used.

For the majority of applications, the balance of air, metal, and adhesive happens with no extraordinary attention.  For example, when an anaerobic adhesive is sealed between a nut and a bolt on a threaded assembly, it rapidly “cures” or hardens to form a tough cross-linked plastic that will bond quite well to many metals.

The significance of this balance is more pronounced when pushing the technology to hone in on the best possible use parameters.  Such as the ideal surface finish to obtain the fastest cure rate.

Surface finish affects the quantity of air, adhesive and metal ions present.   If the surface finish is too small, the air in the adhesive does not have a suitable pathway to escape to permit cure.  If the surface finish is too large, excess air and adhesive is present (relative to the amount of metal) to permit cure through the gap.

To determine the ideal micro finish for a low viscosity wicking grade threadlocker, the % cure after 45 minutes was determined on various surface finishes.

Surface Finish m in

Cure after 45 mins

325

15%

200

90%

100

50%

22

30%

Cure After 45 Minutes (%)

The above shows the ideal micro finish for the application is 200 m in.

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