Surface preparation (Topic: 17115)

The strength of a joint depends strongly on the condition of the bonding surfaces. Contaminants prevent contact between adhesive and substrate and many adhesive bonds collapse due to bondline corrosion. The purposes of the surface preparations are to produce clean bonding surfaces, corrosion resistant surfaces, strong surface oxides. The choice of treatment depends on the adhesive type, joint loading, joint design, costs, service environment and service life.

Some of the applied preparation methods are:

ñ Degreasing with steam, organic solvents or alkaline cleaners.

ñ Mechanical methods such as blasting, brushing or grinding with emery-paper.

ñ Dipping in boiling water after etching in caustic soda (Boehmite treating).

ñ Applying a primer.

ñ Yellow or green chromate treatment.

ñ Anodising in chromic, phosphoric or sulphuric acid.

Anodising in phosphoric acid is today considered as the best treatment method regarding joint strength and corrosion resistance. Immediately after this treatment the surfaces must be covered by a primer.

References: [2,7,8,12]