Surface preparation and pretreatments
Working directions for the surface preparation essential for optimum adhesion between structural materials bonded with Araldite® adhesives. Araldite® adhesives form extremely strong and durable bonds with plastics, metals, glass, rubber and many other materials. Designers in every sphere of industry increasingly find that bonding with Araldite® provides the answer to production problems posed by new materials, new uses of existing materials, and new techniques and manufacturing methods.
Surface pretreatments.indd 1
Araldite® resins adhere firmly to most materials. Bonds of great strength are obtained after removal of grease and loose surface deposits, e.g. rust, from the surfaces to be joined, but when maximum strength is required a more thorough mechanical or a chemical pretreatment is recommended.
Surfaces are prepared by one of the following pretreatment procedures (listed in order of increasing effectiveness). 1. Degrease only. 2. Degrease, abrade and remove loose particles. 3. Degrease and chemically pretreat Care must be taken to avoid contaminating the surfaces during or after pretreatment. Wear clean gloves. Contamination may be caused by finger marking – or by cloths which are not perfectly clean – or by oil – contaminated abrasives – or by sub-standard degreasing or chemical solutions. Contamination may also be caused by other work processes taking place in the bonding area. Particularly to be excluded are oil vapours from machinery, spraying operations (paint, mould release-agent, etc.) and processes involving powdered materials. Whatever the pretreatment procedure used, it is good practice to bond the surfaces as soon as possible after completion of the pretreatment – i.e. when surface properties are at their best. Note If the scheduling of bonding operations on multi-part assemblies causes delay between pretreatment and bonding, optimum surface properties may be preserved by priming the bond surfaces immediately after pretreatment.
Part 1 Degreasing
The removal of all traces of oil and grease from the surfaces to be bonded is essential. Degreasing by one of the four methods given below should be carried out even when the surfaces to be bonded appear clean.
Remove all traces of oil and grease as follows: (a) Suspend in a common degreasing solvent such as acetone, MEK, Ethanol or Iso-propanol solvent *vapour in a vapour degreasing unit. The unit may include a compartment to enable initial washing in the liquid solvent. or where a vapour degreasing unit is not available: (b) Immerse successively in two tanks each containing the same degreasing solvent. The first tank acts as a wash, the second as a rinse. When the solvent in the wash tank becomes heavily contaminated, the tank is cleaned out and refilled with fresh solvent.
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This tank is then used for the rinse, and the former tank for the wash. or (c) Brush or wipe the joint surfaces with a clean brush or cloth soaked in a commercial degreasing solvent. (For fine work, washing down with solvent applied by aerosol spray may be a more suitable alternative; this technique also ensures that the solvent used is clean.) Allow to stand for a minute or two to permit complete evaporation from the joint surfaces. A wide range of proprietary solvent degreasing agents with low hazard ratings are now available. These should be used according to the manufacturers’ instructions or (d) Detergent degreasing Scrub the joint surfaces in a solution of liquid detergent. Wash with clean hot water and allow to dry thoroughly – preferably in a stream of hot air from, e.g. a domestic forced-air heater. Note Non-ionic detergents give generally good results.
(e) Alkaline degreasing is an alternative method to the detergent degreasing. The ingredients may be selected from a...
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