A premium tube of adhesive is no guarantee of achieving an unbreakable bond. Before the adhesive is even applied proper surface preparation should take place. Unless surfaces are free of contaminants like rust, water, oil, dirt and dust, bonding will be sub-standard.
Why is surface preparation so important?
Degreasing, cleaning and priming increases the surface energy of the substrate and gives the adhesive a larger contact area to bond to. Dirt and other contaminants reduce the surface energy of the substrate, so using cleaners and degreasers is an effective way to increase the strength of your bond.
What is surface energy?
Surface energy is a crucial property of a material's surface that directly influences how well an adhesive can bond to it. A substrate with high surface energy allows the adhesive to spread and achieve intimate contact, whereas contaminants such as oil, rust, and dirt can drastically reduce this energy, leading to a weaker bond.
Cleaning & degreasing the substrate/abrasion
Your substrate may hold contaminants from machining, handling, protecting, manufacturing and facility surroundings. It is estimated that even a thin film of oil will reduce adhesive performance by as much as 60%. Applying a cleaner, isopropyl alcohol or a degreasing solvent such as LOCTITE 7063 will remove dirt and debris.
Roughing up the substrate
Giving the substrate a rough abrasive workover with sandpaper or a wire brush will remove heavy deposits as well as creating a surface area with greater peaks and valleys, which has the effect of giving the adhesive more to grip to and increasing adhesive properties. Degreasing should take place before and after the abrasion process.
Applying a primer
Some materials are notoriously hard to bond, like polyethylene, polypropylene, polytetrafluoroethylene (PTFE) and thermoplastic rubber materials. If that is the case, applying a polyolefin primer such as LOCTITE 770 can increase the surface energy of these substrates so adhesives bond more effectively. Apply by spraying, brushing or dipping at ambient temperature.
Applying an activator
You can apply an activator to speed up the curing time of certain adhesives on inactive surfaces. For example, LOCTITE 7452 can be used for cyanoacrylate adhesives to ensure rapid fixturing, and can be post or pre-applied.
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