Preparing surfaces before gluing

So you are ready to start gluing……..glue ready, drawings complete, materials cut to size…….are the materials clean?

Did you know that in many applications, even a thumbprint on an otherwise clean surface, can prevent the adhesive from spontaneously wetting, spreading & sticking to the surface.

Therefore, the strength of the bond is often a function of how clean the surface is! Below, the Glue Guru has listed some important points in surface preparation:

• Organic contaminants (such as oil & grease) must be removed by degreasing.
• Loose material should be  dislodged by scraping or washing with acids, alkali solutions or other such chemicals.
• Non-metallic & non-porous materials should be degreased with a detergent solution, rinsed thoroughly with clean water, and dried.
• Metals are best cleaned by solvent degreasing with pure solvent, followed by sandblasting or, preferably, by chemical etching. We never suggest the use of standard cellulose thinners for degreasing.
• Chemical treatments should be confined to the bonding areas, but degreasing should be done to the entire assembly.
• A cleaned assembly should be bonded as soon after the cleaning operation as possible.

In order to test the material for cleanliness, pour a small amount of water onto the surface. If it distributes evenly then the adhesive should bond well. If it beads or crawls, clean the surface again and re-test.

If storage is necessary, all of the cleaned parts should be tightly wrapped or placed in airtight containers.

Etched surfaces must never be touched with bare hands—-even wiping the surface with a clean towel can affect the bond. Wear clean cotton gloves and use clean tools.

Gluing should be performed in rooms separate from other manufacturing operations. Often, if gluing is done in the same area as, for example plastic or rubber moulding, a physical barrier should be erected between the two operations to prevent airborne mould release lubricants from depositing on the surface.

Surface contamination may also be a problem in factories spray painting. Again, certain additives within some paints, for example silicone based antifoam chemicals, may be present in the air and lead to adhesion issues

In this piece, we have addressed some of the basic points of surface preparation. Further advice is obtainable from our Technical Services Department (-353-1-4573754).