For high strength structural bonds, paint, oxide films, oils, dust, mold, release agents and all other surface contaminants must be completely removed. However, the amount of surface preparation directly depends on the required bond strength, environmental aging resistance and economic practicalities.
There are six basic methods of preparing a surface for bonding: chemical cleaning, abrasion, degreasing, atmospheric plasma, flame, and corona surface treatment.
Recommended Surface Preparation Procedures for Bonding
The following surface treatments are recommended for preparing various materials for bonding. In general, six steps are necessary for cleaning any surface:
For precious metals and jewels, degreasing will generally be entirely satisfactory, with the possible exception of silver where the tarnish should be removed with medium grit emery paper. A stabilized Trichlorethylene vapor phase degreaser is recommended.
Most plastic parts will have residual mold release or wax on the surface; before bonding, this should be removed with a suitable solvent-such as Acetone or Methyl Ethyl Ketone (if necessary)- and then abraded, lightly, with a medium-grit emery paper.
When mechanically abrading, we recommend the use of medium-grit blasting. It is essential, when parts are grit or sandblasted, that they be degreased again before bonding. In all cases, parts should be bonded as soon as possible after pre-treatment. If bonding must be delayed, we recommend that the parts be covered with a light tissue paper and stored in a non-contaminating, dry atmosphere.
Following are several chemical pre-treating formulas recommended for the most common adherents (for industrial use only). All recommendations or suggestions for use are made without guarantee-in as much as conditions of use are beyond our control.
ALUMINUM, ALCLAD OR 24STCAST IRONCONCRETE (Portland Cement Type)COPPER AND ITS ALLOYS (Brass)DIALLYL PHTHALATEGALVANIZED OR ZINC FINISHED METALSGLASSLEADLEATHERMAGNESIUM AND ITS ALLOYSSILICONE STEELSTAINLESS STEELTEFLONPHENOLIC, POLYESTER & POLYURETHANE RESINSRUBBERTINTITANIUMWOOD
ALUMINUM, ALCLAD OR 24ST
***Prepare the chromic acid solution as follows:
(Dissolve the Dichromate in most of the water, add Sulfuric Acid, stirring carefully and then add the remaining water.)
Degrease. Grit-blast or abrade with emery paper. Degrease again.
CONCRETE (Portland Cement Type)
COPPER AND ITS ALLOYS (Brass)
Procedure: Dip 15 seconds in above solution, rinse in running tap water (25C) five seconds, dip in 15% (volume) Hydrochloric Acid, followed by a 2-minute rinse in running tap water (25C).
The following formula may be used:
Immerse the parts 1-2 minutes at room temperature, followed by a thorough water rinse and air dry at 60-65C.
Degrease with a rag containing Acetone or M.E.K. Abrade the surface with medium-grit emery paper. Degrease again with Acetone or M.E.K.
GALVANIZED OR ZINC FINISHED METALS
Degrease. Abrade with medium-grit emery paper. Degrease again or use the following etching procedure:
Treat as follows:
For normal bonding applications, degreasing alone is sufficient for pre-treating glass surfaces. If, however, the very optimum in strength is required, the glass can be grit-blasted with very fine grit until the surface appears frosted.
Degrease. Abrade with medium-grit emery paper. Degrease again.
Degrease with a rag containing Acetone or M.E.K. Roughen with sandpaper. Degrease again.
MAGNESIUM AND ITS ALLOYS
8.0 parts/wt. Hydrochloric Acid
7.8 parts/wt. Sulfuric Acid
84.2 parts/wt. Nitric Acid
The parts should be immersed in the above solution (maintained at 70-75C) for 10-20 minutes, then rinsed with water at room temperature and brushed with a soap solution to mechanically remove scale loosened by the chemical bath. A hot water rinse (70-75 degrees C) followed by a hot air dry (70-75 degrees C) completes the preparation.
Formulas for etching solutions are available; however, because of the danger in the preparation and use of these materials, we recommend that you buy proprietary materials available from:
Acton Technologies, Inc.
P.O. Box 726
100 Thompson Street
Pittston, PA 18640
Teflon and other fluorocarbon plastics are available in bondable form from many suppliers.
PHENOLIC, POLYESTER & POLYURETHANE RESINS
Degrease with a rag containing Acetone or M.E.K. Abrade with medium-grit emery paper. Degrease again.
Surface etching of rubber is recommended for maximum bond strength. A satisfactory bonding surface can be obtained by using the following cyclizing technique:
Immerse the rubber in concentrated Sulfuric Acid (sp. gr. 1.84) for 5-10 minutes in the case of natural rubber and 10-15 minutes in the case of synthetic rubber. Many rubbers are very acid resistant and will require longer cyclizing times to reach a point where the rubber will have fine cracks when flexed.
Alternatively, a paste of concentrated Sulfuric Acid and Barytes can be used. The paste is made by adding Barytes to the acid to give a consistency which will not run. After washing thoroughly with water and drying, the brittle surface of the rubber should be broken by flexing so that a finely cracked surface is produced. It may be necessary to wash with dilute caustic solution to insure neutralization of residual acid which, if not removed, will consume some of the curing agent weakening the bond strength. The surface is then ready for application of the adhesive.
In general, an acid etch is the most effective surface treatment for titanium. Anodizing in 15% Sulfuric Acid or etching in hot Sulfuric Acid solution followed by cleaning in Alkanex detergent-sodium metasilicate solution produces good results. Still better results are obtained in the titanium surface is first plated with a metal such as aluminum or nickel.
Remove any contaminating materials such as oil, rot, etc., with a sander, ax, or plane. Make certain the wood is dry. Smooth with sand-paper.