Surface Treatment Guidelines

Surface preparation determines bond strength. For high-strength structural bonds, surface oxide films, oil stains, dust, mold, mold release agents and all other contaminants must be completely removed. The quality of surface treatment directly determines the degree of bond strength and environmental aging resistance.

There are three methods of removing contamination: chemical cleaning, sanding, and degreasing.

Chemical cleaning: is a common method of treating metals. These include etching the surface to form an oxide layer with high adhesion, or applying an organic coating. Chemical cleaning provides the best bonding surface.

Sanding: Includes sandblasting, steam sanding using abrasives or cleaning materials. Sandblasting is only suitable for thick enough material (otherwise it will distort when sandblasting). The steam grinding method is not very strict on the thickness of the metal.

Degreasing: Degreasing can be used for surface treatment when the bonding strength is required to be high or when it is used outdoors and the weather resistance is strictly required. The surface is cleaned with hot alkaline solvent or solvent steam, but the surface must be free from rust, paint and finely ground particles. Hot caustic solvents are the most effective method for removing residual contaminants.

There are 3 steps to the recommended surface preparation procedure that are necessary to clean any material:

1. Degreasing;

2. Chemical corrosion or mechanical grinding;

3. Degreasing.

For precious metals or jewellery, degreasing is generally adequate. The exception is silver, which will tarnish with a moderate number of emery papers, and a trichlorethylene vapor phase degreaser is recommended. Most plastic products have a release agent or wax on the surface, which needs to be removed with acetone or methyl ethyl ketone solvent before bonding, and then sanded, lightly sanded with a medium number of emery paper. The pre-treated parts should be bonded as soon as possible. If the bonding must be delayed, it is recommended that the parts be covered with tissue paper and placed in a non-polluting dry place.

The following are suggested chemical treatments (for industrial bonding only):

Aluminum, Aluminum Clad or 24ST Silicone Steel

cast ironstainless steel

Concrete (Portland cement type) Teflon

Copper and its alloys Phenolic resin, polyester, polyurethane

Hexadiene Phthalate (Ester) Resin

galvanized metal rubber

glass tin

lead titanium

leather goods wood

Magnesium and its alloys

Aluminum, Aluminum Clad or 24ST

1) Drying after degreasing with solvent;

2) Soak in chromic acid solution at 65 - 70 degrees Celsius for 5-10 minutes;

Preparation of hydrochloric acid solution:

10 parts (weight ratio) sodium dichromate

30 parts (by weight) of 98% sulfuric acid

100 parts (weight ratio) distilled water

Dissolve sodium dichromate in most of the water first, then slowly add concentrated sulfuric acid, stir while adding, and finally add the remaining small part of water.

3) Rinse the metal thoroughly with running water and dry completely;

4) The result of the surface preparation is satisfactory and should be bonded immediately.

cast iron

Degrease, emery paper, and degrease again.

Concrete (Brant cement type)

1) Concrete stained with oil or grease must first be scrubbed with a strong solvent such as ammonium hydroxide, and then rinsed thoroughly with water;

2) Concrete should be surface prepared before being bonded. The following methods are available:

(a) Sand blast at 1/16" away from the adhered surface, and use a vacuum cleaner to remove the dust. If the surface is corroded and deteriorated, it should be polished or removed before dust removal;

(b) remove dust by mechanical wiping;

(c) Chemically etch with a 15% hydrochloric acid solution (operated with a steel brush) until no bubbles are produced. Rinse with high pressure water hose. Test with wet litmus paper, if the surface is acidic, rinse with 1% ammonium solution, and finally dry the surface completely.

Copper and its alloys (brass)

Mixed acid configuration:

430 parts (volume ratio) of sulfuric acid

72 parts (volume ratio) of nitric acid

490 parts (volume ratio) of water

Steps: Soak in the above solution for 15 seconds, rinse the water pipe for 5 seconds (water at 25 degrees). Soak in 15% (volume percentage) hydrochloric acid solution, rinse the water pipe for 2 minutes. (25 degree).

The following solutions may be used:

8.0 (weight ratio) ferric chloride solution

16.3 (weight ratio) of nitric acid

75.5 (weight ratio) of water

Soak in the above solution for 1-2 minutes at room temperature, rinse thoroughly with water, and then dry with air at 60-65 degrees.

Hexadiene phthalate (fat)

Scrub the surface with acetone or methyl ethyl ketone solution with a rag to degrease, and then polish it with medium-grit emery paper. Scrub and degrease again with acetone or methyl ethyl ketone solution.

galvanized metal

After degreasing, sand with medium-grit emery paper and degrease again or chemically etch with the solutions listed below.

Solution: 20 parts (by weight) of concentrated hydrochloric acid

80 parts (by weight) of distilled water

step:

1) degreasing;

2) Soak the metal in the prepared hydrochloric acid solution for 2-4 minutes at room temperature;

3) Rinse with cold distilled or deionized water;

4) Dry in an oven at 60-70 degrees for 20-30 minutes;

5) Bond with adhesive as soon as possible.

Glass

For general bonding applications, only surface degreasing is sufficient. For optimum bond strength, the glass surface should be sanded with fine sandpaper until the surface is "frosted".

lead

Degrease, sand with medium-grit emery paper, and degrease again.

Leather

Moisten the rag with acetone or methyl ethyl ketone solution to degrease, then polish and then degrease.

Magnesium and its alloys

1) Vapor degreasing with stabilized trichlorethylene;

2) Soak in 10% sodium hydroxide at 76-87 degrees for 10 minutes;

3) Spray with cold water for 5 minutes;

4) Soak for 8 minutes at room temperature in a solution consisting of 1.5 pounds of chromic acid and 0.25 pounds of sodium nitrate in 1 gallon of water;

5) Rinse for about 3 minutes;

6) Soak in hydrofluoric acid solution for 5 minutes at room temperature;

7) Rinse for half a minute to one minute;

8) Bake in hot air at 71 to 98 degrees for 10 minutes;

9) Immediately bond or protect with a zinc primer.

Stainless steel

1) degreasing;

2) Corrode for 10 minutes in the following solution at 65-68 degrees;

Solution: 90 parts (by weight) of water

37 parts (by weight) sulfuric acid

0.2 part (weight ratio) Nacconol series surfactant.

3) Rinse with water pipe or distilled water

4) Soak in the following solution for 10 minutes at room temperature.

Solution: 88 parts (by weight) of water

15 parts (by weight) concentrated nitric acid

2 parts (by weight) of hydrofluoric acid.

5 Rinse with distilled water and dry in an oven at 95 degrees

Phenolic, Polyester, Polyurethane

Moisten the rag with acetone or methyl ethyl ketone solution to degrease, then polish, then degrease

rubber

Where maximum bond strength is required, chemical etching is recommended. Satisfactory bonding surfaces can be obtained using the following cyclization technique. Soak rubber in concentrated sulfuric acid, soak natural rubber for 5-10 minutes, and soak synthetic rubber for 10-15 minutes. Many rubbers are resistant to acids, so long cyclization times are required until the rubber cracks finely when it is bent. It can also be soaked in plain concentrated sulfuric acid. When the paste is formed, barite is added to the concentrated sulfuric acid to obtain uniform, non-flowing paste-like concentrated sulfuric acid. The soaked rubber is rinsed with water and dried. Sometimes it may be necessary to neutralize the residual acid with a diluted alkaline solution. If there is acid residue, the opportunity will consume part of the curing agent and weaken the bond strength. The surface is now ready for bonding.

tin

Degrease, sand with medium-grit emery paper, and degrease again.

titanium

In general, the most effective bonding surface can be obtained by acid etching of titanium metal. Titanium is cationized with 15% sulfuric acid solution or with hot sulfuric acid. Then wash with sodium alkylsulfonate detergent. A good bonding surface can also be obtained by pre-plating aluminum or nickel on the titanium surface.

wood

Use sanders, axes, and planes to remove oil stains, rot, and other contaminants on the surface. Make sure the wood is dry. Sand it smooth again.