Bonding Rubber Sheeting to Steel

When using Normac 900R/RF/RC Cold Bond System the key to a good and long lasting bond is preparation. Since Normac 900R relies primarily on mechanical bonding you will find that by increasing the surface roughness or anchor pattern you have increased the actual surface bonding area. This will result in much higher bond strengths and longer service life. Ninetynine percent of all bonding failures are due to improper preparation. The following procedure should provide you with the best possible bond between rubber sheet stock and steel.

THE STEEL SUBSTRATE:

1. Grit blast the areas to be bonded to a white metal finish, (NACE #2 OR SSPC 10-63). Minimum profile of the blasted metal or anchor pattern should be a minimum of 2 mils. This will ensure that the steel is free from all oil, paint, etc. Near-white or commercial blasting, acid pickling, brush blasting and surface grinding are all acceptable preparation methods but the adhesion value will not be as great. With experience you will be able to determine what preparation method will ensure the best possible bond for a given application, but until then use white metal blast.

2. Clean the blasted metal by brushing and vacuuming. Vacuuming is the best method for completely removing blast dust. Should the surface become contaminated with oil or grease, wash with Normac Cleaning Solvent using a clean shop rag.

3. You are now ready to apply the first coat of Normac 900R. Try to apply this first coat as soon as the preparation operation is complete.

4. Allow the first coat or primer coat to dry at least one hour before proceeding with the application of the urethane liner. There will be better adhesion of the first coat if left to dry over night. You may store primed steel for up to 4 days before lining if stored in a cool dry area out of sunlight. Cover with plastic to avoid any contamination by dirt or oils.

RUBBER SHEET PREPARATION

1. The bonding side of the rubber sheet must be roughened to obtain good adhesion. This can be accomplished by two methods:

a) You can use a rotating wire brush attached to an electric drill of about 1400-1700 RPM for roughening. This is the best method as you eliminate the risk of “burning” or “charring” which might occur with a highspeed sander. The wire brush recommended is a stiff bristled 4" diameter with a face width of 1”. You may also use tire rasps as they will provide the same surface texture as the wire brush. When using the wire brush or rasp, allow it to cut into the rubber sheet so a profile is created. Do not leave any “shiny” or nonroughened spots.

b) The second preparation method is the use of a 7" diameter sander of 2000 RPM or less using a 7" aluminum oxide sanding disc of 24 grit. A2000 RPM sander or more will “burn” or “char” the urethane sheet, causing smearing of the rubber. You will not get good adhesion to these areas.

3. Once the rubber sheet has been roughened, clean by brushing. After brushing, use a clean rag soaked with Normac Cleaning Solvent and wipe down the rubber sheet to remove any leftover sanding dust.

4. Mix necessary amount of Normac 900R and apply to roughened rubber sheeting. Allow this to dry of a minimum of 1 hour at room temperature before the application begins. By allowing the primed rubber sheet to sit over night before application will allow for better first coating bonding results.

BONDING THE RUBBER SHEET TO STEEL

1. The bonding operation consists of applying one coat of mixed Normac 900R to both the rubber sheet and steel, allowing each to become tacky or develop adhesion legs, then applying the rubber sheet to the steel. Normal tack times should be anywhere from 10-20 minutes depending upon temperature. You may test this tackiness with the back of your finger. If the rubber sheet is too large to apply all at once, do it in sections. For example, do the first four feet, fold the sheet back and do the next four feet etc. Should the tack coat become too dry, simply re-cement, allow to become tack and re-apply. If the sheet is improperly positioned you can still pull it off the steel, provided you have not pressed or rolled it down. Should this be required you may see the adhesive pull from the steel or rubber sheet. You must re-prime these areas, allowing it to dry before the tack coat and application take place. Once the rubber sheet is in its bonded position, use a 1" or 2" flat roller and roll out to the edges. Make sure your rolling strokes overlap as you roll out towards the edge, as this will push any trapped air out. For edge adhesion it is a good idea for the rubber sheet to be cut oversized so that you may bend the edges by hand over the steel edge after rolling. This usually gives excellent adhesion. The excess can be trimmed with a sharp knife.

   

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