Patching / Cracks

Dunline > Technical Support > Patching / Cracks

NOTE: Do not contaminate patching material with dirty hands or any other unclean surface. Protect patching material from temperature extremes and light. Keep the patching material in its protective wrapping and store it in a cool, dark place – like a refrigerator.

TOOLS REQUIRED:

  1. A small grinding tool of Silicon Carbide, suitable for use in a high speed electric drill or grinder. 60 to 80 grit USA Standard preferable.
  2. A small amount of a solvent cleaner such as Toluol or Toluene. (Typically found in hardware and/or paint stores.)
  3. A thermostatically controlled heated shoe with a flat smooth face surface capable of maintaining a temperature of 225 to 240° F (107 to 115° C).
    NOTE: A REGULAR HOME TYPE STEAM IRON CAN BE USED, BUT BE SURE IT CAN ACHIEVE AND MAINTAIN THE ABOVE TEMPERATURE.
  4. Talcum Powder. (Regular baby powder will suffice.)
  5. A piece of 1/4 inch (6mm) diameter steel rod about 6 to 8 inches (15 – 20 cm) long.
  6. A 10-inch (25-cm) square of Aluminum foil or Teflon coated fiberglass.
  7. Rubber Patching Material.

PATCHING PROCEDURE

  1. Carefully grind out the entire length, width and depth of the crack, being careful to go a little beyond the extremes so that the entire crack is removed.
    The resulting cavity should be rounded in the bottom, with the upper edges slightly curled inward. The significance of this is to help “hold” the patching material in the cavity.
    The belt surface should be lightly polished with the grinding tool 1/4 to 3/8 inches (6 to 10 mm) all around the edge of the ground cavity.
    NOTE: Absolute cleanliness is necessary throughout this operation. All tools should be cleansed with Toluol. Hands must also be thoroughly cleaned to insure removal of natural skin oils.
  2. MIX EQUAL AMOUNTS of the DUNLINE® Rubber Patch Sheeting and Toluol. (Generally this is a small amount of both products, as a little bit goes a long way. Once the rubber dissolves, the viscosity should be about 500 centipoise, which is the equivalent of typical house paint.) When thoroughly dissolved, use the resulting cement or adhesive to paint the entire prepared cavity. After about 15 minutes, paint a second coat of adhesive onto the entire cavity surface being sure to cover the entire surface, including the lightly ground area around the cavity. Allow the cement to fully dry before proceeding (it will take approximately 20 minutes).
    NOTE: It takes our current Rubber Patching material about six hours to dissolve, thus it’s necessary to plan ahead. It’s beneficial to agitate the solution periodically to expedite the process. If, after six hours the rubber patch material hasn’t dissolved, then the patching material has likely passed its shelf life and should be replaced with a fresh sheet.
  3. Cut pieces of patching material to conform to both the length and width of the cavity. Using the 1/4 inch (6 mm) diameter steel rod, carefully press each piece (one at a time) into the cavity. Be very careful to remove all air bubbles or trapped air. Continue this operation using as many strips as necessary to fill the cavity to about 1/8-inch (3 mm) above the level of the surrounding rubber belt.
    NOTE: To insure the best adhesion possible, it’s recommended to paint each strip lightly with the cement. Don’t go overboard, but apply only a very thin coating.
  4. Sprinkle the surface lightly with talc and place a square of Aluminum foil or Teflon coated fiberglass over the patched area.
  5. Set the thermostat and heat the shoe or iron to a minimum temperature of 220° F (104° C) and a maximum temperature of 240° F (115° C); place the shoe over the patched area and attach it in place using a weight or clamp load of about 100 lbs. (45 kgs.)
    NOTE: We recommend not placing the heated shoe on the blanket until it reaches a minimum of 200° F (93° C). Be sure that the heated shoe continues to heat up to the 220-240° F (104 -115° C) range if the shoe is applied at 200° F (93° C).
  6. Two (2) hours minimum curing time is recommended for a cavity depth of up to 1/4-inch (6 mm). An additional hour cure time is recommended for each additional 1/4 inch (6 mm) of depth.
  7. When the necessary cure time has passed, shut off the current to the electrically heated shoe; remove the shoe from the patched area and allow a few hours for cooling of the patch.
  8. Carefully remove any excess rubber from the patch being careful not to go below the level of the belt surface. A disc or belt sander may be used for this purpose; 60 to 80 grit abrasive is suitable.
  9. It is usually necessary to regrind the belt surface to achieve uniformity. If the patch is outside of the cloth line, this may not be necessary.
  10. The patch hardness should be about 40° Shore “A”.