Simple Solutions That Work! Issue 12

T he die should be heated to 600° F (315° C), and care must be taken to heat the die uniformly. A magnetic thermometer, optical pyrometer, or a temple stick should be used to check the temperature periodically. The die should dry- ice blasted to remove any soot that developed. Spray the die lightly with water. This will create a porous oxide film on the die, which will provide a good surface for the die coating to bond. The water spray also cools the die to the desired coating application temperature, 350°-400° F (75°- 200° C). If the die is too hot, the rapidly expanding water vapor front moving away from the die will cause a phenomenon known as “kick back,” and very little coating will adhere to the die. Even the coating that does adhere will not be properly bonded. If the die is too cold the coating might run, resulting in an uneven surface. Extend the ejector pins. While the die is still above 300° F (150° C), spray the extended ends of the ejector pins with HALLCoat986 or comparable graphite die coating spray. Retract the ejector pins back into the die and dry-ice blast the die face to remove all graphite die coating from the die face, as the primer coat will not adhere to the graphite. Now the die is ready to prime. The purpose of the primer coat is to create the best possible adherence of the coating to the die. This occurs because very diluted sodium-silicate solutions allow bonds to form that are more parallel to the die face. This structure forms a stronger bond, which is more resistant to wear. In contrast, high sodium-silicate solutions create bonds that are perpendicular to the die face and can be sheared away. Care must be taken not to over dilute the primer coating as sufficient sodium silicate must be present generate the bond. Once the primer is applied, the main coating can be applied at higher concentrations. Thoroughly stir the HALLCoat 520RH die coating or comparable coating. Transfer the mixed coating into the spray gun can and dilute 6:1 with clean water. Spray the entire cavity, including gates, risers, and pouring cup, with a light primer coat. Avoid spaying the parting line. The next step is die coating. Place a small amount of the die coating in JOHN HALL President CMH MANUFACTURING COMPANY ARTICLE TAKEAWAYS: • Proper heating of dies • Correct preparing for coating the die 55 BACK TO BASICS DIE HEATING & COATING Continued on next page