Simple Solutions That Work! Issue 12

the spray pot. Dilute to a ratio of approximately 2:1. After diluting, place a small amount of coating in a Baume beaker and place a Baume gage in the beaker. The Baume reading should be between 22-26. Spray the entire cavity, gates, and riser, avoiding the parting face. Do not try to cover the cavity with one heavy coating. A gradual build-up of the coating is preferred over one heavy coat. The number of coats and the exact coating thickness will vary with the casting design and may vary within the die itself. Check the coating thickness with a Posi- Pen. A working profile should be developed for areas that require a heavier or thinner application of coating to aid solidification. A coating thickness of 10-20 mils is typical. After the coating has cured, excess coating should be removed from the parting line and core prints with a wire brush or brass scraper. The final step is to paint the gating risers, and pouring cup. A softer highly isolative coating is required, such as HALLCoat600, or equivalent. The coating should be brushed on the desired surfaces with a soft paint bush. The process should be repeated until the coating is the thickness of a dime. Isolated heavy sections in the die will require “trimming.” The next step is to remove or thin the coating in the areas that require rapid solidification. This can be done with a brass scraper, steel wool, or a wire brush mounted in a die grinder. After trimming, the exposed steel should be sprayed with HALLCoat986, or equivalent to prevent aluminum from welding to the steel die. Now, the die should be reheated to pouring temperature approximately 800° F. Once the coating procedure for a particular casting is finalized the method must be recorded for future reference. One method is to mark a sample casting with paint. In the attached photo, the unpainted areas have a standard coating, the blue painted areas are trimmed and coated with graphite coating, and the red painted runners and risers are coated with HALLCoat600 isolative coating or equivalent. Most commercial die coating materials are bonded by sodium silicate with various filler materials for their isolative, lubricating, or cosmetic qualities. Die coating is supplied in 5-gal. cans or 55-gal. drums. The coatings should be stored in their original covered containers with the lids firmly in place when not in use. Die coating should be stored in a dry place away from excessive heat or cold, or drastic temperature change. Ideal storage temperatures range from 50° -75° F (10°-25° C). Under no circumstances should the coating material be allowed to freeze, as subsequent thawing may not restore the coating to its original condition. Refer to the manufacturer’s instructions for additional storage information. Touching up a die while in use follows much the process as preparing a new die, but some extra rules must be used. Make sure any sheared or welded-on aluminum is removed before adding the touch-up coat. If the coating area is spalled, cracked, or blistered, be sure to remove it with sandpaper, steel wool, brass brush or brass scraper. PRODUCT DURABILITY INSULATION TEXTURE APPLICATION TYPICAL DILUTION* HC 500T High High Medium Textured Finish Insulation 1:2 to 1:3 HC 520 HD Medium High Medium Textured Finish Insulation 1:2 to 1:3 HC 520 RH High Medium Medium Textured Finish Insulation 1:2 to 1:3 HC 1204 Highest High Smooth Textured Finish Insulation 1:2 to 1:3 HC 600 Highest Medium Smooth Gates/Risers 1:1 Smooth Finish 1:3 Primer Coat 1:4 HC 411 Low Lowest Smooth Lubrication Release 1:8 HC 989 Medium Low Smooth Release 1:2 to 1:5 * Actual dilution ratios must be determined for each particular job. Contact: JOHN HALL jhall@cmhmfg.com 56