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moldmakingtechnology.com 21 For example, a moldmaker designed and built a 2 by 64 stack mold for a clo- sure, with a 38-millimeter major diam- eter thread and a height of 0.400 of an inch inside the cap, without calculating the actual cooling requirements for the mold. The part was a 3-gram polypro- pylene cap with wall thicknesses in the 0.040–0.050 of an inch range and with maximized cooling. The moldmaker pumped water through the mold at 275 gallons per minute. The moldmaker calculated the amount of water that was necessary to remove the heat from these caps and discovered that the required minimum coolant flow was closer to 50 gallons per minute. Much energy was wasted pumping the excess water through the mold at 225 gallons per minute. 4. Molded-in stresses. When the cooling rate is not the same on both sides of a molded part, the result is molded-in stress. For example, when using semi-crystalline materials, the slower cooling side will form larger crystals that shrink more than smaller crystals, which results in excessive The tamper-evident band in this part, which has thick and thin sections, barely shrank. If a steel-safe adjustment is an economical option, then this may not be a problem. Mold design is critical here. Ask this question: If the molded part is too large in the area with the thin-wall section, can a steel-safe adjustment be made economically? If not, then go back to the larger bubbler and the lower heat-transfer rate. With a little advanced planning at the design stage, a moldmaker can make both optimized and standard bubblers and interchange them as required. FOR MORE INFORMATION DZynSource, LLC / rhuber@dzynsource.com dzynsource.com / moldengineeringsoftware.com CONTRIBUTOR Rocky Huber is an engineering manager for Ivanhoe Tool & Die Co., LLC and owner of DZynSource, LLC. FIGURE 2 stress and warpage. Amorphous materials shrink more on the slower cooling side as well, and the corners of rectangular parts with sidewalls often cool last, which can cause parts to deform inward. 5. Gate freeze. When adding cooling to a cavity, sprue or gate insert, particularly with hot runner molds, moldmakers need to ensure that the cooling is appropriate, as the heated probe may not be able to supply enough heat to keep the gate open. The hot runner supplier can provide cooling recom- mendations and cooling design approval. The bottom line is that moldmakers must put more engi- neering into mold designs to avoid the added expense and problems of over-designing and under-designing molds. The key is properly calculating the required amount and location of cooling. Superior visibility is the new standard in automotive lens tooling. Finkl Steel produces the highest quality mold steel guaranteed to SPI A1 finish for enhanced plastic injection clarity. Headlights have improved, shouldn't your steel? www.finkl.com Chicago 800-DIE-BLOCK Composite 800-521-0420 Sorel 800-363-5540 (USA) 800-363-9484 (CAN) Steel for the Future