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Mold Material 40 MoldMaking Technology August 2015 CONTRIBUTOR Tom Schade is executive vice president of International Mold Steel. FOR MORE INFORMATION: International Mold Steel 800-625-6653 / tos@imsteel.com / imsteel.com tive wire harness clips with blind holes to high-pressure PVC elbows that had reduced structural integrity due to serious burn problems. Retrofitting enhanced venting materials into the molds solved each of these problems. Still, there has been no mold design and molding revolution. Why? Probably because anything published about proper vent- ing techniques includes a lot of conventional wisdom, which creates a sense of risk associated with trying something new and a sense of safety in doing what has always been done. For example, conventional wisdom dictated 30 percent of the part- ing line be reserved for vents, vent dimensions of 0.0005- to 0.003-inch-deep by 0.0625- to 0.5000-inch-wide (depend- ing on where the resins flashes), extremities of the cavity be vented, vents be the last area of the mold to fill, grind flats on ejector pins, etc. As long as conventional wisdom was the guideline on an original mold design, new venting materials would only be used to retrofit an existing mold to solve the worst problems. Although retrofitting is not difficult—a simple installation of the material in the core side, close to the problem area and opening the back side to the atmosphere—oftentimes, water- lines or other obstructions prevent placement of the material in the right spot. Using the material in the original design and build of the mold enables it to be installed in the most effec- Facts about Enhanced Venting Material • The material's porosity yields a maximum polish of 1,000 grit. It will fog clear resins. • Milling the insert will close the pores. They can be reopened 100 percent by EDM or 90 percent by polishing. Make sure to reopen the side into which the gas goes as well as the side through which gas escapes. • Textured enhanced venting materials eliminate gas trapped at the bot- tom of the valleys, creating sharper defnition and dramatically lowering gloss levels. Also, if this textured material is inserted in a textured mold steel, it will always be noticeable. Sometimes this feature is used to high- light logos or instructions on a part, but be aware that you will never get a match between the insert and the mold. • Making two interchangeable inserts is a strategy for mold maintenance, so one is in service while the other is cleaned in an acetone bath. Image courtesy of International Mold Steel. The use of a textured cavity with enhanced venting material reduces gloss (right) compared to a P20 cavity (left). tive area(s). It makes me wonder how many molders still are producing substandard parts because they are fighting venting problems that would not exist if they had designed the original mold using an enhanced venting steel. The advantage of using an enhanced venting steel in an origi- nal installation was the basis of collaborative experiment among an automotive OEM, a molder and a mold builder. The chal- lenge was eliminating flow lines and haloing around the edges of automotive texture standards plaques. The standard mold design for these 8.5-by-11-by-0.125-inch-thick plaques required a full edge gate (10 by 0.060 inches) and land vents 0.5-inch wide by 0.002-inch deep located every 0.5 inch around the perimeter (50 percent of the parting line). A new cavity was built with the same gate, but the only venting was a 10.5-inch piece of porous venting steel opposite the gate. Parts were run side by side to ensure identical temperatures for the mold, resin and machine. The results of using porous metal inserts and no additional venting were chronic flow lines disappeared, ghosting at the edge of the plaques was eliminated, virtual elimination of material splay, reduced injection pressure, increased injection speed, 10°F decrease in nozzle temperature, nearly 4-percent reduction in shot size, and appropriate gloss and appearance. Still, there has been no revolution in the industry. However, we'll continue the fight with education on how to use enhanced venting steels from original part and mold design. Maybe a design contest would work, asking for the most cre- ative solution to a molding challenge using porous metal in the original mold design. First prize could be 5 pounds of vent- ing steel. Maybe this will get the revolution started. Venting issues in a console mold were solved with the use of enhanced venting material and an air line for gas to escape on the core side of the mold. FIGURE 5 Enhanced Venting Material Installed Here Trapped Gas Vent Line To Atmosphere