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50 MoldMaking Technology July 2015 Pg. 5 Mold Components Mold Components 50 MoldMaking Technology July 2015 FOR MORE INFORMATION: Hasco America Inc. / 877-427-2662 info.america@hasco.com / hasco.com Fundamentals of an Optimal Cooling System By Brenda Clark From specialized cooling component materials and conformal cooling inserts to standard machining practices employing new mold components, mold cooling has evolved and increased in efficiency in recent years. Historically, mold cooling systems were designed to circulate water or other media through the base plates, but not necessarily within the cavities. Newer technology creates circulation throughout the mold plates and cavities. Three keys to establishing the most efficient mold cooling process possible and producing quality products are: 1) Keep the cooling system a proper distance from the parting line and the molded part, 2) make sure the cooling line diameter is large enough to overcome the convection of the plastic material tem- perature into the surrounding steel, and 3) use turbulent flow to pick up the maximum amount of heat possible from the steel. There are numerous products available to help you accom- plish the proper cooling setup in your mold design. Traditional cooling components include baffles, bubblers, heat pipes or cooling pipes, spiral cooling cores, standard O-rings, and diverter plugs. More recent advances include conformal cooling inserts, specialized O-ring-type diverters, and flexible cooling lines that are installed into a milled channel and used with a copper paste for improved heat transfer. New mold plate cooling technology also exists that allows cooling lines to cross each other on the same plane. This enables the cooling lines to surround all four sides of a cavity or core, providing even temperature distribution throughout the system without the expense of additional machining. This makes it now possible to achieve cooling flow not only that completely sur- rounds each cavity and core, but also on a single level or plane within a mold base plate or insert. Multiple levels with thicker plates or higher die heights are not necessary. Gundrilled mold plate cooling lines are machined on single and multiple levels to achieve the desired cooling within the mold assembly. Waterline pitch locations along the plane view should be between three and five times the cooling line diameter, with a distance of one to two times the cooling line diameter from the parting line to the first level and the same distance between each additional level. This results in additional steel requirements for the plate thickness and increases overall mold height. Diverters can also be installed on different levels to help the cooling media move in specific directions through the mold base and cool the system properly. Mold cooling lines in the mold base plates generally are 5, 8 and 12 mm (5/16, 7/16 and 9/16 inch) in diameter. Another critical consideration is that the distance between the cooling lines and the mold core wall or insert split should never be less than 3.18 mm (0.125 inch). A thin wall condition between the insert split lines and the cooling lines could jeopardize the life of the mold. To overcome temperature increases and help with cooling and curing of molded products, heat must transfer from the mold steel into the cooling medium or from the mold- ing plastic to the steel. There are two forms of heat transfer cal- culation: conduction, or transfer from plastic to metal material, and convection, or transfer from steel to the cooling medium. Both are calculated in British thermal units (Btu), or the amount of energy needed to cool or heat 1 pound of water by 1°F. Traditional mold design cooling formulas are now integrated within most cooling analysis design software, which works on these same principles and calculations, along with 3D design in finite element data. Of course, the specific mold and molding materials being used will dictate the cooling requirements of any particular molding job. Cooling system designers must identify not only the steel that will be used for the mold plates and inserts, but also the plastic material to be processed and the part geometry. They also should investigate new mold components that can minimize plate thickness, decrease hot spots in cavities and cores, and reduce machining time and costs. This will help achieve an opti- mized cooling cycle time for each application. CONTRIBUTOR Brenda Clark is an engineering manager for Hasco America Inc. Figure courtesy of Hasco GmbH. Cooling analysis software uses 3D data in calculations. Pages 37 to 50