Copper Alloy Molds: The Plastic Industry's Best Kept Secret

The main function of an injection mold, beside defining a part's shape, is to remove heat from the plastic as quickly as possible. The mold should be thought of as a heat transfer device much like the automobile radiator shown above. The faster the mold can transfer heat out of the molten plastic and solidify it, the faster the mold can be run. Reduced cycle time equates to reduced manufacturing cost. This is where copper alloys outperform other metals used for molds. Copper alloys provide the best combination of high thermal conductivity and hardness for molds used in the plastic industry today. As seen in the Comparison of Mold Alloy Properties Table, hardness and conductivity vary over a range for each alloy system-steel, aluminum or copper. Copper alloys have thermal conductivities 3 to 9 times greater than the commonly used Type 420 stainless steel.

Copper Alloy Molds

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ANTEC Reports

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Bronzes are unquestionably the most versatile class of bearing materials, offering a broad range of properties from a wide selection of alloys and compositions.

The high thermal conductivity of copper alloys makes them ideal materials for the injection mold sprue bushing and runner bars.

In North America two injection mold nozzle and sprue bushing radii are used, 1/2 and 3/4 inch. To insure proper fit up, the nozzle radius is nominal -.015 inch, while the sprue radius is nominal +. 015 inch, required tolerances to use.

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