Copper, in-kind, is the common element with the best thermal conductivity; silver and diamond are the only better conductivity elements.
This point makes copper to be an excellent choice for injection moulds, for which we need to remove heat of injected plastic to allow solidification.
Copper has very low mechanical features in his basic version anyway. Fortunately, metallurgy has developed alloys keeping most of conductivity arriving to obtain hardness closest to the steel one.
Relevant features for mold sector are high thermal conductivity, easy machining , high polishing, wear resistance from water and plastic additives and a good scraping resistance. They can be welded and coated to enlarge resistance or even make the separation of printed side easier.
Thanks to the thermal conductivity, which is higher from 2 to 10 times than one of tooling alloys, they can be used to remove hot points, to reduce deformation, to cancel defects and reduce cycle time. For example, a brass mould having a cooling cycle of less 60% (10 seconds instead of 25) remove more heat than a steel mould.
Resulting effect will be the best quality of the final pieces and improved productivity.
There are 4 copper alloys classes used on injection and blow moulding:
Born for sliding components like bushings and gibs on shipbuilding application, although it is the most competitive, it is even the most soft and with less conductivity between the alloys used for plastic moulds.
It was very used in the past, now it can be replaced with Formaplast 200 being with same hardness and price, it allows a relevant increase of conductivity.
Formaplast 160 is even an alternative to obtain hardness and conductivity.
Nichel bronze alloys
Mainly used in engineering areas, they have found application in plastic mould thanks to excellent machining and possibility to produce big thicknesses.
High costs and low conductivity make them to be replaced easily with FORMAPLAST 105LH or alloys beryllium free like Formaplast 200 and Formaplast 160.
Silicon copper alloys (CNS)
Since 1930 they developed and started to be well–known even with the name of “Corson bronzes” by his creator. Starting from the years 80, they have been used in plastic mould, especially when the introduction of new production system have allowed the constitution of chrome and nickel chrome silicuri, increasing hardness.
Formaplast 200 is the most used alloy because of its availability on big thicknesses, with high conductivity and a good compromise between hardness and price.
Since the last decade, above alloys have been further developed until the production of Formaplast 160 with hardness of 30 HRC and conductivity higher than copper-beryllium. Heat treatment is difficult in this case , so further thicknesses to be produced are limited.
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