More Absorption, Less Masse
A considerable improvement in the quality of injection molded parts can be achieved through use of the Variotherm mold temperature control process. For instance, better replication of the surface is possible and the filling resistance reduced. To attain short cycle times, the corresponding regions of the mold must be heated very quickly. This is its now also possible with infrared radiation, even though the polished steel surfaces reflect the majority of the IR radiation. A remedy is provided by a newly developed mold temperature control concept in which the absorption of the cavity surface is increased through use of a special coating. In this way, heating rates of 10 to 13°C/s can be achieved - this is equivalent to the values that can be attained when using steam heating in conjunction with conformal mold temperature control.
Moreover, this mold temperature control concept, which was developed by Engel, heats a relatively small mass. During the heating phase, springs push the mold insert to be heated away from the cooled mold. This creates an air gap that thermally separates the heated insert from the cooled mold base.
Another variant allows the injection molding cycle to be accelerated even further. The insert to be heated is present in duplicate and – like an indexing platen in multi-material injection molding – is rotated out of the mold area. The radiant heater is located above the moving platen. This allows heating to occur during the molding cycle so that it does not contribute to the cycle time. Heating can then take place from the back of the insert, eliminating the need for the coating.