Die heating for hydraulic presses used to be a matter of low-voltage electrical elements (48-50 volts). Where dies were rather small in relation to the press inter-column clearance, that was, actually, quite an effective low-energy solution. Yet things change and the market has changed radically. Demand has undergone sweeping change and, more and more, the ceramic industry has had to provide solutions for large-size tiles, which mean larger presses and, of course, larger dies, which, in turn, need more energy to heat them.
As the laws of electrical engineering clearly state, supplying lots of low-voltage power requires large-diameter wiring, which offers poor flexibility and poor manageability. That problem appears all the more greater if we consider the intrinsic nature of the production process: fixed to the upper part of the press, the die is removed at each pressing cycle; this means the wiring is subject to a degree of movement and tension that requires great flexibility. That problem was beginning to make itself felt on installed production lines with frequent breakdowns caused by cable rigidity - and it is a problem that has successfully been solved by Sacmi simply yet reliably: a machine able to heat the dies using standard factory main power voltage, between 380 and 400 volts. In this case, given the high power, wiring of large cross-diameter is no longer required, also making it easier to apply rapid connectors and make gains in terms of both efficiency and safety during die changeovers as well. Note also that the absence of any transformers on the press reduces consumption by 3-5% (because of transformation efficiency) and also cuts costs in that there is no need to supply transformers and thick wiring. Moreover all the electrical wiring is routed inside the dies in deep-set cavities, giving a more streamlined, ‘aesthetic’ look that prevents the problems so typical of the old-style external wiring (i.e. damage, build up of dust and difficult maintenance).
Sacmi has also had a good look into the second key problem with large dies: they do, in fact, need to be heated uniformly, something that is difficult to achieve owing to the different thermal conditions that exist in different areas of the die during production. For example, the temperature difference between the front and the rear of the die can be significant and that difference can’t be solved using traditional techniques because the two sides of the die cannot be controlled independently.
Not any longer though: Sacmi’s new high voltage heating system allows independent adjustment of up to 16 different die zones! This, Sacmi believes, constitutes an optimal solution to the temperature distribution problem: the system modulates the electrical current to the various die parts automatically according to the thermal conditions that exist within them at any given moment. These variables are, of course, under the control of the press operator, who can manage them as required.