Pressure-determined blowdown period for each of multiple, commonly

Abstract

A curing press for tires, commonly manifolded to other curing presses in a curing room, are operated with a minimum blowdown time which is variable from one cycle of each press to another cycle. A first signal is generated by a pressure transducer ('PT') in pressure communication with the bladder(s) of each curing press; this first signal is compared to a second signal corresponding to a target pressure, which second signal is stored in a programmable controller ('PC'). The PC controls operation of the press, and is used to provide a variable blowdown period; how quickly this target in the PC is reached, is a function of the pressure in a common blowdown manifold for plural presses. Instead of setting a mean blowdown period arrived at by trial and error over years of operation in a particular curing room, and relying on a mechanical safety pressure switch to override the opening of the press if the pressure is too high at the end of the mean period set, the press is opened reliably and reproducibly when the target pressure is matched by the pressure in the bladder. The mechanical pressure switch is nevertheless necessary. But the reliance on the mechanical pressure safety switch is reduced only to those instances when there is (i) a power failure which wipes out the instructions of the PC, so that whether the press will open at any preset pressure is not predictable; and (ii) a failure of any valve which results in leakage of steam or water into the bladder.