Method and apparatus for heating plastic sheet material

摘要

Apparatus is disclosed for heating a plurality of sheets of plastic material between adjacent ones of a plurality of vertically stacked and individually heated platens. The platens are vertically displaceable together and relative to one another, and any two vertically adjacent platens are vertically separable relative to a fixed horizontal pass line to facilitate removing a heated plastic sheet from between the platens and introducing a plastic sheet to be heated therebetween. Vertical separation is achieved by latching the upper one of two adjacent platens in a fixed holding position above the pass line and lowering the lower one of the two platens and any other platens of the stack therebeneath to position the upper surface of the lowered platen at the pass line. Sheet discharge and feed mechanisms are then operable respectively to remove a heated sheet from the lower platen and introduce a sheet to be heated onto the lower platen. In a preferred mode of operation, plastic sheets to be heated are sequentially introduced betweem adjacent ones of the platens from the top of the stack to the bottom thereof and are thereafter removed from between the platens in the same sequence, the elapsed time between introduction and removal providing the required soak time for preparing the plastic sheets for a forming or shaping operation such as in a press.