| 摘要 |
Cupola-shaped plastic pieces with a flat, unwarped rim can be produced from an equally large blank without trimming of the rim, by heating an optionally preheated plastic sheet by radiant heat. The radiant heat acts only on the area surrounded by the rim area until the area exposed to the radiant heat has reached a temperature just below the softening temperature of the plastic. Up to this point, the rim is left without tension, or at most a low clamping pressure is applied which allows a thermal movement of the rim. Then, but before the beginning of the forming, the clamping pressure is increased so that the rim is held tight. The radiation activity continues until the area exposed to the radiant heat has exceeded the softening temperature, the radiation activity is then stopped, and the area heated to the forming temperature is formed. The formed piece is then allowed to cool to just below the softening temperature, after which the clamping force acting on the rim is eliminated or so reduced that it allows contraction movements, and the cooling continues.
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