Vacuum forming mould and stamping ring for thermoplast beakers - hold very thin sheet and provide airtight seal before stamping

In a moulding and puching device for hot vacuum deep-drawing of beakers from thermoplastics sheet, the sheet is stretched across the mouth of the mould, held there by a spring-loaded clamping device to form an airtight seal around the lip of the mould and is finally cut after moulding. The clamping device for the thermoplastics sheet is made up of the end face of the mould and a spring-loaded annular piston biased downwards by its spring as a holding-down device to clamp the sheet against the edge, this piston is guided inside the cylindrical chamber of the cutting tool the internal dia, to the cutting edge of this tool and thus the external dia. of the piston holding-down device being greater than the internal dia. of the mould at its mouth. A highly leaktight seal is formed which is of especial advantage in the handling of very thin sheets, where there is a risk of them becoming cut before the deep-drawing action takes place.