Thermoforming tool for production of beaker-shaped products in plastic film has a pre-stretcher plug and an additional stretcher which moves inside the pre-stretcher

摘要

Products are formed by upper(6) and lower(8) tools, the lower one having a forming cavity(13) and the upper one a pre-stretching tool(18). At the end of the pre-stretching tool(18) facing the cavity there is an additional, coaxial, stretcher(24) which moves between two positions for an initial stretching of the plastic film(14). The end face of the additional stretcher is smaller than the end face of the pre-stretcher facing the cavity. The additional stretcher(24) is attached to the lower end of a shaft(26) guided in the pre-stretcher(18). The upper end of the shaft is connected to the lower end of a drive rod(32) passing through the pre-stretcher drive rod(20). Several pre-stretchers(18), each allocated to a forming cavity(13), may be arranged with the drive rods for each additional stretcher connected to a common stroking plate. At the upper end of the shaft(26) there is a piston section(28) which is guided in a chamber(29) inside the pre-stretcher(18) and the shaft passes through the lower end(30) of the chamber. Operation of the additional stretcher may alternatively be effected by compressed air and/or vacuum which utilizes a channel in the pre-stretcher drive rod. The end face of the additional stretcher is convex.