Method for producing a drum type container with air cushion

Claim 1

In the method of producing a drum container of large capacity formed of a drum forming shell of structurally strong material open at the upper end and closed at the bottom end by a bottom wall, and an inner container of flexible thin plastic joined at its upper end portion about the upper rim of the shell, dimensioned to have a length corresponding to the length of the shell so that the bottom end will rest upon the bottom wall of the shell, and a diameter less than the diameter of the shell to provide an annular space between the outer side walls of the plastic container and the inner side walls of the shell to define an air cushion in between, the steps of positioning the cylindrical outer drum shell, while open at the top and closed at the bottom, in a frame member which engages the outer walls of the shell in sealing relation, heating to the stretchable stage a film of thermoplastic material dimensioned to extend across the open top end of the shell and for a distance beyond, effecting a sealing engagement between the portion of the film extending between the open end of the shell and the frame, drawing a vacuum in the space between the interior of the shell and the heated film to stretch the film by vacuum forming into the interior of the shell and towards the walls thereof until the film just engages the walls without bonding thereto and about the upper rim of the shell, terminating the vacuum drawing while the film material is still above its stretchable stage, rapidly cooling the portions of the film stretched about the upper rim of the shell and in engagement with the bottom wall while the remainder of the film is still in the stretchable stage, and allowing the remainder of the film to cool down to set stage with corresponding shrinkage in the circumferential direction to form an annular air space between the outer walls of the film and the side walls of the shell to function as an air cushion.