Thermoplastic container end for inertial spinwelding of thermoplastic

Abstract

A thermoplastic end (110), particularly a bottom, for a container which has upstanding paperboard sidewalls (112) and which is inertially spinwelded onto the paperboard sidewall for bonding. The end portion (110) has an annular groove (148) for snugly receiving the sidewall (112) and a wall configuration (136, 138, 140, 142 and 144) which minimizes the forces exerted on the bond which would tend to dislodge the end portion. The wall configuration is generally in the form of an inverted U-shape with a portion of an upstanding wall of the U forming a side of the annular groove. The end portion has strengthening ribs (122) positioned generally within the region of U-shape and additional radial ribs imparting strength and rigidity to the container end. The paperboard sidewall may be internally lined with a layer of thermoplastic material or may be unlined. During spinwelding, a sidewall supporting mandrel having an expansible engaging portion is inserted into the sidewall and subsequently expanded to define a cylindrical surface of a diameter equal to that of the specified internal diameter of the sidewall. A Teflon seating member at the end of the sidewall supporting mandrel establishes the depth to which the container end is inserted into the sidewall.