Bottle having ribbed bottom

Abstract

A method of and apparatus for making a concave bottom on a blown thermoplastic container, and a container having such a bottom. A blowable pre-form is initially expanded against a composite mold surface defined by the end faces of a plurality of concentric tubes surrounding a central actuating rod. The rod and the tubes are initially telescopically positioned to define a composite concave surface, so that a first convex bottom is blown. Subsequently, the rod and tubes are actuated telescopically to progressively invert the convex bottom to a concave shape. The end faces of the tubes may be grooved to define reinforcing ribs in the concave bottom wall, if desired. The container has a concave bottom wall of improved resistance to deformation under internal pressure. This is accomplished by forming a support ring at the juncture of a pair of oppositely directed inner and outer bottom walls, the juncture of the walls defining an included angle which is equal to or less than 90.degree. and the internal radius of the support ring is equal to or less than four times the thickness of the walls.

Dependencies are inferred from the claim text.