Method of making a molded internally threaded closure

Abstract

A method of making a closure for a container is accomplished by providing a unitary mold with a mold cavity therein having vertically extending ribs and a rotatable and linearly movable threaded core element is received within the cavity. A formable plastic material is placed within the cavity and the core element is received within the cavity. Alternatively, the formable plastic material may be injected into the mold cavity. Upon contacting the formable plastic material with the core element the plastic material is forced around the outer surface of the core element and the inner surface of the cavity forming a closure with an internal thread and externally extending vertical ribs. The closure and the core element are backed out of the cavity wherein the core element is moved linearly and rotatably, but rotation of the closure is prevented. Once the core element is engaged with the internal threads of the closure only at the terminating end of the external threads of the core element, the article is completely removed from the cavity mold. Upon removal from the cavity mold, the weight of the closure in combination with gravity enables the closure to fall away from the core element. Alternatively, a concentric stripping ring or an ejector pin is used to cause the closure to fall away from the core element.