Insulated runner system for plastic cap molds

Claim 1

A. A multiple molding machine for thermoplastic caps comprising a stationary portion and a movable portion in abutting surface relation with cap cavities and sprue channels cut into their abutting surfaces to form mold cavities, b. said stationary portion comprising two metal blocks having abutting surfaces with runner channels cut into said surfaces, c. said runner channels branching from a common feed inlet aperture to a number of short runner branches of large diameter, all supplied in parallel from the common inlet aperture, d. each of said branches leading to an inlet of a separate spure channel cut into the abutting surfaces of said stationary and movable portions, e. each said sprue channel unit branching from said last inlet to a number of short sprue channels supplied in parallel through said inlet, f. each said short sprue channel supplying a number of cap cavities cut into said last abutting surfaces by means of tapered sprue leads running from said sprue channels to the top portion of said cap cavities, g. means for supplying thermoplastic material under pressure through said runner feed inlet aperture to said cap cavities, h. means for cooling said mold until the thermoplastic material in the sprue and cap cavities has hardened sufficiently to be ejected from the mold, i. said runner channels being of sufficiently large diameter so that the plastic material in them is hardened by said cooling only at a layer adjacent the surfaces of said channels, to form an insulating layer of plastic material of generally tube-like configuration at the center of which the plastic material remains at a sufficiently high temperature to flow through the runners to supply the sprue for successive cycles of operation.