Sprue bushing assembly and method of making same

A method of manufacturing an internally heated sprue bushing assembly which includes a unitary bushing casing-core element having an integral outer side wall, end wall and elongate inner core, said elongate inner core axially extending within the bushing casing and including a melt runner passage therein which is in flow communication with an inlet and an outlet of said sprue bushing assembly, and heating means surrounding said elongate inner core, said method comprising the steps of:

• shaping a metal blank to define a generally cylindrical main body portion of a bushing casing;
• forming an annular cavity in said main body portion to define the axially extending elongate inner core, the annular cavity extending from a first end of the main body portion of the bushing casing and terminating within said bushing casing inwardly of a second end of said main body portion to provide a unitary bushing casing-core element having an integral outer side wall, end wall and elongate inner core;
• inserting a heating means within said annular cavity in surrounding relation to said elongate inner core, said heating means including at least one preformed electrically non-conductive sleeve sized to be received on said elongate inner core and to occupy only a portion of said annular cavity;
• filling the remainder of said annular cavity with a particulate refractory material;
• compacting said particulate refractory material into a unified mass which, together with said heating means, fully occupies said annular cavity of said bushing casing-core element, the unified mass of refractory material and heating means comprising a heater-bushing blank assembly;
• and
• forming a melt runner passage in said elongate inner core, said melt runner passage being interposed between an inlet and an outlet in the finished sprue bushing assembly.