Plastic injector with heat control

The improvement in a plastic injector apparatus comprising, an axially extending barrel having a bore extending axially therethrough, and having a radial passage formed therein at the back end thereof for introducing solid plastic resin into said bore, an injection nozzle for injecting into receiving means amounts of melted resin accumulated in the front end of said bore, an axially reciprocable screw received in the rear opening of said bore and rotatable therein to work said introduced resin so as to heat it while advancing it forwards to said front end of said bore, and a plurality of heater bands ringing and axially spaced over the length of said barrel to provide supplemental heat for heating said resin, in which said improvement comprises:

• annular thermal insulating means comprising insulative material insulating against conductive and convective heat flow and disposed around and outside first heater bands ringing a rear section of the length of said barrel to impede radially outward flow of heat from said first bands, said insulating means being absent forward of said rear section, and annular uninsulating enclosure means disposed around and outside second heater bands ringing a forward section of the length of said barrel, said uninsulated enclosure means comprising at least part of an uninsulating cover containing and surrounding at least said forward section and having heat-absorptive and heat reflective surfaces registering with said forward section and disposed on, respectively, the inside and outside of said cover to promote radially outward flow of heat from said second heater bands through said cover.