In a plasticizing assembly for use in an injection molding machine, the assembly including
- a plasticizing cylinder having a cylinder section and a nozzle section communicating with said cylinder section, said nozzle section having a nozzle orifice defining an injection axis, and clamping means for holding said cylinder and nozzle sections together in axial alignment,
- heating means for heating plastic material in said plasticizing cylinder,
- a feed screw having forward and rear ends and being rotatably and axially movably mounted in said plasticizing cylinder and being axially reciprocable therein between predetermined rearmost and foremost positions and being operable to feed plastic material,
- a back flow valve mounted on said feed screw at said forward end,
- a carrier block;
- a rear end of said cylinder section being detachably mounted in said carrier block,
- a skeleton surrounding said plasticizing cylinder and at least part of said heating means;
- said skeleton extending between a location radially aligned with said back flow valve when said feed screw is in said foremost position and a location radially aligned with a forward end of said carrier block, said skeleton including skeleton elements radially aligned with said heating means and serving to protect said plasticizing cylinder and said heating means and to support said plasticizing cylinder,
- a first needle-guiding bore formed in said nozzle section and being inclined relative to said injection axis and opening into said nozzle orifice,
- a valve needle longitudinally slidably mounted in said first needle-guiding bore and being operable to open and close said nozzle orifice,
- a valve-actuating cylinder adjacent to said carrier block and extending in a direction substantially parallel to said injection axis, and
- a force-transmitting linkage to transmit force from said valve-actuating cylinder to said valve needle to operate said valve needle;
- said force-transmitting linkage comprising a rear link longitudinally aligned with and longitudinally movable by said valve-actuating cylinder, a forward link longitudinally aligned with said valve needle and being inclined to said injection axis and being operable to longitudinally move said valve needle, and a motion-deflecting lever pivoted on a first axis by supporting pivot means radially aligned with said heating means and by additional pivot means being pivoted on at least one second axis spaced from said first axis to said rear and forward links, said lever being arranged to transform a movement along said injection axis imparted by said valve-actuating cylinder to said rear link into a longitudinal movement of said forward link and said valve needle,
- the improvement wherein
- said supporting pivot means are radially aligned with and radially outwardly spaced from said heating means with respect to said injection axis and are mounted on said skeleton elements,
- said motion-deflecting lever and said supporting pivot means are entirely disposed inside said skeleton,
- a second needle-guiding bore extends in said cylinder section as a continuation of said first needle-guiding bore;
- said second needle-guiding bore opening on an outside surface of said cylinder section at a location radially aligned with said back flow valve when said feed screw is in said foremost position;
- said valve needle having a length portion extending in said second needle-guiding bore;
- said second needle-guiding bore having a diameter larger than a diameter of said length portion for defining a radial clearance between a wall of said second needle-guiding bore and said valve needle;
- and
- said valve needle is stationarily connected to said forward link and extends out of said second needle-guiding bore to a location radially aligned with said feed screw when said feed screw is in said foremost position.