Extruder, or extruder-like melting apparatus

Claim 1

An extruder screw comprising a core and a thread thereon having a trailing edge and a leading edge with one of said edges conforming to a substantially uniform pitch throughout the length of the screw, said thread and said core defining a feed section and melting section and a metering section; said thread and core being shaped to define a first channel through said feed section and a second channel through said metering section, and a primary channel and a secondary channel extending coextensively through said melting section, said primary channel being of uniform width, contiguous with said first channel, and progressively decreasing in cross section to insignificance in said melting section by decrease in depth as measured in the radial direction of the screw; said thread having a wider part extending from the junction of the first channel and the primary channel and throughout the melting section, said primary channel being correspondingly reduced in width and cross section at said junction relative to said first channel; said secondary channel being defined by a recess in said wider part extending substantially the full length of the melting section, said secondAry channel merging with said second channel and progressively increasing from insignificance to a cross section to at least that of said second channel; said recess dividing said wider part of the thread into a fullradius portion along the trailing edge and a thread-like dam along the leading edge of the thread at less radius than said full-radius portion, said secondary channel beginning at full thread radius and extending progressively at substantially uniformly gradual reduction in radius in accordance with increase in core radius adjacently within the primary channel, said primary channel gradually and substantially uniformly increasing in radius to its downstream end to the full radius of the thread; said dam being shorter than said full-radius thread portion with its length located between the ends of the full-radius thread portion, said dam beginning in an area of the secondary channel adjacently downstream from its upstream terminus at a point where the radius of the secondary channel has decreased to that of the dam and ending in an area of the primary channel adjacently upstream from its downstream terminus at a point where the radius of the primary channel has increased to that of the dam.