Shaft seal

In an apparatus which includes a housing having a passage extending from the exterior of the housing to an inlet opening within the interior of the housing through which dry particulate thermoplastic material enters the interior of said housing, a shaft rotatably supported in said housing and extending through said passage, and a seal between said shaft and a surface of said passage for limiting flow of the particulate material through said passage along said shaft, the improvement comprising

• the seal including a sleeve surrounding and secured to the shaft to rotate therewith, said sleeve extending along said surface of the passage, and having in its outer surface a variable pitch thread with the threads being directed toward the inlet opening within the housing so as to direct most of the particulate material entering the threads in a direction back into the housing upon rotation of the shaft but allowing a small amount of material to flow along the passage in a direction opposite to the interior of the housing;
• the sleeve having a cylindrical portion extending along the surface of the passage from the threads to the exterior of the housing and being slightly spaced from said surface of the passage;
• and
• heat control means surrounding and being remote from said space between the cylindrical portion of the sleeve and the surface of the passage to maintain the small amount of material which flows into the space in a molten condition.