Melting thermoplastic solid materials
An extruder for producing a thermoplastic material having a first and second portion, namely, an axially extending barrel; first and second screw conveyers co-axially disposed within said barrel, said second screw conveyer co-axially disposed within said first screw conveyer with relative rotatable single screw extruder movement between said first and second screw conveyers so as to define a first passage for conveying thermoplastic material from an input to a melt zone and then an output and define a second passage from said melt zone to said output; a connecting passage for communication between said first and second passages whereby a first portion of said thermoplastic melt is conveyed through said first passage to said output and another portion of said thermoplastic melt is conveyed through said connecting passage and through said second passage to said output; means for changing the characteristic of said portion; means for merging said first and second portions together.
Various devices and methods have heretofore been disclosed which relate to sheet production extruder for melting thermoplastic solid materials introduced into an input end, heated in a heated zone and then extruded through an output. A variety of these extruders exist including screw conveyers which are disposed for rotational movement within a barrel. Some of these screw conveyers include a first and second screw conveyer which are co-axially disposed in the barrel where one of said screw conveyers is disposed co-axially within the other screw conveyer.
The apparatus including a barrel having a screw conveyer therein defining a channel for conveying the material downstream as the material is melted within the channel and a passage communicating with the channel at a downstream location and an upstream location, the locations being chosen such that the unmelted solids enter the passage at the downstream location and are carried through the passage in an upstream direction by passing the channel, to be reintroduced into the channel at the upstream location.