Nanjing GIANT Machinery Co.,Ltd.

In an extrusion apparatus for advancing and working thermoplastic material consisting of an extruder barrel, said barrel having central bore means extending longitudinally therethrough, said extruder barrel cooperative with said central bore means to define a wall along the full length of said barrel, a hopper on one end of said barrel communicating with said central bore, a die means on the other end of said barrel, feed screw means rotatably journaled in said central bore means, said feed screw having compressive flights for working and advancing thermoplastic material through said central bore means operative to provide a continuous compressive action on said material passing through said central bore means, said helical flights defining a compression stage therein, a plurality of spaced vent openings extending through said wall located along the length of said barrel wherein said spaced vents communicate said central bore means with atmosphere, each of said spaced vent openings having a vent screw with shallow flights rotatably journaled therein, and motive drive means connected to said vent screws for rotating said vent screws for advancing worked thermoplastic material back into said central bore means.

In the manufacture of thermoplastic materials, the mixer receives the plastic material in its hopper and delivers such materials to a rotor means located in the mixer barrel wherein the rotor means advances, mixes and works the plastic materials to produce a homogeneous mix for general further processing. The art of converting solid thermoplastic materials into a satisfactory mixed and flowing homogeneous melt without overheating or chemical degradation depends in part on the type of thermoplastic material being worked on as well as the type of design of single screw extruder or mixer used. During such mixing operation, it is essential to remove gases to obtain a high quality mix. Cost consideration requires efficient removal of gases otherwise the entrapped gases show up as porosity in the final product such as wire coating and transparent film.

Entrapped gases lower the effective output capacity of the mixer by as much as twenty percent. Heretofore, degassing, if available, consisted essentially of mere venting of the mixer housing as by vent holes which became plugged with the material being mixed and advanced in the barrel. The remedy for this situation consisted of drilling the vent holes on a timed basis which could result in damage to the mixing screw or housing. The present invention contemplates the use of a vent hole or a series of holes which house a rotating vent screw. There is sufficient clearance between the vent screw and the vent hole to permit the escape of gases. In addition, the gases are permitted to escape through the screw flight openings.