Apparatus for plasticizing granular synthetic plastic materials

Claim 1

Apparatus for the plasticizing and melting of synthetic plastic materials, particularly granular materials which, when plasticized, are introduced into the mold of an injection molding machine, comprising an elongated heatable cylinder having a constant inner diameter, an intake end provided with an inlet opening, a discharge end, and at least one gas-discharging aperture communicating with the surrounding atmosphere and disposed intermediate said opening and said discharge end; adjustable feeding means arranged to deliver metered quantities of granular material into said cylinder by way of said opening; and a feed screw rotatably mounted in said cylinder and including a material advancing section disposed in the region of said opening and having a first helical thread, a first material densifying section between said advancing section and said aperture, a pressure relaxing section disposed in the region of said aperture and having a second helical thread defining a groove of a depth exceeding the depth of the groove defined by said first thread by up to 20 percent, a second material densifying section between said pressure relaxing section and said discharge end, and a collar which is free of threads and is disposed between said first densifying section and said pressure relaxing section, said cylinder having an internal surface defining with said collar an annular shearing gap through which densified material passes from the cylinder portion surrounding said first densifying section into the cylinder portion surrounding said pressure relaxing section, said feed screw being cyclically movable axially of said cylinder between front and rear end positions through a distance which at most equals approximately 3D wherein D is the inner diameter of said cylinder and said aperture being provided in that portion of said cylinder which surrounds the rear third of said pressure relaxing section in the front end position of said feed screw, the axial length of said pressure relaxing section being between 1.6 and 2 times the extent of movement of said feed screw between said end positions thereof and between 5D and 6D.