Abstract An apparatus is disclosed for continuously producing glass fiber reinforced thermoplastic compositions by extrusion techniques whereby surging is minimized or substantially eliminated and products having good appearance and uniformity may be obtained. A blended mixture of glass fibers and thermoplastic resin in divided form are fed and processed through an extruder equipped with a multi-flight screw which provides for two stages, each state including a feed zone, transition zone and metering zone and wherein the compression ratio in the first stage is in the range of about 3:1 to 5:1, the compression ratio in the second stage is in the range of about 1.5:1 to about 3.5:1, and the ratio between the flight depth of the screw in the second stage feed zone and the flight depth of the screw in the first stage feed zone is in the range of about 1:1.25 to about 1:2.5. The mixture is continuously extruded under the above conditions, cooled to solidification, and subdivided into the desired size. The resulting compositions are particularly suitable for molding operations.
An apparatus according to claim 1 wherein the multi-flight extruder screw is of constant flight pitch throughout its length.
Claim 2
Dependent Claim
296 words
An apparatus according to claim 2 wherein, in sequence, the first stage feed zone is defined by a portion of the extruder screw wherein the flight depth is substantially constant at a value H1, the first stage transition zone is defined by the next adjacent portion of the extruder screw wherein the flight depth gradually decreases from a value H1 to a value H11, the first stage metering zone is defined by the next adjacent portion of the extruder screw wherein the flight depth is substantially constant at a value H11, the relationship between flight depth H1 and flight depth H11 being such that a compression ratio is provided in the range of about 3:1 to about 5:1, the juncture between the first stage metering zone and the second stage feed zone being defined by the next adjacent portion of the extruder screw wherein the flight depth increases from a value H11 to a value H2, the relationship between the flight depth H2 to the flight depth H1 being such that the ratio of H2:H1 is in the range of about 1:1.25 to about 1:2.5, the second stage feed zone being defined by the next adjacent portion of the extruder screw wherein the flight depth is substantially constant at a value H2, the second stage transition zone being defined by the next adjacent portion of the extruder screw wherein the flight depth gradually decreases from a value H2 to a value H22, the second stage Metering zone being defined by the next adjacent portion of the extruder screw wherein the flight depth is substantially constant at a value H22, the relationship between flight depth H2 and flight depth H22 being such that a compression ratio is provided in the range of about 1.5:1 to about 3.5:1.
Claim 3
Dependent Claim
75 words
an apparatus according to claim 3 wherein the relationship between flight depth H1 and flight depth H11 is such that a compression ratio is provided in the range of about 3.5:1 to about 4.5:1, the relationship between flight depth H2 and flight depth H22 is such that a compression ratio is provided in the range of about 1.5:1 to about 3:1, and the ratio of H2:H1 is in the range of about 1:1.75 to 1:2.
Claim 4
Dependent Claim
29 words
An apparatus according to claim 1 wherein the extruder has a die plate mounted adjacent the second stage metering zone, said die plate having at least one extrusion orifice.
Claim 5
Dependent Claim
16 words
An apparatus according to claim 5 wherein the extrusion orifice is about one-eighth inch in diameter.
Claim 6
Dependent Claim
26 words
An apparatus according to claim 1 wherein there is additionally provided a means for cooling the extrudate and a means for subdividing the extrudate into pieces.