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摘要
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Processing equipment and parameters will highly influence the properties of long-fiberreinforced
injection-molded thermoplastic composites, leading to different fiber lengths and orientations.
Thus, maintaining fiber length during the injection molding process is always a big challenge
for engineers. This study uses long-glass-fiber-reinforced polypropylene with 25 mm fiber length
and a special-built novel injection molding machine with a three-barrel injection unit, including a
plasticizing screw, an injection plunger, and a packing plunger, to fabricate injection molding parts
while retaining long fiber length. This study also discusses the influence of process parameters,
such as back pressure, screw speed, melt temperature, and different flow paths, on the properties of
long-glass-fiber-reinforced composites. The experiment results show that a higher screw speed and
back pressure will reduce the fiber length in the injection-molded parts. However, using appropriate
parameter settings can maintain the fiber length to more than 10 mm. It was found that by increasing
the back pressure, the cross direction of the fiber orientation can be increased by up to 15% and the
air trap volume fraction can be decreased by up to 86%. Setting appropriate back pressure under a
low screw speed will increase the tensile strength. Finally, it was found that the single-edge-gate path
results in a higher tensile strength than that of the single-sprue-gate path due to the retainment of
longer fiber length in the injection-molded part. |
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