Study Of Complex Screw Structure On Melt Pressure Fluctuation In Polymer Extrusion

The effect of three kinds of novel complex screw on melt pressure and its fluctuation when extruding different polymer materials was studied, which are Maddock mixing section screw (A), Eagan mixing section-BM separation section screw (B) and Maddock mixing section-BM separation section screw (C) respectively. The effect of barrel gap depth and the compounding performance was studied either.In general, three kinds of novel complex screw, A, B and C, have the fluctuation of8%,23%and11%with screw rotation speed at40rpm, while those turn to13%,6%and9%with60rpm rotation rotation speed. The result is much more less than those of segment screw, which is225%at40rpm and356%at60rpm.Comparing with different screws, less melt pressure fluctuation means decling of average melt pressure at the same time. The average melt pressure is ranked B<A<C, and the result stays stable when changing polymer materials and screw rotation speeds. As a result, melting pressure of screw C decline least, leading to highest output. When extruding PP, melt pressure fluctuation of screw A is8%and13%at40rpm and60rpm respectively. Thus, screw A should be used at low rotation speed. However the situation turns to the oppsite side when using screw B, with23%at40rpm and only6%at60rpm. The performance of screw C turns out stable at defferent screw rotation speeds, with11%and9%melt pressure fluctuation at40rpm and60rpm respectively.To the degree of materials, Maddock mixing section-BM separation section screw (C) fits for extruding HDPE, LDPE and ABS most, with1.4%,4.2%and3.9%melt pressure fluctuation at40rpm rotation speed, while turns to1.8%,4.72%and4.7%at60rpm.When processing LLDPE and PP, Maddock mixing section screw (A) should be used at low screw rotation speed while Eagan mixing section-BM separation section screw (B) at high speed. However, three kinds of complex screw are all not fit for extruding PC.When the depth of barrier gap rises from0.4mm to0.8mm, the melt pressure fluctuation decline significantly, accompanyied by decline of average melt pressure at the same time. For instance, the melt pressure fluctuation declines from7.3%to2.6%at40rpm and8.9%to2.3%when extruding LLDPE. SEM result shows that the improved screw performs well in distributing materials. There’s no sign of CaCO3assembling in all ratios of CaCO3/LDPE blends, with uniform particle size and distribution.Impact test and stress-strain test shows that the impact strength of CaCO3/LDPE blends rise at fisrt, and than decline. The elongation of CaCO3/LDPE blends declines while the concentration of CaCO3changes form0%to10%.