Plastics Technology

SEP 2018

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The preferred Maddock mixer design is a typical configuration except for two features. These include setting the mixing flight undercut to about 0.5% of the screw diameter. Most designs set this undercut at 1 to 1.5% of the diameter. The small undercut specified here will disentangle unmixed gels and trap and disperse all solid polymer fragments that happen to flow out of the melting section. A larger undercut of 1 to 1.5% of the diameter can allow unmixed gels and solid polymer fragments to discharge from the extruder. The second different feature of the Maddock mixer recommended here is that the depth of the inflow and outflow flutes should be half the width of the flute. If the flutes are made deeper, resin degra- dation can occur, creating gels in the film product. Maddock mixers with extremely deep flutes and large clearances on the Poorly designed Maddock mixers are sources for two types of gels that can appear at a low and continuous level. Diverse Feeding Solutions for Plastics Processing From polymers to fillers and additives Schenck Process has the most diverse loss-in-weight feeder line to precisely handle your materials. Whether it's a specific agitation method, throughput capacity or helix design, we will find the right solution to meter the most challenging dry materials for plastics compounding applications. Also, for pre- and post-extrusion dry material handling we offer complete pneumatic conveying packages and dry material handling solutions. Schenck Process LLC 7901 NW 107th Terrace Kansas City, MO 64153 816-891-9300 sales-fcp@schenckprocess.com www.schenckprocess.com/us mixing flights are common in smooth-bore extruder designs. In poor designs, the flutes are improperly made too deep in order to reduce pressure consumption in the device. These poor designs will cause resin to degrade at the flute edges, resulting in a low level of gels that contaminate the film product. WHERE DEGRADATION OCCURS ON THE SCREW If the gel analysis indicates that the defects are due to degraded resin, then the best way to locate the region on the screw where A B = 0.4 H R 1 = 1.5 H R 2 H H R 1 R 2 FIG 5 Schematic of small (R1) and large (R2) flight radii: a) This small flight radius will likely create a Moffat eddy and lead to degradation of the PE; b) This large radius will likely not create a Moffat eddy. @plastechmag 65 Plastics Technology G E L S

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