ISSN:
0193-7197
Keywords:
Chemistry
;
Chemical Engineering
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
The melting and extrusion behavior of low shear rigid PVC profile compounds such as Geon 8700A were investigated in order to answer the fundamental question as to why the output rate of this type of compound is relatively low compared to other types of PVC compound. Typically, the extrusion rate of Geon 8700A is less than half those achieveable on other PVC compounds. A part of the reason is that the extrusion melt temperature of Geon 8700A has to be kept below 360°F in order to preserve primary PVC particles in extrudates and to maintain smooth extrudate surfaces.The study showed that Geon 8700A follows an entirely different melting mechanism in extrusion - quite opposite to the one previously accepted. Geon 8700A undergoes the melting mechanism observed by Menges, et al. due mainly to its nonwetting characteristic on the barrel surface while most other PVC compounds follow the mechanism described by Tadmor. The difference between the two mechanisms lies in the location of the melt pool formation - the Tadmor model in the pushing side of the screw flight and the Menges in the opposite leading side of the screw flight. Extruding Geon 8700A on screws - notably 2-channel screws - optimized for the different Tadmor model is one of the major reasons for such a poor performance with this compound.A new dual pitch deep channel screw has been developed. It is optimized for the melting mechanism of Geon 8700A, resulting in a dramatic improvement in both output rates and extrudate quality. Rates of 350 pounds/hour at 350°F and 400 pounds/hour at 363°F have been achieved on the 3-1/2 inch extruder, whereas 150 to 200 pounds/hour at 350°F is common with the standard screws. This new screw technology, with its high output rate and superior extrudate quality capability, makes the extrusion of cube compounds on single screw extruders competitive with powder extrusion on multi-screw extruders.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/vnl.730070107
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