Screw lead decreasing

Screw speed influences the residence time of the powder inside the barrel and torque produced during processing. Residence time of material inside the barrel is reduced by the increase of screw speed. Decrease in residence time is due to conveying capacity of rapidly moving screws. Residence time increases with low material feed and torque decrease, due to restricted packing of material. It leads to porous products or the material degrades inside the barrel. 

Screw and barrel wear can reduce the performance of the extruder by causing the specihc rate to decrease and the discharge temperature to increase. Screw wear is discussed in Sections 13.2 and 13.4.1. Although extremely rare, wear in the feed casing can lead to a rate reduction and process instabilities. This case study is presented in Section 12.7.7. 

A chemical instability which can be distinguished based on the gel effect or Trommsdorff effect, or on the ceiling effect. The influence of the gel effect on stability depends on its location. For example, if it occurs entirely within the screws, the increases in viscosity and reaction rate will stabilize the process, but if it occurs close to the die it will mainly affect viscosity in the die, which leads to destabilization. The ceiling effect will generally decrease the reaction speed, and therefore it will be negative for the stability of the process. 

The parts shown in fig. 1 were mounted in a cylindrical box with flat top and bottom, that could be evacuated to 10- mm. The top plate carried two glass windows for observation. Leads to the condenser-plates Ci and C2, transmission to the micrometer screws and conductance to the pressure boxes K, vt re all vacuum-tight sealed through the cylinder wall or bottom. The evacuation was necessary to decrease the viscous resistance of the air between the glass plates (see 1.6). 

The polymers obtained from D3PyMA and P2BPyMA have a less stable helix than that of poly-(TrMA).59 60 Their helical conformation undergoes helix-helix transition, leading to a decrease in the screw-sense excess as observed for the single-handed helical poly(D2PyMA).66... 

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