Single-screw extruders metering section

Transition section (transition zone, compression section) n. In a metering-type screw for a single-screw extruder the section of decreasing channel volume per turn between the feed and metering sections, in which the plastic is changing state from a loosely packed bed of particles-cwm-voids, to a void-free melt. The transition may be... 

All single-screw extruders have several common characteristics, as shown in Figs. 1.1 and 1.2. The main sections of the extruder include the barrel, a screw that fits inside the barrel, a motor-drive system for rotating the screw, and a control system for the barrel heaters and motor speed. Many innovations on the construction of these components have been developed by machine suppliers over the years. A hopper is attached to the barrel at the entrance end of the screw and the resin is either gravity-fed (flood-fed) into the feed section of the screw or metered (starve-fed) through the hopper to the screw flights. The resin can be in either a solid particle form or molten. If the resin feedstock is in the solid form, typically pellets (or powders), the extruder screw must first convey the pellets away from the feed opening, melt the resin, and then pump and pressurize it for a down-... 

Chang, R. and Lin, K., The Hybrid FEAVPDM Computer Model for Analysis of the Metering Section of a Single-Screw Extruder, Polym. Eng. Set, 35,1748 (1995)... 

Determining the effect of viscous dissipation in the metering section of a single screw extruder. Consider a 60 mm diameter extruder with a4 mm channel depth and a screw speed of 60 rpm. The melt used in this extrusion system is a polycarbonate with a viscosity of 100 Pa-s, a thermal conductivity of 0.2 W/m/K and a heater temperature of 300°C. To assess the effect of viscous heating we can choose a temperature difference, AT of 30K. This simply means that the heater temperature is 30K above the melting temperature of the polymer. For this system, the Brinkman number becomes... 

Newtonian Flow in the Metering Section of a Single Screw Extruder... 

Within this discussion it is understood that die 2 1/2D solution is a 3D flow where the velocity field does not change in the -direction. Such a can be flow through a channel such as an unwrapped screw channel of constant cross-section as encountered in the metering section of a single screw extruder. 

The BMC materials are fed from a hopper into the plasticization section of a relatively low-temperature (to minimize cure) single-screw extruder, where the material is mixed, metered and sheared into a homogenous mixture and collected in an injection cavity is the end of the screw. Once this cavity has been filled the entire screw is hydraulically plunged forwards and the material in the extruder cavity is injected into the mould under high pressures (typically 15 000-30 000 psi). The mould is at high temperature to facilitate curing of the part in the mould. 

Conventional single-screw extruders may be used for the foaming process, but premature decomposition of the CBA, which causes a loss of nitrogen through the feed throat, is difficult to avoid. The object is to reach the decomposition temperature in the metering section of the screw and allow the nitrogen to go into solution... 

Couette flow n. Shear flow in the annulus between two concentric cylinders, one of which is usually stationary while the other turns. By measuring the relative rotational velocity and the torque required to maintain steady flow, one can infer the viscosity of the liquid. Flow in the metering section of a single-screw extruder resembles Couette flow, modified by the presence of the flight and, normally, by the pressure rise along the screw. 

For large unidirectional simple shear, as found in the metering section of a single screw extruder ... 

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