Online Monitoring of the Degree of Fill in a Rotating Full‐Flight Screw of a Corotating Twin‐Screw Extruder

Abstract

It is essential to understand the extent of partial filling of the flight screw, the degree of fill, which is an operational variable of the twin-screw extruder (TSE). This article reports the first attempt to measure, in situ, the degree of fill in a rotating full-flight screw using a specialized light-section method for a TSE. The thickness of the resin sticking to the pushing side decreased with increasing rotational speed. The degree of fill is inversely proportional to the rotational speed and proportional to the feed rate. This result agreed well with the results suggested by the conventional analysis of flow in the TSEs. The fast Fourier transformation of the degree of fill time series indicated that the period of fluctuation correlated with the screw speed rather than the feed rate or throughput. Keywords: twin-screw extruder, degree of fill, molten polymer, light section method As a fundamental research on the flow characteristics of TSEs, many studies have been carried out on the measurement of resin pressure at the barrel surface, the residence time distribution, and the resin temperature of the molten resin along the extrudate direction. 1-7 However, there are few studies measuring the degree of fill of the resin in the TSEs. The degree of fill, also called as the filling ratio, fill ratio, filling level, 8 or fill degree, 9 , is a time-dependent periodic state variable and is fundamentally important for mixing and devolatilizing gases in the operating TSEs. 10 We believe that measuring the degree of fill quantitatively would be useful for the validation of numerical simulations and theoretical calculations, and would facilitate the design, operation, and maintenance of TSEs. The evaluation of degree of fill is carried out by three different methods: (1) direct observation through a viewing window 11,12 ; (2) a transparent barrel is used to measure the

Resin distribution along axial and circumferential directions of self‐wiping co‐rotating parallel twin‐screw extruder

“…However, a more quantitative in‐situ measurement of the resin profile is indispensable because the specific volume of the resin is temperature dependent and the complete profile of the molten resin cannot be estimated from its solid, semicrystallized state. Thus, in‐situ laser light section measurements were developed and employed to determine the resin profile in our previous study 28 . Figure 7 shows the resin profiles of the full‐flight screw (SC‐34/34) observed by the in‐situ laser light measurements at the port indicated in Figure 5.…”

“…The experiments conducted in this study were discussed in our previously published paper on the measurements of the degree of fill 28 . The materials and apparatus used to obtain the results provided in this study were as reported in that previous study.…”

“…The exit die was circular with a diameter of 3.0 mm. Further details of the experiments can be found in our previous study 28 …”

Experimental and Numerical Simulation Study of Devolatilization in a Self-Wiping Corotating Parallel Twin-Screw Extruder

“…The highest devolatilization efficiency is obtained by the fast screw rotation speed. The fast screw rotation speed gives a low degree of fill [ 14 , 17 ], which implies that less resin fills the screw. As the exposed surface boundary length is the length where the local degree of fill is zero, the low degree of fill increases the exposed surface boundary length, which in turn increases the devolatilization efficiency.…”

“…The volatile concentration used for the simulation is larger than that used to obtain the experimental result. To understand the cause-and-effect relationship, we determined the resin profile using the laser-light section method, previously developed by our group [ 17 ]. Figure 9 shows that the resin profiles at 120 and 90 rpm agree well with the simulation and experimental results.…”