Screw temperature

Campbell, G.A., Spalding, M.A., and Carlson, F., Prediction of Screw Temperature Rise in Single Screw-Pump Extruders, SPE ANTEC Tech. Papers, 54, 267 (2008)... 

Figure 5.12 Effect of barrel and screw temperature on HOPE resin solids conveying.

Figure 5.22 Solids conveying rate as a function of barrel and screw temperature for the shallow screw (8.89 mm) at a screw speed of 50 rpm and at zero discharge pressure...

Figure 5.27 The effect of flight radii size on solids conveying rates for a barrel temperature of 75 °C, a screw temperature of 50 °C, and a screw speed of 50 rpm...

The soiids conveying rate data as a function of discharge pressure at a screw speed of 50 rpm and barrei and screw temperatures of 75 °C are provided in Tabie 5.1. 

Table 5.1 Experimental Solids Conveying Rates (Fig 5.24) as a Function of Discharge Pressure at a Screw Speed of 50 rpm and Barrel and Screw Temperatures of 75 °C for the LDPE Resin. Data were Collected Using the Shallow Screw for the Dow Solids Conveying Device...

Figure 5.32 Solids conveying rate data calculate using the modified Campbell-Dontula model for the Dow solids conveying process using the shallow screw, 75 °C barrel and screw temperatures, and a screw speed of 50 rpm. The solids conveying rates measured from the experimental device are provided...

Table 7.7 Comparison of Barrel and Screw Temperature Increase for PC and PS Resin...

High screw temperatures Flow surging and low specific rates 12.7.3... 

Transport of energy in the screws was modeled previously for single-screw extruders [30-32] and for twin-screw extruders [33]. In order to predict the axial screw temperature in a single-screw extruder, heat conduction along the screw has to be modeled. The model developed by Derezinski [32] included heat conduction from the barrel through the screw flights to the screw surface, heat conduction from the polymer to the screw root, and heat conduction in the axial direction. The model showed that the screw does not behave adiabatically and that the steady-state heat conduction in the screw depends greatly on the size of the extruder. 

Figure 10.19 Axial screw temperature profiles during a heating cycle. The screw was not rotating...

The HIPS resin was extruded at screw speeds of 30, 60, and 90 rpm at barrel temperatures of 200, 220, and 240 °C for Zones 1, 2, and 3, respectively. The screw temperatures in Zone 3 as a function of time at the screw speeds are shown in Fig. 10.20. Because the RTDs were positioned within 1 mm of the screw root surface, they were influenced by the temperature of the material flowing in the channels. Prior to the experiment, the screw was allowed to come to a steady-state temperature without rotation. Next, the screw speed was slowly increased to a speed of 30 rpm. The time for the screw to reach a steady state after changing the screw speed to 30 rpm was found to be about 10 minutes. The temperature of the T12 and T13 locations decreased with the introduction of the resin. This was caused by the flow of cooler solid resin that conducted energy out from the screw and into the solids. At sensor positions downstream from T13, the screw temperature increased at a screw speed of 30 rpm, indicating that the resin was mostly molten in these locations. These data suggest that the solid bed extended to somewhere between 15.3 and 16.5 diameters, that is, between T13 and T14. When the screw speed was increased to 60 rpm, the T12 and T13 sensors decreased in temperature, the T14 sensor was essentially constant, and the T15, T16, and T17 sensor temperatures increased. These data are consistent with solids moving further downstream with the increase in screw speed. For this case, the end of the solids bed was likely just upstream of the T14 sensor. If the solid bed were beyond this location, the T14 temperature would have decreased. Likewise, if the solid bed ended further upstream of the T14 sensor, the temperature would have increased. When the screw speed was increased to 90 rpm, the T12, T13, and T14 temperatures decreased while the T15, T16, and T17 temperatures increased. As before, the solids bed was conveyed further downstream with the increase in screw speed. At a screw speed of 90 rpm, the solid bed likely ended between the T14 and T15 sensor positions, that is, between 16.5 and 17.8 diameters. These RTDs were influenced by the cooler solid material because they were positioned within 1 mm of the screw root surface. 

Figure 10.20 Zone 3 screw temperature response to changes in screw speed. The barrel zones were 200, 220, and 240 °C for Zones 1,2, and 3, respectively...

The axial screw temperature profiles for the screw speeds are shown in Fig. 10.21. These profiles were constructed from the data set shown in Fig. 10.20 by using the data collected at steady state. As shown in this figure, the temperature profile would approximate the model developed by Cox and Fenner [30], but the temperature distribution is more complicated than this simple model. 

Figure 10.22 Axial screw temperature profile at a screw speed of 60 rpm and as a function of barrel temperature. The barrel temperatures for the three zones are indicated in the figure. The data point labels for the sensors were omitted for clarity...

Figure 10.23 Select barrel (Z2 and Z3) and screw temperatures as a function of cooling time during a Maddock solidification experiment...

Axial screw temperature profiles have been measured before, but they have been limited by the number of sensors and the quality of the data. The data presented here expand the existing knowledge of extrusion and also provide a new method for determining the ending location of the solid bed. 

The axial screw temperature profiles are consistent with the general trends that would be predicted using the Cox and Fenner [30] model, but the temperature of the screw is obviously affected by all barrel temperature zones and not just the zone over the metering channel. The data shows that heat conduction from the barrel to the screw root is highly important. This conclusion is consistent with the observations and model by Derezinski [32]. 

Altinkaynak, A., Gupta, M., Spalding, M.A., and Crabtree, S.L., Numerical Investigation of the Effect of Screw Temperature on the Melting Profile in a Single-Screw Extruder, SPEANTEC Tech. Papers, 53, 430 (2007)... 

Keum, J. and White, J. L., Heat Transfer Coefficients and Screw Temperature Profiles in Modular Twin Screw Extrusion Machines, SPE ANTEC Tech. Papers, 50,108 (2004)... 

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