Screw Temperature Profile

The temperature of the screw was measured by several investigators [29-32]. The measurements were performed by mounting thermocouples in an axial hole bored in the center of the screw or by protruding the thermocouples into the melt flow. The sensor signals were then transmitted to a chart recorder using an electrical rotary union. The technology available at the time of these measurements limited the number of sensors in the screw and the quality of the data. 

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. 

An empirical model that describes the axial temperature profile was developed by Cox and Fenner [30] based on the research performed by Edmondson [31]. The model is as follows  

RTD Label Axial Position, cm Axial Position, diameters 

The response of the RTDs and the temperature of the screw were tested with the screw not rotating. For this experiment, the temperatures were first measured with the extruder at ambient conditions. Next, the barrel temperature set points were increased to 200, 220, and 240 °C for Zones 1, 2, and 3, respectively. The downstream die system was heated at the same time as the barrel and at a set point temperature equal to Zone 3 (240 °C). The temperature profile of the screw as a function of axial length is shown in Fig. 10.19 for select heating times. For heating 

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

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 10.21 Axial screw temperature profiles as a function of screw speed for barrel temperatures of 200, 220, and 240 °C for Zones 1, 2, and 3, respectively. The data point labels for the sensors were omitted for clarity...

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]. 

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)... 

Points to be considered to avoid screw and barrel wear are the extruder condition, the formulation - including use of lubricants, filling degree of the screw, temperature profile and motor load. 

Figure 7.7 Influence of screw temperature profiles on mixing with Maddock element at end of compression zone. Photomicrographs of screw tip channel section. (Reproduced with Permission from G.M. Gale, Masterbatch Flow Patterns in Polyethylene Extrusion, Rapra Members Report No.16, Rapra Technology, Shawbury, Shrewsbury, UK, 1978, Figure 8. 1978, Rapra Technology)...

In another case where the twin-screw extruder was used, the rubber and plastic were melt mixed with all ingredients in a similar manner as described in blend compositions for static vulcanizations. The product was then dumped, cooled, and granulated. The premixed granules were then fed into a twin-screw extruder where a very narrow temperature profile was maintained with a relative high compression (2 1), and the screw speed was adjusted depending on the final torque and the flow behavior of the extruded stock. The stock was cured by shear force and temperature enforced by the twin-screw extruder. The dynamically crosslinked blend was taken out in the form of a strip or solid rod to determine the... 

The standard injection molding machine used had a screw diameter of 30 mm and the aspect ratio of 23.70. The barrel temperature profile was 270, 280, 290, and 295°C. The mold temperature was about 90°C. The injection molded tensile samples were processed according to the CAMPUS specification (Computer Aided Materials Preselection by Uniform Standards) [24] and DIN 53455 Form 3. To obtain the different flow conditions, four groups of samples were injection molded by varying melt... 

Most of the compounds were extrusion compounded in a conical, partially intermeshing, counter rotating twin screw extruder (Haake Reomix TW-lOO). The extruder speed was set at 50 rpm and the barrel temperature profile was set to produce a melt temperature of 260°C at the die. Samples were injection molded in a 31.8 MT Battenfeld press with a 59 cc shot size. Where noted, samples were compounded in a 60 cc Brabender internal mixer and compression molded. 

The extruder temperature profile for a single-screw extruder is set such that the functions of the process convert the polymer from a solid to a fluid. These two words are in quotation marks because for noncrystalline glassy (or amorphous)... 

Bruker, L, Miaw, C., Hasson, A., and Balch, G., Numerical Analysis of the Temperature Profile in the Melt Conveying Section of a Single Screw Fxtruder Comparison with Fxperimental Data, Polym. Eng. Set, 27, 504 (1987)... 

The baseline extrusion process was numerically simulated using the processing conditions in Table 9.4 and the method described in Section 9.2.1, that is, with a rate of 77 kg/h, a screw speed of 27 rpm, and a discharge pressure of 10.6 MPa. The iterative calculation process was used to estimate a bulk temperature of 160 °C and a pressure of 13.1 MPa at the entrance to the meter section. The axial pressure and temperature profile for the simulation is shown in Fig. 9.5. 

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)... 

Figure 13.9 Simulated axial pressure and temperature profiles for the original pumping screw at a maximum rate of 1590 kg/h and a screw speed of 15 rpm...

Figure 13.14 Simulated axial pressure and temperature profile for the original blow-molding screw at a rate of 156 kg/h and a sorew speed of 12 rpm, for a specific rate of 13.0 kg/(h-rpm)...

The ET section and downstream channel sections were numerically simulated to determine if the screw could meet the target performance. The simulation was performed at a rate of 410 kg/h using the same barrel temperatures for the original screw and process and at an entry pressure and temperature of 7 MPa and 210 °C, respectively. The axial pressure and temperature profiles are shown in Fig. 13.15. The simulation indicates that 410 kg/h can be obtained at a screw speed of 24 rpm for a specific rate of 17.1 kg/(h-rpm) with a discharge temperature of 234 °C. Based on this simulation, the ET screw was fabricated. 

The operation of the screw described in Fig. 15.2 is shown by the simulated axial pressure and temperature profiles shown in Fig. 15.3. The simulation was performed at a rate of 5500 kg/h and at a screw speed of 70 rpm for an ABS resin with... 

The simplified method for calculation of the temperature profile using the control volume method and screw rotation is shown by Eq. A7.20f. The simplified calculation under-predicts the energy dissipation. 

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