Speed of extrusion

Many extruder manufacturers now produce dump extruders which are fitted beneath the discharge door of an internal mixer and receive into their feed hopper the full charge of the mixer. The speed of extrusion of the machine is governed by a series of sensors in the feed-hopper, to ensure that the process is continuous and that the screw will not be starved of compound, thus ensuring a continuous production of the mixed rubber compound. Product from such a machine can be slab or pellets. 

Type and level of binder (e.g., MCC, NaCMC) Rotational speed of extrusion head Temperature... 

The expansion of the tubes also depends on other factors. It increases with an increase in the speed of extrusion, a rise of temperature of the mass in the cylinder, and an increase in its centralite content. An increase in the number of passages between the rollers may also lead to a greater expansion of the tubes. The expansion also depends on the nitrogen content in the nitrocellulose, being nearly inversely pro-... 

Due to the length of the production lines (up to 250 m), the time needed for vulcanization and thus, the slow speed of extrusion, the produced profile takes a long time to reach the inspection zone (up to 30 minutes). Thus, the results of operating parameter changes can only be accurately detected after this time. 

In the blending process, whiskers may become damaged or even broken because of the impact and collision between whiskers and resin particles and the shear caused by the rotation of the screw. The constant length-to-diameter (Z/D) ratio of whiskers is the key for filling modification, so the speed of extrusion, the temperatures of different sections, and the position of the feed inlet of whiskers greatly influence the performance of the composite materials. Ge adds whiskers from the feed inlet of the twin-screw extruder and the first outlet respectively, and the performances of the composite material are shown in Table 4.2. 

A relatively stable era ensued in which better grades of PVC extrusion were developed and the printing of colour spirals on the wire for identification purposes was introduced. In the late 1960s bar marking was introduced. The identification inks were applied to the PVC wire covering during the extrusion process, the heat of the PVC being used to dry the ink. This allowed much faster speeds of extrusion to be obtained with benefits on cost and capacity. 

Furthermore, the head has an extrusion working width of 850 mm allowing the simultaneous extmsion of two-tread profiles at a speed of about 30 m/min. 

Wray The speed of the Ca2+ release seems to be important faster rises will stimulate these mechanisms better than slow ones. For example, if we put on CPA or thapsigargin, often we will see a substantial elevation of basal Ca2+, but it is quite slow. We don t see a corresponding rise of the basal level of force production in many of the tissues. It seems that there is a lot of Ca2+ there but the contractile machinery is not interested in it. It will presumably also be the case that extrusion mechanisms handle small, slow releases, and hence little or no contraction. 

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. 

To illustrate the barrel optimization process [22], an extrusion process was optimized first for rate and then for discharge temperature. Each of the experiments was conducted at a screw speed of 50 rpm. The initial extruder barrel tempera-... 

Figure 10.13 Extrusion rate and motor current for an HDPE resin at a screw speed of 50 rpm. The highest rate was achieved at a Zone 1 temperature of about 230 °C...

Figure 10.14 Extrusion rate and discharge temperature for an HOPE resin at a screw speed of 50 rpm. Discharge temperature increased when the Zone 1 temperature was increased...

Table 10.7 Extrusion Measurements for a Screw Speed of 60 rpm and Different Barrel Temperatures...

After the screw modification, the 148 kg/h rate was obtained at a screw speed of about 69 rpm with an extrudate temperature of 223 °C. Thus, the specific rate increased from 1.63 kg/(h rpm) before the modification to 2.14 kg/(h-rpm) after the modification, a specific rate increase of about 30%. At a screw speed of 69 rpm, the rotationai flow rate was calculated at 173 kg/h now the extruder was operating at about 86% of the rotational flow rate. The calculated axial pressure gradient required to maintain the flow of the extruder at the reported flow rate showed that pressures in the screw never decreased to zero, indicating that the channels were full as shown in Fig. 11.21. No adverse effects were experienced with the reduced discharge temperature (8 °C lower), no unmelted material was observed in the extrudate, and no gel showers occurred after the modification. A summary of the extrusion performance before and after the modification is shown in Table 11.5. 

Figure 11 Torque of extrusion as a function of moisture content of wet mass of MCC at varying screw speeds a-19 rpm, -28 rpm, c-38 rpm, d-4S rpm. Source From Ref 26.

Screw speed is another variable that impacts extrudate quality via residence time. The effect of screw speed on extrusion shear stress is given (22) by the expression... 

Using a melt extruder with only feed screw elements (similar to wet extruder), a dense extrudate was obtained at 20 rpm that became soft and powdery at 50 and 100 rpm (42). At a lower speed, the material resides longer within the chamber and that could lead to greater homogeneity of binding fluid (water) in the material. In addition, the slower rate of extrusion provides a more uniformly dense extrudate. 

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