Barrel temperature measurement

The barrel temperature needs to be measured to provide information on the axial barrel temperature profile and to provide a signal for the controllers of the barrel heaters and cooling devices. The temperature should be measured as close as possible to the inner barrel surface, since the polymer temperature is the primary concern. The worst possible location of the temperature sensor would be in the barrel heater itself. However, there are some commercial extruders where the temperature sensor is placed in the barrel heater to reduce the thermal lag of the system. The major drawback of this approach is that one controls the heater temperature and not the temperature of the polymer in the extruder barrel. Some extruders are equipped with a combination of deep-well and shallow-well temperature sensors to improve 

In the measurement of barrel temperature, a temperature sensor is pressed into a well in the extruder barrel the sensor is generally spring-loaded see Fig. 4.13. Most temperature sensors are constructed with a metallic sheath to obtain sufficient mechanical strength. As a result, significant thermal conduction errors can occur. 

The true barrel temperature is 185°C the measurements were made in still air 

This figure illustrates quite clearly that the depth of the well should be at least 30 mm to minimize the measurement errors. The characteristics of the temperature sensor itself have a strong effect on the accuracy of the measurement. If special precautions have been taken to minimize heat losses along the stem of the temperature sensor, the measurement error can be greatly reduced as compared to standard temperature sensors. 

It is important to realize that barrel temperature measurement with a shallow well can be, and most likely will be, inaccurate. With a well depth of 10 mm, the measured temperature will probably be about 10°C below actual temperature. When air drafts occur around the extruder, the measured temperature can be as much as 25°C below the actual temperature. This is shown in Fig. 4.15. 

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The heating system can be checked by changing the setting to a much higher temperature, for instance 50°C above the regular setting. The heater should turn on a full 100% and the measured barrel temperature should start rising In about one to two minutes. If the heater does not turn full on, the barrel temperature measurement is in error or there is a problem in the electronic circuit of the temperature controller. If the heater turns full on but the temperature does not start to rise within two to four minutes, either the barrel temperature measurement Is Incorrect or there is poor contact between heater and barrel. 

The temperature of the melt downstream from the breaker plate may exceed the front barrel temperature, because of the mechanical work transmitted to the resin by the screw it varies with screw speed and flow rate. The melt temperature is measured by a thermocouple inserted into the melt downstream from the breaker plate. A hooded exhaust placed over the extmder die and feed hopper removes decomposition products when the extmdate is heated. 

Van Driesen and Stewart (V4) have reported temperature measurements for various locations in commercial gas-liquid fluidized reactors for the large-scale catalytic desulfurization and hydrocracking of heavy petroleum fractions (2500 barrels per day capacity). The hydrogenation was carried out in two stages the maximum and minimum temperatures measured were 774° and 778°F for the first stage and 768° and 770°F for the second. These results indicate that gas-liquid fluidized reactors are characterized by a high effective thermal conductivity. 

A schematic view of an extruder is shown in figure 1. The extruder barrel is essentially a ferrous alloy cylinder, with aluminum block heaters attached to the outside. There are several temperature control zones along the length of the extruder. Measurement thermocouples are installed in the extruder barrel itself. Barrel temperature is used to control the temperature of the polymer melt. Energy from the heaters is conducted both radially and axially in the barrel. Below, figure 2 shows a sketch of the extruder barrel, with the heaters and the temperature measurement points used in this paper marked. 

CombiCHEM System (Fig. 3.9) For small-scale combinatorial chemistry applications, this barrel-type rotor is available. It can hold two 24- to 96-well microtiter plates utilizing glass vials (0.5-4 mL) at up to 4 bar at 150 °C. The plates are made of Weflon (graphite-doped Teflon) to ensure uniform heating and are sealed by an inert membrane sheet. Axial rotation of the rotor tumbles the microwell plates to admix the individual samples. Temperature measurement is achieved by means of a fiber-optic probe immersed in the center of the rotor. 

A couple points are emphasized 1) the authors have found no published effort to determine the forces on the barrel as a function of material type and solids conveying discharge pressure, and 2) unlike conventional barrels that are thick to induce a maximum thermal capacitance and strength, the barrel in this device was machined to a minimum thickness in order to enhance heat transfer and thus allow a good estimate of the inner wall temperature from the outside temperature measurements and the local heat flux. 

Figure 5.15 Outside barrel zone temperature measurements for a solids oonveying experiment using HIPS resin and a sorew speed of 50 rpm and a disoharge pressure of 1 MPa...

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... 

Table 10.6 Extrusion Measurements for Barrel Temperatures of 200, 220, and 240 °C for Zones 1, 2, and 3, Respectively...

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

A data acquisition system was attached to the control panel of the extruder in parallel with the existing controllers. Barrel temperatures, discharge pressure, motor current, and several downstream sensors were recorded at a frequency of once per second. The sensors downstream from the extruder were showing that the downstream part of the process was not contributing a significant level of variation to the profile dimensions. The rate was measured at 53 kg/h for a screw speed of... 

Fig. 9.37 Simulated and measured pressure profiles for an LDPE extruded in a 2.5-in-diameter, 26.5 length-to-diameter ratio extruder, with a metering-type screw having 12.5 feed section with channel depth of 0.37 in and 4.5 turns of metering section of depth of 0.1275. The flow rate is 136 lb/h, the screw speed 60 rpm, and the barrel temperature was set at 300°F. The SBP is shown in Fig. 9.24. The screw geometry is shown at the top of the figure. Simulation was carried out by the first computer simulation package for plasticating extrusion developed by the Western Electric Princeton Engineering Research Center team (17). [Reprinted by permission from Z. Tadmor and I. Klein, Engineering Principles of Plasticating Extrusion, Van Nostrand Reinhold, New York, 1970.]...

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