Barrel control transducer

Barrel control transducer Thermocouple and pressure transducers are inserted in different zones of the barrel to sense melt condition they require accuracy in proper locations and recording instrumentation. 

An extrusion trial was performed at the processor s plant using a 38.1 mm diameter production extruder, a proprietary screw design, and resin that had previously exhibited flow surging and reduced rate. The extruder was equipped with three barrel zone heaters with control thermocouples (labeled Tl, T2, and T3) and two pressure sensors. One pressure sensor was located in the midsection (zone 2) of the barrel (P2) and the other at the end of the barrel near the tip of the screw (P3). Both transducers were positioned over the top of the screw such that a pressure variation due to screw rotation would be observed. 

Examples of good preventive maintenance activities include (1) establish the frequency of lubrication and what types of oil or grease must be used (2) check for oil leaks and have a procedure to correct/eliminate them (3) check heaters, thermocouples, pressure transducers, and so on (4) set up schedules and procedure to clean machines and molds/dies (barrels, screws, sliding mechanisms, clamps, etc.) (5) check control circuits (electrical, hydraulic, mechanical, etc.) (6) schedule checks of conditions wherever questions of alignment, level, parallelism (mold parts, mold press, die system, etc.), and other similar situations exist (7) set up a schedule to check safety devices on all equipment and (8) schedule sessions to repeat instructions on safety equipment procedures to all personnel. Figure 11-8 shows where accidents usually occur (324, 325). 

Fig. 35. Diagram of the system used to pressure-eject peptides from multibarrelled pipettes. A pressure of (50 Ib/in ) was supplied to the system from a nitrogen cylinder through a standard gas regulator in series with A, an electronic/pneumatic valve, and an adjustable needle valve control B. A toggle switch two-way valve C was used either to connect the remainder of the system to the pressure cylinder, or to open it to the atmosphere through an exhaust. A pressure transducer (Statham PM6) was connected at D, to each of the individual pipette lines E. Pressure tubing was secured to the side barrels of the multibarrelled electrode by O ring connectors. Z and Y represent a second means of control in which the pressure application was controlled by the output of the conventional electrical stimulator, using a circuit identical to that developed by McCaman et al. (1977). (From Dingledine et ah, 1980.)...

Pressure transducers are often preferred when high-accuracy measurements on a broad range of materials are required. Force transducers see use in quality control labs, where ease of operation and cleaning are important, or when maximum corrosion resistance is desired. Further discussions will assume that a pressure measurement system rather than a force transducer is used. (To calculate stress, the force measurement is converted into a barrel pressure by dividing by the cross-sectional area of the barrel, so no generality is lost.)... 

If the data are different than expected, check to make sure the pressure/ force transducer that was used was calibrated properly, that the correct die was inserted in the rheometer, and that the instrument s temperature controllers accurately reflect the temperature in the rheometer barrel. Most laboratories keep a well-characterized lab standard material available that can be run on an instrument to make sure it is giving the correct results. 

In a typical capillary rheometer, one has a temperature-controlled barrel into which the test material (usually in powder or pellet form) is packed. Directly downstream of the barrel is a cylindrical die with known length and radius. A piston is programmed to force the molten material through the die at a constant rate. A pressure transducer located near the die entry records the pressure drop. The capillary rheometer is widely employed and has been analyzed in detail (see Macosko [25], who gives a thorough discussion). The expression for the shear viscosity is... 

The basic geometry of a capillary rheometer is similar to that of a melt indexer. Molten polymer in a heated barrel is extruded through a capillary die under the influence of pressure exerted by a piston. Either the force applied to the piston or its rate of travel is controllable over a wide range, as are the temperature of the polymer and the dimensions of the capillary. The relationship between the force apphed to the piston and its rate of travel reflects the response of the melt viscosity to the applied shear stress. In modem instmments, experimental control and final calculations are handled by computer. Additional refinements come in the form of interchangeable capillary dies of various lengths and diameters, the use of pressure transducers, and precisely controlled piston rates. Slit flow rheometers are also available but are far less common than capillary rheometers. The theory and practical aspects of capillary flow are extensively covered in the works cited in the bibliography. 

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