Loss of Rate Due to Poor Material Conveyance in the Feed Section

1 Loss of Rate Due to Poor Material Conveyance in the Feed Section 

Large-diameter, melt-fed extruders are almost always flood-fed as described above. As such they will typically operate at a specific rate that is very predictable based on numerical simulations. The extruder will operate at these rates in a very stable manner. That is, the motor current and discharge pressure are essentially constant with time. An improperly designed extruder or a malfunctioning extruder can, however, operate at much lower specific rates and in a very unstable manner. This mode of operation is often referred to as slipping because the feed section of the 

The siipping probiem occurs due to process changes and the solubility of ethylene in the LDPE resin. In order to understand the fundamentals of the process, it is important to understand the soiubiiity of ethylene in LDPE resin. Maloney and Prausnitz [22] studied the soiubiiity of several solutes in LDPE resin, including ethyiene. They measured Henry s constant as a function of temperature. Henry s iaw was shown to be acceptabie for predicting the concentration of ethylene in LDPE resin as foiiows  

The conditions in the low-pressure separator are typically in the range of 0.04 to 0.14 MPa absolute pressure and at a temperature near 250 °C [11, 12]. At these conditions, the LDPE resin in the low-pressure separator is expected to contain about 750 ppm of dissolved ethylene at equilibrium. Another 250 to 750 ppm of ethylene can also be entrained as a gas or at a supersaturated condition in the LDPE. As the resin flows from the low-pressure separator into the first diameter of the extruder, the pressure is expected to be nearly the same since the flow pipes are not restrictive. If the temperature of the inside wall of the feed casing of the extruder is less than 250 °C, then the ethylene will remain in solution, foaming 

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