Screw maximum extrusion rate

With developments in equipment and the fluoropolymers that have high melt viscosities, the maximum extrusion rate using screws is normally limited by melt fracture. However, these plastics have exceptional melt strength. This characteristic makes possible ram extruding using a die with a large opening and apply a draw down of the extrudate to the desired insulation thickness. 

At the startup of the line, the extruder was operated at 91 rpm to produce the required rate of 148 kg/h for a specific rate of 1.63 kg/(h-rpm). The temperature of the extrudate was measured through the transfer line wall at 232 °C. Due to process safety constraints the extrudate temperature could not be measured using a handheld temperature sensor. The extrusion rate was required in order to maintain the downstream take-away equipment at its maximum rate. At first the extruder appeared to be operating well except that the specific rate was lower than predicted. That is, the screw was rotated at an rpm that was higher than expected to produce the 148 kg/h. At 91 rpm, the rotational flow rate was calculated at 228 kg/h the specific rotational flow rate was calculated at 2.51 kg/(h-rpm). Thus, the line was operating at only 65% of the rotational flow rate. A barrier design... 

The target discharge temperature for the extrusion is 240 °C, and the maximum screw speed is 130 rpm (N = 2.167 rev/s). What will be the expected production rates for both resins at 130 rpm At 240 °C the melt density of the resins is 735 kg/mT As presented in Sections 1.4 and 7.4, the net flow in the extruder is the difference between the rotational flow and the flow induced by the pressure gradient Qp. The data in Table 7.2 was calculated from the example in Section 1.5.1 and Table 7.1 ... 

In many chemical and processing applications, fluids need to be heated or cooled and a wide range of equipment may be utilized. Examples include double pipe and shell and tube heat exchangers, and stirred vessels fitted with cooling coils or jackets. Sometimes, heat is generated in the process, as in extrusion which is extensively carried out in the polymer and food industry. It may also be necessary to reduce the rate at which heat is lost from a vessel or to ensure that heat is removed at a sufficient rate in equipment such as screw conveyors. In most applications, it is the rate of heat transfer within process equipment which is of principal interest. However, with thermally sensitive materials (such as foodstuffs, fermentation froths, pharmaceutical formulations), the temperature profiles must be known and maximum permissible temperatures must not be exceeded. 

Controlling extrusion processes takes two types of systems, one on the extruder and another on the finished extruded product. In turn, these controls have to be interfaced. Extruder controls have been reviewed (heats, pressures, hopper feed rate, screw RPM, back pressures, etc.), as have product controls (wall thicknesses, rate of travel, width indicators, weight, etc.). Extensive efforts are continually being made to achieve the maximum in speed and precision. 

Plasticating capacity n. Of an extruder or injection molder, the maximum rate at which the machine can melt room-temperature feedstock and raise it to the temperature suitable for extrusion or molding. This rate is determined mainly by the quotient of the available screw power, divided by the means specific heat of the... 

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