Plasticating extruders

Another feature of an extruder is the presence of a gauze filter after the screw and before the die. This effectively filters out any inhomogeneous material which might otherwise clog the die. These screen packs as they are called, will normally filter the melt to 120-150 fim. However, there is conclusive evidence to show that even smaller particles than this can initiate cracks in plastics extrudates e.g. polyethylene pressure pipes. In such cases it has been found that fine melt filtration ( 45 p.m) can significantly improve the performance of the extrudate. 

Spalding, M.A., Hyun, K.S., and Cohen, B.R., An Experimental Study of the Frictional and Viscous Forces Responsible for Solids Conveying and Melting in Single-Screw Plasticating Extruders, SPE ANTEC Tech. Papers, 43, 202 (1997)... 

Spalding, M.A., Powers, J.R., Wagner, P.A., and Hyun, K. S., Flow Surging in Single-Screw, Plasticating Extruders, SPEANTEC Tech. Papers, 46, 254 (2000)... 

Figure 5.1 A typical plasticating extruder with a smooth barrel solids conveying section...

Potente, H., Existing Scale-Up Rules for Single-Screw Plasticating Extruders, Int. Polym. Process., 6, 267 (1991)... 

Figure 10.7 Schematic for a particle seal for a plasticating extruder...

A 203.2 mm diameter plasticating extruder was running GPPS resin and discharging to a specialty downstream process. Like most processes, the downstream equipment required a nearly steady supply of molten polymer. For this case, the... 

Figure 12.27 The solids-conveying section of a single-screw, plasticating extruder with a worn feed casing. The schematic is not to scale, and it shows a ledge formed between the oversized (worn) feed casing and the flange of a new barrel...

The melt-fed extruder is typically designed with a relatively short barrel length of 6 to 1L/D. Since the resin is molten when it enters the extruder, the motor size is relatively small compared to a plasticating extruder with the same barrel diameter. The extruders are typically starve-fed. That is, the extruder is operating at a screw speed that is higher than required, and thus the rate is not controlled by the screw speed, instead, the rate of the overall process is controlled by the feedstock addition rate to the compounding machine. 

Wire is coated by being passed through a plastic extruder, but most materials are coated with solutions, emulsions, or hot powders. The classic brushing process has been replaced by roll coating, spraying, and hot powder coating. The application of polymers from water dispersions to large objects, such as automobile frames, has been improved by electrode-positon of the polymer onto the metal surface. 

Potente H. Existing scale-up rules for single-screw plasticating extruders. Int Polym Process 1991 4 267-278. 

The powdered aminoplast is supplied from ball mill (1) to buffer tank (2) with an agitator and then to feed hopper (3) of mixer (4) wherein it is processed until a homogeneous plastic extrudate is obtained. 

The plasticating extruder can be divided into three main zones ... 

A square pitch plasticating extruder has the following geometry ... 

Solve the above plasticating extruder problem with a mass throughput to = 1.8 x 102 kg/s. 

M. Kaufman, The Birth of the Plastics Extruder, Polym. Plast., 243-251 (June, 1969). 

Z. Tadmor and I. Klein, Melting in Plasticating Extruders in I. Klein and D. I. Marshall, Eds., Computer Programs for Plastics Engineers, Reinhold, New York, 1968, Chapter 6. 

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