Plastics extruders twin screw

Several commercial products of PVC/TPU blends are available. The BF Goodrich Chemical Group has a PVC/ TPU blend based on their Estane series TPUs. For example, their Estane 54620, a polyester-based TPU with a °ShA 85 hardness, shows excellent compatibility with flexible PVC. The blends are produced by mixing PVC, TPU, plasticizer, stabilizer, and lubricant in a twin-screw extruder. These polymeric blends show intermediate mechanical properties between PVC and TPU. 

In another case where the twin-screw extruder was used, the rubber and plastic were melt mixed with all ingredients in a similar manner as described in blend compositions for static vulcanizations. The product was then dumped, cooled, and granulated. The premixed granules were then fed into a twin-screw extruder where a very narrow temperature profile was maintained with a relative high compression (2 1), and the screw speed was adjusted depending on the final torque and the flow behavior of the extruded stock. The stock was cured by shear force and temperature enforced by the twin-screw extruder. The dynamically crosslinked blend was taken out in the form of a strip or solid rod to determine the... 

Post-consumer PMMA plastics can be depolymerised back into their starting components. Degradative extrusion in twin-screw extruders can be used for this process. 10 refs. Translation of Kunststoffe, 87, No.2, Feb.1997, p.183-8... 

Most plastics e.g. polyolefins and polystyrenes and their derivatives such as ABS (acrylonitrile-butadiene-styrene) and SAN (styrene-acrylonitrile) are supplied by the manufacturers in ready-to-use form with most of the above-mentioned stabilizers or simply need to be additionally stabilized with other additives, e.g. antistatic agents and HALS stabilizers, as required. On the other hand, in the case of other materials (e.g. PVC) it is the end user who adds the additives, pigments or preparations. This is normally done on fluid or high-speed mixers, although in the past gravity mixers or tumble mixers were also used. The mixture is then homogenized on mixing rolls, kneaders, planetary extruders or twin-screw kneaders and further processed. 

Plasticating single-screw extruders will typical range in size from 15 mm up to 250 mm in diameter. Larger diameter plasticating machines are very rare and were likely built years ago. Plasticating rates above about 4000 kg/h are more economically processed using twin-screw machines. 

Mack, M., Corotating Intermeshing Twin-Screw Extruder Berstorff s System, Chapter 5 in Plastics Compounding Equipment and Processing, Todd, D.B. (Ed.), Hanser Publishers, Munich (1998)... 

The twin-screw extrusion (TSE) technology is utilized extensively in the plastics and food industries to complement continuous manufacturing of products. Ghebre-Sellassie et al. [37] and Keleb et al. [36] have cited the application of this technology in the continuous production of pharmaceutical products. Commercially available TSE provide the great Lexibility required for effective continuous mode of operation. The schematic of such a system is shown in Figure 23.6. The twin-screw extruder... 

A possible way to lower the costs of fibers and films of regenerated cellulose would be to run cellulose through a twin-screw ultrasonic extruder with a minimum of solvent and pass the extrudate through a stream of hot air to recover the solvent for reuse. This stronger cellophane could be used in place of many plastic films used today. A great number of derivates of cellulose have been made. Methyl, ethyl, carboxymethyl, hydroxyethyl, and hydroxypropyl ethers are made commercially today. These are used as water-soluble polymers, except for ethylcellulose, which is a tough plastic used in screwdriver handles and such. 

Today, most processes involve some form of mixing. As discussed in the previous section, an integral part of a screw extruder is a mixing zone. In fact, most twin screw extruders are primarily used as mixing devices. Similarly, the plasticating unit of an injection molding... 

Fig. 10.4 Hexalobal, intermeshing, counterrotating twin-screw mixing screw elements. [Reprinted by permission from W. C. Thiele, Counterrotating Intermeshing Twin Screw Extruders, in Plastics Compounding—Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]...

Fig. 10.35 Idealized representation of the solid-melt suspension formed in the melting zone of CRNI twin extruders with staggered screw arrays. The mechanism of melting will he dissipative mix-melting. [Reprinted hy permission from R. J. Nichols and F. Kher-adi, Melting in CRT Twin Screw Extruders, Mod. Plastics, 61(2), 70 (1984).]...

C. Martin, Counterrotating Twin Screw Extruders , in ExfnrsionTooZfcox, Society of Plastics Engineers, Danbury, CT, (2004). 

B. Qian and C. G. Gogos, The Importance of Plastic Energy Dissipation (PED) to the Heating and Melting of Polymer Particulates in Intermeshing Co-rotating Twin Screw Extruders, Adv. Polym. Tech., 19, 287-299 (2000). 

Closely intermeshing co-rotating twin screw extruders occupy a dominant position among extruders and are used in a wide variety of applications. They are not only used extensively in the production, compounding, and processing of plastics, but also employed in large numbers in other branches of industry, e.g., the rubber and food processing sectors. 

Wiedmann, W. Wohlfahrl-Laymann,H. Cost-Effective use of Twin-Screw Extruders for Recycling. Plastics 82 (1992) 10, p. 934-938... 

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