Multiscrew extruders

In addition to single screw extruders, there are twin and multiscrew extruders that perform essentially the same functions, but with additional benefits. Among these, the intermeshing twin screw extruders are the most important ones. They are used primarily for heat-sensitive resins (such as PVC), which are difficult to process. The intermeshing screws create a relative motion of one flight in another, such that it acts... 

H. Herrmann, U. Burkhardt, and S. Jacopin, A Comprehensive Analysis of Multiscrew Extruder Mechanisms, Proc. 35th Annu. Techn. Conf., Society of Plastics Engineers, Montreal, Quebec, Canada (1977). 

Important to the EP industry is the use of multi-screw extruders (two or more screws in a barrel). Multi-screw extruders are primarily used for compounding plastic materials. A major, large market for RP molding compounds prepared by extruders is RTFs. Different designs of multiscrew extruders are used to produce compounds based on the plastic being processed and the products to be febricated. At times, their benefits can overlap, so the type to be used would depend on cost fectors, such as cost to produce a quality product, cost of equipment, cost of maintenance, etc. 

Different types of screw extruders are available such as single or multi-screw extruders. Multiscrew extruders can involve either two screws (twin screw design) or generally up to four. 

The Multiscrew Extruder With More Than Two Screws... 

Twin Screw Extruders. A screw extruder can have one screw or more than one screw. An extruder with one screw is called a single screw extruder it is the most common machine in the plastics processing industry. An extruder with more than one screw is called a multiscrew extruder. The most common multiscrew extruder is the twin screw extruder it has two screws. 

The tremendous growth of rigid PVC markets, especially of pipe and profiles, coupled with the increasing use of low-shear multiscrew extruders permitting lower stabilizer levels, prompted the development of lower-cost mixed metal barium/ butyltin or calcium/butyltin stabilizer systems, which provided adequate processing stability for most low-cost, twin-screw extrusion formulations. Many of these, however, could not be run well on single-screw extruders, thus limiting their versatility. 

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