Extruder Hardware Systems

This chapter covers two main sections extruder hardware systems and extrusion functional zones. The first section identifies the primary components of the extruder and provides detail into their capabilities and size ranges. The second section describes how the hardware interacts with the material as it passes through the system. In other words, it provides a look at what is happening inside each zone of the extruder. The descriptions here are purposefully brief, serving as a foundation to support later discussions specific to blown film extrusion. If the reader is interested in pursuing this topic further, there are many books devoted entirely to the extruder and extrusion processes. For example. Polymer Extrusion by Rauwendaal [3] provides an excellent in-depth analysis. Other references are listed in the back of this book [4-6]. 

The purpose of the extruder is to feed a die with a homogeneous material at constant temperature and pressure. This definition highlights three primary responsibilities that the extruder must accomplish while delivering material to a shaping die. First, it must homogenize, or satisfactorily mix, the material. Second, the material entering the die must have minimal temperature variation with respect to both time and position within the melt stream. Third, there must be minimal melt pressure variation with time. It is important that the design and operation of an extrusion system consider all three of these objectives to produce a quality product. 

Extruders are generally rated by screw diameter. Typical production extruders range in size from 2 to 6 in (50 to 150 mm). A fundamental quantity determined by screw 

Components of the extruder hardware can be categorized into five systems (Fig. 2.1)  

Simulator Exercise When the cursor is paused over any extruder component, an identification tag shows the name of that component. 

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Color concentrates are usually pellets that contain a high percentage of colorant in a compatible polymer carrier. These pellets are then let down into the base polymer in a proportion that will provide the correct final concentration of colorant to the system. Color concentrate pellets are often let down at approximately 4% of the final system and require only minimal effort and hardware beyond using precolored compounds. If the main concern is adequate mixing in the extruder, this is one of the most popular forms for coloring plastics. 

Molded ABS parts are used in both decorative and protective applications in communications equipment like telephones (see Fig. 6-3), and for appliances, business-machine housings, safety helmets, camper tops, pipe fittings, shoe heels, and so on. Chrome-plated ABS has replaced die-cast metals in plumbing hardware and auto grills, wheel covers, and mirror housings. Some typical products vacuum-formed from extruded ABS sheet are refrigerator liners, luggage shells, tote trays, mower shrouds, boat hulls, and recreational vehicle parts. The possible extruded shapes include weather seals, conduit, pipe for drain-waste-vent (DWV) systems, and the like. 

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