Grooved Feed Zones

Friction between solid polymer particles or pellets (termed internal friction). This also influences conveying as well as hopper flow, especially in grooved feed zones. 

Figure 6.4 Grooved feed zone sleeve used with 38 mm extruder.

Combined Barrier Screws and Grooved Feed Zones... 

The development of the grooved feed zone to improve forwarding of plastics pellets and crumb is described in Section 6.2. 

Melting was achieved by a range of devices which achieved their required function with minimal influence on output rate due to the positive solids conveying. Eventually the barrier screw was substituted for the augmented conventional screw, and the combination of barrier screw and grooved feed zone became established in Europe whereas in North America barrier screws are mainly used with smooth feed zones [13]. 

The combination of barrier screws with grooved feed zones is a further variable which complicates comparisons of barrier screws with conventional screws. Although in... 

A comparison of a Maillefer type barrier screw with a conventional screw in Section 7.5.1, showed for the barrier screw, a reduced output rate when used with PP and an increased output rate when used with LDPE. Following the discovery that the metering zone of a Maillefer type screw was running only partially filled when extruding medium density polyethylene (MDPE), Qui and co-workers [25] evaluated a grooved feed zone to ensure the metering channel was filled. 

With so many possible design variables, there are inevitably inconsistencies between reported performances. Schoppner [36] showed that for PP the output rate depended entirely on whether or not a grooved feed zone was used. For the same feed zone the output rates for the conventional and barrier screws were the same. However, output rates from the grooved feed zone were 67% more than for the smooth feed zone. It also produced erratic changes in melt temperature with increasing screw speed for both conventional and barrier screws. 

Using only the smooth feed, the barrier screw increased specific output rate for SAN and PA by 10-15%. Only PP was used in both smooth and grooved feed zone extrusion trials [36]. 

To study the influence of atomized water injection on the cooling time reduction, test series on a blow molding machine KEB 4.01, Krupp Kautex Maschinenbau GmbH, Bonn, were carried out. The machine is equipped with a 50 mm diameter (L/D = 20) extruder with grooved feeding zone. 

The first successfiil tests to combine barrier screws (1) with grooved feed zone barrels were carried out at the end of the seventies, begin of the eighties (2), see figure 1. Since then this system has been continuously fiuther developed and analyzed. The specific, screw speed related throughput til /n, and the relative length L/D (3) and the screw speed (4) have been increased. 

In any cases, the high pressme in the solids channel has to be built up mainly in the grooved feed zone of the extruder where it can lead to severe abrasive wear at screw and barrel. 

Figure 1. Single-screw-extruder with grooved feed zone and barrier-screw with mixing elements.

Figure 2. Principle of melting mechanism in single-screw-extmder with grooved feed zone and bamer-screw (unrolled screw channel)...

Figure 5. Test-extruder with grooved feed zone General arrangement and measuring quantities...

Figure 6. Average melt pressure courses in grooved feed zone extruders with diffo ent grooves in the plasticizing barrels specific throughput 4,30 kg-min/h.

Key Words Single-screw extruder, barrier-screw, grooved feed zone, plasticizing... 

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