High-performance screw

Several case studies are presented in the next sections that show some common root causes of contamination in injection-molded parts. In these case studies, the problem is presented in a manner that the troubleshooter would encounter during a trial or information-gathering session. In each case study, the modifications required to fix the process are detailed along with supporting fundamental information. Two of the case studies used (ET) screws to eliminate the defects. ET screws and other high-performance screws will be discussed in Chapter 14. 

Table 11.12 Screw Channel Dimensions for a 140 mm Diameter, 20 L/D DM2 High-Performance Screw Running a PP Resin in an Injection-Molding Operation...

A high-performance screw was designed for the injection-molding press. This screw was designed with a much higher compression ratio and with large flight radii in all sections of the screw. The details of the screw are provided in Table 11.14. 

The press was started back up using the high-performance screw and natural HIPS resin with 2 % of a light gray color concentrate masterbatch. For this startup the same 2.69 kg part was produced and the barrel set point temperatures were the same as before. After steady operation was obtained (about 10 parts), the 2.69 kg part and gating were plasticated in 33.5 s at a screw speed of 52 rpm and 9.5 MPa... 

Table 12.3 Screw Channel Dimensions for a 63.5 mm Diameter High-Performance Screw Running GPPS Resin for a Profile Extrusion Line...

This chapter will present and discuss the operations and designs for several barrier and high-performance screws that are commercially available. Numerous small companies that manufacture screws have recognized the performance of these screws and have manufactured look-a-like screws based on the technologies presented here and the descriptions in expired patents. These manufacturers will not be discussed here. 

Figure 14.20 Schematic of a wave section of a Fusion high-performance screw (courtesy of Timothy W. Womer of Xaioy incorporated)...

Numerous other high-performance screws are available commercially that are not based on wavy channels. Instead they are designed with flow paths that disrupt the normal flow that would occur in a conventional flighted metering section. The most common screws are the Stratablend designs and the Unimix screw. These screws will be discussed in the next sections. 

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