Variable barrier energy transfer screw

Many of the geometric features of a VBFT screw are similar to those for an FT screw. The VBFT screw, however, has three additional enhanced features that can be adjusted for optimal processing performance. The channel depths for a 114.3 mm diameter VBFT screw designed for use with a specific polyolefin resin is shown by 

A Maddock solidification experiment was performed using ABS resin at a screw speed of 60 rpm [30]. Like the solidification experiment for the ET screw of Section 14.2.2, the feedstock resin contained 2% Ti02 compounded into the pellets, and a black-colored masterbatch was added at a letdown ratio of about 220 1. The cross-sectional views of the resin solidified in the channels are shown by Eig. 14.15. The white pellets and unmixed resin are visible in the views as white regions. The regions that are well mixed are an evenly colored dark or black color. 

As shown In EIgs. 14.10 and 14.15, the cross-sectional views at axial distances less than 10 diameters were similar for both ET and VBET screws. Eor example, the views at 6 diameters were composed of a compacted bed of discrete pellets. The views at 8.4 diameters were In the transition section, where the pellets compacted, softened, and began to melt. For the ET screw, the compaction process had just 

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The first wave-dispersion-type screw was developed and patented by Kruder in 1975 [18], and the device was trademarked as the Wave screw. Numerous other wave dispersion screws were developed later based on Kruder s design. The term wave dispersion screw refers to screws with metering sections that have two or more channels with a flight between them that is selectively undercut to allow the dispersion of solid polymer fragments and molten resin. Several commercially available screws utilize this type of technology and are discussed in this section. These screws include Double Wave screws, Energy Transfer screws. Variable Barrier Energy Transfer screws, DM2 screws, and Fusion screws. 

Some of the more widely used high-performance screws include the Energy Transfer (ET) screw [19], the Variable Barrier Energy Transfer (VBET) screw [20], the Double Wave screw [21], Stratablend [22] and Stratablend II [23] screws, and the Unimix [24] screw. Other devices can, however, act as a trap for solid materials from the melting section. These devices include Maddock-style mixers [25], spiral dams, and blisters. They will be briefly discussed in this section as many of them have been the subject of many articles on secondary mixing processes. 

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