Barr screw

Interestingly enough, Willert s description is essentially identical to the patent of Hsu [32]. This patent was filed in January 1973 and issued January 1975. Screws covered by Hsu s patent used to be sold under the name Maxmelt Screw by the Plastics Machinery Division of Hoover Universal. Coincidentally, Hsu used to work at Hartig at the time when the basic concepts of the Barr screw were being devel-... 

The melting performance of the Barr screw can be analyzed by the same procedure followed for the Maillefer screw. The initial portion of the barrier section can be analyzed just as a Maillefer screw. If Zji is the length of the initial Maillefer portion of the barrier section, the solid bed velocity at z = Zj, is approximately ... 

The total melting of the barrier section is the sum of Eqs. 8.99 and 8.100. This results in the following expression for the melting length of the Barr screw ... 

The screw geometry is very similar to the Barr screw with the one major difference being an abrupt change in helix angle in the main flight at the point where the barrier flight is introduced. This allows the width of the solids channel to stay just as wide as the full channel width of the feed section. Obviously, this is done in an attempt to maintain the solids channel as wide as possible. However, this also causes an abrupt change in the direction of the solid bed velocity, and this can lead to instabilities. 

If typical values are used for cpb and cpf, the melting length of the Dray and Lawrence screw will about 10 to 20% longer than the ideal compression screw. The melting performance of the Dray and Lawrence screw is thus about the same as the Barr screw and slightly better than the Maillefer screw. A patent on this barrier screw... 

This means that the melting performance of the Kim screw is slightly lower than the Dray and Lawrence screw and the Barr screw. It has an advantage over the Dray and Lawrence screw in that the transition from feed to barrier section occurs more smoothly. However, at the end of the barrier section the same difficulty arises as with the Dray and Lawrence screw. 

Figure 1.3 Schematic of a typical single-flighted screw (courtesy of Jeff A. Myers of Robert Barr, lnc.(...

Figure 8.21 Schematic for Maddock-style mixers a) a mixer with the flutes aligned in the axial direction, and b) a cross-sectional view perpendicular to the screw axis showing the clearance for the mixing flight (courtesy of Jeff A. Myers of Robert Barr, Inc.)...

Figure 8.23 Schematic of blister ring mixers a) a blister mixer positioned in a metering section, b) blister section positioned at the discharge end of the screw near the tip, and c) the cross-sectional view showing the region of annular flow between the screw and barrel wall (courtesy of ieff A. Myers of Robert Barr, Inc)...

Figure 8.30 Cross-sectional views [53] of the extrudate samples using a conventional screw with segmented tip for the testing of different types of dynamic mixers a) conventional screw with no mixer, b) Twente Mixing Ring, and c) Barr Fluxion ring mixer. The extruder was operated at a screw speed of 80 rpm and a letdown ratio of 220 1 of a white pigmented ABS resin to a black color concentrate...

Two screws were designed with Energy Transfer (ET) sections from Robert Barr, Inc. [31], and the screws were labeled by Dow as ET-1 and ET-2. The original... 

Figure 14.5 Schematics for the Barr-ll and Barr-Ill barrier screw technologies a) full-length schematic of a Barr-ll barrier screw, b) expanded view of the barrier entry section of a Barr-ll screw, c) full-length schematic of a Barr-Ill barrier screw, d) expanded view of the barrier entry section of a Barr-Ill screw, and e) expanded view of the crossoverflow rearrangement section at the exit of Barr barrier screws (Schematics courtesy of Jeff Myers of Robert Barr, Inc.)...

Chung, C.I., and Barr, R.A., A Novel Energy Efficient Screw Design, SPE ANTEC Tech. Papers, 29, 168 (1983)... 

Barr, R.A., Extruder Screw with Improved Energy Efficient Melting, U.S. Patent 6,599,004 (2003)... 

There are many different barrier screw designs, each offering unique advantages. They include the Uniroyal (the original barrier screw) the MC-3 of Hartig the Efficient of New Castle Ind. the Barr 2 of R. Barr Inc. the VPB of Davis Standard the Willert II of W. H. Willert Inc. and the Double Wave of HPM Corp. 

Table 2-3. Custom-Designed Barrier Screw Barr Et Screw.

Barr, R. A., High Performance Screw Is Custom Designed, SPE IMD Newsletter, No. 18, 1988. 

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