A better herringbone makes a better gear pump.

Gear pumps with herringbone (double helical) gears are used less commonly than single-helix or spur gears in twin-screw compounding. The herringbone gears were previously machined in two pieces, which resulted in looser tolerances. Now Witte Pumpen and Anlagentechnik GmbH in Germany, represented in North America by JLS International in Charlotte, N.C., has commercialized a method of machining what are said to be the first one-piece herringbone gear shafts for melt pumps. They are reportedly stronger and more precise than two-piece herringbone gears. Single-piece construction also allows a larger shaft journal that withstands higher torque and pressure. The herringbone's opposing steep angles--around 35[degrees] compared with the 6[degrees] angle of a single helix--prevent axial thrust and reduce pulsation by 75% vs. a single helix and nearly 90% vs. spur gears. Bearing and melt temperatures reportedly are also reduced, potentially allowing higher throughput. Tel: [phone], www.jlsintl.com

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