Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.
Issue link: http://concrete.epubxp.com/i/551927
34 • August 2015 www.concreteproducts.com FEATURE BY KEN STADDEN Seven BHS twin-shaft mixers are producing the lion's share of the esti- mated 210,000 yd. of concrete for New NY Bridge cast-in-place struc- tures, as well as tens of thousands of additional cubic yards for the bridge's main precast structural elements, primarily tubs for pile caps and pier caps. TZC's three floating ready mixed plants on the Hudson River each have a BHS DKXS 4.5 6-yd. mixer, two running within an enclosure (the new plant shown here will get an enclosure before winter). "Our pre- vious experience was with drum mixers, so we relied on research and reputation" when selecting a twin-shaft mixer, says TZC Lead Engineer Wayne Dabrowski. "Our mix design needed that shear for uniformity, and BHS came highly recommended. So far, mixing has been consistent, and is the main reason we've had success with this project." At its Cape Charles, Va., location, Bayshore Concrete Products Corp. has been split batching with two BHS DKXS 4.5 6-yd. models for seven years, noting minimal maintenance requirements. "Paddle replacement has been routine, and one mixer was relined for the first time since 2008," says Bayshore Plant Manager Chuck Hook. At Coastal Precast Systems in Chesapeake, Va., a second BHS DKXS 3.0 4-yd. mixer has joined an initial model. "The first was a routine upgrade over a previous twin-shaft mixer," explains Paul Ogorchock, owner and president. "The second is for Tappan Zee and other projects, and will allow us to do split batching." For the Tappan Zee and other projects, "the BHS mixers help us reach that 5,000 psi strength in 24 hours," says Ogorchock. BHS-Sonthofen GmbH is based in Sonthofen, Germany, with sub- sidiaries in the U.S., China, India and Russia. A member of the Con- crete Plant Manufacturers Bureau, BHS is credited with inventing the twin-shaft mixer in 1888, and is a dominant player in the worldwide market with a line of heavy-duty models. Unique features of BHS mixers include hexagonal shafts which place mixing paddles 60 degrees apart, outside-mounted V-belts for easier replacement, worm-drive gearbox rather than planetary gears, and shaft bearings mounted in separate bearing boxes to protect them from seal leakage. "The worm drive is mounted directly on the shaft using a torque arm, providing float that absorbs shock," notes Stuart Bentley, Mixing Division manager of Char- lotte, N.C.-based BHS-Sonthofen Inc. Driven at only 19 rpm, he adds, the closely-spaced paddles promote intense mixing that is 95 percent complete in as little as 30 seconds. BHS TWIN-SHAFT MIXERS EXHIBIT METTLE FROM THE HUDSON RIVER TO THE CHESAPEAKE BAY BHS DKXS 4.5 twin-shaft mixers are at the heart of TZC's three foating batch plants on the Hudson River. BHS en- gineers underscore the location of the outboard-mounted V-belt drives to facilitate replacement. The main shaft bearings are likewise mounted outboard, away from the shaft seal, to curtail contamination. A hexagonal shaft allows mixer arms to be spaced 60 degrees apart for rapid mixing at low rpm.