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To eliminate waste, reduce maintenance and minimize risk of airborne dust and fugitive material build-up, a producer of cement, ready-mix concrete and related products significantly upgraded its bulk-material handling conveyors. Moreover, avoiding accumulations that required clean-up meant maintenance personnel worked less in close proximity to fast-moving conveyors, diminishing the chance of accident or injury.
Grupo Cementos de Chihuahua (GCC) serves the construction industries in Mexico, the United States and Bolivia. The company began operation in 1943, with a capacity of just 60,000 metric tons. Expanding gradually based on a clear strategic vision, the company says its innovative processes and technologies contribute to its dynamic growth, while fostering an environmentally responsible, community-oriented culture.
As at any cement manufacturing site, at GCC Dakotah an extensive conveyor system handles raw materials and moves finished product. In keeping with plans to employ industry best practices for bulk-handling and fugitive-material control in its plants, an extensive assessment of its conveyors was conducted in early 2013. Spillage and dust emissions could be reduced significantly, it was determined, through upgrading of conveyor transfer points.
“Virtually any time bulk material is moved, especially in large quantities or at high speeds, the potential exists to create and release dust,” explains Dan Marshall, product engineer, Martin Engineering. “Dust accumulation affects both safety and productivity, so it’s really more than just a housekeeping issue. Complicating the situation is the fact that bulk-handling systems frequently must accommodate changing weather and material conditions, making dust management an even bigger challenge.”
Assessing the scope
The upgrade amounted to a significant overhaul of six transfer points on four conveyors originally constructed in the late 1970s. All belts are 24-inches wide and range in length from 40 feet to 110 feet. During normal operation, they remove 200-250 tons per hour of clinker from the storage building and carry it to bins feeding the finish mills.
“Most of the material handling system at this plant was fairly standard issue for its time, but some of the components were nearing the end of their useful life,” commented Ralph Denoski, maintenance manager, GCC Dakotah. “We were also aware that significant advances had been made in some areas of bulk handling, and we wanted to take advantage of the newest technologies.”
With a detailed proposal from Martin Engineering in hand, GCC planned the upgrade for a scheduled shutdown in March. In addition to supplying the components, Martin Engineering also eventually assumed responsibility for project planning and supervision, working with a contractor for installation.
Beginning to work
Work began on all four conveyors by disconnecting the material-inlet chutes from the existing skirtboard system and removing the worn rubber skirt seals, clamps, supports, skirtboard chute walls and tail boxes. Removing existing idlers also allowed mounting new belt-support systems and troughing-roll assemblies.
On each conveyor, three Martin Trac-Mount idlers were installed, spaced for optimum belt support. The unique idler design delivers proper belt carriage, while stabilizing the belt line to improve sealing. Its slim profile requires only 8 inches of space for 6-inch idlers, and the slide-in / slide-out frames allow service without the need to raise the belt or remove adjacent idlers.
With new idlers and troughing-roll assemblies in place, each transfer point received a new impact cradle and two belt-support cradles. Installed under the loading zone, these cradles absorb the force of falling material in a transfer point and stabilize the belt line to prevent dust or fines escaping. Rugged impact bars include a top layer of low-friction, ultra-high molecular weight (UHMW) polymer and a lower layer of energy-absorbing styrene butadiene rubber (SBR).
Working in conjunction with the impact cradles on each conveyor is a pair of slider cradles. Installed under the skirt board of the transfer point, the cradles eliminate sagging of the belt edges. Thus properly supported in place, the pinch points that trap material and can gouge the belts are eliminated, improving both sealing efficiency and belt life. When the top eventually wears out, the bars flip over to provide a second wear surface.
Wear liners included
Sixteen-foot sections of skirt board were installed at each transfer point, with new side/center supports and covers. The skirt board is 7 inches high on two of the conveyors, and 12 inches high on the other two. Each also includes internal skirt-board wear liners and tail-box assembly with sealing components.
To deliver positive containment of fugitive dust, each transfer point was outfitted with skirting, a dual design with two sealing surfaces. A primary seal is clamped to the steel skirt board to keep lumps on the belt, and a secondary seal or “outrigger” strip captures any fines or dust particles that may pass beneath the primary seal. The secondary seal lies gently on the belt and self-adjusts to maintain consistent strip-to-belt pressure, despite high-speed material movement and fluctuations in the belt’s line of travel.
Each conveyor was then fitted with a tracker for the return side, installed approximately 10 feet ahead of the tail pulley. By providing immediate and continuous precision adjustment of the belts, the Tracker helps reduce edge damage, prevent spillage and extend belt life.
Finally, each belt received one QC1 primary cleaner and one QC2 cleaner. The QC #1 features a special polyurethane blend and tungsten carbide tip to deliver service life two to three times longer than conventional urethane blades. They deliver excellent cleaning performance immediately, avoiding any break-in period. The assembly maintains consistent tension without frequent adjustment.
The upgrade was done in just 11 days during the scheduled outage, with crews working 12-hour days.
“The production team responsible for that area has nothing but good things to say feedback about the upgrades,” Denoski says. “We don’t lose product to spillage and dust, so that material is sold instead of cleaned up off the floor. The manpower formerly spent on cleanup is now be directed to core business activities.”
“Our experience with Martin Engineering has been very positive,” Denoski concluded. “
Martin Engineering’s greatest strengths are its knowledge of bulk-material handling challenges and solutions, Denoski concludes. “And their no-excuses guarantee gives us the confidence of knowing it stands behind its solutions.”
Martin Engineering supplies conveyor products and industrial vibrators around the world for a wide variety of bulk material handling applications, including cement & clinker, rock & aggregate, coal, biomass, grain and other materials. Founded in 1944, Martin Engineering makes bulk-materials handling cleaner, safer and more productive. Hadquartered in Neponset, IL, it offers manufacturing, sales and service from factory-owned units in Latin America, Asia and Europe and under exclusive licensing agreements in Australia. Visit www.martin-eng.com or call (309) 852-2384. Global representatives for Martin Engineering can be found at www.martin-eng.com/rep-finder.