Rexnord® Bucket Elevator and Conveyor Upgrades Cut Downtime at Cemex Cement Plant
CASE STUDY
Since upgrading its bucket elevators and conveyors, the Dixon, Illinois plant of Cemex USA has improved productivity with substantial reductions in downtime. The dry process facility, originally built in 1956, produces clinker and Portland cement 1, 2 and 3. It has a capacity of 700,000 tpy of cement and 550,000 tpy of clinker.
One elevator at the Dixon, Illinois Cemex
plant needed to be completely replaced.
Rexnord designed the new elevator to fit
into the existing location. The boot end of
the new elevator is shown here.
Malfunctions in bucket elevators and drag conveyors resulted in unplanned shutdowns. Maintenance Manager Paul Biggerstaff says, “Modern plants often have only one kiln and two mills, but we have four kilns and six mills, so there is a lot of maintenance needed.”
First to be replaced was a worn clinker reclaim elevator that would no longer meet environmental or safety standards. Rexnord’s design includes heavier buckets for longer wear life, as well as traction wheels and other improvements. Other elevators were upgraded with some of the same features, including larger boot access doors, equipped with easily opened latches instead of being bolted like the previous doors. Rexnord upgraded these elevators with new gravity take-up units and traction wheel rims.
An 85-foot long clinker drag conveyor that runs in a concrete trough underneath the floor was experiencing weekly shutdowns. The chain had worn out the sides of the trough and exposed the rebar, so when the chain wandered, it caught and broke. Also, the chain’s return run lacked the catenary sag needed for smooth operation. Rexnord engineered a new return system with the chain riding on low-cost, long-life Rexnord Ni-hard wear blocks. An hourglass-shaped steel liner for the trough in the pit area under each cooler re-centers the chain and keeps it away from the exposed rebars. Biggerstaff says the changes have virtually eliminated the previous problems. Where the life of the cast chain was one year, it now has lasted two years with three being possible.
Changing economics resulted in the plant’s using more reclaim clinker with a higher percentage of fines. The pushing surface of the previous drag chain allowed fines to escape around and under the chain, overloading the system. Rexnord designed a new chain to fit inside the existing casing, which simplified the changeover. It is based on Rexnord WH5157 chain but incorporates thick flights that project down from the chain to form more aggressive pushing surfaces. All wear surfaces are hard-faced to extend the chain’s life. Biggerstaff reports, “We’ve definitely increased our mill uptime, because the inclined drag was kicking off several times a week. Even when it was running, the drag physically wouldn’t move the tonnage we needed.”
Closeup of head end shows drive components, including
Rexnord SK3 reducer.
Pins on one of the finish mill bucket elevators were experiencing wear from dry cavitation. Rexnord replaced the chain with its patented sealed joint chain system that is factory lubricated and sealed to keep material out of the space between the pin and the bushing. The retrofit was so successful that it has been repeated on three finish mill elevators and is being planned for the fourth. Biggerstaff says, “We only got about one year of life out of the chain before, but it looks like the replacement chain will last well past the three years that Rexnord promised.”
Drag chain on inclined conveyors special Rexnord
welded drag chain with heavy-duty flights that
extend below the chain to form more
aggressive pushing surfaces to move the fines.
7-154CS/3-23-04
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