Plant Services - April 2008 - (Page 23)

WHAT WORKS Short seal life problem pulverized Cement plant cuts vertical roller mill downtime with bearing isolator eadquartered in Scottsdale, Ariz., the Salt River Materials Group (SRMG) produces coal combustion products, aggregates and Portland cements. SRMG uses the dry process to manufacture cement. In the first stage, limestone is fed through a series of crushers that reduce rock to a maximum size of about 6 in. Secondary crushers reduce it to about 3 in. or smaller, which is then sent to rotary kilns where it’s heated to about 2,700°F and discharged as redhot, marble-sized clinkers. The clinker is cooled, combined with gypsum and ground into powder so fine that nearly all of it passes through a 75 micron sieve. This fine, gray powder is Portland cement. SMRG uses a vertical roller mill as the finish-grinding method at its Clarkdale, Ariz., plant. Clinker and gypsum are ground on a rotating table under large rollers. A classifier transfers the larger particles back to the mill table for additional grinding. A rotor within the separator operates at temperatures as high as 220°F while it rotates on upper and lower bearings. Very fine particles can contaminate bearings, so they are sealed using V-ring shaftmounted rubber lip seals. “The lip seals failed miserably,” says Don Hammond, SMRG mechanical maintenance supervisor. “We were experiencing seal failure issues constantly and having to inject grease into the v-ring seals 24-7 just to stay running.” The heat generated during the manufacturing process caused the lip seals to crystallize, harden and fail. Failed April 2008 H The lip seal at the bottom of the rotor would burn up in less than three weeks, leaving the bearing vulnerable to cement dust and leaking $25/gallon synthetic oil at rates as high as 200 gallons per week. seals lose as much as 200 gallons of synthetic lube in a single week. “At $25 per gallon, this was a costly failure,” Hammond continues. “Add to that the fact that replacing these lip seals could take as long as six days working around the clock, and you can see how much this was really costing us. Trying to counter this impending failure by greasing the seals 24/7 wasn’t exactly inexpensive either.” Joe Johnson, a maintenance supervisor at Salt River, contacted Inpro/Seal (www.inpro-seal.com) about a gearbox problem. When SMRG understood the advantages of bearing isolators, the conversation quickly turned to lip seal failures in the classifier. “We replaced this inadequate sealing method with one of our Articuwww.PLANTSERVICES.com lated Air Mizer designs,” says George Gillespie, the local Inpro/Seal regional manager. “Two major considerations were addressed. The first was that due to the abrasiveness of the product, stainless steel was used as the material of construction rather than the standard 660 bronze. The second was that because of the difficulty, time and cost of disassembling the equipment to install a solid seal design, a split design was used. These split designs operate just like our standard solid designs.” The split design did not require removing the shaft and bearings to install the seal. With the air supply system installed ahead of time, seal installation took about four hours. “The Air Mizer operates without contact as the air purge does the actual sealing,” Gillespie says. “Now they have a permanent, non-contact shaft seal that will typically outlast the equipment it is installed on.” Before meeting with Inpro/Seal, SMRG had tried a number of methods to seal the classifier. “None of them lasted,” Hammond says. “In the past, by now, the lip seals would have failed at least six times, we would have had that many shutdowns, spent lots of man hours replacing the seal and lost a lot of lube. Do the math and you will see how much this product has really saved us.” Though SMRG has not had a problem with the lip seal in the upper bearing, Hammond expects that it also will fail. “And when the upper seals fail, we are ready,” he says, “as we ordered a second bearing isolator, which is ready for immediate installation.” 23 http://www.inpro-seal.com http://www.PLANTSERVICES.com

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Plant Services - April 2008 Contents From the Editor Letters The PS Files Up and Running Crisis Corner What Works Asset Manager Technology Toolbox Cover Story Compressors Motors Flooring Web Hunter In the Trenches Product Picks Classifieds Energy Expert

Plant Services - April 2008

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