Focus on Alignment: balancing act
By Carroll McCormick
Taming a 100-ton jaw crusher doing the jitterbug on 12-ft high legs was not an average house call. "When they started up the crusher, the whole thing was jumping around four inches off the floor," rec...
By Carroll McCormick
Taming a 100-ton jaw crusher doing the jitterbug on 12-ft high legs was not an average house call. “When they started up the crusher, the whole thing was jumping around four inches off the floor,” recalls Martin Duggan, co-owner with Jeff Miller, of PM Mechanical in Windsor, N. S.
Part of a new crushing plant a gypsum company commissioned last year, the machine, instead of being bolted to the floor, had been elevated to make room for a conveyor to take away the crushed gypsum.
The business end of the crusher consists of a 2-ft-dia by 10-ft-long shaft with a big cam in the middle two-thirds. Bearings hold up the shaft ends, each of which has a 10-ft-dia, 10,000-lb flywheel connected to a 200-hp motor. This assembly spins at 300 rpm, and the cam bashes a 6×6-ft vertically-oriented steel plate into another plate to crush the gypsum.
“The flywheels were out of balance and out of synch with each other, creating something like a twisting motion,” says Duggan. “It was really challenging balancing something like that. Some people didn’t think we could do it.” Duggan and Miller did their dynamic balancing act and decided to bolt 110 lb of steel at a precisely determined spot on one flywheel, and 60 lb of steel at just the right spot on the other. This reduced the vibration levels from 7.3 in./sec to 0.06 in./sec, a level that is below the G1 rating for this type of machinery. “It turned out perfect,” says Duggan.
Dynamic balancing is one of several services offered by PM Mechanical, which the pair formed, along with another partner who has since left, in June 1996. Its clients represent industries such as pulp and paper, mining, food processing, pharmaceutical and natural gas.
The company’s bread and butter work is vibration analysis. It is typically commissioned by companies that already have predictive or preventive maintenance programs in place, but are not large enough to have their own employees to do the work.
Portable vibration analyzer
The partners bring a full set of tools to the job site with them, but the most important piece for vibration analysis is a portable CSI Model 2120 data collection vibration analyzer and a laptop computer. The software they use is Mastertrend for Windows, by CSI (Computational Systems Incorporated) in Tennessee.
The vibration analyzer can collect data and aid in doing vibration analysis on the spot. The partners did this, for example, during their work for the onshore natural gas processing facilities and the North Triumph platform for the Sable Offshore Energy Project (SOEP). “They were starting up several pieces of equipment at one time. They were under the gun … they sometimes needed equipment checked right away,” says Duggan.
More typically though, the partners collect data and periodically download it to the laptop for later analysis. “The vibration analyzer has a two-megabyte memory. We can fill that in about four hours,” says Duggan.
Duggan and Miller have about 30 clients they visit on a monthly or quarterly basis. They collect from 1,000 to 3,000 vibration readings per client, and compare them with fault frequency data for each different bearing they have stored in the software. Most jobs take a day on site and another day in the office to do the vibration analysis and prepare the report.
A typical report will list equipment problems such as bearings noted by machine, measurement point, problem and recommendation. There are four repair priorities: 1) immediate action; 2) repair next outage; 3) repair within one month and; 4) fault detected — no immediate action required. Priority 1, says Miller is, “bad enough that you should start to plan [replacement] that day as opposed to during a scheduled outing. The bearing and labour to replace it isn’t too expensive, but if you get into the cost of replacing [the machine], it can run into thousands of dollars, depending on the application.”
PM Mechanical also does one-off vibration analysis jobs for clients who, for example, are commissioning new equipment; the partners did all of the initial vibration analysis and laser alignment for the conveyor drives for the gypsum company with that jumpy gypsum crusher. “PM is an independent, unbiased source of assessment to decide whether a client should accept the equipment,” says Duggan.
Miller and Duggan say they operate the only for-hire company in Nova Scotia specializing in vibration analysis. Duggan trained as a mechanical engineering technologist and spent 17 years at Michelin Tire as an industrial mechanic. Miller’s career prior to PM Mechanical consisted of 15 years divided between National Gypsum as maintenance supervisor and Fundy Grinding doing turbine work. Miller trained as a millwright and a high-pressure welder. Both partners are Canadian Machining Vibration Association-certified and have received extensive training from CSI.
How easily a company will embrace vibration analysis depends on its exposure to predictive-type maintenance, explains Miller: “Without [the exposure], it will be hard to convince them that the cost will be lower than breakdown maintenance.” Some companies are used to parting with their money only when there is something lying broken on the shop floor. But, Miller says, “Anyone who is into the PM mode, they’ll see the value in vibration analysis.”
One such client, which mines gypsum in Nova Scotia, used to do costly scheduled teardown inspections during yearly shutdowns. “They were actually sending motors out for overhauls … checking bearings and clearances.” Yet, says Miller, “You aren’t actually checking for wear. Sometimes they found nothing. And often times they were checking bearings, but a month down the road they would fail.
“With vibration analysis you can pinpoint the problems without tearing anything apart. We told them they could get rid of scheduled teardowns.” Was it difficult to convince the company of this? “Not at all,” says Miller.
The partners usually do laser alignments for new installations, or when equipment that has been removed for repair is being reinstalled. They use a Fixturelaser Shaft 100 from Sweden. If the client company has a union, Miller and Duggan stand back when the equipment has to be moved; otherwise they do everything themselves.
Aligning unusual equipment
Horizontal and vertical shaft alignments, motors to gearboxes and gearboxes to pulleys, for example, are typical assignments. During about two months of work for the Sable Offshore Energy Project, however–some of it as recent as March 2000–the partners worked on some very unusual equipment.
Two hundred kilometers off Nova Scotia’s south shore, natural gas from geological formations containing 85 billion cu m of reserves is being extracted to a complex of offshore platforms. From there, the gas is then piped onshore to a gas plant in Goldboro. After some processing, two compressors re-compress the gas for discharge to a fractionation plant in Point Tupper and onward to markets in Canada and the U.S.
The compressors are run via 10-in., hollow, stainless steel driveshafts connected to two, 15,000-hp turbine jet engines that are 7 ft in dia and 40 ft long. PM Mechanical did the laser alignment. “The first look at it was pretty awesome. This was quite exotic,” says Duggan. “We also did laser alignment of two V12 internal combustion engines. That was exotic too. V12 engines 20-ft long and 10-ft high–you don’t see them every day.”
Miller and Duggan spent 10 days lining up those compressors. “We were working 12 hours a day, weekends, nights–whatever was required,” recalls Duggan, who says the whole SOEP experience was, really good. “We got to see a lot of things.”
Montreal-based Carroll McCormick is senior contributing editor for Machinery & Equipment MRO. He can be reached at email@example.com.