Poorly aligned machinery can be costly, and it’s more common than we’d like to think. It can damage equipment, create energy inefficiency, and cause unplanned downtime. No one runs misaligned rotating machinery on purpose. The problems occur when we don’t know, so how do we detect when there are issues?
“If increased vibration levels or noise are noticed or premature coupling, bearing, or seal failures are experienced, it’s a pretty safe bet that you have a shaft alignment problem,” says Alan Luedeking, vice president of Ludeca. “In some cases declining product quality can be an indicator. The best way to check, once the machines are down, is to put a laser shaft alignment system on and take a set of readings. With a good one, this will take less than three minutes from setup to results, after all safety lockout/tagout procedures have been observed and the coupling guard has been removed.”
If you have coupled machines, you will have alignment problems, declares Stan Riddle, trainer/technical support team at VibrAlign. “The trick is to catch them early and minimize them,” he says. “The markers I always use to determine alignment problems are vibration analysis, frequent seal and coupling insert replacement, and information from machine operators.”
Robert X. Perez, author of “Is My Machine OK?” indicates high vibration levels that show up either axially or radially at the coupling end of a machine also can be indications of an alignment problem.
“You know you have an alignment problem if you use a PdM method that identifies multiples of rpm in a frequency spectrum,” explains Heinz Bloch, owner of Process Machinery Consulting in Westminster, Colorado. “In most instances, a twice-per-rpm peak with an amplitude roughly twice the amplitude of the background noise would be a rather clear indication. Since I'm in the failure avoidance business, I would say that doing proper alignment as a matter of routine is the best strategy toward avoiding misalignment in the first place. It's a bit like, ‘How do I know if I'm overweight?’ I could stand on a scale and look up a chart that recommends weight vs. height for my age group, or I could eat right, do a little exercise, and look in what hole my belt stem is located compared to where it was last year.”
If you notice an increase in consumption of couplings, bearings or seals, that is a pretty good indicator of alignment problems,” confirms Luedeking. “However, long before you should notice such deleterious trends, you should have nipped this problem in the bud by noticing worsening vibration trends via your properly set up and configured condition monitoring systems. Your reliability program should include both on-line and handheld vibration monitoring and trending systems to catch these problems long before your spares inventory is unnecessarily affected.”
For monitoring alignment, both vibration analysis and infrared are good, but not perfect, says Riddle. “The best way is to actually measure for misalignment, with either laser tools or dial indicators, as part of a coupling inspection,” he says.
|Mike Bacidore is chief editor of Plant Services and has been an integral part of the Putman Media editorial team since 2007, when he was managing editor of Control Design magazine. Previously, he was editorial director at Hughes Communications and a portfolio manager of the human resources and labor law areas at Wolters Kluwer. Bacidore holds a BA from the University of Illinois and an MBA from Lake Forest Graduate School of Management. He is an award-winning columnist, earning a Gold Regional Award and a Silver National Award from the American Society of Business Publication Editors. He may be reached at 630-467-1300 ext. 444 or firstname.lastname@example.org or check out his Google+ profile.|
“An ounce of prevention is worth a pound of cure,” offers Bloch. “So I would use laser alignment just as routinely as I would use a box wrench instead of vise grips when I work on a classic automobile. Plan B would be to use a device made by Ludeca or a similarly smart company. Basically, these are frequency spectrum analyzer-annunciators-data collectors.”
Luedeking concurs with using a laser alignment system. “This lets you set up on running equipment and continuously monitor positional changes in the machines from any cause such as thermal growth, load changes, dynamic forces exerted by connected piping, and process flows,” he says. “If you set up on running machines and monitor them through shutdown and coast down to the full rest condition, you can derive true target specs to realign the machines while in this cold and stopped condition, to precisely compensate for all positional changes that will occur in the machines when you start them up and put them under load again. Of course, you can also monitor the startup to the fully loaded running condition over several hours, or even days if need be.”
Spares history also can be used to recognize alignment problems by analyzing parts usage per machine and across families of similar machines, explains Riddle. “Most good mechanics already know which machines have alignment problems,” he says. “They are the ones that constantly need seals and coupling inserts. Another good way is to look into the trash can closest to the machine in question. If it has lots of shredded inserts and failed seals in it, it probably has an alignment problem.”