Understand shaft alignment fundamentals

Friction can cause damage, but it also can be an energy hog.

11/25/2011


 

Keeping your rotating shafts in alignment is a fundamental—and often overlooked—maintenance project. Alan Luedeking, the manager of technical support for Ludeca Inc., Doral, Fla., talked with Plant Engineering (PE) about some of the critical issues in shaft alignment, and how they affect safety, energy, and productivity.

PE: Maintenance personnel aren’t always looking for issues with shaft alignment. Are there some warning signs or performance cues that operators or maintenance staff should be on the lookout for that might indicate a problem?

Luedeking: Yes indeed. If you hear unusual noise or feel increased vibration, those are important warning signs that should not be ignored. All the senses should be involved. Smell your environment: chemical leaks, overheating grease, and unusual stains, all are diagnostic clues and warning signs. One should always be alert to everything in one's surroundings in the plant, for safety as much as for good maintenance. Most importantly, a proactive maintenance program should include condition monitoring-based strategies and solutions to prevent unnecessary repairs and unscheduled downtime in the first place.

PE: Let’s talk about the ROI of shaft alignment. When you’re out of alignment, what are the potential losses in terms of both productivity and uptime?

Luedeking: They are great. Besides the obvious risks of a broken coupling or shaft, misaligned shafts lead to increased radial load on the bearings with consequent great reduction in service life. Besides wear and tear, less obvious is that misalignment also results in increased power consumption, which several careful studies have shown to range as high as 10%, although more conservative estimates easily reach 4%. The efficiency of the machines is impacted, and product quality may be affected by the increased vibration resulting from misalignment.

PE: What’s the correlation between shaft alignment and energy efficiency? This would seem to be an overlooked area.

Luedeking: Funny you asked—I was just thinking about that in my previous answer. This aspect is often overlooked, and a savings of 4% on an energy bill of $50,000 a month easily justifies the best laser shaft alignment on the market in less than a year, without even considering the benefits of greater uptime, less repair expense, and time saved on the alignment itself.

PE: What are a few basics about shaft alignment that should be on the minds of operators and maintenance staff?

Luedeking: Safety and quality. Safety first, always. Make sure your machines are locked out and tagged out before you set up. When I say quality I refer to two things: the suitability of your laser alignment system for the task at hand, and the excellence of your alignment procedures. Are the machine bases properly designed, installed, and cared for? Always check for, analyze, and correct soft foot. Does your laser system help you do this?

Do you have jackscrews in place to move your machines? Do your millwrights have access to good-quality stainless steel shims? Are your machines under pipe strain? Can your laser system even measure that and help you find it? Are you considering thermal growth and dynamic load shifts in the positions of your machines? If not, you may be grossly misaligning your machines by aligning them to zero when cold.

Your laser system should let you input target specs, or thermal growth values at the feet, and calculate this growth from observed changes in temperature, or even measure and monitor this growth live as you run the machines! Only the best-quality laser system will let you do all of these things, thereby achieving better results and saving you time and money at every step.



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