News flash: Electrical issues aren’t at the root of all speed fluctuations and vibration you might encounter in offset-shaft-driven equipment.
Problems with offset-shaft driven rotating equipment are common in production facilities across a variety of industries, and they can cause headaches ranging from production flaws to outright machine downtime. Maintenance teams often assume the cause is electrical in nature, but the issue could be related to alignment.
Such was the case for O’Sullivan Films in Winchester, VA, a maker of plastic films used in automotive interiors, flooring, and pool liners. O’Sullivan had a problematic offset-shaft driven roll that was causing sheet breaks and unplanned downtime. The maintenance team observed associated speed fluctuations and high vibration with the roll, says Tim Ray, O’Sullivan’s reliability engineering manager/safety manager.
“When you hit that speed anomaly…you can see a defect show up,” Ray says. And because the offset shaft in question was driving the company’s embossing tools, the problem was especially pronounced.
Ray decided to see whether a newly purchased laser alignment tool from VibrAlign could help in diagnosing and solving the problem. Working with Tom Shelton, a technical trainer at VibrAlign, it was quickly determined that misalignment of the offset shaft was the culprit behind the speed fluctuations and vibration.
But rather than just perform a laser-enabled, corrective offset shaft alignment on their own, Ray and Shelton coordinated to have five members of the O’Sullivan maintenance crew receive offset shaft alignment training from VibrAlign.
“They approached me and said, ‘Hey, we’re looking to do some training,’ ” Ray says. He recognized in that offer the chance to see how well O’Sullivan’s optical alignment compared with laser alignment.
So on a scheduled down day late in 2014, VibrAlign founder David Zdrojewski conducted classroom and on-the-floor alignment training with Ray and the O’Sullivan maintenance team.
An offset shaft (or Cardan shaft) is a drive shaft that has u-joints and is used to transfer power from the driver (the motor) to a driven piece of equipment; the fact that the shafts of the driver and the driven elements aren’t in line lends this type of shaft the “offset” name. If the driver and the driven equipment aren’t parallel – both horizontally and vertically – the driven equipment’s speed will fluctuate.
Laser alignment tools can detect and correct vertical and horizontal angular misalignment in offset shafts. But before a laser alignment system can be used, four prealignment steps must be performed, according to VibrAlign’s Shelton. These are:
- Clean the base of the driver/motor and feet to ensure that debris doesn’t create unintended movement. Do a rough alignment of the equipment.
- Correct soft foot by leveling base plates and foundations and using thin, clean shims as necessary.
- Establish and perform a tightening sequence on hold-down bolts.
- Eliminate any residual soft foot.
At the O’Sullivan plant, after lockout procedures were verified, the maintenance team removed the guards around the equipment. The offset shaft was then removed, exposing the coupling faces on the motor and the driven elements. Pre-alignment steps were taken, and an offset shaft fixture – a precision bracket that overcomes the parallel offset between the motor and driven elements – was mounted to the face of the driven coupling flange.
Two rotating turrets then were mounted: one on the offset shaft fixture and another on the coupling flange. A laser embedded in the turret assist the aligner to center the laser alignment tool so that laser lines would be visible to detectors across the long span. The detectors were then mounted to the turrets, allowing for the measuring process to begin.
After this prep work, what did laser alignment reveal? “In one direction, we were very good already,” Ray says. “In the other, we were off, and we were off by a good amount. We knew something was there; we just weren’t sure what it was.”
VibrAlign’s Verti-Zontal alignment process is designed to allow for speedy vertical and horizontal alignment, starting with correcting vertical angularity. Once vertical misalignment is fixed and hold-down bolts are tightened, horizontal misalignment is corrected. One of the top benefits of laser alignment, Shelton notes, is that the live alignment display (available either via a dedicated display device or through an app that can run on a user’s mobile device) provides a real-time view into a user’s corrective actions. If a user moves a machine or adjusts a shim, he or she will know immediately whether the corrections were, in fact, correct.
“It reduces human error,” O’Sullivan’s Ray says. “When you’re (aligning) with other methods, human error enters in. This is also faster.”
Laser alignment enhances repeatability, too, he notes. Because the corrective actions were effectively and efficiently made the first time around, vibration and speed fluctuation issues are less likely to crop up again. And if they do, as machines continue to age, then precision alignment can quickly remediate the problem.
Since beginning the use of laser alignment for the offset-shaft-driven roll, Ray says, production has increased and product flaws have declined.
Prep work is the key to success with laser alignment, Ray cautions. “Take your time with the setup,” he says, “especially in putting that initial piece (the offset shaft fixture) that goes on the flanges.”
Ray says O’Sullivan has been so pleased with laser alignment that it’s looking ahead to new applications of the tool, in particular as a new production line is added this year. “You start with a clean slate,” he says.