Pumps & Systems, November 2012
Precisely aligning shafts and belts in rotating machinery has become critical maintenance-related tasks across many industries—for good reasons. Misalignment historically accounts for a significant percentage of the costs associated with rotating machinery breakdowns, leading to unscheduled downtime, lower productivity, and heightened maintenance time and labor. When shafts or belts are inaccurately aligned, greater loads are imposed on machine components. This can result in increased wear and escalating energy consumption, among other adverse and expensive effects.
While operations spend vast amounts each year to remedy misaligned shafts and/or belts, a more practical approach should be implemented—preventing problems before they occur. By adhering to best practices—including preventive maintenance and using innovative, enabling technologies—operators can help eliminate misalignment issues and realize longer and more efficient machinery performance.
Whenever a turbine, electric motor or other driver is coupled to a pump, generator or other equipment, the centerlines of rotation of the two machinery shafts must be in line with one another. Otherwise, parallel (or offset) misalignment, angular misalignment or usually a combination of the two will cause stress on the shafts and negatively impact machinery health and operation. Misaligned shafts can lead to premature bearing or coupling failure, shaft fatigue, damage to seals, and increased vibration levels, friction, overheating and energy consumption.
Properly and accurately aligned shafts of rotating machinery can:
• Reduce excessive axial and radial forces on the bearings
• Minimize the amount of shaft bending from the point of power transmission in the coupling to the coupling end-bearing
• Minimize wear in the coupling components
• Reduce the potential for mechanical seal failure
• Maintain proper rotor clearances
• Eliminate the potential for shaft failure from cyclic fatigue
• Help keep vibration, noise, friction and higher energy consumption at bay
Through the years, methods for aligning shafts have evolved to the extent that traditional rough and quick approaches have taken a back seat to more advanced (and more accurate) technologies. Conventional, low-tech methods for shaft alignment have included straight edge and feeler gauge, which are notoriously inaccurate, or dial indicators, which may offer a higher degree of accuracy but will require specialists and time-consuming implementation.
The demands for accuracy, simplicity and reliability in the methods used to enable, detect and fix shaft misalignment have paved the way for highly precise laser alignment systems. Highly precise laser alignment systems introduce affordable and easy-to-use solutions to align the shafts of rotating machinery quickly and with pinpoint accuracy. The latest versions of laser-enabled technology have been engineered to perform proper alignment in a fraction of the time needed for traditional methods, require no special skill and will prove more accurate by comparison.
Laser technology alignment tools include displays for real-time alignment values, allowing users to confirm the results of alignment corrections as they are performed. Other notable features include:
• Quick-start guides
• Fast measuring unit positioning capabilities
• Built-in tolerance checking and memory facility to allow for results to be stored and shared by downloading
The shaft alignment process essentially operates under the “MAD” principle: Measure, align and document. As an example, with the latest handheld technology (employing two measuring units—both provided with a laser diode—and positioning detectors and display unit), three measurements are taken:
• The distance between both laser heads
• The distance between the laser head on the moveable piece of equipment (in most cases, an electric motor or other driver) and the first bolt hole on the moveable piece
• The distance between the first and second bolt hole on the moveable piece of equipment