Alignment Matters

One of my friend was suffering from neck pain for past few weeks. When consulted with the doctor, it was identified that his bad posture while using smart phone and sitting on his office desk was the main reason for this problem. The doctor advised him to make small changes to take care of his posture from now on wards, and prevent the spinal misalignment and associated problems in the future.

By taking care of our posture, we all can reap the health benefits for years to come. So take a break from your smart phone, practice good posture, and work toward a greater quality of life. It doesn’t take long at all!

Relating this to the rotating machinery, we must recognize how harmful the shaft misalignment could be to the long term reliable operation of rotating machines.

The University of Tennessee, College of Engineering, Maintenance and Reliability Center Knoxville, has conducted research on shaft misalignment and reached to conclusion that relatively small amounts of shaft misalignment can have a significant impact on the operational life of a bearing. The magnitude of the bearing life reduction varies with the coupling type, bearing load capacity, and dimensions of the motor. The results from this research show that, in some cases, up to 50% percent of the expected bearing life can be lost with as small as a 5 mils (0.005") offset misalignment. (Ref:1)

Up to 50% percent of the expected bearing life can be lost with as small as a 5 mils (0.005") offset misalignment

In summary, one of the study’s conclusions was that as little as 1-3 mils (.001”-.003”) can reduce bearing life by 10 percent due to increased load on the drive end bearing, depending on the type of coupling used to connect driver to driven component.

As per study conducted by SKF >24% of bearing failures are due to Installation errors and Bearing Overload and one of the major reason for these defects is due to shaft misalignment.

In addition to being detrimental to bearing life, misalignment has been shown to increase energy consumption as much as 9 % and reduce lubricant film thickness by as much as 75 percent in journal bearings.

In addition to aligning the shafts, a critical step in installation is detection and elimination of "Soft foot". Soft foot causes machine frame distortion and results in an uneven air gap between the rotor and stator in a motor and can result in additional increases in power consumption of up to 17.4%. (Ref:2)

Precision Alignment is key step in achieving higher Reliability ?

In fact, many machine failures and defects can be eliminated up front by correctly installing and aligning shaft and belt-driven equipment by, among other things:

• Ensure that the base-plate is properly bolted or grouted to the foundation; both should be flat and level.
• Make sure the foundation is properly sized for the weight and operating conditions of the asset.
• Centering equipment horizontally on the base-plate, with equal amounts of shims placed under each foot. Installing jack bolts is also recommended to facilitate horizontal movement of the machines.
• Tightening all anchor bolts to the proper torque.
• Check for Piping Strain during alignment. Effect of pipe strain can be checked by loosening the flange bolt Using dial indicator or Laser alignment tool. Pipe strain is caused by misaligned pipes and flanges, or improper piping support, which causes casing distortion resulting in shaft misalignment which leads to bearing and and seal failures. It is one of the most common problem seen in pump installations. Determine if pipe strain is present or not, obtain alignment readings before and after the piping is connected, or disconnected.

Zero pipe strain is probably unrealistic, but as a "Rule of Thumb" if the alignment changes more than 2 mils while loosening or tightening the pipe flanges, modifications to the pipe header and / or pipe supports should be considered essential.

• Requiring precision alignment of the machines to proper tolerances prior to releasing the asset to operations.
• Selecting the right length and material belt and its pitch angle, then correctly installing the belts and sheaves.
• Provide the correct tension to the belt. Over tension causes overload on the motor resulting in increased power consumption, in addition to the risk of shaft failure due to fatigue. Over tension causes overheating of bearing which would also reduce the life of bearing due to lubrication failure.
• Correcting all three types of misalignment – vertical angularity, horizontal angularity and axial offset – as part of the precision alignment process.
• Never forget to use 'Laser Alignment' tool for accurate alignment.
• Inspect the failed bearings for the symptoms of misalignment to prevent recurrence.
• Look for possibility of using Self aligning ball bearings where applicable. But be careful; they have their limitations. Don't consider that they will be dealing with whatever misalignment is left remaining. 

It is totally 'Wrong' to think that there is no need for Precision alignment in the presence of Self aligning bearings. You still need to align them precisely.

• Inspect the failed bearings for the symptoms of misalignment to take necessary proactive mitigation and prevent recurrence of future failures due to misalignment.

Educate, Educate, Educate

It is very important to educate the staff who are responsible in execution of these above tasks. Provide your people with the right tools, training, proper installation techniques, and precision shaft alignment to achieve long term reliability of your rotating machinery. 

References

University of Tennessee. “Study Shows Shaft Alignment Reduces Bearing Life.” Maintenance Technology Magazine, April 1999.

Lambley, J. C. Misalignment – Its Effects on Power Consumption. Runcorn: August 1994. and Olsen, Alfred. “Benefits of Comprehensive Motor Maintenance.” Maintenance Technology: September 1996.