Machines vibrate for lots of different reasons-some good, others not so good. Over the next few months, we are going to write about some of the most common machinery vibration causes, and possible solutions.
One of the most common problems in coupled rotating equipment is misalignment. Simply stated, misalignment is when the driving and driven machine shafts are not collinear, or sharing the same centerline.
Misalignment can often be diagnosed with vibration tools. It can certainly be diagnosed with a good quality alignment tool. It is obvious that diagnosing misalignment only identifies the problem. The misalignment must be eliminated to “fix” the problem.
COUPLING MISALIGNMENT CAUSES
• The most common-the machines were not aligned accurately to start with.
• Thermal or stress changes in piping or the machines themselves.
• Base movement, curing grout or concrete.
• Machines moving because they were not properly tightened down.
• Soft foot.
COUPLING MISALIGNMENT SOLUTIONS
• Precision alignment of the shaft centerlines.
• Properly compensating for thermal growth.
• Regular alignment checks-as part of a good PM program.
• Proper tensioning of hold down bolts in the driver and driven machines, as well as bases, risers, piping systems, etc.
• Minimizing soft foot.
While most aligned machines will stay aligned, never assume a properly aligned machine will stay properly aligned forever. Regular vibration testing is a good method to determine alignment quality, and alert you to changes in alignment.