Vibration is everywhere! Vibration is a “back and forth” movement of a structure or component. Vibration can also be referred to as a “cyclical” movement. It can be inherent in a piece of equipment or can be induced by another form of energy. The real question is whether the vibration is detrimental to the equipment and its internal components.
Vibration is typically monitored through some form of analyzer, either online or offline such as the VIBWORKS analyzer.
What causes vibration? Here are just a few causes, but there are so more which can lead to elevated vibration levels. More importantly, if caught early enough, they can be corrected and thereby maximize the life of our equipment:
- Installation of the machines
- An improperly mounted bearing can cause severe vibration. This can lead to damage of the bearing as well as other components within the machine.
- Operation of the machine
- Pushing our machine beyond its recommended maximum output. Our machines respond by vibrating more than the recommended allowable limits and will eventually fail.
Watch our video ‘What’s Misalignment’ to learn more about the causes and effects of having misalignment in your rotating equipment
Some common machine problems that generate mechanical vibration:
- Misalignment is one of the most common issues that leads to high vibration and eventually failure of the machine. It can be easily detected and corrected. Take the time to laser align machines properly to the recommended tolerance.
- Unbalance is another easily missed problem that causes severe damage to our equipment. It can also lead to cracks of the housing itself. If not detected and corrected soon enough it can lead to dangerous catastrophic failure. Unbalance can be easily detected and corrected extending the life of equipment.
We never have enough time to do things right the first time but always find time to do them again.”
These few issues can be easily detected with properly set-up software. Often, the setup is incorrect and inaccurate. Invalid data is captured in the FFT. Please consult an expert to make certain you are utilizing your condition monitoring software to its fullest potential. Remember… If it’s Critical and Rotates it should be Aligned, Balanced and Monitored.
by Ana Maria Delgado, CRL
May 2016 · Plant Services Magazine
Like a lot of reliability engineers, Joe Anderson, former reliability manager at the J.M. Smucker Co., appreciated – in theory – that precise pulley alignment is critical to preventing vibration problems and ensuring successful operations.
My understanding was, ‘Yeah, we need to do it,’ ” Anderson says. “But you always have these excuses.”
When the Smucker’s plant at which Anderson worked launched a dedicated vibration monitoring and control program a year-and-a-half ago, though, Anderson quickly became a convert to making precision alignment a priority.
The plant purchased a vibration analyzer (VIBXPERT) and laser alignment tool (the SheaveMaster Greenline) from Ludeca to help aid in identifying machine defects that appeared to be linked to vibration caused by misalignment. Laser alignment allowed for correcting vertical angularity, horizontal angularity, and axial offset – the three types of misalignment – simultaneously. Whoever was using the laser alignment tool, then, could be sure that adjustments made to correct one alignment problem didn’t create an issue on another plane.
Read entire article to learn how J.M. Smucker Co. made precision alignment a priority: Get your alignment in line: Don’t jiggle while you work
by Ana Maria Delgado, CRL
Smith Pump modeled the discharge head in Solidworks. Since the measured natural frequency was 1500 cpm, and the pump operating range was 1500 to 1800 rpm, we wanted to lower the natural frequency below 1500 cpm. We knew by removing stiffeners from the discharge head we would lower the unit’s natural frequency. We removed stiffeners and ran a finite element analysis to determine how much we would lower the natural frequency. Our model study showed that by removing all the external stiffeners and half of all the internal stiffeners we would lower the natural frequency by 30%. Pump #2 was removed and its discharge head modified by removing stiffeners.
Pump #2 was put back into service with its modified discharge head and vibration testing was performed. The new bump test data gave a measurement of 86 cpm in line with discharge. The vibration measured at 50 HZ at the top of the motor was 0.05 in/sec rms. The vibration dropped from 0.47 to 0.05 in/sec rms.
In conclusion, determining a unit’s natural frequency is very important when designing a vertical turbine pump. Every fabricated steel discharge head that Smith Pump makes is modeled in Solidworks and goes through a finite element analysis to make sure the unit’s natural frequency (mainly discharge head and vertical motor) is 25% away from any running speeds. In this example, the discharge head (built by others) was too stiff and had a natural frequency at the pump operating speed causing high vibration. Since Pump #2 was so successful, we are currently modifying Pumps #1 and #3 the same way. Common sense tells us that the stiffer and stronger the discharge head the better, but this case study clearly shows us that is not the case!
Special thanks to our customer Josh Jurgensen, service engineer at Smith Pump Company for sharing this case study with us!
by Yolanda Lopez