How Big is a Micron?
The human eye can only see something that’s a minimum of around 40 – 50 microns!.
If you take your pen, put a small dot on a sheet of paper, that measures around 60 microns and a human hair is between 50 & 120 microns thick
Microscopic Micron Contaminants and Their Impact
Microscopic contaminants are not always from an obvious source. For example when a technician is using any form of blunt force on any metal object near a bearing, there are chances of “particulate” or metal smaller than 50 microns getting into that bearing. When a divot is created in something like a lock nut for a bearing, that metal has to go somewhere, with a high chance of it going into the bearing. Since most 25mm bearings have a .051 mm oil film between the rolling elements and the outer race of the bearing, something smaller than what you can see can get between these components. Any particle smaller than say 50 microns can get into the oil film, creating scratches or cracks in the outer race (false brinelling). While such tiny dimensions are invisible to the eye, their impact on machine health can be profound.
But Micron Accuracy Counts in Machine Alignment!
Industry statistics show that approximately 50% of machine failures have a root cause in misalignment. Misalignment leads to increased vibration and noise levels, accelerated wear and tear on bearings and seals, excessive energy consumption, elevated operating temperatures and the premature failure of machine components.
In critical level machinery, the precision required for alignment is stringent. For example, in steam turbines, alignment tolerances are often within 0.02 mm (20 microns). Any deviation beyond this can lead to:
Increased Rotor Dynamics Issues: Resulting in higher vibration amplitudes and potential resonances.
Thermal Growth Miscalculations: Leading to inaccurate predictions of expansion and contraction during operation, further exacerbating misalignment.
Operational Downtime: Misalignment in critical machinery can result in unscheduled downtimes, costing industries millions in lost productivity.
Misalignment Creating Contaminants = Double Whammy!
Siemens Gas Turbines Study in Alignment and Particle Contamination
Issue: Alignment and Particle Contamination Siemens conducted a study on gas turbines used in power generation and found that even minute misalignments caused by microscopic contaminants could lead to substantial efficiency losses and increased maintenance costs.
Findings:
- Efficiency Impact: Misalignment of just 10 microns resulted in a 2-5% decrease in turbine efficiency, translating to significant financial losses over time.
- Mitigation Strategies: Siemens developed enhanced alignment techniques and introduced particle monitoring systems to detect and address contamination early.
Case Study: Impact of Particle Contamination on Aircraft Engine Bearings *
Study Overview:
The study investigated the impact of microscopic contaminant particles on the performance and alignment of bearings in aircraft engines. The researchers conducted extensive experiments to determine how particle contamination affects the bearing surfaces and the overall alignment of the shaft.
Key Findings:
- Contaminant Size and Impact:
- The study focused on contaminant particles ranging from 5 to 20 microns.
- It was found that even particles as small as 10 microns could significantly affect the performance of the bearings, leading to misalignment.
- Surface Wear and Misalignment:
- The particles caused abrasive wear on the bearing surfaces, which in turn led to misalignment of the shaft.
- Increased wear was observed on the surfaces of the bearings, causing deviations in the intended alignment.
- Vibration and Operational Efficiency:
- The misalignment induced by particle contamination led to increased vibration levels in the machinery.
- This vibration not only affected the smooth operation of the engine but also reduced its overall efficiency and lifespan.
- Preventative Measures:
- The study suggested enhanced filtration systems to capture and remove microscopic particles from the lubrication system.
- Regular maintenance and monitoring were recommended to detect early signs of particle contamination and misalignment.
Preventive Measures
To mitigate the impact of contaminants and ensure precise alignment, several best practices can be implemented:
1. Use the Correct Tools for the Job: Utilise appropriate tools and techniques for assembly and disassembly to minimise the creation of metal particles.
2. Keep it Clean: Maintain a clean working environment to prevent contaminants from settling on machinery components.
3. Regular Monitoring: Implement regular alignment checks using precision laser alignment tools to detect and correct misalignments promptly.
4. High-Quality Lubricants: Use high-quality lubricants with proper filtration to capture and remove microscopic particles.
Conclusion
In conclusion, the precision of shaft alignment cannot be overstated in the pursuit of optimal machine health. Even microscopic contaminants, invisible to the naked eye, can cause significant disruptions. Understanding the scale at which these particles operate and their potential impact highlights the importance of meticulous maintenance practices. For professional engineers, acknowledging the mantra “How many microns can you see?” serves as a reminder of the unseen yet important factors that dictate the longevity and performance of industrial machinery. Through vigilant monitoring and adherence to best practices, the adverse effects of contaminants on alignment can be effectively mitigated, ensuring the sustained health and efficiency of critical machinery.
* Source: The study “Investigation of the Effects of Contaminant Particles on the Performance of Aircraft Engine Bearings” published in the Journal of Tribology.
Authors: Chenglin Liu, Michael M. Khonsari, and T. W. Scharf
Journal: Journal of Tribology, ASME, Vol. 132, Issue 3, 2010.
With thanks to Terry C. Southall, MA. Ed, Global Brand and Distribution Manager, X-Series(tm) Shaft Alignment Lasers, Hamar Laser Instruments, Inc for his input.
