Ferrography is an analytical technique that has been widely applied to understand the process of machine wear since the 1970s. Today, analytical ferrography is one of the most powerful diagnostic tools in oil analysis.
First developed by Vernon C. Westcott to analyse ferrous particles in lubricating oils as a part of predictive maintenance, ferrography is a technique for analyzing contaminant particles present in fluids. These fluids are commonly lubricating oils, hydraulic fluids and greases used in machinery that is in danger of mechanical wear.
Process Of Ferrography
In Ferrography, the ferrous particles are magnetically separated from the lubricant and placed onto a microscope slide for examination.
To be able to separate the particles from the liquid, the sample has to be diluted for improved particle precipitation and adhesion.
Then the diluted sample is made to flow down a specially designed glass slide called a ferrogram. The ferrogram is placed on a magnetic cylinder, which attracts ferrous particles out of the oil. The largest ferrous particles tend to get deposited at the entry point while the nonferrous particles get deposited across the length of the slide.
The particles are washed to remove any remaining lubricant. The ferrogram is then placed under a bichromatic microscope to determine the concentration, composition, morphology, particle size, and surface condition of the ferrous and non-ferrous wear particles. This examination helps to understand abnormal wear condition by pinpointing the root cause.
The particles are then classified to determine the type of wear and its source. Particle composition is divided into six groups - copper, white nonferrous, babbitt, contaminants, fibers and ferrous wear. The ferrous particles can be further divided into five categories - high alloy, low alloy, cast iron, dark metallic oxides, and red oxides.
By analyzing the color, size, shape, magnetism light effects and surface of the wear particles, a trained analyst can provide data regarding the nature, severity and root cause of abnormal wear. This data then enables maintenance to execute effective corrective action.
The Basics of Ferrous Density in Oil Analysis
Advantages of Ferrography
Although ferrography is an expensive and lengthy process requiring well-trained analysts, the benefits far outweigh the costs. The following are the key benefits of using ferrography:
- Decrease of maintenance costs
- Effective maintenance scheduling
- Improved equipment reliability and safety
- Minimal machine power consumption over a period
- Reduction in unscheduled downtime due to wear of rotary components such as gears and bearings
- Improves environmental cleanliness of the process, due to optimized oil changes.
Companies Involved in Ferrography
The following is a list of various ferrography producers with a brief introduction:
- Trico Corporation is a lubrication management company located in Wisconsin, USA. Their chief product is the new and improved Ferrogram Maker (FM-6). The FM-6 dual slide maker is used in the first step of analytical ferrography. To enhance productivity, the FM-6 is designed with two independent stations allowing two samples to be prepared concurrently. The FM-6 is provided with an interactive 7" LCD touch screen, and USB and Ethernet port so that consumers can plug into a keyboard and mouse, and access important reports on the web and connect it to Trico’s other ferrography instruments like the DR-6 Direct Reading Ferrography and the FS-6 Ferroscope.
- Spectro Inc specializes in analytical tools and software for machine condition monitoring. Their key products include LaserNet Fines, Particle Counter and particle Shape Classifier, Ferrography Laboratory, Turnkey Laboratory, Spectro Industrial Tribology Laboratory, and Spectro 5200 TrivectorTM Analyzer. The company is located in Massachusetts, USA.
- Intertek Group plc. provides analytic ferrography testing services for all types of companies around the world. Their offices or laboratories are spread across the globe for easy access.
Applications of Ferrography
Ferrography is widely used in many industrial areas including the following:
- Chemical plants
- Offshore installations
- Oil condition monitoring
- Power stations
- Insurance companies
- Railroad industry
- Manufacturing plants
- Public transport
- Food processors
- Jet engine OCM testing
- General Industry
- Metallurgical applications
- Engine maintenance
- Ships, barges, maritime sector
- In steel mills to solve issues with key components such as an Ingersoll Rand single-stage centrifugal pump, Westinghouse 5,000 HP Motor, heat transfer systems, and heat treatment systems
Sources and Further Reading