Analytical ferrography is among the most powerful diagnostic tools in Oil Analysis today. When implemented correctly it provides a tremendous return on your oil analysis investment. It is frequently excluded from oil analysis programs because of its comparatively high price and a general misunderstanding of its value.
The test procedure is lengthy and requires the skill of a trained analyst. As such, there are significant costs in performing analytical ferrography not present in other oil analysis tests. But, if time is taken to fully understand what analytical ferrography uncovers, most agree that the benefits significantly outweigh the costs and elect to automatically incorporate it when abnormal wear is encountered.
To perform analytical ferrography the solid debris suspended in a lubricant is separated and systematically deposited onto a glass slide. The slide is examined under a microscope to distinguish particle size, concentration, composition, morphology and surface condition of the ferrous and non-ferrous wear particles. This detailed examination, in effect, uncovers the mystery behind an abnormal wear condition by pinpointing component wear, how it was generated and often, the root cause.
Analytical ferrography begins with the magnetic separation of machine wear debris from the lubricating oil in which it is suspended using a ferrogram slide maker (Figure 1). The lubricating oil sample is diluted for improved particle precipitation and adhesion. The diluted sample flows down a specially designed glass slide called a ferrogram. The ferrogram rests on a magnetic cylinder, which attracts ferrous particles out of the oil (Figure 2).
Due to the magnetic fluid, the ferrous particles align themselves in chains along the length of the slide with the largest particles being deposited at the entry point. Nonferrous particles and contaminants, unaffected by the magnetic field, travel downstream and are randomly deposited across the length of the slide. The deposited ferrous particles serve as a dyke in the removal of nonferrous particles. The absence of ferrous particles substantially reduces the effectiveness with which nonferrous particles are removed.
The ferrogram is examined under a polarized bichromatic microscope equipped with a digital camera. The microscope uses both reflected (top) and transmitted (bottom) light to distinguish the size, shape, composition and surface condition of ferrous and nonferrous particles (Figure 4). The particles are classified to determine the type of wear and its source.
Particle composition is first broken down to six categories: white nonferrous, copper, babbitt, contaminants, fibers and ferrous wear. In order to aid the identification of composition, the analyst will heat treat the slide for two minutes at 600ºF.
Ferrous particles can be broken down to five different categories, high alloy, low alloy, dark metallic oxides, cast iron and red oxides. Large ferrous particles will be deposited on the entry end of the slide and often clump on top of the other. Ferrous particles are identified using the reflected light source on the microscope. Transmitted light will be totally blocked by the particle.
After classifying the composition of particles the analyst then rates the size of the particles using a micrometer scale on the microscope. Particles with a size of 30 microns or greater are given the rating of “severe” or “abnormal.” Severe wear is a definite sign of abnormal running conditions with the equipment being studied.
Often, the shape of a particle is another important clue to the origin of the wear particles. Is the particle laminar or rough? Laminar particles are signs of smashing or rolling found in bearings or areas with high pressure or lateral contact. Does the particle have striations on the surface? Striations are a sign of sliding wear. Perhaps generated in an area where scraping of metal surfaces occurs.
Does the particle have a curved shape, similar to drill shavings? This would be categorized as cutting wear. Cutting wear can be caused by abrasive contaminants found in the machine. Is the particle spherical in shape? To the analyst, these appear as dark balls with a white center. Spheres are generated in bearing fatigue cracks. An increase in quantity is indicative of spalling.
Analyzing the size, shape, color, magnetism light effects and surface detail of wear particles, a skilled analyst can paint a picture above the nature, severity and root cause of abnormal wear. This information enables maintenance to implement effective corrective action.
Lubricants Brochure
Need help or have a question?
UNITED ARAB EMIRATES
Tribocare FZC
A2-74 SAIF Zone
Sharjah, UAE
T: +971 65528799
E: sharjah@tribocare.com
SINGAPORE
Tribocare PTE LTD
32, Pandan Road,
Singapore 609279
T: + 65 62642840
E: singapore@tribocare.com
CHINA
Tribocare Shanghai CO., LTD.
Room 202 Block 32, No.3999
Xiupu Road, Pudong District,
Shanghai, China
地址:上海市浦东新区秀浦路3999弄, 32号二层202室
T: +86 18621601008
E: china@tribocare.com
GERMANY
Tribocare GMBH
E: germany@tribocare.com
GREECE
Pentelis 53
Marousi 15126
Greece
T: +30 213 031 9384
Mob: +30 694 649 0604
E: greece@tribocare.com
NETHERLANDS
Tribocare B.V.
Delta-Industrieweg 14
Stellendam,
Netherlands
3251 LX
E: netherlands@tribocare.com
USA
Tribocare INC
E: americas@tribocare.com
Ut enim ad minima veniam, quis nostrum exercitationem ullam corporis suscipit laboriosam, nisi ut aliquid ex ea commodi consequatur? Quis autem vel eum iure reprehenderit qui in ea voluptate velit esse quam nihil molestiae consequatur, vel illum qui dolorem eum fugiat quo voluptas nulla pariatur. " Quis autem vel eum iure reprehenderit qui in ea voluptate velit esse quam nihil molestiae consequatur.