http://www.machinerylubrication.com/Read/28424/power-patch-particle-analysis
Shows some of the methods that filter patches can be used for in machinery diagnostics, including colorimetry.
Pertinent to some of the statements on what can be determined by looking at a used oil filter.
Quote:
Patch Test
One of the main benefits of this method is its low cost, simplicity and portability. An aliquot of oil is pushed through a 4-5 micron membrane by positive pressure or pulled by vacuum (syringe, sample pump or vacuum pump) after the sample is diluted in solvent. Particles larger than the pore size remain on the membrane’s surface for later inspection. Low power microscopes can be used for this, but often the patch is simply examined without magnification using patch comparators. An excellent comparator with a convenient scale is sold for use with fuel samples based on ASTM D2276. This comparator can be used for oils as well. Because of the amount of fluid filtered in patch testing, the debris is typically too dense on the patch to attempt to count or characterize individual particles.
Quote:
Patch Ferrography
This method is almost identical to microscopic particle counting, but combines various particle identification and characterization techniques. These include the use of bi-chromatic microscopy, magnetism and assessment of particle color, texture, shape and size. In this sense, it is very similar to analytical ferrography, where particles are magnetically and gravitationally deposited on a glass slide called a ferrogram. However, with patch ferrography, a cellulose nitrate membrane is used, called a filtergram. A clarifying solution is applied to enable both bottom and top lighting to be used during examination. Unlike ferrograms, heat treatment of the particles and chemical microscopy are not practical options. Patch ferrography is particularly popular for samples having non-ferromagnetic wear particles (brass, aluminum, Babbitt for instance). Additionally, unlike ferrograms, particles don’t generally pile or clump (obscuring them from view).
Quote:
Gravimetric Analysis
Just as the name implies, gravimetric analysis uses a laboratory scale to weigh particles and sediment on a membrane (typically 0.45 microns). No attempt is made to count, size or visibly characterize the particles. Often, the particles on the membrane are dominated by organic “soft” particles such as resins from oxidation, sludge and additive degradation. Some laboratories use a series of solvent washes of various polarities to extract soluble fractions from the membrane in an effort to approximate composition. Common solvents used for this purpose include pet ether, toluene, trichloromethane and methanol.
Note that the filter medium is cleaned with a solvent to remove the oil proper from the process, and that the filter media are all of standard composition and therefore colour.
The last one, Membrane Patch colorimetry at the time of the article was heading for ASTM status for varnish detection in turbine oils...an undergrad who was working for me demonstrated that with a properly calibrated flat bed scanner, the varnish potential can be tracked (Engineering thesis, he got an HD for it).
Shows some of the methods that filter patches can be used for in machinery diagnostics, including colorimetry.
Pertinent to some of the statements on what can be determined by looking at a used oil filter.
Quote:
Patch Test
One of the main benefits of this method is its low cost, simplicity and portability. An aliquot of oil is pushed through a 4-5 micron membrane by positive pressure or pulled by vacuum (syringe, sample pump or vacuum pump) after the sample is diluted in solvent. Particles larger than the pore size remain on the membrane’s surface for later inspection. Low power microscopes can be used for this, but often the patch is simply examined without magnification using patch comparators. An excellent comparator with a convenient scale is sold for use with fuel samples based on ASTM D2276. This comparator can be used for oils as well. Because of the amount of fluid filtered in patch testing, the debris is typically too dense on the patch to attempt to count or characterize individual particles.
Quote:
Patch Ferrography
This method is almost identical to microscopic particle counting, but combines various particle identification and characterization techniques. These include the use of bi-chromatic microscopy, magnetism and assessment of particle color, texture, shape and size. In this sense, it is very similar to analytical ferrography, where particles are magnetically and gravitationally deposited on a glass slide called a ferrogram. However, with patch ferrography, a cellulose nitrate membrane is used, called a filtergram. A clarifying solution is applied to enable both bottom and top lighting to be used during examination. Unlike ferrograms, heat treatment of the particles and chemical microscopy are not practical options. Patch ferrography is particularly popular for samples having non-ferromagnetic wear particles (brass, aluminum, Babbitt for instance). Additionally, unlike ferrograms, particles don’t generally pile or clump (obscuring them from view).
Quote:
Gravimetric Analysis
Just as the name implies, gravimetric analysis uses a laboratory scale to weigh particles and sediment on a membrane (typically 0.45 microns). No attempt is made to count, size or visibly characterize the particles. Often, the particles on the membrane are dominated by organic “soft” particles such as resins from oxidation, sludge and additive degradation. Some laboratories use a series of solvent washes of various polarities to extract soluble fractions from the membrane in an effort to approximate composition. Common solvents used for this purpose include pet ether, toluene, trichloromethane and methanol.
Note that the filter medium is cleaned with a solvent to remove the oil proper from the process, and that the filter media are all of standard composition and therefore colour.
The last one, Membrane Patch colorimetry at the time of the article was heading for ASTM status for varnish detection in turbine oils...an undergrad who was working for me demonstrated that with a properly calibrated flat bed scanner, the varnish potential can be tracked (Engineering thesis, he got an HD for it).
