The lubricant or oil analysis is a task that is part of predictive maintenance, an activity that is necessary in many cases to check the state of wear of the internal components of the machines, more specifically of the elements that rub together, such as bearings or bearings.
Lubricant studies are performed to:
- Know the lubricant used in each piece of equipment
- Optimize the number of lubricants to be used in an installation
- Save costs on lubrication
- Save maintenance costs
- Avoid mistakes when supplying lubricant to equipment.
Oil sampling and analysis programs require prior design based on the designated objective. For example; more or less loose preventive maintenance in terms of lubricant replenishment, the programs must specify a series of basic aspects such as the following;
- Location of sampling points in equipment or systems
- Procedures for sample collection (sampling frequency, routes, etc.)
- Suitable containers to collect the samples (cleanliness and adequate material)
- Identification process and immediate shipment of samples to the laboratory.
- Designate the tests to which the samples will be subjected.
- Standards, methods, and frequency of calibration of instruments used in the analyses.
- Information to present as a result of the analysis.
- Interpretation and action in consequence of the results by the technical department.
Types of Wear:
Wear is given by the different processes to which the equipment is subjected during its useful life and is classified into the following categories:
- Abrasive wear: it is produced by the effect of hard particles, such as dust, sand, and metals, coming into contact with internal metallic components. To reduce this type of wear, a filtering system can be installed. The existence of the filtering system is considered very important in any physical asset management related to machinery.
- Adhesive Wear: Occurs when two metal surfaces come into contact, allowing particles to dislodge from the friction surfaces. The causes of this wear are given by poor lubrication or contaminated lubricant.
- Cavitation: occurs when the bubbles formed by a decrease in pressure in the oil collapse and bombard the metal surfaces, producing pitting or cracks.
- Corrosive wear: it is produced by the chemical reaction that releases the material from the surface of an element. It occurs when the metal is in the presence of water, combustion products, or electric currents.
- Fatigue wear: when a crack occurs on the surface of an element subjected to cyclic stress, this process generates a detachment of particles.
Wear volume classification:
- Initial wear: occurs when the machine is started for the first time, and a percentage of particle detachment is generated that decreases after two or three oil changes.
- Normal wear: it is the wear that occurs with the normal operation of the machine. At this stage, the wear is stabilized, and it increases with the aging of the equipment.
- Abnormal wear: occurs when there is a failure or breakdown in the machine and the percentage of particle shedding is increased.
When we carry out oil analysis, it is necessary to know which elements are part of the lubricant and which represent wear of friction metals or a contaminant.
- Lubricant additives: Ba, Ca, Mg, P, B
- Wear Metals: Fe, Cu, Pb, Ag, Al, Ni
- Pollutants: Si, Na, K, Ba
For the detection of these elements and their ppm, we can use the following methods or tests:
Spectrometallographies:
This technique is used to detect and quantify trace amounts of metallic elements. It is performed to measure metal particles smaller than 10 microns.
Emission Spectrometry:
Emission spectrometry or ICP (Inductively Coupled Plasma) consists of using a sample it is heated and brought to a plasma state. In this state, the elements contained in the lubricant emit certain radiations in the visible and ultraviolet aspects. The received radiation intensity is separated by diffraction into different wavelength parameters. This allows the concentrations of different elements contained in the oil sample to be calculated. This technique allows measurements of concentrations from 1 to 1,000ppm and is used to measure concentrations of additives, wear metals, and contaminants.
Infrared spectrometry analysis:
Infrared analysis is a form of restricted absorption spectroscopy in the infrared spectral wavelength region. The test consists of making a beam of infrared light pass through a sample of used oil; this generates an infrared spectrum that is reproduced on a graph. Each oil has its own characteristic spectrum, so this technique is reduced to the comparison of the spectrum of the new and used oil. The differences between the graphs of the spectra show some of the changes in the components that make up the lubricant.
Analytical Ferrography:
Ferrographs are one of the most important techniques to determine the composition, they are used to capture metal particles in the range of 0.1 to 500 microns, so the amplitude field not only covers the field of abnormal wear (10 to 100 microns) but also which also includes the range of spectrography. With this system, metal particles are classified according to shape and size, determining the type of wear.
Particle Counter:
This system works with a laser optical base that allows the absolute measurement of particles with two microns in an oil sample.
As we can see, various methods can be used in lubricant analysis. We hope this information was helpful.