Most of the wear that a machine endures during its lifespan comes by way of particle contamination. Through a machine’s life, particles are ingested, generated, or built-in. But no matter how they get there, particles cause a variety of problems for lubricants and machines alike. Fortunately, by combining high[1]quality filtration with contamination exclusion tools such as desiccant breathers, it is possible to mitigate or avoid many problems that stem from particle contamination and reduce the total cost of machine ownership.
THE GROWING PROBLEM OF PARTICLE CONTAMINATION
A typical particle population growth lifecycle may look something like this: new oil arrives onsite and is stored unsealed; later, the oil is pumped with a dirty drum pump, then the oil, without being filtered, is transferred to a dirty top-up container; the oil is then poured through a dirty funnel into a machine that does not have a proper breather. These are just a few of the ways that particles contaminate lubricants before they are even introduced to the machine system. But the good news is that if this story sounds familiar to you, you have a major opportunity to improve contamination control and decrease maintenance costs at your facility.
Contaminant Origins
Built-in contaminants are contaminants created during the manufacture of servicing of a machine — this category also includes contaminants from new machine parts. Manufacturing debris includes burrs, drill turnings, filings, machine swarf, and other such abrasives. Debris commonly enters a machine system during service and repairs through dirty hoses and fittings, unfiltered new oil, and contaminated top-up containers. The solution to built-in contaminants is cleanliness. For example, new machines and parts should be flushed or cleaned thoroughly before use, and new oil should be filtered before it is applied to the machine system.
Ingested contaminants are contaminants that enter a machine during use or are ingested because of improper storage techniques. There are three categories of ingested contaminants:
• Process — These particles, typically byproducts of a machine’s environment, include compressed air, ore dust, cement, and process chemicals.
• Atmosphere — Particles that enter the machine through a tank opening, seals, a breather, or other areas where outside air can enter the system. These particles can include quarry or foundry dust, slag, and mill scale.
• Combustion — These contaminants are created by the machine’s functions and include soot, fly ash, and blow-by.
The solution to ingested contaminants is to configure machines for exclusion — this can be done using tools like desiccant breathers
Generated contaminants are produced within a machine system during use — either from surface wear or oil degradation. Surface particles, such as hose fibers, filter fibers, paint chips, and break-in debris can be generated from mechanical and corrosive wear, cavitation, and exfoliation. The particles generated from the oil degradation process, such as oxidation, include sludge, varnish, coke, and oxide insolubles.
DAMAGE CAUSED BY PARTICLE CONTAMINANTS
The primary cause of machine failure is the degradation of component surfaces — and the primary cause of surface degradation is particle contamination. The damage that a particle is capable of inflicting depends on two factors: the particle’s size and the particle’s hardness
Size A particle’s size determines how much damage it can cause. Particle size is typically measured in microns (µ). The majority of machine damage is caused by particles between 3 and 10 microns in size, roughly the same size as the lubricating film. As a reference of scale, human hair has a thickness of about 80 µ, fine floor dust a size of 40 µ, and red blood cells typically measure in at 5 µ. When in-service lubricants are submitted to a particle count, smaller particles are generally present in greater numbers than larger particles.
Hardness Some solid particles have higher compressive strengths than others; this strength, or hardness, influences the amount of damage a particle will cause. Particles with a high compressive strength cause more significant damage than softer particles. This damage is also influenced by the angularity of a particle, which refers to a particle’s sharp edges. Dirt particles are particularly hard relative to machine surfaces and can be very crystalline in nature, thus having sharp edges.
FILTERS
The goal of filtration is to achieve equilibrium — a state where the particle removal rate is equal to or exceeds the particle ingression rate. For filtration efforts to be effective, high-performance filters should be used. Additionally, timely filter servicing should be prioritized. Filters should be seen as an asset in your reliability or maintenance efforts, and choosing the right filter comes down to several key factors.
Factors for Proper Oil Filter Selection
Structural Integrity- Structural Integrity refers to a filter’s ability to prevent oil from passing through an unfiltered flow path. The International Organization for Standardization (ISO) has created methods for testing fabrication integrity, flow fatigue, material compatibility, and other structural factors.
Contamination– (Dirt-Holding) Capacity A filter’s contamination capacity is the amount of contamination that a filter can hold. Exceeding this limit hinders a filter’s efficiency.
Pressure Loss- A filter’s placement within a system can affect overall differential pressure. The filter’s surface area and media porosity influence the degree of pressure loss.
Particle Capture Efficiency– The particle capture efficiency of a filter refers to its effectiveness in extracting and retaining oil contaminants.
System/Environment -Flow rates, location, vibration, contamination expectations: these are all factors that influence performance and are produced by a filter’s machine and environment; these factors should be considered when selecting a filter.
Particle Counters
Particle counters are used to test a filter. These counters measure the size and quantity of particles upstream (before passing through the filter) and downstream (after passing through the filter). The upstream particle count is divided by the downstream count, resulting in the beta ratio. It must be considered when comparing filters, that beta ratios do not account for actual operating conditions. Filter performance can be influenced by factors like flow surges and temperature changes. Additionally, beta ratios do not indicate a filter’s dirt-holding capacity or long-term stability. Beta ratios serve best as an indication of a filter’s expected performance.
Analyzing the Filter
Besides their ability to keep oil clean, filters can also be used to determine what is occurring within a machine system. Analysis of a filter’s contamination contents can be used to determine why a machine is malfunctioning or be used to portend impending issues. Typically, laboratory analysis is needed to determine problems based on a machine’s filter. Occasionally, clues to an issue can be seen with the naked eye. Changes in oil appearance can be indicative of metal contamination, a suspicion that can be confirmed by cutting a filter open and using a strong magnet to extract metal particles, which can then be more easily identified. Metal contamination is a sign of more significant problems. If a machine is experiencing problems, the filter should not be discarded; rather, it should be maintained in its removed condition and analyzed by the manufacturer or a laboratory. The filter is a bank vault of information that has been collected and stored through its service life.