12 Tipos de Contaminação
De pistões e sistemas hidráulicos a rolamentos e sistemas de engrenagens, a vida útil dos componentes em equipamentos automotivos, industriais e outros é reduzida quando os contaminantes circulam através de seus sistemas. Água, partículas sólidas, verniz e até mesmo o ar pode levar a uma diminuição nos intervalos de drenagem e a um aumento na formação de espuma, oxidação, borra e verniz — potencialmente causando sérios danos. Se você já assistiu o canal Turner Classic Movies, você pode ter visto um filme intitulado The Dirty Dozen: The Fatal Mission, que tem uma combinação de personagens ruins e maus atores intrinsecamente envolvidos no enredo do filme. Usando esta analogia, foi estabelecida uma lista dos contaminantes mais comuns e mais prejudiciais que afetam a limpeza do óleo, que pode contribuir para a falha dos motores, das transmissões, do sistema hidráulico, dos rolamentos, dos sistemas da engrenagem, etc. Embora existam mais de 12 tipos de contaminantes, os principais são: espuma, ar aprisionado, água livre, água emulsionada, água dissolvida, sujeira, particulado, partículas de desgaste, verniz macio e duro, líquido refrigerante e combustível ou fuligem.
LUBES’N’GREASES – Vol. 24 Issue 10
The Dirty Dozen – 12 Types of Oil Contamination
by Henry Neicamp
From pistons and hydraulics to roller bearings and gear systems, the service life of components in automotive, industrial and other equipment is reduced when contaminants circulate through their systems. Water, solid particles, varnish and even air can lead to a decrease in drain intervals and an increase in foaming, oxidation, sludge and varnish formation—potentially causing serious damage. If you have ever watched the Turner Classic Movies channel, you may have seen a film entitled The Dirty Dozen: The Fatal Mission, which has a combination of both bad characters and bad actors intricately involved in the plot of the movie. Using this analogy, I’ve established a list of the most common and most harmful contaminants affecting oil cleanliness, which can contribute to The Fatal Mission in the failure of engines, transmissions, hydraulics, roller bearings, gear systems, etc. While more than 12 types of contaminants exist, the Dirty Dozen are: foam, entrained air, free water, emulsified water, dissolved water, dirt, particle byproducts, wear particles, soft and hard varnish, coolant and fuel or soot.
Air contamination, whether foam or entrained, can be very difficult to quantify, and oil analysis cannot directly measure it. Foam contamination occurs when large air bubbles sit on top of the oil. It can be superficial; for example, when oil splashes into the reservoir, it causes foam to form. However, it also may be a sign that the antifoam agent is depleted and the oil needs to be treated, sweetened with a partial drain and fill, or replaced. In general, the factors that cause or amplify foaming in oil can be divided into two major categories: lubricant contamination and mechanical design problems. Entrained air is a sneakier type of contamination that happens when air is dispersed in a large amount of oil, which will make it appear cloudy. It is often mistaken for water contamination. However, there is an easy way to visually tell the difference between air and water contamination: Take a small oil sample in a clear container and allow it to sit undisturbed for 24 hours. Air will rise to the top, while water will fall to the bottom.
Water contamination is the easiest to test for, identify and quantify. Water typically gets into systems through vapor in the air, but it’s not unusual for it to enter in liquid form via rain, splashing, cracks, power washing and missing reservoir covers or breathers. When water is dissolved in the oil phase, the oil will appear bright and clear. While mostly benign in this state, dissolved water may be an early sign of water contamination. This volume of water can only be detected and quantified using the Karl Fischer test method. Emulsified water is dispersed in very small droplets (fewer than 150 microns) in the oil phase. Hazy or lacy emulsions typically dissipate slowly, but creamy emulsions (even if they dissipate quickly) indicate high water concentrations that can damage equipment. Free water is dispersed as large droplets (greater than 150 microns) and will readily settle out under gravitational forces. Free water will separate over time and will be easily visible. It is easily removed by simply draining it off. By measuring the current moisture level in the oil and then reducing the fluid moisture level, your machine’s life can be significantly extended. In addition, desiccant breathers can help lengthen equipment life exponentially when incorporated as part of a reliability-centered maintenance plan.
The sources of particle contamination are endless but typically fall into four categories: built-in, externally-ingressed, internally-generated and maintenance generated.
Some factors in how these particles are generated include how the oil is handled, where the oil is stored, dispensing equipment and procedures and internal machine contamination by wear particles, among others. Hard particles (dirt, wear or byproducts) are the most destructive form of contamination and cause more than 80 percent of machine wear. But, removing the particles via filtration isn’t always easy—or inexpensive. The industry spends upwards of $200 billion annually filtering fluids to prevent mechanical problems caused by hard particles. Dirt is the most common external particle contamination and most often comes in through air movement. However, studies have proven that particle levels increase anytime a system is opened—even during filter replacement. When tested via oil analysis, dirt contamination is identified via Inductively Coupled Plasma (ICP) test results as silicon—specifically alumina-silica, which is the most common form of dirt. Another pathway for hard particle contamination is oil degradation and combustion byproducts. Instead of taking an external pathway into the system, these particles develop due to environmental conditions and activities in the system, such as engine combustion. When hard particles are wider than the oil film, they get caught or compressed between moving metal surfaces, causing wear metals to break off. These wear metals then travel through the system and end up causing additional wear. This cycle of wear-causing movement escalates and damages the component to the point where it may no longer be operable. Typically, it’s the particles you can’t see that are causing the most damage. It’s important to know particles are measured in microns (one micron is a millionth of a meter or .000039 inches). The human eye can only see something as small as 40 microns. Because the particles that cause the most damage range from one to a few microns, they are only able to be seen and studied through a microscope or ICP.
Estimated Fluid Life Extension through Moisture Removal
For mechanical systems utilizing mineral based fluids
The life extension factor corresponds to the moisture levels at which the life expectancy of the mechanical system has doubled (2), tripled (3), quadrupled (4), etc. For example, by reducing average fluid moisture levels from 2,500 ppm to 156 ppm, machine life is extended by a factor of 5. Current Moisture Level
Varnish buildup can occur in reservoirs and throughout lube and hydraulic systems on components and filter elements. Once varnish formation begins, unfortunately, equipment becomes unreliable and potentially unsafe. The first surfaces to begin collecting varnish are those surfaces in cooler zones, low clearance areas and low flow areas, because that is where the solubility/saturation point drops as temperature drops, precipitation can start and agglomeration can go on undisturbed. Hard varnish is a firm, thin, lustrous, oil-insoluble deposit, composed primarily of organic residue and most readily definable by color intensity. It is not easily removed by wiping with a clean, dry, soft, lint-free wiping material and is resistant to saturated solvents. Its color may vary, but it usually appears in gray, brown or amber hues. It can form on moving surfaces (lacquer) and may become hard and brittle. Varnish may also deposit as stalactites on reservoir ceilings or plate out on reservoir floors. Soft varnish, which generates sludge, is soft and gooey and can be easily moved and wiped, but it is just as vital to remove it from a system as hard varnish.
For engine oils and others that require cooling, it is vital to ensure coolant/antifreeze does not get in the oil. When gaskets and valves break down and contact is made, coolant and water alike cause contamination and can harm not only the oil, but also the engine. The corrosion inhibitor additive package in coolants is detected as sodium and potassium by ICP oil analysis, which is used to confirm coolant contamination. Typically, engines are the only systems that can experience fuel/soot contamination, but it is possible to accidentally contaminate lubricants during storage or when transferring them to another container. Fuel dilution will occur as the direct result of raw, unburned fuel that ends up in the crankcase. The presence of fuel is a concern because it lowers the oil’s viscosity and weakens its film strength, resulting in friction-induced wear. On the other hand, the presence of soot is a concern because it increases the oil’s viscosity and is very abrasive, resulting in upperend wear of the engine.
Fighting the Dirty Dozen
If there’s nothing else you take away from this article, remember the following two things when it comes to fighting the Dirty Dozen: filtration and desiccant breathers. Filter the oil using pressure line filters, return line filters, kidney loop/off-line filters and an oil transfer cart with a filtration system, just to name a few. For the inevitable contamination that does occur (including degradation and combustion byproducts), filtering the oil will pay dividends down the road by preventing wear and eventual breakdown. In addition, this extends the life of equipment and improves productivity. Installing desiccant breathers is one of the easiest and most cost-effective ways to fight oil contamination caused by water. Desiccant breathers make sure the air flowing in and out won’t contain water. It’s important to identify contamination early, and it’s even more important to proactively prevent contamination before it occurs. Simply blocking the entry of contaminants and moisture is one of the most effective ways of preventing oil contamination. Using other control tools such as mechanical seals, proper sampling techniques, appropriate storage and dispensing practices can prevent contamination, as well. In addition, using the right oil analysis test is critical to identifying contamination early, reacting to it appropriately and preventing it in the future.
Essa informação foi útil para você?
Por que essa informação, não foi útil para você?
Obrigado pela sua participação!