With few exceptions, the chemical and physical stability of lubricants are threatened by even the slightest amount of suspended water. Water can promote a host of chemical reactions (hydrolysis) with compounds and atomic species including oil additives, base stock and suspended contaminants. In combination with oxygen, heat, and metal catalysts, water is known to promote the oxidation and the formation of free radicals and peroxide compounds. Oxidation inhibitors are sacrificed by both neutralizing peroxides and breaking oxidation chain reactions to form stable compounds.

Other oxidation inhibitors are known to form hydrogen sulfide and sulfonic acids when reacting with water. Experiments have shown the protection provided by zinc dialkyldithio phosphate (ZDDP), a common antiwear additive and antioxidant, to be destroyed by as little as one drop of water in a gallon of oil, with oil temperature above l 80°F.

Water is also known to attack rust inhibitors, viscosity improvers, and the oil’s base stock. The effects are undesirable by-products such as varnish, sludge, organic and inorganic acids, surface deposits and lubricant thickening (polymerization). Large amounts of emulsified water can lower viscosity, thereby reducing a lubricant’s load carrying ability. When water is combined with metal catalysts such as iron or copper, accelerated stressing of the oil can occur. This results in base stock oxidation and the forming of free radicals (which continue the oxidation process), hydroperoxides, and acids (see figure 2).

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Moisture is generally referred to as a chemical contaminant when suspended in lubricating oils. Its destructive effects in bearings can reach or exceed that of particle contamination, depending on conditions. Like particles, control must be exercised to minimize water accumulation and damage to bearing surfaces. Once water enters a machine with bearings (i.e., an engine, turbine, or gear box) it may move through several chemical and physical states. Water will often enter an oil in one of the five following ways.

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Countless times, I’ve devoted this column to stressing the virtues of contamination control. With each passing year, we seem to receive more and more user feedback detailing and validating the business case for clean, dry and cool oil. Of course it’s one thing to preach its value, but it’s quite something else to actually achieve and sustain near-contaminant-free conditions. Therefore, it is this subject that I’ll tackle with the current and a few future columns, beginning with exclusion and removal of water.

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Water, once in an oil, is in constant search of a stable existence. Unlike oil, the water molecule is polar, which greatly limits its ability to dissolve; and many additives have polar extremities which can markedly increase water solubility. Water may cling to hydrophilic metal surfaces or form a thin film around polar solid contaminants such as silica particles. If a dry air boundary exists, water molecules may simply choose to migrate out of the oil to the far more absorbent air interface. This migration can be accelerated if air and oil mix, Such as in splash lubricated and oil mist systems or any system where a stable fluid foam may exist.

If water molecules are unable to find polar compounds on which to attach, the oil is said to be saturated. Any additional water will create a supersaturated condition causing free water to be suspended or settle at the bottom of the sump. This supersaturation can also occur as a result of lower oil temperature.

The post Moisture… the Second Most Destructive Lubricant Contaminant, and its Effects on Bearing Life appeared first on Tesibis.

Water, once in an oil, is in constant search of a stable existence. _Unlike oil, the water molecule is polar, which greatly limits its ability to dissolve; and many additives have polar extremities which can markedly increase water solubility. Water may cling to hydrophilic metal surfaces or form a thin film around polar solid contaminants such as silica particles. If a dry air boundary exists, water molecules may simply choose to migrate out of the oil to the far more absorbent air interface. This migration can be accelerated if air and oil mix, Such as in splash lubricated and oil mist systems or any system where a stable fluid foam may exist.

If water molecules are unable to find polar compounds on which to attach, the oil is said to be saturated. Any additional water will create a supersaturated condition causing free water to be suspended or settle at the bottom of the sump. This supersaturation can also occur as a result of lower oil temperature.

The post Moisture… the Second Most Destructive Lubricant Contaminant, and its Effects on Bearing Life appeared first on Tesibis.