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Liquid Table of Contents Physical & Chemical Properties Liquid contaminants come in four forms: 1.) additions of the wrong oil. 2.) water. 3.) solvents. 4.) process liquids. The addition of the wrong oil with a different viscosity will affect oils film thickness, pumping, and other properties depending upon viscosity. The simplest method of detection is a viscosity measurement. If the added oil has different base oil or additives, the first visual evidence may be a precipitate due to additive interaction. Metal analysis using Emission Spectroscopy (ES) may reveal the presence of wrong oil by detecting unexpected metallo-organic additives. For example, if one was using a Rust and Oxidation inhibited oil (R and O), and ES indicated the presence of zinc and phosphorous (possibly from the anti-wear additive zinc dialkyldithiophosphate), then contamination by a wrong oil could be suspect. In ES analysis, metallic elements in the oil sample are excited by a high temperature arc and emit light energy. Each metallic element emits light at a unique wave length. The resulting light is focused and passed through a diffraction grating to separate the beam into component wavelengths. The intensity of light at specific wave lengths is measured using photo multiplier tubes, and compared to calibration standards, and reported as parts per million (ppm) concentrations. Large (greater than 10 microns) and dense particles, such as metallic wear chips or sand, may not be measured as accurately as the soluble materials because the particles may not be effectively introduced or completely volatilized in the excitation region of the spectrometer. Other methods involving acid digestion or spark on residue are available that analyze all particles. (The user should remember that the results are reported as elemental metals with no indication of the compounds of which they are a part. For example, silicon could be from silicone or sand (SiO2), iron could be from metallic iron wear fragments, from rust (hydrated iron oxide Fe2O3.H2O due to corrosion), or from iron sulfide. Water contamination comes from two primary sources; leaks in the system or condensation of moisture in the air space. Leaks may be from steam, seals or gaskets. Water in oil is detrimental to the formation of the oil film, and in the promotion of contact fatigue of gear teeth and rolling element bearings. In many systems, water in the oil as low as 0.01% can shorten bearing life substantially. Water contamination may be detected by observing a layer of free water in the bottom of a container of drained oil, or in oil withdrawn from the bottom of a sump. Water may be present if the oil appears hazy or milky. A useful test for water is the "crackle test", where a drop of oil is placed onto a hot surface, if it crackles, or sputters, a large quantity of water is present. Another "in the shop" test is to immerse a hot soldering iron into a container of oil and observe sputtering if the oil is wet. Water is measured quantitatively by titration or distillation tests in the laboratory. The common method is ASTM D 1533 or ASTM D 1744 "Water by Karl Fischer Method". Almost any measurable water (greater than 0.05%) is a sign of a problem and should be addressed. Levels as low as 0.01% may be a sign of impending problems in some systems such as refrigeration compressor oils. The source of the water may be determined by ES, knowing what metal compounds are in the source water. For example, high sodium, boron, and potassium indicate cooling water may be the source. Process liquids and solvent contaminants also interfere with oil film formation as does water, but the effects are mostly chemical (see later). Process liquid contamination is common in pumps. Contamination can be indicated by changes in odor, color, flash point, or viscosity of the oil. The amount may be measured (depending on the liquid) by Total Acid Number (TAN), density, flash point, and Infrared (IR) spectrum. Interpretation of the problem is fairly straight forward since the process liquid is usually known. For more information call 1-888-HERGUTH (437-4884) | |||||||||||||||||||
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