Machinery Lubrication

Machinery Lubrication March April 2017

Machinery Lubrication magazine published by Noria Corporation

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Page 22 of 88

18 | March - April 2017 | ASK the EXPERTS Color can be used as an indicator of oil health, and in many cases it is a reliable field indicator. However, color alone cannot tell the whole story of the oil's condition. For a complete understanding of oil condition, it is important to use an appropriate test slate. The color of lubricating oils can range from transparent to opaque. The color is based on the crude from which it is made, its viscosity, method and degree of treatment during refining, and the amount and types of additives included. A change in oil color signifies a change in the chemistry of the oil or the presence of contaminants. For example, oil oxidation, mixing "Is there an oil color standard for oil analysis? We have taken samples of engine lubricants, and some have colors that look like coffee with milk. Is this color acceptable in oil analysis? Do you know the color standard in oil analysis?" "Is there any way to clean our oil up to two ISO codes other than with loop filtering?" Best practices recommend that lubricants are filtered when they are transferred from one container to another or to a machine. This practice can improve lubricant cleanliness with just a single pass. The filter must have a high beta ratio (greater than 200) at the right micron size to achieve the expected cleanliness level. Of course, the use of a high-efficiency filter will require the proper lubricant flow rate and pressure according to the viscosity and volume to be filtered. Installing a temporary online filtration system or "kidney loop" to clean the lubri - cant in a machine or container is a low-cost option to remove solid contaminants. Since the filtered lubricant returns to the same sump from which it was obtained, it is mixed with non-filtered lubricant. The new sump cleanliness is the result of the mixed concentrations. For this reason, the lubri- cant must pass through the filter several times. The number of passes will depend on the existing and desired cleanliness level. The lubricant volume will play a factor as well. In the field, it is common to have a lubricant pass through the filter seven times to clean it, but this is just an estimate. Other alternatives can also be employed to clean the oil, including modern centrif- ugal technologies. These can be very effective in removing solid contaminants and improving ISO cleanliness codes. They are used for industrial engine oils and frequently applied as a bypass system for the main filtration and lubrication circuit. Most centrifuge designs utilize the pres- sure of the fluid going through the system to spin the rotor at speeds high enough to sepa- rate contaminant particles from the fluid. In engine applications, the oil is directed to the centrifuge in a bypass loop, which uses 5 to 15 percent of the pump's flow, depending on the application. This pressurized flow travels through the centrifuge rotor. As it exits the rotor, the oil goes through two small nozzles. The reaction force created by the exiting fluid creates the torque necessary to over- come any friction, and the rotor begins to spin. Typical speeds between 5,000 and 8,000 revolutions per minute can be achieved in most applications. Other methods such as gravity settling or magnetic f ilters may not be as effective in removing smaller par ticles or different materials.

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