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Industrial Lubrication Standards
What Are Lubricants?
Lubricants are substances used to reduce friction between moving parts, minimize wear and tear, cool parts, remove debris as parts wear down and water and help prevent rust.
Most lubricants are oils or liquids, like motor oil. Some of the most commonly used lubricants are derived from petroleum oil and synthetic oils. Vegetable oils like rapeseed oil and fatty oils such as those derived from fish are also sometimes used. If you do not lubricate assemblies, the heat caused by parts rubbing against each other could cause mechanical failure in motors or rapid wearing out of gear assemblies.
Lubrication systems are the mechanical systems used to cycle lubricants through mechanical assemblies The lubrication assemblies push clean oil between parts or among gears before returning the oil or lubricant to a central pump where it is filtered for metal debris and excess moisture is removed.
Physical Testing of Lubricants
Lubricants have physical properties that can be tested. Physical tests measure attributes like the material's viscosity, density or fire point. Chemical tests determine the acidity of the lubricant, its chemical composition or percentage of metal particles contained within spent lubricant.
Performance tests measure the performance of the lubricant when it is used. How well does it prevent rust when used? How well does it prevent wear of components? How easily does it separate from water?
The kinematic viscosity of lubricants is measured per ASTM D445 using capillary tubes. Saybolt viscosity is rarely used, but it can be determined from the kinematic velocity test results per ASTM standard D2161.
Dynamic viscosity is related to the kinematic viscosity, but dynamic viscosity can be found separately using ASTM tests like ASTM D4684 or ASTM D2983. The variation of viscosity for petroleum based lubricants can be determined by using the equations outlined in ASTM D341, if the temperatures used in the calculation are below the boiling point and above the wax point when the lubricant becomes a solid. The cloud point is when a lubricant begins to show crystals in the liquid before it turns into a waxy solid. The cloud point is found using ASTM D2500, if the crystals are visible to the human eye.
The pour point is the temperature when lubricants can barely be poured. The pour point is found using ASTM D97. At a lower temperature than the pour point, it is essentially solid and cannot be poured out of its container. The pour point is separate from the cloud point.
The density and specific gravity of lubricants are found using ASTM D1298.
The ISO has created a viscosity grading system. The ISO viscosity grade or VG is a number that represents the viscosity of that lubricant at 40°C. The 18 viscosity grades or VG recognized by the ISO go from 2 centistokes to 1,500 centistokes.
The viscosity index can be looked up on the ASTM DS 39B tables or calculated from the kinematic velocity using the equations in ASTM D2270.
Lubricants that contain polymer additives see sheer effects on the viscosity, something that does not affect the viscosity of pure petroleum lubricants. When polymers have been added to a lubricant, the viscosity loss can be measured using ASTM standard D4683 or ASTM D4741.
Testing the Physical Properties of Lubricants
The flash point is when a lubricant's vapors can create a flash fire. The fire point is when the lubricant will continue burning after the initial fumes are burned away. ASTM D92 is the standard for determining the flash point and fire point of lubricants.
The color of lubricants is found using a colorimeter per ASTM D1500. The ASTM color scale with colorimeters ranges from 0.5 to 8.0. When the color is less than 0.5, the ASTM D156 test is used. For lubricants darker than 8.0, ASTM D1500 allows for kerosene to be added to determine its color and dilute the existence of particles.
The ash content of lubricants can be found using ASTM D482, while sulfated ash levels are determined using ASTM D874.
Chemical Testing of Lubricants
The total base number is found through the test procedures in ASTM D2896. The total base number or TBN correlates to the ability of oil to protect engines from corrosion.
The foaming of lubricants are tested per the procedure in ASTM D892. The total acid number may be found using ASTM D664.
The oxidation of lubricants increases their viscosity and acid level. Oxidation is generally the result of high temperatures and contact with air. Oxidation effects begin at operating temperatures around 150°F or 66°C. Oxidation testing is done per ASTM D943 or ASTM standard D772.
Lubricants can be used to prevent rust or carry away water before it causes rust. The ability of a lubricant to prevent rust can be evaluated using ASTM D665. For high humidity environments, ASTM D1748 can be used.
After the lubricant absorbs the water, the water must then separate from the lubricant, a process called water separation or demulsibility. ASTM D1401 is used to measure the water separation of light viscosity oils. ASTM D2711 measures the water separation in high viscosity oils.