Machinery Lubrication

Machinery Lubrication November-December 2017

Machinery Lubrication magazine published by Noria Corporation

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www . | November - December 2017 | 55 Additives are employed to impart new properties or to suppress or enhance existing properties of the base oil. ey can make up between 0 to 10 percent of the grease and typically offer protection to rotating equipment during startup and shutdown. Additives can also help protect against rust and corrosion. e thickener is critical, as it is the vessel that delivers the base oil and additives to the equipment. It can represent between 3 to 30 percent of the grease. There are many types of thickeners, but most fit into two categories: simple soap or complex soap. Other thickeners, such as polyurea, clay and silica, do not fall into these categories but also act as thickening agents in specialty grease formulations. Selecting a Grease Now that you have a better understanding of how grease is formulated, let's look at four tests that can reveal how the grease's ingredients will interact inside a lubrication system. e first prop- erty to consider is the base oil's apparent viscosity. 1. Apparent Viscosity Test Viscosity is the most important property of any lubricant. To determine the required base oil viscosity, you must identify the optimal viscosity for each system component you plan to lubricate. A grease's base oil viscosity is noted on its product data sheet. Once you have established the required viscosity, test the grease to find its apparent viscosity. is relates to mobility of a grease moving through lines and components of a central- ized lubrication system. Apparent viscosity involves the collective influence of the base oil, additives and thickener. e ASTM D1092 standard test is ideal for measuring the apparent viscosity of lubricating greases. It can help predict pressure drops in a centralized lubrication system under a steady flow and at a constant temperature. e results of this test are reported in centipoise. 2. Cone Penetration Test You also will need to determine the required consistency or NLGI grade of the grease. A general starting point is the expected operating temperature and speed factor. Other variables that can impact the required consistency include the bearing type, thickener type, base oil viscosity and base oil type. A cone penetration test (ASTM D217) is frequently employed to gauge a grease's consistency. It utilizes a weighted cone to penetrate a block of grease, with four standards of testing the grease's consistency: undisturbed, worked, prolonged worked and block. e focus of this article will be on the undisturbed and worked tests. An undisturbed penetration test provides information on the grease's consistency during storage conditions. Worked penetration tests reveal what the consistency of the grease will be while inside a machine or component. is is imperative with centralized grease systems, as the grease may be in "storage conditions" for a prolonged period before it reaches the component. Storage conditions apply to grease both while it is in a drum or other storage container and in supply lines. Among the factors to keep in mind when planning a supply-line path are the temperature exposures, vertical paths, and the time it takes for the grease to enter the supply line and reach its destination. ese factors can cause the base oil and thickener to separate, leading to oil starvation in the equipment. 3. Structural Stability Test Next, assess how stable the grease will be as it is subjected to operating conditions. You must know if the grease will be able to handle the intended loads and for how long before it begins to fail. e ASTM D1831 structural stability test method utilizes a penetrometer test of unworked grease. e same grease is then worked in a standard roll stability device for two hours at a temperature between 20 to 35 degrees C (68 to 95 degrees F). e grease is then put through the penetrometer test again. e differ- ence between the two tests is used to measure the effect of low shear stability of the oil in the grease. 4. Ventability Test The final test relates specifi- cally to matching the grease to the lubrication system's design and the size of tubing to be utilized. Depending on how far the grease will be pumped, the tubing size can ML 50% of lubrication professionals use centralized lubrication systems at their plant, based on a recent survey at

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