TAILIEUCHUNG - Tribology Handbook 2E Episode 9

Tham khảo tài liệu 'tribology handbook 2e episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Other liquids TEMPERATURE C Figure The viscosity of various water-based mixtures For all practical purposes the above fluids may be classed as Newtonian but other fluids such as water-in-oil emulsions are non-Newtonian. The viscosity values given for the typical 40 water-in-oil emulsion are for very low shear rates. For this emulsion the viscosity will decrease by 10 at shear rates of about 3000 s -I and by 20 at shear rates of about 10 000 s-1. Plain bearing lubrication C7 Mineral oils and greases are the most suitable lubricants for plain bearings in most applications. Synthetic oils may be required if system temperatures are very high. Water and process fluids can also be used as lubricants in certain applications. The general characteristics of these main classes of lubricants are summarised in Table . Table Choice of lubricant Lubricant Operating range Remarks Mineral oils All conditions of load and speed Wide range of viscosities available. Potential corrosion problems with certain additive oils . extreme pressure see Table Synthetic oils All conditions if suitable viscosity available Good high and low temperature properties. Costly Greases Use restricted to operating speeds below I to 2 m s Good where sealing against dirt and moisture necessary and where motion is intermittent Process fluids Depends on properties of fluid May be necessary to avoid contamination of food products chemicals etc. Special attention to design and selection of bearing materials The most important property of a lubricant for plain bearings is its viscosity. If the viscosity is too low the bearing will have inadequate load-carrying capacity whilst if the viscosity is too high the power loss and the operating temperature will be unnecessarily high. Figure gives a guide to the value of the minimum allowable viscosity for a range of speeds and loads. It should be noted that these values apply for a fluid at the mean bearing temperature. The viscosity of .

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