PRINCIPLES OF NAVAL ENGINEERING 



speeds. More adhesiveness is required to make 

 a lubricant adhere to bearing surfaces at high 

 speeds than at low speeds. At low speeds, greater 

 cohesiveness is required to keep the lubricant 

 from being squeezed out from between the bear- 

 ing surfaces. 



Large clearances between bearing surfaces 

 require high viscosity and cohesiveness in the 

 lubricant to ensure maintenance of the lubricat- 

 ing oil film. The larger the clearance, the greater 

 must be the resistance of the lubricant to being 

 pounded out, with consequent destruction of the 

 lubricating oil film. 



High unit load on a bearing requires high vis- 

 cosity of the lubricant. A lubricant subjected to 

 high loading must be sufficiently cohesive to hold 

 together and maintain the oil film. 



LUBRICANTS 



Although there is a growing use of synthetic 

 lubricants, the principal source of the oils and 

 greases used in the Navy is still petroleum. By 

 various refining processes, lubricating stocks 

 are extracted from crude petroleum and blended 

 into a multiplicity of products to meet all lubri- 

 cation requirements. Various compounds or ad- 

 ditives are used in some lubricants (both oils 

 and greases) to provide specific properties re- 

 quired for specific applications. 



Types of Lubricating Oils 



Lubricating oils approved for shipboard use 

 are limited to those grades and types deemed es- 

 sential to provide proper lubrication under all 

 anticipated operating conditions. 



For diesel engines, it is necessary to use a 

 detergent-dispersant type of additive oil in order 

 to keep the engines clean. In addition, these lu- 

 bricating oils must be fortified with oxidation in- 

 hibitors and corrosion inhibitors to allow long 

 periods between oil changes and to prevent cor- 

 rosion of bearing materials. 



For steam turbines, it is necessary to have 

 an oil of high initial film strength. This oil is 

 then fortified with anti-foaming additives and 

 additives that inhibit oxidation and corrosion. In 

 addition, it isnecessary to use extreme pressure 

 (EP) additives to enable the oil to carry the ex- 

 tremely high loading to which it is subjected in 

 the reduction gears. 



For the hydraulic systems in which petro- 

 leum lubricants are used, and for general 

 lubrication use, the Navy usesa viscosity series 



of oils reinforced with oxidation and corrosion 

 inhibitors and anti-foam additives. The com- 

 pounded oils, which are mineral oils to which 

 such products as rape seed, tallow, or lard oil 

 are added, are still used in deck machinery and in 

 the few remaining steam plants that utilize recip- 

 rocating steam engines. 



A great many special lubricating oils are 

 available for a wide variety of services. These 

 are listed in the Federal Supply Catalog. Among 

 the more important specialty oils are those used 

 for lubricating refrigerant compressors. These 

 oils musthavea very low pour point and be main- 

 tained with a high degree of freedom from mois- 

 ture. 



The principal synthetic lubricants currently 

 in naval use are (1) a phosphate ester type of 

 fire-resistant hydraulic fluid, used chiefly in the 

 deck-edge elevators of carriers (CVAs); and (2) 

 a water-base glycol hydraulic fluid used chiefly 

 in the catapult retracting gear. 



Classification of 

 Lubricating Oils 



The Navy identifies lubricating oils by sym- 

 bols. Each identification number consists of four 

 digits (and, in some cases, appended letters) . The 

 first digit indicates the class of oil according to 

 type and use; the last three digits indicate the 

 viscosity of the oil. The viscosity digits are ac- 

 tually the number of seconds required for 60 mil- 

 liliters of the oil to flow through a standard 

 orifice at a specified temperature. The symbol 

 3080, for example, indicates that the oil is in the 

 3000 series and that a 60-ml sample flows 

 through a standard orifice in 80 seconds when the 

 oil is at a specified temperature (210 F, in this 

 instance). To take another example, the symbol 

 2135 TH indicates that the oil is in the 2000 se- 

 ries and that a 60-ml sample flows through 

 a standard orifice in 135 seconds when the oil is 

 at a specified temperature (130' F, in this case). 



The letters H, T, TH, or TEP added to a basic 

 symbol number indicate that the oil contains ad- 

 ditives for special purposes. 



Lubricating Oil Characteristics 



Lubricating oils used by the Navy are tested 

 for a number of characteristics, including vis- 

 cosity, pour point, flash point, fire point, auto- 

 ignition point, neutralization number, demul- 

 sibility, and precipitation number. Standard test 

 methods are used for making all tests. 



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