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lubricants and hydraulic fluids Episode 2 Episode 3

Tham khảo tài liệu 'lubricants and hydraulic fluids episode 2 episode 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EM 1110-2-1424 28 Feb 99 2 Calcium complex grease is prepared by adding the salt calcium acetate. The salt provides the grease with extreme pressure characteristics without using an additive. Dropping points greater than 260 C 500 F can be obtained and the maximum usable temperature increases to approximately 177 C 350 F . With the exception of poor pumpability in high-pressure centralized systems where caking and hardening sometimes occur calcium complex greases have good all-around characteristics that make them desirable multipurpose greases. b. Sodium grease. Sodium grease was developed for use at higher operating temperatures than the early hydrated calcium greases. Sodium grease can be used at temperatures up to 121 C 250 F but it is soluble in water and readily washes out. Sodium is sometimes mixed with other metal soaps especially calcium to improve water resistance. Although it has better adhesive properties than calcium grease the use of sodium grease is declining due to its lack of versatility. It cannot compete with water-resistant more heat-resistant multipurpose greases. It is however still recommended for certain heavy-duty applications and well-sealed electric motors. c. Aluminum grease. 1 Aluminum grease is normally clear and has a somewhat stringy texture more so when produced from high-viscosity oils. When heated above 79 C 175 F this stringiness increases and produces a rubberlike substance that pulls away from metal surfaces reducing lubrication and increasing power consumption. Aluminum grease has good water resistance good adhesive properties and inhibits rust without additives but it tends to be short-lived. It has excellent inherent oxidation stability but relatively poor shear stability and pumpability. 2 Aluminum complex grease has a maximum usable temperature of almost 100 C 212 F higher than aluminum-soap greases. It has good water-and-chemical resistance but tends to have shorter life in high-temperature high-speed applications. d. .