Tham khảo tài liệu 'handbook of lubrication episode 2 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 528 CRC Handbook of Lubrication field testing and field development of lubrication requirements for a particular equipment installation are often necessary. Bearings and bearing units are designed for service ranging from nonregreasable lubri-cated-for-life to almost continuous relubrication by means of automatic systems. Advantages of grease over oil lubrication include the ease of sealing it within the bearing the ability of grease to seal out contaminants and its ability to coat parts and provide good corrosion protection. Disadvantages of grease include its inability to remove heat or flush away wear products the possibility of accumulating dirt or other abrasive contamination and a potential incompatibility problem if thickeners of different types are mixed. Oils Oil can be pumped circulated filtered cleaned heated cooled and atomized. Its advantages over grease include its ability to remove heal flush away wear products and contaminants and to be recycled. It is more versatile than grease and is suitable for many severe applications involving extreme speeds and high temperatures. On the other hand it is more difficult to seal or retain in bearings and housings. Oil level or oil flow in highspeed bearings is critical and must be properly controlled. Selection of proper oil viscosity is essential and is based primarily on expected operating temperature speed and bearing geometry. Excessive oil viscosity many cause skidding of rolling elements and undue lubricant friction with severe overheating and raceway damage. Insufficient oil viscosity may result in metal contact and possible premature failure. Other oil properties such as viscosity index flash point pour point neutralization number carbon residue and corrosion protection are of varying significance in specific installations. Synthetic Lubricants Development of synthetic lubricants was initially prompted largely by the extreme environmental demands of military and aerospace activities. Currently the .
