tailieunhanh - Volume 18 - Friction, Lubrication, and Wear Technology Part 20

Tham khảo tài liệu 'volume 18 - friction, lubrication, and wear technology part 20', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | mm Fig. 8 Compressive yield strength levels typically obtained in the individual layers of a trilayer construction bearing material Corrosion Resistance. Bearing failure due to corrosion alone is rare. Corrosion usually interacts with mechanical and thermal factors to produce failure by fatigue or seizure under conditions the bearing normally would be able to tolerate. To a considerable extent bearing corrosion can be avoided by use of oxidation inhibitors in commercial lubrication oils and by periodic oil changes. There are however many situations in which neither of these practices is dependable and where bearing materials with inherently high corrosion resistance should be used. Commercially pure lead is susceptible to corrosion by fatty acids. Lead-base and copper-lead bearing alloys can suffer severe corrosion damage in acidic lubricating oils. Tin additions in excess of 5 provide effective protection against this kind of corrosion and for this reason tin is used extensively in lead-base bearing alloys. Both copper and lead are attacked by acidic oils that contain sulfur. This is of particular concern with copper-lead and leaded bronze bearing alloys. Effective protection can be obtained by employing layered construction with a surface layer of either a lead alloy containing tin or a tin alloy. As long as the corrosion-resistant surface layer is intact the underlying copper-lead alloy will not suffer damage by corrosion. Tin and aluminum bearing alloys are substantially impervious to corrosion by the products of oil oxidation and they are used extensively in applications where the potential for lubricating oil corrosion is known to be high. Although lubricating oil oxidation and contamination are the most common causes of bearing damage by corrosion other sources of bearing corrosion such as seawater animal and vegetable oils and corrosive gas should be recognized. Selection and specification of a bearing material for a specific application should .