Solid Lubricants
Solid lubricants provide thin solid ?lms on sliding or rolling/sliding surfaces to reduce friction and wear.
They are particularly useful for applications involving high operating temperatures, vacuum, nuclear
radiation, or other environments which limit the use of oils or greases. Solid lubricant ?lms do not
prevent moving surfaces from contacting each other, so they cannot eliminate wear and their lives are
. limited by wear. The properties of some of the most common solid lubricants are given in Table 3.10.7
Fluid Film Bearings
Journal Bearings
A journal bearing consists of an approximately cylindrical bearing body or sleeve around a rotating
cylindrical shaft. In general, journal bearings are found in motors, pumps, generators, appliances, and
internal combustion engines in which a ?uid lubricant is used; and in smaller mechanisms such as
switches, clocks, small motors, and circuit breakers in which a solid lubricant such as graphite, grease,
or certain plastics serves to reduce friction. Air (gas) bearings are designed to utilize both ?uid mechanics
principles when operating and solid lubricant?surfaced materials for start, stop, and emergency operations.
A hydrodynamic journal bearing maintains separation of shaft from bearing because the lubricant
viscosity and the speed of the shaft create pressure in the converging portion of the ?uid ?lm which
carries load. The governing equations were ?rst developed by Reynolds (1886). Their solution has led
to numerous computer solutions, including those used for this section.
Journal Bearing Design. Figure 3.10.5 shows schematics of frequently used types of journal bearing in
which one or more lobes of cylindrical shape are positioned around the shaft, their axis being assumed
parallel to the shaft axis. The features of each design and applications where it is often found are listed
in Table 3.10.8.
Noncontact journal bearings are designed to assure a continuous supply of lubricant to the loadcarrying
section, and the bearing grooves in Figure 3.10.5 are designed for that purpose. Oil must be
resupplied to the bearing because of the continuous loss of lubricant as it is forced from the bearing by
the load-carrying pressures generated within it. The subsection on lubricant supply methods describes
some of the many systems designed to assure this supply and to cool the lubricant at the same time.
Controlling Variables. De?nitions of the variables involved in journal bearing analysis are contained
in Table 3.10.9. Because of the large range of many variables, nondimensional quantities are often used
which are independent of the dimensional unit system involved. Examples are given in the English
system unless otherwise stated.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
الرجوع الى لوحة التحكم
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