2021年中国海洋大学机电工程专业外语

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Machine 11春15
欧阳光明(2021.03.07)
June7,201112/7002
文件:Machine11春15
Friction and LubricationⅡ(86-91)《机械工程专业英语教程》施平主
编电子工业出版社
Unit22Lubrication and Journal of Bearing
The object of lubrication is to reduce friction, wear, and heating of machine parts which move relative to each other. A lubricant is any substance which, when inserted between the moving surfaces, accomplishes these purposes.Most lubricants are liquids (such as mineraloil, silicone fluids, and water), but they may be solid for use indry bearings, greases for use in rolling element bearing, or gases (such as air)for use in gas bearings. The physical and chemical
interaction
between the lubricant and lubricating surfaces must be understood in order to provide the machine elements with satisfactory life.
The understanding of hydrodynamic lubrication began with the classical experiments of Tower, in which the existence of a film was detected from measurements of pressure with lubricant. This work was
closely followed by Reynolds’ paper in whic h he used a reduced form
of Navier-Stocks equations in associate with the continuity equation to generate a second-order differential equation for the pressure in the narrow, converging gap between the bearing surfaces. This pressure enables a load to be transmitted between the surfaces with extremely
low friction, since the surfaces are completely separated by a fluid film. The understanding of boundary lubrication is normally attributed to Hardy and Doubleday, who found the extremely thin films adhering
to surfaces were often sufficient to assist relative sliding. They
concluded
that under such circumstances the chemical composition of liquid is important, and they introduced the term “boundary lubrication”. Boundary lubrication is at the opposite end of the spectrum from hydrodynamic lubrication.
Five distinct of forms of lubrication may be identified:
(a)hydrodynamic;
(b)hydrostatic;
(c)elastohydrodynamic;
(d)boundary;
(e)solid film.
Hydrodynamic lubrication means that the load-carrying surfaces of the bearing are separated by relatively thick film of lubricant, so as to
prevent
metal to metal contact, and that the stability thus obtained can be explained by the laws of fluid mechanics.。