دانلود رایگان مقاله لاتین مکانیزم سایش بلبرینگ از سایت الزویر
عنوان فارسی مقاله:
تحقیق در مکانیزم سایش بلبرینگ های استفاده شده در سطل بیل چرخ
عنوان انگلیسی مقاله:
Investigation into wear mechanisms of the bearing raceway used in bucket wheel excavators
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
The main problem with the basic machines, used for open mining, is the construction of the rotational connection between the upper and lower structure. This must be constructed in such a way that it is possible to transfer large axial and radial forces and significant overturning moments. One of the basic movements of these machines is the rotation of the superstructure around the vertical axis. The joint for structural rotation, used in the surface mining machines, is usually constructed as a double shell element connected with the large sized bearing. A significant problem, which occurs only in this type of machine, is deformation wear of the raceway during the initial operation period. The high intensity of rolling, during the initial rotational movements of the upper body, alters the raceway geometry. For this reason, it becomes crucial to forecast the growth of plastic deformation and to determine the maximum loads that occur until the deformation and wearing become stable. The large sized bearings are constructed differently to the conventional bearings used in working machines. These differences include: much larger dimensions; a large number of rolling elements (up to several hundred in the largest bearings); slower running; the material used (meaning that an individually prepared heat treatment process according to this material must also be carried out); a small range of rotational movement of the upper body relative to the chassis during the whole working cycle; complexity of the external load transmitted through the bearing; difficulty in determining their exact kind and value; and the individual working conditions of machines in which the large bearings have been used. The large sized rolling element bearings, used for turning the upper body of machines working in open-pit mining, are made in the form of single- or double-row ball bearings. As shown in [1], the bearing section diameter may be up to 20 m and the rolling element diameter ranges from 100 to 250 mm. These are both put under eccentric axial loads which range from a few to tens of MN. The load exerted on the rolling elements is uneven due to the supportive element's low stiffness and its non-uniform distribution around the bearing circumference. The load stream flow concentrates at points within areas of high stiffness. The bearing raceways are made of structural steels, which are usually normalized or occasionally thermally toughened. At present no quenched surface raceways are used. This is due to the technological difficulties of creating an adequate layer of hardened surface and the rapid process of damage to the surface, since the first hardened part of the surface is separated. In [2], the formula for the approximation of the rate of deformation wear in largesize bearings is described. This is given as a function of the ball diameter; number of load cycles; and two constants, which depend on rolling element specific load.
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کلمات کلیدی:
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