1、附录 附录 1 英文原文 Rolling Contact Bearings The concern of a machine designer with ball and roller bearings is fivefold as follows:(a) life in relation to load； (b) stiffness,i.e.deflections under load； (c) friction； (d) wear； (e) noise. For moderate loads and speeds the correct selection of a standard be
2、aring on the basis of a load rating will become important where loads are high,although this is usually of less magnitude than that of the shafts or other components associated with the bearing. Where speeds are high special cooling arrangements become necessary which may increase fricitional drag.
3、Wear is primarily associated with the introduction of contaminants,and sealing arrangements must be chosen with regard to the hostility of the environment. Because the high quality and low price of ball and roller bearing depends on quantity production,the task of the machine designer becomes one of
4、 selection rather than design. Rolling-contact bearings are generally made with steel which is through-hardened to about 900HV,although in many mechanisms special races are not provided and the interacting surfaces are hardened to about 600HV. It is not surprising that,owing to the high stresses inv
5、olved,a predominant form of failure should be metal fatigue, and a good deal of work is based on accept values of life and it is general practice in bearing industry to define the load capacity of the bearing as that value below which 90 percent of a batch will exceed life of one million revolutions
6、. Notwithstanding the fact that responsibility for basic design of ball and roller bearings rests with he bearing manufacturer, the machine designer must form a correct appreciation of the duty to be performed by the bearing and be concerned not only with bearing selection but with the conditions fo
7、r correct installation. The fit of the bearing races onto the shaft or onto the housings is of critical importance because of their combined effect on the internal clearance of the bearing as well as preserving the desired degree of interference fit. Inadequate interference can induce serious troubl
8、e from fretting corrosion. The inner race is frequently located axially by against a shoulder. A radius at this point is essential for the avoidance of stress concentration and ball races are provided with a radius or chamfer to follow space for this. Where life is not the determining factor in desi
9、gn, it is usual to determine maximum loading by the amount to which a bearing will deflect under load. Thus the concept of static load-carrying capacity is understood to mean the load that can be applied to a bearing, which is either stationary or subject to slight swiveling motions, without impairi
10、ng its running qualities for subsequent rotational motion. This has been determined by practical experience as the load which when applied to a bearing results in a total deformation of 0.0025mm for a ball 25mm in diameter. The successful functioning of many bearings depends upon providing them with
11、 adequate protection against their environment, and in some circumstances the environment must be protected from lubricants or products of deterioration of the bearing design. Moreover, seals which are applied to moving parts for any purpose are of interest to tribologists because they are component
12、s of bearing systems and can only be designed satisfactorily on basis of the appropriate bearing theory. Notwithstanding their importance, the amount of research effort that has been devoted to the understanding of the behavior of seals has been small when compared with that devoted to other aspects
13、 of bearing technology. Lathes Lathes are widely used in industry to produce all kinds of machined parts. Some are general purpose machines, and others are used to perform highly specialized operations. Engine lathes Engine lathes, of course, are general-purpose machine used in production and mainte
14、nance shop all over the the world. Sized ranger from small bench models to huge heavy duty pieces of equipment. Many of the larger lathes come equipped with attachments not commonly found in the ordinary shop, such as automatic shop for the carriage. Tracer or Duplicating Lathes The tracer or duplic
15、ating lathe is designed o produce irregularly shaped parts automatically. The basic operation of this lathe is as fallows. A template of either a flat or three-dimensional shape is placed in a holder. A guide or pointer then moves along this shape and its movement controls that of the cutting tool.
16、The duplication may include a square or tapered shoulder, grooves, tapers, and contours. Work such as motor shafts, spindles, pistons, rods, car axles, turbine shafts, and a variety of other objects can be turned using this type of lathe. Turret Lathes When machining a complex workpiece on a general
17、-purpose lathe, a great deal of time is spent changing and adjusting the several tools that are needed to complete the work. One of the first adaptations of the engine lathe which made it suitable to mass production was the addition of multi-tool in place of the tailstock. Although most turrets have
18、 six stations, some have as many as eight. High-production turret lathes are very complicated machines with a wide variety of power accessories. The principal feature of all turret lathes, however, is that the tools can perform a consecutive serials of operations in proper sequence. Once the tools h
19、ave been set and adjusted, little skill is require to run out duplicate parts. Automatic Screw Machine Screw machines are similar in construction to turret lathes, except that their heads are designed to hold and feed long bars of stock. Otherwise, their is little different between them. Both are de
20、signed for multiple tooling, and both have adaptations for identical work. Originally, the turret lathe was designed as a chucking lathe for machining small casting, forgings, and irregularly shaped workpieces. The first screw machines were designed to feed bar stock and wire used in making small sc
21、rew parts. Today, however, the turret lathe is frequently used with a collect attachment, and the automatic screw machine can be equipped with a chuck to hold castings. The single-spindle automatic screw machine, as its name implies, machines work on only one bar of stock at a time. A bar 16 to 20 f
22、eet long is feed through the headstock spindle and is held firmly by a collect. The machining operations are done by cutting tools mounted on the cross slide. When the machine is in operation, the spindle and the stock are rotated at selected speeds for different operations. If required, rapid rever
23、sal of spindle direction is also possible. In the single-spindle automatic screw machine, a specific length of stock is automatically fed through the spindle to a machining area. At this point, the turret and cross slide move into position and automatically perform whatever operations are required. After the machined piece is cut off, stock is again fed into the machining area and the entire cycle is repeated. Multiple-spindle automatic screw machines have from four to eight spindles
