【正文】 l deflect under load. Thus the concept of static loadcarrying 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 impairing 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 for a ball 25mm in diameter. The successful functioning of many bearings depends upon providing them with 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 ponents 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 pared with that devoted to other aspects 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 generalpurpose machine used in production and maintenance shop all over the the world. Sized ranger from small bench models to huge heavy duty pieces of equipment. Many of the larger lathes e equipped with attachments not monly found in the ordinary shop, such as automatic shop for the carriage. Tracer or Duplicating Lathes The tracer or duplicating 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 threedimensional shape is placed in a holder. A guide or pointer then moves along this shape and its movement controls that of the cutting tool. 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 plex workpiece on a generalpurpose lathe, a great deal of time is spent changing and adjusting the several tools that are needed to plete the work. One of the first adaptations of the engine lathe which made it suitable to mass production was the addition of multitool in place of the tailstock. Although most turrets have six stations, some have as many as eight. Highproduction turret lathes are very plicated 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 have 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 designed for multiple tooling, and both have adaptations for identical work. Originally, the turret lathe was designed as a chucking lathe for machining small casting, fings, and irregularly shaped workpieces. The first screw machines were designed to feed bar stock and wire used in making small screw 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 singlespindle automatic screw machine, as its name implies, machines work on only one bar of stock at a time. A bar 16 to 20 feet long is feed through the headstock spindle and is held firmly by a collect. The machi ning 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 reversal of spindle direction is also possible. In the singlespindle 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. Multiplespindle automatic screw machines have from four to eight spindles located around a spindle carrier. Long bars of stock, supported at the rear of the machine,pass though these hollow spindles and are gripped by collects. With the single spindle machines, the turret indexes around the spindle. When one tool on the turret is working, the others are not. With a multiple spindle machine, however, the spindle itself index. Thus the bars of stock are carried to the various end working and side working tools. Each tool operates in only one position, but tolls operate simultaneously. Therefore, four to eight workpieces can be machined at the sa me time. Vertical Turret Lathes A vertical turret is basically a turret lathe that has been stood on its headstock end. It is designed to perform a variety of turning operations. It consists of a turret, a revolving table, and a side head with a square turret for holding additional tools. Operations performed by any of the tools mounted on the turret or side head can be controlled through the use of stops. Machining Centers Many of today39。 (c) friction。附錄 附錄 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, under load。 (d) wear。s more so