机械外文翻译---实验研究激光加工表面微观造型平行的推力轴承(编辑修改稿)

机械外文翻译---实验研究激光加工表面微观造型平行的推力轴承(编辑修改稿)内容摘要：

These values represent a reduction of clearance between 33 and 10% pared to the unidirectional case. However, as can be seen from figure 8 the performance of the partialLST bidirectional bearing is still substantially better than that of the untextured bearing. The friction coefficient of partialLST unidirectional and bidirectional bearings was pared with that of the untextured bearing in figures 9 and 10 for the two speeds of 1500 and 3000 rpm, respectively. As can be seen the friction coefficient of the two partialLST bearings is very similar with slightly lower values in the case of the more efficient unidirectional bearing. The friction coefficient of the untextured bearing is much larger pared to that of the LST bearings. At 1500 rpm (figure 9) and the highest load of 460 N the friction coefficient of the untextured bearing is about pared to about for the LST bearings. At the lowest load of 160 N the values are about for the untextured bearing and around for the LST bearings. Hence, the friction values of the untextured bearing are between and 3 times higher than the corresponding values for the partialLST bearings over the entire load range. Similar results were obtained at the velocity of 3000 rpm (figure 10) but the level of the friction coefficients is somewhat higher due to the higher speed. The much higher friction of the untextured bearing is due to the much smaller clearances of this bearing (see figures 7 and 8) that result in higher viscous shear. Bearings fail for a number of reasons， but the most mon are misapplication，contamination， improper lubricant， shipping or handling damage， and misalignment. The problem is often not difficult to diagnose because a failed bearing usually leaves telltale signs about what went wrong． However， while a postmortem yields good information， it is better to avoid the process altogether by specifying the bearing correctly in The first place． To do this，it is useful to review the manufacturers sizing guidelines and operating characteristics for the selected bearing. Equally critical is a study of requirements for noise, torque, and runout, as well as possible exposure to contaminants, hostile liquids, and temperature extremes. This can provide further clues as to whether a bearing is right for a job. 1 Why bearings fail About 40% of ball bearing failures are caused by contamination from dust, dirt, shavings, and corrosion. Contamination also causes torque and noise problems, and is often the result of improper handling or the application environment． Fortunately, a bearing failure caused by environment or handling contamination is preventable， and a simple visual examination can easily identify the cause． Conducting a postmortem il1ustrates what to look for on a failed or failing bearing． Then， understanding the mechanism behind the failure, such as brinelling or fatigue, helps eliminate the source of the problem. Brinelling is one type of bearing failure easily avoided by proper handing and assembly. It is characterized by indentations in the bearing raceway caused by shock loading－ such as when a bearing is droppedor incorrect assembly. Brinelling usually occurs when loads exceed the material yield point(350,000 psi in SAE 52100 chrome steel)． It may also be caused by improper assembly, Which places a load across the races． Raceway dents also produce noise， vibration， and increased torque. A similar defect is a pattern of elliptical dents caused by balls vibrating between raceways while the bearing is not turning． This problem is called false brinelling. It occurs on equipment in transit or that vibrates when not in operation. In addition, debris created by false brinelling acts like an abrasive, further contaminating the bearing. Unlike brinelling, false binelling is often indicated by a reddish color from fretting corrosion in the lubricant. False brinelling is prevented by eliminating vibration sources and keeping the bearing well lubricated. Isolation pads on the equipment or a separate foundation may be required to reduce environmental vibration. Also a light preload on the bearing helps keep the balls and raceway in tight contact. Preloading also helps prevent false brinelling during transit. Seizures can be caused by a lack of internal clearance, improper lubrication, or excessive loading. Before seizing, excessive, friction and heat softens the bearing steel. Overheated bearings often change color， usually to blueblack or straw colored． Friction also causes stress in the retainer， which can break and hasten bearing failure． Premature material fatigue is caused by a high load or excessive preload． When these conditions are unavoidable， bearing life should be carefully calculated so that a maintenance scheme can be worked out． Another solution for fighting premature fatigue is changing material． When standard bearing materials， such as 440C or SAE 52100， do not guarantee sufficient life， specialty materials can be remended. In addition， when the problem is traced back to excessive loading， a higher capacity bearing or different configuration may be used． Creep is less mon than premature fatigue． In bearings． it is caused by excessive clearance between bore and shaft that allows the bore to rotate on the shaft． Creep can be expensive because it causes damage to other ponents in addition to the bearing． 0ther more likely creep indicators are scratches， scuff marks， or discoloration to shaft and bore． To prevent creep damage， the bearing housing and shaft fittings should be visually checked． Misalignment is related to creep in that it is mounting related． If races are misaligned or cocked． The balls track in a noncircumferencial path． The problem is incorrect mounting or tolerancing， or insufficient squareness of the bearing mounting site．。