機械專業(yè)外文翻譯--如何延長軸承壽命

1、<p>　　本科生畢業(yè)論文（設(shè)計）</p><p><b>　　英文翻譯</b></p><p>　　學 院 機電工程學院 </p><p>　　專業(yè)班級 </p><p>　　撰寫日期：2010年5月12日</p><p&

2、gt;　　EXTENDING BEARING LIFE</p><p><b>　　Abstract：</b></p><p>　　Nature works hard to destroy bearings, but their chances of survival can be improved by following a few simple guidelin

3、es. Extreme neglect in a bearing leads to overheating and possibly seizure or, at worst, an explosion. But even a failed bearing leaves clues as to what went wrong. After a little detective work, action can be taken to a

4、void a repeat performance.</p><p>　　Keywords: bearings failures life</p><p>　　Bearings fail for a number of reasons，but the most common are misapplication，contamination，improper lubricant，sh

5、ipping 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．</p><p>　　However，while a postmortem yi

6、elds 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 characteristic

7、s for the selected bearing.</p><p>　　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 c

8、an provide further clues as to whether a bearing is right for a job.</p><p>　　1 Why bearings fail</p><p>　　About 40% of ball bearing failures are caused by contamination from dust, dirt, shaving

9、s, 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 contamin

10、ation is preventable，and a simple visual examination can easily identify the cause．</p><p>　　Conducting a postmortem il1ustrates what to look for on a failed or failing bearing．Then，understanding the mechani

11、sm behind the failure, such as brinelling or fatigue, helps eliminate the source of the problem.</p><p>　　Brinelling is one type of bearing failure easily avoided by proper handing and assembly. It is charac

12、terized by indentations in the bearing raceway caused by shock loading－such as when a bearing is dropped-or incorrect assembly. Brinelling usually occurs when loads exceed the material yield point(350,000 psi in SAE 5210

13、0 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.</p><p>　　A similar defect is a pattern of ell

14、iptical 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, de

15、bris 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.</p><

16、;p>　　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.

17、Also a light preload on the bearing helps keep the balls and raceway in tight contact. Preloading also helps prevent false brinelling during transit.</p><p>　　Seizures can be caused by a lack of internal cle

18、arance, improper lubrication, or excessive loading. Before seizing, excessive, friction and heat softens the bearing steel. Overheated bearings often change color，usually to blue-black or straw colored．Friction also caus

19、es stress in the retainer，which can break and hasten bearing failure．</p><p>　　Premature material fatigue is caused by a high load or excessive preload．When these conditions are unavoidable，bearing life shou

20、ld be carefully calculated so that a maintenance scheme can be worked out．</p><p>　　Another solution for fighting premature fatigue is changing material．When standard bearing materials，such as 440C or SAE 52

21、100，do not guarantee sufficient life，specialty materials can be recommended. In addition，when the problem is traced back to excessive loading，a higher capacity bearing or different configuration may be used．</p>&

22、lt;p>　　Creep is less common 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

23、other components in addition to the bearing．</p><p>　　0ther more likely creep indicators are scratches，scuff marks，or discoloration to shaft and bore．To prevent creep damage，the bearing housing and shaft fit

24、tings should be visually checked．</p><p>　　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 incorr

25、ect mounting or tolerancing，or insufficient squareness of the bearing mounting site．Misalignment of more than 1/4·can cause an early failure．</p><p>　　Contaminated lubricant is often more difficult to d

26、etect than misalignment or creep．Contamination shows as premature wear．Solid contaminants become an abrasive in the lubricant．In addition。insufficient lubrication between ball and retainer wears and weakens the retainer．

27、In this situation，lubrication is critical if the retainer is a fully machined type．Ribbon or crown retainers，in contrast，allow lubricants to more easily reach all surfaces． </p><p>　　Rust is a form of moistu

28、re contamination and often indicates the wrong material for the application．If the material checks out for the job，the easiest way to prevent rust is to keep bearings in their packaging，until just before installation．<

29、;/p><p>　　2 Avoiding failures</p><p>　　The best way to handle bearing failures is to avoid them．This can be done in the selection process by recognizing critical performance characteristics．These i

30、nclude noise，starting and running torque，stiffness，nonrepetitive runout，and radial and axial play．In some applications, these items are so critical that specifying an ABEC level alone is not sufficient．</p><p&

31、gt;　　Torque requirements are determined by the lubricant，retainer，raceway quality(roundness cross curvature and surface finish)，and whether seals or shields are used．Lubricant viscosity must be selected carefully because

32、 inappropriate lubricant，especially in miniature bearings，causes excessive torque．Also，different lubricants have varying noise characteristics that should be matched to the application. For example，greases produce more n

33、oise than oil．</p><p>　　Nonrepetitive runout(NRR)occurs during rotation as a random eccentricity between the inner and outer races，much like a cam action．NRR can be caused by retainer tolerance or eccentrici

34、ties of the raceways and balls．Unlike repetitive runout, no compensation can be made for NRR.</p><p>　　NRR is reflected in the cost of the bearing．It is common in the industry to provide different bearing ty

35、pes and grades for specific applications．For example，a bearing with an NRR of less than 0.3um is used when minimal runout is needed，such as in disk—drive spindle motors．Similarly，machine—tool spindles tolerate only minim

36、al deflections to maintain precision cuts．Consequently, bearings are manufactured with low NRR just for machine-tool applications．</p><p>　　Contamination is unavoidable in many industrial products，and shield

37、s and seals are commonly used to protect bearings from dust and dirt．However，a perfect bearing seal is not possible because of the movement between inner and outer races．Consequently，lubrication migration and contaminati

38、on are always problems．</p><p>　　Once a bearing is contaminated, its lubricant deteriorates and operation becomes noisier．If it overheats，the bearing can seize．At the very least，contamination causes wear as

39、it works between balls and the raceway，becoming imbedded in the races and acting as an abrasive between metal surfaces．Fending off dirt with seals and shields illustrates some methods for controlling contamination．</p

40、><p>　　Noise is as an indicator of bearing quality．Various noise grades have been developed to classify bearing performance capabilities．</p><p>　　Noise analysis is done with an Anderonmeter, which

41、 is used for quality control in bearing production and also when failed bearings are returned for analysis. A transducer is attached to the outer ring and the inner race is turned at 1,800rpm on an air spindle. Noise is

42、measured in andirons, which represent ball displacement in μm/rad.</p><p>　　With experience, inspectors can identify the smallest flaw from their sound. Dust, for example, makes an irregular crackling. Ball

43、scratches make a consistent popping and are the most difficult to identify. Inner-race damage is normally a constant high-pitched noise, while a damaged outer race makes an intermittent sound as it rotates.</p>&l

44、t;p>　　Bearing defects are further identified by their frequencies. Generally, defects are separated into low, medium, and high wavelengths. Defects are also referenced to the number of irregularities per revolution.&l

45、t;/p><p>　　Low-band noise is the effect of long-wavelength irregularities that occur about 1.6 to 10 times per revolution. These are caused by a variety of inconsistencies, such as pockets in the race. Detectab

46、le pockets are manufacturing flaws and result when the race is mounted too tightly in multiplejaw chucks.</p><p>　　Medium-hand noise is characterized by irregularities that occur 10 to 60 times per revolutio

47、n. It is caused by vibration in the grinding operation that produces balls and raceways. High-hand irregularities occur at 60 to 300 times per revolution and indicate closely spaced chatter marks or widely spaced, rough

48、irregularities.</p><p>　　Classifying bearings by their noise characteristics allows users to specify a noise grade in addition to the ABEC standards used by most manufacturers. ABEC defines physical toleranc

49、es such as bore, outer diameter, and runout. As the ABEC class number increase (from 3 to 9), tolerances are tightened. ABEC class, however, does not specify other bearing characteristics such as raceway quality, finish,

50、 or noise. Hence, a noise classification helps improve on the industry standard.</p><p>　　GEAR AND SHAFT INTRODUCTION</p><p><b>　　Abstract:</b></p><p>　　The important po

51、sition of the wheel gear and shaft can't falter in traditional machine and modern machines. The wheel gear and shafts mainly install the direction that delivers the dint at the principal axis box. The passing to proc

52、ess to make them can is divided into many model numbers, useding for many situations respectively. So we must be the multilayers to the understanding of the wheel gear and shaft in many ways .</p><p>　　Key w

53、ords: Wheel gear Shaft</p><p>　　In the force analysis of spur gears, the forces are assumed to act in a single plane. We shall study gears in which the forces have three dimensions. The reason for this, in t

54、he case of helical gears, is that the teeth are not parallel to the axis of rotation. And in the case of bevel gears, the rotational axes are not parallel to each other. There are also other reasons, as we shall learn.&l

55、t;/p><p>　　Helical gears are used to transmit motion between parallel shafts. The helix angle is the same on each gear, but one gear must have a right-hand helix and the other a left-hand helix. The shape of th

56、e tooth is an involute helicoid. If a piece of paper cut in the shape of a parallelogram is wrapped around a cylinder, the angular edge of the paper becomes a helix. If we unwind this paper, each point on the angular edg

57、e generates an involute curve. The surface obtained when every point on the edge </p><p>　　The initial contact of spur-gear teeth is a line extending all the way across the face of the tooth. The initial con

58、tact of helical gear teeth is a point, which changes into a line as the teeth come into more engagement. In spur gears the line of contact is parallel to the axis of the rotation; in helical gears, the line is diagonal a

59、cross the face of the tooth. It is this gradual of the teeth and the smooth transfer of load from one tooth to another, which give helical gears the ability to tran</p><p>　　Crossed-helical, or spiral, gears

60、 are those in which the shaft centerlines are neither parallel nor intersecting. The teeth of crossed-helical fears have point contact with each other, which changes to line contact as the gears wear in. For this reason

61、they will carry out very small loads and are mainly for instrumental applications, and are definitely not recommended for use in the transmission of power. There is on difference between a crossed helical gear and a heli

62、cal gear until they are mou</p><p>　　Worm gears are similar to crossed helical gears. The pinion or worm has a small number of teeth, usually one to four, and since they completely wrap around the pitch cyli

63、nder they are called threads. Its mating gear is called a worm gear, which is not a true helical gear. A worm and worm gear are used to provide a high angular-velocity reduction between nonintersecting shafts which are u

64、sually at right angle. The worm gear is not a helical gear because its face is made concave to fit the curvatu</p><p>　　Worm gearing are either single or double enveloping. A single-enveloping gearing is one

65、 in which the gear wraps around or partially encloses the worm.. A gearing in which each element partially encloses the other is, of course, a double-enveloping worm gearing. The important difference between the two is t

66、hat area contact exists between the teeth of double-enveloping gears while only line contact between those of single-enveloping gears. The worm and worm gear of a set have the same hand of heli</p><p>　　When

67、 gears are to be used to transmit motion between intersecting shaft, some of bevel gear is required. Although bevel gear are usually made for a shaft angle of 90 deg. They may be produced for almost any shaft angle. The

68、teeth may be cast, milled, or generated. Only the generated teeth may be classed as accurate. In a typical bevel gear mounting, one of the gear is often mounted outboard of the bearing. This means that shaft deflection c

69、an be more pronounced and have a greater effect on the c</p><p>　　Straight bevel gears are easy to design and simple to manufacture and give very good results in service if they are mounted accurately and po

70、sitively. As in the case of squr gears, however, they become noisy at higher values of the pitch-line velocity. In these cases it is often good design practice to go to the spiral bevel gear, which is the bevel counterpa

71、rt of the helical gear. As in the case of helical gears, spiral bevel gears give a much smoother tooth action than straight bevel gears, an</p><p>　　It is frequently desirable, as in the case of automotive d

72、ifferential applications, to have gearing similar to bevel gears but with the shaft offset. Such gears are called hypoid gears because their pitch surfaces are hyperboloids of revolution. The tooth action between such ge

73、ars is a combination of rolling and sliding along a straight line and has much in common with that of worm gears.</p><p>　　A shaft is a rotating or stationary member, usually of circular cross section, havin

74、g mounted upon it such elementsas gears, pulleys, flywheels, cranks, sprockets, and other power-transmission elements. Shaft may be subjected to bending, tension, compression, or torsional loads, acting singly or in comb

75、ination with one another. When they are combined, one may expect to find both static and fatigue strength to be important design considerations, since a single shaft may be subjected to static str</p><p>　　T

76、he word “shaft” covers numerous variations, such as axles and spindles. Anaxle is a shaft, wither stationary or rotating, nor subjected to torsion load. A shirt rotating shaft is often called a spindle.</p><p&

77、gt;　　When either the lateral or the torsional deflection of a shaft must be held to close limits, the shaft must be sized on the basis of deflection before analyzing the stresses. The reason for this is that, if the shaf

78、t is made stiff enough so that the deflection is not too large, it is probable that the resulting stresses will be safe. But by no means should the designer assume that they are safe; it is almost always necessary to cal

79、culate them so that he knows they are within acceptable limits. W</p><p>　　Although the von Mises-Hencky-Goodman method is difficult to use in design of shaft, it probably comes closest to predicting actual

80、failure. Thus it is a good way of checking a shaft that has already been designed or of discovering why a particular shaft has failed in service. Furthermore, there are a considerable number of shaft-design problems in w

81、hich the dimension are pretty well limited by other considerations, such as rigidity, and it is only necessary for the designer to discover somethin</p><p>　　Because of the similarity of their functions, clu

82、tches and brakes are treated together. In a simplified dynamic representation of a friction clutch, or brake, two inertias I1 and I2 traveling at the respective angular velocities W1 and W2, one of which may be zero in t

83、he case of brake, are to be brought to the same speed by engaging the clutch or brake. Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation, resulting in a te

84、mperature r</p><p>　　Rim type with internally expanding shoes</p><p>　　Rim type with externally contracting shoes</p><p><b>　　Band type</b></p><p>　　Disk or

85、 axial type</p><p><b>　　Cone type</b></p><p>　　Miscellaneous type</p><p>　　The analysis of all type of friction clutches and brakes use the same general procedure. The f

86、ollowing step are necessary: </p><p>　　Assume or determine the distribution of pressure on the frictional surfaces.</p><p>　　Find a relation between the maximum pressure and the pressure at any

87、point</p><p>　　Apply the condition of statical equilibrium to find (a) the actuating force, (b) the torque, and (c) the support reactions.</p><p>　　Miscellaneous clutches include several types,

88、such as the positive-contact clutches, overload-release clutches, overrunning clutches, magnetic fluid clutches, and others.</p><p>　　A positive-contact clutch consists of a shift lever and two jaws. The gre

89、atest differences between the various types of positive clutches are concerned with the design of the jaws. To provide a longer period of time for shift action during engagement, the jaws may be ratchet-shaped, or gear-t

90、ooth-shaped. Sometimes a great many teeth or jaws are used, and they may be cut either circumferentially, so that they engage by cylindrical mating, or on the faces of the mating elements.</p><p>　　Although

91、positive clutches are not used to the extent of the frictional-contact type, they do have important applications where synchronous operation is required.</p><p>　　Devices such as linear drives or motor-opera

92、ted screw drivers must run to definite limit and then come to a stop. An overload-release type of clutch is required for these applications. These clutches are usually spring-loaded so as to release at a predetermined to

93、que. The clicking sound which is heard when the overload point is reached is considered to be a desirable signal.</p><p>　　An overrunning clutch or coupling permits the driven member of a machine to “freewhe

94、el” or “overrun” because the driver is stopped or because another source of power increase the speed of the driven. This type of clutch usually uses rollers or balls mounted between an outer sleeve and an inner member ha

95、ving flats machined around the periphery. Driving action is obtained by wedging the rollers between the sleeve and the flats. The clutch is therefore equivalent to a pawl and ratchet with an infin</p><p>　　M

96、agnetic fluid clutch or brake is a relatively new development which has two parallel magnetic plates. Between these plates is a lubricated magnetic powder mixture. An electromagnetic coil is inserted somewhere in the mag

97、netic circuit. By varying the excitation to this coil, the shearing strength of the magnetic fluid mixture may be accurately controlled. Thus any condition from a full slip to a frozen lockup may be obtained.</p>

98、<p><b>　　如何延長軸承壽命</b></p><p>　　摘要： 自然界苛刻的工作條件會導致軸承的失效，但是如果遵循一些簡單的規(guī)則，軸承正常運轉(zhuǎn)的機會是能夠被提高的。在軸承的使用過程當中，過分的忽視會導致軸承的過熱現(xiàn)象，也可能使軸承不能夠再被使用，甚至完全的破壞。但是一個被損壞的軸承，會留下它為什么被損壞的線索。通過一些細致的偵察工作，我們可以采取行動來避免軸承的再次失效。