【正文】 n 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 3 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． Misalignment of more than 1/4t 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 process 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 . 6 Key words: Wheel gear Shaft 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 the 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. 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 righthand helix and the other a lefthand helix. The shape of the 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 bees a helix. If we unwind this paper, each point on the angular edge generates an involute curve. The surface obtained when every point on the edge generates an involute is called an involute helicoid. The initial contact of spurgear teeth is a line extending all the way across the face of the tooth. The initial contact of helical gear teeth is a point, which changes into a line as the teeth e into more engagement. In spur gears the line of contact is parallel to the axis of the rotation。 it is almost always necessary to calculate them so that he knows they are within acceptable limits. Whenever possible, the powertransmission elements, such as gears or pullets, should be located close to the supporting bearings, This reduces the bending moment, and hence the deflection and bending stress. Although the von MisesHenckyGoodman method is difficult to use in design of shaft, it probably es closest to predicting actual 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 shaftdesign problems in which the dimension are pretty well limited by other considerations, such as rigidity, and it is only necessary for the designer to