Reliability of bearing knots презентация

Reliability of bearing knots

FUNCTION OF A BEARING The main function of a rotating shaft is to transmit power from one end of the line to the other. It needs a good support to ensure stability and frictionless rotation. The support for the shaft is known as “bearing”. The shaft has a “running fit” in a bearing. All bearing are provided some lubrication arrangement to reduced friction between shaft and bearing.

Bearings are classified under two main categories: Plain or slider bearing : - In which the rotating shaft has a sliding contact with the bearing which is held stationary . Due to large contact area friction between mating parts is high requiring greater lubrication. Rolling or anti-friction bearing : - Due to less contact area rolling friction is much lesser than the sliding friction , hence these bearings are also known as antifriction bearing.

LOAD DIARECTION AND NAME:

Sleeve Bearing

Description: Bearing used to constrain, guide, or reduce friction in rotary applications. Work by means of sliding action as opposed to the rolling action used by ball, roller and needle bearings. Proper lubrication is required to reduce wear and friction.

Sleeve Bearing Materials Relative softness (to absorb foreign particles), reasonable strength, machinability (to maintain tolerances), lubricity, temperature and corrosion resistance, and in some cases, porosity (to absorb lubricant). A bearing element should be less than one-third as hard as the material running against it in order to provide embedability of abrasive particles.

Materials Whitemetal - usually used as a lining bonded to bronze, steel or cast iron. Copper Based alloys - most common alloys are copper tin, copper lead, phosphor bronze: harder and stronger than whitemetal: can be used un-backed as a solid bearing. Aluminium based alloys - running properties not as good as copper based alloys but cheaper.

Materials Sintered bronze - Sintered bronze is a porous material which can be impregnated with oil, graphite or Ptfe. Not suitable for heavily loaded applications but useful where lubrication is inconvenient. Nylon - used only in very light applications.

Types of Lubrication Hydrostatic Hydrodynamic Boundary Lubrication Dry Bearings

Advantages and disadvantages of the plain bearing Plain bearing are cheap to produce and have noiseless operation. They can be easily machined, occupy small radial space and have vibration damping properties. Also they can cope with tapped foreign matter. Disadvantages are they require large supply of lubricating oil, they are suitable only for relative low temperature and speed; and starting resistance is much greater than running resistance due to slow build up of lubricant film around the bearing surface.

Ball and roller bearings due to low rolling friction these bearings are aptly called “antifriction” bearing. Frictional resistance considerably less than in plain bearings Rotating – non-rotating pairs separated by balls or rollers Ball or rollers has rolling contact and sliding friction is eliminated and replaced by much lower rolling friction. In plain bearing the starting resistance is much larger than the running resistance due to absence of oil film. In ball and rolling bearings the initial resistance to motion is only slightly more than their resistance to continuous running. Hence ball and rolling bearing are more suitable to drives subject to frequent starting and stopping as they save power. Owing to the low starting torque, a low power motor can be used for a line shaft running in ball bearing.

Ball and Roller bearing

Types of bearing

Types of ball bearings

Thrust ball bearings

Tapered roller bearing (TRB): Tapered roller bearing (TRB): TRB can take both radial and axial loads and used for gear boxes for heavy trucks, bevel-gear transmission, lathe spindles, etc. Thrust ball bearing: It can take only thrust loads. Thrust ball bearing are used for heavy axial loads and low speeds. Needle roller bearing: It use small diameter of rollers. They are used for radial load at slow speed and oscillating motion. They have the advantage of light weight and occupy small space. They are used in aircraft industry, live tail stock centers, bench-drill spindles, etc.

Needle ball bearing

Bearing life at rated reliability Bearing life depends on: Load and revolutions From experimentation: For a given R, linear log behavior Reliability = % chance that the part will function as expected Where a = 3 for ball bearings a = 3.333 for roller bearings

How to handle combined loading So far we have only considered radial loading… What about combined radial, Fr, and axial loading , Fa? Use an equivalent load, Fe, that does the same amount of damage. Where V = 1.2 for outer ring rotation and 1 for inner ring This has to do with the fact that outer ring fails more often Xi and Yi are a function of the Axial load, Fa Static load rating, Co

Bearing Mounting For instrument bearings, certain special considerations should be emphasized: Heavy press fits should be avoided. Accuracy of mounting surfaces should be equal to accuracy of mating bearing surface. Misalignment for low torque and running accuracy should not exceed 1/4°. Loading across the bearing during assembly should be avoided.