Presentation On Rolling Contact Bearing Budhaditya Goswami Mechanical 3rd Year 09/ME/53 Future Institute of Engineering and Management
CONTENTS 1) What is a Bearing? 2) Classification of Bearing. 3) Types of Rolling Contact Bearing. 4) Selection of Bearing type.
5) Equivalent Bearing Load. 6) Load-life Relationship. 7) Bearing Failure.
8) Designation. 9) Applications.
What is a Bearing ? A bearing is a mechanical element that permits relative motion between two parts, such as the shaft and the housing, with minimum friction. The functions of bearing are1)The bearing ensures free rotation of the shaft or the axle with minimum friction. 2)The bearing supports the shaft or the axle and holds it in correct position. 3)The bearing takes up the forces that act on the shaft or the axle and transmits them to the frame or the foundation.
Classification of Bearing 1)
Depending upon the direction of force that acts on the bearings• Radial Bearing that supports the load which is perpendicular to the axis of the shaft. • Thrust Bearing that supports the load which acts along the axis of the shaft.
2) Depending upon the type of friction between the shaft and the bearing surface• Sliding Contact Bearing where the shaft slides over the surface of the bush resulting in friction and wear which can be reduced by a film of lubricating oil. • Rolling Contact Bearing where rolling elements, such as balls or rollers are introduced between the surfaces that are in relative motion.
Types of Rolling Contact Bearing 1) Ball Bearings:
Deep Groove
Angular Contact
Self-Aligning
2) Roller Bearings:
Cylindrical Roller
Needle Roller
Tapered Roller
Spherical Roller
3) Thrust Bearings:
Ball Thrust Bearing
Roller Thrust Bearing
Selection Of Bearing-Type The guidelines for selecting a proper type of bearing are as follows: For low and medium radial loads, ball bearings are used, whereas for heavy loads roller bearings are selected. Self-aligning ball bearings and spherical roller bearings are used in applications where a misalignment between the axes of the shaft and housing is likely to exist. Thrust ball bearings are used for medium thrust loads whereas for heavy thrust loads, cylindrical roller thrust bearings are used.
Deep groove ball bearings, angular contact bearings and spherical roller bearings are used in applications where the load acting on the bearing has two componentsradial and thrust.
Static Load Carrying Capacity of a bearing is defined as the static load which corresponds to a total permanent deformation of balls and races, at the most heavily stressed point of contact, equal to 0.0001 of the ball diameter.
Dynamic Load Carrying Capacity of a bearing is defined as the radial load in radial bearings that can be carried for a minimum life of one million revolutions.
Equivalent Bearing Load The equivalent dynamic load is defined as the constant radial load in radial bearings (or thrust load in thrust bearings), that if applied to the bearing would give same life as that which the bearing will attain under actual condition of forces. The expression or the equivalent dynamic load is written as,
P=XVF(r) + YF(a) where, P= equivalent dynamic load(N) F(r)= radial load(N) F(a)= axial or thrust load(N)
V= race-rotation factor X & Y are radial and thrust factors respectively.
Load-Life Relationship The relationship between the dynamic load carrying capacity, the equivalent dynamic load and the bearing life is given by,
L(10)=( C/P )^p Where, L(10)= rated bearing life(in million revolution)
C= dynamic load capacity(N) p= 3(for ball bearings) p= 10/3(for roller bearings) Rearranging, C=P[L(10)]^1/p
Bearing Failure The principal types of surface wear are: Abrasive wear: It occurs when the bearing is made to operate in an environment with dust, foreign particles, rust or spatter. Corrosive wear: The corrosion of the surface of bearing parts is caused by the entry of water or moisture and also corrosive elements present in the extreme pressure additives that are added in the lubricating oil. This results in fine wear uniformly distributed over the entire surface.
Continued... Pitting: It is a surface fatigue failure that occurs when the load on the bearing part exceeds the surface endurance strength of the material. This type of failure is characterized by pits, which continue to grow resulting in complete destruction of the bearing surface. Scoring: Excessive surface pressure, high surface speed and inadequate supply of lubricant result in breakdown of the lubricant film. This results in excessive frictional heat and overheating at the contacting surfaces. Scoring is a stick-slip phenomenon, in which alternate welding and shearing takes place rapidly at high spots.
Designation The main designation is a seven digit number with optional alphanumeric digits before or after to define additional parameters. Here the digits will be defined as: 7654321.
Digits one and two together are used to define the inner diameter (ID), or bore diameter of the bearing. For diameters between 20 and 495, the designation is multiplied by five to give the ID; e.g. designation 08 is a 40 mm ID. For inner diameters less than 20 the following designations are used: 00 = 10 mm ID, 01 = 12 mm ID, 02 = 15 mm ID, and 03 = 17 mm ID. The third digit defines the "diameter series", which defines the outer diameter (OD). The diameter series, defined in ascending order is: 0, 8, 9, 1, 7, 2, 3, 4, 5, 6. 0) 2) 4) 6) 8)
Ball radial single-row 1) Ball radial spherical double-row Roller radial with short cylindrical rollers 3) Roller radial spherical double-row Roller needle or with long cylindrical rollers 5) Roller radial with spiral rollers Ball radial-thrust single-row 7) Roller tapered Ball thrust, ball thrust-radial 9) Roller thrust or thrust-radial
Continued.... The fourth digit defines the type of bearing. The fifth and sixth digit define structural modifications to the bearing. For example, on radial thrust bearings the digits define the contact angle, or the presence of seals on any bearing type. The seventh digit defines the "width series", or thickness, of the bearing. The width series, defined from lightest to heaviest, is: 7, 8, 9, 0, 1 (extra light series), 2 (light series), 3 (medium series), 4 (heavy series). The third digit and the seventh digit define the "dimensional series" of the bearing.
Applications of Rolling Contact Bearing Rolling Contact Bearings are used in following applications: Machine tool spindles. Automobile front and rear axle.
Gear boxes. Small size electric motors. Rope sheave, crane hook and hoisting drum.
REFERENCES Design of Machine Elements- V.B.Bhandari http://en.wikipedia.org/wiki/Ball_bearing http://en.wikipedia.org/wiki/Rollingelement_bearing
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