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Back to basic: Rolling Bearings

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INTRODUCTION

Rolling bearing Selection needs careful attention. The rolling bearings are a machine element that keeps our machine parts in motion all the time. Our machines can not move without the use of rolling bearings.  Rolling bearing Selection to be done precisely to avoid premature failure. Toys to spacecraft are installed with rolling bearings. The function of the rolling bearing is to reduce the friction between moving parts of a machine. Rolling bearing Selection and installation to be made. There are many that can withstand both radial and axial loads.

A reduction in the friction between machine parts smoothens the movement and increases the efficiency of the machine. The machine exerts various kinds of loads on machine parts while in motion. These loads may be in the radial direction or in an axial direction. Rolling contact ball bearings absorb the radial and axial loads of the machine and make the machine movement easy. Depending on the kind of load exerting in the machine, Rolling bearing Selection and installation to be made. There are many bearings that can withstand both radial and axial loads.

TYPE OF BEARINGS:

Rolling contact bearings are classified into two main categories depending on their rolling element’s geometrical shape. They are as follows:

(1) Ball roller bearings

(2) Cylindrical Roller bearings

BALL BEARINGS

Rolling contact Ball-bearing is consists of the following parts:

(1) Outer ring

(2) Inner ring

(3) Ball

(4) Cage or Separator

 

Rolling Ball-bearing selection
Rolling Ball-bearing selection

Depending on the various load acting on rolling bearings, rolling contact ball bearings are further categorized as follows:

(1) Single row deep groove ball bearing

(2) Double row deep groove ball bearing

(3) Single row angular contact ball bearing

(4) Double row angular contact ball bearing

(5) Three-point/ Four-point contact ball bearings

(6)Self-aligning ball bearing

ROLLER BEARING

The cylindrical  line contact roller bearing is consists of parts:

(1) Outer ring

(2) Inner ring

(3) Roller

(4) Cage or Separator

Depending on the design, cylindrical roller bearings are further categorized as follows:

(1) Single-row Cylindrical roller bearing

(2) Double-row Cylindrical roller bearing

(3) Long roller bearing

(4) needle roller bearing

(5) Single row Tapered roller bearing

(6) Double row taper roller bearing

(7) Spherical roller bearing

BEARING USES:

Ball bearings

Rolling ball bearings are a common type of use. They are found in many machines from skateboards to washing machines and PC drives. These ball bearings are capable to withstand both radial and axial thrust loads. They are used in applications where the load is light to medium and constant in nature.

 

Various loads on rolling ball bearing

BALL THRUST BEARING

Rolling Ball thrust bearings are used in low-speed applications. They can not take many radial loads however suitable for thrust loads. They are used in turntable and farm equipment.

ROLLER BEARINGS

Roller bearings are used for heavy load applications like conveyor belt rollers where heavy radial loads exist. In these bearings the rolling element is the cylindrical roller, hence there is the line contact between outer race, inner race, and roller. This line contact distributes the load over a large area, so the cylindrical roller bearings handle a much greater load than a rolling ball bearing.

ROLLER THRUST BEARINGS

Cylindrical Roller thrust bearings can withstand very heavy thrust loads. They are used in car gear transmission, Power transmission between gear and sprockets, Helical gear power transmission that causes heavy thrust loads, which can be supported by roller thrust bearings.

TAPERED ROLLER BEARINGS

Tapered cylindrical roller bearings are designed to withstand heavy radial and thrust loads. They are capable to withstand constant and impact loads.

ANGULAR CONTACT BALL BEARING

Angular contact rolling ball bearings are constructed in such a way that their inner race, outer race, and ball are in contact at some angle. Standard contact angles are 15,30 and 40 degrees. Preloading is done in angular contact rolling bearings during bearing assembly. Preloading minimizes the gap between the rolling bearing ball, inner race, and outer race. They are used for heavy thrust loads and moderate radial loads.

SELECTION OF BEARING TYPE

Rolling contact Bearing is of many types and designs. Rolling bearing selection to be done in such a way, that it enables machine parts to perform their work satisfactorily without any failure. The following factors to be considered when selecting a Rolling bearing:

(1) Machine Type, space available for bearing installation.

(2) Bearing operating condition, continuous or intermit ant

(3) The weather condition of the area

(4) Bearing location

(5) Bearing load, direction, and magnitude

(6) Bearing vibration and impact load

(7) Bearing temperature

(8) Machine shaft size

(9) Bearing inner diameter

(10) Bearing outer diameter

(11)Bearing overall dimensions

(12) Bearing rolling element, depending on load

(13) Bearing lubrication, oil, or grease

FUNCTION  OF BEARING LUBRICATION

Rolling contact Bearing lubrication reduces friction between the machine rolling parts. The purpose of rolling bearing lubrication is to prevent direct metal-to-metal contact between the various parts of the rolling bearing. A thin layer of oil or grease is formed between the contact surface of the rolling element, to smoothens movement. Lubrication has other advantages as follows:

(1) Reduce friction

(2) Reduce wear and tear

(3) Heat dissipation

(4) Prolonged bearing life

(5) Prevent rust

(6)Prevent water and dust ingression in the rolling bearing.

Type Of Bearing lubrication 

(1) Oil lubrication

(2) Grease lubrication

OIL LUBRICATION

Oil lubrication is most suitable for high-speed and high-temperature applications. Oil lubrication can dissipate heat generated by rolling bearing very effectively. Spindle oil, machine oil, turbine oil, and other mineral oil are used as lubricants in normal operating conditions. For temp. Above 150 degrees centigrade, synthetic oil such as silicone and fluoro silicone is used.

The viscosity of oil determines the oil lubrication application. If viscosity is too low, the oil film will not be formed, and if the viscosity too high, creates viscosity resistance and heat dissipation will be reduced, which causes the bearing temperature to rise. For higher speed, a low viscosity oil to be used, and for heavy loads higher viscosity oil to be used.

OIL BATH

Oil bath lubrication is used for horizontal shaft application. Oil level in the bath to be maintained at the center of the lowest rolling element of bearing. Housing design should be such that the oil level does not fluctuate. Drip lubrication is used for high speed and light to medium load applications. The constant toiler is mounted on the housing above the bearing and allows the oil to drip in the bearing.

Constant oiler connected to bearing housing

OIL SPLASH

Oil splash lubrication is carried out with an impeller-like device that is mounted on the shaft to pick up the oil and spray it on the balls or roller of the bearing. This is used for high-speed applications. Drip lubrication is used for high speed and light to medium load applications.

GREASE LUBRICATION

Grease lubrication of rolling contact bearing is easier than oil lubrication, due to its high viscosity index. Grease lubrication is long-lasting and requires simple sealing arrangements. New grease is pumped through a grease nipple in the machine that replaces the old and dry grease out of the equipment bearing. Grease is composed of mineral oil-based and synthetic oil bases like silicone oil and fluorocarbon oil mixed with a thickener. The base oil determines the properties of the grease. Grease with low viscosity base oil is best suited for low temperature and high speed, while grease made from high viscosity base oil is suited for heavy load application.

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