Couplings Nizwa College of Technology NCT NIZWA 08

Couplings Nizwa College of Technology NCT NIZWA 08 January 2022 1

Couplings Coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power Coupling Motor Pump NCT NIZWA 08 January 2022 2

Uses of coupling � To provide connection of shafts of units made separately � To allow misalignment of the shafts or to introduce mechanical flexibility. � To reduce the transmission of shock loads � To introduce protection against overloads. � To alter the vibration characteristics NCT NIZWA 08 January 2022 3

Types of coupling � � � Rigid Flexible Universal Flexible coupling Rigid coupling Universal coupling NCT NIZWA 08 January 2022 4

Rigid Coupling Sleeve or Muff Coupling NCT NIZWA 08 January 2022 5

Rigid coupling Flanged Coupling Flange Hub Key Driven Shaft Driving Shaft • Rigid couplings are used when precise shaft alignment is required • Simple in design and are more rugged • Generally able to transmit more power than flexible couplings • Shaft misalignments cannot be compensated NCT NIZWA 08 January 2022 6

Flexible Coupling Flange Driven Shaft Driving Shaft Pin Bush • A flexible coupling permits with in certain limits, relative rotation and variation in the alignment of shafts • Pins (Bolts) covered by rubber washer or bush is used connect flanges with nuts • The rubber washers or bushes act as a shock absorbers and insulators. NCT NIZWA 08 January 2022 7

Elastomeric coupling (Tyre Coupling) Elastomeric member Flange Bolt • An assembly of components designed to connect axially oriented shafts in order to provide power transmission • Able to accommodate shaft misalignment through elastomeric materials NCT NIZWA 08 January 2022 8

Advantages and Limitations Advantages � Torsionally stiff � No lubrication or maintenance � Good vibration damping and shock absorbing qualities � Less expensive than metallic couplings � More misalignment allowable than most metallic couplings Limitations � Sensitive to chemicals and high temperatures � Usually not Torsionally stiff enough for positive displacement � Larger in outside diameter than metallic coupling � Difficult to balance as an assembly NCT NIZWA 08 January 2022 9

END NCT NIZWA 08 January 2022 10

Terminologies Used in Couplings Nizwa College of Technology NCT NIZWA 08 January 2022 11

Contd…… � ANGULAR MISALIGNMENT � ANGULAR STIFFNESS � PARALLEL MISALIGNMENT � AXIAL MISALIGNMENT OR END FLOAT � AXIAL STIFFNESS � BORES � DAMPING � DISTANCE BETWEEN SHAFTS (BE dimension) � ELASTOMERIC COUPLING � ELASTOMERS NCT NIZWA 08 January 2022 12

Contd…… � HOURSE � HUBS POWER � KEY WAY � MAXIMUM SPEED � PEAK LOAD CAPACITY � RADIAL STIFFNES � SPLINE BORE � TORSIONAL VIBRATION � BACKLASH NCT NIZWA 08 January 2022 13

ANGULAR MISALIGNMENT The center lines of connected shafts are neither parallel nor co-axial. NCT NIZWA 08 January 2022 14

ANGULAR STIFFNESS �A measure of a coupling’s resistance to angular displacement. Measured in inch pounds per degree NCT NIZWA 08 January 2022 15

PARALLEL MISALIGNMENT The lateral displacement between nonintersecting axis of the connected shafts. NCT NIZWA 08 January 2022 16

AXIAL MISALIGNMENT OR END FLOAT � The axial movement from the normal gap setting for a standard coupling. Frequently associated with thermal growth stated as a +/- value from the normal setting as specified by the coupling manufacturer. NCT NIZWA 08 January 2022 17

AXIAL STIFFNESS �A measure of a coupling’s resistance to axial displacement. Measured in pounds per inch NCT NIZWA 08 January 2022 18

BORES � Cylindrical or conical holes in hubs of couplings with axes coincident with the rotational axis of the coupling. NCT NIZWA 08 January 2022 19

DAMPING � Is the dissipation of energy (usually as heat) in a manner which decreases peak strain in a mechanical member. NCT NIZWA 08 January 2022 20

DISTANCE BETWEEN SHAFTS (BE dimension) The distance between the face of one shaft to the next. This is commonly called the “BE” dimension, for between ends. NCT NIZWA 08 January 2022 21

ELASTOMERIC COUPLING � An assembly of components designed to connect axially oriented shafts in order to provide power transmission and accommodate shaft misalignment through elastomeric materials. NCT NIZWA 08 January 2022 22

ELASTOMERS � Resilient materials having elastic properties (rubber, synthetic rubber or plastics). NCT NIZWA 08 January 2022 23

HOURSE POWER � Is the unit of power that has been adopted for engineering work in the English system. One HP is equal to 33, 000 foot pounds (of work) per minute or 550 feet pounds per second NCT NIZWA 08 January 2022 24

HUBS � The rigid components of the elastomeric coupling which are attached to the shafts of the driving and driven equipment. NCT NIZWA 08 January 2022 25

KEY Metallic load transmitting members placed in a groove between the shaft and hub. NCT NIZWA 08 January 2022 26

KEY WAY The axial groove in the hub and shaft that holds the key in the proper location. NCT NIZWA 08 January 2022 27

MAXIMUM SPEED The manufacturer’s definition of the rotating speed limit of the coupling usually defined in revolutions per minute. PEAK LOAD CAPACITY The maximum load a coupling can transmit for momentary periods NCT NIZWA 08 January 2022 28

RADIAL STIFFNES Measure of a coupling’s resistance to parallel offset NCT NIZWA 08 January 2022 29

SPLINE BORE A series of parallel keyways formed internal with the bore and mating with the corresponding grooves cut in a shaft. Splined hubs and shafts are used when relatively heavy torques are to be he most common splines conform to standards published by other organizations, such as SAE and ANSI, and are in the form of involutes or straight, parallel sides. NCT NIZWA 08 January 2022 30

Contd, , NCT NIZWA 08 January 2022 31

TORSIONAL VIBRATION The periodic variation in torque of a rotating system. NCT NIZWA 08 January 2022 32

BACKLASH The amount of free movement between two rotating, mating parts. The freedom of movement between couplings, or looseness, is the backlash and may be expressed in degrees. NCT NIZWA 08 January 2022 33

END NCT NIZWA 08 January 2022 34

Soft Foot Soft foot is a condition in which one of the feet does not sit flat on the base One leg is too short or one base plate-mounting pad is not level with the other three The bottom of one foot is not parallel with the base NCT NIZWA 08 January 2022 35

Soft Foot Dirt; grease; paints; rust, bent or burred shims; or too many shims are found under the foot External forces on one end of the equipment causes uneven settlement on the base NCT NIZWA 08 January 2022 36

Procedure to check for Soft Foot � Position the machine on its bed plate � Tighten all the bolts to its normal torque value. � Install DTI with magnetic base between bed plate and foundation, on one of the four feet. � Move indicators to 12 o'clock position, depress indicators and then zero. � Loosen one base bolt. If indicator moves away form zero, record the positive reading � Place the amount of shims that will slide under that foot. � Retighten bolt and make sure the dial indicator needle does not move. � Repeat this procedure for the remaining feet. NCT NIZWA 08 January 2022 37