A SEMINOR REPORT ON COUPLING.pdf

7/27/2019 A SEMINOR REPORT ON COUPLING.pdf

1/24

1

CHAPTER 01

INTRODUCTION

1.1 INTRODUCTION

A mechanical system often requires an axial connection between two

components such as a motor to a pump. The connection is accomplished between the

two component shafts with use of a mechanical coupling. The coupling is designed to

transmit power (torque) from one shaft to the other, causing both to rotate in unison

and at the same RPM. Perfect alignment between the two shafts is almost impossible

and not compensated, mechanical wear of attached components will increase.

Therefore another purpose of the mechanical coupling is to compensate for minor

amounts of misalignment and random movement between the two shafts.

Still another common purpose of a coupling is the provision of a break-point

between the driving and driven shafts acting as a fuse if a severe torque overload

should occur. This inclusion of a safety coupling can protect a serious high-cost

equipment failure. Each of these coupling applications results in many unique designs

of mechanical couplings depending on torque requirement, rotating speed, expected

shaft misalignment, backlash limitations, vibration and other factors unique to the

application and operating environment. A typical mechanical coupling is shown in

figure

Fig.1.1 Typical Mechanical Coupling


2/24

2

CHAPTER 02

TYPES OF COUPLINS

2.1 RIGID COUPLING

A rigid coupling is a unit of hardware used to join two shafts within a motor or

mechanical system. It may be used to connect two separate systems, such as a motor

and a generator, or to repair a connection within a single system. A rigid coupling

may also be added between shafts to reduce shock and wear at the point where the

shafts meet.

When joining shafts within a machine, mechanics can choose between flexible

and rigid couplings. While flexible units offer some movement and give between the

shafts, rigid couplings are the most effective choice for precise alignment and secure

hold. By precisely aligning the two shafts and holding them firmly in place, rigid

couplings help to maximize performance and increase the expected life of the

machine. These rigid couplings are available in two basic designs to fit the needs of

different applications. Sleeve-style couplings are the most affordable and easiest to

use. They consist of a single tube of material with an inner diameter that's equal in

size to the shafts. The sleeve slips over the shafts so they meet in the middle of the

coupling. A series of set screws can be tightened so they touch the top of each shaft

and hold them in place without passing all the way through the coupling.

Clamped or compression rigid couplings come in two parts and fit together

around the shafts to form a sleeve. They offer more flexibility than sleeved models,

and can be used on shafts that are fixed in place. They generally are large enough so

that screws can pass all the way through the coupling and into the second half to

ensure a secure hold. Flanged rigid couplings are designed for heavy loads or

industrial equipment. They consist of short sleeves surrounded by a perpendicular

flange. One coupling is placed on each shaft so the two flanges line up face to face. A

series of screws or bolts can then be installed in the flanges to hold them together.

Because of their size and durability, flanged units can be used to bring shafts into

alignment before they are joined together. Rigid couplings are used when precise

shaft alignment is required; shaft misalignment will affect the coupling's performance

as well as its life.


3/24

3

Fig. 3.1 Rigid Coupling

2.1.2 TYPES OF RIGID COUPLING

1. CLAMP OR SPLIT-MUFF COUPLING

Clamp coupling is a coupling method that can be used when joining two piping

units or hoses. It is one of the most popular methods and is also the most simple in

design. The clamp couple is typically used to join two hoses at their end, or to join a

hose end securely to the end of a pipe, though these particular coupling devices come

in many variations of form and function depending on what they are used for.

Consisting in most cases of a circular metal strap that has measured holes in it

that are fit to the threads of a screw, a clamp coupler is easily tightened with a screw

or nut driver. This means clamp coupling can be a secure way to connect any two

items of any material. A clamp coupling device is by far the most commonly utilized

type of coupling unit when a rubber or polyurethane hose has a metal component

attached to one end. Such devices are also used for a spacer that connects two hoses

together.

Clamp couplings come in many different shapes, sizes, and options. Some are

rubber grommets that have screwed tension-clamping rings around them used for

compression. Others are hinged plastic cylinders with threaded holes that line up on

each side so a screw can be used to tighten the cylinder around the joined materials.


4/24

4

Fig.3.2 Clamp or Split-Muff Coupling

Any clamp coupling, no matter what application it is used for, has a

certain strength rating according to both pressure and material tolerances. For

instance, if the clamp couple is used to connect two hoses together that are used to

transfer a chemical such as a catalyst or other acid, the clamp coupler must be able to

tolerate that material or it will deteriorate and provide a poor seal. Also, if the material

passing through the hose unit is pressurized, the pressure capacity for the clamp

coupling must be one that will tolerate the amount of pressure inside the line being

joined or the seal could break at the junction, causing a leak or a spill.

2. FLANGE COUPLING

A flange coupling is a type of coupling device meant to bring two tube

ends together in a flush, sealed manner. This two-piece coupling unit consists of a

keyed receiving side for the flanged end to be fastened to, so it may be married to the

opposing tube end, which also has a flanged end. Each flange has either a male

orfemale coupleropening so that when the two ends are brought together, they are

aligned without causing resistance or drag in the material being passed through them.

This male/female coupling method also creates a stable connection that is resistant to

shifting, keeping the flange coupling sturdily in place.

Flange couplings are typically used in pressurized piping systems

where two pipe or tubing ends have to come together. The connecting methods for

flange couplings are usually very strong because of either the pressure of the material

or the sometimes hazardous nature of materials passed through many industrial piping

systems. High thread count nut-and-bolt connections are used to secure the flange

couplings in place. These nuts and bolts are usually made from tempered steel oralloys to provide enduring strength and the ability to be tightened to the utmost level
http://www.wisegeek.com/what-is-a-flange.htmhttp://www.wisegeek.com/what-is-a-flange.htmhttp://www.wisegeek.com/what-is-a-female-coupler.htmhttp://www.wisegeek.com/what-is-a-female-coupler.htmhttp://www.wisegeek.com/what-is-a-flange.htmhttp://www.wisegeek.com/what-is-a-flange.htm


5/24

5

to ensure the piping system doesnt leak at any flanged junction. Most flange

couplings utilize four, six, or up to 12 bolt assemblies.

Fig.3.3 One-Half-of-Complete-Flange-Coupling

2.2 FLEXIBLE COUPLINGS

A flexible coupling is used to connect two shafts, end-to-end in the same line, for two

main purposes. The first purpose is to transmit power that is torque from one shaft to

another, thereby causing both to rotate in unison, at the same RPM. The second

purpose is to compensate for small amounts of misalignment and random movement.

Flexible couplings are made of elastic materials, like rubber, or have various

other configurations. During rotation, flexible couplings can accommodate

misalignment and motion.

1. HOW FLEXIBLE COUPLING OPERATES?

It is a known fact that in any direct mechanical drive system, there is the need

to couple the variety of driven elements that are included. The majority of drive

elements which include gear reducers, lead screws, and a host of other components,

are driven by shafting. The shafting is supported by multiple bearings. This allows the

shafting to be held extremely straight and rigid while rotating which at the same time

avoid any kind of possible balancing and support problems. Because of this rigid

support, it practically becomes impossible to avoid slight misalignments between a

driving and driven shaft when they are connected.


6/24

6

Fig.3.4 Flexible Coupling

The simple and most common solution to the problem of shaft

misalignment is using a flexible coupling to absorb lateral, angular, and axial

restoring forces, while maintaining some rigidity or fixed position in rotation. The

degree to which this torsional rigidity is applied varies from one application to

another. The basic function of flexible coupling is to join two pieces of rotating

equipment while permitting some degree of misalignment or end movement or both.

2. MATERIALS USED:

Various materials are used to make flexible couplings like as follows:

1. Brass

2. Aluminum

3. Cast Iron

4. Stainless Steel

5. Carbon Steel

6. Rubber etc.

3. TYPES OF FLEXIBLE COUPLING:

There are three basic types of flexible couplings. They are as follows:

1. Mechanically Flexible Coupling: The mechanical flexible coupling generally

obtains their flexibility from loose-fitting parts or rolling or sliding of mating

parts or from both.

2. Metallic Element Coupling: The metallic flexible couplings obtain their

flexibility from the flexing of thin metallic, disc or diaphragms.


7/24

7

3. Elastomeric Element Coupling: The elastomeric element flexible coupling

obtains their flexibility from stretching or compressing a resilient material like

for example rubber or plastic.

4 FUNCTIONS OF FLEXIBLE COUPLING:

There are three basic functions of a flexible coupling. They are as follows:

A. Transmit power: Flexible couplings are used to transmit mechanical power

from one machine to another. The mechanical power is in the form of torque

at some speed, or work per unit of time, In general, the power lost by a

flexible coupling is small.

B.

Accommodate misalignment: There are two types of misalignment. They are

shaft misalignment and coupling misalignment. Both the misalignments are

accommodated through flexible coupling.

C. Compensate for end movement: Most flexible couplings are designed in

such a way that they can accommodate axial movement of the connected

equipment or shaft ends.

5 APPLICATIONS OF FLEXIBLE COUPLINGS:

1. Off-highway vehicles

2. Agricultural machinery

3. Marine propulsion

4. Rail traction

5. Pump sets etc.

2.2.1 TYPES OF FLEXIBLE COUPLINGS

1. BEAM COUPLINGS

The beam coupling is an all-metal, non-lubricated coupling made from bar

stock. It is manufactured by cutting a helix in a hollow bar forming a curved beam

spring. The variations in OD, ID, number of helix starts, width of the beams (related

to thickness of coils) and number of coils within a specific coupling length all serve to

define the characteristics of the coupling.


8/24

8

The coupling is formed from a single piece of aluminum or stainless steel and

can be cut with single or double flex planes. Some beam models can far exceed the

bellows in angular misalignment, while others have configurations that make them act

like a different device than a coupling. The devices include U-joints and springs. The

flexure allowed by the curved beam portion of the coupling is capable of

accommodating angular, parallel and axial misalignment while continuing to transmit

torque between the attached shafts.

The beam coupling has a torsional stiffness that ranges from medium high to

very high, which makes it a "constant velocity" coupling i.e. at every point during

rotation, the driven half turns exactly the same amount and at the same rate as the

driving half. It is highly appropriate for power transmission and motion control

applications where extremely accurate positioning, frequent start/stop or reversing,

and zero backlash are essential. It operates either clockwise or counter clockwise

without sacrificing windup or torque capabilities. It has a very high tolerance to heat,

chemicals, and corrosion.

The beam coupling can be used up to 10,000 RPM while misaligned and

produces very low reactionary loads. Consequently the support bearings will be

lightly loaded even when the coupling is misaligned within its specified limits.

Reactionary loads are proportional to the spring flex constant.

2. DISC COUPLINGS

Disc couplings can be made as a close-coupled design, or built as spacer type

couplings. Close-coupled units that are designed to drop in the place of standard gear

couplings have split centerpieces for replacing the disc pack. Spacer couplings, the

most popular configuration, are either the marine type or reduced moment type. Themarine type, with the flex element positioned outside the shaft hub, is easier to

disassemble, and the ID of the disc pack is not controlled by the shaft hub diameter.

Reduced moment couplings place the flex point and therefore flexing element directly

over the shaft hubs nearest to a support bearing. The moment arm is reduced, reducing

bearing loads and changing the lateral critical speed. Reduced moment couplings can

increase the diameter of the flexing element or limit the hub bore.


9/24

9

The basic industrial disc coupling consists of two hubs, two disc packs, and a

center or spacer piece. The disc packs are bolted to the spacer and then to the shaft

hub.

It is possible to build disc couplings as vertical units, electrically insulating

units, and shear pin units or to include a floating (torsion) shaft. The spacer units can

be built with lightweight composite fiber spacers between two single flex element

couplings, a design often-used on cooling tower applications. Couplings with axial

movement limitations are available, as are split spacer close-coupled units. The

industrial units can have flange adapters rather than hubs or hubs can be adapted to

use either internal or external clamping devices (shrink discs).

All varieties of the disc coupling can be inspected for damage without

disassembly as long as you can see the discs. It is also possible to check the coupling

with a strobe light while in operation. Under a strobe light the discs can be seen

flexing and moving and a damaged disc would show up.

Disc couplings should not be used when rugged environmental conditions

exist or when axial movement is required and must be carefully applied when

transient loads are encountered. It is more expensive than a gear coupling.

Fig. 3.5 Disc Couplings

3. FLUID COUPLING

A fluid coupling is a hydrodynamic device used to transmit rotating

mechanical power. It has been used in automobile transmissions as an alternative to a

mechanical clutch. It also has widespread application in marine and industrial
http://en.wikipedia.org/wiki/Hydrodynamicshttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Transmission_(mechanics)http://en.wikipedia.org/wiki/Clutchhttp://en.wikipedia.org/wiki/Clutchhttp://en.wikipedia.org/wiki/Transmission_(mechanics)http://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Hydrodynamics


10/24

10

machine drives, where variable speed operation and/or controlled start-up without

shock loading of the power transmission system are essential.

A fluid coupling consists of three components, plus the hydraulic fluid:

1. The housing, also known as the shell (which must have an oil tight seal around

the drive shafts), contains the fluid and turbines.

2. Two turbines (fan like components).

3. One connected to the input shaft; known as the pump or impellor, primary

wheel input turbine.

4. The other connected to the output shaft, known as the turbine, output

turbine, secondary wheel or runner.

The driving turbine, known as the 'pump', (or driving torus) is rotated by

the prime mover, which is typically an internal combustion engine orelectric motor.

The impellor's motion imparts both outwards linear and rotational motion to the fluid.

The hydraulic fluid is directed by the 'pump' whose shape forces the flow in

the direction of the 'output turbine' (or driven torus). Here, any differences in the

angular velocities of input stage and output stage result in a net force on the 'output

turbine' causing a torque; thus causing it to rotate in the same direction as the pump.

1 APPLICATION

1. Industrial

2. Rail transportation

3. Automotive

4. Aviation

The most prominent use of fluid couplings in aeronautical applications

was in the Wright turbo-compound reciprocating engine, in which three power

recovery turbines extracted approximately 20 percent of the energy or about

500 horsepower (370 kW) from the engine's exhaust gases and then, using

three fluid couplings and gearing, converted low-torque high-speed turbine

rotation to low-speed, high-torque output to drive the propeller.
http://en.wikipedia.org/wiki/Hydraulic_fluidhttp://en.wikipedia.org/wiki/Enginehttp://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Hydraulic_fluidhttp://en.wikipedia.org/wiki/Wright_R-3350http://en.wikipedia.org/wiki/Propellerhttp://en.wikipedia.org/wiki/Propellerhttp://en.wikipedia.org/wiki/Wright_R-3350http://en.wikipedia.org/wiki/Hydraulic_fluidhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Enginehttp://en.wikipedia.org/wiki/Hydraulic_fluid


11/24

11

Fig. 3.6 Fluid Coupling

4. GEAR COUPLING

Gear-couplings are the king of coupling types. They can do things that many

other couplings cannot do, can only do with difficulty or with expensive

modifications and de-rating. Gear couplings are more power intensive, offer more

modifications, and a wider size, torque bore range than any other type, and can

perform at extremely high speeds. Gear couplings have axial slide capability, low

speed high torque capability, shifter capability and spindle capability not found in

other couplings. They are easily modified for shear pin service, floating shaft type,

vertical type, insulated type, limited end float, and can have a brake drum or disc

added. While those latter items may be available on other couplings, it is usually

easier and less costly to modify the gear coupling. With all these advantages the gear

coupling is used on twice as many applications versus the nearest competitor type.

Gear couplings can also perform at extremely high rates of speed. As implied

by the name, gear couplings use the meshing of gear teeth to transmit the torque and

to provide for misalignment. External gear teeth are cut on the circumference of the


12/24

12

hub. Both toothed hubs fit inside the ends of a tubular sleeve that has matching gear

teeth cut around its interior circumference, with each tooth extending axially the full

length of the sleeve. Hub and sleeve teeth mesh so torque transfers from the driving

hub's teeth to the sleeve teeth and back to the driven hub's teeth.

While the hub and sleeve teeth are cut to fit loosely side to side, they are cut

to fit closely where the tip diameter of the hub teeth meet the root diameter of the

gaps between the sleeve teeth. That is called a major diameter fit. When the coupling

is not rotating, those two surfaces rest upon each other if it is a horizontal installation.

Minor diameter fits (where the tips of the sleeve teeth meet the root diameter of the

hub teeth) are purposely avoided, because a close fit here would preclude suitable

misalignment capability and torque transmission capability.

It was noted earlier that gear couplings are power intensive. That means more

torque transmitted per pound of coupling weight and per cubic inch of space

consumed than other couplings. In many cases the gear coupling has more torque

capability than the shaft can transmit. The resulting relatively small size of the gear

coupling allows the addition of attachments without having the coupling grow to

impracticable proportions.

Fig 3.7 Gear Coupling

5. HIRTH

A Hurth joint or Hurth coupling is a type of mechanical connection

named after its developer Albert Hurth. It is used to connect two pieces of a shaft


13/24

13

together and is characterized by tapered teeth that mesh together on the end faces of

each half shaft.

1. CONSTRUCTION

Hurth joints consist of radial teeth formed by

grooves milled orground into the end face of a cylindrical shaft. The teeth mesh

around a ring, as the torque capacity of teeth increases with their diameter. This ring

is arranged to be at the maximum.

Possible diameter for the space available. The center of a shaft is not

toothed, as this would add little torque capacity to the coupling and the increasingly

narrow teeth would become impractical to cut.

The coupling is defined by the groove count, the outer diameter of the cylindrical

feature, the bottom angle of the grooves (to the axis of the cylindrical feature), and

their depth. Hirth joints are designed as mating pairs and, unlike splines, there is no

standardized off-the-shelf sizing system for them.

2. ADVANTAGES

1. Very high loads can be transferred in a small enclosure of only a few parts

(two serrated faces and a bolt fixing them together).

2. There is no lag in the joint.

3. The joint is self-centering (because of this the Hurth coupling is used in very

high RPM gas turbines).

4. If there is some fretting wear resulting in looseness, tightening the axial thread

can regain tightness.

3. DISADVANTAGES

1. The manufacturing process is complex, time consuming and consequently

expensive.
http://en.wikipedia.org/wiki/Milling_machinehttp://en.wikipedia.org/wiki/Grinding_machinehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Frettinghttp://en.wikipedia.org/wiki/Frettinghttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Grinding_machinehttp://en.wikipedia.org/wiki/Milling_machine


14/24

14

4. USES

Hurth joints were first used in aircraft engine crankshafts. The large

number of cylinders and often the need for reduction gears and supercharger drives

too, made it impractical to manufacture a one-piece crankshaft and so Hurth jointswere used to couple the sections. They were used in complex crankshafts for many

years afterwards, particularly where the output power was taken from a central drive

gear.

Large diameter Hurth couplings can effect extremely accurate and

repeatable rotational positioning. For this reason they are used in indexing heads and

rotary tables for precision machining and inspection tasks. Commercial products such

as the Untraded achieve sub-arc-second accuracy.

Fig.3.8 Hurth joints

6. OLDHAM

OLDHAM COUPLING

Oldham couplings consist of three members. A floating member is trapped by

90 displaced grooves between the two outer members which connect to the drive

shafts as shown in figure.

Oldham couplings can accommodate lateral shaft misalignments up to 10% of

nominal shaft diameters and up to 3 angular misalignments. Lubrication is a problem

but can in most applications be overcome by choosing a coupling that uses a wear

resistant plastic or an elastomer in place of steel or bronze floating members.
http://en.wikipedia.org/wiki/Crankshafthttp://en.wikipedia.org/wiki/Indexing_headhttp://en.wikipedia.org/wiki/Indexing_headhttp://en.wikipedia.org/wiki/Crankshaft


15/24

15

1. OLDHAM COUPLINGS HAVE THE

FOLLOWING ADVANTAGES:

1. No velocity variation as with universal joints.

2. High lateral misalignments possible.

3. High torque capacity.

4. Ease of dismantling.

2. DISADVANTAGES: Fig. 3.9 Oldham Coupling

1. Limited angular displacement of shafts.

2. Need for periodic lubrication due to relative sliding motion unless nylon or rubber

construction is employed.

3. Possible loss of loose members during disassembly.

7. RAG JOINT

A rag joint refers to certain flexible joints (flexure bearings) found

on automobiles and other machines. They are typically found on steering shafts that

connect the steering wheel to the steering gear input shaft, usually at the steering gear

end. They provide a small amount of flex for a steering shaft within a few degrees of

the same plane as the steering gear input shaft. It also provides some damping

ofvibration coming from the steering system, providing some isolation for the

steering wheel.

This type of joint has also been used on drive shafts. Farm tractors and lawn

and garden equipment have often used them in this application, and even some

higher-power applications, such as some 1960s race cars, featured them. Inautomobile and truck prop shaft designs, they have now mostly been replaced by

constant or drive shafts with pairs ofuniversal joints. Rear-wheel drive cars have

commonly used a lengthwise propeller shaft with a rubber doughnut joint at the

gearbox end (limited movement) and a universal joint at the rear axle (greater

movement). This gives articulation where needed, but also stops some of the vibration

being transmitted into the body.

The joint consists of a piece ofdoughnut shaped rubberwith reinforcingcords vulcanized in it, similar to a tire. This disc is bolted orriveted to flanges
http://en.wikipedia.org/wiki/Kinematic_pairhttp://en.wikipedia.org/wiki/Flexure_bearinghttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Steeringhttp://en.wikipedia.org/wiki/Steering_wheelhttp://en.wikipedia.org/wiki/Vibrationhttp://en.wikipedia.org/wiki/Drive_shafthttp://en.wikipedia.org/wiki/Universal_jointhttp://en.wikipedia.org/wiki/Doughnuthttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Vulcanizehttp://en.wikipedia.org/wiki/Tirehttp://en.wikipedia.org/wiki/Bolted_jointhttp://en.wikipedia.org/wiki/Rivethttp://en.wikipedia.org/wiki/Rivethttp://en.wikipedia.org/wiki/Bolted_jointhttp://en.wikipedia.org/wiki/Tirehttp://en.wikipedia.org/wiki/Vulcanizehttp://en.wikipedia.org/wiki/Rubberhttp://en.wikipedia.org/wiki/Doughnuthttp://en.wikipedia.org/wiki/Universal_jointhttp://en.wikipedia.org/wiki/Drive_shafthttp://en.wikipedia.org/wiki/Vibrationhttp://en.wikipedia.org/wiki/Steering_wheelhttp://en.wikipedia.org/wiki/Steeringhttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Flexure_bearinghttp://en.wikipedia.org/wiki/Kinematic_pair


16/24

16

mounted on the ends of the shafts to connect the steering wheel shaft to the steering

gear. The ragged cords can be seen on the edge of this piece of rubber, hence the term

"rag joint". The bolt holes themselves are often reinforced by steel tubes molded into

the doughnut.

Fig. 3.10 Rag Joint


17/24

17

CHAPTER 03

REQUIREMENTS OF GOOD SHAFT ALIGNMENT /

GOOD COUPLING SETUP

A major part of keeping equipment running smoothly involves regular

maintenance and upkeep and ensuring that the machinery is kept lubricated and

properly aligned.

When shafts or belts on rotating equipment are misaligned, the risk of costly,

unplanned machine downtime rises dramatically. Misalignment also damages seals

and couplings. Lubrication problems often can be traced to seals that have been

compromised by shaft or belt misalignment. Simply replacing a seal will not stop

future seal failure and associated loss of lubricantonly correcting the misalignment

will solve the problem

1. It should be easy to connect or disconnect the coupling.

2. It does allow some misalignment between the two adjacent shaft rotation axes.

3. It is the goal to minimize the remaining misalignment in running operation to

maximize power transmission and to maximize machine runtime (coupling and

bearing and ceilings lifetime).

4. It should have no projecting parts.

5. It is recommended to use manufacturer's alignment target values to set up the

machine train to a defined non-zero alignment, due to the fact that later when the

machine is at operation temperature the alignment condition is perfect.


18/24

18

CHAPTER 04

METHODS TO CHECK ALIGNMENT

4.1 STRAIGHT EDGE AND TAPER GAGE ALIGNMENTA straight edge is used to determine the shaft offset by eye. It is used

for both vertical and horizontal planes. The taper gage (or calipers or feeler gage) is

used for angular misalignment. The shaft separation or "BSE" dimension is measured

with a ruler. It is a trial and error process.

4.2 DIAL INDICATOR ALIGNMENT

Dial indicators are used with the reverse indicator or the face and rim

method. The dial indicators are mounted on the shaft opposite to the reading to be

taken.

In the reverse indicator method, readings are taken from coupling hub

on shaft "A" to the rim of the coupling hub on shaft "B". A second set of readings are

taken from the coupling hub on shaft "B" to the rim of the coupling hub on shaft "A".

Both sets of readings are plotted on graph paper or become the input to a personal

computer program. With the proper calculations in plane geometry, the misalignment

of both parallel offset, and angularity of the shafts can be determined.

Fig. 5.1 Reverse Dial Indicator

The face and rim method uses the dial indicator mounted on one

coupling hub to take readings on the face and the rim of the second coupling hub.

Again with graphical plotting or a computer and plane geometry the misalignment ofboth types can be determined.


19/24

19

This method can be very accurate if done with graphical assistance or

computer assistance. Other commercial mechanical and electrical devices can obtain

the results by measuring the positions of two shafts.

4.3 LASER BEAM ALIGNMENT

Laser beam alignment uses the laser to replace the dial indicator. It is a

little more accurate, but is much more costly. Included with the laser package is the

means of direct input to a computer program that calculates the moves necessary to

align the equipment. Lasers are accurate to 3 micron or better.

The laser is a light beam that is very narrow and focused. The beam generating

equipment is mounted on the equipment shaft and aimed at a device on the opposite

shaft. The device can be a reflector or can be the photodiode target cell that will

generate a voltage. The amount of voltage that is generated will depend on the

position of the light beam as it hits the cell. A reflector will cause the beam to return

to a target cell that is mounted with the laser generator. The generated voltage

becomes the input to a system that calculates the misalignment and needed

corrections.


20/24

20

CHAPTER 05

COUPLING MAINTENANCE AND FAILURE

Coupling maintenance is generally a simple matter, requiring a regularly scheduled

inspection of each coupling. It consists of:

1. Performing visual inspections, checking for signs of wear or fatigue, and cleaning

couplings regularly.

2. Checking and changing lubricant regularly if the coupling is lubricated. This

maintenance is required annually for most couplings and more frequently for

couplings in adverse environments or in demanding operating conditions.

3.

Documenting the maintenance performed on each coupling, along with the date.

Even with proper maintenance, however, couplings can fail. Underlying reasons for

failure, other than maintenance, include:

1. Improper installation

2. Poor coupling selection

3. Operation beyond design capabilities.

The only way to improve coupling life is to understand what caused the

failure and to correct it prior to installing a new coupling. Some external signs that

indicate potential coupling failure include:

1. Abnormal noise, such as screeching, squealing or chattering

2. Excessive vibration or wobble


21/24

21

CHAPTER 06

USES OF COUPLING

Shaft couplings are used in machinery for several purposes, the most common of

which are the following.

1. To provide for the connection of shafts of units that is manufactured separately

such as a motor and generator and to provide for disconnection for repairs or

alterations.

2. To provide for misalignment of the shafts or to introduce mechanical

flexibility.

3. To reduce the transmission of shock loads from one shaft to another.

4. To introduce protection against overloads.

5. To alter the vibration characteristics of rotating units. To connect driving and

the driven part


22/24

22

CHAPTER 07

CONCLUSION

Selecting the right coupling is a complex task because operating

conditions can vary widely among applications. Primary factors that will affect the

type and size of coupling used for an application include, but are not limited to:

horsepower, torque, speed (RPM), shaft sizes, environment conditions, type of prime

mover, load characteristics of the driven equipment, space limitations and

maintenance and installation requirements. Secondary but possible essential factors

can include starts/stops and reversing requirements, shaft fits probable misalignment

conditions, axial movement, balancing requirements or conditions peculiar to certain

industries.


23/24

23

CHAPTER 08

BIBLIOGRAPHY

1. MICHAEL NEALE, PAUL NEEDHAM, ROGER HORRELL - COUPLINGS

AND SHAFT ALIGNMENT- MECHANICAL ENGINEERING

PUBLICATIONS, 1991

2. TAYLOR & FRANCIS, JON R. - COUPLINGS AND JOINTS: DESIGN,

SELECTION & APPLICATION

3. ALEXANDER BLAKE -DESIGN OF MECHANICAL JOINTS

4. SILANE COUPLING AGENTS EDWIN P. PLUEDDEMANN - 1982
http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Michael+Neale%22http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Paul+Needham%22http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Roger+Horrell%22http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Roger+Horrell%22http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Alexander+Blake%22http://books.google.co.in/books?id=SgA7vf4DLj0C&printsec=frontcover&dq=books+for+coupling&hl=en&sa=X&ei=GQNmUoGBEo2flQXt0oDwDg&ved=0CD0Q6AEwAAhttp://books.google.co.in/books?id=SgA7vf4DLj0C&printsec=frontcover&dq=books+for+coupling&hl=en&sa=X&ei=GQNmUoGBEo2flQXt0oDwDg&ved=0CD0Q6AEwAAhttp://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Alexander+Blake%22http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Roger+Horrell%22http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Paul+Needham%22http://www.google.co.in/search?tbo=p&tbm=bks&q=inauthor:%22Michael+Neale%22


24/24

A SEMINOR REPORT ON COUPLING.pdf

Documents

Transcript of A SEMINOR REPORT ON COUPLING.pdf