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Part II

Mechanical system

Introduction

Drive

1. Electric motor

2. I.C.E

Diesel Eng.

Benzene Eng.

3. E.C.E

Boiler

Steam Turbine

Gas Turbine

Jet Eng

4. Water power

5. Wind energy

6. Solar energy

7. Chemical energy

8. Tidal energy

9. Nuclear energy

10. Geothermal energy

11. Fossil Fuels

Connection Driven

1-Coupling

2-Clutch

3-Break

4-Belt

5-Chain

6- Gear

Any Machine

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Chapter 1

Drive

Drive may be one of the following

1. Electric motor

2. I.C.E ( internal combustion engine ) Diesel Eng.

Benzene Eng.

Four-stork engine

3. E.C.E ( external combustion engine ) Boiler

Fire tube boiler

Water tube boiler

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Steam Turbine

Gas Turbine

Jet engine

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4. Water power

Frances turbine Pelton wheel

The power available in a stream of water is;

where:

P = power (J/s or watts)

= turbine efficiency

= density of water (kg/m)

g = acceleration of gravity (9.81 m/s)

h = head (m). For still water, this is the difference in height between the inlet and outlet

surfaces. Moving water has an additional component added to account for the kinetic

energy of the flow. The total head equals the pressure head plus velocity head.

= flow rate (m/s)

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5. Wind energy

Wind Turbine Power Equation

WP = 0.5 x AD x SA x WV3 x CP

(HWP) Wind Power (w/hr)

AD (air density 1.23 kg/cu m)

SA (sweep area m^2)

WV (wind velocity m/s)

CP (coefficient of performance 0.25 for most systems)

6. Solar energy

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Solar collector Solar cell Solar reflector

7. Chemical energy Dry battery

Wet battery

Rechargeable battery

8. Tidal energy

Maximum Tidal Energy, E = 2HQ kWh/yr,

Where

H is the tidal range (m)

Q is the tidal flow (m3/sec of seawater)

2 (2 tides)

9. Nuclear energy

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10. Geothermal energy

11. Fossil Fuels Natural gas

Petrol oil

Wood

coal

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Chapter 2

Coupling Clutch break

2-1 Terms

1. Coupling: device used for permanent connection of two

shafts, so that the two shafts are forced to run at equal speed.

2. Clutch: device used for connection of two shafts which

permits rapid connection and disconnection.

3. Brake: device used for deceleration of rotating bodies.

2-2 Coupling

Types of coupling are

1. Rigid coupling:

Rigid coupling applied only if

a) Both shafts have constantly the same.

b) The axial distance between the shafts is constant.

And can be used in the following shafts position

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Some types of rigid couplings

a) Box coupling

The simplest coupling type.

Material: steel (e.g. st. 34, st .50)

Design rules

The pins are stressed on shear. And Maximum torque can be transmitted is

b) muff coupling DIN 115

Maximum torque can be transmitted

Z.. Number of bolts

Material: cast iron

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c) Flanged coupling

For transmission of big torques

d) Flanged coupling, flanged integral with the shafts

Maximum torque can be transmitted

(

)

Q force acting in each bolt

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2. Self aligning couplings with no torque- elasticity

The can accommodate misalignments of shafts and / or variation of axial distance between the shafts.

Some types described below

a) Jaw coupling (accommodates variation of axial distance only)

b) Cardan joint (for angular misalignment)

3. Flexible couplings (self aligning couplings with torque-elasticity) They accommodate small misalignments and reduce ( reduce and damp) torque shocks

a) Coupling with rubber sleeves

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Flexible-disk coupling

b) Periflex coupling

Both rigid parts of coupling are connected by rubber member

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4. Safety couplings

These coupling limit the transmitted torque, and when torque exceed the limit , the coupling will slip or

be disconnected.

a) Shearing pin coupling

Pins transmits torque and will break at a certain torque. It must be replaced before the coupling

is used again.

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2-3 CLUTCHES

Clutch is a machine member used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped at will, without stopping the driving shaft. A clutch thus provides an interruptible connection between two rotating shafts. Clutches allow a high inertia load to be stated with a small power.

Mechanical Model

Two inertias I1and I2 traveling at the respective angular velocities I and 2, and one of which may be zero, are to be brought to the same speed by engaging. Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation, resulting in temperature rise. 2 1 1 1 2 Clutch or brake Dynamic Representation of Clutch or Brake

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TYPES OF CLUTCHES

1. Positive clutches

a) Jaw Clutch

The teeth of the mating sets of jaws are brought into engagement by sliding one or both members

axially. The teeth may be straight-sided or triangular, or they may incorporate some smooth curve to

facilitate engagement. Once the teeth are engaged, there is a positive transmission of torque. The jaw

clutch is normally engaged while the system is stopped or is running very slowly.

b) Toothed clutch

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2. Friction clutches An axial clutch is one in which the mating frictional members are moved in a direction parallel to

the shaft. A typical clutch is illustrated in the figure below. It consist of a driving disc connected

to the drive shaft and a driven disc co9nnected to the driven shaft. A friction plate is attached to

one of the members. Actuating spring keeps both the members in contact and power/motion is

transmitted from one member to the other. When the power of motion is to be interrupted the

driven disc is moved axially creating a gap between the members as shown in the figure.

a) Single disk clutch (plate clutch)

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b) Multi-disk clutch

The operating force is

Z.. Number of contact surfaces.

P pressure

coefficient of frication

c) Cone clutch

3. Hydraulic clutche

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2-4 BRAKES

TYPES OF BRAKES

A brake decelerates a system by transferring power from it. A clutch such as that illustrated (for the

most part) accelerates a system by transferring power to it. The two devices in rotary applications are

thus very similar as they both transmit torque whilst supporting a varying speed difference across them.

1. Shoe brake

Before examining a practical twin-shoe brake we must understand the behavior of a single shoe.

Various shoe configurations are illustrated. Each consists of a body whose motion is braked together

with a shoe which can swing freely about a fixed hinge H. A lining is attached to the shoe and contacts

the braked body. The actuation force P applied to the shoe gives rise to a normal pressure and

corresponding braking friction distributed over the area A of contact between lining and braked body.

2. Twin shoe brakes

Shoe behavior has been discussed at length. Two such shoes are combined into a complete practical

brake unit, two being used to minimize the unbalanced forces on the drum, shaft and bearings, and

because, as has been seen, linings become increasingly ineffective if they extend much beyond 90o to

110o. The shoes will be designated 1 and 2.

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The brake torque of the complete brake To is the sum of the torque contributions of the two shoes. The

shoes are operated by a single brake actuation source Po which may be a force in a brake rod or an

hydraulic pressure for example. This source is converted into the individual shoe actuations by some

actuating linkage, examples of which are shown at the beginning of the chapter. Since the two shoes

usually behave differently - one leading while the other trails - the actuating linkage is arranged to have

different transformation ratios between the source and the shoes so that the linings' peak pressures and

lives are not too different.

3. Band brake

A band brake consists of a flexible band faced with friction material bearing on the periphery of a drum

which may rotate in either direction.

The actuation force P is applied to the band's extremities through an actuation linkage such as the

cranked lever illustrated. Tension build-up in the band is identical to that in a stationary flat belt.

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These are external rigid shoe brakes - rigid because the shoes with attached linings are rigidly connected

to the pivoted posts; external because they lie outside the rotating drum. An actuation linkage

distributes the actuation force to the posts thereby causing them both to rotate towards the drum - the

linings thus contract around the drum and develop a friction braking torque.

4. Drum brake (inner shoe brake)

We now investigate the stability of road vehicles whilst braking during straight line motion, and consider

first a typical single non-driven wheel equipped with a drum brake of the type examined above. There

are three contacts between the wheel/brake drum/tyre system and its surrounds :

the ground, characterized by a tyre/ground adhesion coefficient k, and represented on the free body by

a normal force component N and a friction component F whose sense opposes vehicle translation vO

and whose magnitude cannot exceed the adhesion limit Fmax = kN when the wheel slides without

rotation on the ground, a condition known as wheel lock l the two brake shoes, which give rise to the

braking torque T and the force resultant R which are proportional to the brake actuation Po as discussed

above - provided the wheel is turning since friction force = m*normal reaction at the lining- drum

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contact only when there is relative motion between lining and drum l the wheel bearing at O, taken to

be essentially frictionless so that the sole effect here is the bearing reaction RO.

5. Disk brake

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Chapter 3

Belts Chains Gears

3 -1 Terms

Mechanical power may be transmitted between shafts , which have no common axis, by the following ways :

Belts Chains Gears

3-2 Belt Drive

1. characteristic

Belt drive has the folowing good characteristic

1. Connection of waidly as well as closely speed shafts is possible

2. There is only little noise in operation

3. There is chock absorption because of elasticity of the metrical

4. Safety against excessive load by belt slip

And bad characteristic is:

5. Because of slip an exact ratio of shaft speed cannot be maintained

2. material of belts

high cofficinet of firicition with metal

small resistance against bending

high tensile strength

remining expansion under load as small as possible

3. Types belt drive

Round belt Flat belt V- belt Timing belt

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4. Round belt pully

5. Flat belt drive

a) Open drive

b) Crossed drive

c) Half-crossed drive

d) Drive with giude rollers

e) Drive with stop pullys

f) Drive with fixed pulle and idler pulley

g) Drive with belt tensining pulley

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6. Flat belts pulleys Generally made from cast iron, light casting metal or welded parts

Symetric hub Asymetric hub Holes in web Welded pulley

One piece Two pieces

7. V- belts drive A v-belt drive has some imported advantage compered with flat belt

Extremely small slip

Higher transmittible power at equal maximum tension

Soft starting

Small angel of contact

Little space

8. V- belt pulleys

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9. Timing belt drive

10. Timing belt bulleys

11. Basic laws of belt dirive

Speed ratio

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3-3 Chain Drive

Chain = sequence of inner link and pin link articulated to form a flexible device for power transmission

1. characteristic

- Pitch: distance between two consecutive pins

- Roller diameter: dimension of the outside diameter of the chain rollers

- Inside width: distance between the two opposite inner sides of the inner link plates

2. Types of power chain

- roller chain

1. pin link plate

2. roller link plate

3. pin

4. bushing

5. roller

- silent chain

1. roller link plate

2. center plate

3. pin

3. Roller chains drive

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Two load conditions are generally considered for chain dimensioning:

- Normal tension in the side plates

- Shear on the pins

These verification may be useful to identify the load capacity of a chain installed on a mechanism

4. Silent chains drive

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3-4 Gear transmission

Gears are machine elements provided with teeth transmitting rotation and torque from one shaft

to the other one. Tramsmation of mation occures without slipping, by meshing of teeth.

1. Used of gear drive

To transimitte power from one rotating shaft ( driving ) to another ( driven) which may be

parallel, intersecting or skew under the following conditions:-

o The distance between the axes of the connecting shafts is short. o The speed is low and the belt drive is not recommended . o The torque transmitted is high. o The speed or velocity of the connecting shafts is to be maintained constant. o To step up or step down the speed

2. Gear wheel made from :

o By casting ( low speed ) o By drop forged ( low speed ) o By milling or grinding ( high speed )

Casting Drop forged Machined

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3. Basic type of gears :

gears may be classified as follows :-

o According to the form of tooth

Straight Helical Curved Double helical

o According to shaft position

Parellel Intersction Skew

o According to the position of gears in mech

External Internal Rack-super

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Solved problem

1. Drives

1-1 What are the possible types of drive can used in mechanical

system?

1-2 Calculate the power generated from water turbine, if waterfall

from 80 m height, with flow rate equal 500 m3/hr. if turbine

efficiency is about 80%. ( answer : 87200 watt/sec).

1-3 Calculate wind turbine power , if sweep area of blade equal

10m2, and wind velocity 30m/sec. ( answer: 46.125 watt/sec).

1-4 Calculate maximum tidal energy can be generated if seawater

level difference can reach to 20m and average flow rate

5000m3/sec. ( answer: 200000 watt/sec).

2. Coupling

2-1 What are the main differences between the following devices?

1- Coupling 2- clutch 3- brake

2-2 What are the main type of coupling?

2-3 Draw the possible position of shafts can be connected by

coupling.

2-4 Calculate the maximum torque can be transmitted by box

coupling if shaft diameter is 20mm , yield and shear stresses are

200, 400 MPs ( answer: 2x105 N-m).

2-5 Calculate the number of bolts used in muff coupling if maximum

torque can be transmitted is 2x105 N-m. and each bolt subject

to force equal 3x106 N, Dshaft =50mm.

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2-6 Calculate shearing pin diameter in safety coupling if number of

pins equal 10 and ultimate shearing stress 3.39x109 N and pitch

diameter 30mm. and maximum limit torque 10000 N-m .

( answer: 10 bolt).

3. Clutch

3-1 What are the main types of clutch?

3-2 Draw free hand sketch to show

A ) The different types of Jew clutch.

b) Friction clutch

c) Cone clutch

4. Break

4-1 Draw only the following types of brake

1- Shoe brake 2- Band brake

3- Disk brake 4- Draw brake

5. Belt

5-1 What are the good , bad characteristic of belt drive?

5-2 What are the types of belt drive?

5-3 Mention the belt material properties.

5-4 Draw a free hand sketch for

1. different arrangement of belt drive 5-5 What are the advantages of v belt over flat belt?

5-6 Draw a free hand sketch for the following belt drive pulleys

1. Round belt 2. Flat belt

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3. V- belt 4. Timing belt

Single belt drive:

Double belt drive:

Because

Where

(

)

(

)

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5-7 The transmission pulley of grinding wheel rotates with

n=360rpm, the cutting speed, or the grinding wheel has to be 25

m/s.

Find: 1) transmission ratio. 2) Diameter d4.

Solution:

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(Answer 1)

(Answer 2)

5-8 In double belt derive system shown below find I1, I2, I3,

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6. Chain

6-1 What are the main types of power chain

7. Gears

7-1 What are the main advantages of using gear drive?

7-2 Draw a free hand sketch to show types of gears.

1) Single gear drive:

2) Double gear drive:

7-3 The driven shaft of a gear drives rotates with speed

.

Find: 1- Transmission ratio 2-Number of teeth

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Solution:

Worm gear drive

Where: i= transmission ratio

n1= rpm of worm

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n2= rpm of worm gear

z1= number of teeth of worm (usually 1, 2 or 3)

z2= number of teeth of worm gear

7-4 The worm gear drive is provided with worm gear having z2=15

teeth. The single threaded worm rotates at 2880 rpm.

Find: 1. Transmission ratio 2. Rpm of worm gear

Solution: 1. i =

2.

Dimensions of spur gears:

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Circumference of circle

Where

t= m. x

Center distance between two gears c

c=

c=

7-5 The driving gear of spur gear drive rotates with n2=560 rpm.

Find 1. Transmission ratio

2. Rpm of the driven gear

3. Center distance between the two gears,

if the module m=3 mm

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Solution: 1. i =

=

i= 1:0.75

2.

n2 =

3. c=

=

Good luck