Theory Of Machine

Attempt any ten questions:(10X2=20)

1. Name the factor which affects the critical speed of a shaft.

Ans. Critical speed depends upon the magnitude and location of the shaft unbalance,
the length of the shaft, its diameter, and the kind of bearing support.

2. What is law of belting?

Ans. The law of belting states that the center line of the belt when it approaches the
pulley must lie in the mid-plane of that pulley which should be perpendicular to the axis
of the pulley. Otherwise the belt will run off the pulley.

3. Name two inversions of single slider crank chain.

Ans.
• First Inversion. Reciprocating engine or compressor.
• Second Inversion. Whitworth quick return mechanism, Rotary engine etc.
• Third Inversion. Slotted crank mechanism, Oscillatory engine.
• Fourth Inversion. Hand pump, Pendulum pump or Bull engine.

4. What do you mean by static and dynamic balancing?

Ans.
Static balancing definition refers to the ability of a stationary object to its balance.
Dynamic balancing is when the rotating system doesn’t yield any other force or couple.

5. What is basic difference between governor and flywheel?

Ans. Flywheel is used to reduce the fluctuation in speed with respect to mean speed.
Governor is used to maintain the mean speed with respect to given particular value.

6. What is natural frequency?

Ans. Natural frequency refers to the number of vibrations a freely vibrating body produces per
second.

7. Define addendum in context of gear.

Ans. The distance between the pitch circle and its tooth tip circle is called the addendum of
the gear.

8. What is the need of governors?

Ans. Governor is the device used to control the speed in engines.
9. Spur gear have which type of teeth?
Ans. The spur gear is cylindrical and has straight teeth cut parallel to its rotational axis.
10. Define effort and power of a governor.
Ans. The effort of a governor is the mean force exerted at. The sleeve for a given percentage
change of speed or lift of the Sleeve.
The power of a governor is the work done at the sleeve for a. given percentage of change in
speed.

11. Write the function of a flywheel.

Ans. The function of the flywheel is to store mechanical energy to balance the engine so that it
continues to have good performance.

12. What is the use of dynamometer?

Ans. A dynamometer or “dyno” for short, is a device for simultaneously measuring the torque
and rotational speed (RPM) of an engine, motor or other rotating prime mover so that its
instantaneous power may be calculated, and usually displayed by the dynamometer itself as kW
or bhp.

13. Define coefficient of friction.

Ans. Coefficient of friction, ratio of the frictional force resisting the motion of two surfaces in
contact to the normal force pressing the two surfaces together.
 14. Define transmissibility.
Ans.
Transmissibility is the ratio of output to input.
It is defined as the ratio of the force transmitted to the force applied.

2. Answer any five questions: (5X4=20)

1. Define Kinematic pair. Classify kinematic pair on various account.

Ans.
A kinematic pair refers to the connection between two links or elements in a mechanism
that enables relative motion or constraint between them.
Kinematic pairs are basically classified into two types: Lower pairs and Higher pairs
Lower Pairs are those that transmit motion or force through sliding or rolling contact
between the two elements, while Higher Pairs are those that transmit motion or force
through turning or pivoting contact between the two elements.

2. Distinguish between flat belt and V belt on the basis of power

transmitted, space, grip and application.
Ans.
Flat Belt Drive:
• This type of belt drive cannot transfer more power than v-belt drives.
• The contact surface is more than V-Belt type.
• Simple in design.
• Efficiency is more comparatively.
• Slip of belt occurs at the time of running.
• Less expensive than V-Belt drives.
• This type of belt drives is used for long distance than V-belt drives.
• Operation by this belt drive is not smooth.

V-Belt Drive:
• The v-belt drive can transfer more power than the flat belt drive.
• The contact surface is comparatively less than flat belt drives.
• No Maintenance is required.
 • Complex in the design of belt and pulley than flat belt drives.
• Efficiency is comparatively less.
• Slip is negligible in this type of belt drives.
• V-Belt drives are expensive than flat belt drives.
• This type of belt drives are used for heavy machinery’s.
• We can use this type of drives only for less distance.
• This type of belt drive operation is smooth than flat belt drives.

3. Derive an expression for the ratio of the driving tensions in a rope

drive. (assume any angle of the groove)
Ans.
Rope Drive
The rope drives are widely used where a large amount of power is to be transmitted, From
one pulley to another, over a considerable distance. It may be noted that the use of Flat
belts is limited for the transmission of moderate power from one pulley to another when
the two pulleys are not more than 8 meters apart. If large amounts of power are to be
transmitted by the flat belt, then it would result in excessive belt cross-section. It may be
noted that frictional grip in case of rope drives is more than that in V-drive. One of the main
advantages of rope drives is that a number of separate drives maybe taken from the he one
driving pulley. For example, in many spinning mills, the line shaft on each floor.

4. Discuss the function of double slider crank chain.

Ans.
Two sliding pairs and two twist pairs make up the double slider crankshaft. The double
slider crankshaft is so named because it has two sliding pairs. It consists of two sliders, a
moving frame, and a link that links the two slides and fixes the distance between the two
sliders.
5. Draw neat sketch of- Hartnell Governer.

Ans.
a).Define Torsional Vibrations?
Torsional vibration is often a concern in power transmission systems using rotating shafts
or couplings, where it can cause failures if not controlled.

b)Draw turning moment diagram for a reciprocating machine.

c)What is hunting of governor?

Hunting. A governor is said to be hunt if the speed of the engine fluctuates continuously
above and below the mean speed.

PART-B
Attempt any three questions:
(3x20=60)

3.

(a) What is meant by ‘Stability of a governor. Derive the

necessary condition of suitability for a centrifugal governer.
Ans.
Stability: A governor is said to be stable when for each speed within the working range
there is only one radius of rotation of the fly-ball at which the governor is in equilibrium.

The condition of stability of a governor requires that the slope of the controlling force
curve should be less than that of the line representing the centripetal force
at the equilibrium speed under consideration, is true for a centrifugal governor.
 (b) Describe with neat sketch the principle and working of
the pantograph.
Ans.

A pantograph (from Greek παντ- ‘all, every’, and γραφ- ‘to write’, from their original use
for copying writing) is a mechanical linkage connected in a manner based on
parallelograms so that the movement of one pen, in tracing an image, produces identical
movements in a second pen. If a line drawing is traced by the first point, an identical,
enlarged, or miniaturized copy will be drawn by a pen fixed to the other. Using the same
principle, different kinds of pantographs are used for other forms of duplication in areas
such as sculpting, minting, engraving, and milling.

Because of the shape of the original device, a pantograph also refers to a kind of
structure that can compress or extend like an accordion, forming a characteristic
rhomboidal pattern. This can be found in extension arms for wall-mounted mirrors,
temporary fences, pantographic knives, scissor lifts, and other scissor mechanisms such
as the pantograph used on electric locomotives and trams.
4.
a) Derive the expression for finding the length of belt in
open belt drive.

b) Explain the effect of slip on velocity ratio during

relative motion between pulley and belt .
Ans.
o Consider an open belt drive rotating in a clockwise direction, this rotation of the
belt over the pulleys is assumed to be due to a firm frictional grip between the
belt and pulleys.
o When this frictional grip becomes insufficient, there is a possibility of forwarding
motion of the driver without carrying the belt with it and there is also a
possibility of the belt rotating without carrying the driver pulley with it, this is
known as a slip-in belt.
o Therefore slip may be defined as the relative motion between the pulley and the
belt in it.
o This reduces the velocity ratio and is usually expressed as a percentage slip.
 The velocity ratio of the belt drive is given by:

5.
(a) What are the different types of chain? Define the terminology
used in chain with neat sketch?
Ans.
In the field of Mechanical Engineering chain drives can be classified into three broad
categories and those are:

• Hoisting Chains
• Conveyor Chains
• Power transmission Chains
• Roller chain (bush roller chain)
• Silent chain or inverted tooth chain
• Leaf chain
• Flat-top chain
• Engineering steel chain

Terminology Of Chain Drive

Chain pitch:
This is the distance between the hinge center of a link and the corresponding hinge center of an
adjacent link. It is usually denoted by p.

Pitch circle diameter of chain sprocket:

This is the diameter of the circle on which the hinge centers of the chain lie when the chain is
wrapped with a ball. The hinge centers of the chai and the circle drawn through these centers
are called pitch circles and its diameter is known as pitch circle diameter.

(b) Explain different types of gears and their applications.

Ans.
 6.
(a) Define the causes of vibrations in machines, their harmful
affects and remedies?
Ans.
Machine vibration is an unavoidable result found in the rotating, moving, and sliding
machine assemblies due to improper tolerancing and clearance between rotating
parts, misalignment, imbalance, wear, and no use of proper packing materials.
Sudden vibration in the machinery is a sign, or the intimation of wrong is happening
with the machine, which may cause an accident

Effects of Machine Vibration

• Wear and tear of the various machine components
• Creates noise
• Damage the machine
• Creates safety issues
• Consume more power
• Lower the product quality
• May cause accidents and stop production plants.
• Unplanned downtime

There are few ways to correctly treat vibration problems, these include:

• Precision balancing
• Bearing replacement
• Identifying any additional bad parts and having them sourced then replaced.
• Precision Alignment
• Precision Lubrication. That is, ensuring the correct lubricant win the correct volume at
the correct time.
 (b) Define construction and working of porter governor?
Ans.
Construction of Porter Governor:
The balls are connected to the arms as shown in the figure and these arms get
connected at a single point called pivot as in the figure, and the sleeve present on the
bottom of the spindle connected to the balls to move in up and down direction, due to
this momentum the supply of fuel is done.

Working of Porter Governor:

When the balls attached to the arms rotate, the sleeve gets moved in an upward
direction due to the connection between the balls and sleeve, and this momentum helps
to flow the fuel from storage tank to engine.
When the sleeve moves in the upward direction the fuel pump connected to it supplies
the fuel according to the momentum of the sleeve, with the help of this process the
fluctuations can be reduced and helps to function in a smooth condition.

7.
Three masses of 10kg, 15kg, & 20kg, attached at radial distances
of 80mm, 90mm, and 50mm. respectively to a disc on a shaft are
in complete balance. Determine angular position of masses of
15kg and 20kg. relative to the 10kg. mass?