Experiment
No.2
Objective:
1. To determine the relationship between
crank angle and stroke.
2. To study the effect of changing the (a)
crank radius (b) connecting rod length.
3. To investigate by graphical
differentiation by graphical relationship between different crank and
connecting rod combination.
connecting rod combination.
Apparatus:
Crank of different lengths, Connecting rods of
different lengths, Block, Slider
Theory:
Slider-Crank Mechanism:
A crank is an arm attached at right angles to a
rotation shaft by which reciprocating motion is imparted to or received from
the shaft. It is used to convert circular motion into reciprocating motion, or
sometime reciprocating motion into circular. The arm may be a bent portion of
the shaft, or separate arm attached to it. Attached to the end of the crank
by a pivot is a rod, usually called a connecting rod. The end of the rod
attached to the crank moves in a circular motion, while the other end is
usually constrained to move in a linear sliding motion, in and out.
The term often refers to a human-powered crank which
is used to manually turn an axcle, as in bicycle crankset or a brace and bit
dril. In this case a person’s arm or leg serves as the connecting rod, applying
reciprocating force to the crank. Often there is a bar perpendicular to the
other end of the arm, often with a freely rotatable handle on it to hold in the
hand, or in the case of operation by a foot (usually with a second arm for the
other foot), with a freely rotatable pedal.
Slider-crank chain inversion
arises when the connecting rod,
or coupler, of a slider-crank linkage becomes the ground link, so the slider is
connected directly to the crank. This inverted
slider-crank is the form of a slider-crank linkage that is often used to
actuate a hinged joint in construction equipment like a crane or backhoe, as
well as to open and close a swinging gate or door.
Reciprocating
motion, used in reciprocating engine and other mechanism, is back-and forth
motion. Each cycle of reciprocating consists of two opposite motions: there is
a motion one direction and than a motion back in the opposite direction. Each
of these is called a stroke. The term is also used to means the length of the
stroke.
The
stroke length is determined by the cranks on the crankshaft. Stroke can alo
refer to the distance the piston travels. Bore is diameter of the cylinder,
which means that engine displacement is dependent on both the bore and the
stroke of the cylinder.
Parts:
The
principal parts of slider are as follows:
·
Crank:
In mechanical engineering, a bent
portion of an axle, or
shaft, or an arm keyed at right angles to the engd
of a shaft,by which motion is imparted to or received from it.
·
Crank
Pin: in a reciprocating engine, the crank
pins, also known as crank journals are the journals of the big end bearings, at
the ends of the connecting rods opposite to the pistons.
·
Connecting
Rod: In a reciprocating piston engine, the
connecting rod or condor connects te piston to the crank or crankshaft.
Together with the crank, they form a simple mechanism that converts linear
motion into rotating motion and vice versa.
·
Guide
Frame: A frame held rigidly in place by roof
jacks or timbers, with provisions for attaching a shaker conveyor pan line to
the movable portion of the frame; prevents jumping or side movement of the pan line.
·
Slider
or Sliding Block: In reciprocating engine, the slider
is actual the piston that moves in the cylinder.
·
Wrist
Pin: In internal combustion engines, the
gudge on pin or wrist pin is that which connects the piston to the connect rod
and provides a bearing for the connecting rod to pivot upon as piston moves.
·
Crank
Shaft: The crankshaft, sometimes causually
abbreviated to crank, is the part of an engine that translates reciprocating
linear piston motion into rotation.
Simple Harmonic Motion:
In mechanics and physics, simple harmonic motion is
a type of periodic motion where the restoring force is directly proportional to
the displacement. It can serve as a mathematical modal of a variety of motion,
such as the oscillation of a spring. In addition, other phenomena can be
approximated by simple harmonic motion, including the motion of a simple
pendulum as well as molecular vibration. Simple harmonic motion is typified by
the motion of a mass on a spring. When it is subject to the linear elastic
restoring force given by hook’s Law. The motion is sinusoidal in time and
demonmonst a single resonat frequency.
Procedure:
1. Calculate the mobility of the apparatus
using the appropriate equation.
2. Select the desired crank € and
connecting rod (F).
3. Place the selected crank and connecting
rod to the crank holder © and the slider holder (G). record the length of the
crank and connecting rod to the table provided. (NOTE: The length is the
distance between the centre of two holes. Not the total length of the crank and
the connecting rod.)
4. Connect the crank and connecting rod
together using the turning knob (D) as the joint.
5. Rotate the crank to 0°, by rotating
the turning knob. The angle measurement can be read directing from the
protractor (B) provided.
6. Once the crank to 0°, record down
the initial position of the connecting rod using the linear scale provided(A)
7. Slowly rotate the crank of the
apparatus. For every 15° increment, record down the displacement
value for the connecting rod, take the reading up to 180°. (NOTE: the
displacement value is obtained by using the final value minus the initial
value).
8. Repeat the experiment using different
values of rotation radius and connecting rod length.
9. Plot the graph against crankshaft
rotation angle (q) for all the combination.
10. State and discuss the finding shown in
the graph.
Application:
Reciprocating Engine Produce
power
Reciprocating Pump Utilize Pump
Reciprocating Compressor
Crank and slider mechanism is used in engines. Used
to raise and lower auto windows.
Conclusion:
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