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.

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.

  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.

                

    Stroke:

       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:

___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________