Experiment No.3
Objective:
To perform quick return mechanism on the slider crank apparatus.
Apparatus:
Crank, Connecting rod, Block, Slider
Theory:
Quick-Return mechanim:
A quick return mechanism such as the one seen below is used where there is a need to convert rotary motion into reciprocating motion. As the disc rotates the block slide moves forwards and backwards. Many machines have this type of mechanism and in the school workshop the best example is the shaping machine.
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 pista 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 demonstrate a single resonant frequency.
Procedure:
In this mechanism, there is a block, a link wire and a connecting rod. The connecting rod connect the crank to the block. If the crank moves, the block also moves. The motion of the block is like a piston which moves upward and downward. The quick return mechanism is a bit different from the slider crank mechanism. In this method the slider does not completes its movement in the slider area.
Application:
Its major application is in shaper machine, where cutting is done at some specified angle.
A shaper is a type of machine tool that uses linear relative motion between the workpiece and a single-point cutting tool to machine a linear toolpath. Its cut is analogous to that of a lathe, except that it is (archetypally) linear instead of helical. (Adding axes of motion can yield helical toolpaths, as also done in helical planning.) A shaper is analogous to a planer, but smaller, and with the cutter riding a ram that moves above a stationary workpiece, rather than the entire workpiece moving beneth the cutter. The ram is moved back and forth typically by a crank inside the column; hydraulically actuated shaper also exist.
Table:
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Crank position angle(degree) |
Linear position |
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Graph:
Conclusion:
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