Explain single slider-crank mechanism.

Short Answer:

A single slider-crank mechanism is a type of four-bar linkage used to convert rotary motion into reciprocating motion or vice versa. It consists of four main parts: the frame, crank, connecting rod, and slider. The crank rotates continuously, while the slider moves back and forth in a straight line within the guide.

This mechanism is commonly used in internal combustion engines, compressors, and pumps. When the crank rotates, the connecting rod transmits motion to the slider, causing it to move in a reciprocating manner. It is a simple and efficient mechanism widely used in mechanical systems for motion transformation.

Detailed Explanation:

Single Slider-Crank Mechanism

A single slider-crank mechanism is one of the most fundamental mechanisms used in machines for motion conversion. It is a modification of a four-bar chain in which one of the turning pairs is replaced by a sliding pair. This mechanism converts rotary motion into reciprocating motion or reciprocating motion into rotary motion, depending on the application.

In its simplest form, the single slider-crank mechanism consists of the following parts:

  1. Frame (Fixed Link):
    It is the stationary part of the mechanism that supports other links. It provides a fixed axis of rotation for the crank and a guide for the slider to move back and forth.
  2. Crank:
    The crank is the rotating link that turns about a fixed point. It receives rotary input and transmits motion to the connecting rod. The crank is usually the shortest link in the mechanism and is responsible for initiating motion.
  3. Connecting Rod (Coupling Link):
    The connecting rod connects the crank to the slider. It transmits motion and force between these two links. Its motion is both rotational and translational, depending on the crank position.
  4. Slider:
    The slider is the link that moves in a straight line along the guide of the frame. It is connected to one end of the connecting rod through a pin joint and moves back and forth as the crank rotates.

Working Principle

When the crank rotates about the fixed axis, it drives the connecting rod, which in turn pushes or pulls the slider. This causes the slider to move linearly inside the guide. When the crank rotates through a complete revolution, the slider completes one full reciprocating cycle.

  • During the forward stroke, the crank rotates in one direction and pushes the slider forward.
  • During the return stroke, the crank continues its rotation and pulls the slider backward.

Thus, continuous rotary motion of the crank results in a continuous reciprocating motion of the slider.

This mechanism can also work in reverse. If the slider is given a reciprocating motion (as in a reciprocating engine), the connecting rod will cause the crank to rotate, converting linear motion into rotary motion.

Applications

The single slider-crank mechanism is used in many practical applications, including:

  1. Internal Combustion Engines: Converts the reciprocating motion of the piston into rotary motion of the crankshaft.
  2. Reciprocating Pumps and Compressors: Converts rotary motion of the crankshaft into reciprocating motion of the piston to compress or move fluids.
  3. Steam Engines: Used to convert reciprocating motion of the piston into rotary motion of the flywheel.
  4. Automobiles: Used in the piston-cylinder arrangement of engines.
  5. Mechanical Presses: Used to produce linear motion for shaping or cutting materials.

Inversion of Single Slider-Crank Mechanism

By fixing different links of the single slider-crank chain, different mechanisms can be obtained. The inversions are:

  1. First Inversion – Reciprocating Engine Mechanism:
    The frame is fixed, and the crank rotates to drive the slider back and forth. Example: Internal combustion engine.
  2. Second Inversion – Rotary Engine Mechanism:
    The connecting rod is fixed, and both the crank and frame rotate around it. Example: Rotary I.C. engine.
  3. Third Inversion – Oscillating Cylinder Mechanism:
    The crank is fixed, and the cylinder (slider guide) oscillates. Example: Cradle-driven steam engine.
  4. Fourth Inversion – Hand Pump Mechanism:
    The slider is fixed, and the crank rotates to create an oscillating motion of the connecting rod. Example: Hand-operated reciprocating pump.

Advantages

  • Converts rotary motion into linear motion effectively.
  • Simple design with fewer moving parts.
  • Provides a strong and continuous motion transmission.
  • Can be used in both directions (rotary to reciprocating or vice versa).

Limitations

  • The motion of the slider is not perfectly harmonic.
  • Frictional losses occur due to sliding contact.
  • The connecting rod and crank arrangement requires proper alignment to avoid mechanical imbalance.
Conclusion

The single slider-crank mechanism is a vital element in mechanical engineering, forming the basic structure for engines, compressors, and pumps. Its simple design and effective motion conversion make it one of the most widely used mechanisms in machines. Understanding its components, working, and inversions helps in analyzing and designing motion systems efficiently.