Today, I am going to discuss Crank. If you are looking to know a short and sweet article on the What is crank?, its types with Pictures, Working and all. This is the place for you.
Stick with me and I will take you to the mainstream of the same.
Before I start, Let me give you the definition first…
So, Dive in…
What is a Crank?
A crank is a machine element that converts rotating motion into reciprocating motion and vice-versa.
It is mainly used in internal combustion engines (I.C. engines) and steam engines where the reciprocating motion of the piston, is converted into the rotary motion of the crankshaft by means of a crank.
Cranks are situated on one side of the crankshaft, so they are balanced by counterweights.
Types of Crank-
There are three types of cranks, listed and described below-
- Overhung crank
- Disc crank
- Centre crank or side crank
1. Overhung Crank-
Overhung crank has two ends whose one end is rigidly fixed to a shaft by means of a key and the other end overhangs like a cantilever so that it is called Overhung Crank.
It is made of forged steel.
The crank pin is fitted to the crank arm by a rivet or by a press fit or shrinkage fit.
An overhung crank is generally used in medium and large horizontal engines.
2. Disc Crank-
It has a shape of a disc. From the centre of the disc, a crank pin is fixed at some distance. It works like an overhung crank.
The disc is made thicker at the place where the crank pin is fixed and the rest of the disc is made thinner in order to balance the weights of the crank pin and connecting rod whose big end is fitted to the crank pin.
Disc crank is mostly used for high-speed and medium-speed engines.
3. Centre or Side Crank-
A centre crank has crank arms on both sides of the crank pin. So it is called a centre crank.
Crank arms are connected to the crankshaft which is supported by bearings.
Centre cranks are used in multi-cylinder engines in which two or more cylinders produce power at a single crankshaft.
Working of Cranks-
A piston moves in a cylinder with a reciprocating motion. The piston is connected to one end of a piston rod whose other end is connected to the cross-head which slides between guides with a reciprocating motion.
The cross-head is connected to the small end of a connecting rod whose big end is connected to the crank through the crank pin. The other end of the crank is connected to the crankshaft.
The piston moves between two extreme positions P1 and P₂ in the cylinder. These two extreme positions P1 and P2 are called outer dead centre (ODC) and inner dead centre (IDC) respectively.
As the piston moves towards P2, the crank moves in a clockwise direction. When the piston reaches P2, the crank pin comes to point C2.
The distance between P1 and P2 is called piston stroke and C1 to C2 is called crank throw.
When the piston moves from its extreme position P₂ back to P1, the crank pin moves clockwise in a circular path.
This imaginary circular path on which the crank pin moves is called the Crank pin circle. When the piston reaches its extreme position P1, then the crank pin reaches point C1.
In this way, the piston moves in the cylinder from P1 to P₂ with a reciprocating motion and the crank moves from C1 to C2, with a circular motion.
Similarly, the circular motion of a prime mover can be converted into reciprocating motion by means of a crank. For example, reciprocating pump, reciprocating compressor, etc.
So we can say that crank is such a lever which can convert reciprocating motion to rotary motion and rotary motion to reciprocating motion.
Material and Manufacturing Methods of Crank and Crankshaft-
The crank is normally made of cast iron, wrought iron or steel. For special purposes, it is made of cast-iron alloys and alloy steel.
Cranks and crankshafts are generally made by casting and forging processes.
Small crankshafts are made by the drop forging process whereas large crankshafts are made by the forging process.
Crankshafts of complicated shapes are made in permanent moulds by the casting process. Crankshafts prepared by the above processes are machined and ground to bring them to finished sizes.
At last, the crankshaft is tested for its strength and balance.
Applications of Cranks-
Here are some of the main uses or applications of cranks-
- Multi-cylinder automobile engines such as cars, trucks, buses, etc.
- IC Engines
- Marine Engines
- Locomotive Engines
- Steam Engines
⇒Must Read: CAMSHAFT VS CRANKSHAFT: All you need to know
Examples of Cranks-
Here are some of the major and everyday life examples of cranks-
- Sewing Machine
- Cycle Peddle Unit
- Fishing Rod
- Manual Handle for Car window opening in car interior
- Hand bicycles for Handicaps
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Abhishek Tiwary is a blogger by passion and a Quality Engineer by profession. He completed his B.Tech degree in the year 2017. Now working in a reputed firm. He loves to share his knowledge with others.