The piston is described along with basic understanding, definition, types, characteristics, functions, advantages, disadvantages, etc.
The piston is an integral part of especially in the reciprocating engines. They are an important aspect of automobile vehicles. Not only in engines it can be found in,
Basically, it is a small moving part enclosed tightly by the piston rings. We will get to know more details of pistons and all the information associated with pistons.
The piston is defined as a piece of metal that works against fluid pressure in a cylinder.
Talking about its shape, it has a cylindrical kind of shape. In case of engine, the piston’s reciprocating motion is converted to a revolving motion for crankshafts. They are made of different materials.
Generally, pistons are made of cast aluminium alloys.
There are other materials as well like,
These materials have high strength and are used according to the requirements. For low-speed application, cast iron is used and for high-speed application, alluminium alloy is used.
So, before knowing more about the piston types and parts, let’s know about the general functions of pistons.
The function of piston are as follows,
So, to get the effective operations as expected from the piston, they need to have some characteristics. Here are some desired characteristics a piston should have for a ideal working operation.
Let’s refer to the main desirable characteristic of the piston, as below:
There are various types of pistons and they are named according to their various working principles and arrangements. We will see the generally used pistons each in brief details.
Let’s know about the parts or components of the pistons.
There are few parts of a piston, as follows:
Let’s try to look at all this in brief,
The piston rings are kind of split rings that are mounted on the recessed area of the piston.
So, what is the function of piston rings? They seal off the combustion chamber and regulate the lubricating oil usage.
Also, they serve to conduct the heat away to the cylinder bore. As we said above there are 3 types of rings used.
Let’s check each one of them.
The compression rings are located at the top side of the piston nearer to the combustion chamber.
Oil Scraper rings
The scraper rings are located in the middle of compression rings and the oil rings.
They have a tapered surface and does the work of sealing the combustion chamber and wipe the oil off from the piston cylinder.
Oil control rings or Oil rings
These are located below the scraper rings. The oil rings consist of two surfaces with holes all around. These slot holes allow the oil to flow back into the sump.
As the piston moves back and forth the oil rings will remove the excess oils from the cylinder walls.
Piston groove means the grooves or the slots where the piston ring fits.
The round section on the piston is known as the piston skirt.
The function of piston skirt is to guide the piston travelling up and down the cylinder. The design is made such that it will help the piston to overcome the side forces.
There are two types of skirts used.
You may have heard the name “Gudgeon Pin” if you ever studied or know about the piston. The Gudgeon pin provides the bearing support and helps piston for functioning properly.
In simple words, it joins the connecting rod and piston-like a pivot joint. There are three methods by which pins can be mounted on the pistons.
The piston head is also known as the piston crown. As the name suggests it is the tope portions of the pistons. The combustion gases come in contact at the piston crown.
As the combustion gases temperature are high hence the piston heads are made of special alloys, steel alloys.
Here are the functions of the piston head.
The place where the pivotal rotations take place the bearings are provided.
Check a nice VIDEO from Habib Mechanics!
There are lots of types of pistons based according to their arrangements and applications.
So here are the generally used types of pistons.
Let’s learn the basic of all these types of piston,
As the name suggests in this type, the piston is offset towards the major thrust side of the piston.
This arrangement helps to reduce wear as well as piston noise.
Mostly, the pistons used are cam ground pistons. These are not perfectly round and the diameter of these pistons is large on the non-thrust side. Because when the piston temperature increases, they tend to expand.
In this oil-cooled type, a cavity is provided underneath the piston crown. Why is that? Because to reduce the piston temperatures at the top ring and prevent carbon formation in the groove.
They are provided in medium and heavy speed diesel engines.
In this type, the crown side of the piston is smaller than the skirt diameter end. When the high temperature comes to the crown the side expands and piston diameter becomes uniform under conditions.
The band of steel wire under the tension is put between the oil ring and piston pin.
These pistons are equipped with the raised pads that are specially shaped and assists the hydrodynamic lubrication.
In these pistons, there is a groove cut near the top of the piston. It will reduce the heat travel from crown to skirt. So, the skirt will run cooler and will not expand much.
These pistons contain low expansion steel inserts at piston pin bosses. When at the higher temperatures the arrangements will cause the piston to expand along with the piston pin.
The contraction occurs in the direction perpendicular to the piston pin due to metallic action.
As the name suggest they are made of two metals. The one is steel and other is aluminium. The skirt is made of steel whereas aluminium cats inside forms piston head and piston pin bosses.
There are some cases, the piston failure can be occurred. So we should know how the usual piston damages and their descriptions.
Energy is produced in the cylinder due to the combustion process. Piston is operating within the cylinder and it is connected to the crankshaft through the connecting rod.
So, after combustion, this energy is transferred to the crankshaft through the connecting rod.
Piston also dissipates the heat produced from the combustion.
Let’s see the step by step working principle of piston.
Step by Step Working Principle
Let’s learn the basic of failures,
The piston scuffing is caused due to excessive heat due to which the piston will expand and become tighter in the cylinder. Due to expansion the lubricant will be squeezed out of cylinder walls causing the metal-to-metal contact.
The burnt piston may be a major cause of detonation and preignitions. In the detonation the gases release tremendous amount of energy. In preignition the burning occus generally near the piston head.
Piston dry run
The dry run piston failure can be caused due to unburned fuel condensation at the cylinder. This results into long narrow friction marks due to interaction of sliding parts.
Piston pin boss damage
When the mechanical overstressing of the piston happens the piston pin boss gets damaged. Also, if the oil supply is insufficient a crack will occur in the piston pin boss and later it will spread evenly on the normal loads, and eventually, the piston will split.
There are many advantages of the piston, as follows:
There are many disadvantages of the piston, as well:
As we have discussed earlier there are wider applications of pistons in lots of machines. The common applications of the pistons are given below.
Hence, we have got a basic idea about what is piston, piston definition, types, different parts, advantages, disadvantages, etc. Any doubt, please let us know.
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