The piston is the "heart" of the car engine. It is subject to alternating mechanical and thermal loads and is on of th most critical parts  of the

engine.

      Piston types are generally divided into: diesel engine piston, gasoline engine piston,general piston.

      The function of the piston is to withstand the pressure of the gas and transmit it to the connecting rod through th piston pin to drive the

 crankshaft to rotate. The top of the piston is also a component of the combustion chamber.

      Working condition piston in high temperature.
      Rodless cylinder for flexographic press.
      Working conditions.
      The piston works under high temperature, high pressure, high speed and poor lubrication. The piston is directly in contact with the high

 temperature gas, and the instantaneous temperature can reach 2500K or more. Therefore,the heat is severe and the heat dissipation condition

 is very poor, so the temperature of the piston is high, the top is as high as 600~700K, and the temperature distribution is very uneven; The top

 of the piston is subjected to a large gas pressure, especially the maximum pressure of the working stroke, the gasoline engine is as high as 3~5MPa,

and the diesel engine is as high as 6~9MPa, which causes the piston to impact and bear the side pressure; the piston is high in the cylinder. Speed

 (8~12m/s) reciprocating motion, And the speed is constantly changing, which creates a large inertia force, causing the piston to be subjected to

a large additional load. When the piston is operated under such harsh conditions, it will deform and accelerate wear, and will generate additional load

 and thermal stress, while being chemically corroded by the gas. 

      The piston test is mainly measured by the diameter of the skirt, the height of the piston ring groove and the size of the piston pin hole: 

      1.The selection of piston shall be determined according to the repair size of the cylinder. Usually increase the size of the number marked on the

 top of the piston; 

      2. In the same series of fish feeding, the structure of the piston is not necessarily the same, so when purchasing the piston, the corresponding

 type of piston must be selected according to the type of engine. On the same engine,Should use the same brand, the same group or the same

 product code of the piston; the same model must use the same product code piston, to ensure that the piston diameter difference and quality

 difference does not exceed the original factory specifications. Otherwise, it will cause the engine to burn badly, Work rough, fuel economy and

 power performance decline and other failures. Therefore, in the selection of pistons, according to the type of engine must choose the

 corresponding 

type of piston.

      Requirements.
      1. It is necessary to have enough strength, rigidity, small mass and light weight to ensure the minimum inertia force.
      2. good thermal conductivity, high temperature, high pressure, corrosion, full heat dissipation, heating area is small.
      3. There should be a small friction coefficient between the piston and the piston wall.
      4. When the temperature changes, the change of size and shape should be small, and the gap between the cylinder walls  should be kept to

 the minimum. 

      5.The coefficient of thermal expansion is small, the specific gravity is small, and it has good wear resistance and thermal strength. 

      Piston structure.
      The whole piston can be divided into three parts: the piston top, the piston head and the piston skirt.
      The main function of the piston is to withstand the combustion pressure in the cylinder, and this force through the piston pin and connecting

 rod to the crankshaft. In addition, the piston and cylinder head, cylinder wall together constitute a combustion chamber. 

      The piston top is part of the combustion chamber and is often made into different shapes. The piston of gasoline engine adopts flat top or concave

 top at most in order to make the combustor compact, the area of heat dissipation is small and the manufacturing process is simple. Protruding pistons are

 commonly used in two-stroke gasoline engines.

      The piston crown of a diesel engine is often made into various pits.
      The part between the top of the piston and the lowest groove of the piston ring is called the piston head. Its function is to bear gas pressure, prevent 

air leakage. The heat is transferred to the cylinder wall through the piston ring. The piston head is cut with a plurality of ring grooves for placing the piston

 ring. 

      The top 2 and 3 slots are used to place the air rings, and the bottom 1 and 2 slots are used to install the oil rings. A plurality of small holes are drilled at the

bottom of the oil ring groove through which excess lubricating oil scraped from the cylinder wall can flow back to the oil pan. 

      All parts below the groove of the piston ring are called piston skirts. Its function is to guide the piston in the cylinde rreciprocating  movement and bear lateral 

pressure. When the engine is working, the piston will bend and deform due to the effect of the gas pressure in the cylinder. When the piston is heated, because

 there is more metal in the piston pin, the expansion of the piston is larger than that of other places. In addition, the piston under the action of

lateral pressure will also produce extrusion deformation. As a result of the above deformation, the piston skirt section

becomes the ellipse of the long axis in the direction of the piston pin. In addition, the piston along the axis direction

of temperature and mass distribution are not uniform, resulting in the thermal expansion of each section is up and

down small.
Because the piston of internal combustion engine works under the condition of high temperature, high pressure and

high load, the requirement of piston is relatively high, so the classification of piston of internal combustion engine is

mainly discussed.
1. According to the fuel used to divide, can be divided into gasoline engine piston, diesel engine piston, natural gas

piston.
2. According to the material of manufacturing piston, it can be divided into cast iron piston, steel piston, aluminum

alloy piston and composite piston.
3. According to the process of manufacturing piston blank, it can be divided into gravity casting piston, squeeze

casting piston and forging piston.
4. According to the working condition of the piston, it can be divided into two kinds: unpressurized piston and

supercharged piston.
5. According to the use of piston, can be divided into car piston, truck piston, motorcycle piston, marine piston,

tank piston, tractor piston, lawn mower piston and so on.