What is piston?
Piston is a part of an automobile engine, Piston, together with other details such as cylinders and cylinder caps, forms a combustion chamber, and at the same time transmits the force of the gas to the connecting rod, as well as the piston receiving force from the connecting rod to compress the air. In addition, in some 2-stroke engines, the piston is also responsible for opening and closing the intake and exhaust ports of the distribution mechanism.
Piston working conditions
The working conditions of the piston are very harsh, namely:
The load of the dynamic force is large and periodic:
– High pressure, can be up to 420 kg/cm2 or more
– Large force of inertia, especially in high-speed engines
High thermal load
Due to direct contact with combustible gas with a temperature of 2200 – 2800 K, the piston top temperature can reach 500 – 800 K. Due to high temperature, the piston is reduced in strength or stuck, cracked, reducing the coefficient of friction. kill, detonate…
Great friction and chemical corrosion
Due to the horizontal force N, there is a large friction between the piston and the cylinder. Lubrication conditions here are very difficult, usually just by splashing, so it is difficult to ensure perfect lubrication. On the other hand, due to frequent direct contact because the combustion product has corrosive substances such as hydrochloric acids, the piston is also subject to chemical corrosion.
Piston’s Crafting Materials
Piston materials must meet its working conditions, which are high strength, high temperature resistance, small band deformation, small friction. Of course, there is no material that meets the above requirements at the same time. Therefore, it is necessary to choose the most optimal material, compared with cast iron alloy, aluminum alloy has lower strength, greater long deformation, but aluminum alloy has a smaller density and also has good castability like cast iron. Therefore, aluminum alloy is chosen as the piston material. The material for making the piston must ensure that the piston works stably and for a long time in the harsh conditions mentioned above. In practice, several of the following materials are used to make pistons.
– Cast iron: Usually gray cast iron, ductile iron, and cast iron are used. Cast iron has high heat resistance and durability, the coefficient of expansion is small, so it is difficult to get stuck, easy to manufacture and cheap. However, cast iron is very heavy, so the inertia force of the piston is convex. Therefore, cast iron is only used to make low-speed dynamic pistons. On the other hand, the thermal conductivity of cast iron is small, so the piston top temperature is high.
–Steel: Steel has high strength, so it must be light. However, the coefficient of thermal conductivity also remembers and is difficult to cast, so it is rarely used today. Some companies used steel to make pistons such as Ford (USA) or Junkcr (Germany) during World War II.
– Aluminum alloy: Aluminum alloy has many advantages such as lightness, large coefficient of thermal conductivity, coefficient of friction with cast iron (the cylinder is usually cast iron), easy to cast, easy to process, so it is very popular for processing. create pistons. However, aluminum alloy has a large coefficient of expansion, so the clearance between the piston and the cylinder must be large to avoid jamming. Therefore, a lot of air leaks from the combustion chamber to the crankcase, the engine is difficult to start and works with a knock when the piston changes direction. At high temperatures, the strength of the piston decreases quite a bit. On the other hand, the piston is made of aluminum alloy with poor wear resistance
Depending on the output, the structure of the piston and the specific production conditions of the factory, there are different technological processes when manufacturing.
The machining process is performed in order according to the following basic jobs:
1- Cut off the beans of the cast.
2- Heat treatment: heat in boiling oil at a temperature of 200 ¸ 250C for 5 hours.
3- Sub-standard machining.
4- Rough machining of piston pins.
5- Rough turning of the outer surface and grooves.
6- Turning vertical lengths and grooves.
7- Semi-finished processing of dowel holes (drilled).
8- Drill the knife exit holes on the body.
9- Drill the oil drain holes on the oil sleeve sec groove.
10- Milling groove hatching room.
11- Drill the correct pin hole, chamfer the edge of the hole.
12- Correctly grinding the piston body (machining the oval and cone of the piston body if any).
13- Turning the locking grooves.
14- Cold fix sharp edges.
15- Total check, size classification and weight.
16- Packaging for preservation.In the video below, we can see Manufacturing of Truck Engine Piston Complete Process in Factory – Production Truck Engine Piston
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Video resource: Amazing Technology
