Piston ring is one of the key parts of the engine, and its performance directly affects the performance of the engine. At the same time, the piston ring is a vulnerable parts, overhaul the piston ring, usually to lift the piston, therefore, often repair or replace the piston ring as the engine’s first overhaul period.
In recent years, due to the development of the engine to the direction of high speed and strengthening, the working condition of the piston ring is more and more harsh.
Wear of piston ring and its influencing factors in North Baotou heavy duty truck
The wear of piston ring and cylinder liner of automobile engine has the following characteristics:
1 piston ring in the upper and lower stops between reciprocating motion, the speed changes from the static state to the highest 30m/s or so, so repeated changes.
2 reciprocating motion, in the working cycle of the intake, compression, work and exhaust stroke, the cylinder pressure varies greatly.
3 because of the burning process, the movement of the piston ring is often in high temperature, especially the first gas ring, chemical produced in high temperature and high pressure and combustion products, it is difficult to establish oil film, to achieve full lubrication is more difficult, and often in critical lubrication.
According to the wear mechanism, piston ring wear can be divided into normal wear, wear and tear (scratch, scratch), abrasive wear and corrosion wear. However, these wear phenomena do not exist alone, but exist and interact with each other. According to the wear parts, piston ring wear can be divided into sliding surface wear and upper and lower end wear. Generally speaking, the sliding surface wear is bigger than the upper and lower end surface, the sliding surface is mainly abrasive wear and abrasive wear; the upper and lower end of the piston to do reciprocating motion caused by the impact of wear and tear.
The maximum wear of piston ring sliding surface often appears on the top of the cylinder, because it is affected by the high temperature gas, and the oil film is damaged. The so-called normal wear actually involves a slight wear and abrasive wear. The ring sliding surface wear is the same, the first gas ring wear is the largest, the second ring is about half of the first, the minimum amount of oil ring wear. For example, packed in WD615 engine piston ring after 500h reliability test, the first gas ring gap wear is 0.4 ~ 0.6mm, second gap wear is 0.25 ~ 0.4mm, the oil ring gap wear is 0.3 ~ 0.55mm. But sometimes the oil ring wear is larger than the middle ring, which is due to the influence of the surface of the cylinder oil distribution and adsorption of impurities.
On the lower end of the piston ring wear is mainly because the mechanical grinding oil fuel of rigid residue and from the atmosphere into the dust particles formed on the lower end, is the essence of abrasive wear. However, when the abnormal thermal deformation of the piston and the gap of the annular groove become smaller, the wear may occur.
Many factors affect the piston ring wear, the piston ring material and shape, cylinder piston material and structure, lubrication and engine structure, operating conditions, fuel oil and lubricating oil quality is the main factor. Of course, in the same cylinder, the lubrication state of the piston ring wear is the largest, it can be said that the wear of the piston ring to a large extent depends on the state of lubrication. The ideal torus between lubrication for two sliding surface with a uniform layer of oil film, but this fact does not exist, especially the first gas ring, due to high temperature, it is difficult to establish ideal lubrication state.
Piston ring grinding measures
There are many factors that affect the wear of piston rings, and these factors are often intertwined. In addition, the type of engine and the use of different conditions, the piston ring wear also have very big difference, thus not only by improving the structure of piston ring and the material itself to solve the problem, mainly to begin from the following aspects: piston ring and cylinder sleeve material and good matching; surface treatment; structure; lubrication oil and additive; because the assembly and the operation of heating in cylinder sleeve and piston deformation etc..

The following is the main material, structure and surface treatment measures.
1 choose the material with good performance
To reduce wear, as the piston ring material, must first have good wear resistance and oil storage. In general, must be the first gas ring wear more than the others, therefore, it is necessary to use especially good at keeping oil film without destruction of materials. One of the reasons for the cast iron with graphite structure is that it has good oil storage and wear resistance.
In order to further improve the wear resistance of piston ring, alloy elements can be added into different kinds and content in iron, such as chromium molybdenum copper alloy is commonly used in engine casting hoop, abrasion resistance and oil storage both showed obvious advantages.
In short, the material used in the piston ring is the best to form a reasonable soft substrate plus hard phase of the wear-resistant structure, so that the piston ring in the initial wear is easy to wear, after running and difficult to wear.
In addition, the piston ring with the material of the piston ring wear also has a great impact. Generally speaking, the hardness of the grinding material is zero, and the wear is increased with the increase of the hardness difference. However, in the material at the same time, it is best to have the premise of long life in two parts, so that the piston ring cylinder before reaching the wear limit, this is because the change of the piston ring cylinder sleeve is economical and easy to replace.
For abrasive wear, in addition to hardness, but also consider the flexibility of the piston ring material, toughness of the material is difficult to wear, wear resistance is also high.
2 structural shape improvement
For decades, domestic and foreign structure of piston ring made many improvements, the most significant of the top ring into the barrel surface ring effect. Because the surface of the bucket has a series of advantages, in terms of wear, the barrel surface, whether upward or downward movement, the oil can rely on the role of oil wedge floating ring to ensure good lubrication. In addition, the bucket face ring can avoid edge load. At present, it has been widely used in the diesel engine as the first ring, and other types of diesel engines are also widely used in the bucket face ring.
As for the oil ring, both at home and abroad is now widely used in supporting the spiral spring cast iron oil ring has great advantages, the flexible oil ring itself is very good, has excellent adaptability to the casing after deformation, which can maintain good lubrication, reduce wear.
In order to reduce the wear of the piston ring, the structure of the piston ring should be matched reasonably to maintain the good sealing and lubricating film.
In addition, in order to reduce the wear of the piston ring, the structure of cylinder and piston to a reasonable design, such as the Baotou beiben accessories WD615 engine cylinder adopts the structure of platform screen, in the process of running, the contact area of the cylinder and the piston ring is reduced, can keep the liquid lubrication, the wear volume is very small; furthermore, the from the oil storage tanks, improve Baotou beiben ability, parts of cylinder lubricating oil to keep it is favorable to reduce the wear of piston ring and cylinder sleeve. Now the engine is widely used in the shape of the cylinder sleeve structure. In order to reduce the wear and tear of the upper and lower ends of the piston ring, the proper clearance between the piston ring and the ring groove should be maintained to avoid excessive impact load. In addition, the piston ring groove wear resistant austenitic cast iron lining, but also can reduce the wear of the upper and lower ends, but this method is not necessary in addition to the special promotion. Because it is difficult to master the process, the cost is also high.

3 surface treatment
The method of reducing the wear of piston rings is to carry out surface treatment. Many of the surface treatment methods used now, in terms of their role, can be summarized as the following three categories:
Improve surface hardness to reduce abrasive wear. That is, a very hard metal layer is formed on the working surface of the ring, so that the soft cast iron abrasive is not easy to be embedded on the surface, and the wear resistance of the ring is improved. Now the most widely used is the loose hole chrome, chrome plated layer is not only the hardness (HV800 ~ 1000), the friction coefficient is small, and the loose hole chrome layer has good oil storage structure, which can significantly improve the wear resistance of piston ring. In addition, low cost, good stability, in most cases have better performance.
The high speed or strengthen the engine, the piston ring should not only cylindrical surface chrome, and upper and lower end surfaces to the chrome plating, reduce wear of surface, all rings outside the park on top of all the chrome plating, to reduce wear of the piston ring group.
To improve the oil storage capacity and resistance to melting of the piston ring working surface to prevent wear and tear. Piston ring lubrication oil on the surface of the membrane was destroyed at high temperatures, sometimes the formation of dry friction, if applied a layer of surface coating and oil storage – weld on the surface of piston ring, can reduce weld wear, improve the ability of anti scuffing ring. The piston ring has a very high resistance to wear and tear. On the one hand, due to the spray coating is a porous structure of the oil storage structure coating; on the other hand, the melting point of molybdenum is relatively high (2630 degrees C), dry friction can still work effectively. In this case, the chromium plated ring has higher resistance to melting. Such as the R4100 type diesel engine, start with chrome ring, found the piston ring cylinder, the molybdenum spraying ring basically solves the problem. However, the abrasive wear resistance of the molybdenum ring is worse than that of the chromium plated ring. In addition, the cost of the molybdenum ring is higher and the structural strength is difficult to be stable. Therefore, unless it is necessary to spray molybdenum, the best use of chromium plating.
Surface treatment to improve initial run in. This surface treatment is a layer of soft material covering wearing appropriate degree and elastic on the surface of piston ring, the ring and the cylinder sleeve protrusion contact accelerated wear, so as to shorten the running in period, the ring is good into a stable working state. At present, the phosphating treatment is more commonly used. The formation of a soft, easy to wear the phosphate film on the surface of piston ring, the phosphating treatment required simple equipment, convenient operation, low cost and high efficiency, so the piston in the small engine technology widely used. In addition, tin plating and oxidation treatment can improve the initial run in.
In the surface treatment of piston ring, chrome plating and molybdenum spraying are the most popular methods. In addition, according to the type of engine, structure, use and operating conditions are also used other surface treatment methods, such as soft nitriding treatment, curing, filled with Fe3O4, etc..
The wear of piston ring is a complex phenomenon, the formation of many factors, and often complex intertwined, therefore, to solve the problem of wear of piston ring, we must make a comprehensive analysis of various factors, in order to design, materials, manufacturing process, surface treatment and lubrication aspects of reasonable arrangement, finally achieve satisfactory results.