1 parts wear and tear
Friction parts (such as piston and cylinder, crankshaft neck and bearing, etc.) during the working process, the changes in the size, shape, and surface quality of the friction surface are called wear. Wear is an important cause of failure. The wear of diesel engine parts is generally divided into abrasive wear, adhesive wear, corrosion wear, fatigue wear and wear. Abrasive wear is the most common and most common form of wear in fretting wear. Adhesive wear is the most dangerous form of wear.
(1) abrasive wear: abrasive wear is a form of destruction of the surface of a part by hard particles. The diesel engine often works in the field and in the dusty environment, such as the improper maintenance of the air filter (some drivers dismantle the air filter directly), a large number of dust into the cylinder liner and the piston, and increase the wear speed by dozens of times. When the oil is unclean, the main friction parts, such as crankshafts and cylinder liners, are seriously abrasive wear. When the diesel filter is broken and blocked, a large number of impurities in the fuel enter the precision even parts (plunger even, oil valve couple and nozzle couple), cylinder and piston. The wear of dust to the diesel engine is more serious.
(2) adhesion wear: the adhesive pad caused by the contact micro area is characterized by the adhesion of metal from one surface to the other friction surface. The surface of these parts is found to have rough scratching marks on the surface of the parts. In serious case, the local adhesive wear and tear expand and the temperature of the parts is sharp.
When the load is high or the friction temperature is high, the lubrication effect becomes worse. Especially when the lubricating oil is deteriorated, the oil channel is blocked, the friction surface is lacking in lubricating oil, it is most likely to be adhesive wear. If the diesel engine is used and maintenance is used correctly, the general adhesion wear is not easy to occur. However, the defects in manufacturing and repair are not easy to occur. A new diesel engine, such as a new diesel engine, does not have the ability to bear normal load due to the existence of machining marks on the surface of the parts, and the working surface is not able to bear the normal load. It is necessary to remove the adhesive diffusion layer thoroughly, and attempt to remove the bulge in a simple way (for example, using a thin rasp stone for grinding) to restore the friction surface. After assembly, it will often regenerate the adhesive in its original position.
(3) fatigue wear: under the action of contact alternating stress, the surface of the diesel engine is spalling along the shallow layer. The fatigue wear of the diesel engine is usually caused by the inner surface of the crankshaft and the gear tooth surface.
(4) corrosion wear: in the process of wear, there are both mechanical and chemical or electrochemical action, and the wear speed is very high. When the cooling water temperature is below 65 C, the suction of the internal wall of the cylinder liner and the acid gas is formed to form corrosion wear, and the corrosion wear will be formed when the lubricating oil is deteriorated.
(5) fretting wear: a kind of wear phenomenon between the static fittings (thread connection, the outer circle of rolling bearing and the seat hole), a kind of wear phenomenon occurring under the action of variable load vibration. The characteristics of fretting wear are the accumulated and tiny brown iron oxide debris (for iron and steel), and the wear surface has a crush mark outside the wear. Generally this is oxygen. It is diffused to the metal surface to oxidize the surface, and then the oxide film is crushed and shedded. The process is repeated. The result of the fretting wear is to make the part of the original interference fit or become a fatigue source, and cause the fatigue of the parts to be damaged.
2 parts corrosion
Corrosion is one of the common damage phenomena of diesel engine. It can be divided into two kinds of corrosion and aging. Corrosion is mainly caused by chemical or electrochemical action of metal and external medium. Corrosion results make the composition and properties of metals change. The common corrosion on diesel engine is corrosion, acid or alkali corrosion, and high. Oxidation and cavitation erosion at high temperature and pressure. Aging mainly refers to rubber parts, which lose elasticity, brittleness, rupture or decay due to oil or light and heat.
3 fatigue fracture
Under the action of alternating loads, the parts can produce cracks in the micro view. These cracks appear on the surface of the cracks or break the whole part. This phenomenon is called fatigue fracture. Some parts of the diesel engine, such as crankshafts, are mainly damaged by fatigue.
4 friction fixed joint loosening
In order to adjust and disassemble, a large number of detachable connections are used on diesel engines, such as threaded connections, keys and tight fit. These parts rely mainly on the friction between the components to maintain the relative position. If no loosening device or relaxation device is invalid, it is easy to have a long time repeated load (especially alternating load). Loosening. There are several reasons for loosening.
(1) the plastic deformation of the table: the connection strength between the friction fixed parts depends on the friction force between the connecting parts, and the friction force is determined by the elastic deformation of the connector. The plastic deformation may be produced because of the long-term compression of the parts of the connecting part, which reduces the pre stress of the connector, thus reducing the connection strength and loosening of the parts.
(2) the frictional force vanishes instantaneously: when the connector bears the alternating load (especially the vibration load), sometimes the pressure and the variable load of the connector will be counteracted at some moment, which makes the friction close to zero or equal to zero, resulting in the instantaneous drop of the connection strength and the loosening of the connection.
Five the relative sliding of the deformation: the deformation of the screw and nut is different when the load is subjected to the alternating load, and the screw becomes thinner, and then the screw is restored to the original shape, and the nut deformation is small. In this uneven deformation process, the screw and nut may be slid relative to the screw. This sliding force may overcome the friction force and make the static friction force change. As a result of friction, there is a possibility of loosening. The loosening of the friction fasteners caused by these causes will cause serious accidents if they can not be found in time, the cylinder pad is burned down, the body and the outer shell are damaged. Therefore, the connecting parts which bear the alternating load in the work and the connecting parts without the automatic anti loosening device should be checked regularly. Tightness. If it is found, it must be tightened in time.
