Abstract: The main failure modes and damage characteristics of engine components are briefly described. A variety of commonly used surface engineering techniques are introduced to improve the wear resistance, corrosion resistance and fatigue resistance of engine components.
Keywords: surface engineering engine repair
Foreword
The engine is one of the main power machinery in industrial and agricultural production, and has been widely used in ships, automobiles, airplanes, engineering and construction machinery. With the development of the industry, the requirements for the engine are getting higher and higher. Due to the high load and high parameters, the operating conditions of the engine are more severe, causing damage and failure of the engine components, thus affecting the reliable operation of the engine.
The manifestations of engine damage and failure are diverse and are mainly manifested in the following aspects:
(1) Wear. Wear is a major factor limiting the service life of the engine and its components. It depends on the degree of wear of the cylinder liner, piston, crankshaft, bearing and other components.
(2) The abrasion of the friction pair and the pulling of the cylinder may cause a major accident, which may have adverse consequences.
(3) Damage caused by the structural strength of the engine is also an important factor affecting the reliability and durability of the engine. For example, crankshaft fracture, connecting rod fracture, piston fracture, cylinder liner fracture, piston cracking, cylinder head crack, frame breakage, bearing bush burnout, journal napping, transmission gear damage, etc. Damage to the strength of these structures is a damage characterized by fatigue damage.
(4) Cavitation, ablation and other damage may occur in individual parts of the engine.
In summary, the damage of engine components can be roughly classified into two cases: one is the damage caused by the mechanical stress caused by the volume load, such as cracks, fractures and impermissible deformation; the other is the surface mechanical or chemical The role of causing damage, corrosion, ablation and other damage.
Forms and characteristics of engine component damage
Faults in the engine due to wear and tear account for a large proportion of various faults. Poor lubrication, poor pairing materials, poor manufacturing and assembly quality, deterioration in service conditions, dust and temperature effects, and alternating load effects all contribute to the four main forms of wear: abrasive wear, adhesive wear, corrosion Wear and surface fatigue wear [3] occur to varying degrees during the operation of some major parts of the engine.
1.1 Damage to the cylinder liner, piston and piston ring set
The cylinder liner, piston, and piston ring set are the heart parts of the engine and are also extremely harsh working conditions. In summary, the damage forms of the cylinder liner, piston and piston ring group are wear, corrosion, cavitation, crack, ablation and the like.
(1) Damage to the cylinder liner
The wear rate of the cylinder liner determines the overhaul interval of the engine. Generally, the maximum allowable wear amount of the cylinder liner is 0.4% to 0.8% of the inner diameter. The surface quality of the cylinder liner, the quality of the fuel oil, the quality of the lubricating oil, the temperature of the cooling water and the working conditions will have a great influence on the wear of the cylinder liner [6], resulting in wear, cylinder and cavitation of the cylinder liner. Damage, resulting in unstable engine speed, increased vibration, noise, white smoke or black smoke.
(2) Damage to the piston
The working conditions of the piston are poor, especially the top is the part with the most serious mechanical and thermal loads. The main forms of damage are cracks, fractures, ablation and corrosion.
(3) Damage to the piston ring
The wear rate of the piston ring determines the length of the engine overhaul cycle. It suffers from bending, impact and wear in high temperature and high pressure gas environment, and is prone to breakage and excessive wear, which leads to a decrease in sealing performance and further deteriorates engine performance [8].
1.2 damage to the cylinder head
The cylinder head has a complicated structure, and has inlet and exhaust valve holes, an indicator hole, a safety valve hole, a starting valve hole, a fuel injector hole, etc., and a series of irregularly shaped cooling water chambers and inlet and exhaust passages therein. The horizontal and vertical directions are respectively connected to the intake and exhaust pipes and the fuselage. The working conditions are relatively harsh. The bottom (hot) surface is affected by the high temperature, high pressure and corrosion of the gas. The water interlayer is also corroded by the cooling water, and the cold and heat are uneven, the force is complicated, and other parts of the cylinder head are also Mechanical stress is generated by tightening the bolts. The main forms of damage are: cylinder head cracks, valve seat damage (valve seat distortion, wear, cracks, etc.).
1.3 Cam tappet damage
A cam tappet is one of a pair of friction pairs in the engine that often wear out. As the engine continues to develop at high speed, high power, the spring force of the valve train, and the relative sliding speed between the friction surfaces, the lubrication conditions between the cam tappets are more severe. The main form of damage is scratches and pitting caused by adhesive wear and fatigue wear.
1.4 crankshaft damage
The crankshaft is one of the most important components on the engine, and it is subjected to bending, torsional loads and certain impact loads during operation. The reliability and longevity of the crankshaft largely determine the reliability and longevity of the engine. The main forms of crankshaft damage are: (1) wear of the journal; (2) cracks and fractures of the fillet at the crank pin or the main journal connected to the crank arm; (3) cracks and breaks in the crank pin or the oil neck of the main journal (4) Fracture caused by corrosion; (5) Slippage of the combined crank cylinder liner; (6) Cracks and strains on the crankshaft surface caused by burning of the tile; (7) Bending and twisting of the crankshaft.
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