Introduction to marine diesel engine parts friction and wear

When the ship's machinery is running, the moving parts with relative motion on it produce friction on the mating surface, causing surface wear. Even under normal operation, the machine performance will gradually deteriorate, the efficiency will be reduced, or even completely fail due to inevitable friction and wear. Therefore, wear is the failure mode of marine machinery and the factor that affects the normal operation of marine machinery and the safe navigation of ships. Friction consumes energy. It is estimated that 1/3~1/2 of the world's energy is consumed in overcoming friction. At present, the fuel consumption rate of marine diesel engine has been reduced to about 163g/(kW · h), the thermal efficiency has reached more than 50%, and the energy consumed in the friction of the moving pair accounts for more than 10% of the lost energy. Therefore, in order to give full play to the efficiency of marine power plant, engineers must learn the tribological knowledge of marine engine parts.

The concept of friction

Friction surface: the surface of the interaction of relative moving parts, that is, the friction and wear of the friction surface is closely related to its surface morphology, surface layer structure and performance.

Morphology and representation of friction surface

The surface of mechanical parts is formed by various mechanical processing. The processing marks on the surface are peaks and valleys of different sizes, heights and shapes, which make the surface rough and uneven. The geometric shape of the part surface is called the surface morphology, which is caused by the final processing method of the surface, the tool mark, the deformation during chip splitting, the friction between the tool and the surface, and the vibration of the processing system.

Concept of wear

During the operation of the machine, the material on the friction surface in relative motion is gradually lost, which changes the size, shape, position accuracy and surface quality of the parts. The wear of parts will change the nature of mating parts and affect the performance and service life of the machine. According to statistics, about 80% of machine parts fail due to wear. In marine machinery, wear is also an important failure mode. For example, the reliability of marine main and auxiliary diesel engines is directly affected by the wear of piston ring-cylinder sleeve, crankshaft-bearing and other important mating parts.