Table 1 Changes in microhardness (Hv) of the cylinder surface Distance from the working plane of the engine to the upper surface of the cylinder block (mm) New engine (initial value) High temperature after engine running-in Heavy load 60h Bench test Using quartz ash 24h Bench test city The deformation and chemical reaction of the metal surface of the internal bus transport 150 in the intercity freight transport resulted in a corresponding change in surface microhardness. If the microhardness of the cylinder surface is changed during the friction process due to changes in the operating conditions, the change values ​​are very different.
Table 1 shows the variation of the microhardness of the cylinder surface with the friction conditions.
It can be seen from the table that due to the different friction conditions of the cylinder, the change of the surface microhardness value reflects the change of the wear pattern of the cylinder and the wear process.
In the top dead center zone of the first ring (ie, the site where the cylinder wears the most), the microhardness changes are most intense. This is due not only to the effects of load and temperature but also to other factors. Sharp changes in microhardness indicate the complexity of the wear process. The microhardness of the cylinder surface (non-friction zone) at a distance of 5 mm from the upper plane of the cylinder is higher than the initial value, mainly due to the phase change caused by the high temperature and high pressure in the combustion process.
During the friction process, metal surfaces undergo cold hardening as a result of plastic deformation, which improves the microhardness of the surface. Whether the surface wear resistance is improved or not depends on the strength of the bonding between the surface strengthening layer and the base metal material. If the surface-reinforced layer is firmly bonded to the matrix material, the resistance to damage of the surface layer is increased. On the other hand, the cold hardening produced during the friction process will aggravate the wear of the friction surface.
From the standpoint of improving the impermeability of the friction surface and the effect of the anti-abrasive effect, the hardness of the friction surface is somewhat higher. Therefore, the commonly used mechanical processing methods strengthen the surface of the part to increase its wear resistance. If any crankshaft journals use surface hardening to improve wear resistance and fatigue strength. However, it cannot be said that the microhardness of the friction surface is always better, and even higher is better, depending on the friction conditions. The surface has a high microhardness and can improve the wear resistance under certain friction conditions.
3 Concluding remarks The above analysis shows that the most important direct cause of the operational reliability and service life of automotive engines is the wear of their components.
When the engine is working, it will inevitably lead to relative movements between the mating pairs, which in turn will cause wear of the parts. There are many factors that affect the wear of engine parts, but mainly the use of factors and the surface quality of the parts. Therefore, in order to effectively suppress wear and prolong the service life of the engine, it is necessary to use the vehicle reasonably, and at the same time, using modern tribology, design scientific parts surface processing technology, and improve the surface quality of the parts.
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