| Camshaft is one of the five key components in the automobile engine valve mechanism,and its function is to open and close the valve in time.The camshaft works under the environment of high pressure,vibration and periodic impact load,and the surface of the cam is easy to wear,which affects the working efficiency and service life of the engine.Therefore,it is important to improve the wear resistance of the material and then improve the performance of the engine.In this paper,based on the existing Fe-Cr-Mo-Si-C-P Fe-based powder metallurgy cam material,the effects of load and speed on friction and wear properties of materials in oil lubrication are first studied,so as to determine the test load and speed;then based on that,the effects of C,Cr and B on the friction and wear properties of materials are discussed in order to optimize the material composition;finally the friction and wear properties of cast iron,powder metallurgy and steel cam materials under the same experimental conditions are measured,and the wear mechanism of the said cam materials are also analyzed.The conclusions are as follows:(1)The designed speed is 500r/min and the designed load is 300N-900N:when the load is 500N,the running time of the material is 750s;the friction coefficient is 0.086,which is the lowest;the wear volume is 0.0131mm3.500N is chosed as the test load.The wear mechanism of the material is mainly abrasive wear.(2)The designed load is 500N and the designed speed is 500r/min?2000r/min:when the rotational speed is 1500r/min,the running time of the material is 500s;the friction coefficient is 0.1;the wear volume is 0.0095mm3.1500r/min is chosed as the test speed.At low speed,the wear mechanism is mainly abrasive wear.At high speed,the wear mechanism is abrasive wear and adhesive wear.(3)The designed content of graphite is 0%-2.6%:when the content of graphite is 2.2%,the material density and higher hardness are respectively 7.66g/cm3 and 52HRC;the friction coefficient is 0.0075,which is the lowest;the wear volume is 0.012mm3.It is indicated that 2.2%C is the best content of graphite.With the increase of graphite content,the wear mechanism of materials mainly changes from adhesive wear to abrasive wear..(4)The designed content of chromium is 5%-9%:when the content of chromium is 6%,the material density and higher hardness are respectively 7.559g/cm3 and 51.5HRC;the friction coefficient is 0.0379;the wear volume is 0.1502mm3,which is the lowest.It is indicated that 6%Cr is the best content of chromium.With the increase of chromium content,the wear mechanism of materials mainly changed from adhesive wear to abrasive wear.(5)The designed content of boron is 0%?0.3%:when the content of boron is 0.1%,the material density and higher hardness are respectively 7.565g/cm3 and 53.5HRC;the friction coefficient is 0.0704;the wear volume is 0.006mm3,which is the lowest.It is indicated that 0.1%B is the best content of boron.Without boron element,the wear mechanism of the material is mainly adhesive wear.The wear mechanism of the material is mainly abrasive wear when the material contains boron element.(6)Compare with cast iron and steel cam materials,PM cam material with 0.1%B has the best wear resistance.It has the shortest running-in period of 30s,moderate friction coefficient of 0.0704,and the lowest wear volume of 0.006 mm3.The wear volume of cast iron cam material is 6157 times more than that of PM and the wear volume of steel cam material is 1.8 times more than that of PM.The wear mechanism of PM cam material is microploughing and slight flaking pitting.The wear mechanism of cast iron cam material is severe abrasive wear and adhesive wear caused by plastic deformation.The wear mechanism of steel cam material is microploughing and severe flaking pitting. |
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