| The engine valve which works under high temperature, high impact, high frictional wear and corrosion environment is a key part of valve-train engine, which needs high temperature alloy steel with high temperature strength, high impact toughness and good thermal shock resistance. Although many new valve materials frequently developed at domestic and abroad,and prices increase fast. Though these new materials show excellent performance, they can’t meet the valve tough working condition resulting by the increasing demand of output power of engine. It is an effective method to improve the performance of the valve and control the cost by strengthening the different surfaces of parts base on the working condition such as depositing high temperature resistance alloy on the plate of valve, plating high hardness Cr layer on the surface of valve stem and quenching a cap-like hard layer on the valve top.In this paper the stress and the temperature field distribution of CP169 valve were carried out by simulation and hardness analysis method, respectively. The reasons lead to the failures of the former products made by Huaiji Dengyun Auto-parts Company is analyzed. In addition,this dissertation researches strengthening surface of the CP169 valve, such as conical surface of valve head, the valve stem and valve rod end face. The conclusion shows as follows:The temperature of valve at work was tested. The highest temperature is 575℃ which is at the base of the valve plate, the second high temperature is 530℃ which is at the R position of valve. Valve stem working temperature is under 200℃. According to the actual situation,these parts form thermal fatigue because of alternate hot and cold work temperature. Valve of the maximum tensile stress is 121 MPa appears in the valve head R position; maximum compressive stress is 56.3 MPa appears on the contact region of valve seat and valve cone.The valve presents fatigue stress when works as repeatedly high speed open and close.Statistical analysis of the mode and reasons of the failure valve has be done in this paper especially the surface failure of the valve. This paper puts forward the prevention and control approach- is to strengthen the valve surface.The T400 super-hard cemented carbide layer was welded on conical surface of valve head instead of Stellite alloy layer. The flaw of welding with T400 on 4Cr10Si2 Mo had been solved by many times technological test optimize, such as gas pocket, slag inclusion and incomplete joint penetration.The surface crack is also found at welding valve with T400 powder, because of tensile stress. And this flaw was solved by induction heating. According to the characteristics of the valve, this topic developed a rapid detection method of the stress of valve head.Study on CP169 valve surface treatment with thick chromium plating, it using tubular anode high-speed hard chromium plating technique. This method greatly improving the thickness uniformity of valve stem chromium plating layer, reduced the precision grinding after chrome plating and the production cost.Investigation and study on CP169 valve, this paper proposed improved Measure, which found that cap-like quenching process is poor reinforcement and not up to standard. Since the implementation of improvement measures, the cap-like quenching process of CP169 valve meet customer requirements, namely the CPK is higher than 1.33.After a variety of bench test is carried out in engine plant which is use CP169 valve with the improved surface strengthening process, the CP169 valve is stable and reliable within the stipulated time. Followed by small batch supply also completely satisfying the requirements of customers. Now the CP169 valve is bulk supply, because comprehensive performance of the CP169 is completely same as the imported valve. |
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