| Metal sealed ball valves are widely used in pipeline systems to transport liquid and solid-liquid mixtures.The addition of hard particles in the fluid,will accelerate wear and failure of seals(ball and seat).In order to reduce wear and improve the life of seals,surface spraying or spray welding are often used to increase the surface hardness of the ball to achieve this purpose.Oxy-acetylene flame spray welding is a common ball hardening process,which can produce thicker coatings and achieve metallurgical bonding with the substrate.Coatings with small thickness are produced suitably using PVD technology,which has very small effects on the mechanical performances of the substrate.In this paper,combining the advantages of spray-welding process and PVD technology.Focus on the analysis and research on three types of CrN,Ni60,Ni60 + CrN surface strengthening coatings prepared on ball of Cr-Ni stainless steel(06Cr19Ni10).A ball valve-potential pressure life test bench was designed to test the three types of wear resistance and service life of coating under simulated working conditions.CrN coatings prepared by PVD under different nitrogen pressures and bias voltages have been tested and analyzed to obtain:With the increase of nitrogen pressure,the hardness of CrN coating increases first and then decreases,and the friction coefficient decreases first and then increases.With the increase of bias voltages,the hardness of CrN coating increases first and then decreases,and the friction coefficient decreases first and then increases.When the nitrogen pressure is 1.5Pa and the bias voltage is-200 V,the coating has the highest hardness and the lowest friction coefficient.Test and analysis of the thickness,hardness,roundness,coating adhesion and friction coefficient of the CrN,Ni60,Ni60 + CrN coating.The test results show that CrN can improve the surface hardness and reduce the friction coefficient;Ni60 transition coating has obvious effect on CrN hardness improvement;Ni60+CrN composite coating has the best comprehensive performance;The roundness of the test ball conforms to national standards,It shows that the preparation of CrN coating by PVD no need to process again.Designed and built a ball valve life test equipment,This equipment includes high pressure opening and closing life test and solid-liquid mixed fluid opening and closing life test function.The life test of metal sealed floating ball valve can simulate actual working conditions.In the high pressure opening and closing life test,the ball valve treated by the CrN coating was damaged at the earliest,and the coating was extensively worn.The Ni60 and Ni60 + CrN coatings have passed 5000 high pressure opening and closing life tests,and the coatings are intact without wear.After the solid-liquid mixed fluid opening and closing life test,the Ni60 + CrN composite coating test has the best effect,with an opening and closing life of 13,000 times,and the effect is far better than 5000 times for the Ni60 coating.According to the analysis,although the hardness of a single CrN coating is higher than that of a single Ni60 coating,but the hardness of the coating is not necessarily proportional to the wear resistance,also related to the hardness of the material itself.The test results show that in the soft matrix material,the CrN coating made by a single PVD is not suitable for the metal sealing ball valve.After spray-welding Ni60 coating,the Ni60+CrN composite coating prepared by PVD technology,according to the high pressure opening and closing life test and solid-liquid mixed fluid life test,the life of Ni60+CrN composite coating reached 18,000 times,which is 1.8 times that of Ni60 coating.The Ni60+CrN composite coating process has the best wear resistance and the longest service life in the life test of metal sealed ball valve,which is 1.8 times longer than the life of single spray welding Ni60 coating.It is a feasible surface hardening process for metal sealed ball valve. |
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