Study On Ion Chemical Heat Treatment And Friction And Wear Properties Of Screw Extruder Screw

Screw extruders are widely used in the fields of plastics,food and feed processing,and their core parts are inextricably linked to the production efficiency and the product quality of the equipment.In the real working process,the screw often experiences the rapid wear and further fails because it is not only subject to huge friction and shearing force but is in the high temperature and corrosive environment,which affects the production plan of the product and increases the maintenance cost of the equipment.In order to reduce the wear speed of the screw and prolong the service life,the surface treatment technology is generally used to improve the wear resistance of the screw.In this paper,the screw material 42CrMo is treated by the surface technology of ion nitriding and ion nitriding and sulfurizing.By scanning electron microscopy(SEM),X-ray diffraction(XRD)and X-ray electron spectroscopy(XPS),the micro-morphology observation and phase analysis of the sample were carried out,and the tribological properties of the samples surface were also studied by a friction and wear tester.This paper discussed the friction and wear mechanism according to the morphology and chemical composition of the wear scars,and the wear rate was calculated through using a super depth of field three-dimensional microscope.Based on the working environment of the screw extruder screw,a friction and wear tester for the simulated bench test was designed to evaluate the wear life and process of the screw comprehensively.The main research contents are as follows:(1)The effects of ion nitriding process parameters on the microstructure and tribological properties of 42CrMo steel nitriding layer were studied by a comparison experiment around the nitriding temperature,gas ratio and furnace pressure in the process parameters.The results show that proper increase of nitriding temperature is beneficial to promoting the wear resistance of the nitriding layer.However,a nitriding temperature exceeding 480?will change the phase composition of the nitriding layer,resulting in a sharp drop in wear resistance.The reduction of hydrogen-nitrogen flow ratio can effectively improve the overall hardness gradient curve of the nitrided layer,and also improve the wear resistance of the nitrided layer within a certain range.When the flow ratio of hydrogen to nitrogen flow ratio is less than 1/3,the brittleness of the nitrided layer will increase,resulting in the reduce of wear resistance.The change of furnace pressure between 100 Pa and 200 Pa has no obvious effect on the hardness gradient curve of the nitriding layer,but the increase of furnace pressure will slightly reduce the wear resistance of nitriding layer.When the nitriding temperature is 480?,the hydrogen-nitrogen flow ratio is 1/1 and the furnace pressure is 100 Pa.And the wear rate obtained in the 42CrMo steel ion nitriding layer is 2.33×10~-77 mm~3/Nm and the friction coefficient is 0.35.In this condition,the optimum tribological properties were shown in the set ion nitriding parameters.(2)The surface microstructure and friction and wear properties of 42CrMo steel after processed with ion sulfurizing,ion nitriding and ion nitriding and sulfurizing were compared and analyzed.The experimental results show that the ion nitriding and sulfurizing technology can form a sulfurizing layer with FeS as the main component on the nitriding layer.The sulfurizing layer can effectively reduce the friction and increase the effect of lubrication.The high hardness nitriding layer greatly extend the time for the sulfurizing layer to exert the effect of lubrication stably.The wear rate of the composite treatment layer is 1.55×10~-77 mm~3/Nm,the friction coefficient is 0.3,and the wear of the grinding parts is also the least.It exhibits the best tribological properties in the three surface treatment processes.(3)The mechanical structure design of the screw extrusion friction and wear tester was also completed,and the structural static analysis and vibration analysis were performed on the key components by using ANSYS Workbench software.The calculation results show that the maximum stress value and maximum deformation value generated by the bearing seat under load meet the requirements of safety design,and the resonance phenomenon is not generated by the excitation of the power system.