| The application of ultrasonic vibration in the metal melt has the functions of refining the solidified structure,degassing and removing impurities,reducing macro segregation,microscopic defects,and improving material properties.Prerequisites.The metal horn on the ultrasonic probe and the ceramic tool rod are usually connected by a threaded screw.During the working process,the ultrasonic vibration transmitted on the ultrasonic rod and the high temperature transmitted by the melt will affect the threaded connection between the ceramic and the metal.It will affect the continuous operation of ultrasonic equipment.Therefore,this paper studies the loosening law of ceramic-metal threaded connections under the action of ultrasonic vibration and temperature.The main research contents are as follows:(1)The finite element simulation of the ceramic-metal threaded connection was carried out,and the loosening laws of the ceramic-metal threaded connection under the action of single ultrasonic vibration and the dual action of ultrasonic vibration and high temperature were studied respectively.The results show that when the threaded connection structure is subjected to a single ultrasonic vibration,the tension force in the early stage of the vibration decreases,and then the tension force remains basically unchanged,mainly due to the plastic deformation of the thread bottom;When subjected to the dual action of ultrasonic vibration and high temperature,the tension force in the early stage of vibration also decreased,but in the later stage,the tension force decreased more,mainly because with the continuous increase of temperature,the thread bottom continued to plasticize.In addition,due to the large difference in thermal expansion coefficient between the titanium alloy rod and the threaded screw,and the rotation angle of the ceramic rod and the screw is similar,that is the relative rotation of the ceramic rod and the titanium alloy rod eventually leads to a decrease in the tension force.(2)The effects of different factors on the tension force of the ceramicmetal threaded connection under the action of single ultrasonic vibration and the dual action of ultrasonic vibration and high temperature were studied respectively.The research shows that the larger the initial preload force,the lower the ultrasonic amplitude,the larger the friction coefficient of the thread meshing surface and the friction coefficient between the ceramic rod and the titanium alloy rod,the smaller the tension force drop.The decrease in tension force is greater,especially under high temperature,the change of screw material has a more obvious effect on the tension force.Therefore,increasing the initial pre-tightening force,increasing the friction coefficient of the thread meshing surface and the friction coefficient between the ceramic rod and the titanium alloy rod,and selecting a screw material with a thermal expansion coefficient similar to that of the titanium alloy rod can prevent the ceramic-metal threaded connection of loosening.(3)The variation law of the tension force of the ceramic-metal threaded connection under the action of single ultrasonic vibration and under the dual action of ultrasonic vibration and high temperature is studied through experiments.The results show that the decreasing process of the tension force can be divided into two stages in the two working conditions.The tension force in the first stage decreases obviously,and the tension force in the second stage decreases slowly,but the thread under the dual action of ultrasonic vibration and high temperature The connection tension decreases more.Comparing the experimental results and the simulation results,it is found that the two laws are similar,which verifies the validity of the finite element simulation.The optimal initial preload parameters for the stable operation of the ceramic-metal threaded connection structure under the dual action of ultrasonic vibration(frequency 20 k Hz,amplitude 5um)and high temperature(100℃)are determined.The results show that the effect is best when the initial preload is 19998 N.62 Figures,4 Tables,80 References... |
