Study On The Mechanism Of Temperature Rise Induced By Titanium Alloy Collision Friction

With the rapid development of science and technology,energy saving and low consumption is an important direction in the development of structural materials.Replacing traditional steel and iron with light and high strength materials is one of the important methods to realize this development.While the frictional impact temperature rise of light alloys are one of the most dangerous potential ignition sources of methane-air mixture.The study on the mechanism of the frictional impact temperature rise of light alloys is an urgent needed for using light metals for mining equipments or modified mineral light alloys.This paper uses theoretical calculation,numeracal simulation and experiment to study the frictional impact hot surfaces,friction flash temperature and sparks generated by TC4 titanium alloy based on the heat transfer principle,Hertz contact theory and elastic-plastic collision theory.The main research contents and conclusions are as follows:On the basis of friction and collision models which established by simulating actual working conditions combined with the testing method and judging rule of safety to friction spark of metallic material for coal mine,the hot surfaces and sparks generated by frictional impact of TC4 titanium alloy are studied by experiment,numeracal simulation and regression analysis.It provides a mathematical model for the calculation of the maximum temperature of frictional hot surfaces,friction flash temperature,impact flash temperature and the energy released by sparks,and provides a new method for setting the critical friction conditions for igniting gas.First,by limiting friction conditions to separate the research of hot surfaces and sparks,it is determined whether the lowest ignition temperature or the minimum detonation energy is used to measure the ignitability of potential ignition sources.The friction temperature field of TC4 titanium alloy is studied under low relative friction speed and the change law of the maximum temperature of friction contact point with load and relative speed is obtained.Combined with regression analysis,the frictional critical load where the maximum temperature of the hot surface reached the minimum ignition temperature of gas was calculated.For a low contact-stress situation,the frictional flash temperature is often much higher than the bulk temperature.Therefore,based on the theory of rough surface tribology,starting from the micro-thermodynamics and the contact heat conduction between the asperities during sliding is analyzed combined with the elastoplastic contact theory.The frictional flash temperature during sliding contacts between TC4 titanium alloy and Q235 A steel is calculated.It reveals the leading factors for the friction bulk temperature and the maximum flash temperature that reach the lowest ignition temperature of gas,and provides a more accurate method for setting critical ignition conditions.The research on the collision hot surface is based on the simulation of the falling gavity hammer test.The change law of the collision temperature field of TC4 titanium alloy with the impact conditions is obtained by numeracal simulation combined with the elasto-plastic collision theory.The mathematical model for calculating the maximum flash point temperature is derived.Thus,an important method can be obtained that controlling the coefficient of friction between the acting surfaces within a critical range by improving the processing accuracy of the material surfacces may ensure the safety of the hot surfaces generated by impact.Use simple and safe experimental equipment to obtain the flight speed,particle size,existence time and other related parameters of sparks generated by friction of TC4 titanium alloy.The ignitability of sparks is evaluated while the pure copper and Q235 A steel are used as the comparative material for TC4 titanium alloy.The results show that copper is basically free of frictional sparks at low speed and low load.The igniting ability of frictional sparks generated by titanium alloy is indeed greater than that of steel frictional sparks,and the leading factor which effect the ignition ability of sparks is the nature of materials.And setting critical conditions cannot completely prevent the occurrence of detonation,but by controlling the relative friction speed,the probability of sparks detonating gas can be reduced.Study on the mechanism of sparks induced by titanium alloy combining the ignition conditions of the gas.According to related theories of gas ignition,spark ignition theory and the theory of high-temperature groove and airflow and rock wall the necessary conditions for sparks to become effective ignition sources and the critical duration of the spark required for an explosion are obtained.