The Research On Terminal Heating Device Of Cold Spraying System

Cold spraying is a new technology for material surface modification and strengthening.High spraying speed,high deposition efficiency,compact coating,less porosity,small impact on the matrix thermal and low residual stress on coating are the advantages of cold spraying compared with thermal spraying.Now,the deposition efficiency of copper,aluminum,zinc,tin and other metal is higher than 90～95%at low gas working temperature.But for other coatings such as MCrAlY,stainless steel and Ni-based alloy,it is difficult to form sedimentation when the gas working temperature is lower than 600℃,and the technology is unripe.For above metals,in order to achieve high deposition efficiency of more than 80%and forming dense coating at the same time,we need to raising the speed of the particles or reduce the critical speed.And the critical speed depends largely on the particle temperature,When the cold spraying particles at higher temperatures,the deposition critical speed is reduced,deposition efficiency will be rised and the bonding strength will also be increased.The results are:(1)Electromagnetic induction heating process is used in the terminal heating device of cold spraying system.And layers of cylinder porous flow channels are set in the heater,making the gas flows like"S"-shape.Then the gas could transfer heat with the heater fully,and it also has a small size,high efficiency and rapid-heating.The heating device mainly includes sensor and heater.(2)The sensor is composed by a induction coil,bar,and a cooling water inlet and outlet.The induction coil is cylindrical helical shape,made of empty rectangular section T3 copper,located in the outermost layers of the heating device.(3)The heater is cylindrical and put concentrically with induction coil,could made by tungsten,molybdenum and rhenium.To be convenient for processing,the heater can be divided into four parts:the center,left inner end cover,left end cover and right end cover,and each part connected with others by threads.(4)We use graphite as the heater material at first,and the thermocouple system which is made by ourselves was used to measure temperature,electrifying the coil with medium frequency power source,and then conduct experiment to heat up heater device.The results show that the heater can be heated up to about 830℃ under the condition of I=50A and f=4000Hz,and the gas temperature can be raised to 690℃ when the heater temperature is 730℃ and the gas flow speed is 0.6m3/min.The heat between heater and gas will transfer steadily,and then raise the gas temperature.(5)Numerical simulation of induction heating device shows that,induced eddy current heating body and joule heat are gathered in the largest heating body surface within the scope of a few millimeters,and the geometric center of the heating body in the y direction along the x direction is symmetric structure.The heater temperature rise changes uniformly with time,current density and frequency have great influence on the heater and the heater temperature can be raised to 1500℃.The experiment temperature of the heating body agrees well with the simulation temperature,and the heater temperature in induction heating can be forecasted by the numerical simulation.