The Research Of Cold Rolled Strip Temperature With Liquid Nitrogen Cooling Condition

Cooling and lubrication in cold rolling process is an important technological link, and it is the key technology of cold strip rolling process. In traditional cold rolling process, water/oil emulsions are often used to have a smooth rolling process. Taking into account of existing problems of the traditional emulsion rolling, this paper puts forward a method of using liquid nitrogen to replace the water/oil emulsion for cooling and lubricating technology. It is hopeful to solve problems in the traditional cold rolling process, for example, emulsion pollution, circulation system maintenance difficulties and problem of controlling the surface of strip and so on. The research aims at the problems of liquid nitrogen cooling for cold rolling lubrication theory and design of the cooling system. Through the research,the nature of liquid nitrogen cooling in the cold rolling process has been made clear in this reasearch, and it’s hopeful to set up the new cold rolling mill cooling system. In addition, it provides new ideas for a new generation of rolling cooling and lubrication technology development. The main work and results are as follows:(1) Liquid nitrogen’s cooling nature is not clear as a new subject. Through cooling process physical description of liquid nitrogen, this paper establish convective heat transfer coefficient model between liquid nitrogen and strip and heat transfer coefficient model between cold nitrogen gas and strip from the view of heat transfer theory. From the view of heat transfer of solid surface contact, conditions contact heat transfer coefficient model between strip and roll is established in liquid nitrogen cooling in this paper.(2) In order to study heat transfer law of spray process between liquid nitrogen and strip, this paper design experiment of liquid nitrogen spray cooling thin steel plate. And we can obtain heat transfer coefficient of liquid nitrogen spray cooling thin steel plate in different experimental scheme through inverse heat conduction differential program solution. On the basis of this, this paper analyses influence factors of heat transfer coefficient of liquid nitrogen spray cooling thin steel plate.(3) In order to study the strip temperature under the liquid nitrogen cooling condition, we need to know not only boundary conditions of liquid nitrogen cooling strip but also deformation heat and frictional heat in rolling process. The paper divide the deformation zone into five parts such as inlet-elastic region, inlet-plastic region, stick region, outlet-plastic region and outlet-elastic region. And based on calculate the length of each segment, we solve frictional heat through the integral for each segment. For deformational heat, taking into account of the change of deformation degree, this paper solve plastic deformation heat through the integral of deformation degree. For the problem of distribution between strip and roll, this paper establish model of distribution of frictional heat, the model can reflect the temperature change(4) According to the model aboves, the research developes cold rolled strip temperature calculation software through VC++6.0. In order to verify the validity of the calculation software, this paper design measurement temperature experiment of the emulsion rolling. Compared experimental measurement temperature with calculated values of software, results shows that the software of calculation accuracy is very high. Using this software, this paper calculates parameter change of cold rolled strip to strip temperature influence.(5) On the premise of software’s precise, through changing boundary conditions of emulsion cooling to of liquid nitrogen cooling, this paper calculate the strip temperature under using liquid nitrogen cooling, and this paper analyses influence factors of strip temperature under liquid nitrogen cooling condition.