Research On High-temperature Molten Salt Cleaning Technology For Paint Coating Of Remanufacturing Parts

Remanufacturing,as an emerging industry vigorously developed in China,is the most active and highly technical element in China's circular economy and is one of the best ways to realize the efficient recycling of resources.Remanufacturing cleaning is an important part of the remanufacturing process of mechanical products.The quality of cleaning directly affects the subsequent inspection and repair of the product,and ultimately affects the quality of remanufacturing.To achieve high efficiency,high quality and green cleaning process is the key problem to be solved in the field of remanufacturing cleaning.Molten salt cleaning technology is to use inorganic salt in high-temperature molten state as cleaning medium,and combine with physical and chemical removal mechanisms to realize efficient cleaning of various complex organic pollutants on the surface of remanufacturing parts.This paper focused on the cleaning of paint coating on the surface of parts and components and carried out the relevant research on molten salt cleaning technology.Through the research on the cleaning mechanism,thermal stability and paint removal effect of a new developed high-temperature molten salt,the superiority of high-temperature molten salt in cleaning paint coating was verified.Then,by optimizing the cleaning formula and process parameters,and studying the thermophysical properties of the optimal molten salt,fast and high-quality cleaning of paint coating was achieved,providing guidance for simulation and industrial application of molten salt cleaning.In this paper,the physical and chemical properties of NaOH-KCl-Na2CO3 high-temperature molten salt and the structural composition of the paint coating on mechanical parts were analyzed,thus confirming the feasibility of paint removal by molten salt.Then the cleaning mechanism of high-temperature molten salt was analyzed.By using TG-IR-GC/MS and DSC,the removal mechanism of thermal decomposition of paint coating was studied.It was confirmed that the thermal decomposition reaction began to play a significant role when reaching a certain cleaning temperature in the process of cleaning paint coating with molten salt,leading to a significant increase in cleaning efficiency.Through thermogravimetric analysis of high-temperature molten salt,it was confirmed that the molten salt with NaOH-KCl-Na2CO3 formula had high thermal stability within 600 0C.The results of cleaning test showed that cleaning temperature and NaOH concentration were the key factors affecting cleaning efficiency and surface quality of metal matrix.Under high temperature and alkaline environment,the surface of metal materials will be oxidized,and the surface roughness will be increased,but the residual stress will be eliminated to some extent.Due to short cleaning time,the material hardness will not be changed.Then,for high cleaning efficiency and cleaning quality,the high-temperature molten salt cleaning formula and process optimization were carried out.45 steel was selected as the base material,and the central composite surface test design method was adopted.By taking the sample cleaning time and surface oxygen content as response variables,the cleaning temperature and NaOH mass fraction were optimized,and the regression equation between response variables and independent variables was obtained.Aiming at both cleaning efficiency and quality of molten salt,the two response variables were optimized to obtain a shorter cleaning time and a lower surface oxygen content at the same time.Finally,the cleaning temperature of molten salt was determined to be 500? and the NaOH content in the formula to be 50%Finally,through the melting point test of different proportion of high-temperature molten salt,it was found that when the mass fraction ratio of NaOH,KCl and Na2CO3 was 5:3:2,the melting point of molten salt was the lowest(268.50?).By calculating and measuring the thermophysical parameters of the high-temperature molten salt with optimum proportion,the variation law of the density,viscosity,specific heat and thermal conductivity of the molten salt with the temperature was obtained,and the regression equation was fitted for the simulation of high-temperature molten salt cleaning and the guidance of engineering application.