Molten Salt Cleaning Research And Process Parameters Optimization For Paint Layer Of Remanufacturing Parts

With the new requirements of resource conservation,green process and technological innovation proposed by the state for the development of the manufacturing industry,the traditional manufacturing industry is in urgent need of upgrading and transformation.Remanufacturing engineering provides a strategic and effective choice for the sustainable development of manufacturing industry,and it is also a necessary development process in the future.On the premise of meeting the maximum utilization of resources,the energy consumption and waste output in the manufacturing process are greatly reduced.Remanufacturing cleaning process is the key link after disassembly.The cleaning efficiency and quality have a key influence on the whole remanufacturing process.The cleaning technology that can efficiently and qualitatively remove the surface pollutants of remanufacturing parts needs to be studied,developed and applied urgently.Molten salt cleaning technology can effectively clean pollutants with ideal removal effect,and the molten salt can be recycled after cleaning,But the melting point of the existing cleaning formula is high,leading to long melting time.This paper studies the practical application of molten salt cleaning technology in enterprises.Through the low-temperature molten salt cleaning formula optimization,the molten salt cleaning mechanism and process products research and the optimization of cleaning process parameters for surface properties,the goals of reducing melting preparation time of molten salt before cleaning,improving the cleaning efficiency and cleaning life span are achieved.Thus,energy consumption and cleaning cost can be reduced.It also provides the basic theory for the molten salt cleaning technology to remove paint layer,and promotes the development process of the demonstration and application of molten salt cleaning technology in enterprises.Firstly,the formulation optimization of low-temperature molten salt cleaning is optimized for the surface paint layer pollutants of remanufacturing parts in this paper.Based on the melting point theory of eutectic system,the mixing ratio of the eutectic components KNO3 and NaNO3 at low melting point was obtained by theoretical calculation,The melting point was measured by differential scanning calorimetry(DSC)to verify the result of proportion optimization.The optimized proportion of other components in the formulation was obtained through the coating pollutant removal proportion optimization experiment.Considering the influence of adding other components on the mixed melting point of eutectic components,the low melting point and cleaning effect of mixed molten salt were verified.Considering melting point,cleaning effect and surface oxidation degree of matrix material,the formula of low-temperature molten salt cleaning was determined.The specific composition of formulation is that mass(KNO3):mass(NaNO3):mass(NaOH)= 7:7:6(35%:35%:30%),and the melting point of mixed molten salt is 243.621℃.Next,aiming at the cleaning process of removing the paint layer with the optimized fonnula of low-temperature molten salt,the cleaning mechanism was analyzed.The specific gasification,thermal expansion and oxidation were studied in detail.Compared with air atmosphere,molten salt can intensify the effect of thermal expansion on paint layer removal.Through gas chromatography-mass spectrometry(GC-MS)of cleaning process gas,composition and content were determined.And comparing with the composition and content of air.the generations of gasification and oxidation were verified to occur.Meantime the product morphology of molten salt cleaning process was analyzed.And by comparing with the infrared spectrum of paint layer.the oxidation reaction was further verified.By comparing the experimental results.it is found that the physical separation of process products can significantly improve cleaning efficiency and shorten cleaning time.And the paint quality that unit quality of mixed molten salt can remove increased,so as to extend the cleaning life span of molten salt and to achieve the purpose of reducing cleaning cost.Finally.the cleaning process parameters for surface quality of matrix material were optimized.And the commonly used materials of construction machinery products were selected:QT500 and 27SiMn.The surface roughness variation(△Ra)and surface residual stress variation(△F)were taken as response variables to optimize the process parameters of cleaning temperature(T)and the distance between painted surface and molten salt free liquid surface(D).And the corresponding regression equations were obtained.Based on the optimization objective that the molten salt cleaning process can achieve minimum influence on the surface roughness parameters of the matrix material and the best effect of eliminating the surface residual stress,in other words,surface roughness variation(△Ra)tends to zero and surface residual stress variation(△F)tends to maximum.The corresponding cleaning temperature(T)and the distance between painted surface and molten salt free liquid surface(D)were obtained.