Optimization of coating process parameters for bionic drag reduction and efficiency increasing coating of centrifugal pumps

Abstract: Bionics is based on the structure of natural biological system and the process of life activities as the basis of technological innovation and design, and consciously imitates and replicates it. Through the coupling of 2 or more different factors, organisms can effectively realize various functional characteristics of organisms and fully display their best adaptability to habitats，this phenomenon of biological coupling is ubiquitous in the biological world. The multi-bionics of learning and simulating the coupling mechanism of organisms is called coupling bionics. The drag reduction mechanism of dolphin skin is a typical representative of the bio-binary coupling. Dolphin skin is composed of smooth elastic keraphyllous epidermis and hard dermis, which are intertwined with each other. The coupling effect of the 2 parts is one of the main reasons why dolphins can swim fast. According to the principle of bionic similarity, Jilin University has designed a coupling functional surface which imitates the skin structure of dolphins, and applied it to the surface of the key parts (centrifugal impeller) of centrifugal pump, which can significantly improve the pump efficiency. The specific method is to directly cast the ribbed structure similar to the dolphin skin dermis on the upper and lower cover plate of impeller by one-step casting technology, and then coat the cover plate with high viscous polyurethane as the surface material. The ribbed structure at the bottom and the polyurethane coating on the surface constitute a coupling bionic functional surface. The thickness parameters of surface material coating have the greatest influence on the efficiency of coatings， and polyurethane is the main material for coating, but because of the complicated and twisted space structure of the inner passage of centrifugal pump impeller, the high viscosity characteristics of polyurethane and the limitation of traditional coating technology, it is difficult to achieve high efficiency and high quality coating on the surface of complex impeller inner runners with coupling bionic functional surface layer materials. and it is difficult to control the thickness of the coating. In order to solve the above problems, a self-made rotating coating equipment by means of centrifugal force was introduced in this paper, using which, the coating thickness could be controlled by pouring temperature, rotating speed, coating time and other parameters. According to the combination design principle of Box-Behnken Design in Design-Expert software, taking the coating thickness of impeller runner as test index, a 3 factors and 3 levels orthogonal combination experiment was designed, the above parameters were optimized and the quadratic fitting equation was established. The test results showed that the main and secondary factors affecting the coating thickness were rotating speed of equipment, pouring temperature and coating duration. The comparative coating tests were carried out on the impeller of 200QJ50-26 centrifugal pump, the results showed that the errors between tested coating thickness controlled by coating parameters and calculated value of quadratic fitting equation was less than 5%, the results were credible. According to the previous research results, when the coating thickness is 0.5 mm, the drag reduction and efficiency increasing of 200QJ50-26 centrifugal pump is the best. The test results showed that the optimum coating parameters for 200 QJ50-26 centrifugal pump to obtain the optimum coating thickness of 0.5 mm were as follows: coating duration was 53.7 s, rotating speed was 401 rad/min, pouring temperature was 90.1℃. The research can provide a reference for the engineering construction of the coupling functional surface on the centrifugal pump.