Study On The Cavitation Resistant Coating And The Anti-Cavitation Mechanism

Cavitation is one of the most serious corrosion and erosion problems which occur on the surface of machine parts under the influence of high speed fluid. Polymer coatings can be applied to prevent or reduce the damage caused by cavitation. Base on one kind of cavitation resistant coating(HGCR) developed by our research group, a systematic and detailed study on the coating composition and anti-cavitation mechanism was carried out.The first part of the work is about the development of flexible epoxy curing agents. Among several kinds of flexible-chain curing agents designed, synthesized and tested, one kind of di-amine with flexible ether chain was selected and studied in detail.According to the results of curing test, shear strength test and vibration induced cavitation test, the curing agent not only has flexibilizing effect, but also shows better mechanical properties.The second part is about the introduction of a new kind of chelating agents. The chelating agent added in the coating could increase the corrosion resistance and improve the adhesion between the coating and the metal surface. So they can improve the cavitation resistant behavior of the coating. The chelation mechanism and the anti-corrosion mechanism were studied by means of a model compound. The anti-corrosion mechanism of the chelate film was proved to be the retardation of the dissolution of anode.The relationship between the mechanical properties and the cavitation resistant behavior was examined in detail in the third part. According to the results of tensile tests, it is found that the greater thestrain energy ,the better the cavitation resistant behavior of the polymer coating will be. The coating with EP/PU weight ratio 4 : 6 shows the best cavitation resistant behavior.Dynamic mechanical properties were studied. DMS curves clearly indicate that EP/PU 4 : 6 film show better energy absorbing characteristics. An interesting phenomenon was found that when one kind of active filler with suitable coupling agent is added, the compatibility between EP and PU as well as the energy absorbing behavior can be significantly improved. The filler can also impart the coating thixotropic property which is needed in daubing application. The energy absorption mechanism of the coating was proposed and discussed.At last, the working principle of the vibration-induced cavitation test apparatus was theoretically analyzed. The mathematical model of the test set was derived and numerical data were obtained by using the finite element method. The velocity potential distribution on the surface of the sample was calculated. The distribution of pressure and the cavitation number were finally obtained. According to these results, the cavitation condition of the sample surface can be predicated. The influence of frequency on the cavitation test was studied quantitatively.