Study On Rheological Behavior Of Alcohol-based Zirconium Coating For Casting

Foundry refractory coatings protect bonded sand cores and moulds from producing defective castings during the casting process by providing a barrier between the core and the liquid metal. The use of refractory coatings on cores and moulds is fundamental to obtaining acceptable casting surface quality and dimensional accuracy. The alcohol-based foundry coatings with quickly drying, low energy consumption, and high production efficiency, have widely been used in castings production in China.The technical property of foundry coating is dominated by its rheological characteristics. So, it is a necessary for alcohol-based coatings with excellent technical properties preparation to investigate effects of components of coatings on their rheological behaviour at varying ambient temperatures.In the present work, alcohol-based zircon coatings contained phenolic resin as adhesive were prepared. The effects of contents of phenolic resin, bentonite, and PVB in coatings on the rheological behaviour of the coatings at different temperatures and shear rates were investigated by rheometer, type M08-219, respectively.The results show that the coatings all belong to yield-pseudoplastic fluids. As the content of the phenolic resin increased from 1.0wt% to 3.0wt%, the apparent viscosity, the maximum of shear stress, the area of thixotropic loop, the yield stress, and the viscosity at high shear rate all increase gradually. The shearing thinning ratio increase firstly and then decrease. But it is not found that the suspension properties vary obviously. However, the shear thinning rate of the coating contained 2.0wt% phenolic resin increases up to 51.21%. Then the maximum yield stress is about 2.24 times the minimum, and the maximum of high shear viscosity is about 1.88 times the minimum.As the content of bentonite increases from 2.0wt% to 6.0wt%, the apparent viscosity, the shear thinning ratio, the maximum of shear stress, and high shear viscosity all increase first and then decrease. At the mean time, the area of thixotropic loop, the yield stress, and the suspension properties also increase gradually. The shear thinning ratio of the coating contained 4.0wt% bentonite increase up to 51.21%. The maximum of yield stress is about 1.54 times the minimum and the maximum of high shear viscosity is 1.75 times the minimum.As the content of PVB increased from 0.1wt% to 0.5wt%, the apparent viscosity, the maximum of shear stress, the area of thixotropic loop, the yield stress, and the viscosity at high shear rate all increase gradually. However, the shear thinning ratio increases first and then decreases. The shear thinning ratio of the coating contained 0.3 wt% PVB reaches to 54.01%. The maximum yield stress and the maximum of high shear viscosity are almost 1.54 times and 2.17 times higher than the minimum, individually.Although, it is not found that shearing dilution ratio and the area of thixotropic loop of the coatings vary remarkably wtih the increasing of temperature from 10 to 30℃, the maximum of shearing stress, apparent viscosity, the yield stress, and the viscosity at high shear rate decrease, gradually. And the maximum of yield stress and the maximum of high shear viscosity are about 1.81 times and 1.76 times higher than the minimum, repectively.