Abstract
It is shown how to determine parameters of a material obeying Casson's equation by some rheometers.Casson has proposed an equation for the flow of varnishes relating to the shear stress F to the rate of shear D. This relation has the formF1/2=k0+k1D1/2, k0 and k1 being constants depending on the properties of suspensions. This equation is generally called Casson's equation.We have determined the parameters k0 and k1, that is, the viscosity η corresponding to k1 and the yield value τf corresponding to k0, by a rotating coaxial cylinder viscometer and a cone and plate viscometer.In the case of a rotating coaxial cylinder viscometer, η and τf are determined from the relationship between the torque M and the angular velocity Ω as follows:η=(1/a2-1/b2)/(4πhtan2θ)τf=(1/a+1/b)2M0/8πhIn the case of a cone and plate viscometer, there is a following relationship between the torque M on the plate and the angular velocity Ω for a non-Newtonian liquidΩ=1/2∫τaτbf(τ)/√τ(τ-c)dτ, c=3M/2πa3Making use of this relation, we can get η and τf as follows:η=3α/(2πa3tan2θ), τf=3M0/2πa3)Further we have tried to find the flow curve f(τ)=γ from the known relationship between Ω and M. The flow curve is approximately given byf(τ)=3/α3τ-(1/2+3/α2)∫τ0ξ(3/α2-1/2)Ω(ξ)dξ.
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