Extension of the Temperature and Shear Rate Range for Polymer Containing Lubricants Using the Cannon HTHS Capillary Viscometer

The Cannon High Temperature High Shear (HTHS) capillary viscometer is currently used in the ASTM D4624 procedure to measure the viscosity of polymer containing lubricants at 150°C and shear rate of 10⁶ sec^-1. An expansion of the utility of this Cannon instrument is described in this paper to cover the temperature range of lubricants from 35 to 175°C and shear rates of up to 10⁶ sec^-1. A finite difference model is used to solve the transport equations for capillary flow at each temperature. The solution accounted for temperature, pressure, non-Newtonian and kinetic energy effects on viscosity. Fitting these data to a double truncated power law model provides the incipient non-Newtonian shear rate γ̇₁, the power law index n, and the incipient second Newtonian shear rate γ̇₂. All these parameters can be measured at temperatures of around 100°C or less. The n and γ̇₂ were found to be regular functions of temperature while γ̇i is always in the measured range. The behavior of typical polymer containing multigrade crankcase lubricants fit this model thus providing an accurate measure of viscosity at 150°C and 10⁶ sec^-1 shear rate and allowing for an accurate prediction of viscosities at temperatures of 150 to 175°C and 10⁷ sec^-1 shear rates.