Question 1

What is the Refutas method for oil blending viscosity?

Accepted Answer

The Refutas method is an empirical mathematical formula used to calculate the viscosity of a blend of two or more liquids. It converts the kinematic viscosity of each component into a Viscosity Blending Number (VBN), averages them linearly based on mass or volume fraction, and converts the resulting VBN back into centistokes.

Question 2

Can you mix PAG base oils with mineral oils in this calculator?

Accepted Answer

While this calculator mathematically predicts blend viscosity, PAG base oils are generally incompatible with mineral oils and will cause phase separation. This tool is designed to calculate blends of compatible fluids, such as different viscosity grades of water-soluble PAGs or water-insoluble PAGs.

Question 3

How does ASTM D7152 apply to base oil blending?

Accepted Answer

ASTM D7152 is the standard practice for calculating the kinematic viscosity of blends of petroleum products and lubricants. It outlines the approved logarithmic and double-logarithmic calculations required to predict viscosity blending behavior with high precision.

Question 4

Is viscosity blending based on volume fraction or mass fraction?

Accepted Answer

The Refutas method and ASTM D7152 can utilize either volume or mass fractions for blending. For the most accurate physical results in laboratory formulations, mass fraction (weight percentage) is preferred because volume can change slightly due to temperature and thermal expansion.

PAG Lubricant Blending and Viscosity Calculator