A Charn Cup is a device for measuring viscosity that is commonly used in the paint and coatings industry. It is a field instrument for checking the viscosity of fluids at the job site, made of stainless steel with a small hole in the center of the bottom.
Charn cups are also known as Viscosity Cups.
Determining fluid viscosity helps prevent corrosion. A highly viscous substance is less likely to cause corrosion because it has a lower flow rate for free-moving molecules to react with the metal surface.
Charn cups are used to determine the thickness and resistance to flow of fluids. This is accomplished by introducing a fluid sample into a container with a hole in the bottom and recording the time it takes for the container to empty as the fluid is expelled through the opening. This time is called the outflow time. The faster the fluid is expelled, the lower the fluid's viscosity, and vice versa.
There are five cup sizes , labeled Zahn cup #x, where x is a number from 1 to 5. Large cup sizes are used for high viscosity fluids, while small cup sizes are used for low viscosity fluids. Using the Zahn cup, it is possible to estimate the kinematic viscosity of a fluid in centistokes.
Zahn cup #1: v = 1.1 (t - 29)
Zahn Cup #2: v = 3.5 (t - 14)
Zahn cup #3: v = 11.7 (t - 7.5)
Zahn Cup #4: v = 14.8 (t - 5)
Zahn cup #5: v = 23t
Where v stands for kinematic viscosity and t stands for outflow time.
