A Zahn cup is a viscositymeasurement device widely used in the paint industry. It is commonly astainless steel cup with a tiny hole drilled in the center of thebottom of the cup. There is also a long handle attached to the sides.There are five cup specifications, labeled Zahn cup #x, where x is thenumber from one through five. Use large number cup sizes when viscosityis high, use low number cup sizes when viscosity is low.
To determine the viscosity of aliquid, the cup is dipped and completely filled with the substance.After lifting the cup out of the substance the user measures the timeuntil the liquid streaming out of it breaks up, this is thecorresponding "efflux time".
On paint standard specifications, one denotes viscosity in this manner: efflux time, Zahn cup number.
Conversion
One can convert efflux time to kinematic viscosity by using an equation for each cup specification number, where t is the efflux time and ν is the kinematic viscosity in centistokes.
- Zahn Cup #1: ν = 1.1(t - 29)
- Zahn Cup #2: ν = 3.5(t - 14)
- Zahn Cup #3: ν = 11.7(t - 7.5)
- Zahn Cup #4: ν = 14.8(t - 5)
- Zahn Cup #5: ν = 23t
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