What information is required to choose the correct Zahn cup for measuring paint viscosity?

Question

BlackTom AI · Accepted Answer

The orifice number listed on the paint manufacturer's product data sheet.

Zahn cups are simple flow-through viscometers: a cup with a specific-size orifice at the bottom is filled with paint, the cup is lifted, and the time for the paint to drain to a marked point is measured. Each Zahn cup number corresponds to a specific orifice diameter (and therefore a characteristic flow rate). Because the drain time depends directly on the orifice size, the manufacturer must specify which cup (which orifice number) should be used so the measured flow time correlates to the product’s intended viscosity specification.

Step-by-step reasoning:
1. Identify the measurement method required by the paint maker. The product data sheet will state viscosity in a particular cup and reading (e.g., “Zahn cup #2, 20 seconds at 25 °C”).
2. Select the Zahn cup matching the orifice number on the data sheet (Zahn #1, #2, #3, etc. — higher numbers mean larger orifices).
3. Condition the paint to the specified temperature (temperature affects viscosity).
4. Fill the specified Zahn cup, lift it, and time the drain to the indicated mark. Compare the measured seconds to the target given by the manufacturer.

Why this is correct: the orifice number is the defining characteristic of a Zahn cup and determines the relationship between drain time and viscosity. The manufacturer’s data sheet gives the cup number so users measure viscosity in the same way the specification was derived; using a different orifice would give an inconsistent (and meaningless) time-to-viscosity correlation.

Why other possible pieces of information are incorrect: paint color, recommended film thickness, dry time, or substrate type do not define which Zahn cup orifice to use. A numeric viscosity in centipoise alone does not tell you which cup to use unless the product sheet also provides a corresponding cup number or conversion; without the orifice number you cannot ensure equivalence between cup seconds and the product specification.

Conclusion: therefore the required information is the orifice number listed on the paint manufacturer's product data sheet, which matches the provided correct answer.

What information is required to choose the correct Zahn cup for measuring paint viscosity?单项选择题

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