Density Cups (SPECIFIC GRAVITY CUP)
Density is defined as weight per unit volume at a specified temperature.
Density cups are used for quality control because errors in paint composition will result in different density readings. Density cups have also been described as liquid pycnometers.
Density cups use a cylindrical shape which provides a large opening for easy filling, emptying, and cleaning. The tightly fitted stainless steel covers have an upward slope to a small hole in the center to allow excess sample material to be expelled without entrapping air bubbles, which increases accuracy. |
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ASTM Cup Volume
In North America the term "weight per gallon" ( wpg ) is used in the coating industry. The volume of the weight per gallon cup is such that, at a specified temperature, the numerical value in grams of water that it can hold is equal to, or ten times greater than, the numerical value in pounds of water that a gallon container can hold. A US gallon of water weighs 8.32 pounds, thus a Regular US weight per gallon cup holds ten times this amount in volume, 83.2 ml. When taking a measurement, the cup and the sample must be brought to the same equilibrium temperature (usually 25 °C or 77 °F).
ISO Cup Volume
ISO Cups are machined from stainless steel, using the metric system. The cups hold a defined volume of liquid of 50 or 100 ml. A tolerance of 0.1 % is guaranteed. Testing is carried out in accordance with ISO at 23 °C ± 2 °C.
Standards:
■ ASTM D 333, D 1475, D 2805.
■ BS 3900 A 19.
■ DIN 53217.
■ ISO 2811.
Procedure:
■ Weigh cleaned density cup empty and record weight.
■ Temper density cup and test liquid (Refer to appropriate test standard for proper temperature).
■ Fill density cup.
■ Put cover on without tilting.
■ Avoid air bubbles.
■ Remove overflowing liquid carefully with absorbent cloth.
■ Weigh filled density cup.
■ Calculate density.
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Determination of Density and Secific Gravity |
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Volume (ml) |
Density Specific Gravity |
(relative to water) |
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ISO Cup |
100 or 50 |
[weight full (g) - weight empty (g)] : volume (ml) = g/cm3 |
specific gravity = density |
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British imperial Cup |
100 |
[weight full (g) - weight empty (g)] : volume (ml) = g/cm3 |
specific gravity = density |
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1 ml = 1 cm³; 1 liter = 1000 ml; specific gravity of water = 1 g/ml
1000 ml = 0.2646 U.S. gallon; 1 U.S. gallon = 3.785 liter
Made of corrosion resistant steel |