WHITFORD TEST METHOD 101A
VISCOSITY MEASUREMENT BY ORIFICE DIP [ZAHN] TYPE
CUP
1
Scope:
The procedure is used to determine the viscosity of coatings for in-plant coatings
production or for reduction of coatings to the proper viscosity for application. By this
method, viscosity is measured as the time required for a given volume of coating to
run through an orifice (hole) of standard size. There are several
national/international cups developed for this measurement. This test method
describes viscosity measurement with a Zahn Signature Cup. However, the
procedure is applicable for similar dip cups.
2
3
Equipment and Materials:
2.1
Set of viscosity cups (Zahn Signature Nos. 1, 2, 3, 4, & 5. are available)
2.2
Timer (stopwatch) capable of measuring in 0.1 seconds.
2.3
Thermometer
2.4
Cold or hot water.
2.5
Solvent or water (as appropriate) and cloth for cleaning cup.
Procedure:
3.1
If measuring viscosity for control of paint production, the temperature of the
coating must be adjusted as specified. Measure the temperature and
immerse the sample of coating in hot or cold water (as appropriate) to bring
the temperature of the sample to the specified temperature. If measuring
temperature for viscosity reduction during field application, this step can be
ignored. However, the temperature at which the measurement is made must
be recorded.
3.2
Use the viscosity cup specified or if the viscosity cup is unknown, select a
cup that is likely to give an efflux time of 20 to 60 seconds. Repeat the
measurement with a different cup if the viscosity falls outside the optimum
range.
Whitford Test Method 101A
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5
3.3
Hold the cup so that it will hang vertically. There is a loop or ring on most
cups that can be hooked around one finger so that it hangs vertically.
Immerse the viscosity cup in the coating and hold the top of the cup just
below the surface of the liquid. Try to avoid surface bubbles as much as
possible. Hold the cup in the coating for at least 1 minute to bring the cup to
the temperature of the paint.
3.4
Lift the cup vertically out of the coating in a quick steady motion. As the top
edge of the cup breaks the surface, start the timer. Hold the cup steadily and
vertically about 15 cm (6 inches) above the liquid. Observe the flow of
coating from the cup and stop the timer at the first definite break in the
stream at the base of the cup.
Evaluation:
4.1
Report type and number of cup used, efflux time to the nearest 0.5 second,
and temperature at which the measurement was made.
4.2
It is common to make a single measurement. However, for greater accuracy,
the average of 3 measurements should be taken.
Comments/Precautions:
5.1
Entrapped air in the coating is a common source of error in the
measurement. If there is a significant quantity of entrapped air apparent or
suspected, the sample should be slowly stirred, sieved or gently vibrated to
release as much of the entrapped air as possible.
5.2
The cups must be carefully cleaned after use with the appropriate solvent
and soft cloth. Do not use metal tools to clean the orifice. Do not use the
cup as a stirrer as in doing so one might hit the bottom of the container and
damage the cup or orifice.
5.3
The temperature of the coating significantly affects viscosity. A
temperature/viscosity conversion chart can be constructed for a particular
coating that will facilitate control of the viscosity.
5.4
There are conversion charts available to allow estimation of viscosity in one
type of cup by knowing the viscosity in another.
5.5
Viscosity cups should be calibrated on a regular schedule using standard
viscosity oils. If the efflux time from a cup differs more than + 1 second from
the expected time, the cup should be discarded.
Whitford Test Method 101A
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5.6
6
General Electric originally designed standard Zahn cups. As they are now
made by various manufacturers, considerable cup variations are therefore
possible and these can cause great difficulty if cups are user to set
specifications. Whitford use Zahn Signature cups, from Paul N. Gardner Co.,
which do not exhibit this problem.
References:
ASTM D 4212-82
Detailed Procedure: 3101A
Date Issued:
05 Jan. 1997
Issue:
USA Issued by:
Europe Issued by:
USA Checked by:
Europe Checked by:
5
M. W. Miller
H. C. Wilson
B. Silsby
Whitford Test Method 101A
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Appendix: 101
Approximate Correlation of Standard Flow Cups
Flow Time in Seconds at 23°C [73°F]
BS 4
Din 4
Afnor 4 Ford 4
Zahn 2
16
13
15
16
17
18
15
16
17
19
21
16
18
19
21
23
18
20
21
23
26
19
23
23
26
28
21
25
24
28
31
22
27
26
31
34
24
30
29
34
37
26
32
31
36
40
27
34
33
39
43
29
37
35
42
46
31
40
37
45
49
33
42
40
48
52
35
45
42
51
55
37
47
44
53
58
39
50
47
56
61
41
53
49
59
64
43
55
51
62
67
45
58
54
65
70
47
61
56
68
73
49
63
58
71
77
50
66
61
74
80
52
69
63
77
83
55
72
66
81
86
57
74
68
84
89
59
77
71
87
93
61
80
73
90
96
63
82
76
93
99
65
85
78
96
102
67
88
81
99
105
69
91
83
102
109
71
93
86
105
112
73
96
88
108
115
75
99
91
111
118
77
102
93
114
121
79
105
96
118
125
81
107
98
121
128
83
110
101
124
131
85
113
103
127