Using Viscosity cups [Archive] - Sawmill Creek Woodworking Community

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David Scigliano

06-01-2006, 8:25 PM

I have a devilbiss finishline hvlp gravity fed system. I keep reading about using viscosity cups to see how thick or thin a finish is. My question is what do I use to do this and what does #4 ford cup mean? And how does this relate to my air gun?

Don Baer

06-01-2006, 8:34 PM

Here is the proceedure.

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1. Select the viscosity cup which is sized appropriately for the liquid to be tested. Be sure that the cup is absolutely clean, and free of any burrs or other defects.
2. Adjust, as necessary, the temperature of the test liquid.
3. Use your index finger to lift the cup by its ring. Avoiding all bubbles, froth, foam, etc., immerse the cup fully into the test liquid. Make sure the cup is vertical and free of air pockets.
4. Measure and record the temperature of the liquid inside the cup.
5. Smoothly and rapidly remove the viscosity cup. Start the timing device exactly as the top of the filled cup breaks the surface of the liquid vessel you are drawing the sample from.
6. Stop the timing device at the first obvious break in the efflux stream, as observed about one to two inches below the base of the cup.
7. Record the exact drain time (to 0.1 sec), temperature, cup number, and all necessary product data. This can be converted to centistokes by using the conversion table furnished with the viscosity cup.
8. For improved assurance and precision, perform three tests, record the results from all three, and use the average as a best estimate of actual viscosity.
9. Be sure to clean the cup thoroughly, immediately after each use (nylon fishing line can be used to clean the orifice).

<TABLE cellSpacing=0 cellPadding=3 width="100%" border=1><TBODY><TR><TD colSpan=7 height=19>
Molecular Weight, Density, Surface Tension,
and Viscosity of Selected Liquids
</TD></TR><TR><TD class=products>Name</TD><TD class=products>
Molecular Formula
</TD><TD class=products>
Mol.Wt.
</TD><TD class=products>
Specific
Density
(1)
</TD><TD class=products>
Surface Tension
(2)
</TD><TD class=products colSpan=2>
Viscosity
</TD></TR><TR><TD> </TD><TD> </TD><TD> </TD><TD> </TD><TD> </TD><TD class=products>
Centipoise
</TD><TD class=products>
Centistokes
</TD></TR><TR><TD class=products>Acetic acid</TD><TD class=products>
C2H4O2
</TD><TD class=products>
60.05
</TD><TD class=products>
1.043
</TD><TD class=products>
27.5
</TD><TD class=products>
1.06
</TD><TD class=products>
1.02
</TD></TR><TR><TD class=products>Acetone</TD><TD class=products>
C3H6O
</TD><TD class=products>
58.08
</TD><TD class=products>
0.786
</TD><TD class=products>
23.5
</TD><TD class=products>
0.31
</TD><TD class=products>
0.39
</TD></TR><TR><TD class=products>Butyl acetate</TD><TD class=products>
C6H12O
</TD><TD class=products>
116.16
</TD><TD class=products>
0.876
</TD><TD class=products>
24.3
</TD><TD class=products>
0.69
</TD><TD class=products>
0.78
</TD></TR><TR><TD class=products>Cyclohexane</TD><TD class=products>
C6H12
</TD><TD class=products>
84.16
</TD><TD class=products>
0.773
</TD><TD class=products>
25.3
</TD><TD class=products>
0.89
</TD><TD class=products>
1.16
</TD></TR><TR><TD class=products>Cyclohexanol</TD><TD class=products>
C6H12O
</TD><TD class=products>
100.16
</TD><TD class=products>
0.960
</TD><TD class=products>
33.4
</TD><TD class=products>
57.5
</TD><TD class=products>
59.9
</TD></TR><TR><TD class=products>Ethanol</TD><TD class=products>
C2H6O
</TD><TD class=products>
46.07
</TD><TD class=products>
0.787
</TD><TD class=products>
22.5
</TD><TD class=products>
1.08
</TD><TD class=products>
1.37
</TD></TR><TR><TD class=products>Ethanolamine</TD><TD class=products>
C2H7NO
</TD><TD class=products>
61.08
</TD><TD class=products>
1.014
</TD><TD class=products>
48.9
</TD><TD class=products>
21.1
</TD><TD class=products>
20.8
</TD></TR><TR><TD class=products>2-Ethoxyethanol</TD><TD class=products>
C4H10O2
</TD><TD class=products>
90.12
</TD><TD class=products>
0.931
</TD><TD class=products>
28.9
</TD><TD class=products>
1.85
</TD><TD class=products>
1.99
</TD></TR><TR><TD class=products>Ethyl acetate</TD><TD class=products>
C4H8O2
</TD><TD class=products>
88.11
</TD><TD class=products>
0.894
</TD><TD class=products>
23.9
</TD><TD class=products>
0.42
</TD><TD class=products>
0.47
</TD></TR><TR><TD class=products>Ethylene glycol</TD><TD class=products>
C2H6O2
</TD><TD class=products>
62.07
</TD><TD class=products>
1.110
</TD><TD class=products>
48.3
</TD><TD class=products>
16.1
</TD><TD class=products>
14.5
</TD></TR><TR><TD class=products>Formamide</TD><TD class=products>
CH3NO
</TD><TD class=products>
45.04
</TD><TD class=products>
1.130
</TD><TD class=products>
58.1
</TD><TD class=products>
3.34
</TD><TD class=products>
2.96
</TD></TR><TR><TD class=products>Formic acid</TD><TD class=products>
CH2O2
</TD><TD class=products>
46.03
</TD><TD class=products>
1.220
</TD><TD class=products>
37.1
</TD><TD class=products>
1.61
</TD><TD class=products>
1.32
</TD></TR><TR><TD class=products>Methanol</TD><TD class=products>
CH4O
</TD><TD class=products>
32.04
</TD><TD class=products>
0.787
</TD><TD class=products>
22.4
</TD><TD class=products>
0.54
</TD><TD class=products>
0.69
</TD></TR><TR><TD class=products>Methyl acetate</TD><TD class=products>
C3H6O2
</TD><TD class=products>
74.08
</TD><TD class=products>
0.927
</TD><TD class=products>
24.7
</TD><TD class=products>
0.36
</TD><TD class=products>
0.39
</TD></TR><TR><TD class=products>Methyl ethyl ketone</TD><TD class=products>
C3H8O
</TD><TD class=products>
72.11
</TD><TD class=products>
0.799
</TD><TD class=products>
24.6
</TD><TD class=products>
0.41
</TD><TD class=products>
0.51
</TD></TR><TR><TD class=products>1-Propanol</TD><TD class=products>
O4H8O
</TD><TD class=products>
60.10
</TD><TD class=products>
0.802
</TD><TD class=products>
23.7
</TD><TD class=products>
1.95
</TD><TD class=products>
2.43
</TD></TR><TR><TD class=products>Toluene</TD><TD class=products>
C7H8
</TD><TD class=products>
92.13
</TD><TD class=products>
0.865
</TD><TD class=products>
28.5
</TD><TD class=products>
0.56
</TD><TD class=products>
0.65
</TD></TR><TR><TD class=products>Water</TD><TD class=products>
H2O
</TD><TD class=products>
18.02
</TD><TD class=products>
0.998
</TD><TD class=products>
72.8
</TD><TD class=products>
0.89
</TD><TD class=products>
0.89
</TD></TR></TBODY></TABLE>
(1) g/ml @ 20°C (2) dynes/cm @ 20°C (3) Viscosity as measured @ 25°C. Centistoke is a measure used in viscosity cup tests; it equals centipoise divided by specific density

a #4 cup refers to a standard it has to do with the hole size. by testing the viscosity it will give you an idea as to how the paint will flow.

Personaly I think I'd just cut the paint with some solvent and keep trying until I get the flow I want.

Allen Bookout

06-02-2006, 12:59 AM

After reading those instructions I don't think that I will ever spray again. My degree is in business----not chemistry.

Steve Schoene

06-02-2006, 1:17 AM

Gee, I though business education required counting--the only difference is that this calls for counting seconds, not beans. ;)

Allen Bookout

06-02-2006, 2:07 AM

Well that us see. First I need to adjust the temperature of the test liquid. I suppose that is the purpose of a microwave and a special temperature measureing device. The next thing that I need to know is what the "efflux stream" is so that I can do the timeing thing. Then convert to "centistokes", whatever that is. Now I have to do that three times and take an average. Give me a break! OK, Ok. Suppose that I do it all and get a precise figure and adjust the fluid, as close as I can. Now what? Take three more measurements, average them, and hope like the dickins that it came out right so that I do not have to do it three times again? I suppose.

By the way, what is that chart? I do not see anything there that I am interested in dealing with.

I think that you are going to laugh when you hear how I have always done it. I thin as recommended by the manufacturer, see how it drains off of a stir stick, put it in a gun and test spray on a piece of cardboard. If it gets any more complicated than that I am just out of business. Or if it does get more complicated, as I learned in school, I could hire a secretary for that sort of thing.

Your scientific friend, Allen

Ken Garlock

06-02-2006, 10:49 AM

Don, your response reminds me of a short story that supposedly took place in the Seattle area.

It seems that there was a young pilot was flying around the area when suddenly a fog rolled in. The poor guy was lost, as you might guess. He spied an office building through the fog, so he made up a sign saying 'where am I?' and held it up to the plane window. A person in the building held up a sign that said 'you are in a plane.' The pilot then proceeded 5 miles north and landed.

The air field was just north of the office building that housed the Microsoft customer service center. He knew immediately that the building was a M/S center because the answer was perfectly correct but totally useless.:eek:

Now, can you tell us how to measure paint viscosity without a chem lab?:confused: :D

Allen Bookout

06-02-2006, 2:01 PM

I really like that story Ken. Think that I will send it on to some of my Windows friends. Allen

tod evans

06-02-2006, 2:15 PM

for spraying wood finishes shoot for the consistancy of 1/2-n-1/2 cream....it ain`t rocket science! this ol` hillbilly has been doing it well for lotsa years without viscosity cups or a chemistry degree. if you spend 1/2 as much time messing with your equipment as reading confusing literature about it you`ll have it down shortly....02 tod

Joe Pelonio

06-02-2006, 4:42 PM

I actually got decent grades in chemistry but it was a long time ago. I've lately been spraying some latex with a touch up gun and found that if it's about like cheap catsup, or maybe buttermilk it works fine. Half-n-half would work but I found it didn't have to be quite that thin.

Byron Trantham

06-03-2006, 1:39 PM

David, my gun (an Apollo conversion HVLP) came with a viscosity cup (a Zahn #2). I pretty much ignored it beause every thing I measured didn't seem to line up anything on the chart provided. Anyway, I ignored it for almost two years. I had varying level of success with spraying but I kept at it. A couple months ago I went to our local yearly wood show and attended one of those mini lectures (put on by Apollo) and the first thing they covered was viscosity. Bingo! I knew what my problem was. As soon as I got home I measured the stuff and it took like almost two minutes to go through the cup. I cut it 20% and measured again. Now it was within the recommended range for my #3 needle. The coverage was supper and I was able to reduced the air pressure significantly thus virtually eliminating over spray! The whole purpose of getting viscosity correct is atomization - the ability of the run to combine air and material in such a way as to allow it to flow properly. If your gun came with recommended times for various materials, stain, lacquer, WB material, etc. use it as a guide. If the time is too long you can thin it with water, mineral spirits or lacquer thinner depending on what you are working with. I hope this helps.

Steve Clardy

06-03-2006, 4:07 PM

No cups for me. I hust add thinner,, reducer, retarder as necessary.
Test on cardboard

David Eisenhauer

06-04-2006, 11:25 AM

I'll try to hit the middle between the "White Paper" on viscosity and Steve's "thin as required". :D . Different fnishes work best with a certain level of atomization to achieve "flowout". Different sized needles on spray guns provide different amounts of atomization. There are a few "standard viscosity measurers" (is that a word?) common to the industry. They use names like "Ford, Zahn, etc" and have a number associated with the name. The combination of name/number indicates a particular amount of finish flow (viscosity) through the measuring cup. The finish literature and spray gun literature tell you what the preferred or available viscosity level of the finish or gun setup is. There are conversion tables that allow you to use a "#2 Zahn" cup when the finish or gun literature provides a #4 Ford" cup viscosity number.The cup is dipped completely under the surface of the finish (100% filled with finish-no air trapped) and pulled quickly-smoothly out of the finish. You are supposed to note how many seconds it takes for the finish to first break the steady flow of draining finish through the bottom hole in the cup. That doesn't mean how long it takes to completely empty the cup, just the first break or interruption in the flow.That number of seconds will tell you the viscosity of the finish. If it is significantly longer than called for, then some thinner is probably called for. Steve has probably been doing this long enough so that his eye tells him what will run through his gun or he uses the same finishes through the same guns and only has to adjust his standard setup for weather conditions. I hope this helps, if not, sand it off and try again.:p

Byron Trantham

06-04-2006, 12:02 PM

David, right on. During that mini-lecture I attended through Apollo, the guy asked us if we ever watched an auto body painter open a can of paint stir it and pull the stick out and watch the fluid flow off the stick back into the can. Well he is checking viscosity. With experience, the instructor said, you can do the same. I have been practicing and he is right. Now I can pretty much see when something needs thinning. I still rely on my Zahn cup but I am getting faster as making the material ready for spraying.

tod evans

06-04-2006, 12:23 PM

Steve Clardy

06-04-2006, 12:41 PM

i think this is what steve and i do? after the first few hundred gallons ya` kind of get a feel for it..02 tod

Yep. Works for me.

Lacquer is easy. Waterbase poly is a little more trial and error for me.
Haven't used much of it.