Replies

1. 
   Andy_Charron | Mar 09, 2000 03:42pm | #1

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   I used to have this information but I moved a few years ago and it seems to have gotten lost (or tossed.) Probably the best thing to do would be call DuPont and see if they can help you. However, another alternative is to not worry about how the cup correlates to other cups and just figure out how it works best for you. By that I mean start by timing an unthinned finish through your cup and see how it sprays. If it needs thinner, add a small, measured amount, time the finish through the cup and see how it sprays. Keep doing this until you get the viscosity that works best with your gun. At this point you will know how long it will take for the viscosity cup to empty. In the future, you can thin any finish until it reaches this viscosity and you know it will work. Granted, it would be easier if you could simply convert the manufacturers recommended viscosity for one cup to your own. However, I have found that what the label on a can of finish recommends is not always what's best for your equipment. Once you know how fast the finish should flow through your particular viscosity cup, the type of cup and time recommended by the finish manufacturer becomes unimportant. Hope this helps.

1. 
   Bruce_B. | Mar 09, 2000 04:59pm | #2

   *After reading your fine "Spray Finishing", I got inspired to take a more scientific approach to nozzle selection and thinning, and I measured the viscosity of a number of waterborne finishes using a Gardner #4 Ford cup. When I then used my measured viscosities (after converting to Zahn seconds) to determine the recommended nozzle sizes for my spray gun (Accuspray 10-Gun), I found that the predicted nozzle sizes were much greater than those recommended by the two finish manufacturers that actually put out nozzle recommendations. For example, Compliant Spray Systems suggests a .041" nozzle with their Enduro poly, whereas my viscosity measurement indicated a .062" nozzle. When I talked to them about this discrepancy and asked them what the viscosity of their product should be, they said not to get too scientific about all this, just use the .041" nozzle, because that's the one that works best. And they are right about that. All of this is to second your point about not worrying too much about absolute calibration. I still measure viscosities, but have worked up my own system to determine nozzle size and thinning schedule. Also of course viscosity is a strong function of temperature. Thanks for writing such a useful book.

1. 
   Phillip_Nethery | Mar 10, 2000 01:12am | #3

   *Thanks--I'll try it. Also, thanks for a great book.