Viscosity testing

The benefits of checking fluid consistency as part of the finishing process. October 2, 2001

Question
What are the benefits of viscosity testing?

Forum Responses
There are several reasons why you should check viscosity.

1. When you use the correct viscosity, you will have less solvent popping, runs and a more consistent wet film thickness from day to day production.

2. If you operate several shifts, it will allow spray equipment to work properly from shift to shift and finisher to finisher.

3. It will also allow the spray guns to work their best, as certain gun tips are for certain viscosity products.

Make sure you always check viscosity at the same temperature. Temperature has a big part to play with the viscosity. If possible, always use the same temperature as the manufacturer uses on the data pages. This way we all are talking "apples to apples".

Bob Niemeyer, forum technical advisor

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When temperature is mentioned, is this the material or the working space?

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The material.

Bob Niemeyer, forum technical advisor

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Temperature is critical. That is why a lacquer heater is so good. If you check the viscosity at 70 F and then take some material out of the heater at say 125 F and check the viscosity, you will find it is much lower. So it atomizes better without adding solvent and has higher solids and builds faster. (Lower VOC to boot.) On the other side, if your shop is cold, the viscosity will be higher. So even though your technician added the same amount of solvent, now the finish mysteriously comes out orange-peeled. ("I don't understand--I did everything the same!")

Also, we used to order our material in 55 gallon drums that were supposed to be at spray viscosity. It helps to have a zahn cup to check and make sure the supplier hasn't changed something. Our manufacturer started sending higher viscosity material to get around VOC regulation in Southern Cal. If we weren't checking, we could have had problems.