Viscosity Cups Revisited

Q. I enjoy reading your Painting Clinic column in PRODUCTS FINISHING from time to time.

However, allow me to take exception to a few points you made regarding Viscosity Cups in the October issue.
There are numerous ASTM Specification covering dip and laboratory-type viscosity cups which address both precision and correct method of use.

As for control in the manufacture of viscosity cups, I cannot speak for others, but the cups we produce are made to strict standards and are calibrated in accordance with ASTM and ANSI and can be certified traceable to NIST. I am attaching a .pdf version of our 2006 Viscosity Cup Equivalent Wall Chart which will attest to this by the accuracy tolerances stated for each cup.
The importance of temperature control and the nature of Newtonian flow cannot be stressed more and is often overlooked to the detriment of flow cups in general.

 

A.Thank you for reading my column, if only from time to time. For the record, I don’t just make up my answers. Instead they are generally based on personal experience. I was the paint consultant for a corporation that had more than 100 paint lines applying organic finishes ranging from electrocoating to powder coating, with all the various liquid coating methods in between,
When I was a fellow scientist at the corporate research laboratories, managing the paint lab, my people used a lot of your equipment and found it to be of high quality. We also used most of the available viscosity cups and found them to be lacking in reproducibility of results. Tests were always conducted under controlled conditions. We saw the same variations that D.M. described in the October Painting Clinic question.

You and I agree that temperature control and the effects of Newtonian and non-Newtonian flow are important. I think you will also agree with me that in a paint company’s quality control laboratory, the technician should be measuring viscosity using one of your viscometers rather than a viscosity cup.