On 2/9/13 1:07 PM, wrote:
On Feb 9, 11:29 am, -MIKE- wrote:
While we're on the subject.... do you guys use the viscosity cups that
come with HVLP guns?
Do you know of a good resource explaining their proper use?
Many of the sources I've seen on the internet contradicts one another
(big surprise!).

Lab grade cup and its proper use:

http://www.youtube.com/watch?v=LJDmQt_xpco

Reality is sentence #3, starting with "However":

http://en.wikipedia.org/wiki/Ford_viscosity_cup

As I understand it (take that for what it is worth) the Ford Cup was
developed by Ford auto engineers in the 30s to assure that their black
paint was the right viscosity for their cranky spray machines. They
were able to use and batch paint correctly with this simple system as
they kept all the note required to record successful spray days that
also recorded the existing environment conditions at the time of
spraying.

For me, they are a waste of time. ALL approximations used in
viscosity cup recommendations are given based on results from lab
tests. When will it be a perfect 77 degrees with 33% humidity where
you live? Conditions at the time of application never match the data
given by the manufacturer, and with temperature being the most
influential, their data is of no use.

Many years ago I had this discussion with a paint rep that came out to
inspect a finish I had applied. He wanted to know if I had used the
cup to determine viscosity. His application data showed all
measurements for proper viscosity taken at 77 degrees. During the
summer, it may only get down to the upper 80s here, ten degrees hotter
than the data sheet, and by noon it is in the low/mid 90s. These
temperatures rendered his viscosity tests irrelevant. I sent him
packing and got the industrial rep out there and we resolved the
problem.

So the point of all that is that temps are the biggest problem for any
sprayer. And they are at any time since they affect the viscosity of
the materials so much.

A viscosity cup can get you in the ballpark to get going and they are
good for that, sometimes when it is cold. If you are spraying at 55
degrees, it is easy to over thin to get the material out of the gun.
A viscosity cup is good for that. But past about 65 or so, I wouldn't
think of using one. Mix, spray, test on scrap. Record results so
next time you will have them at hand.

Since your equipment can be a factor as well, you have remember that,
too. Do you have the same tip size on your gun that they used when
determining recommended viscosity? Are you using the same air
pressure? Are you using a device to remove moisture from the air (a
must here with our super high humidity) before it hits the gun? All
of those things factor in, and unless your spray equipment is the same
as the test equipment used by the manufacturer, you results won't be
optimal.

So, after all of that.... find a product line you like that suits your
needs and stick with it to learn it. Then mix, spray, test on scrap.
Record results so next time you will have them at hand. As I told
Karl before he started his plaque, with an unfamiliar product I would
buy two quarts of product. One to mix up and test my setup with, and
one to open as pristine to mix for finishing. No viscosity cup can
match an actual test shot.

Probably a lot more than you ever wanted to know.

Robert


Not at all.
Thanks for taking the time to present such a thorough opinion.


--

-MIKE-

"Playing is not something I do at night, it's my function in life"
--Elvin Jones (1927-2004)
--
http://mikedrums.com

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