As you review a process used to wet a powder into a liquid,
consider what happens to the material as it goes through
the system and bear in mind the principles taught in the
previous sections of this tutorial.
Here's a problem that is typical of what you may encounter
in your manufacturing career.
Why Aren't These Plants Functioning Similarly?
A paint manufacturer has several facilities around the country
to make paint (so as not to have to ship it too far).
These plants were supposed to have very similar equipment
and very similar operating procedures. For years the product
from both plants was almost always acceptable to customers,
but in recent months the product from plant Q continued
to be good, but the product from plant R has sometimes
contained an unacceptable level of tiny bubbles that
ruin the finish on the customers' products, so they
have threatened to buy paint from your competitor.
You are a particle technology engineer and have been
asked to visit the two plants, consult with the resident
technical staff (whom you know from company seminars),
review the processes, have a guided tour through the processes,
talk with the plant workers, and help the plants solve the problem.
You agree and spend two weeks doing the first part. Now what?
You find that the equipment, materials, and processes
are nearly identical. The process is as follows:
-- 1. Inspect the tank for cleanliness.
-- 2. Measure 500 gallons of liquid into the tank.
-- 3. Start the agitator running at 45 RPM.
-- 4. Get five 20 kg bags of pigment.
-- 5. Slit the bags across the top.
-- 6. Pour the pigment in over a 10 minute period.
The stirred tank into which pigment is poured.
The Envelope Please
So, if they followed the same procedure with the
same material in the same equipment, what went wrong?
It turned out from the discussions with the plant workers
that they interpreted step 6 of the procedure differently.
One dumped in a bag, waited two minutes,
and repeated this with the next bag.
The other poured a bag in gradually over two minutes
and repeated this with the next bag.
Questions: a) Which one worked at plant R and why was this causing
microbubbles? b) What can you do to improve quality?
Answers: a) The first one.
b) You can explain to the operator that rapid addition of
a powder that takes a while to wet in creates
deep piles of dry pigment that are then drawn into the agitator
vortex and submerged before they are fully wetted.
You can then demonstrate how to gradually sift the contents
of a bag into the tank (if you remembered to observe how the
operator at plant Q did it).
While this may not involve any advanced theory, it is typical
of the problems that people unfamiliar with the principles of
particle technology get into. Those who know the principles can
consistently make high quality products.
Those who don't know, won't survive the competition.
You are now among those who know. Congratulations!