The objective in writing about coolants on a regular basis
is to inform those who use coolants of all the “secrets”
about coolants so you never have to think about coolant
again. In the February 2006 issue of Shop Talk you read,
“Don’t change coolant suppliers over price!”
Introducing you to the idea that pricing is relative and
many coolant suppliers have a “value added”
service that you can’t put a price tag on.
In
the May 2006 issue of Shop Talk you read, “Five steps
to improve total coolant performance.” We thought
this was such a good topic, we invited 300 coolant users
to a one day seminar just to talk about what can be done
to save money when using coolants.
With
this background information the next logical step is to
explain the results of testing coolant from your shop. Let’s
consider that you already have a coolant supplier you trust.
Then, you implement the “five steps”:
1.
Improving water source
2.
Removing tramp oil
3.
Removing metal fines
4.
Controlling concentration
5.
Using the right coolant to begin with
Now,
your coolant supplier visits you on a regular basis and
takes samples from various machines for analysis in their
laboratory. The whole idea here is to evaluate the condition
of the coolant and make recommendations that will prevent
problems and extend the life of the coolant. But what if
you receive a “lab report” and you don’t
know what it means? Let me help you out!
A
typical lab report will list:
1.
Coolant concentration
2.
pH
3.
Bacteria level
4.
Fungus/mold level
5.
Percentage of tramp oil
6.
Percentage sediment
7.
Rust test
Let’s
look at each of these to get a better understanding of what
the tests results mean.
Coolant
concentration
Here
we measure the strength of the mixture of your coolant.
Depending on the product you are using and the machining
operation, your concentration may vary anywhere from four
percent to 10 percent, sometimes higher with exotic metals.
Whatever the specific circumstances it is important to maintain
the coolant at a consistent concentration. For example,
if you are machining cast iron and using your coolant at
five percent concentration, from day to day you will notice
a change in the concentration. Water evaporates so the coolant
concentration increases. The coolant deposits rust preventive
on parts and coolant is carried off with chips so the concentration
decreases. Slight variations in concentration are acceptable;
so a five percent solution should be designed to work well
at 4.5 percent or at 5.5 percent without creating any difficulty.
Problems do arise when the coolant concentration goes outside
these limits. As the coolant concentration decreases, when
only water is added to the sump, rust protection starts
to suffer along with tool performance. At lower concentrations
you aren’t lubricating the tool. The other extreme
is too high a concentration. Here, tool life will improve;
but by continuing to increase the concentration, operators
are more likely to develop skin irritations. With the use
of a “refractometer,” you can maintain your
coolant on a daily basis and avoid problems.
pH
pH
measures the degree of alkalinity or acidity of a solution.
This is important to you because as the coolant’s
pH value changes, so does the coolant’s ability to
protect against rust and product instability. pH is a number
on a scale from 0-14. On this scale 7 is neutral, below
7 is acidic and above 7 is alkaline. Typical coolant pH
values are 8.5 to 9.2; this may vary slightly with the particular
coolant you are using. The coolant’s pH value will
change from week to week depending on what is happening
with the coolant. When bacteria are rapidly growing your
pH value will move from 9.2 towards 8.5 and perhaps even
lower. If there is a contaminant such as a cleaner (cleaners
are usually alkaline) you may see your coolant’s pH
increase.
Why
measure pH? By watching pH over time, a chemist will be
able to forecast what may happen to the coolant in the future.
Taken by itself, one pH reading does not tell us a lot.
But numerous readings over time allow us to predict future
coolant performance and stability.
Bacteria,
fungus, and mold
These
tests inform us of the biological condition of the coolant.
What harmful things are growing in the coolant? Bacteria
are ever-present in our world. High levels of bacteria start
to smell bad and will also degrade the quality of the coolant.
Coolants are typically designed to provide resistance to
bacteria, fungus, and mold; however, sometimes the biology
in the coolant takes over. Why would this happen? If your
coolant concentration gets too low, the ability of the coolant
to fight off bacteria is impaired. Diluting the coolant
dilutes any biocide or fungicide that may be in the coolant
to help protect it. The by-product of bacteria in your coolant
is acidic which causes the pH to move from an alkaline position
to an acidic position. This can affect rust protection and
over time degrade the coolant even further.
Testing
for bacteria, fungus, and mold will help determine what
steps need to be taken to keep the coolant fresh.
Percentage
of tramp oil
Tramp
oil is unavoidable because before this oil became “tramp”
oil, it was your hydraulic oil or gear lube that helped
the machine function. Now, since it’s leaked into
the coolant we call it “tramp” oil. A little
unfair, I know! Tramp oil is a contaminant to the coolant
and must be removed. Levels above one percent can be a real
problem because this oil, floating on the coolant, prevents
the coolant from breathing (taking in oxygen) and allows
types of bacteria known as anaerobic bacteria (bacteria
that live and breed in the absence of oxygen) to multiply
quickly. This explains why a machine sump with heavy tramp
oil might smell bad on Monday mornings. The coolant sat
all weekend and the oil came to the surface, sealing off
the oxygen and the bacteria took over. You start the coolant
up on Monday and it smells terrible for 20-30 minutes until
the bacteria are killed off by oxygen. Removing tramp oil
not only helps prevent bacteria from taking over, it gives
your coolant longer sump life.
Percentage
of sediment
One
of the other contaminants in the coolant is sediment. This
is dirt introduced from the air or from the surfaces of
parts. It is also carbon from the metal you are machining
and metal fines that the filter didn’t remove. Removing
sediment may require some special filters or magnetic separators.
Acknowledging that sediment is present allows the chemist
to make proper recommendations to improve your coolant performance.
Testing
for rust
For
the rust test, we take a small Petri dish with filter paper
on the bottom and add 1.0 gram of cast iron chips (special
chips of uniform size and shape designed just for this ASTM
procedure). Then, we add enough coolant to cover the chips
and allow the dish to set for a short period of time. Once
the coolant is removed the dish is left undisturbed for
48 hours; then, the chips are examined for rust. If your
coolant concentration was maintained at the proper level,
your laboratory report will likely indicate “no rust.”
Otherwise, you may have “slight rust” on the
edges of the chips, “moderate rust” on the surface
of the chips, or “severe rust” where the chips
weld themselves together.
Conclusion
Taking
proper care of coolant isn’t as difficult as it may
seem, especially if you have a partnership with a coolant
company that provides laboratory testing of your coolant.
All of the tests described above are relatively easy to
run. The results from all these tests help the chemist or
the sales representative diagnose the condition of your
coolant and write the proper prescription for improving
coolant health. Just like a visit to the doctor!
If
you have low coolant concentration and tramp oil, you will
probably see increased bacteria levels and a lower pH. If
this condition goes untreated, the coolant will get “sicker”
and the bacteria level will continue to rise and start to
smell bad. The lower pH will also cause the coolant to underperform
and your tool life will decline drastically. All this could
be avoided with proper diagnosis and treatment
Please
keep in mind that regular testing of coolant concentration
along with removal of tramp oil and metal fines will greatly
improve the condition of your coolant and allow it to last
a good long time. There are also other tests that can be
run to evaluate a coolant’s condition that are not
included in this article. We have covered the most important
tests; but, if you have any questions, give me a call at
1-888-729-0176.
This article originally appeared in Shop Talk magazine in August of 2006. Shop Talk is published
by Magellan Publishing.
