I answer so many customer questions on such
a variety of topics that sometimes I feel like a contestant
on a TV game show named, “Stump the Coolant Guy!” So,
you can understand why I imagine saying, “Alex, I’ll take
Coolant Longevity for $500 please.” “Alright Ed,” Alex says,
“Here’s your first answer: ‘Much longer than you think.’”
My reply: “What is, ‘How long should coolant last?’”
“Right!”
Alex shouts as the studio audience cheers. For those of
you playing along at home (or in the machine shop) here’s
a more complete answer. No one looks forward to cleaning
out a coolant sump, so the longer the coolant lasts, the
better.
Coolant
longevity is generally controlled by two primary factors:
1)
Choosing the right coolant for the type of metal you are
machining; and
2)
Following best practices in coolant maintenance.
Choosing
the Right Coolant
Some
machine shops buy a certain coolant because the manufacturer
offers the absolute lowest price per gallon. Others buy
a coolant because the brand is advertised as extending tool
and/or sump life. And some coolant is chosen only after
a salesman has looked at your operation, assessed your needs,
and made an appropriate recommendation.
How
do you buy coolant? A company that has a central coolant
system made of untreated concrete buried eight feet underground
will not be buying a coolant that is designed to last a
year or more because this “high-end” coolant is not the
right coolant for the application. Even a “super” coolant
would have a difficult time in this environment.
Your coolant sales professional should be able to
recommend the best coolant for your operation. Choices are
made based on the type of metal you machine and your specific
operations. In general, synthetic coolants have a longer
sump life than soluble oils, but synthetics have more limiting
tool life properties. Semi-synthetics have very good operator
acceptance, but some of the newer semis are high priced.
Coolant Maintenance
How well coolant is maintained is a key to the success
of your coolant longevity. Cleanliness does matter! Removing
tramp oil, maintaining coolant concentration at the recommended
level, and improving filtration will help an average coolant
to perform better. And it will help superior coolants last
even longer than you thought possible. Many coolants on
the market today are capable of lasting a year or more in
your individual sumps as well as central systems. A two-year
life expectancy for central systems is not unusual.
“Is My Coolant Wearing Out?” Maintenance
Yes and No! How’s that for an answer that covers
all the bases? The truth is your coolant does wear out.
You simply may not notice it because you are regularly adding
fresh coolant to the sump. Some large systems will lose
10 percent to 15 percent of their total volume in water
evaporation just setting over a weekend.
As your coolant ages, the rust preventive part of
the coolant plates-out on freshly machined parts, doing
its job to eliminate rust. However, as it does its job,
the level of rust preventive remaining in the coolant is
reduced.
Similarly, the biocide, another component of your
coolant, is used up as it kills bacteria. The same is true
for fungicide which is used up preventing mold and fungus
growth. We usually don’t notice these subtle changes in
the coolant because every day or two we add some fresh coolant
to the sump with the makeup water.
There have been many advances in coolant technology
over the years that allow manufacturers of metalworking
fluids to provide coolants that have greatly extended sump
lives, improved tool life, and achieved greater operator
acceptance. Concern arises when the coolant has been in
a system for a long time and proper filtration is lacking.
If you pay a premium price for a high-end coolant made to
last a year or more but you don’t maintain it, you’ll likely
be pouring your dollars down the drain. The manufacturer
of your coolant has done everything it can to provide the
best, longest lasting product. But to make it last, you
have to maintain it.
As soon as you start using fresh coolant, several
things begin to occur. Water hardness in the form of minerals
slowly increases in the coolant system along with metal
fines that are too small to be filtered out. The coolant
begins to deteriorate due to chemical contamination from
outside sources such as coatings on castings, cleaners used
by operators, and just plain dirt. In time, even the best
coolants need to be changed.
You can usually tell when the coolant is past its
useful life because problems begin to occur. If you purchased
a coolant and expected it to last a year and it’s only been
11 months, perhaps your level of contamination was greater
than you predicted.
There was a time when I was asked by a customer,
“Why is my coolant usage up 25 percent?”
My response: “How is your production?”
“Why, we’re up 30 percent,” he said, answering his
own question.
Well that’s the way it works for coolant life.
If, in the past, you maintained your coolant well and you
continue the same good practices and now your coolant life
is a little shorter than usual, perhaps your production
has been up and you’ve put more stress on the coolant.
What is the Best Way to Clean a Coolant System?
I usually answer this question by asking, “How much
time do you have?” Production downtime costs money and unless
you’re not using the machine, time is always an important
part of the equation. Here is our:
Clean-Out Procedure for Individual Coolant Sumps
with Central Systems
1. Remove all old coolant from the sump.
2. Remove metal fines and sludge.
3. Fill sump with enough water to circulate through pump.
4. Add 1.0 percent to 1.5 percent machine cleaner to the
water in the sump.
5. If possible, add one-quart biocide for each 100 gallons
of water. (DO NOT USE BLEACH)
6. Circulate for 2-4 hours through all coolant lines and
nozzles.
7. Rinse off machine surfaces and thoroughly clean.
8. Pump out cleaner/biocide mixture and dispose of properly.
9. Remove any residual dirt, oil, etc.
10. Add water to the sump until it is about half full.
11. Add water and coolant together until the sump is completely
full.
12. Check coolant concentration with a refractometer and
adjust if necessary.
You might find that this procedure will take
more time than you have. A shorter, albeit less thorough,
approach is possible. Consider these steps:
Clean-Out Procedure for Individual Coolant Sumps
& Central Systems (in a Hurry)
Add 1.0 percent to 2.0 percent of a mild machine
cleaner to the existing dirty coolant. A mild biocide at
one-quart per 100 gallons is also a good idea at this point.
Circulate through hoses and pumps for several hours if possible.
This will loosen some of the more difficult deposits of
metal fines and dirt. Remove the old coolant and rinse down
the system. Remove that small portion of water used for
rinsing. Follow steps 10, 11, and 12 from the previous listing.
Your system will not be as clean, but the time you save
will get you back in production sooner.
Summary
A good coolant that is designed to last a long time
in your system will last a long time if you provide adequate
filtration and take care to remove contaminates. When it
is time to change your coolant it’s a good idea to clean
out the system properly. Then, your fresh coolant charge
will last even longer than before.
Of course, the information provided here is general
in nature and is best used as a guideline or starting point.
If you have specific questions regarding coolant longevity,
ask a qualified metalworking fluids provider. Maybe you
can even play a round of “Stump the Coolant Guy!”
This article originally appeared in Shop Talk magazine in August of 2005. Shop Talk is published
by Magellan Publishing.
