Trample Tramp Oil - Master Chemical Corporation

COOL
TALK
BY
WILLIAM SLUHAN
Trample
Tramp Oil
A fluid-management program
that does what it is supposed to
do saves a company money and
time. Conversely,
poor fluid management
can cost a
company tens of
thousands of dollars
annually in
broken tools,
employee-health
problems, unnecessary
disposal
fees, wasted concentrate,
and lost
labor time. Improperly maintained
metalworking fluids can
lead to corrosion, bacterial
degradation, fungal growth, dermatitis,
poor tool life, and poor
product finish.
Cutting fluids are only as
effective as the
fluid-management
program backing
them up.
These problems are often considered
endemic to cutting and
grinding fluids. In reality, all
coolant problems result from
poor coolant selection and poor
maintenance of the fluids selected
to do the job. Plus, overarching
attitudes such as “all
coolants are the same” and “all
coolants are trouble” foster the
continual repetition of mistakes.
Such thinking is based on a reactive
approach to fluid management
- treating symptoms of a
larger problem. More
effective is a preventative
approach to fluid
management - regularly
maintaining and
monitoring fluid performance,
preemptive
cleaning, and recycling
the fluids before
they seriously
degrade.
Coolant Recycling
Fluid disposal in the 1960s was
virtually cost-free, but today disposal
costs generally equal the
cost of the replacement fluid and
frequently exceed purchase cost
when dilution factors are taken
into account. Furthermore, with
the enactment of the Resource
Conservation and Recovery Act
(RCRA) of 1976, legal disposal
of cutting and grinding fluids has
become both more difficult and
more expensive.
For example, an inexpensive
fluid selling for $2/gal. at a 20-
Editor’s Note: William Sluhan is chairman of the board of directors and CEO of
Master Chemical Corporation, Perrysburg, OH. Mr. Sluhan has 30 years of experience
in the formulation, selection, application, and maintenance of water-miscible
metalworking fluids and in the development of coolant-management programs.

to-1 dilution costs $0.10/gal. in
the machine sump. A more
expensive fluid selling for $8/gal.
at the same dilution costs
$0.40/gal. in the sump. Typically,
disposal costs for used fluids are
$0.40/gal. to $0.80/gal., and in
many areas these costs run as high
as $5/gal. RCRA is rapidly
changing us from a “disposal society”
to a “recycling society.”
When referring to water-miscible
coolants, recycling is an oft-misunderstood
term. In most managers’
minds, recycling means “contaminate
the fluid until it is no longer
usable and then clean it up for use
again.” Recycling destroyed
coolant isn’t really possible,
despite what some recyclingequipment
suppliers have claimed.
Actually, coolant recycling is a
preventative-maintenance program
designed to maintain the fluid in
such condition that it does not
require disposal. A successful
coolant-recycling program
requires:
1. High-quality (more costly)
fluid concentrates;
2. Reliable, effective industrial
recycling equipment.
3. Management control of the
fluids.
Items 1 and 2 above can be
purchased, but item 3 must be
instituted from within.
It’s best to purchase a coolantrecycling
system from a supplier
that can provide both the fluids
and the equipment. Only a supplier
of both fluids and equipment
has the practical experience in
controlling fluids to help implement
the management control
needed for successful recycling.
Recycling Processes
Coolant recycling can be done via
two very different processes;
batch recycling for machines
operating with individual coolant
sumps, or continuous recycling
for machines operating on central,
recirculating filtration systems.
In batch recycling, the machine’s
coolant sump is first cleaned thoroughly,
rinsed, and charged with
fresh coolant. This coolant is run
until it is contaminated with fines
and tramp oils. The length of a
run depends on operating conditions
that vary considerably from
machine to machine and from
plant to plant. Once the fluid is
contaminated, the fluids and
solids are vacuumed from the
sump and replaced with clean
fluid. The contaminated fluid is
transported to the recycling system,
where rejected tramp oils are
removed with a belt skimmer.
The fluid is then processed by a
high-speed, disc-bowl centrifuge
to remove tramp oils and fine particulate
matter. This recycled
fluid is then blended with fresh
fluid to the proper concentration.
Fluid concentration typically is
determined with a refactometer
after centrifuging. The fluid normally
is diluted to the volume
needed for makeup, and sufficient
concentrate is added to bring the
batch to the correct concentration.
The resulting clean fluid is used
to charge machines and to maintain
fluid levels in machines on
the system.
In continuous or central recycling,
the central system, flumes, pipes,
and machine tools are first
cleaned thoroughly, rinsed, and
charged with fresh coolant. All
makeup fluid to maintain both
system level and fluid concentra-
tion is added automatically.
Tramp-oil contamination is controlled
by a properly sized, highspeed,
disc-bowl centrifuge operating
continually in bypass mode,
since only a small percentage of
the system’s total fluid volume
must be processed per hour.
Since no central clarifying or filtration
system is 100% effective in
removing all solids, fines will
accumulate in tanks, flumes,
pipes, and machines. These accumulations
must be removed from
the system, and the system must
be thoroughly cleaned and rinsed
at least once per year. During the
cleaning process, the fluid is
removed and stored in tanks or
rented tank trucks. Upon completion
of the system cleaning, the
fluid is returned to the system for
continued use.
Controlling Tramp Oil
As machine tools age, it becomes
virtually impossible to prevent
contamination of coolants by
tramp oils, which include lubrication,
cutting, and hydraulic oils
and greases. Without a comprehensive,
integrated fluid-management
and recycling program,
tramp-oil contaminants can pose
serious threats to the proper function
and longevity of cutting and
grinding fluids.
Fluids contaminated by tramp oils
cause several problems in the
machine-shop environment.
They:
1. Inhibit wetting and, thereby,
degrad workpiece finish, and
shorten tool life;
2. Reduce coolant and, thereby,
shorten tool life;
3. Impede filtration;
4. Contribute to unfavorable

esidues on machine tools and
parts;
5. Contribute to smoke and oil
mist in the shop air;
6. Stimulate bacterial growth.
These adverse affects are proportional
to the amout of tramp oil
present and, therefore, are most
pronounced on machines that leak
the most oil. As bad as these
effects are on the individual sump
machines, they are even worse in
central systems where continuous
recirculation through powerful
pumps keeps the tramp oil emulsified.
We have observed that tramp-oil
emulsification has been a greater
problem since the 1973-1974 oil
embargo. Prior to the embargo,
many machine-lubricating oils
were relatively water resistent
and, given some quiescent time,
these oils would float to the surface
where they could be
skimmed off with oil-attracting
belts or wheels. Since the embargo,
many lubricating and
hydraulic oils have been reformulated
due to the drastically
reduced availability of certain
crude oils. (There has been no
incentive for lube-oil blenders to
go back to the original base oils.)
The oils used today are highly
emlusifiable and, once emulsified,
will not separate no matter how
much quiescent time is available.
Water miscibility of some
hydraulic oils is now so pronounced
that the oils will emulsify
in water almost like a soluble
oil and will occasionally even
emulsify in chemical-true-solution
coolants (nonsurface-active grinding
fluids), which traditionally
have been thought to reject tramp
oils.
Because of tramp oils’ numerous
ill effects, tramp-oil contamination
should be minimized.
Machine maintenance should be
kept up diligently. Hydraulic-oil
leaks require immediate repair.
In batch recycling systems, trampoil
removal should be accomplished
to the maximum degree
possible. The tramp-oil removal
should be accomplished to the
maximum degree possible. The
tramp-oil content of recycled fluid
should not exceed 0.5% by volume.
Determine the tramp-oil
content of the recycled fluid
before adding fresh makeup fluid.
Central systems generally will
perform satisfactorily as long as
tramp oil does not exceed 2% by
volume. But again, the lower the
tramp-oil contamination, the better.
Above 2%, bacterial growth
increases, and above 3%to 4%,
tool life, workpiece finish, oil
mist, and residues become problematic.
Numerous techniques and devices
have been employed to remove
tramp oils from coolants with
varying degrees of success:
1. Wheel and belt skimmers
will remove floating or rejected
oils once they have reached the
surface, though they will not
remove emulsified oils.
2. Coalescers are devices that
often contain oleophilic (oilattracting)
media designed to
make small oil droplets merge,
forming larger oil droplets that
will then rise to the surface where
they can be skimmed off. The
presence of chemical anionic
(negatively charged) or nonionic
(no electric charge) wetting agents
or emulsifiers negates the function
of the coalescing media and,
therefore, coalescers will work
best with chemical-true-solution
coolants, which have no wetting
agents or emulsifiers. Coalescers
require periodic cleaning to prevent
sludge accumulations that act
as bacterial breeding grounds.
This cleaning can be difficult,
messy, and time-consuming. Our
experience with coalescers indicates
that they are no more effective
in removing tramp oils than
settling tanks used with effective
oil-skimming belts.
3. Centrifuges are the only
truly effective devices for removing
free, dispersed, and emulsified
tramp oils. High-speed,
disc-bowl centrifuges can exert a
minimum force of 4000 Gs on the
fluid. Low-speed centrifuges that
only generate forces of 800 to
1800 Gs (such as those made by
Barrett, Donaldson, and Mohawk)
will remove particulate matter
from coolants but will not remove
emulsified oil, even with repeated
passes.
High-speed centrifuges can reduce
tramp-oil content to 0.5%or less
by volume and can reduce particulates
to 2μm to 5μm in one pass.
Although such centrifuges can
remove solids, their primary function
is to remove tramp oils.
Therefore, only filtered or settled
fluids should be supplied to the
centrifuge to minimize the solids
load on the centrifuge. Solids
that do reach the centrifuge must
be removed periodically by manual
cleaning. Self-desludging centrifuges
are normally applied to
central filter systems and do not
require manual cleaning, but they

do require dismantling once or
twice a year for inspection of
seals, gaskets, etc. to ensure proper
functioning.
Generally, manually cleaned centrifuges
are used for tramp-oil
removal in batch recycling systems.
Either manually cleaned or
self-desludging centrifuges can be
applied to central, recirculating
coolant-filtration systems. Selfdesludgers
usually are preferred
by large plants that have their own
oily-waste-treatment facilities to
process the desludge waste from
the centrifuge. Of course, a plant
should always decide these matters
according to its specific needs
and the demands of individual
applications.
Although there are a handful of
applications in which dry machining
is an accpetable practice,
there is a little debate about the
importance of cutting and grinding
fluids in most metalworking
processes. Machining quality
parts at high production rates is
no more possible with faulty tools
or improperly maintained
machine tools than it is with
improperly managaed fluids.
Reprinted from
CUTTING TOOL
ENGINEERING ®
Volume 49 Number 6 September 1997