United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-90/033 Sept. 1990
&EPA Project Summary
Machine Coolant Waste
Reduction by Optimizing
Coolant Life
Joseph Pallansch
Machine shops use coolants to
improve the life and function of
machine tools. With use, these
coolants become contaminated with
oils, and this contamination can lead
to growth of anaerobic bacteria and
shortened coolant life. This project
investigated methods to extend
coolant life through improved coolant
maintenance; the goal was to reduce
the volume of coolant waste.
Skimmers to remove oil from the
surface of coolants were cost-
effective. Practices for changing the
coolant were documented and
modified for improved coolant life. A
specific coolant with wide
applicability and tolerance was tested
and found to have a life of at least 7
mo when using the documented
procedures.
This Project Summary was
developed by EPA's Risk Reduction
Engineering Laboratory, Cincinnati,
OH, to announce key findings of the
research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
Machine shops use coolants to
transfer the heat generated during the
machining process away from cutting
tools and parts being produced. The
coolant is collected in and recirculated
from a sump. During use, the coolant
collects oil from the machining process.
This oil, called tramp oil, contributes to
the growth of anaerobic bacteria that
produce hydrogen sulfide gas, shorten
coolant life, and eventually force disposal
of the coolant as waste.
Coolant sumps contain from 20 to 100
gal each, and depending on maintenance
practices, the coolant may require
monthly or even weekly replacement.
Even a small shop will have several
machine tools, and large shops can have
100 and more. The exact management
scheme for this waste coolant is
determined by the type,of coolant, level
of contamination, presence of regulated
materials (metals, organic solvents) and
availability of treatment. Disposal costs
vary from $20 to $200 per 55-gal drum
depending on management required.
Washington Scientific Industries (WSI)
is a machine shop that uses a wide
variety of tools to make parts from
materials such as steel, aluminum,
copper, and stainless steel. The
machines are medium-sized and similar
to those used in many machine shops.
The volume of waste coolant generated
by WSI is affected by business activity,
but averages 120 55-gal drums per yr
with a management cost of $150 per
drum.
This project was designed to study the
following:
• a specific water-soluble coolant
(Blasocut 2000 Universal*) used
Mention of trade names or commercial products
does not constitute endorsement or recommen-
dation for use.
-------
with a variety of machines, tools,
and materials;
• coolant maintenance practices
associated with three types of
machines;
• observable health effects when
using and handling recycled
coolants;
• handling practices for chips and
waste coolant;
• chip/coolant separation; and
• oil/water separation
The goal was to identify factors and
techniques that contribute to the
extension of coolant life and to document
procedures and effects of the entire
coolant life cycle. This information
should be useful for decision making in
other shops attempting to reduce the
volume of waste coolant generated.
Procedures
The coolant selected by the
company, Blasocut 2000, is a mineral oil
based, water-soluble, metal-working fluid.
Its use is intended for all chip-forming
operations except grinding and all
materials except magnesium. The
concentration is made up of 60% refined
mineral oils, to which emulsifiers and
corrosion inhibitors are added. No
biocides are present in the concentrate,
and none are needed to maintain the
solution. Company literature indicates
that use of this coolant does not
adversely affect worker health and that
the coolant is recycled extensively in
other applications.
Machines chosen for the project are
1 to 4 /r old and used for jobs with long
(2 to 4 wk) production runs. Operators,
material, and process were held constant
during the project as much as possible.
Standard industrial engineering practices
wore used to determine direct and
indirect labor required for coolant change
practices, coolant maintenance, waste
handling, and waste containment.
Sampling was done to establish
baselines for new coolant, way oil,
coolant dilution water, air quality, and
health effects. Ongoing sampling and
analysis were also performed to monitor
recycled coolant quality, air quality, and
health effects. All sampling and analysis
wore performed by an independent
consulting laboratory.
After several months of character-
ization, various coolant maintenance
practices were evaluated: disk and belt
skimmers for removing tramp oil, a
centrifuge for removing tramp oil, and
coolant change and sump cleaning
practices. Sump modifications were
required to mount equipment on the
control group of machines, and additional
equipment such as timers and coolant
circulating pumps were also evaluated.
Chip handling practices from
generation to storage before salvage
were evaluated to address the problems
of inefficient handling, poor salvage
quality, and escape of coolant and oil
draining from chips in storage. Time-
and-motion studies were used to develop
an efficient system for moving chips from
the machine tools where they are
generated to a waste management
building specifically designed to capture
and store draining coolant and oil and to
protect chips while in storage.
Results and Discussion
Coolant Changing Procedure
The following changing procedure
was established as the most efficient for
extending coolant life.
1) skim all tramp oil from coolant sur-
face
2) pump coolant from sump
3) vacuum chips from sump
4) remove sump access covers
5) vacuum chips from sump
6) steam clean and vacuum sump
(repeat until clean)
7) replace sump access covers
8) replace coolant
This new practice takes about 5 hr
and 12 min to do on a cast sump. Sumps
made of sheet metal take several hours
less because corners are more easily
cleaned. This new coolant changing
procedure, when combined with
improved ongoing coolant maintenance,
holds promise for extending coolant life.
Coolant Maintenance
Both belt and disc-type skimmers
effectively reduced coolant oil and grease
concentrations. This- increases aerobic
activity in the coolant and contributes to
longer coolant life. When a centrifuge
was evaluated for cleaning the coolant in
the sumps of 25 machines not in the
study group, it was not cost-effective, at
least as a mobile unit.
Coolant
Blasocut 2000, even after being
recycled for 7 mo, met or exceeded
metal removal rates for aluminum, steel,
copper, and stainless steel. The use of
recycled coolant also did not appear to
be associated with any increase in
dermatitis on operators' hands.
Laboratory research showed that when
the recycled coolant must be disposed
of, oil and water can be separated by
acidifying the coolant and allowing -the oil
fraction to separate. Elevated levels of
2.5 to 3.5 mg/L copper and 8 to 10 mg/L
zinc were found in the water fraction of
the coolant left after this separation.
Conclusions and
Recommendations
The life of machine tool coolant can
be significantly extended, and the volume
of waste coolant generated can be
reduced. Using a coolant and way oil
with wide applicability and suitability for
recycling is important. Key factors seem
to be tolerance of hard water, resistance
to anaerobic bacteria growth, and stability
over a range of concentrations.
Simple skimming of tramp oil using
any of several different methods was cost
effective and reduced oil and grease con-
centrations significantly. This extended
coolant life to at least 7 mo; previously,
used coolant may have been changed
after 1 wk.
Although using this single coolant
meets 90% of WSI s requirements, many
machine shops will balk at switching to a
different coolant. Therefore, further
research is needed on the coolant
maintenance and changing procedures
documented in this project and on their
effect on the life of a variety of coolants.
Research is also needed on alternative
cooling methods and schemes for
preventing contamination of coolant by
way and hydraulic oil.
This study was conducted through
the Minnesota Technical Assistance
Program and the Minnesota Waste
Management Board. The full report was
submitted in partial fulfillment of
Cooperative Agreement No. CR 813437-
01 under the sponsorship of the U.S.
Environmental "Protection Agency.
. S. GOVERNMENT PRINTING OFFICE: 1990/748-012/20091
-------
-------
Joseph Pallansch is with Washington Scientific Industries Inc., Long Lake, MN
55356
James S. Bridges is the EPA Project Officer (see below).
The complete report, entitled "Machine Coolant Waste Reduction by Optimizing
Coolant Life." (Order No. PS 90-257 7831 AS; Cost: $17.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penally for Private Use S300
EP/V600/S2-9Q/033
------- |