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5 SIGNS THAT
COOLANT NEEDS TO BE REPLACED
-
Coolant Has
Foul Odor
-
Tooling Life
has Drastically Declined
-
Coolant Flow
no Longer Adequate - Pumps clogged
-
Parts &
Machines Rust
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Operators
Have Health Reactions
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START FRESH &
MONITOR
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Measuring the pH of your coolant will indicate the amount
of acid present in the fluid. These acids are caused primarily by bacterial
contamination due to incorrect concentration, excessive tramp oil, poor
circulation, or chemical breakdown by metals accumulation. Monitor sump pH on a
daily basis to keep the coolant with in its proper pH range and thus chemically
stable. If it falls below the proper pH range for your fluid, then the above
preventative maintenance protocols need to be addressed.
To verify that you are starting with a properly cleaned sump before it is
recharged with fresh fluid, measure the pH of its rinse bath. The target pH for
any rinse bath is 7 (neutral and that of water). If the pH is below 7 then
there is still contamination present, and you should repeat the cleaning
process. Recharging fluid to an improperly cleaned sump only exposes the fresh
fluid to the same conditions that were present when it failed in the first
place. |
Use pH Test Strips which have the accuracy range for that of coolant and
which are simple, and the most convenient, to use.
When mixing your coolant, verify its concentration with the use of a
refractormeter. The reference scales of mixing equipment are graduated,
no calibrated, and proportions may be affected by factors such as the
concentrate’s viscosity and your incoming water pressure.
Monitor individual sump concentrations to deep them where they need to be for
the machining process. Low concentrations cause dull or broken tools, encourage
rust, and create conditions for bacterial growth. High concentrations are a
waste of raw material and can lead to negative health reactions. Daily
monitoring is recommended so you can correct for increased concentrations due to
water evaporation.
Measure the hardness of your water supply for it may have an overabundance of
calcium or magnesium, causing insufficient coolant emulsions. This situation
renders the fluid useless for the machining process because the concentrated
separates from the water portion. Low hardness levels can cause foaming
problems, which inhibit the tramp oil removal process and possible sump
overflow.
Individual sumps should also be monitored, on a weekly basis, for their hardness
levels, as the overall mineral count may increase due to water evaporation and
accumulation of the materials machined.
Use hardness Testing Sticks which provide a simple visual readout of the
hardness level and which are convenient to use. |
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MIX IT RIGHT |
| Proper proportions are necessary when mixing your coolant
so you use the correct amount for the machining process yet not waste raw
material. Proper emulsions are also needed so the mixture dose not separate
easily. The process of mixing your coolant is best achieved using coolant
mixers. |
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KEEP SUMP CLEAN
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Skim tramp oil
daily from the surface of your coolant. These oils are a food source for
bacteria, which then thrive and cause coolant rancidity and dermatitis. Tramp
oil, if left in the fluid, will also eventually emulsify into the coolant and
promote shop mist.
Many new machines separate the way oil from the coolant however Tramp oils still
get into the coolant sump from other sources,
To skim tramp oils you can choose one of many mechanical units Disk Skimmer,
Belt Skimmer, or Tube Skimmer.
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| When the
machine pump is not moving coolant, utilize an aerator or a
circulation pump to keep oxygen in the fluid for prevention of bacterial
contamination and rancidity. |
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| Odor control tablets are effective in the
interim, and in conjunction with aeration, lessen foul odors. |
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The metals that you machine are harmful to your coolant and regular particle
filtration is necessary. When left to interact with your fluid, they degrade
the fluid on a chemical level due to the ionic activity taking place between the
coolant and metal (iron, aluminum, and magnesium are most harmful). These
chemical reactions weaken coolant, affecting its overall performance. Sumps
that accumulate piles of chips also provide a great environment for bacterial to
next and reproduce.
You may choose to remove these chips daily with a coalescing unit which also
draw and filter chips that stay in suspension. Or you may utilize our sump
vacuum for interval sump cleaning and general maintenance. |
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More
Information on Coolant Maintenance products
More on Cutting
Fluid Maintenance
Metal cutting
fluids are in themselves dynamic systems due to their usage and environment.
Characteristics may vary widely during time, so the same coolant product may
have a many different compositions after being used in for a long enough time
period. Critical cutting fluid maintenance is very important for its proper
application in processes. In addition, keeping the fluid properties within the
proposed limits will increase its lifetime. Many companies are running different
maintenance programs, all focused on monitoring particular fluid properties and
proper addition of chemicals in order to keep fluid parameters between the
proposed limits. Most of the more important parameters that are monitored in
order to keep a fluid’s ability to perform its machining purpose are:
 Oil
Concentration:
Concentration of cutting fluids is essential for performance characteristics.
Proper concentration maximizes tool life, and is a good indicator of microbial
growth rates. High concentration increases fluid costs through wasted
concentrate, reduces dissipation of heat, increases foaming, lubrication,
increases risk for generating “Built Up Edge” (BUE), etc. Since the fluids
evaporate under standard temperature pressure (STP), high concentration can
additionally increase its toxicity. Basic reasons for high concentration in
cutting fluids are water evaporation due to heat generated in machining
processes. Low concentration usually causes poor lubricity, shorter tool life,
increased biological activity and increased risk of rust formation on contacted
metal surfaces. Many chemical and physical processes influence decay of oil
concentration: bacterial attack, reaction of oil molecules with elements in
water or metal, lubricant adhesion to the metal parts, degradation due to
temperature and pressure in the cutting region, etc. The most widely used
methods for measuring fluid concentration are: Refractometry. Oil
concentration measurements using a refractometer are based on the property of
the fluid refraction index (how much light is bent as it passes through a
liquid); which depend on fluid density. A hand held optical instrument called
refractometer is used for these measurements. This is an inexpensive tool with a
satisfactory accuracy, it is often used in the industry for in process
control of concentration. An additional advantage of this device is the ability
for measuring concentration in a wide variety of fluids. Being an optical
instrument, the most important disadvantage is that the accuracy of measured
results is influenced by fluid contamination, the more contaminated a fluid is
the less accurate the results. For a more precise measurement other techniques
are recommended. Oil and water separation (oil split). The idea of this test is
to destabilize cutting fluid emulsion and separate it in two layers, one of
which is water, and other with oily material present. Mineral acid, Sulfuric
Acid (H2SO4) is added to the mixture, and after heating it separates into two
layers. Oily material is concentrated in the upper layer, while water is
separated on the bottom. Relation between volume of oily material and fluid
volume represents the oil concentration. Detailed description of this testing
method is covered with DIN 51368. This method is as accurate as refractometry,
but it requires laboratory equipment sensitive to excess oil. If the
contamination from machine lubrication system is present in the sample this will
have an influence on accuracy because oil volume will reflect both oil from the
emulsion and tramp oil. In addition, this method can not be used for solutions.
Titration: By using titration method concentration of specific chemicals or
group of chemicals in the mixture can be measured. Titrant is adding into a
measured fluid volume until a color change is noted. The coolant concentration
is proportional to the number of titrant drops added. This method is more
accurate than other two and is less affected from tramp oil or water quality.
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pH Level:
Cutting fluid pH is a very good indicator of consistent fluid quality. It
represents a concentration of hydrogen ions (pH=-loh[H+]). Practically, it is
measurement of fluid alkalinity or acidity. Neutral pH value is 7. Lower values
represent acidic solutions while pH values higher than 7 represent alkaline
solutions. Recommended pH region for water-miscible cutting fluids is 8.8-9.2.
For pH value lower than 8.0 fluid is loosing its efficiency, its corrosion
prohibition properties are becoming reduced and increased microbial
contamination is recognizing. If the pH level becomes more than 9.5 risk for
skin irritation and dermatitis significantly increases. Litmus paper provides
the cheap and fast indicator of pH. Indicator stripes are dipped into the
cutting fluid and it is changing color will depend on the pH level. Since the
accuracy of this method is limited and it can not predict biocontamination of
the fluid, another pH indicators are using more often. Electronic pH meters are
more expensive, but provide more exact measurements. Their usage is standardized
according to DIN 51369. This method can be very accurate (high cost pH meters
are accurate up to hundredths of a pH unit), but its degree of accuracy is of
little benefit for a fluid management. Titration, as a quantitative method for
determining alkalinity, is also developed. Advantage of this method is that it
additionally determines the rate of change of alkalinity. This helps in
estimating the cause of alteration.
>top
Microbial
Contamination: Most common tests for microbial contamination are plate
counts and dipslide test. In the plate count test, microbial growth is allowed
on the plate, which is than counted. The number obtained by counting is
multiplied by the dilution factor and the amount of organism per milliliter is
obtained. This test is standardized by ASTM D 3946-92. Dipslides method is more
simple but still very common for estimating microbial population. A plastic
slide coated with a nutritive gel is dipped into the test fluid and after
draining microbes will start growing. Interpretation of bacterial and yeast
infection depends on individual judgment and genuine differences on
reproducibility, but this method is still acceptable for estimating microbial
growth in metal working fluids. If there is additional rancidity problem,
observations by using dipslide method could be used as a good indicator for
adding biocides before problems arise. Microbial contamination of a cutting
fluid can be additionally estimated by indicating dissolved oxygen in the
mixture. At STP a circulated fluid can dissolve about 9ppm oxygen when it is
exposed to the air. Since the oxygen is necessary for aerobic bacteria growing,
by measuring the dissolved oxygen good estimation of biological contamination
can be obtained.
>top
Corrosion inhibition:
Testing corrosion properties of cutting fluids is very important for protecting
metal parts that are in touch with the fluid. In addition, since the corrosion
protection of cutting fluid decreases significantly when oil is completely
dissolved in water, this is a good indicator for adding oil into the system.
Fluid corrosion tests are standardized in DIN 51360 part 1 and 2 erwalleney, S.,
1996]. DIN 51360 is a well known Herbert test. Four small piles of clean steel
chips are positioned on the cleaned and polished cast iron plate and are then
whetted with the test mix. Four different dilutions of the same mix are used for
four different chips. Plate and chips are placed in a closed container for 24
hours, after which the formation of pits and staining is assessed. Institute of
Petroleum, London applies the same test (IP 125) with steel chips on the cast
iron plate [Rudson S.G. and Whitby, R.D. [1985]. DIN 51360 part II and ASTM
D4627 describe a testing method for cast iron chips on filter paper. About 2 g
of clean iron chips are spread onto a filter paper in a Petra dish, the fluid
mixture is pipetted on to the chips and the dish is covered. After a certain
period of time the chips are removed and the paper is examined for staining.
Similar test is developed by Institute of Petroleum, England (IP 287 test),
presented by Rudson S.G. and Whitby, R.D. [1985]. The disadvantage of all
presented tests is that they are developed for one particular material. IP 329
test by the Institute of Petroleum is a multi-metal corrosion test that examine
the effect of water-based fluids on steel, cast iron, copper, brass, aluminum,
zinc and cadmium [Rudson S.G. and Whitby, R.D. [1985].
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