Mix it Right
Always mix your coolant properly by using equipment such as venuturi-style or positive displacement proportioners. This will ensure that the concentrate is thoroughly blended with the water portion, and will help to gage the correct concentration for use at the machine tool. Too low a concentration can dull tools prematurely, or even break them during the first cut. Too high a concentration not only causes higher usage rates, but can also lead to health and safety issues.
The easiest method to check for concentraion is use of a refractometer. It is a simple instrument which uses light refraction to indicate the concentration percentage. A couple drops of coolant are put onto the lens and the lens then held toward a light source. The molecules on the lens will bend the light rays in relation to the volume of concentrate in the mixture. This indicates your concentration.
When refilling your sump at the end of the shift, you must take into consideration your coolant’s evaporation rate. Since the water portion evaporates during the machining process, the concentration of the remaining sump volume is higher than what you started with. At this point, you will need to refill the sump with a lower concentrated mixture.
To determine this concentration, see Advanced Science, Concentration Measurement section.
Remove Tramp Oil
Removal of the tramp oil layer is critical to the longevity of your coolant. If left unattended, it will form an oxygen-depleted zone, creating an ideal environment for bacteria to feed and grow. These bacteria then turn the oil layer into a biomass layer which is hard to skim, and can aid in cross-contamination in a centralized coolant system.
Once the bacteria overtake the chemistry of the coolant mix, it lowers the pH of your sump, turning the liquid into an acid bath, which rusts machine interiors and your valuable parts. Soon the sump will give off foul odors, and contribute to dermalogical disease.
Over time, the oil will emulsity into the coolant blend, rendering it useless for heat displacement at the tool interface. This process takes very little time, since both the coolant and tramp oil flow through the machine pump many times over the course of a day.
If using high-pressure pumps for through-the-spindle coolant flow, the oil will emulsify into the coolant to such a degree that an inverse layer will form. This layer is a blend of the two components, and may never separate, but should still be removed.
Emulsified oils aid in the formulation of mists during the machining process. These mists may accumulate to dangerous levels, which can lead to health and safety issues. They also settle on your expensive equipment, helping to cause premature electrical and mechanical failure.
There are many methods used to handle accumulation of tramp oils. Electrical mechanical skimmers, using a variety of pick-up devices, work well for those machines that run all shifts. For sumps that sit idle for more than one shift, a coalescer is better, as it also incorporates fluid transfer, which helps to keep oxygen in the environment. Centrifuges are best for deeply emulsified oils. For those on a tight budget, even a $29 shop vac will do the trick.
Understand that there may always be oils present in the sump, as the drops of way oil which provide way lubrication mix in with the coolant. If you have a leak, however, repair action should be taken as soon as possible. It will save on oil and coolant costs, and help to prevent any negative result that could be caused by oil contamination.
Chips play a big role in degrading the chemistry of your coolant. The positive ions in the metals latch on to the negative ions of the coolant components, causing premature failure. Your coolant may split into into constituent parts, preventing lubrication to the machine tool. The following chart illustrates metals that if left in the system will cause this type of failure.
The type of metal and chip size in relation to the volume of coolant will determine at what rate this degradation takes place. A coolant within a small grinding application can split in as little as 15 minutes. The following chart illustrates which operations need the most attention:
In general, the materials you machine affect your coolant blend as well as the chip size created during the process. Removing these chips prevents coolant failure, but also any bad finishes that are cuased by recirculation of the particulates within the system.
So, removing as many chips as possible from the overall system on a regular basis is critical. Remove large chips via a conveyor. Smaller suspended chips via a filtration system, as they tend to cause failure and bad finishes. Use an industrial vaccuum during regular machine clean-up to gather as many chips as possible from the various areas of your machine where chips tend to accumulate.
Circulate when Needed
Just as your body has a circulatory system with a heart to pump and blood vessels to carry blood, your machine tool has a main pump and fluid lines to keep the fluid at the point of cut. The question is, what happens to the fluid when those pumps are not running?
The coolant is now a static system, keeping absolutely still--at least to the naked eye. On a microscopic level, bacteria are multiplying and turning your coolant into a slime machine.
You’ll notice that when the machine pump is turned back on Monday morning, or even for the next shift, a foul odor will rise up, and there may even be a green haze above the machine. This is the work of bacteria and their waste products.
When bacteria are left to their own devices, the smell will appear more often and linger longer. They also may cause allergic reactions when they come in contact with your skin, and even lead to infection. Your coolant will chemically deteriorate so it isn’t able to control rust, and it may even split apart.
To fight bacterial infestation, in part, keep your fluids moving. Otherwise, your coolant (blood) will turn to slime (clot). The harmful bacteria will stay at bay because oxygen levels will then increase as the fluid circulates.
For small sumps of under 100 gallons, an aeration device is sufficient to do the job. For sumps over 100 gallons, incorporate a centrifugal pump. Keep these devices running whenever the machine tool pump is turned off.
See the Advanced Science, Microbiology section for more information on bacterial contamination.
Clean the Machine
Failure to properly clean the machine before recharging is exposing your fresh batch of coolant to the same conditions as before. To prevent the new batch of being just as contaminated as the first, the machine sump, its interior surfaces, and its flood lines must be thoroughly cleaned.
Ask your coolant supplier what cleaner they recommend to use with your particular blend of coolant. A 10% bleach solution also works well.
First, remove as many chips as possible from the sump and any crevices they may accumulate in.
Next, introduce your cleaning solution, and circulate it through the system for at leat 1-2 hours to kill any bacterial contamination. Remove this bath and properly dispose of it.
Rinse for 1/2 an hour with straight water, then again. Keep rinsing until your water bath is a pH of 7. This indicates a balanced environment in which to recharge.
Since the machine is down, this is a good time to repair any oil leaks or do any other necessary maintenance on the equipment.