Coolant recycling and maintenance:

What to remember

– Bill Gimbel, VP, Sales, Universal Separators, Inc. & SmartSkim® 
In most metalworking plants, used coolant makes up the largest volume of the waste. Smart plant managers know one successful way to address this issue is to recycle the coolant due to the economic benefits of coolant recycling, such as:

Shops that have multiple metal working machines with stand-alone coolant sumps can benefit from better coolant maintenance and recycling. Small shops with as few as 5 -10 machines and large shops with hundreds of machines have successfully instituted in-house recycling & maintenance programs.

Coolants fail and are dumped due to several reasons:    

  1. Extraneous Tramp Oils – Come in 3 States: Free, Mechanically Dispersed, and  Emulsified. They can promote bacteria, odors, misting, & residue buildup.
  2. Chips – Lead to sump volume reduction which affects temperature and settling. 
  3. Particulate/Solid Contaminants – include fine solids, grinding fines, cast iron dust, carbon/graphite, aluminum oxides, grease/sludge buildup & foreign material such as candy wrappers, cigarette butts, ear plugs and sunflower seeds.
  4. Bacteria – Fungus from excessive tramp oil, stagnant coolant, or poor concentration control.
  5. Rancidity – Odor from biological, poor concentration control. 
  6. Dermatitis – Due to allergic reaction to the metals or tramp oils, concentrations too high.
  7. Water – Poor emulsion stability,  hard water soaps.
  8. Corrosion, Rusting or Staining of parts.  
cost efficiency by reducing coolant waste and coolant purchase

Dirty Coolant from CNC Machine

Coolant maintenance program

These problems are all maintenance related and can be controlled with a good Coolant Maintenance Program and recycling system.

Coolant maintenance

When you have a recycling program there is more than just the equipment to consider. To have a successful program you need to also maintain your coolants in the machine sumps.

  1. Coordinate with your coolant supplier. Your coolant supplier can help you set up a monitoring program that fits your facility.
  2. Keep Records. You can contact us for some sample Daily Coolant Log Sheets.
  3. Concentration Control. This is the number 1 control variable and the easiest thing a plant can do to save money. In most plants the coolant concentration typically increases due to water evaporation caused by the machining process. Your coolant supplier will recommend the concentration range to stay within. Using a manual or digital refractometer can assist you in this. We always suggest using a diluted mixture of fresh coolant to adjust concentration down. To raise it, add a high concentration mixture. Never add straight water or raw coolant. Due to the preferential depletion of additives, rust preventatives, and biocides it is critical to add new coolant in.
  4. Daily/Weekly Data
    1. Concentration Control. (as mentioned in the last segment).
    2. pH Control. pH needs to be monitored because it can be an early indicator that something is not right with the coolant. Your coolant rep will tell you what range you should be in. Typically 8.5 – 9-5 is normal. Anything below needs to be addressed by adding a ph boost. pH dipslides or a digital meter can be used.
    3. Microbial. You may need to check for bacteria, fungus, yeasts and mold on a weekly or biweekly basis using a dipslide or digital bacteria monitor.
    4. Observations. We recommend having your operators and/or maintenance personnel check the sump conditions on a regular basis.  Observe the following:
    1. Coolant appearance
    2. Smell, color, fungus, bioslime
    3. Tramp oil
    4. Foaming tendency
    5. Tool life

See a Coolant Recycling System in action

Cleanout of sumps

Depending on the quality of the coolant used as well as contamination & production levels, you will have to set up a cleanout schedule for your machine sumps. Every machine tool has a different sump design, oil leakage, solids buildup, and production usage. Set up a schedule that evacuates the sump as required by that machine. Some sumps could require monthly cleanouts while others can go 6 months. Make sure you remove all the coolant, chips, and sludge. Follow your coolant manufacturers’ instructions for proper cleanout. The use of a high powered sump sucker (vacuum) will speed up the job and be much easier for your personnel.  

Recharge versus top-off coolant

Recharge coolant is what you put in a sump when new or after sump cleanout. If your coolant supplier wants the sump at a 8% concentration, this is what you recharge at. Top-off coolant is what you put in the machine to keep it filled. Normally this is at a lean concentration because of the evaporation we talked about earlier in this paper. Always add some emulsion, never straight water. This will keep your coolant in good condition by adding back into the sump fresh additives to the fluid such as biocides, ep additives, defoamer, etc. In the recycling system we add the top-off coolant into the dirty side because this is the side of the system that loses level first. This also gets  the biocide and additives into the coolant as soon as possible, which helps promote tramp oil removal and kills biological growth upon impact.  

See a Sump Caddy in operation

In conclusion

As part of your coolant maintenance, use the tools and experience a good “team-mate” can provide. Your coolant supplier and equipment supplier should be on the same page with you and must see the “big picture” for your plant.

If you follow these steps and use a reliable and effective coolant recycling system process, you should see great economic and production benefits while reducing overall operating costs.  

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