The Management of Cutting Fluid Systems

By September 24, 2015 Article, Marine News, Technology No Comments

^ Well Managed Coolant Systems Provide Excellent Cutting & Machine Shop Hygiene (Image Courtesy of Hywit Dimyadi at ShutterStock.com)

Monday Morning Stink!

This is as bad as Monday Morning Blues will ever get. Leaving behind the relaxed euphoria that only weekends can offer, you start your machine shop early on a Monday. A little while later, machine operators report to work and turn on the coolant system left idle over the weekend.

And that is when it hits you. The unbearable, vomit-inspiring stench of rotten eggs! If you ask your operators, they will tell you what they call it (disdainfully of course) – Monday Morning Stink.

Hydrogen Sulphide gas gives the coolant this odor. And this is the surest indicator that your coolant / Metal Working Fluid (MWF) / cutting fluid system needs maintenance. For, the odor is a symptom of the contamination of the MWF with tramp / lubricating oil.

You must manage cutting fluid systems through periodic checks and necessary actions to prevent the buildup of obnoxious elements that make hazardous wastes out of the MWF. Such management also boosts the efficiency and life span of the coolant.

The Troublemakers

Contaminant particles sized between 10 microns and 1/10th of a micron are most lethal for machines, tools, and human health. Because, large particles of around 100 microns are caught in nose hair and throat while those under 1/100th microns are easily breathed in and out.

Problematic elements include:

  • Microbes
  • Tramp / Lubrication Oil
  • Metal Swarfs, Chips, and Fines
  • Greases

Machining operations make metal fines, chips, and swarfs harder than the parent material. If not separated, these find their way to the cutting zone to slash tool life and scratch the surface finish. Plus, they erode the tubes and channels of the machine that they pass through.

Cutting Fluid Maintenance

Practices that maintain MWF systems and inspire them for superior performance include:

  • Maintaining Excellent Quality of Water
  • Proper Concentration & Mixing of the MWF
  • Tramp / Lubrication Oil Removal
  • Filtration

That apart, you must sensitize shop personnel on the importance of best MWF management practices and train them with it. Management includes:

  • Monitoring:
  • Checking Concentration with Refractometers or Titration Kits: the former are faster, the latter more accurate
  • Measuring Rancidity with pH Meters and/or Dip Slides
  • Maintenance:
  • Fluid Concentration Adjustments
  • pH Adjustment
  • Biocide Addition
  • Removing Chips and Fines via Sump Cleaning

Water Quality: i.e. the quality of water used to dilute the coolant is critically important because final MWF blends contain over 90% water. And the quality of this water determines the coolant life, stability, tool life, corrosion control, foam properties, and product residue.

Coolants Flushing Away Metal Chips (Image Courtesy of Nikola Bilic at ShutterStock.com)

Coolants Flushing Away Metal Chips (Image Courtesy of Nikola Bilic at ShutterStock.com)

As water evaporates from the coolant mix, coolant concentration rises and you have to add water. Dedicated water treatment such as Deionization or Reverse Osmosis (RO) is necessary if such local water:

  • Hikes the concentration of Chlorides (above 100ppm) and Sulphates in the final mix. These salts promote corrosion, imbalance, and rancidity while shortening coolant life
  • Boosts the Percentage of Magnesium and Calcium Salts that destabilize the coolant
  • Is Excessively Conductive and thereby escalates instability and corrosion
  • Is of Inappropriate pH

Mixing: When filling the sump, do not pour water first and add the coolant concentrate later. Instead, use a mixing system or proportioner for chemical MWFs and a volumetric pump for soluble oil MWFs.

Dark and humid, the sump can be a great breeding ground for microbes particularly because MWFs serve as nutrients. Operators may, knowingly or otherwise, introduce glass and floor cleaners in the sump that harmfully alter the MWF’s stability and pH.

Cutting Fluid Concentration: determines the percentage of active ingredients that endow the necessary properties on the MWF. Incorrect concentrations end up escalating coolant costs, foaming, corrosion, emulsion splitting, and microbial activity while shortening tool life.

Check fluid concentrations every day for single machines and stand alone systems. For other machines and systems, check concentrations at least every week.

Refractometers check the total amount of solubles in aqueous solutions by measuring the bending of light as it passes through the liquid. Although fast, refractometers lose accuracy when confronted with tramp oil-contaminated MWFs.

This is where Titration Kits come into play, for they are immune to contamination. You take a measured volume of the MWF, add an indicator, and then add the titrant drop by drop till you note a color change. The number of titrant drops gives you the MWF’s concentration.

pH Value measures the alkalinity / acidity of a substance. The ideal pH range for cutting fluids is between 8.5 and 9.5. Values below 8.5 indicate heightened biological contamination that lowers coolant efficiency and exposes tools and workpieces to rusting.

Low-Cost Test Papers are accurate to ±1 pH unit while medium-cost pH Meters have a precision tolerance of ±0.2 pH unit and high-cost pH Meters are accurate to hundredths of a pH unit. Although highly accurate, the last variant is of little use for us.

Microbial Growth: You can monitor microbial growth with Microbial Growth Dip Slides and add biocides before the issue assumes unmanageable proportions. The problem of microbial contamination is more common with water-based coolants.

Higher, less-frequent biocide doses are more effective than lower, more-frequent doses. Biocides do not reach metal fines and chips that settle at the bottom of the tanks and facilitate microbial growth thereby escalating the MWF’s toxicity.

Clogged Filter  (Image Courtesy of Baloncici at ShutterStock.com)

Clogged Filter
(Image Courtesy of Baloncici at ShutterStock.com)

Lubrication / Tramp Oil Removal: Lubricants and spindle oils lower the wear of moving machine parts. Sadly, most tramp oil ends up in the MWF and adds to the MWF’s capacity to cause wear.

Tramp oil promotes bacterial growth and dissolves metal chips and fines that turn the MWF into a toxic waste. It also creates oil mist and smoke that pollute the shop ambience and affect the working of sensitive electronic gadgets.

A powerful symptom of tramp oil contamination in MWF is the smell of rotten eggs caused by hydrogen sulphide gas. It is particularly strong on Monday mornings when you turn on the coolant system that is left idle over the weekend.

Equipment for eliminating tramp oil, metal particles, and greases include:

  • Settling Tanks: are the simplest instruments of separation. Heavy particles settle at the bottom while oils and greases float at the top of the coolant surface

You can then skim off oils from the top and remove heavier particles with automatic chip conveyors or baskets

Cleaning fabricated sheet metal sumps with rounded corners is far easier as compared to sharp-cornered sumps made through the casting process

  • Skimmers: collect tramp oil that floats on top after you allow the coolant to settle. These work best with coolants that do not mix with oil

Types include Belt, Rope, or Disc Type with disc and belt skimmers being economical for small and large operations alike. Most are made of plastic as oils stick to plastic

  • Coalescers or Separators: have a porous, polypropylene media that separates tramp oil from water. They cause the oil to collect at the top of the tank that is removed by skimming

Devoid of moving parts, these are self cleaning. Coalescer units cost between $1,000 and $5,000. Use them only for removing tramp oils that do not mix with water. Clean them regularly lest the unclean media turn into a microbe-breeding hotspot

  • Centrifuges: spin out free, dispersed, and emulsified tramp oil as well as solid particles. These are however expensive and can occasionally separate out the coolant concentrate from the coolant solution
  • Hydroclones: force the coolant into a cone-shaped vessel. Density differences separate out dense particles towards the bottom and the sides. These can however emulsify tramp oil. Use with caution
  • Floatation: follows the removal of heavier particles in settling tanks. You aerate the coolant to form bubbles that carry oil and finer particles to the surface where you skim them off
  • Magnetic Separators: remove particles of ferrous materials such as iron, cobalt, or nickel. The coolant passes over slow-rotating magnetic cylinders that attract and separate ferrous material particles

Settling tanks remove non-ferrous particles. Separators are good for removing ferrous particles only. With the increasing use of more complex alloys that possess even more convoluted magnetic properties, magnetic separators are losing their applicability

  • Absorbent Fabrics, Blankets, or Pillows: absorb hydrocarbons but repeal water. These are effective for small sumps. You do have to undertake the tedious task of disposing these fabrics later

Filtration: Filtration Systems use a media to separate chips and fines from MWFs. Micron Rating is the size of the largest particle that will pass through the filter under specified test conditions.

Oils and greases are filter killers, for they clog filters even causing sudden shut downs. Use filter systems after you separate oil and grease from coolants.

Filtration systems can be:

  • Vacuum Filtration Systems: create vacuum / suction to pull the contaminated cutting fluid through the filtration media
  • Pressure Filtration Systems: pump the soiled coolant through the filtering media
  • Gravity Filtration Systems: involve the vertically downward pouring of the coolant over the filtration media

Required level of surface finish and the machining process dictate the level and type of filtration. Earlier filtration systems were prohibitively expensive, particularly for small shops. But with the rise of costs of MWFs and their disposal, shops are increasingly investing in them.

Ceramic, metal, and plastic media usually make up re-usable filter media. You can clean these through scraping, back-flushing, and ultrasonic cleaning. Increasing volumes of dirt and decreasing particle sizes complicate the operation of re-usable filters

Felt, wound yarns, papers, and loose fibers generally serve as disposable filter media. You get high removal rates for low flow rates and low removal rates for high flow rates.

Fluid Recycling is a great way to boost coolant life while cutting down waste disposal costs. You can directly purchase self-contained, easy-to-operate-and-maintain recycling units for smaller machine shops or individual machines.

Also called Contaminant Removal Systems, recycling systems lower the deleterious effect of tramp oil, dirt, microbes, chips, and fines on coolant life while also readjusting the coolant concentration as needed.

Recycling: The Call of the Present   (Image Courtesy of jointstar at ShutterStock.com)

Recycling: The Call of the Present
(Image Courtesy of jointstar at ShutterStock.com)

Batch Treatment Systems are portable or non-portable systems that are necessary if you are not using filters. They extract the cutting fluid from a machine’s sump using a mobile sump cleaner and recycle it by removing contaminants and adjusting concentration.

You have to batch-treat a MWF for every one-third or half of its expected life. If, for example, a coolant’s life is six weeks, batch-treat it:

  • every two weeks; or
  • (at least) every three weeks

These systems cost between $7,500 and $15,000 for small machine shops. Recycling frequency depends on:

  • water quality
  • coolant type, age, and control
  • contamination levels
  • filtration efficiency
  • machine usage

Finally

While maintenance is a tedious and somewhat expensive task, it is more cost effective over the long run because it extends the life and efficiency of the coolant, machines, tools, and associated systems.

Want more practical tips on best machine shop work practices. Visit our blog. And if you want to witness the execution of such practices, contact Kemplon Engineering for stellar marine fabrication services, marine pipe fitting, and large scale custom metal fabrication.