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Machine Coolant Management Program

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Machine Coolant Management Program

The three components of a successful machine coolant management program are:

  1. Administration
  2. Machine coolant Monitoring and Maintenance
  3. Machine coolant Recycling 

Introduction

A great number of industrial processes such as grinding, milling and turning create heat and particles. Machine coolants are used to keep the work surface cool and to carry away chips and particles.  Refer to the Main Filtration Indexfor more articles on Machine Coolant and Filtration. 

Typically machines and grinders are flood cooled which means that water is flooded over the work area.  This cools the work and washes particles out of the way.  The liquid is typically 90 to 95% water and 5 to 10% machine coolant.  The liquid runs over the work area and then down the machine where it collects in a sump at the bottom of the machine.  The liquid is pumped out of the sump and constantly recirculated.   As the work is done, the tool material and pieces of the, metal or composite or other material being machined collect in the sump. 

If the machine coolant is recirculated these fine particles are pumped up to the spray head and sprayed onto the work area.  Some of the particles are thrown into the air where they can be inhaled.   Other particles are reground into even finer particles.  These recirculated chunks will cause rougher grinds and will increase the chance of burning during grinding. 

The whole area of machine coolant management is generally poorly understood.  It is estimated that somewhere between $100,000,000 and $500,000,000 worth of machine value is lost each year due to improper machine coolant management. 

$500,000 is not all that expensive a machine any more.  Improper machine coolant management can shorten the serviceable time between rebuild and / or replacement by as much as 10% a year.  As the need for precision gets ever greater, the need to keep machine coolant cleaner is more important than ever.  When 0.001" was a tight specification machine coolant filtered to ten microns was allowable.  Now that specs are increasingly closer to 0.0001" machine coolant needs to be maintained to below one micron.  Yet a great many shops consider a system that filters to ten microns to be state of the art. 

Machine coolant filtering is something that large, sophisticated shops have been doing for years.  The recent development of smaller, less expensive and more efficient filter units combined with the needs for greater quality and tighter government regulations seem to be pointing to the day where every machine will have a machine coolant filter just as every automobile has an oil filter. 

Machine coolants need to be filtered for the same reason that oil in a car engine needs to be filtered.  The oils or machine coolant trap small, abrasive particles.  Unless these particles are removed they abrade away critical surfaces.  If you are filtering the oil in your $20,000 car then you ought to be filtering the machine coolant in your $30,000 machine for exactly the same reasons.  

Administration

1.  Commit the personnel, equipment and other resources necessary for the program.

2.  Provide management reference for implementing and tracking the program

3.  Encourage employee support and participation.

4.  Designate machine coolant management personnel to implement the program.

5.  Educate personnel on things effecting machine coolant performance and failure.

6.  Survey the machine coolants, machines and sump capacities of the shop.

7.  Develop a record keeping system to track the program.

8.  Identify corrective action procedures and execute them 

Record Keeping

Record keeping is an important aspect of machine coolant management, and it begins with the initial preparation of the machine coolant. Following its preparation, the pH and concentration of the machine coolant should be measured and recorded. These initial readings should correspond to the acceptable product quality ranges provided by the machine coolant supplier. They also provide a baseline from which to evaluate the condition of the machine coolant over time. machine coolant pH and concentration measurements are compared to "new machine coolant" values to assess machine coolant quality. 

A detailed logbook documenting machine coolant usage information should be maintained. machine coolant management logs for each machine should include the following information:

1.   Brief description of the machine and sump/reservoir capacities

2.   Type of machine coolant used

3.   Machine coolant mixing ratios and initial parameter readings

4.   Water quality data

5.   Monitoring data including pH readings, biological monitoring data, machine coolant concentration measurements and inspection observations

6.   Adjustments made as part of machine coolant maintenance

7.   Machine coolant recycling and/or disposal frequencies, including dates of machine coolant change out and reason for change out

8.   Equipment cleaning and maintenance activities, dates and comments

9.   Quantity of machine coolant added (both change out and periodic additions)

10.  Documentation of problems that occur

11.  General comments 

Plant

Chemical maintenance -which includes checking:

Water

Bacteria growth

Tramp oil control

Lubricant chemistry 

Physical maintenance - which includes upkeep of:

Filtration

Clarification

Skimmers

Heat exchange

Tooling  

Machine Coolant Management System Checklist

1.    Determine the fewest different machine coolants that can be used.
2.     Check compatibility of machine coolant with cleaning system.
3.     Find substitutes for chlorinated oils.
4.     Use quality products that last longer.
5.     Use a lubricant that can remain on the piece as long as necessary
6.     Consider substituting hot lime bath or borax soap for oil.
7.     Determine whether deionized water should be used.
8.     Train employees on machine coolant changes. Get their feedback.
9.     Train employees to keep foreign material out of machine coolant system.
10.   Assign machine coolant control responsibility to one person, with backups. Provide adequate training.
11.   Use non-chlorinated biocides, pasteurization, or aeration to kill bacteria (check with your machine coolant supplier)       Check the effect on your waste handler or recycler.
12.   Analyze and monitor biocides, machine coolant composition, acidity, and possibly bacteria levels. Keep records.
13.   Adjust machine coolant composition and acidity as necessary. Make sumps easy to access and sanitize (line with             sheet metal, round comers, etc.).
14.   Remove machine coolant and sanitize the system on a regular basis. Sanitize reservoirs, sumps, trenches, machine coolant feed systems, and metal working equipment using an alkaline cleaner, steam cleaning, etc.
15.   Remove metal fines from machine coolant and sumps on a regular basis.
16.   Install vacuum devices or other machine coolant recovery system for machines not on a separate machine coolant sump. Remove tramp oils from machine coolant on a regular basis, using disk or belt skinners, coalescers, filters, dissolved air flotation.
17.   If skimming equipment cannot be placed near the pump, use a baffle or weir system to contain the oil near the skimmers. Run skimmers intermittently, to prevent excessive machine coolant loss. Perform regularly scheduled gasket, wiper, and seal maintenance.
18.   If possible hard to reach areas as well as nooks and corners should be eliminated.
 

Recycling & Disposal

1   Recover lost machine coolant from metal fines and scrap, using methods such as draining, centrifuging, chip wringers, and scrap conveyors.

2   Do not mix different waste machine coolants.

3   Segregate metal waste by material type. 

4   Recycle oils if possible. Consider "splitting" emulsions to recycle oil. Check with sewer utility before discharging water portion.

5   Know whether your waste machine coolant tests to be a dangerous waste.

6   Check with sewer utility for discharge restrictions.

7   Do not discharge to septic or storm systems or dry wells. Know where your drains discharge.

8   Store drums and containers where they won't collect rainwater.

9   Keep Material Safety Data Sheets (from your suppliers).

10  Train employees in emergency procedures, health and safety, regulations, and material management procedures.

11  Ask vendors for less hazardous products.

12  Contact regulatory agencies for applicable laws and assistance.

13  Use proper safety equipment and clothing.

Mixing

Machine coolant should always be mixed by following the suppliers' directions and by measuring.  Mixing machine coolant "by eye" doesn't work well enough.   Mixtures should be prepared according to the manufacturer's directions (as obtained through the machine coolant supplier and/or product literature). 

Mixing should always be done outside the sump.  Mixing in the sump is quick and easy method but the machine coolant doesn't get fully mixed and it is almost impossible to measure machine coolant concentration accurately. 

Machine Coolant Concentration

If the concentration is too high it means there is too much machine coolant and not enough water.  This means wasted concentrate, poorer heat transfer, foaming, reduced lubrication, residue formation and more built‑up edges for shorter tool life.  Over-concentrated machine coolant can stain the work and / or the machine and it increase the toxicity of the machine coolant, which means increased skin irritation. Low concentration means poor lubricity, shorter tool life, more bacterial growth activity and an increased risk of rust. 

Evaporation means a loss 3% to 10% of water daily. Water and concentrate are both lost as a result of splashing, misting and dragout. The daily loss of machine coolant mixture maybe as much as 5% to 20% from all these.  This means the machine coolant concentration will change every day. 

The machine coolant needs to be checked daily at the start.  As the system gets more stable weekly checks may be appropriate.  It depends on how well your system is functioning and how much it changes from day to day.  

Cooling units or chillers on machine sumps or central reservoirs reduce evaporation losses, help extend tool life by inhibiting microbial activity and increase the machine coolant's ability to remove heat. 

System Inspections

Inspections of the machine coolant and over all system for cleanliness are important to monitor machine coolant quality and avoid premature machine coolant failure.  Operators and maintenance personnel should both do this. 

Signs, which indicate a need for machine coolant maintenance or recycling

Excessive tramp oil accumulation

Buildup of metal cuttings within the sump

Foaming problems

Leaky machinery

Dirt and bacterial slime accumulations 

Routine Maintenance Practices

Maintaining clean machines, machine coolant lines and sumps is an essential part of machine coolant management. Clean machines use metalworking machine coolants more economically and extend machine coolant life. Any dirt and oil allowed to remain in the system simply recirculates, resulting in plugged machine coolant lines, unsightly machine buildup and bacterial growth 

Chips and swarf

Excessive chip accumulation and swarf reduces sump volume, damages machine coolant and provides an environment for bacterial growth. Excessive solid buildup can cause increase machine coolant temperature.  Chips and swarf should be removed as often as possible. 

Tramp oil control. Tramp oils such as hydraulic oil, lubricating oil or residual oil film from the work piece can cause machine coolant to break down prematurely. These oils provide a source of food for bacteria, interfere with the cooling capability of the machine coolant and contribute to the formation of oil mist and smoke in the workplace. Tramp oils also interfere with machine coolant filtration and form residues on machining equipment. Tramp oil is controlled through prevention and removal. 

Routine preventive maintenance should be performed on machine systems to prevent tramp oil and grease from contaminating the machine coolant.  Some tramp oil contamination will always occur.  Tramp oil will either "float out" when the machine coolant is allowed to sit for a period of time or it will be emulsified into the machine coolant.  Free floating tramp oil should be removed on a regularly as part of machine coolant maintenance.  Oil skimmers, filter systems coalescers, or oil‑absorbent pads can remove floating oils and help remove emulsified oils. 

General Housekeeping. Machine coolant contaminants such as lubricating oils, greases and metal particulates are an expected part of machining operations. Many of the contaminants that cause machine coolants to be disposed of prematurely consist of foreign materials such as floor sweepings, cleaners, solvents, dirt, waste oils, tobacco, and food wastes. These contaminants have obvious detrimental effects on machine coolant quality and should be eliminated through improved housekeeping and revised shop practices. Facility personnel should learn not to dispose of these materials in machine sumps.  

Maintenance of Straight Oils

Straight oils are generally easier to maintain than water‑based machine coolants.  Maintenance on straight oils consists of keeping the machine coolant free of contaminants (such as water or tramp oils generated in other areas of the shop), adequate particulate removal through filtration and the addition of antioxidants. The presence of water promotes microbial growth while tramp oil contamination dilutes the ingredients added to straight oil for enhanced lubricity and wettability. Tramp oil contamination also increases the viscosity of the straight oil, lowering its filterability. 

Straight oils that are kept contaminant free and adequately filtered may still require replacement due to the effect of oxidation. Oxidation of straight oil increases its viscosity, making particulate filtration more difficult. As a result, additives referred to as antioxidants may need to be used to prevent oxidation from occurring. 

Foaming

Sometimes the conditions are right so that the additives and surfactants in machine coolants cause foaming.  Foam layers are mostly air and insulate the machine coolant, which prevents water from evaporating and traps heat in the machine coolant.  This can seriously affect the ability to control part dimensions.  Machine coolants are more likely to foam when machine coolant concentrations are too high or when soft water is used for machine coolant mixing.   These combine with mechanical effects such as agitation, air etc. to cause foaming.   Foam generation requires a surface-active liquid (one with wetting agents or emulsifiers) and the agitation of that liquid in the presence of air.  Foam control can be tough because of high pressure and high flow rate machine coolant systems. 

Ways to decrease machine coolant foaming

1.  Using a non-foaming machine coolant

2.  Decrease machine coolant flow rates

3.  Reduce agitation

4.  Decrease machine coolant concentration

5.  Modify airflow in the machine coolant stream.

6.  Consider replacing high velocity nozzles with low velocity, high volume nozzles.

7.  Eliminate areas of free‑falling machine coolant by extending return piping outlets beneath the machine coolant level in the sump.

8.  Replace undersized piping and eliminate sharp comers and interruptions in machine coolant return lines.

9.  Clean nozzles of dirt, grease, etc.

10. Make sure pumps are good

11. Check pumps and piping for air leaks

12, Keep the sump full so the pump isn't sucking air.

13. Keep phosphate-based cleaners away from machine coolants since they can promote foaming.

14. Use antifoaming agents such as a liquid calcium water hardener to reduce or eliminate foaming.

15. Be careful using silicon-based antifoaming chemicals since they coat and absorb into the pores of metal surfaces. 

Foaming is more likely to occur with fresh machine coolant because the concentration of wetting agents is highest, and the concentration of tramp oils, metal fines, and abrasive grains is low.  Contaminants help to reduce foaming.  With a fresh charge of machine coolant, it may be necessary to make tank side additions of antifoam until the machine coolant gets "a little dirty" and has a reduced tendency to foam. 

When to change machine coolants and clean the sump

1.  pH is less than 8.0 (normal pH range is 8.5 to 9.4)

2.  Machine coolant concentration is less than 2.0% (normal is 3.0% to 12.0%)

3.  Appearance is dark gray to black when normal is milky white, clear green or other)

4.  Odor is strongly rancid or sour (normal is a mild chemical odor)


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