Total Lubricants USA Technical Training Series: Metalworking Coolants

Coolants Water-containing fluids designed to: provide lubrication between tool and workpiece remove heat from surfaces flush away debris created during machining Coolants are used in place of cutting oils because: heat removal is about 2-3 times faster than oil much thinner in composition which allows faster machining with closer tolerances produce less misting than similar viscosity oils typically are easier to dispose of

Coolant Use Coolants are used to perform many different metalworking tasks including: turning boring drilling sawing honing milling grinding broaching gear hobbing, etc.

Metalworking Fluid Selection Selection of a particular MWF depends on the: type of machine and operation type of metal and speed of cut machine lubrication requirements MWF’s must provide effective rust & corrosion protection for the tool, workpiece, and machine MWF’s consist of 4 basic types: straight oils emulsifiable (“soluble”) oils synthetic fluids semi-synthetic fluids

Types of Metalworking Fluids

Emulsifiable Oils Known in the industry as “Soluble Oils” Consist of about 75 - 90% oil Usually formulated with naphthenic oils Common additives include sulfur, chlorine, & fats Form oil-in-water emulsions Provide good tool life, anti-weld properties, and rust & corrosion properties Typically provide the best lubricating properties

Synthetic Coolants Contain large quantities of water but no oil Form a clear or translucent solution when mixed with water Have a higher pH than emulsifiable type oils Provide benefits such as increased workpiece visibility, good wetting properties, stability, tramp oil rejection, and little rancidity Formulated with rust & corrosion inhibitors, extreme pressure enhancers, biocides, surfactants, anti-foam agents, & more

Semi-Synthetic Coolants Formulated much like a synthetic fluid but contain from 5 to 25% oil Designed to combine the best features of both emulsifiable oils and synthetic fluids Offer better lubricity than synthetic fluids and better visibility & tramp oil rejection than emulsifiable oils Provide a good finish on most non-ferrous metals and recommended where other fluids are not practical

Coolant Performance Successful performance of any coolant depends primarily on proper: storage of the concentrate (neat coolant); preparation of coolant dilutions for the initial charge and for daily makeup; maintenance of coolant dilutions including the use of good housekeeping techniques; and routine condition monitoring by a laboratory to detect and correct discrepancies before problems arise

Proper Storage Storage methods are important to the success of the finished product Improper handling can render a coolant useless or may lead to premature solution failure Coolant concentrate should be stored inside between 50o and 100oF; outside storage should be avoided Concentrate must be protected from moisture

Coolant Make-Up Water Make-up water must be of suitable quality The pH & water hardness along with chlorides, sulfate, and iron content must be considered Hard water can split emulsions and form scum Chlorides can split emulsions and create rust Sulfates may promote microorganism growth Hard water discourages foam; soft water provides the best emulsion stability

Coolant Dilutions Coolant should be added at the point of maximum agitation Coolant mixtures should be prepared using dedicated mixing equipment and containers To initially charge a system, it is necessary to know the sump capacity of a machine or system

Maintenance of Coolant Coolant maintenance is absolutely essential to ensure consistent quality of manufactured parts Daily checks are needed since coolant dilutions are constantly changing through carry-off on parts, water evaporation, oil leaks, etc. Individual operators have the best ability to detect potential problems and maintain coolant solutions by performing simple daily checks

Maintenance of Coolant Daily checks by operators should include: verifying coolant concentration noting abnormal conditions such as excess tramp oil, solids, and/or foam, abnormal appearance or odor, etc. Routine lab testing is performed by Total Lubricants to ensure satisfactory fluid performance If a problem is detected from lab testing, corrective actions are implemented to ensure uninterrupted service from the coolant Water vaporization from machine sumps usually makes it necessary to add makeup coolant at a reduced concentration level

Coolant Concentration Concentration is the single most important factor to coolant success: concentration must be maintained as consistently as possible within an established range rich concentrations may cause an increase in skin irritation, produce excessive foaming, reduce the coolant’s ability to remove heat, & increase costs lean concentrations can destroy tool life, create rust and corrosion problems, promote growth of microorganisms, and lead to rapid fluid failure

Concentration by Refractometer A fast and easy method for checking coolant concentration is with a handheld refractometer. A refractometer is an optical instrument that reads the amount of total solids by passing light through a sample of coolant. Synthetic coolants produce the sharpest line on a refractometer; soluble oils are often difficult to read accurately Tramp oil or chemical contaminants may cause inaccurate readings

Routine Lab Testing Coolant condition monitoring tests include: concentration total alkalinity total oil content (“soluble”/semi-synthetic) pH microbe activity (aerobic/anaerobic bacteria & fungi) solids tramp oil cation levels (Ca, Mg, Na, Fe, Al) conductivity rust prevention properties

pH pH expresses the hydrogen ion concentration in a solution pH scale ranges from 0-14; 0-6.9 is acid; 7.0 is neutral; and, 7.1-14 is alkaline pH is measured with pH paper or electronic meter A high pH (8.5+) promotes good protection from corrosion and microorganisms A low pH is best for non-ferrous metals and is kinder to an operator’s skin.

Control of Microorganisms Coolants provide an excellent environment for the growth and reproduction of microorganisms Common microorganisms consist of bacteria and fungi (yeast and molds) Microorganisms digest helpful ingredients and produce foul odors Microorganism content is determined by growing cultures from coolant samples Biocides may be added to fluid to combat growth

Foam Some foam is good since it cleans machine surfaces and promotes good wetting properties Excessive foam, however, is a safety hazard and may cause pump cavitation Foaming is dependent on coolant concentration, water hardness, type of coolant, agitation, and severity of the operation Foam may be effectively controlled with anti-foam agents

Tramp Oil A layer which floats on the surface & consists of split-out oil, carry-over oil, and/or process oils Tramp oil causes incorrect refractometer readings, severe loading of grinding wheels, and a reduction in heat removal capacity and wetting ability Failure to control tramp oil often leads to an increase in the growth of microorganisms Effective control can usually be obtained by using oil skimmers and felt-covered wipers

Solid Contaminants Solids are formed during the machining process and consist of fines, shavings, and dirt Solids which are not effectively removed can scratch surfaces and interfere with close tolerances Solids provide additional breeding ground for microorganisms and promote operator dermatitis Most solid contaminants can be reduced or eliminated through the use of magnetic skimmers, filters, and chip separator devices

Operator Procedures Prior to the beginning of the shift & throughout the work day: observe the holding tank to detect any significant changes in tramp oil levels, dirt, or fungal growth (slime) slime-type growth on walls should be reported as soon as observed so that an anti-fungal treatment can be added (line clogging can quickly become a problem) “dirty” sumps should be changed out as soon as production & maintenance schedules permit operators will obtain a “feel” for the general operating condition of their machine through daily inspections

Dermatitis Dermatitis is an irritation or inflammation to the skin Coolants contain surfactants and wetting agents (soaps) which tend to dry skin Alkaline cleaners, degreasers, solvents, and abrasive cleaners further irritate the skin Common industrial irritants include kerosene, chlorinated solvents, acidic solutions, and metals including chromates, zinc, cadmium, & mercury

Dermatitis Factors external to the work environment which may cause dermatitis include: poison ivy, poison oak, ragweed, and sumac white pine, Frazier fir, & teak trees lemons, oranges, & onions penicillin, sulfa-drugs, & anti-histamines dyes, bleaches, deodorants, & nail polishes wool, silk, nylon, leather, & fur detergents, polishes, & waxes

Dermatitis Synthetic coolants tend to dry out skin the most Dermatitis, by definition, is not caused by bacteria although bacteria may aggravate an existing case of dermatitis Factors such as age, type of skin, previous exposure, & duration of contact determine an individuals’ susceptibility level to dermatitis Proper fluid maintenance and operator hygiene are key factors in preventing or reducing dermatitis