A world of choice in metalworking fluids: foaming and misting not wanted. (Fluids).

Metalworking manufacturers have a lot riding on the quality of the metalworking fluids (MWF) used in their machining and grinding operations today--perhaps more than at any time in the recent past. Demands for higher productivity and higher quality of workpieces, coupled with concern for the health and safety of workers and protection of the environment, are making choices that much more important.

Whether used in a large plant's central fluid system or in the sumps of individual machines in large or small shops, metalworking fluids must strike a balance between higher productivity process rates and operator and machine friendliness, says Raymond Dick, manager, CIMCOOL Technical Service, Milacron's Consumable Products Division.

Twin machining challenges

There are two parallel paths in machining developments that continue to drive R&D in coolant and fluid formulation. "Higher speeds and feeds and through-tool delivery are testing the lubricity and foaming and misting control of our products every day," says Dick.

Coolant pressures can easily reach 1,000 psi and as high as 4,000 psi with high-pressure coolant delivery systems available today. The continuing emergence and adoption of high-speed machining with spindle speeds over 10,000 rpm, and up to 50,000 rpm, are pushing feeds and speeds to hitherto unknown performance regions.

For these feeds and speeds, MWFs must exhibit low foaming and misting characteristics. In addition, such important qualities as biostability, good corrosion control and lubricity are being joined by demands for recyclability, ease of disposal in the wastewater treatment stream, and compatibility with varying degrees of water quality.

That's exactly where users need to begin evaluation of their machining processes. What exactly is the quality of the water available? Metalworking fluid mixes, which are 90 to 95 percent water, may require pretreatment of water to eliminate "hardness" or minerals. Deionization or reverse osmosis treatments are preferred choices, since they remove not only the hardness ions (i.e., magnesium and calcium) but also other undesirable ions such as chlorides and sulfates.

The trick is to match MWF chemical formulation to the specific applications. A starting point is to identify the metals being processed and the severity of your operations. (See Exhibit A, "Evaluate Your MWF Requirements," for key considerations.) Grinding operations pose their own special considerations and require special attention paid to filtration, heat removal (cooling) as well as foam and mist control.

The right combination

Metalworking fluid users fall into several general categories. Larger plants and production facilities may use central fluid systems of 1,000 gallons or more. Other plants, such job shops may use individual machines with sumps containing from 5 to 100 gallons of metalworking fluids.

Fluid formulations for large plant users often break out along the lines of industry served. High-speed machining of aluminum and high temp alloys holds sway in aerospace. Steel, cast iron and-increasingly--light metals like aluminum and magnesium are encountered more often in the auto industry.

For the aerospace industry, a synthetic product like Milacron's CIMTECH 310 metalworking fluid has shown excellent results for milling aluminum at high speed or for machining high-temperature alloys and titanium.

Typical reactions of users run the gamut from "eliminated rancidity" and "extremely low-foaming," to "provided much longer sump life" and "extended tool life."

For a major aerospace manufacturer CIMTECH 310 is being used in place of a semisynthetic fluid in a variety of operations including milling, boring, tapping, reaming and even some grinding. Materials include 7075, 7051, and 7075 aluminum, titanium, and some steel for such parts as rockets, panels, aerospace hydraulics and commercial and space station assemblies.

Customer comments after three months of testing reveal the range of problems that improperly maintained MWFs can cause and that CIMTECH 310 remedied: "no foam and it doesn't smell bad;" "CIMTECH 310 is cleaner and doesn't develop any smell;" "the oil floats and CIMTECH doesn't degrade;" and "it's cleaner and lower misting in grinding operations."

For job shop or production machining, a soluble oil product like CIMPERIAL 1070 metalworking fluid fills the bill as a kind of universal fluid for moderate- to heavy-duty machining and grinding of all metal types.

In one job shop, for example, a wide variety of parts and materials including 1704, stainless steel, 4340, H-11 and 2024 and 7075 aluminum were being turned. Carbide and ceramic inserts and CIMPERIAL 1070 have improved surface finish.

An automotive part manufacturer, high-speed drilling 1018 steel on a Cincinnati Machine Arrow 750 with TNC-coated tooling has found that CIMPERIAL 1070 provided very good lubricity and eliminated a corrosion problem experienced previously using a soluble oil product.

Grinding applications are among the most difficult challenges. MWF choices are as varied and specific as the metals being ground and the type of grinding wheel being used. Milacron, as one of the largest and most diversified manufacturers of grinding wheels, specializes in researching and customizing formulations to match wheel types, i.e., vitrified-bonded abrasive, resin-bonded abrasives, or superabrasives like diamond/CBN, to the metals for best grinding performance, says Dick.

For a supplier of steel motor shafts from 3" to 65" long, CIMPERIAL 1070 has been used in center grinding and hard turning carbon steel, stainless steel, and steel alloys to good effect. Results have included improved rancidity control, very good lubricity, and elimination of a dermatitis problem from previous soluble oil product, according to the, Ohio company.

The right mix

There is nothing more damaging to good machining performance than the wrong MWF concentration and contamination. "You can trace 90 percent of the problems to failure to maintain the proper concentration of fluid," says Dick. Next in line is contamination from tramp oil, fines, cleaners, etc. Milacron provides training classes for metalworking fluid users that help them minimize contamination and maximize fluid life.

"The metalworking fluid system is a dynamic mix that must be monitored and maintained daily," he says. "The correct concentration with the right balance of biocides, corrosion inhibitors and lubricants is maintained by daily makeup and concentration monitoring."

Milacron provides a variety of fluid management equipment including proportioners, wall-mounted mix stations and positive displacement metering pumps. Proportioners are simple and inexpensive. The CIMCOOL Mix Master II is installed on a 55-gallon drum and connected to a water line to provide premixed fluid at about 3 gpm. These proportioners are simple, inexpensive, yet effective for automatic fluid premixing and makeup.

The wall-mounted CIMCOOL Mix Station is a venturi-type proportioner that has the advantage of having two mixing selections, one for charging a machine sump and one for adding makeup. Positive displacement metering pumps enable premixed fluid to be piped throughout the shop providing fluid to many machines.

Monitoring the mix

Milacron offers fluid monitoring services to both its large and small users. For its larger customers, those with central fluid systems of 1,000 gallons or more, Milacron provides a weekly monitoring service of fluids. "Things change quickly in the dynamics of a fluid system," says Dick.

Milacron performs the necessary lab tests for concentration and pH, among other tests for particulates/dirt, free oil, tramp oil, as well as bacteria and mold levels. Each metalworking fluid has assigned "control test parameters" for optimum fluid control and performance. For example, the normal control range for pH is 8.8 to 9.2. If the pH trends low, bacteria growth may be a problem. If the pH trends high, contamination with alkaline cleaners may be a concern.(See Exhibit B, "Analyzing Water-Soluble Metalworking Fluids.")

Small shop users can monitor their own fluids right on the shop floor by utilizing a variety of fluid checks. An operator can quickly check fluid concentration using a refractometer, a hand-held optical measurement device. An alternative to the refractometer is Milacron's CIMCHEK test strips that can be used to check concentrations in individual machine sumps. Similarly, pH test strips give a quick indication of microbial control, corrosion control and possible contamination.

Whence contaminants?

The sources of contaminants are as varied as the working conditions in any shop. Fluids can be contaminated by lubricants like hydraulic oils, spindle oils, slideway lubes and greases, cleaners, solvents, and other metalworking fluids. Users are benefiting today from efforts of machine tool builders to design lube systems that are permanently sealed and self-lubricating, improved hydraulic systems, and protective coverings for critical machine components.

In its own studies, Milacron has identified leak or tramp oil as a major contributor to increasing the mist levels for all types of water-based fluids. The study underscores the importance of a good maintenance program to reduce oil leakage and the necessity of properly functioning equipment to remove tramp oil. The data indicate that the amount of leak oil present has a greater impact on mist levels than does the general class of metalworking fluid type being used.

Adopting the best fluid maintenance systems from simple oil skimmers to elaborate filtration and recycling systems is essential to optimize machining processes by removing metal chips, grinding fines, and any other contaminating particulates from the MWFs. Similarly, machine tool builders have responded to user demands and fluid supplier recommendations to design machines with full enclosures, fluid handling systems, and machine work envelopes with a negative pressure that prevent fluid mist from escaping even through open machine doors.

Milacron Consumable Products Division, Cincinnati, OH, http://www.OneRS.net/105tp-270 or circle 270

RELATED ARTICLE: EXHIBIT A

Evaluate your metalworking fluid requirements

Checklist

What types of metals are being machined?

_Steel (4000 series, etc., carbon alloys, tool and die steels)

_Iron

_Aluminum (high silicon automotive)

_Aluminum (low silicon aerospace)

_Nonferrous (copper, brass, other)

_Stainless Steel (200-500 series)

_High Temp Alloys (nickel-based, iron-base, cobalt-base; titanium)

What is the severity of your machining operations?

_Very Heavy Duty (broaching, tapping, reaming)

_Heavy Duty (drilling, sawing)

_Medium Duty (turning)

_Light Duty (milling)

How are your metalworking fluids used?

_Central System

_Individual Machines

_Both central and individual

What product types do your prefer?

_Oil (straight oil)

_Water-based fluids, including:

_Soluble Oil (milky as fresh mix)

_Semi-Synthetic (translucent to milky as fresh mix)

_Synthetic (may be transparent or milky as fresh mix)

EXHIBIT B

What's the condition of your water soluble metalworking fluids?

Here are the elements of MWFs that are monitored and why.

Concentration is the percentage of metalworking concentrate in the mix. It can be expressed as a ratio, the amount of MWF concentrate to the total volume of mix. Adding four gallons of concentrate to 96 gallons of water yields a 4 percent or 1:25 mix concentration.

pH is a measure of the acidity or alkalinity of the MWF mix. It is a good indicator of the condition of your fluid mix. Most MWFs operate in a pH range of 8.8 to 9.2. If the mix pH is too low, rancidity control, ferrous corrosion control, and mix stability are affected. If pH is too high, mildness and nonferrous corrosion control are affected.

Dirt volume is the percentage of solids in the MWF mix. High dirt volumes usually indicate inadequate filtration or filter problems and can lead to such problems as residue, poor finish, poor grinding wheel or tool life, and microbial growth. Dirt values should be less than 0.1 percent.

Free oil is the percentage of oil or oil-like material that is not emulsified and floats on. the surface of your MWF mix. High free oil percentage can lead to such problems as microbial growth, residue, and grinding wheel loading. Free oil should be 0.5 percent or less.

Tramp oil is the percentage of oil or oil-like material that is not product oil. Product oil is that oil that comes from, the metalworking fluid concentrate. A tramp oil percentage that is high can promote problems such as residue, poor grinding and machining performance and microbial growth. Significant performance problems can be expected when tramp oil levels reach half the MWF fluid concentration.

Bacteria count that is high can lead to offensive odors and failure of MWF fluid mix. Most MWFs can tolerate a bacteria count of 100,000/mL.

Mold count that is high can lead to offensive odors, plugged fluid lines, and failure of MWF mix. Mold counts may not detect the mold present in or around the system because mold is more likely to cling to surfaces and not be detected in small fluid samples.

Conductivity is a measure of the conductance of a MWF and is expressed in MilliSiemens/cm. As the amount of dissolved materials, i.e. calcium, magnesium, sodium, chlorides etc. increases, the conductivity increases. Conductivity is expected to increase slowly over time. The rate of the increase depends on the quality and amount of water used and' the amounts and types of other contaminants. High levels of conductivity can promote problems such as insoluble, residues, mix instability, and loss of overall performance. Emulsion instability can be expected with a conductivity that reaches the 4 to 5 mS range.

* AUTOMOTIVE CASE HISTORY

System: Individual machines

Part: Various

Material: 1018 steel

Operation: High speed drilling on Cincinnati Arrow 750 using TNC-coated tooling

Concentration: 5 percent CIMPERIAL 1070

Results: Replaced competitive soluble oil; very good lubricity; improved rancidity control; eliminated dermatitis problem

* AEROSPACE CASE HISTORY

System: Individual machines: G&L vertical boring; Cincinnati 30V 5-axis; Mazak vertical machining center; Thompson surface grinder 

Part: Rockets, panels, aerospace hydraulics and commercial assemblies

Operations: Milling, boring, tapping, reaming, some grinding

Concentration: 5 to 7 percent CIMTECH 310

Results: No foam and doesn't go bad; cleans and doesn't smell; lower misting

* JOB SHOP CASE HISTORY

System: Individual turning center

Part: Various

Material: 17-4, stainless steel; 4340, H-11 and 2024 and 7075 aluminum

Operation: Turning using carbide and ceramic

Concentration: 5 percent CIMPERIAL 1070

Results: Improved surface finish