Cutting fluids have been used for a long time to perform generally the following functions : -lubricate the chip/tool and tool/workpiece contacts, reduce friction (decrease cutting forces and torques) ; extend tool life ; improve surface finish ; -cool the workpiece and the tool, in order to : dissipate heat in the cutting zone ; protect the metal tool and workpiece ; improve dimensional accuracy ; -protect the workpiece, tool and machine, flush and remove metal chips ; prevent chip/tool welding ; and control the Built Up Edge (BUE).

There are two main types of cutting fluids : neat cutting fluids and water-miscible cutting fluids.

Neat cutting fluids are usually preferred when excellent lubrication, good rust protection and surface finish are required.

However, they tend to evaporate and generate oil mists.

There is a therefore a need to reduce evaporation and oil mist generation in neat cutting fluids, in order to improve working conditions and provide a safer working environment. However, reducing evaporation usually means increasing viscosity, which reduces the cooling efficiency.

There is no teaching or suggestion in the prior art as to how a neat cutting fluid satisfying the above need can be produced without impairing its cooling efficiency.

The invention thus provides a neat cutting oil composition which, besides exhibiting low misting and evaporation tendencies, has satisfactory cooling properties.

Specifically, the invention provides a neat cutting oil composition comprising, based on the total weight of the composition : from 10 to 99%, preferably from 70 to 95% of a white mineral oil ; and from 3 to 40%, preferably from 5 to 30% of an ester from a dicarboxylic acid and a monoalcool.

The invention further provides a process for preparing the neat cutting oil composition.

The invention also provides a process for machining metals, comprising applying an effective amount of the neat cutting oil composition of the invention to the metal being machined.

Finally, the invention provides the use of the neat cutting oil composition of the invention in a metal machining operation.

The invention is now disclosed in more details in the following specification and in reference to the drawings in which : Figure 1 is a graph showing the Noack volatility at 200°C as a function of the kinematic viscosity, when using the neat cutting oil of the invention and a neat oil of the prior art ; Figure 2 is a graph showing the mist generation as a function of the kinematic viscosity, when using the neat cutting oil of the invention and a neat oil of the prior art ; Figure 3 is a graph showing the kinematic viscosity under shearing as a function of the number of cycles, when

using the neat cutting oil of the invention and a neat oil of the prior art ; and Figure 4 is a graph showing the mist percentage of the neat cutting oil of the invention and of a neat oil of the prior art.

By"white mineral oil", it is herein intended very highly refined oils which consist entirely of saturated components, all aromatics having generally been removed by treatment with fuming sulphuric acid or by selective hydrogenation. Their name reflects the fact that they are virtually colourless and the most highly refined medicinal white oils are used in medical products and in the food industry.

The white mineral oils used in the invention are preferably those which can be safely used as a component of nonfood articles intended for use in contact with food.

These oils are described in 21 CFR Ch. 1 §178. 3620 (a) and (b) of the Food and Drug Administration, HHS.

White oils are for example sold by the company SIP Limited of LONDON.

The white mineral oils typically have a viscosity from 3 to 500, preferably from 4 to 30 cSt at 40°C.

According to one embodiment, the cutting oil composition of the invention comprises a combination of a fatty acid ester with a phosphoric acid ester. This combination provides in flute grinding operations : 1) a reduced wheel rehardening (twist drills and taps production) ; 2) a reduction in drill structural damages ; and 3) less discoloratin on drill run-out.

An example of such a fatty acid ester is a fatty acid ester based on triglycerides and containing approximately 10 wt % sulfur including less than 1 wt % active sulfur.

The phosphoric acid ester is preferably amine neutralized and contains approximately 95 wt % phosphorus and 3. 8 wt % nitrogen.

According to a further embodiment, the cutting oil composition of the invention comprises a combination of oleic acid and tri-octyl phosphate. This combination provides in ball bearing grinding an excellent surface finish and extended wheel life.

According to yet a further embodiment, the cutting oil composition of the invention comprises a combination of sulfurized sunflower oil, tri-octyl phosphate and oleic acid. This combination provides an extremely fine finish in the honing of steel bore holes and shafts.

The neat cutting oil composition of the invention may comprise conventional additives, such as lubricity agents, antioxidants, extreme-pressure and anti-wear agents, anti- mist agents.

Examples of lubricity agents are long chain polar molecules, like fats, fatty acids, vegetable oils and esters.

Examples of extreme-pressure and anti-wear agents are sulphur and sulphur organic compounds, phosphorus organic compounds, or chlorine organic compounds.

Examples of phosphorus organic compounds include dilauryl phosphate, didodecyl phosphite, trialkylphosphate such as tri (2-ethylhexyl) phosphate, tricresylphosphate (TCP), zinc dialkyl (or diaryl) dithiophosphates (ZDDP), phospho-sulphurized fatty oils, tricresylphosphate (TCP), trixylylphosphate (TXP), dilauryl phosphate, amine phosphates, phosphoric acid esters.

Examples of sulphur phosphorus organic compounds include mercaptobenzothiazole, sulphurized fatty oils, sulphurized terpenes, sulphurized oleic acid, alkyl and aryl polysulphides, sulphurized sperm oil, sulphurized mineral oil, sulphur chloride treated fatty oils.

Examples of chlorine organic compounds include chlornaphta xanthate, cetyl chloride, chlorinated paraffinic oils, chlorinated paraffin wax sulphides, chlorinated paraffin wax, and zinc dialkyl (or diaryl) dithiophosphates (ZDDP).

Examples of anti-oxidants are metals deactivators like triazole derivatives, chain breakers like phenols, cresols derivatives, peroxyde decomposers like zinc dithiophosphates, metal dithio carbamates.

Further elements on base oils and additives can be found in"Chemistry And Technology Of Lubricants", R. M.

Mortier and S. T. Orszulik, VCH Publishers, Inc, First published in 1992.

The neat cutting oil composition of the invention is prepared by blending the base oil and the other ingredients, preferably under stirring or with any mixing device and whilst controlling the temperature so that it does not exceed 70°C, and more preferably, 50°C.

The neat cutting oil composition of the invention can be used in various machining operations like internal, surface or external broaching, tapping, threading, honing, gear cutting, gear shaving, gear hobbing, gear generating, reaming, automatic works, milling, form turning, planing, parting off, drilling, boring, sawing or superfinishing.

The neat cutting oil of the invention is particularly adapted in machining operations like honing, superfinishing, bearing grinding, gear grinding or flute grinding.

A great number of metals can be machined with the oil composition of the invention. Examples include titanium alloys, nickel alloys like Nimonics"', stainless steel like inconel, tool steel, high alloy steel, high carbon steel, mild steel, wrought iron, silicon aluminium alloys, cast iron, copper, copper alloys, bronze, brass, aluminium and aluminium alloys.

The following examples illustrate the invention without limiting it. All parts and ratios are given by weight, unless otherwise noted.

Examples Compositions 1 to 3 are prepared by mixing the ingredients of Table 1 in the order in which they appear in this table. The temperature is maintained at a maximum of 50°C to ensure a complete dissolution and homogeneisation of the ingredients without impairing the properties of the cutting oil.

TABLE 1 Composition number and content (watt) Ingredients 1 2 3 White oil with a 86. 60 viscosity of 4 cSt at 40°C White oil with a 81. 40 viscosity of 9 cSt at 40°C White oil with a 84. 80 viscosity of 24 cSt at 40°C 2-ethyl-hexyl adipate 5. 00 2-ethyl-hexyl cocoate 3. 00 10. 00 Oleic acid (lubricity 5. 00 3. 00 4. 00 agent) Lecithin (lubricity 2. 50 agent) Polyisobutylene (anti-0. 50 0. 50 0. 50 mist agent) DBPC (anti-oxydant) 0. 10 0. 10 0. 20 Tri-octyl phosphate 1. 80 2. 00 (extreme pressure agent) Fatty acid ester (1) 2. 50 (extreme-pressure agent) Fatty acid ester (2) 0. 50 (extreme-pressure agent) I Sulfurized sunflower oil 3. 00 3. 00 (anti-wear) (fatty acid ester based on triglycerides containing approximately 10% sulfur including less than 1% active sulfur (2) : phosphoric acid ester, amine neutralized containing approximately 95% phosphorus and 3. 8% nitrogen

The characteristics of the composition of Table 1 are set out in Table 2.

TABLE 2 Composition numbers and typical characteristics 1 2 3 Kinematic cSt ASTM D 445 5. 2 10. 2 21. 5 viscosity at 40°C Kinematic cSt ASTM D 445-2. 9 4. 5 viscosity at 100°C Copper 3h, ASTM D130 1A 1A 1A corrosion 100°C Phosphorus wt % ASTM D4951 0. 17 0. 18 0. 08 Colour ASTM D 1 1 1. 5 1500 Density at G/cm3 ASTM D 834. 8 839. 9 850. 1 15°C 4052 Total acid mg ASTM D 664 <0. 03 <0. 03 <0. 03 number KOH/g Sulphur wt % DIN 51400 0. 31 0. 32 0. 22

EXPERIMENTAL TESTING A cutting neat oil of the prior art having the composition set out in Table 3 is selected :

TABLE 3 Ingredients Content (wt%) Paraffinic base oil viscosity 150 96. 5 Saybold Universal Second at 100°F Oleic acid (lubricity agent) 3. 5

A Noack volatility test (CEC L40-A93) at 200° as a function of the kinematic viscosity is carried out with the neat cutting oil composition of Table 1 and with the neat oil of Table 3.

The results are shown on Figure 1. It can be seen that the neat cutting oil composition of the invention is less volatile than the neat oil of the prior art.

The Renault mist test D65/-649 is carried out with the neat cutting oil composition of Table 1 and with the neat oil of Table 3.

The results are shown on Figure 2. It can be seen that the neat cutting oil composition of the invention generates much less mist than does the neat oil of the prior art.

A resistance to shearing test according to the CEC L- 14-A-78 method as a function of the number of cycles is carried out with the neat cutting oil composition of Table 1 and with the neat oil of Table 3.

The results are shown on Figure 3. It can be seen that the kinematic viscosity of the oil composition of the invention varies less than that of the neat oil of the prior art, whatever the number of cycles.

The mist generated by the neat cutting oil composition of Table 1 is compared to that generated by the neat oil of Table 3.

The method used to measure the mist consists in using an optical instrument (Data-Ram@) fitted on the exhaust pipe of a Traub TNS 42 CNC machine. The Data-Ram is a high sensitivity light scattering photometer and the intensity of the light scattered over the forward angle of 45 to 95 degrees by airborne particles passing through the sensing chamber is linearly proportional to the concentration.

The results are shown on Figure 4. Again, it can be seen that the neat cutting oil composition of the invention generates much less mist than does the neat oil of the prior art.