CA1059980A - Cutting oil compositions having low air misting compositions - Google Patents

Abstract

CUTTING OIL COMPOSITIONS HAVING
LOW AIR MISTING PROPERTIES
(D#73,816-F) ABSTRACT OF THE DISCLOSURE
Fine mists of cutting oil compositions can be substantially reduced by incorporating into said cutting oil minor portions of an amorphous ethylene-propylene copolymer.

-I-

Description

BACKGROUND OF THE INVENTION
This invention relates to metal working lubricant compositions having low air mist forming properties. In particular, this invention is directed to metal working lubricant compositions used as cutting oils in metal machining and grinding operations. This invehtion is directed more particularly to cutting oil additives which will surpress the mist generation in these industrial metal working lubricants.
~he economy of industrial nations is closely associated with metal products and the design, construction and use of machines to fashion these metals into useful tools and products. Metal working lubricants play a significant role in increasing the efficiency of metal working machines used in forging, drawing quenching, cutting and grind ing processes. Approximately half of the total quantity of metal working lubricants used in the metal working industry are consumed in metal cutting and grind ing .
Cutting and grinding are metal working processes ~ ~ wherein the shape of the final object is obtained by progressive removal of metal in the form of chips rather than by plastic reforming of the metal as in other metal working processes, such as forging and drawing.
~ Cutting and grinding lubricants are generally ; ~ termed cutting fluids and perform two basic functions: (1) ; as a coolant (to cool the tool and reduce wear and loss of hardness and to cool the work to prevent distortion and ~; dimensional inaccuracies), and (2~ as a lubricant (to lubricate the chip-tool interface and reduce frictional heat, tool wear and power consumption and improve surface finish;
also to prevent welding of metal to the tool point and subsequent rough surfaces). In addition, the cutting fluids should flush chips away from the work area, protect the finished work surfaces, the tools and the machines from rust and discolorization and resist smoking and fogging in use.
Cutting fluids can be broadly classified as mineral oil base cutting oils, soluble oil and chemical coolants.
This invention is concerned with the mineral oil base cutting oils. These cutting oils include several general types:
straight mineral oils, mineral-fatty oil blends, mild EP oils, dark heavy duty oils and multi-purpose oils. Straight mineral oil cutting oils are used in mild cutting operations. Where additional lubricity is needed, fatty oils or fatty acids may be added. Paraffinic or mixed base mineral oils are preferred since in severe service they generally form less smoke than naphthenic oils. In most metal cutting operations, an additive-containing oil having extreme pressure (EP) characteristics is required. Useful additives include fatty oils and acids, sulfurized oils and fatty oils, chlorinated oils, organic phosphorous materials and waxes. The dark colored, highly sulfurized oils possess excellent performance characteristics and are the workhorse of the industry.
Their dark color and pungent odor are not acceptable in some operations, leading to th~ development and increasing use of transparent cutting oils. The principal advantage of these oils is that easier inspection of parts is possible, resulting in increased production and reduction of rejects. The quality of transparent oils has been improving rapidly and they have been receiving more wide spread acceptance and lOS9980:
use. They are formulated with various combinations of sulfur, chlorine and phosphorous additives, depending on service requirements. Some cutting oils are prepared to serve as a multipurpose oil, particularly in automatic screw machines. They can be used as a cutting oil, a general machine lubricant and/or a hydraulic fluid in hydralically-powered machines. In addition to reducing oil inventories and eliminating cross-contamination when filling oil reservoirs, ; these dual and tri-purpose oils avoid the problems attendant from leakage from one oil system to the other. Dilu~ion of the cutting oil by ordinary machine tool lubricant or hydraulic fluid will reduce its EP level and eventually its performance.
On the other hand, contamination of the machine tool lubricant or the hydraulic fluid by one of the usual cutting oils, particularly one of the corrosive ones, has serious consequences.
This~is avoided with a multipurpose cutting oil.
During cutting and grinding processes (generally referred~to hereinaftor as a machining process), an oil mist or fog is oten generated from the cutting oil, particularly 20~ during high opeed metal cutting operations. This oil mist or fog can create an occupational health hazard to machine operators. In fact, the Federal Occupational Safety and Health Act (OSHA) recognizes this danger by establishing maximum levels of oil spray or mist content in the air of machine shop work areas during the presence of machine operators and other personnel. To comply with these federal standards~, polymers havs been found to be successful in ~; surpressing the mist generation in cutting oils. However, .
- many of the cutting oils containing these polymers do not retain their mist surpression qualities after continued use under ihdustrial conditions.

lOS9980 It is therefore an object of this invention to provide a cutting oil composition which will not only have a low air misting quality when manufactured but will maintain this property over prolonged use in industrial applications.

SUMMARY OF THE INVENTION
We have found that additions of an amorphous ethylene-propylene copolymer to a cutting oil will not only surpress the mist generation of the cutting oil but will maintain the air misting at significantly low levels during prolonged use of the cutting oil. The ethylene-propylene copolymer found useful for these purposes has an amorphous structure, a number average molecular weight between about 10,000 and 100,000,preferably between about 30,000 and 80,000, a propylene content of 20 to 70, preferably 30 to 55,mole percent and a MW/Mn of less than about 5. Minor quantities of this copolymer, between about 0.01 and 1.0, preferably between about 0.04 and 0.35, weight percent of the cutting oil composition are found to be effective in reducing the ~20 air misting of the cutting oils to below the standards established by the OSHA. Concentrations of the copolymer higher than 1.0 weight percent may be used but there is no apparent further improvëment in product quality or mist resistance.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
:~ Broadly, we have found that the mist generation of a cutting oil can be significantly reduced by incorporating therein small quantities of an amorphous ethylene-propylene copolymer. Further, this particular copolymer maintains the air misting at acceptable low levels for prolonged periods of time despite the continuous s~bjection of the cutting oil to high shearing forces during the machining operation. -4-lOS9980 More specifically, our invention relates to a process for reducing the air misting of a cutting oil during metal machining operations which comprises supplying to a metal machining tool, for use as a lubricant,a cutting oil composition comprising a major portion of a mineral oil base cutting oil and a minor portion, sufficient to reduce the air misting qualities of said cutting oil composition, of an ethylene-propylene copolymer having an amorphous structure, a number average molecular weight of between about 10,000 and 100,000, a propylene content of 20 to 70 mole percent of a MW/Mn of less than about 5.
As discussed above, our invention is directed to cutting oil compositions comprising a major portion of a mineral oil base cutting oil and a minor portion,sufficient to reduce the air misting qualities of said cutting oil composition when used as a metal machining lubricant during metal machining operations, of an ethylene-propylene copolymer - having an amorphous structure, a number average molecular weight of between about 10,000 and 100,000, a propylene content of :~ 20 2~0 to 70 mole percent and a MW/Mn of less than about 5.
The cutting oils whose misting qualities can be successfully suppressed by admixing therewith the amorphous ethylene-propylene copolymers disclosed herein include a wide variety of mineral oil base cutting oils. In fact, where misting of a cutting oil is a problem, the addition of a quantity of an amorphous ethylene-propylene copolymer will . control the misting. Examples of these cutting oils include the dual and tri-purpose cutting oils, transparent cutting oils, EP cutting oils, cutting oils compounded with sulfur, chlorine and/or phorphous compounds, as well as a wide variety of cutting oils compounded for special purposes such as for the machining of magnesium, aluminum and other metals and alloys having special machining characteristics.
In general, cutting oils have viscosities coverlng a broaa spectrum, viz, 30-500 SUSeDI00 F.
The ethylene propylene copolymers we utilize are amorphous by infra red analysis and have a narrow molecular - weight distribution. These copolymers may be prepared as described in U.S. 3,522,180. This patent discloses that amorphpus ethylene-propylene copolymers may be prepared in a hydrogen moderated reaction at moderate temperatures and pressures in the presence of a solvent soluble Ziegler-Natta catalyst. In U.S. 3,522,180, amorphous ethylene copolymers having a number average molecular weight of 10,000 and 4~,000, a propylene content of 20 to 70 mole percent and a MW/Mn of less than 5 are disclosed as viscosity index improvement additives for lubricating oils. We have found that these same copolymers are useful as mist suppressing additives for cutting oils. In fact,we have found that the number average molecular weight of the amorphous ethylene copolymers we employ may be 10,000 to 100,000 although we prefer to use those whose number average molecular is 30,000 to 80,000.
The concentration of the amorphous ethylene-propylene copolymers necessary to suppress the misting of cutting oils should be between about 0.01 and 1.0, preferably between about 0.04 and 0.35,weight percent of the final cutting oil blend. Those skilled in the art will realize that some experimentation may be necessary to arrive at the minimum concentration required by both economic and service requirements. In general, the more ~OS9980 severe the shearing experienced by the cutting oil the higher the concentration of a given amorphous ethylene-propylene copolymer necessary for satis~actory service.
EXAMPLE I
This example shows the mist surpression properties of a number of materials when added to a cutting oil. In a series of tests a small quantity of each material was added to a cutting oil composition and the misting properties of the resultant blend evaluated by visually observing the quantity of mist formed above a small quantity of the oil while a stream of air was passing through the oil. Then the oil was subjected to severe shearing conditions and its misting propensities were then re-evaluated. The cutting oil used was a tri-purpose oil compounded from paraffin base oils and containing rust and oxidation inhibitors and an extreme pressure additive. The cutting oil used in this series of tests had the following properties:
Gravity, API 28.1 Flash,COC, F. 390 Viscosity, SUS 157 ~p 100F
SUS~p210F 43.1 Pour, ASTM,F +10 Chlorine, % 1.39 Antioxidant~% 0.29 The misting characteristics were determined visually in an apparatus consisting of a vertical glass cylinder, 2 inch I.D., 12" long, attached to a stainless steel plate. After cleaning the cylinder with a light solvent and blowing it dry,180 ml. of the oil under test were introduced into the cylinder filling it to a height of approximately 3 l/4 inches. Air was introduced into the cylinder through a 0.018 inch orifice in the stainless steel plate at a regulated pressure of 35 psig while the cylinder was maintained in an upright position. After allowing one minute for the formation of an oil mist to stabilize, an observer made a visual evaluation of the quantity of mist or fog which had formed in the vicinity of the top of the tube and assigned a qualitative rating as follows:

Very Good - No mist or fog to barely perceptible mist or fog Good - Very slight mist or fog Fiar - Slight mist or fog Poor - Much mist or fog The oil under test was then subjected to high shearing by pumping the oil for either 10 or 20 passes through a Bosch fuel injection nozzle. This equipment is utilized in Fuel Injector Shear Stability Test (FISST) as described in Paper No~ 57A, entitled "Simplified Shear Stability Testing"
~ by R. Rawson, presented at the June 1958 meeting of the Society of Automotive Engineers. Following the shearing, the oil was re-evaluated in the misting test. The screening test results are shown in Table I below:

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o ~1 These series of tests show that initially many materials tested had very poor mist suppression properties, others were moderately successful in this area while still others did a very good job in suppressing mist. After subjecting the cutting oils containing these additives to severe shearing, most of the tested materials were unsatis-factory. Only the ethylene-propylene copolymers, particularly those of the amorphous type (Runs 18-27),showed an ability to suppress misting of the cutting oil after being subjected to severe shearing forces. Subsequent testing in a machine shop of those ~lends which passed these screening tests confirmed their suitability in actual service.
These tests also show that although as little as 0.008 wt.% of a particular ethylene-propylene copolymer provided good mist control (Run 27), 0.04 wt.~ of this copo~ymer was required to retain these anti-misting properties after severe shearing (Run 25).
ExAMæLE II

This example demonstrates that amorphous ethylene-propylene copolymers similar to those employed in Runs 22-27 of Example I are effective in controlling the misting of other types of cutting oils.
The testing procedures were the same as those used in ExampIe I. In all instances a copolymer concentration of 0.16 wt.~ was used. A description of the cutting oils tested and the results are shown in Table II below:

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g ~ 0 CO o~ o ,1 lOS9980 This series of runs demonstrates the superiority of amorphous ethylene-propylene copolymers in suppressing the misting properties of a wide variety of cutting oils subjected to severe shearing forces.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for reducing the air misting of a cutting oil during metal machining operations which com-prises supplying to a metal machining tool for use as a lubricant a cutting oil composition comprising a major por-tion of a mineral oil base cutting oil and a minor portion, sufficient to reduce the air misting qualities of said cut-ting oil composition, of an ethylene-propylene copolymer having an amorphous structure, a number average molecular weight of between about 10,000 and 100,000, a propylene content of 20 to 70 mole percent and a ?w/?n of less than about 5.

2. A process according to Claim 1 wherein the minor portion is between about 0.01 and 1.0 weight percent.

3. A process according to Claim 1 wherein the minor portion is between about 0.04 and 0.35 weight percent.

4. A process according to Claim 1 wherein the ethylene-propylene copolymer has a number average molecular weight of between about 30,000 and 80,000.

5. A process according to Claim 1 wherein the ethylene-propylene copolymer has a propylene content of between 30 and 55 mole percent.