United States Fatent 3,946,225 Patented July 24, 1962 tire 3,046,225 SOLUTION METAL CUTTING AND GRINDING FLUES John L. Murray, Westfield, and Roy A. Westlund, Jr.,

Roselle, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Oct. 8, 1958, Ser. No. 765,957

4 Claims. (Cl. 252-336) This invention relates to new and improved solutiontype cutting and grinding fluids. These fluids are also known in the trade as chemical coolants. More particularly, it relates to rust-inhibiting solution-type metal working fluids comprising the synergistic combination of alkali metal nitrites and alkali salts of N-acyl sarcosines in an aqueous solution with surface-active agents to form metal working fluids. These compositions are prepared as concentrates which are diluted with water when used, usually with 50 to 100 or more volumes of water per volume of concentrate.

The use of alkali metal nitrites and amides in preparing eflective corrosion-inhibiting compositions is well known in the art. It has now been found that alkali metal nitrites and alkali metal salts of N-acyl sarcosines in a water solution, both with and without surface-active agents, combine synergistically to give excellent inhibition to rusting at unexpectedly low concentrations.

In the prior art, whenever alkali metal nitrites were used in metal working fluids, a toxicity problem was encountered, with the degree of toxicity being directly proportional to the concentration of nitrite employed. The fluids of this invention, by having a very low nitrite concentration, 1% and less in the diluted form, are substantially free of this problem. Another advantage of the metal working fluids of this invention, resulting from the low nitrite concentration, is the ability to use unbuifered nitrites. However, bufiers or other materials to maintain a basic pH can be used where desired, and still remain within the spirit of this invention. Also, in the metal working fluids of the prior art which contain alkali metal nitrites, only those surfactants which could resist the oxidation attack of sodium nitrite could be employed. This problem is not present in the metal working fluids of the instant invention due to the very low nitrite concentration, and a wide variety of surfactants can be used.

Solution metal working fluids are contrasted to conventional soluble or emulsified cutting oils in that single phase, clear transparent solutions are formed on dilution with water in normal use, whereas soluble oils form a milky or at best a translucent emulsion, depending on the amount and type of emulsifier.

Solution metal working fluids offer advantages over soluble oils in several respects. First, soluble oils have an inherent tendency to become rancid as a result of bacterial attack on the emulsifiers or the mineral oil itself. Solution coolants, on the other hand, can be formulated to have greater resistance to this bacterial attack and subsequent odor formation. Second, the solutions of this invention are far clearer than even the most translucent soluble oils, thus permitting better visibility of the work being machined. Transparent solutions are often essential in grinding operations. Third, there is some indication that at very high cutting speeds (greater than about 400 surface feet per minute), solution metal working fluids give better tool life in lathe turning with carbide tools than soluble oils. This is believed to be because cooling the cutting tool is more important than lubrication at these high speeds, and solutions give better cooling than do soluble oil emulsions.

The solution coolants of this invention offer a definite advantage in behavior toward cast iron over soluble oils containing petroleum mahogany sulfonate emulsifiers. Mahogany sulfonates tend to stain cast iron. Also, inhibition of rust on cast iron by mahogany sulfonate soluble oils is very difflcult. Cast iron rusts far more easily than steel and requires particularly effective rust inhibitors. Rusting and staining of cast iron is important because most machine tools have parts made from cast iron which normally come in contact with the cutting fluid. Cast iron is commonly machined without a coolant, but in some operations a coolant is used. This places a severe quality requirement on a fluid to be used in all applications, including machining and grinding of cast iron. The composition of this invention is particularly eflective in inhibiting rusting on cast iron.

The solution-type metal working fluids of this invention will contain alkali metal nitrites and alkali salts of N-acyl amino carboxylic acids, particularly sarcosine, in ratios in the range of 1:1 to 11:1, nitrite to carboxylate. These two specific types of alkali metal salts, when present in the above ratios, will combine synergistically to prevent rust at concentrations as low as 0.2% and 0.02% nitrite and sarcosinate, respectively, in the diluted fluid. Concentrations, however, as high as 10.0 wt. percent nitrite and 1.0 wt. percent sarcosinate can be used in preparing stock solutions which are subsequently diluted with water for use as metal working fluids. A particularly eflective composition consists essentially of about 96.88 to 99.38% water, 0.22 to 1.25 wt. percent of a mixture of sodium nitrite and sodium lauroyl sarcosinate in ratios between 9:1 and 11:1 in water solution, with 0.4 to 1.87 wt. percent of a surfactant of the polyoxyalkylene class, having a molecular weight between 3000 and 4000.

Lower concentrations in the range of 0.2 to 0.5 wt. percent nitrite and 0.02 to 0.05 wt. percent sarcosinate are preferred in the working fluid. The surface-active agent may be present in concentrations ranging from 0.1 to 20 wt. percent in stock solutions, but concentrations in the range of 0.2 to 0.5 wt. percent are preferred in the final metal Working fluid. All of the above concentrations for final metal working fluid are expressed as weight percent of the total weight of the diluted solution of cutting fluid concentrate and water. The presence of a surface-active agent is not essential to the formation of the rust inhibiting metal working fluids of this invention. However, use of such agents is preferred when the fluid is used for metal working. Solution-cutting fluids of this invention can also contain dyes, perfumes, bactericides, sequesterants, defoamers or other materials.

The alkali metal nitrites useful in the present invention include sodium, potassium and lithium nitrite, with sodium nitrite being particularly preferred.

The alkali metal salt of the N-acyl amino carboxylic acid is preferably sodium lauroyl sarcosinate, however, any alkali metal salt of an N-acyl amino carboxylic acid wherein the acyl group is derived from a C to C fatty acid may be used. The alkali metal salt of an N-acyl sarcosine can be prepared according to the following equation:

HN (CH CH CO ONa-l-RCOCI RCON(CH CH COOH+NaCl N-acyl sarcosine+NaOH- Water+ sodium N-acyl sarcosinate The alkali metal N-acyl amino carboxylic acid salts useful in the present invention have the following general formula:

wherein R represents the alkyl group of a C to C fatty acid, M represents the alkali metal, e.g., lithium, sodium or potassium, and n is an integer from 1 to 4. Examples of suitable fatty acids are capric, 2-ethyl-hexoic, lauric, caprylic, oleic and stearic acids.

The surface-active agents that can be employed in the solution metal working fluids of this invention are anionic or nonionic materials that are compatible with the other components of the system. Suitable and readily available surfactants may =be selected from the following list: Span products (partial esters of common fatty acids and hexitol anhydrides derived from sorbitol) and Tween products (polyoxyethylene derivatives of the Span products), both manufactured by Atlas Powder Company; polyalkaylene glycol type fluids sold by the name of Ucon Fluids by Carbide and Carbon Chemicals Company; alkyl phenyl polyethylene glycol ethers (typical products commercially available are Carbide and Carbons Tergitol nonionics); Ethomids (polyoxyethylene substituted fatty acid amides) and Ethofats (monofatty or resin acid esters of polyethylene glycols), both sold by Armour Chemical Division of Armour and Company, and block polymers of ethylene oxide and propylene oxide (Pluronic materials sold by Wyandotte Chemicals Corporation).

Surface-active agents such as alkyl ethers of polyoxyalkylene glycols, etc., are preferred. A particularly pre-' .ferred type of these ether materials are the copolymers of ethylene and propylene glycols which are commercially available under the trade name of Pluronic. These materials have the following formula:

where a and c represent integers of 2 to 300 and b is an integer of about 10 to 45. The molecular weight may vary considerably but generally is between 1,000 and 30,000, with the percentage of ethylene oxide groups in the total molecule ranging from 10% to 90%.

'The solution-type fluids of this invention can be prepared as highly conceutrated' base solutions for further dilution in normal use. In fact, this is one of the important advantages of the fluids of this invention, i.e., since superior rust-inhibiting properties are shown to exist at extremely low concentrations of inhibitor, very highly concentrated base solutions, relative to the concentrations required for operable metal working fluids, can be easily prepared.

The following example will help to illustrate the basis of this invention.

EXAMPLE I The concentrated base solution-type metal working fluid of this invention was prepared by combining the following materials, with stirring at room temperature:

1 A liquidpolyoxyalkylene glycol made from propylene oxide and alkylene oxide having 40% polyoxyethylene in its molecular structure and having about 4,000 average molecular weight.

The concentrated base solution prepared above was diluted with tap water, as shown in column 2 of the following table. These dilute solutions were then subjected to testing for rust on cast iron. Said rust test consisted of placing one drop of solution of the indicated compositions upon a cast iron plate which had been polished with 120 then 180 grit emery cloth, followed by a washing with precipitation naphtha. Normally, duplicate tests are run. The above plate containing the drop of solution was then placed in a 52% relative humidity atmosphere for 1 8 to 24 hours and then removed for inspection, followed by washing with naphtha. to permit observation of stain under the rust or residue. In this test, solutions with fair to poor inhibiting properties 5 start to rust in 15 to 30 minutes or less.

The table below shows the results obtained with dilute solutions of the cutting fluids of this invention as well as V a comparison of its rust-inhibiting properties with other known inhibitors.

Table I Actual Concentration Tested,

Dilution of Wt. percent in Solution Concentrate, Cast Iron Test Parts Water Rust Test N 07 Per Part Sodium Rating 1 Concentrate 11-64 Sodium Butler Lauroyl Pluronic Nitrite Borax sarcosinate 1 Infinite (tap 4 water alone). 2.. 0 (concentrate 10 4 alone).

0 2 0 2 2 8 0 3 l0. 1. 0 0 81 t 12 13. 0.5 0 14. 0.05 0 l5. 0.02 0-1 16. 0.05 0 l7. 0. 02 l2 l Rust; test rating scale: 0, no rust; l, trace rust; 2, light rust; 3, medium rust; 4, heavy rust.

The following conclusions can be drawn, from the data given in the above table, about the rust-inhibiting properties of the composition of this invention in an aqueous solution with a polyoxyalkylene surface-active agent. This material is typical of a number of surface-active agents that might be used.

1) A surfactant alone has little or no effect on rust inhibition (Tests 1 and 2).

(2) More than 1.0% of unbuifered sodium nitrite, used alone or with a surfactant, is necessary to inhibit rust (Tests 3, 4 and 7).

(3.) Buffered sodium nitrite is good at 1.0% concentration or higher, but poor at 0.25 to 0.50% (Tests 5, 6, 8 and 9).

(4) Sodium lauroyl sarcosinate prevents rust at 1.0%

but is only fair at 0.5% and poor at 0.1% (Tests 10, ll and 12).

(5) Sodium nitrite and sodium lauroyl sarcosinate in ratios of 1.5 :1 and 10:1 combine synergistically to prevent rust at concentrations as low as 0.2% and 0.02% nitrite and sarcosinate, respectively (Tests 13 through 17).

In Tests 14 and 16, no rusting was observed where the ratio of nitrite to sarcosinate was 10:1 and the total concentration was only 0.55% by weight. When 0.55 wt. percent of either of the two components were used alone, they were not as effective in inhibiting rust.

The nitrite-sarcosinate combination oifers the following advantages over the obvious alternative of higher concentrations of buffered nitrite:

(1) Sodium nitrite presents a toxicity problem at higher concentration. Low concentrations of about 1% and less have been used with no harmful results.

(2) Solubility of many surfactants potentially useful in solution metal working fluids is often limited by the presence of other materials in the system, particularly ionic salts such as sodium nitrite. This invention permits "5 low concentrations of nitrite and doesnot require a buffer as is usually necessary when sodium nitrite is used, although a buiier may be used which does not reduce the efiectiveness of the nitrite-sarcosinate combination.

(3) A base solution can be prepared for dilution with very large amounts of water and still maintain excellent rust inhibition, because of the superior rust-inhibiting properties of lower concentrations of inhibitor.

(4) Surfactants with desirable properties but with poor resistance to the oxidation attack of sodium nitrite can now be used because high nitrite concentrations are not necessary to provide good rust inhibition. The oxidation of surfactants by sodium nitrite is a problem which has seriously limited the use of many materials as surfactants.

What is claimed is:

1. An aqueous metal working fluid comprising a major proportion of water, 0.5 to 10.0 wt. percent of sodium nitrite and 0.05 to 1.0 wt. percent of sodium lauroyl sarcosine in ratios of 1:1 to 11:1, respectively.

2. An aqueous metal working fluid comprising a major proportion of water, 0.2 to 10.0 Wt. percent of sodium nitrite and 0.02 to 1.0 wt. percent sodium lauroyl sarcosine in ratios of 1:1 to 11:1 respectively, wherein said metal working fluid also has dissolved therein 0.2 to 20.0 Wt. percent of a surface-active agent selected from the group consisting of nonionic surface-active agents and anionic surface-active agents.

3. A metal working fluid according to claim 2 wherein said sruface-active agent is a polyoxyalkylene glycol having the following formula:

where a and 0 represent integers of 2 to 300, b is an integer of 10 to and the molecular weight of said p0lyoxyalkylene glycol is between 1,000 and 30,000.

4. An aqueous solution-type metal working fluid consisting essentially of about 96.88 to 99.38 wt. percent water, 0.22 to 1.25 wt. percent of a mixture of sodium nitrite and sodium lauroyl sarcosinate in ratios of about 9:1 to 11:1 nitrite to sarcosinate, and 0.4 to 1.87 wt. percent of a liquid polyoxyalkylene glycol which contains about propylene oxide groups and 40% ethylene oxide groups and has an average molecular Weight of about 4000.

References Cited in the file of this patent UNITED STATES PATENTS 2,692,859 Talley et al. Oct. 26, 1954 2,790,779 Spivak et al Apr. 30, 1957 2,825,693 Beaubien et al. Mar. 4, 1958 2,931,700 Oakes Apr. 5, 1960 FOREIGN PATENTS 716,354 Great Britain Oct. 6, 1954 721,526 Great Britain Jan. 5, 1955