US2737495A - Grinding oil containing pyrophosphatidic acid and sulfur - Google Patents

Description

GRINDING 01L CQNTAINING PYROPHOS- PHATEDIC ACID AND SULFUR Harold. W. Johnston, Cleveland Heights, Ohio, assignor to The Standard Gil Company, Cleveland, Ohio, a corporation of (thin 4 Claims. (Cl. 252-461 This invention relates to grinding oils of a superiornature, more particularly to improved grindingoil compositions which greatly increase the life of abrasive wheels and reduce temper color formation and to a method of grinding with such oils.

Grinding oils are used when grinding metal with-an abrasive grinding wheel and are to be distinguished from cutting oils. Some oils which are good for cutting purposes are not good for grinding and vice-versa. A cutting oil is generally used in cutting steel or othermetalwith a cutting tool such as in a lathe whereas a grinding oil is used in grinding steel or other metal with an abrasive wheel or with a loose abrasive. The' grinda'bility of steel is extremely sensitive to the type of grinding oil used particularly under severe conditions of operation;

in plant practice where articles are being manufactured by a process involving a grinding step, the grindingoil.

used is often a very important part of the economics of the operation. A primary consideration in most grinding operations is wheel wear because excessive wear. results in changes of dimension of the article outside the specification limits. Wheel wear is customarily measured in terms of wheel life, i. e., the number of parts which may be ground before it becomes necessary to replace or redress the grinding wheel. Any grinding oil. which will increase wheel life is an important asset to mostgrinding operations because it will lower the number of wheels required and consequently lower the processing cost.

It has been discovered that the rate ofwheel wear is greatly dependent on the nature of the lubricant employed and it has been found that wheel life may be considerably prolonged by the use of the grinding oils of this invention.

The principal object of this invention is the provision of grinding oil compositions containing certain prescribed additives by the use of which a great increase in wheel life and a reduction in temper color formation areobtained. A second object is the provision of a method. of using the new compositions. Other objects willbecome apparent as the invention is described hereinafter.v

in the past, it has been proposed to add pyrophosphatidic acid to grinding oils for the purpose of reducing temper color formation. It has also been proposed to add sulfur to grinding oils. However, as far as is known, thereis no suggestion in the prior art that the two additives may be combined in a grinding oil formulationp According to this invention it has been found that a combination of the two additives in a grinding oil base results in unforeseen advantages.

The grinding oil compositions of this invention comprise a major proportion of a grinding oil base and, as additives thereto, minor proportions of pyrophosphatidic acid and sulfur. A preferred grinding oil compositionis that comprising at least 88 weight per centof av base oil which is composed of at least 90 weight per cent of a mixture of an amount of a mineral oil of viscosity not over 100 SUS (Saybolt Universal seconds) at 100 F. within the range of 53 to 95 weight per cent and an nited States Patent amount of a mineral oil of 2000 to 6000 SUS at 100 F. within the-range -of47 to 5 weight per cent to provide a viscosityin the range of 150 to 300 SUS at 100 F., from about 0.5 to about 10 per cent by weight of pyrophosphatidic acid and from about 0.25 to about 3.0 per cent lily-weight of sulfur.

The method of this invention comprises grinding metal with an abrasive in the presence of a grinding oil of the composition described above;

Pyrophosphatidic acid is essentially the fatty ester of pyrophosphoric acid and it has the formula:

Into a suitable vessel are placed 70 parts of a conventionally refined petroleum oil having a viscosity of SUS 'at F. Into the conventionally refined oil there is dissolved 0.56 parts (0.8% of the conventionally refined oil) of sulfur. There is then blended in 28 parts of a so-called bright stock oil having a viscosity of SUS at 210 F. and 2 parts of pyrophosphatidic acid. The order of addition is not critical. The two oils from the base and the sulfur and pyrophosphatidic acid comprise the additives.

EXAMPLE 1A The grinding oil composition of Example 1 is used in an operation of grinding aircraft engine valves composed of Inconel X within the following tolerances:

Valve head radius, +0.00l" to 0.00l

Inconel X is an alloy of the following composition:

Weight 1 Element (percent) Ni 70.0 max. Cr 14.0!10 l .0. Ti. 2.25 to 2.75. 0b-- 0.70 to 1.20. A1- 0.40 to 1.00. Te 9.00 max. Mn. 1.00.

The grinding operation is continued until the tolerances are exceeded because of excessive Wheel wear. It is thereby determined that the wheel life in this particular operation is approximately 50 work pieces on the rough cut and 70 pieces. on the finishing cut. The terms rough out and.finishing cut refer to the depth of cut or rate of metal removal. Thus on the rough cut all but about the last 0.005" of metal are removed quickly and in the finishing cut the last 0.005" of metal are removed slowly, the R. P. M. of the grinding wheel remaining unchanged.

The following examples are given to demonstrate the eflect of omitting either the sulfur or the pyrophosphatidic acid from the formulation of Example 1.

EXAMPLE 2 A composition is prepared according to Example 1 except that the sulfur is omitted from the formulation. The resultant composition is used as a grinding oil in the procedure of Examples 1A. The wheel life thereby obtained is only 8 to 12 pieces as compared with the 50 to 70 pieces obtained by the use of the grinding oil of this invention.

EXAMPLE 3 A composition is prepared in accordance with the procedure of Example 1 except that the pyrophosphatidic acid is omitted from the formulation. The composition is subjected to a grinding test in accordance with the procedure of Example 1A. The wheel life obtained is 26 pieces on a rough grain cut and 30 pieces on a H finished grain cut.

The following table is a compilation of Examples 1 through 3 and is presented for ease of comparison.

The type of oil base described in the examples is preferably comprised of two mineral oils of widely divergent viscosities. One of the oils should have a relatively low viscosity of not over 100 SUS at 100 F. and may be, for example, a shale oil or conventionally refined neutral oil. The one restriction is that it should not be so light as to flash under grinding conditions. The other oil should have a relatively high viscosity in the range of 2000 to 6000 SUS at 100 F. (Generally the viscosity is measured at 210 F. and that at 100 F. calculated in a manner well-known in the art.) This heavier oil may be, for example, a so-called bright stock and the following are given as examples with the viscosities at 100 F. and 210 F.:

SUS at 210 F... SUS at 100 F."

These heavy viscosity oils are also characterized by their high boiling point.

This oil base should preferably comprise from about 53 to 95 weight per cent of the low viscosity oil and from about 47 to weight per cent of the high viscosity oil. These proportions are subject to the further qualification that they be selected within the above ranges so that the mixture of oil should have a viscosity in the range of 150 to 300 SUS at 100 F., in order that the oil may flow properly as it is fed to the wheel during grinding. The above oil mixture should comprise at least 90% of the base oil, since the presence of about of other oils or oil-like components does not interfere with the beneficial results from a composition, the major portion of which is made in accordance with this invention. A very similar type of oil base is further described in U. S. Patents Nos. 2,453,708 and 2,453,709.

Although the oil base described above, when used as an ingredient of the compositions of this invention, is productive of especially good results, it is also possible to employ other grinding oil bases. Such bases in general are hydrocarbon oils of lubricating viscosity and produced by any of the known methods of refining. Thus there may be employed either singly or in admixture, solvent-extracted oils, conventionally refined oils or any other oil that has been found useful for grinding operations. The addition of both pyrophosphatidic acid and sulfur to any of such oils results in the improvement of the properties of the oil when used in grinding operations.

Several of the grinding oils of this invention were tested in practical grinding tests by industrial companies using commercial grinding oils and it was found that those of this invention showed marked superiority in practical grinding operations.

The superiority of the grinding oil compositions of this invention is obscure in theory. It is explainable in the light of present knowledge only by the premise that there occurs a synergistic effect between the combined activities of the two additives, sulfur and pyrophosphatidic acid. As far as is known, there occurs no chemical reaction between the two additives or between the additives and the oil. It is believed that the improved results obtained herein may be attributed to a physical phenomenon traceable to the combination of additives.

It is intended to cover all changes and modifications in the examples of this invention, herein chosen for purposes of illustration, which do not constitute departure from the spirit and scope of the appended claims.

I claim:

l. A composition comprising at least 88% by weight of a mineral oil base having a viscosity in the range of 150 to 300 SUS at 100 F., from about 0.5 to about 10% by weight of pyrophosphatidic acid and from about 0.25 to about 3.0% by weight of dissolved sulfur.

2. A mineral grinding oil composition comprising at least 88 weight per cent of a base oil which is composed of at least 90 weight per cent of a mixture of an amount of a mineral oil of not over 100 SUS at 100 F. within the range of 53 to weight per cent and an amount of a mineral oil of 2000 to 6000 SUS at F. within the range of 47 to 5 weight per cent to provide a viscosity in the range of to 300 SUS at 100 F. and from about 0.5 to about 10% by weight of pyrophosphatidic acid and from about 0.25 to about 3.0% by weight of dissolved sulfur.

3. A method of grinding which comprises grinding metal with an abrasive in the presence of a grinding oil comprising at least 88% by weight of a mineral oil base having a viscosity in the range of 150 to 300 SUS at 100 F., from about 0.5 to about 10% by weight of pyrophosphatidic acid, and from about 0.25 to about 3.0% by weight of dissolved sulfur.

4. A method of grinding which comprises grinding metal with an abrasive in the presence of a grinding oil comprising at least 88 weight per cent of a base oil which is composed of at least 90 weight per cent of a mixture of'an amount of a mineral oil of not over 1.00 SUS at 100 F. within the range of 53 to 95 weight per cent and an amount of a mineral oil of 2000 to 6000 SUS at 100 F. within the range of 47 to 5 weight per cent to provide a viscosity in the range of 150 to 300 SUS at 100 F. and from about 0.5 to about 10% by weight of pyrophosphatidic acid and from about 0.25 to about 3.0% by weight of dissolved sulfur.

References Cited in the file of this patent UNITED STATES PATENTS 2,138,546 High Nov. 29, 1938 2,339,371 Becker Jan. 18, 1944 2,396,345 Rogers Mar. 12, 1946 2,431,652 Trueger Nov. 25, 1947 2.670.330 Clark Feb. 23, 1954

Claims (1)

1. A COMPOSITION COMPRISING AT LEAST 88% BY WEIGHT OF A MINERAL OIL BASE HAVING A VISCOSITY IN THE RANGE OF 150 TO 300 SUS AT 100*F., FROM ABOUT 0.5 TO ABOUT 10% BY WEIGHT OF PYROPHOSPHATIDIC ACID AND FROM ABOUT 0.25 TO ABOUT 3.0% BY WEIGHT OF DISSOLVED SULFUR.