NO120202B - - Google Patents

Description

Grease.

This invention relates to a lubricating grease.

According to the invention, a lubricating grease is provided comprising a base lubricating oil which may comprise an organo-substituted silicone liquid, a colloidally dispersed, coated clay for pre-

thickening the base lubricating oil to grease consistency, which clay has acidic surfaces and is capped with an aminoamide formed by reaction between a predominantly saturated CD fatty acid and a polyethylene polyamine; sodium sebacate, and a phenyl-naphthylamine. The lubricating grease is characterized by the fact that the lubricating oil contains at least 30 percent by weight, based on the oil, of a diester of azelaic acid or sebacic acid, or a mixture thereof, and a monoalkyl-substituted primary alcohol.

From Swedish patent no. 183,720, lubricating grease containing lubricating oil and clay is known. The patent's examples concern lubricating greases based on a mineral oil, but it is indicated in general in the description that synthetic lubricants, for example silicone etc., or mixtures thereof can be used. In examples A and B in the patent, the base oil is thus a 100% mineral oil. "Mean Hertz Load" (MHL) is, for example, for grease B 30. If 5% by weight molybdenum disulphide is added to grease B, MHL becomes 48. It is surprising that the lubricating greases according to the invention, even without an extreme pressure additive, have better MHL values than the lubricating greases according to the Swedish patent which contain an extreme pressure additive. As indicated below in Table III,

according to the invention, the lubricating greases K, L and M have an MHL value of 53, 57 and 59 respectively.

As will be noted later in the description, the grease has excellent power bearing and bearing wear characteristics over a wide temperature range without requiring the presence of expensive extreme pressure (EP) additives.

The lubricating base oil can be selected in accordance with the conditions under which the lubricating grease is to be used. Thus, when used under high temperature, most mineral oils will be stable up to temperatures of> >about 150°C (300°F), and synthetic esters can be used at temperatures up to about 180-205°C.

For use at temperatures above approx. 205°C, the lubricating base oil may comprise an organo-silicone liquid or halogen-carbon compounds. Examples of such halogen-carbon compounds are found in U.S. Pat. Patent No. 2,679,479. Halogen-carbon compounds include in particular fluorocarbon oils, preferably those which distil above about 200°C at atmospheric pressure.

If the grease is to be used at very low temperatures, the lubricating base oil must be selected based on its low temperature rheological properties. Most petroleum lubricating base oils are far too viscous to be used at low temperature, and they must be replaced with other materials that have good rheological properties at low temperature, for example synthetic lubricating oils. One can thus choose synthetic lubricating oils to

provide a grease that meets the following requirements:

Apparent viscosity at -54°c and 20 sec

10,000 max.

Apparent viscosity at -54°C and 50 sec-"''

6,000 max.

Torque, low temperature, at start 5,000 gem max.

Torque, low temperature/cycle 500 gem max However, even stricter requirements may be required if the grease is to be used at temperatures as low as -73°C.

One group of preferred synthetic lubricating oils that can be used in the lubricating grease includes organically substituted tilicone fluids (essentially polysiloxane oils) having lubricating oil viscosity. Examples of such fluids are the following unreactive and heat-stable silicone fluids:

Methyl silicone fluids

where n is 0 or an integer Methylphenyl silicone liquids and/or

Methyl phenyl silicone fluids are preferred because of their greater thermal stability. In all the liquids, other organic groups or inorganic atoms can stand in place of some of the methyl groups; for example, some of the methyl groups may be replaced by alkyl groups or hydrogen, or halogen atoms. However, the replacement will depend on the grease's application.

Another preferred group of synthetic lubricating oils comprises pentaerythritol esters of saturated fatty acids. Some typical properties of these esters are:

When the grease is to be used either at extremely low or high temperature conditions, the presence of at least 30% by weight of a diester of azelaic or sebacic acid, or a mixture thereof, with an aliphatic monohydric alcohol together with, for example, one of the two preferred groups of synthetic lubricating base oils greatly improve the performance of the lubricating grease, for example at the extreme temperatures of -75°C or 95°C. In the case of polysiloxane liquids, the lubricating base oil preferably comprises 70-90 weight percent (especially at least 80, for example around 85 weight percent) calculated from the diester oil. If the lubricating base oil contains a pentaerythritol ester of a saturated fatty acid, the lubricating base oil preferably comprises 30 to 50 percent by weight (especially at least 40 percent by weight) calculated from the diester oil.

The clays for the purposes of the invention may have a high ability to exchange base, preferably from about 60 to about 100 milli-equivalents of exchangeable base per 100 grams of clay.

Examples of such clays are montmorillonites, especially sodium, potassium, lithium or other bentonites, such as Wyoming bentonite, magnesium bentonite (hectorite) and saponite. The clay is preferably treated to remove the largest part of the gait that is normally mixed with it. This can be done by dispersing the raw clay in water, and letting it separate into fractions that can be separated from each other either by gravity or by high-speed centrifugation. The clay forms a hydrosol with water, in which there is preferably 1 to 5 percent by weight of clay, which gives a system that is relatively easy-flowing and easy to transport, for example by pumping.

In order to make the surface of the clay acidic, the clay is preferably treated in the hydrosol form just mentioned. The treatment should be carried out with a mineral acid (preferably a phosphoric acid, for example phosphoric acid) in an amount at least equal to the base yield capacity of the clay. When phosphoric acid is used, this acid will generally be used in an amount of from about 4 to about 12 percent by weight calculated from the clay. The clay is covered in stages with 45 to 70 weight percent aminoamide calculated on the weight of dry clay.

The aminoamide is preferably added to the acidified clay hydrosol under such conditions that the aminoamide is liquid.

The aminoamide is a viscous liquid when freshly made, but changes on standing to a soft granular paste that is easy to handle. The aminoamide can be prepared by heating the fatty acid with a polyethylene polyamine at a temperature of 200° to 225°C for 1 to 4 hours. The fatty acid is suitably in the form of C8-18 fatty acids of which at least 80% by weight are saturated fatty acids,

and preferably has an iodine number below 50. Coconut oil fatty acids are preferred. Polyethylene polyamine can be about 40% amidated. For example, the amino amide can be formed with 35 to 45% of the active nitrogen material. The polyethylene polyamine is conveniently the residual product from the production of ethylenediamine. Such residual product usually consists of a mixture of ethylene amines that boil above triethylenetetramine's boiling point (for example tetraethylenepentamine) diluted with a smaller amount of diethylenetriamine so that it has a suitably low viscosity for appropriate treatment. This polyamine mixture may also contain very small amounts (eg 5% or less) of ethylenediamine. Some properties of such a polyamine mixture are:

The mixture of polyamines may consist of 20 to 80 (preferably less than 50)% diethylenetriamine, the remainder being polyethylene polyamines having an average molecular weight of 2 20 to 450.

The lubricating grease according to the invention preferably contains 0.75 - 1.25 weight percent antrium sebasate, and preferably 0.75 - 1.25 weight percent phenylnaphthylamine (especially B-phenylnaphthylamine), both percentages calculated from the weight of lubricating grease. The spreading fat can also contain antioxidants other than phenylnaphthylamine, for example phenothiazine or diphenylamine.

The invention will now be illustrated by the following examples.

Example 1.

The procedure used for each individual grease was as follows. A 2% aqueous suspension of Hectorite clay freed from gaiter was heated to 70°C. Diluted phosphoric acid, aminoamide water repellent (coating) and the base oil were added to the hot suspension. After complete mixing of these components, "lumps" or "beads" were formed at the same time as a water phase separated. The clumps were separated from the separated water and heated to 130°C, then a water solution of either sodium nitrite or sodium sebasate was slowly added. After holding the mixture at 130°C for about 15 minutes, the water content was reduced somewhat by evaporation. Phenylnaphthylamine was added to the hot mixture. The mixture was then cooled and ground to produce the final grease.

The greases E, F and G were produced according to the procedure described in the previous section, and tested in accordance with Military Specification MIL-G-7118 A "Grease; Aircraft and Actuator Screw, for Low and High Temperatures".

The composition of the lubricating greases can be found in table i.

The test results of these greases are in Table II compared to different specifications "MIL-C-7118A test".

The previous results clearly show that the lubricating greases

E, F, G have excellent performance characteristics throughout, and, in particular, excellent high and low temperature properties. It is also clear that the greases E and F can be used over the entire range from -75 to + 180°C under difficult bearing lubrication conditions. This has never before been achieved.

Example 2

The following greases were subjected to the "Mean Hertz Load" test (according to the following list) to compare the load bearing capacity of the soap base greases (with and without EP additives) and greases according to the invention without the use of any EP additives: <

Grease H: A lithium-soap-thickened grease containing di-2-ethylhexyl sebasate as a base oil with no EP additive. Grease I: Likewise, a lithium-soap-thickened grease identical in composition to grease H, except that (1) it contained 0.22 weight percent metal deactivation additive instead of 0.02 weight percent, and (2) it contained 5 weight percent of a chlorosulfur EP -addition (chloronaphthaxanthates).

Grease J; Identical in composition to EP soap base grease I, except that the lubricating base oil was changed to be the same as grease E (Table III).

Grease K; Identical in composition and manufacturing method to the lubricating greases E and L, but containing the same base oil (di-2-ethylhexyl sebasate) as the lubricating greases H and I, instead of the mixture of di-2-ethylhexyl azelate and pentaerythritol ester.

Lubricating grease L: Identical in composition and manufacturing method with lubricating grease E (table III).

Grease M: Identical in composition and manufacturing method to grease F (table III).

"Mean Hertz Load test" refers to method 6503, Federal Test Method Standard No. 791a. In this test, which is a modification of the "Shell Four-Ball EP test", one runs a series of 20 ten-second tests with increasingly higher loads until a jamming of the four balls takes place. The average diameter after wear is determined for each of the 20 mentioned samples. A correction factor is applied for each load to take into account the static subsidence caused by the deformation of the balls due to the load at the start of the test. It

corrected load is determined by the following formula:

The sum of the 20 corrected loads is divided by 20 to get the "Mean Hertz Load". The lowest load at which a marked increase in wear takes place is called the "first grip point" and it indicates the load at which shearing first occurs. It is of great importance because it indicates the load at which the grease no longer provides complete lubrication.

The results of the Mean Hertz Load tests can be found in the table

III.

In addition to the Mean HertzLoad tests, the greases H, I, L and M were also subjected to the "Screw-Jack Actuator Test (CRC designation L-44) which provides a measure of particularly high load capacity. The purpose of this test is to study the ability of to withstand the load of variously composed greases and additives for particularly high pressures in a screw transmission at -34 to +200°C. The device consists of a top screw working in a bronze nut to which suitable weights are attached. It is equipped with an oven for working at high temperatures. For low temperatures, the set-up is placed in a cooled box. Normal operating load is 500 kg. During the test, the load is increased and decreased after a given cycle and the required torque is measured below. The results of this test can be found in table IV.

500 kg load, 55 to 60°C. Two minute cycle.

The overall excellent ability to withstand load in a grease according to the invention is evident when comparing the greases K, L and M according to the invention with the soap-based greases H, I and J. Comparison of the greases L and M with the pig K shows the advantage of to use the preferred lubricating base oil composition according to the invention.

It is clear that lubricating greases in accordance with the invention (for example the lubricating greases K, L and M) are extremely superior to the soap-based lubricating greases even if the soap-based lubricating greases contain significant amounts of effective EP additives.

Thus, the lubricating greases according to the invention are unique in two ways: (1) They show (without the use of EP additives) a better ability to withstand stress than corresponding soap-based lubricating greases and even

than many clay-thickened greases that contain special EP-

additives; and

(2) in the Mean Hertz Load test, the first grip point is broadly the same as the fixed cut-off point, compared to the large distance between these values for the soap base greases.

These two advantages are quite important in that the loss of

metal prior to bearing failure is reduced to a minimum, thereby ensuring highly satisfactory work at the bearing for a maximum period of time, without a long period of time during which the bearing works

is more or less plain.

Claims (9)

1. Lubricating grease comprising a base lubricating oil which may comprise an organo-substituted silicone liquid, a colloidally dispersed, be- added clay for thickening the base lubricating oil to grease consistency, which clay has acidic surfaces and is covered with a aminoamide formed by reaction between an essentially saturated CQb—zO fatty acid and a polyethylene polyamine; sodium sebacate, and a phenyl-naphthylamine, characterized in that the lubricating oil contains contains at least 30 percent by weight, based on the oil, of a diester of azelaic acid or sebacic acid, or a mixture thereof, and a monoalkyl-substituted primary alcohol. 2. Lubricating grease as stated in claim 1, characterized in that the base lubricating oil contains 70 to 90 percent by weight, based on the oil, of the diester. 3. Lubricating grease as stated in claim 2, characterized in that it is in the base lubricating oil at least 80 percent by weight, based on the oil, of the diester. 4. Lubricating grease as stated in claim 1, characterized in that the base lubricating oil comprises a pentaerythritol ester of a saturated fatty acid. 5. Lubricating grease as stated in claim 4, characterized in that the base lubricating oil contains 30 to 50 percent by weight, based on the oil, of the diester. 6. Lubricating grease as stated in claim 5, characterized in that the base lubricating oil contains at least 40 percent by weight, based on the oil, of the diester. 7. Lubricating grease as specified in one of claims 1 to 6, characterized in that the diester in the base lubricating oil is derived from a monoalkyl-substituted, primary alcohol with 5 to 8 carbon atoms. 8. Lubricating grease as stated in claim 7, characterized in that the diester in the base lubricating oil is derived from a mono-C₁-C₂ alkyl-substituted butanol. 9. Lubricating grease as specified in claim 8, characterized in that the diester in the base lubricating oil is derived from 2-ethylhexanol.