METHOD OF APPLYING FRESH PURIFIED LUBRICATION OILS
By S.I. Fishgal
(International Design and Development Corp., Cedar Falls, Iowa, Jan 1977)
Abstract of the Disclosure
A method of applying fresh purified lubrication oils by using the products of their thermal-oxidative ageing (pitch, asphaltene, carbenes, carboids, etc.). The latter can be obtained directly in the oil before its use (for example, simultaneously with impregnating of sintered self-lubricating bearings), the impregnated oil being heated and bubbled through by an oxidizing gas.
Background of the invention
This invention relates to a method of improving the working properties of lubrication oils for their main applications (excluding at high temperatures like those in the combustion chambers of internal-combustion engines).
The antifriction properties, the reliability, and the longevity of lubrication systems depend on the quality of the lubrication oils. That is most research is directed to improving this quality by means of additives and purification. At the same time, antifriction properties, the reliability, and the longevity of work of the oils can be considerably increased by selecting the optimal-quality lubricants to fit the particular conditions of the service of the specific material.
There are no difficulties of choosing lubricants because there is a deep insight into the interaction between the friction surfaces and environment. Requirements to the lubricants depend on the conditions of the service and on the materials of a sliding pair. Yet, not all of this data can be used in the selection of lubricants because most research has been directed to decreasing the varnish formation and carbonization of internal-combustion engine oils in the cylinders. That is why the presence of the products of ageing or the ability of oils to produce them during the friction process are considered as the negative property of the oils. These products are removed from the oils in plants by means of different and sometimes expensive methods of purification.
We disagree that the thesis of the harm of oxidation products for the engine application is transferred to the lubricants for other antifriction units. We disagree with the opinion of most specialists that the better the oil is purified the higher its quality for non-combustion applications, for example, sliding bearings (especially the powder metallic ones).
Another reason to consider that the oxidation products are harmful has been founded on the intensification of friction pairs wear. We disagree with this reason too because the primary products of the oil oxidation cause this intensification, but not the oxidation itself.
Summary of the Invention
For all these reasons, the present invention (which is quite unusual from the point of view of a specialist in the art) uses the neutral products of thermal-oxidative ageing or creates such a regime in the oil that the useful oxidation products are obtained. The latter are those forming the neutral pitchy substances during friction processes and preventing the formation of organic acids intensifying the friction wear under certain conditions. Consequently, there is a possibility of using not only considerably cheaper oils, but decreasing the friction wear and the friction coefficient, increasing the allowable load and the temperature workability of sliding pairs.
Brief Description of the Drawings
FIG. 1 is a graph with the percentage lines showing the decrease of the friction coefficient (line A) and the increase of the temperature workability (line B) for the oil previously oxidized at 2700C and petrolatum in comparison with the fresh purified oil in dependence on the load (P) in a sliding pair;
FIG. 2 is a graph with the percentage line C showing the decrease of wear on the sliding pair with the above lubricants in dependence on the time (t) of running up;
FIG. 3 is a design scheme of a bath for enriching the oil lubricants with the oxidation products;
FIG. 4 is a graph with the percentage line D showing the decrease of wear on the sliding ran-up pair using petrolatum in dependence on the time (t), the load being P = 25 kgf.cm-2;
FIG. 5 is a design scheme of the bath for impregnating self-lubricating sintered bearings and simultaneous oxidation of oil lubricants.
Description of the Embodiment
At stationary conditions, technological processing, or in a thin lubrication oil film, the hydrocarbons of lubrication oil products have a chain of consequential chemical conversions depending on the temperature, the oxygen influence time, and the rate of oxygen diffusion into the oil. This chain can be hydro-peroxides – alcohols – aldehydes – ketones – high molecular acids – low molecular acids – oxyacids – pitches – carbenes – carboids – asphaltenes, etc.
The primary oxidation products are organic peroxides of which further oxidation forms carboxylic acids. Oxygen decomposes them on oxyacids with further conversion into asphaltenes and other products. Depending on the nature of oil products, after the hydro-peroxide formation, another consequence of conversions can take place with the formation of pitches, asphaltenes, carbenes, etc.
The oil lubrication film is also subjected to the different temperatures in the friction zone, to the diffusion of air oxygen and to catalysts (the metallic friction surfaces). Every loading regime with its sliding velocities, temperatures in friction zones, etc., forms one or another oxidation product dependent on the kind of the lubricant. These products can have different oiliness and be useful, neutral, or harmful.
The primary oxidation products (alcohols, aldehydes, ketones) are neutral. Low molecular oxyacids and high molecular acids (also being the primary oxidation products) are corrosive and impart the corrosion-mechanical character of destroying to the mechanism of wearing the friction surfaces. Residual stresses (especially the tensile ones) and plastic deformations intensify this wear because they lighten the migration of corrosive molecules into cracks. Mineral oil without fatty acids decreases fatigue strength by 3-8%, whereas that with the acids – by 20%, vegetable oil – by 16%. Used oil lubricants decrease the fatigue strength less than fresh ones (this is also one of the reasons for adding some used purified oil to fresh oil).
Low molecular and even some high-molecular acids are especially corrosive in the presence of water and act not on the metal, but on its hydrated oxide formed under the influence of water and oxygen of air.
Corrosion process by organic acids is
2Me + O2 + H2O -> 2Me(OH)2;
Me(OH)2 + RCOOH -> (RCOO)2Me + 2H2O;
where Me is metal.
The separation of water and carbonic acid gas from the oil begins at 200oC when diatomic hydro-peroxides decay. The hydro-peroxide formation begins at 100-120oC with 60-80% oxygen consumption. At 170-175oC, 40-70% oxygen is consumed for the formation of water, 3-10% of carbonic-acid gas, 3% – of carbonic oxide and 7-8% – of volatile acids.
In the friction regimes in the presence of water, carbonic oxide and carbonic-acid gas in the lubrication layer, the oily additives of a high molecular fatty acid type convert themselves from being useful to harmful, the load being P >50 kgf.cm-2. One of the causes of the lubricant’s corrosion intensification can be the inorganic acid formation:
H2O + CO2 = H2CO3.
The oxygen polymerization products (pitches, asphaltenes) are not only neutral, but can be useful for many lubricants’ applications, except in high-temperature conditions like those of combustion chambers.
For engine applications, we are not excluding the cases when it is expedient to have two lubrication systems instead of one: one with the expensive purified oil for a cylinder-piston group and another system with cheap, chemically-lower purified oil for bearings and the like.
The neutral pitchy substances are polar as high molecular acids, are better for load carrying and more thermally stable. That is why highly purified oils have lower thermal stability than lower purified oils.
The lubrication ability of mineral oil products shows itself as providing the friction surface by oxygen, forming the adsorbing-on-and-attached-to-friction-surface polar multi-molecular quasi-elastic layers preventing the formation of juvenile surfaces, and lightening the plastic flow of the finest surface friction layers. The products of the oxygen polymerization are like a buffer between rubbing surfaces.
The lubrication ability of oils without additives considerably depends on its oxygen concentration, its active oxygen-containing compounds, and oxygen-entering conditions into a friction zone. Without this, lubricants are ineffective. The intensification of oil oxidative processes increases allowable loads and sliding velocities, and decreases the sticking process.
The most important function of the lubricants is normalizing the process of feeding oxidizers into the friction zone. At light friction regimes, the quantity of oxygen transported by oil is sufficient for bearings to work at the oxidative regime of wear, when an oxidant film on the surface has time to regenerate after its wear. At heavy friction regimes, when the rate of wearing the films leaves behind the velocity of their restoration, it is necessary to lighten oxygen diffusion into the lubricant and to enrich the latter with oxygen-containing products. In thin oil films, the sticking sets in at higher regimes of loading and easily stops because of lightening the oxygen diffusion. The sticking in oil baths is disastrous with a greater wear than that at the conditions of boundary friction. That is why lubrication by oil fog and aerosols, when the smallest particles of lubricants have the possibility to be oxidized by oxygen of air, provides higher allowable loads than the oil bath.
During rubbing, the oxygen polymerization products enrich oil, the friction force and bearing wear decreasing.
The ability of lubrication oil products to be oxidized during the friction process determines the character of the bearing wear. Because of the gradual accumulation of oxidation products, the constant value of the friction coefficient is not established at once, but at the end of some time, which can be decreased by mixing the oil and by rising the temperature and load, the established value of the friction coefficient being less than the initial one. Experiments show that the antifriction properties of working oil are higher than those of fresh oil are and depend on sufficient quantities of the products of oil change during friction.
The oil oxidation products are also useful for abrasive wear. Then separate abrasive grains adsorb the film of the polar molecules on themselves and thus lose their abrasiveness (the property of the oxidation products to be adsorbed by the finest metallic particles has been utilized in our previous application “Method of Improving the Working Properties of Lubrication and Hydraulic Liquids”).
In the presence of surface-active substances in the oil, the attached-to-surface layer is resistant to pressing-out loads, and the attached-to-wall layer has higher viscosity because of intermolecular mutual interaction depending on a dipole moment and polarizing ability. Every molecule of the surface-active substance is neutral in whole. Yet, since the centers of gravity of positive and negative charges are situated on the opposite ends of molecules, the dipole molecules of the surface-active substances can be turned either way with each other by the opposite sign charges, or one after another, or anti-parallel. In order to neutralize the field of force, it is necessary to join several layers of the molecules sited one after another. This explains the multi-molecular properties of the attached-to-wall layers of the surface-active substances.
Since the potential energy of the dipole molecules in the electrical field of other molecules depends on the value of the moment and geometrical dimensions of the molecules, the oxidation products of high-viscous mineral oil lubricants have higher lubrication ability than those of low-viscous oil products with the smaller dimension molecules.
The surface-active substances, when adsorbed on the friction surface, decrease the surface energy of the metal. That is why the plastic deformation is located in the finest layers forms. This decreases friction and surface roughness, and speeds-up running-in processes.
There is a critical temperature (dependent on a compromise between the material and the lubricant) in a friction zone. Above this temperature, boundary lubricants lose their viscosity, tangential shearing ability, and resistance to smashing. That brings the surfaces to the immediate contact.
The temperature workability of lubricants containing 2-4% fatty acids is determined by the fusing temperature of their metallic soaps. In case of boundary friction, the temperature of destroying the lubricant film is the best criterion of oil lubricating capacity because other criterions (resistance to shearing in a lubrication film, the work of destroying the film, wear, etc.) depend on the methods of testing.
The quantity of the oil oxidation products that is desirable to have in oil lubricants depends on the particular conditions in the lubricated details and the installation in general (the area of friction surfaces, loads, temperatures, air supply, oil flow regime, etc.). The lesser quantity is not enough to achieve the desirable effects. The greater quantity can cause the shortage of fresh oil for further oxidation during the service and decrease the term of the latter. As a rough guide, the quantity can be 2-8% in many cases, but the best approach is to get out the rates for similar particular applications.
As it can be seen from the drawings, the late products of oil oxidation decrease friction coefficient and an allowable load (FIG. 1, line A) and wear (FIG. 2, line C) by 10-50%, and increase temperature workability at high loads by 10% (FIG. 1, line B). The decrease of wear for petrolatum is 40% (FIG. 4, line D).
The friction coefficient (FIG. 1, line A) is wavy and changed because of the different temperatures causing certain sequences in the formation of one or another product. At first, this can be hydro-peroxides, alcohols, high molecular acids, increasing the oiliness of the lubricant and decreasing the friction coefficient. As the temperature rises, hydro-peroxides join the oxygen in air and form binary peroxides decomposed on water, carbonic oxide, etc. The latter form not only inorganic corrosive acids, but also favor the development of corrosive properties by fatty acids. At these temperatures, high molecular fatty acids can be also decomposed on oxyacids and the low molecular ones. The formation of all these products increases the friction coefficient after it decreases. However, further growth of the load and temperatures favors the formation of corrosion-neutral product and pitches, and decreases, again, the friction coefficient.
These processes are not the only cause of the wavy improvement of the friction coefficient. They are the part of complicated physical-chemical and mechanical phenomena in a friction zone (plastic deformation, diffusion, structural conversions, etc.).
During the short time (especially at the initial service), fresh non-polar oil cannot form layers that are resistant to smashing at elevated loads. In lubrication with oxidized oil, the late products of oxygen polymerization have higher load-carrying capacity.
At a self-lubricating regime, mineral oil with the products of deep oxidation (of pitchy type) allows a sliding pair to work longer and at higher temperature, than in the case of purified oils. The products of oxidation are more wear-resistant than the non-polar mass of mineral oil. That is why self-lubricating bearings impregnated with the oil previously oxidized at 270oC work 4 times longer.
Enrichment of oil with the oxidation products can be carried out by blowing air through the oil in a bath heated to the temperature sufficient for forming the useful oxidation products (in many cases around 270oC).
An oil bath 1 (FIG. 3) is closed by a cover 2 connected to the inlet branch pipe of a fan 3. The walls and bottom of the bath 1 have electro heater elements 4 and branch pipes 5 through which air is bubbled. Fan 3 sucks oil fumes and air out.
The bubbling duration depends on the fan capacity, the volume of the oil bath, the kind of oil, the desirable consistency, etc. The process of the oil oxidation at high temperatures is exothermal.
The offered method improves the conservation properties of the lubricants too. This is explained by a higher polarity of the oxidation products preventing the conservation layer from slipping off the surface.
Thus, this method improves simultaneously both the antifriction and conservational properties of the lubricants.
A compromise between different oil products creates good antifriction properties in a broad spectrum of loads (e.g. petrolatum gives low values of the friction coefficient to sliding pairs at low loads, the products of oxygen polymerization – at the high loads).
At present, a significant part of sliding bearings is made by powder metallurgy. These bearings are especially effective for the friction units working at a restricted irregular lubrication when a lubrication film forms at the cost of the lubricant located in the pores of the sintered bearings. In these self-lubricating bearings, petrolatum, for example, not only serves 1.5-2 times longer than highly purified oil used now, but it is also cheaper, the effect being especially great at high temperature and loads in the friction zones.
The process of impregnating the sintered self-lubricating bearings with simultaneous oxidizing can be achieved in the bath in Fig. 3 provided with a grid 6 for the bearings 7 (Fig. 5), the duration of the process being around one hour.
Before the impregnation of the first details (when the fresh oil does not contain the useful. oxidation products), the oil is treated as above.
I claim:
1. A method of applying fresh purified lubrication oils for non-combustion applications wherein the neutral products of their thermal-oxidative ageing are used.
2. The method defined in claim 1 wherein said products are obtained directly in the fresh oil previously to its use.
3. The method defined in claim 2 wherein said obtaining is achieved simultaneously with impregnating of sintered self-lubricating bearings.
4. The method defined in claim 3 wherein, the oil is heated to the temperature sufficient to form useful oxidation products.
5. The method defined in claim 4 wherein an oxidizing gas bubbles through the oil.
6. The method defined in claim 5 wherein said oxidizing gas is air.
7. The method defined in claim 1 wherein said products are added into the lubricant.
8. The method defined in claim I wherein said products are the late products of oxygen polymerization.
9. The method defined in claim 8 wherein said products are pitchy substances.
10. The method defined in claim 8 wherein said products are asphaltenes.
11. The method defined in claim 8 wherein said products are esters.
12. The method defined in claim 1 wherein said products are fatty acids.
13. The method defined in claim 8 wherein said products are carbenes.
14. The method defined in claim 8 wherein said products are carboids.
15. The method defined in claim I wherein said products are those of uncompleted purification.
16. The method defined in claim 1 wherein said products are petrolatum.
17. The method defined in claim 7 wherein said product is used purified lubricant.
18. The method defined in claim I wherein said products are used in a compromise between their different types.
19. The method defined in claim 18 wherein said types of the products are petrolatum and the products of oxygen polymerization.
20. The method defined in claim 5 wherein the volatiles of the oil are removed out.
21. The method defined in claim 20 wherein said removing is achieved by vacuuming the oil.
22. The method defined in claim 4 wherein said heating is to 260-280°C.
23. The method defined in claim 1 wherein said products are used for the lubricants of transmissions and related equipment of internal combustion engines whereas convention oil is used for the cylinder-piston and the like parts of the engines.
