SI21813A - Assembly of interacting machinery parts lubricated with biologically degradable lubricant - Google Patents

Abstract

The intention of the invention is to modify interacting machinery parts, especially surfaces of these interacting parts, exposed to friction and wear, in order to enable - under loading and other conditions as well, where application of lubricants, either of mineral or synthetic origin, has been required indispensably to assure proper lubrication because of decrease of the coefficient of friction and prevention of wear of machinery parts - the use of biologically degradable lubricants for lubrication, especially oils of plant origin and/or saturated esters and/or unsaturated esters, without threatening in this manner the efficiency and reliability of lubrication. According to the invention, at least one of the mentioned machinery parts is fitted with the so-called DLC (diamond-like carbon) coating which contributes to an essential decrease of friction, at least under the limit lubrication regime, and thus also decrease of temperature which negatively affects the stability of lubricants, so that a biologically degradable lubricant can be used either with admixed additives made of biologically acceptable materials or even without any additives.

Description

In the field of mechanical engineering, the invention belongs to the field of machine elements, and in particular to solutions that are engaged in the implementation of machines and devices with respect to lubrication. For the purposes of this application, the term assembly of cooperating machine parts means any assembly of at least two cooperating parts, at least one of which is at least occasionally either sliding or rolling or otherwise, under a certain load, movable over at least one sliding surface of the rest or others with it of the participating parts. The term biodegradable lubricant for the purposes of this application means either a liquid or at least substantially solid, gel-like vegetable or animal lubricant, i.e. natural or. biological origin, which is also biodegradable in the context of natural processes; at the same time, the term includes biodegradable saturated or unsaturated natural or synthetic esters, but excludes all lubricants of mineral origin as well as all those synthetically obtained non-biodegradable lubricants, i.e. with the help of microorganisms that can be found in the natural environment. Preferred biodegradable oils are vegetable oils, e.g. rapeseed oil, sunflower oil and other similar oils, including waste oils of vegetable origin that have already been used e.g. when preparing food.

The invention is based on the problem of how to modify cooperating machine parts, in particular at least the friction and wear of exposed surfaces of these cooperating components, so that even under load conditions and other conditions which have hitherto been due to the reduction of the coefficient of friction and prevention wear and tear on machine parts to ensure proper lubrication necessitates the use of lubricants of either mineral or synthetic origin, biodegradable lubricants, in particular vegetable oils and / or saturated esters and / or unsaturated esters, can be used for lubrication without compromising efficiency and reliability of lubrication.

Biodegradable lubricants that could be used in mechanical engineering are natural oils of vegetable origin, e.g. rapeseed or sunflower oil, or synthetic lubricants such as saturated and unsaturated esters. Natural lubricants that are inexpensive would be most suitable to use, they can be obtained from renewable sources, and they also have very good lubricating properties, which can be even better than those of synthetic or mineral oils. The only major problem with these lubricants, which has remained unsolvable at least so far, is their poor oxidation stability. At elevated temperatures (typically above 75 ° C; typically at 90 ° C, they are already very difficult to operate for a long time) they start to age rapidly and lose their good properties and become unsuitable for machine use. In order to achieve sufficient productivity, machines and appliances have to be operated under demanding conditions, even at higher temperatures, which makes them unsuitable for such lubricants. On the other hand, environmental awareness is increasing, and the use of biodegradable lubricants is, at least in some countries, already dictated by the law, so that the use of biodegradable lubricants is at least in some proportion, if not mandatory but at least advisable. In these cases, users, if they want / need to use natural biodegradable lubricants, are faced with a very short interval of operation since, due to aging of the oil, e.g. after 1000-2000 hours, the oil must be replaced. The main problem, on the one hand, stems from the temperature above which natural biodegradable lubricants cannot even work, namely above 90 ° C, and on the other hand, the problem is a considerably short operating interval or. oil change, which is related to the cost of the lubricant itself and its replacement and the loss of capacity at the time of change.

One solution that can extend to some extent the change interval under normal operating conditions, e.g. up to about 3000 hours is the use of synthetic biodegradable esters that have better oxidation stability. However, such lubricants are much more expensive (up to 10 times or more) and at the same time their lubricating properties are worse. In general, when the oxidation stability of the oil is higher, the latter may operate at a higher temperature, but is more expensive and has less lubricating properties. These are mainly saturated esters (up to 110 ° C), and unsaturated esters are inherently (up to 90 ° C) between natural oils and synthetic esters. Notwithstanding the many disadvantages, they can at least satisfy the legislation, customers and technical requirements of the system in the case of operation at higher temperatures. Of course, it is necessary to lease the poorer tribological properties of the system, namely greater wear and friction, and thus, by the way, an even higher operating temperature, and at the same time a high price.

It is obvious, therefore, that a solution that would allow the operation of naturally biodegradable lubricants at higher temperatures, e.g. at 80 - 90 ° C, which is already the appropriate temperature for most gear units and related structural elements and systems, e.g. bearings, guides, as well as hydraulic components, significantly helped to reduce the cost of lubricants and their replacement (maintenance), even by 5 times to 10 times. In addition, in this way we would contribute to accelerating the use of renewable and environmentally friendly resources, while also improving the technical, i.e. tribological properties of the system.

The use of biodegradable lubricants is one measure to prevent excessive pollution of the environment. CA 2223326 also proposes the use of fatty acid-based vegetable oil as a lubricant, and hydroxy fatty acids and, in addition, liquid vegetable waxes as additives. This kind of oil is easily degradable by microbes after use in nature, but its use in conventional machine parts is very limited because the durability of the lubricant is relatively short or low. significantly too short for machines and appliances to function normally. In practice, when the machine parts are engaged in the mixed friction regime, at least occasionally there is a direct contact with each other and high pressures between the respective sliding surfaces, which also releases a relatively high amount of heat, which leads to heating and oxidation of the lubricant and ultimately to a significant deterioration lubricating properties of the lubricant.

Furthermore, it is also known from the patent literature that friction between sliding surfaces can be substantially reduced by coating carbon-coated, diamond-like-carbon (DLC) diamond-like coatings with mutually interacting metal surfaces. ). Such coatings have been particularly commonly used in dry friction conditions, e.g. when mounting computer memory units. These DLC coatings (eg KR 2001110609 A) have also been used in the case of highly loaded mechanical and hydraulic devices in which such a measure can either increase the capacity of the devices or, thanks to the reduction of certain parts, minimize the dimensions of the entire device. In this case, it is a tribological situation in which, without imposing the aforementioned measure, even the best mineral-based lubricants are not sufficient to provide sufficiently effective lubrication of certain parts that would allow the device to operate for a specified period of time without frequent lubricant change. Each lubricant change results in a certain amount of waste that is one way or the other burdening the environment, ideally either at higher or lower cost to be recovered in the environment at least essentially a non-hazardous substance. In addition, in certain cases (US 5,947,710), said DLC coatings have also been used in installations, such as in compressors of refrigeration systems where, due to the presence of other substances, it is simply not possible to effectively lubricate the sliding surfaces with conventional mineral-based lubricants.

The purpose of the present invention is to basically develop an improved tribological system for use in various mechanical assemblies of machines and devices, in particular for lubrication of gears, bearings, guides, shafts as well as hydraulic components, based on a suitable combination of suitable contact materials and biodegradable lubricants and additives , especially lubricants based on vegetable oils or biodegradable saturated or unsaturated esters. Such a tribological system should have at least a significantly less harmful, if not completely harmless, effect on the environment, taking into account the comparison with existing tribological systems.

For this purpose, the invention provides for the use of suitably adapted carbon-based diamond-like (DLC) hard coatings and an appropriate biodegradable lubricant, which may be either vegetable oil or a synthetic ester, which may be saturated and unsaturated, or a combination of these substances. optionally using appropriate anti-wear and high pressure additives, which are biologically acceptable, which means that they are non-toxic and have no adverse effect on the biodegradability of the lubricating oil in the final formulation. Such tribological system is applicable in many cases in all industries, from machine elements such as gears, bearings and shafts, to other machine parts such as guides, mountings, to working and forming tools, and to all types of hydraulic components such as pumps, valves, pistons, except in the food and medicine industries, construction, forestry, mining, agriculture and elsewhere, where by deliberate or unintentional action, e.g. accident, maintenance, replacement, use of conventional mineral or non-degradable synthetic lubricants causes damage in the natural environment.

The present invention generally relates to an assembly of cooperating machine parts, generally consisting of at least two parts, at least one of which is translationally and / or rotationally movable relative to the rest, and which are arranged at least intermittently against each other. interlocking, wherein a lubricant layer is provided between said sliding surfaces of said cooperating machine parts.

According to the invention, the problem described above is solved in that at least one of said machine parts is provided with a DLC coating and a biodegradable lubricant is used as a lubricant, either with the addition of biologically acceptable substances or without any additives. In particular, it is advantageous if the DLC overcurrent is provided with each of the adjacent surfaces of the interacting parts, using as a biodegradable lubricant a vegetable lubricant or a biodegradable saturated ester or a mixture of biodegradable saturated esters or a biodegradable unsaturated ester, or a mixture of biodegradable unsaturated esters or one of the possible combinations of these biodegradable substances, taking into account the possibility of using other non-toxic or non-toxic substances. biologically acceptable additives.

It is a further object of the invention to use a biodegradable lubricant of plant origin or biodegradable saturated ester or a mixture of biodegradable saturated esters or a biodegradable unsaturated ester or a mixture of biodegradable unsaturated esters or one of the possible combinations of these biodegradable substances as lubricants for lubricating machine parts the contact surface of at least one of these parts is provided with a DLC coating, and it is particularly preferred if the DLC coating is provided with all cooperating surfaces of said machine parts.

The invention is based on the premise that such a modified tribological system can achieve a significant reduction in system temperature under the same nominal operating conditions, which is essentially the equivalent of finding options to operate at an increased system operating temperature, which is usually sought by others. The lower oxidation and thus the longer life of the biodegradable lubricants is obtained thanks to the lower temperature, which is due to the lower friction in the contacts between the DLC coatings and the oil under the boundary lubrication conditions.

In practice, heat generation is shown to be critical especially under boundary lubrication conditions, when there is a considerable amount of direct contact between surfaces in direct contact at least in the most exposed surface areas or even in large areas of the surface, when the lubricant or due to the insufficient relative speed of these surfaces or excessive forces or too high a temperature of the lubricant, thus lowering the viscosity no longer guarantees the effective separation of surfaces or surfaces. keeping them at a suitable distance from each other. In this case, conditions that are virtually identical to those of frictionless lubrication occur, since complete lubrication of the lubricating film occurs and therefore the direct contact of two surfaces. Such instances occur mainly when starting, stopping, or also when instantaneous shocks and vibrations occur. For machines and devices with reciprocal / oscillating motion, this occurs at the end of each half cycle. In all of these locations, direct contact of surfaces or surfaces. thus, the breakthroughs of the lubricant film at the exposed locations, especially at the peaks of the irregularities on each real surface, give rise to a certain tangential force that resists movement and represents a fraction of the total friction. It follows that a significant reduction in the friction due to the contact between the surfaces of the interacting parts in the area of said contact peaks, as in the case of non-lubricant contact, could significantly contribute to the goal.

Until now, so-called anti-wear additives have been used to prevent such phenomena, which in the case of such contacts form a layer or layer formed on the basis of a chemical reaction. the film, which immediately declines thereafter, but in this way prevents the direct contact of the two metals. Such additives are already used in existing lubrication systems, and consequently, all the facts and temperatures mentioned above already include the effect of the additives. It is approximately the same for all types of oils, which means that, despite the use of lubricants that include such additives, excessive amounts of heat are generated in practice, resulting in overheating to a temperature that prevents the desired biodegradable lubricants from being used more permanently. . It is therefore clear from all of the above that, even with additives known so far, it is not possible to sufficiently contribute to the solution of the aforementioned problem.

DLC coatings are known to provide substantially lower friction than the j / ec / steel contacts in dry conditions, in DLC / DLC or DLC / steel contacts. Differences in the coefficient of friction can range from 10% to several size classes, depending on the working conditions and the surrounding medium. So, if similar lubrication conditions are achieved between DLC coatings and oils and additives as in conventional currently used systems, and in the case of breakage of the lubricating film, friction coefficients are obtained which are significantly lower than in conventional conventional systems, then heat generation will be significantly lower, since the greatest amount of friction occurs precisely in these contacts / breakouts, ie in the conditions of boundary lubrication rather than liquid (hydrodynamic) when the surface is separated by a thin layer of lubricant.

The research, which was first performed on model tests with numerous DLC coatings, various oils and various additives, found that the goal set was feasible and, in fact, achievable. The final verification test was performed on a gear test within the standardized FZG test site. Different possible combinations of gears and pinions were used in the test, namely, steel / steel, DLC / steel, steel / DLC, and DLC / DLC.

The results obtained are shown in the diagram in FIG. 1. The results of measurements of oil in an oil bath apply to all four of the above-mentioned combinations of materials of cooperating gears and stepchildren. The temperature measurements were carried out in an oil bath (reservoir), which is relatively far away from the place of heat generation on the sliding surfaces itself, which means that the quantities of heat generated and the differences between the individual materials in the contacts are significantly larger. Very extensive oil degradation is also carried out at the points where the film breaks, where temperatures rise the most. The difference between DLC / DLC and steel / steel combinations in the reservoir is approximately 10 ° C, which is a realistic basis for a significant reduction in oxidation and a corresponding extension of oil life, as is also known in the literature.

A further experiment was carried out in a suitable test site on two axial piston pump systems, which means the application of the solution according to the invention to a hydraulic system. The test was run in parallel on a conventional system (steel) and on a system with DLC coatings on piston surfaces sliding on a thrust plate. Biodegradable oil was prepared using its own recipe. The test lasted 2000 hours, equivalent to a 12-month operation of 8 hours a day. Based on the measurements of the total acid number (the so-called TAN number; Fig. 2), which represents a direct measurement of the oxidation of the oil, it appeared that the oxidation of the oil in the system using the DLC coatings was due to lower temperatures, which were also indirectly measured, about 50% slower than in the conventional system, which again and directly proves the aforementioned assumption and the applicability and effectiveness of the solution according to the invention.

That said, the findings were verified on two rather different systems, namely, an axial piston pump representing a hydraulic tribological system and a gearbox representing a mechanical tribological system. The hydraulic system has relatively low contact pressures, while mechanical hydraulic systems generally have higher contact pressures.

Claims (32)

PATENT APPLICATIONS 1. An assembly of interacting machine parts, consisting of at least two parts, at least one of which is translationally and / or rotationally movable relative to the rest, and whose laterally facing surfaces are adapted for at least occasional interposition with said sliding surfaces of said cooperating machine parts provided with a lubricant layer, characterized in that at least one of said machine parts is provided with a DLC coating and that biodegradable lubricant is used as the lubricant, either with the addition of biologically acceptable additives or without any additives. . Assembly according to claim 1, characterized in that each of the contact surfaces of the two cooperating machine parts are each provided with their own DLC coating, and that a layer of biodegradable lubricant is provided between said contact surfaces, either with the addition of biologically acceptable additives, or without any additives. Assembly according to claim 1 or 2, characterized in that the biodegradable lubricant is a plant-derived lubricant. Assembly according to claim 3, characterized in that vegetable oil is used as a biodegradable lubricant. Assembly according to claim 4, characterized in that the vegetable oil used is oil from the group consisting of rapeseed and / or sunflower and / or pumpkin and / or olive and / or peanut and / or almond oil. Assembly according to claim 1 or 2, characterized in that a saturated ester or a mixture of saturated esters is used as the biodegradable lubricant. Assembly according to claim 1 or 2, characterized in that a biodegradable lubricant is used an unsaturated ester or a mixture of unsaturated esters. Assembly according to claim 1 or 2, characterized in that a saturated ester or a mixture of saturated esters in combination with an unsaturated ester or a mixture of unsaturated esters is used as a biodegradable lubricant. Assembly according to claim 1 or 2, characterized in that a biodegradable lubricant is a saturated ester or a mixture of saturated esters in combination with a plant-based lubricant according to one of claims 3 to 5. Assembly according to claim 1 or 2, characterized in that a biodegradable lubricant is used an unsaturated ester or a mixture of unsaturated esters in combination with a plant-based lubricant according to one of claims 3 to 5. Assembly according to claim 1 or 2, characterized in that a biodegradable lubricant is a saturated ester or a mixture of saturated esters in combination with an unsaturated ester or a mixture of unsaturated esters, both in combination with a plant-based lubricant according to any one of claims 3 to 5. Assembly according to one of the preceding claims, characterized in that the lubricant contains an anti-wear additive made from environmentally harmless substances. 13. The use of a biodegradable lubricant for lubricating non-contact sliding surfaces of at least two cooperating machine parts, at least one of which is translationally and / or rotationally movable, at least one of said surfaces being provided with a DLC coating. Use of a biodegradable lubricant to lubricate non-contacting sliding surfaces of at least two cooperating machine parts, at least one of which is translationally and / or rotationally movable, each of said surfaces being provided with a DLC coating. 15. Use of biodegradable vegetable-derived lubricant for lubricating interlocking sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable, at least one of said surfaces being provided with a DLC coating. 16. Use of biodegradable vegetable-derived lubricant to lubricate interlocking sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable, each of said surfaces being provided with a DLC coating. Use of biodegradable vegetable oil for lubrication of non-contact sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable, at least one of said surfaces being provided with a DLC coating. 18. The use of biodegradable vegetable oil for lubricating non-contact sliding surfaces of at least two cooperating machine parts, at least one of which is translationally and / or rotationally movable, each of said surfaces being provided with a DLC coating. 19. The use of biodegradable vegetable oil for lubricating non-contact sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable, at least one of said surfaces being provided with DLC coating, and this being an oil of the group consisting of rapeseed and / or sunflower and / or pumpkin and / or olive and / or peanut and / or almond oil. 20. The use of biodegradable vegetable oil for lubricating non-contact sliding surfaces of at least two cooperating machine parts, at least one of which is translationally and / or rotationally movable, each of said surfaces being provided with a DLC coating, and wherein it is an oil of the group consisting of rapeseed and / or sunflower and / or pumpkin and / or olive and / or peanut and / or almond oil. 21. The use of a biodegradable saturated ester or mixture of saturated esters to lubricate interlocking sliding surfaces of at least two cooperating machine parts, at least one of which is translationally and / or rotationally movable, at least one of said surfaces being provided with a DLC coating . 22. The use of a biodegradable saturated ester or mixture of saturated esters for lubricating interlocking sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable, each of said surfaces being provided with a DLC coating . 23. The use of a biodegradable unsaturated ester or mixture of unsaturated esters to lubricate non-contact sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable, with at least one of said surfaces provided with a coating DLC. 24. Use of a biodegradable unsaturated ester or mixture of unsaturated esters to lubricate non-contact sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable, each of said surfaces being provided with a DLC coating . 25. The use of a biodegradable unsaturated ester or mixture of unsaturated esters in combination with a saturated ester or a mixture of saturated esters to lubricate non-contact sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable, at least one of said surfaces provided with a DLC coating. 26. The use of a biodegradable unsaturated ester or mixture of unsaturated esters in combination with a saturated ester or a mixture of saturated esters to lubricate non-contact sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable, each of said surfaces provided with a DLC coating. 27. The use of a biodegradable unsaturated ester or mixture of unsaturated esters in combination with a saturated ester or a mixture of saturated esters, both in combination with a plant-based lubricant according to any one of claims 3 to 5, for lubricating adjacent sliding surfaces of at least two interacting machine parts , at least one of which is translationally and / or rotationally movable, wherein at least one of said surfaces is provided with a DLC coating. Use of a biodegradable unsaturated ester or mixture of unsaturated esters in combination with a saturated ester or a mixture of saturated esters, both in combination with a plant-based lubricant according to any one of claims 3 to 5, for lubricating the adjacent sliding surfaces of at least two interacting machine parts , at least one of which is translationally and / or rotationally movable, each of said surfaces being provided with a DLC coating. 29. The use of a biodegradable saturated ester or mixture of saturated esters in combination with a plant-based lubricant according to any one of claims 3 to 5 for lubricating interlocking sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable , wherein at least one of said surfaces is provided with a DLC coating. Use of a biodegradable saturated ester or mixture of saturated esters in combination with a plant-based lubricant according to any one of claims 3 to 5 for lubricating interlocking sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable , each of said surfaces being provided with a DLC coating. 31. The use of a biodegradable unsaturated ester or mixture of unsaturated esters in combination with a vegetable-based lubricant according to any one of claims 3 to 5 for lubricating non-contacting sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable , wherein at least one of said surfaces is provided with a DLC coating. Use of a biodegradable unsaturated ester or mixture of unsaturated esters in combination with a plant-based lubricant according to any one of claims 3 to 5 for lubricating non-contact sliding surfaces of at least two interacting machine parts, at least one of which is translationally and / or rotationally movable , each of said surfaces being provided with a DLC coating.