Patent Application
20140235515
The invention relates to a method and a device for lubricating a tribological system.
Tribological systems comprise at least two parts, which perform a relative movement to one another while in contact, thereby creating friction and wear. Such friction and wear created by the movement and the contact of such parts can result in a deterioration of the system and a shorter lifetime.
For example, heavy load bearings for machine tools, gear boxes, turbines (gas turbines) or space equipment are subject to wear and friction, which must be minimized in order to ensure longevity.
To this effect, special bulk materials, surfaces and/or lubricants are constantly being developed, in order to decrease friction and wear, thereby increasing the lifetime of such systems.
As lubricants, it is well known to use oil-based substances. The atmosphere surrounding such tribological systems is usually air. However, air is not inert and reacts with the surfaces or bulk material of the components of a tribological system (for example metals) and also with lubricants. Especially, air can lead to deterioration due to oxidation of metals and/or lubricants. These disadvantages are especially prominent in case of high temperatures.
Such interactions between the tribological system and the surrounding atmosphere have an important overall effect on the lifetime of the system as well as its efficiency.
From WO 2006/119047 A2 it is known to use supercritical carbon dioxide as a lubrication means for metal work pieces during metal working processes. The provision of supercritical carbon dioxide is, however, relatively expensive. Also, the provision and handling of supercritical carbon dioxide is time-consuming.
The present invention thus seeks to provide a lubricant for tribological systems which is efficient, as well as easy and cheap to provide and handle.
The invention thus provides a method according to the independent claims.
Advantageous embodiments of the invention are the subject matter of the dependent claims.
According to the invention, a highly effective lubricant for numerous tribological systems is provided, which is both inexpensive and easy to handle.
It has been found that carbon dioxide reduces friction and wear. Therefore, the invention proposes to bring gaseous carbon dioxide in contact with the regions of the tribological system which shall be lubricated. However, it has also been found that high carbon dioxide concentrations at the tribological system can cause the formation of metal oxides at the surface of the tribological system, such as a gear or a bearing. Furthermore, high carbon dioxide formation can also cause oxidation of the lubricant. Therefore, according to the invention gaseous carbon dioxide and an inert gas are provided in order to avoid too high carbon dioxide concentrations. Compared to air, inert gases will reduce friction and due to their inertness oxidation of the lubricant and the system to be lubricated will be prevented.
The gaseous carbon dioxide and the inert gas can be provided as a mixture or as separate gas feeds. In any case the carbon dioxide is diluted with the inert gas in order to avoid too high carbon dioxide concentrations at the tribological system.
In addition to its inertness, nitrogen has shown to reduce wear compared to air. Therefore, using nitrogen as inert gas in the inventive process will improve the friction and wear behavior of the tribological system and reduce oxidation of the metal surfaces of the tribological system and of the lubricant and its components.
The amount and concentration of carbon dioxide at the tribological system, e.g. a gear or a bearing, is preferably controlled to be such that a tribological layer is formed on the surfaces of the tribological system but oxidation of the system and the lubricant is prevented.
It is preferred to analyze the lubricant and/or to monitor a parameter characterizing the operation of the tribological system and to control the supply of carbon dioxide and/or inert gas based on these data. For example, when friction increases during operation of a tribological system this has an influence on the required energy input, the power output and/or the speed of the system. Monitoring these parameters provides information on the friction. A reduction of speed or an increase of the power and energy input to a gear indicate an increased friction. In that case the amount of carbon dioxide and/or the ratio of carbon dioxide to inert gas are increased to improve the lubricating behavior.
The analysis of the lubricant can also be an indicator for the status of the tribological system. The supply of carbon dioxide and/or inert gas to the tribological system is preferably controlled based on an analysis of the lubricant. At too high carbon dioxide levels or at too low inert gas levels the lubricant or components of the lubricant can be oxidized. When the analysis of the lubricant shows the formation of oxides the amount, pressure and/or gas flow of carbon dioxide provided to the tribological system will be reduced and/or the amount, pressure and/or gas flow of inert gas will be increased.
For example part of the lubricant can be continuously passed through an analyzer which determines the presence of oxides in the lubricant.
According to a preferred embodiment, gaseous carbon dioxide is provided by expanding liquid carbon dioxide provided in a gas cylinder or vessel. It can be transformed into the gaseous state for example using membrane techniques. After being directed to the tribological system to be lubricated (i.e. regions of the tribological system, which are to be lubricated), this gaseous carbon dioxide can be released into the atmosphere. As is well known, health hazards in connection with carbon dioxide are minimal, so that no specific measures for protecting users in the vicinity of the lubricated tribological system are necessary. Gaseous carbon dioxide can be supplied from cylinders with gaseous content. It is also possible to collect carbon dioxide after lubrication in order to recycle it, for example to provide synthetic fuels.
Gaseous carbon dioxide can easily be handled. For example, it can be provided in cylinders or containers containing liquid carbon dioxide. Such a cylinder can be provided with means for gaseous extraction, as is commonly known. Carbon dioxide is cheap and readily available.
The invention will now be described in more detail on the basis of a preferred embodiment as shown in the FIGURE.
The invention has several advantages compared to the prior art. Carbon dioxide has shown to reduce friction and wear of a tribological system. However, when the tribological system is lubricated by a lubricant, such as oil, the lubricant can be oxidized by excess carbon dioxide. Therefore, the invention proposes to use a mixture of carbon dioxide and inert gas as the atmosphere surrounding the tribological system and the lubricant.
Nitrogen shows a wear reducing behavior as well as it avoids oxidation of the lubricant and of parts of the tribological system. Therefore, a mixture of carbon dioxide and nitrogen is advantageous.
By controlling the operation and/or efficiency of the tribological system or characteristic parameters of the tribological system, such as energy input and output, power input and output, or speed of moving parts of the tribological system, the actual status of friction can be determined and the provision of carbon dioxide and/or inert gas can be controlled accordingly. The analysis of the lubricant or its components can be another parameter indicating the effectiveness of the lubrication. High oxide concentrations in the lubricant indicate too high carbon dioxide levels. In that case the carbon dioxide flow to the tribological system is reduced and/or the ratio of carbon dioxide to inert gas is reduced.
As an example of a tribological system to be lubricated, a bearing 10 is shown. A cylinder 20 containing liquid carbon dioxide is provided with a nozzle device 22 (not shown true to scale relative to the cylinder 20), through which liquid carbon dioxide can be expanded to provide a stream 24 of gaseous carbon dioxide. A closing valve 21 is expediently provided between cylinder 20 and nozzle device 22.
By expedient placement of nozzle 22 in relation to the bearing 10, lubrication of the latter by means of gaseous carbon dioxide can be effectively provided.
As carbon dioxide is non-hazardous for users, no means for retrieving gaseous carbon dioxide subsequently to its contact with bearing 10 are necessary.
Injection of gaseous carbon dioxide enables an effective lubrication of regions of tribological systems to be lubricated. Especially, specific shapes of nozzles 22 can be used in order to transport gaseous carbon dioxide to desired regions or places.
Wear and friction of tribological systems, especially metal parts of such systems, is thus effectively reduced.
This observation especially holds for tribological systems operating at elevated temperatures, especially for temperatures above 200° C.,
It is presumed that by usage of gaseous carbon dioxide as lubricant metal or iron carbonates are formed on the surface of components of tribological systems, resulting in efficient protective layers.
A continuous supply of gaseous carbon dioxide is usually necessary, since such protective layers of metal or ion carbonates will be removed by rubbing, i. e. components of a tribological system moving relative to one another.
It has been shown that usage of gaseous carbon dioxide as lubricant requires no further addition of other lubricants, such as oil based lubricants.
The invention constitutes a dry lubrication, which can especially be utilized for applications in which any kind of dampness is to be avoided.
In most tribological applications, liquid or grease lubricants are used against friction and wear. However, under extreme conditions e. g. (very high or low temperature, vacuum, radiation, extreme pressure) solid lubricants (i.e. molybdenum disulfide, graphite, hexagonal boron nitride) have conventionally been the only choice. At least for some of these applications, gaseous carbon dioxide may now be used as lubricant.
Examples of applications are: air compressors, food industry applications, railway track joints, open gear, ball bearings, machine-shop works, space vehicles (bearings, rings).
The invention is also useful to reduce wear and friction in tribological systems containing materials such as ceramics and polymers.
Further preferred examples of tribological systems, with which the invention can advantageously be used, are, for example, bearings, magnetic storage devices, transmission devices, driveline devices, brakes, cylinders, valves, wheels, dampers, equipment used in mining and mineral processing, cutting devices, gearboxes, turbines and space equipment. Spacecraft contain a variety of instruments and mechanisms that require lubrication. Such devices include solar array drives, momentum, reaction and filter wheels, tracking antennas, scanning devices and sensors.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP 13000876.6 | Feb 2013 | EP | regional |
