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 and a device according to the independent claims.

Advantageous embodiments of the invention are the subject matter of the independent claims.

According to the invention, a highly effective lubricant for numerous tribological systems is provided, which is both inexpensive and easy to handle.

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. Gasous 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 figures.

Figure 1 shows a preferred embodiment of a device according to the invention with which a tribological system can be lubricated.

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 dioxid. A closing valve 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 proctective 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.