Pipe joints or couplings – Having plural independent paths
Reexamination Certificate
2000-07-07
2002-06-18
Swann, J. J. (Department: 3611)
Pipe joints or couplings
Having plural independent paths
C280S124178, C280S098000, C137S580000
Reexamination Certificate
active
06406065
ABSTRACT:
The present invention relates to a rotary joint for alternating passage of a lubricating medium and a non-lubricating medium from a stationary to a rotating machine part, having a first seal in the form of two flat, substantially circular ring-shaped sliding sealing surfaces arranged so as to slide one on the other, which sealing surfaces are substantially concentric relative to the axis of rotation of the rotating machine part and may be moved at least far enough from one another, in the axial direction, that they do not come into contact with each other during relative rotation of the rotating machine part.
Such rotary joints, which are also known as “dry run-safe rotary joints”, are already known. If a lubricating medium is supplied, the two flat sliding sealing surfaces are brought into contact with each other, the lubricating medium forming a lubricating film between the sealing surfaces sliding one on the other, such that it is ensured in this way that excessive frictional heat does not arise even at high rotational speeds, which could otherwise lead very rapidly to destruction of the sliding sealing surfaces.
However, the sliding sealing surfaces have to be moved apart in the axial direction If the rotating machine part rotates at a certain rotational speed without the lubricating medium being fed thereto. In this case no lubricating film can form between the sliding sealing surfaces and the dry sliding sealing surfaces, which are generally made of a ceramic material, very rapidly become hot and may be destroyed thereby, even if the rotational speed of the rotating machine part is comparatively low and way below the maximum rotational speed at which the seal is designed to operate when lubricating medium is supplied.
Dry run safety is thus achieved in that the two flat sliding sealing surfaces are moved a short distance away from one another, the increasing sealing gap having in any case to be large enough to ensure that the sliding sealing surfaces do not come into contact during the period without lubricating medium even taking account of the tolerances which may be exhibited by all the components of the device.
A series of applications exists in which another medium, without lubricating properties, has also to be supplied during rotation of the rotating machine part. For example, a water/oil emulsion may be supplied to a machine tool as coolant and lubricant during a first operating phase through a hollow spindle, the one end of which is connected to the rotating part of the rotary joint or constitutes this rotating part, whilst, during another operating phase, compressed air may be supplied for example for blowing through a drilled hole or blowing clean the working area or a tool, while the tool continues to turn.
The deliberate enlargement of the sealing gap for the purpose of protecting the sliding sealing surfaces during supply of this non-lubricating medium has the disadvantage, however, that compressed air may escape through this sealing gap in very considerable quantities, which leads not only to a drop in pressure and thus to reduced efficiency of the compressed air supplied to an operating point but additionally to a considerable loss of energy.
Taking this prior art as basis, the object of the present invention is to provide a rotary joint of the above-mentioned type which, despite its so-called dry run safety, nonetheless exhibits only small leakage losses even during passage of a non-lubricating medium and even when the rotating machine part is operating at high rotational speeds.
This object is achieved in that, in addition to the first flat seal, an additional cylindrical seal is provided, the sealing surfaces of which are formed of cylindrical circumferential surfaces arranged concentrically relative to one another with a narrow sealing gap, the cylindrical seal being arranged in the direction of potential leakage flow between the flow passage of the rotary joint and the first seal.
The above-mentioned features ensure that the non-lubricating medium has to pass through the seal formed by cylindrical circumferential surfaces and the narrow sealing gap formed therebetween before it can pass at all through the enlarged axial gap of the flat seal, which narrow sealing gap may be kept substantially narrower and smaller than the axial gap between the flat sliding sealing surfaces in the event of feed of a non-lubricating medium.
The cylindrical sealing surfaces may therefore be made with substantially tighter, smaller tolerances, because very tight tolerances may be observed in the case of cylindrical surfaces having appropriately small diameters. In contrast, the axial distance between flat sliding sealing surfaces is influenced by all the components connected therewith, which may be relatively long, such that a substantially greater safety gap has to be established at the axial surfaces, in order to make the rotary joint dry run safe. In addition, any case in the preferred embodiment of the invention, the radius of the cylindrical circumferential surfaces is smaller than the Internal diameter of the flat, annular sliding sealing surfaces of the first seal. Because of the small radius of these cylindrical circumferential surfaces, the relative speeds between the mutually opposing sealing surfaces are also lower and only relatively little frictional heat therefore arises even in the case of slight contact.
In this way, it may be ensured that even a medium with very low viscosity, such as compressed air for example, may be conveyed through the rotary joint with a very low leakage rate, even if the rotating machine part rotates at high speeds of, for example, 20,000 revolutions/minute relative to the stationary machine part.
If the lubricating medium is supplied, said medium naturally also penetrates into the narrow radial sealing gap between the cylindrical sealing surfaces and thence also into the axial gap between the flat sliding sealing surfaces, wherein, in this case however, the sliding surfaces are pressed together and thus reduce the sealing gap virtually to the thickness of the lubricating film produced by the lubricating medium.
The outer cylindrical circumferential surface of the second seal is appropriately connected to the rotating machine part, while the inner cylindrical circumferential surface of the second seal is connected to the stationary machine part. It goes without saying that the reverse arrangement is in principle also possible.
In any case, however, it is appropriate for the cylindrical sealing surfaces to be so arranged that the inner cylindrical circumferential surface overlaps the area of he first flat seal in the axial direction. In other words, the inner cylindrical circumferential surface, located on a sleeve, is connected either to the stationary or to the rotating machine part and the seal with the flat sealing surfaces comprises this sleeve, wherein each of the flat sealing surfaces is respectively connected with the stationary machine part or the rotating machine part. The part of this sleeve or cylindrical wall projecting beyond the first flat seal in the axial direction forms the inner or outer sealing surface of the second seal.
It is also appropriate for the flat sealing surfaces to be resiliently prestressed against each other. This means that the flat sliding sealing surfaces normally contact each other with a well-defined contact pressure, such that the rotary joint is designed for the supply of a lubricating medium, while, for the supply of non-lubricating media, the sliding sealing surfaces have to be moved apart in the axial direction against the spring force. In many instances of application this is the shorter working cycle.
The respective sealing surfaces or the parts directly or indirectly carrying these sealing surfaces are preferably so designed that the flat sealing surfaces may be moved apart to an axial sealing gap width which is at least ten times the radial sealing gap width between the cylindrical circumferential surfaces of the second seal.
Conversely, it could also be said that the radial sealing ga
Mittermeier Norbert
Ott Stephan
GAT Gesellschaft fur Antriebstechnik mbH
Paul & Paul
Shriver J. Allen
Swann J. J.
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