Patent Application
20050242521
This application claims the benefit of German Patent Application 10 2004 020 966.9, filed Apr. 28, 2004. The disclosure of the above application is incorporated herein by reference.
The invention relates to a radial shaft sealing ring with a backing ring and a sealing element made of an elastomer attached thereto by vulcanization. The sealing element is made of an elastomeric material and has a lip seal which, when the sealing ring in not yet installed, protrudes from the backing ring in radial direction. When the sealing ring is fitted into the opening of a housing, the lip seal is pre-stressed and, with its curved sealing surface, surrounds the shaft.
Sealing rings are widely known and are used to seal an internal space filled with liquid from the surroundings. Such a seal should provide good sealing both statically during shaft stoppage and dynamically when the shaft is rotating. Leaks should be virtually prevented. Moreover, the seals should also provide tight sealing for different directions of rotation.
The possibility of sealing a shaft that can rotate in both directions is indicated in U.S. Pat. No. 4,834,397. Among other things, this patent shows, in
A seal comparable to the afore-described embodiment is shown in EP 0 798 498 A1. In this case, too, the sealing surface is interrupted by an all-around extending groove, so that two partial surfaces are present. Unlike in the afore-described embodiment, here the groove is sloped in the opposite direction and, moreover, the terminal surface of the lip seal is provided with an adapting part. The groove bottom is fitted with an undulation which, when the rotational movement starts, causes the first sealing surface to lift from the shaft surface as a result of which the leaking liquid is returned. In the examples given in this case, too, a lip seal made of PTFE is used. Such a seal can be used for shafts that are to be sealed when rotating in either direction.
Another method of shaft sealing is described in DE 100 33 446 C2. In this case, a shaft sealing ring made of an elastomeric material is used. On the side facing the shaft, the lip seal is provided with a thread which, while the shaft is rotating, returns the escaping medium to the space to be sealed. To achieve static sealing, also when the shaft is standing still, the thread is isolated from the surroundings by means of a stem. The thread is present on both sides of the stem. Such an embodiment permits rotation in the opposite direction for only a short time, because extended back-rotation of the shaft results in considerable positive and negative pressures at the stem, which enables large amounts of leaking fluid to escape. Moreover, such embodiments do not lend themselves to sealing against pressure
The object of the invention is to provide an improved radial shaft sealing ring that provides good sealing over a prolonged period of time, and that will withstand a reversal in the direction of shaft rotation for at least a limited length of time. Moreover, the ring should provide adequate sealing also against elevated pressures.
In the radial shaft sealing ring according to the invention, a lip seal is provided having a sealing surface that consists of a sealing bulge disposed at the end of the lip seal that extends all around the shaft, and an adjacent surface segment that holds back or returns the leaking liquid. The terminal surface of the lip seal, for the installed sealing element, is directed toward the internal space of the housing to be sealed. The sealing bulge provides good static sealing when the shaft is standing still. The surface segment directly adjacent to the sealing bulge holds back or returns the leaking liquid. In this respect, it is of importance that the terminal surface of the lip seal, for the installed sealing element, is oriented toward the internal space of the housing to be sealed.
For the leaking liquid to be retained or returned by the surface segment, the segment is provided with hydro-dynamically acting return grooves for the leaking liquid. To this end, it is advantageous for the return grooves to be formed by a single-flight thread. The thread extends in the sealing bulge over a fairly long distance and becomes gradually flatter. The distance should amount to at least ¼ of the sealing bulge circumference.
The thread can be of a triangular sharp-V kind. Good results were also obtained with saw-toothed threads with inward-oriented tips. The leading front of the teeth are then approximately perpendicular to the middle plane of the lip seal.
The thread of the surface segment extending in the sealing bulge imparts to the sealing bulge a different contact width with which it touches the shaft. It is important to note that at its narrowest point this contact width amounts to 0.1 to 0.8 mm. Smaller contact widths can cause insufficient sealing, whereas excessively large contact widths can hinder lubrication.
The depth of the thread relative to the thickness of the lip seal is in preferably the range from 0.46 to 0.67 of the lip seal thickness. The ratio of lip seal thickness to thread depth is then preferably from 1.5 to 2.2. Note in this respect that the contact width of the sealing bulge is inversely proportional to the thread depth so that a smaller contact width means a larger thread depth, and a larger contact width a smaller thread depth.
To make sure that dirt particles or the like stemming from the internal space will not end up below the sealing bulge, the terminal surface of the lip seal is oriented toward the surface of the shaft so that it forms an angle α that is preferably between 800 to 1000. On the outside, for an installed sealing element, an angle β that is preferably from 0° to 200 is formed at the lip seal.
Also exerting an influence on the sealing performance is the extent to which the sealing surface covers the shaft. It was established by tests that best results are obtained when the overlap (φD-φB) amounts to about 3 to 10% of the shaft diameter. For many applications for which the shaft diameter is 45 mm, an overlap of 2 to 5 mm is preferably chosen.
A displacement C of the center line of the lip seal 4 from the center line of the shaft 6 is advantageous. The displacement results in locally different pressures of lip seal 4 against shaft 6 and in an edge 7 which extends sinusoidally and is displaced over the circumference of shaft 6. This leads to a better lubricant exchange.
The sealing ring is provided with a conventional backing ring. Preferably, however, the backing ring consists of a curved metallic ring. The outer, axially extending part of the ring is at least partially surrounded by the elastomeric material of the sealing element and is inserted into the housing as a pinching or static sealing ring. The inner, radially extending ring part is enclosed on its internally disposed edge by the material constituting the sealing element.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The invention will now be described in greater detail by reference to the exemplary embodiments represented by the drawings in which:
The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102004020966.9 | Apr 2004 | DE | national |
