JPH03163272A - Dry gas seal - Google Patents

Abstract

PURPOSE: To ensure a V-shaped seal clearance by providing a web between a support ring and a slide ring and selecting a distance from a shaft of the web to give a resultant force acting in the direction in which the seal clearance is expanded as a force pressing the slide ring on a seal body leaves the shaft. CONSTITUTION: A seal body 5 is supported on a shaft bush 3 through a packing ring 8. A slide ring 7 which cannot rotate and can move slightly in the axial direction is positioned in a seal holder 2' formed in a part of a casing wall to support a slide body 9 and form the seal body 5 and a V-shaped clearance S. A support ring 4 is provided on a rear surface on inner peripheral side of the slide ring 7 so as to travel in the axial direction, and a web 14 is provided between the support ring 4 and the slide ring 7. Gas lubricates the clearance S and presses the support ring 4 from the rear surface. A distance from a shaft of the web 14 is selected in such a way that a resultant force of gas pressure acts in the direction in which the clearance S is expanded. Consequently, it is possible to ensure sealing while ensuring gas lubrication.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is a dry gas seal configured as an axial shaft seal for a rotating shaft guided through a casing wall, comprising: It has a shaft bush that rotates together with the shaft as a support for a sealing body with a sealing surface, and a stationary sliding ring that is pressed against the sealing surface by a gas and has a sliding surface that is lubricated by the gas. and is constructed in such a way that a gas-filled gap between the sealing surface and the sliding surface is maintained.

[Prior Art] The above-mentioned type of axial shaft seal is, for example, EP-B-13.
678 and which seals the housing interior of a turbomachine under constant pressure, for example a turbocompressor or a turbine, at the through-guide of the shaft from the outside or from an intermediate chamber. This serves to prevent the medium from flowing out from the inner chamber. This is done using a gas as the sealing medium, which presses the sliding surface of the sliding ring against the sealing surface, thus minimizing the escape of gas from the interior chamber. The gas-filled gap is at the same time designed for contactless operation of the seal. In this case, the aim is to maintain a uniform gap with a width of a few micrometers, which is largely independent of the distance from the axis.

Such gaps tend to close in the event of a pressure disturbance, which can lead to undesired contact between the sealing surface and the sliding surface. It has already been proposed to eliminate the above-mentioned drawbacks by making the sealing gap widen outwards, ie away from the axis, in order to increase the rigidity of the gas gap. This so-called "v" shape achieves a greater gas stiffness, which results in a greater reaction force, which prevents contact between the two sides. The desired "V" shape is obtained by the oval shape of each sealing member and their cooperation.The shaft bushing is constructed such that it is supported on the annular surface of the shaft bushing in the zone adjacent to the shaft, In this case, the sealing body forms a small gap on the outside. An O-packing ring was inserted into the shaft bushing in the central zone. However, there is a risk of damage as the O-ring is crushed in the gap under the action of the sealing gas pressure, thereby impairing the sealing effect. On the other hand, the acting radial forces deform the stationary sliding ring, so that the desired V-shape of the gap occurs. However, such a V-shaped sealing gap can only be achieved to a limited extent with the small structural lengths required in practice.

[Problem to be Solved by the Invention J] It is an object of the invention to obtain a V-shaped sealing gap slightly widening towards the outside in a dry gas seal of the type mentioned in the introduction to suit different requirements and operating conditions. Moreover, the leakage must be as small as possible while the seal can operate optimally at a given gas pressure and shaft rotation speed without significant structural changes.

[Means for Solving the Problems 1] The means of the present invention for solving the above problems is to provide an elastic packing ring between the seal body and the shaft pusher at approximately the center of the distance from the shaft. The sealing body is supported directly on the inside of the packing ring via a coaxial web on the shaft bushing, so that the packing ring is pressed directly onto the outer surface of the web and the sliding ring is A support ring is provided on the rear side of the inner part, which is movable in the axial direction and is sealed against the sliding ring and the casing wall or a structural member connected thereto, the support ring being arranged on the inside, on the shaft. In an adjacent zone it is pressed against the back side of the sliding ring by another coaxial web, and the distance of this web from the axis in the supporting ring presses the sliding ring against the sealing body, created by the gas pressure. It is selected to provide a resultant force that acts in a direction that increases the seal gap as the force moves away from the axis.

Effects of the Invention The point of action of the resultant force is determined by the position of the web in the support ring, ie by the axis or the distance of the web from this axis. By changing this position, it is therefore possible to adjust the reaction force which acts to prevent the closing of the gap in the event of a failure. In a particularly simple way, this is possible by replacing the support ring with a support ring having webs of different diameters in different positions.

Embodiment In the embodiment shown, the shaft l is sealed and passes through the casing wall 2 (for example of a turbomachine) from a relatively high pressure 1) I to a relatively low pressure p. You will be guided to this point. The seal comprises a shaft bushing 3 fitted onto the shaft l, which supports a sealing body 5 on the outside. The sealing body forms an annular sealing surface 6 on the outside. Advantageously, the sealing body 5 is made of a hard metal, for example silicon carbide, or another material with similar sliding properties.

The shaft pusher 3 has an annular web 1 coaxial with the axis l between the central part of the radial surface and the inner part adjacent to the shaft.
3, on which a sealing body 5 is supported on the rear side, while the sealing body 5 forms a minimum clearance between the shaft bushing 3 in the inner and outer zones of the web 13. The web 13 is directly surrounded on its outer surface 13' by an O-ring-shaped seal 8 inserted into the groove of the shaft pusher 3.

A seal holder 2' is introduced into the borehole, which forms a through guide for the shaft of the housing wall 2. The seal holder forms a part of the casing 112 and in the seal holder is located a stationary, i.e. non-rotating, but slightly axially movable sliding ring 7, which is located on the inside. The sliding body 9 has a sliding surface 9' facing the oppositely located sealing surface 6 and made of a material with good sliding properties, for example a carbon ceramic material, on the side facing away.

Pressure p from the casing wall 2 to the shaft seal via the line lO
．． gas is supplied. This gas may be slightly higher than the turbomachine pressure p, which is to be sealed. The gas of the turbomachine itself can be extracted or supplied as an external foreign gas. The gas passes through the gap 11 between the seal holder 2' and the sliding ring 7, reaches the rear side of the sliding ring 7, and presses this sliding ring against the sealing body 5.

However, at the same time, a gas film several micrometers thick is formed within the sealing gap S by the supplied gas, which provides a contactless seal. In this case, the sliding surface is lubricated in a known manner, for example aerodynamically via pockets or grooves in the sliding surface or sealing surface or aerostatically by supplying gas to the sliding surface by flowing through the sliding body. This can be done by The leaking gas that has passed through the seal gap and the various packing rings is leaked out via the conduit 12. A support ring 4 is inserted into the inner recess on the back side of the sliding ring 7 toward the axis l, the supporting ring being movable in the axial direction and forming a seal between the sliding ring 7 and the seal holder 2'. has been done. A coaxial, annular web 14 is provided on the side of the support ring 4 facing the sliding ring 7, with which the support ring 4 is pressed against the sliding ring 7. Position and axis of web 14
The distance from axis A of is selected such that the pressure of the sealing gas, which is received by the back side of support ring 4, is transmitted relatively fully to sliding ring 7 at a location from the inside. A resultant force is obtained via the web 14 from the pressure acting on the rear side of the sliding ring 7 and the support ring 4, and this resultant force is relatively fully internal and acts adjacent to the shaft, so that the sealing gap S A pair of forces together with the resultant force of the internal pressures act on the sliding ring 7 to move it closer to the axis l than in the zone from the outside, where the sealing gap is relatively farther from the axis 1. It is deformed so that it is compressed more strongly in the relatively inner zone. In this case, the deformation of the sliding ring in the direction of the V-shaped sealing gap exceeds the deformation of the sealing body 5 acting in the other direction. This ensures that a slightly outwardly widening, ie V-shaped, gap is maintained during operation.

Instead of a step formed on the radial surface of the shaft bushing 3, as described above, the first web 13 is provided on the sealing body 5, and instead of a further web 14 on the support ring 4, it is provided on the sliding ring 7.
may be provided.

The shape of the sealing gap S can be adjusted by the position of the annular web 14 of the support ring 4, ie the distance from the axis l. Adaptation to changes in operating conditions can be achieved in a simple manner by replacing support ring 4 with a support ring having webs 14 in other positions. The gas seal can therefore be adapted in a simple manner and without structural changes to different operating conditions and requirements, i.e. to different gas pressures and shaft rotational speeds, and the pressure of the sliding ring on the sealing body can be increased by II4wJ. Due to the combined force, a gap geometry with as little leakage as possible is achieved with the greatest possible reliability.

In addition to the gas seals mentioned above, a second
A contactless seal l5 of similar construction is provided, but this seal can be omitted in some cases.

[Brief explanation of the drawing]

Fig. fsl is a sectional view along the axis of an embodiment of the dry axial shaft seal according to the present invention, and Fig. 2 is a partially enlarged view of Fig. 1. l...Shaft, 2...Casing wall, 2'...Shaft bushing 4...Support ring, 5...Seal body, 6...Seal surface, 7...Sliding ring, 8...・Packing, 9・
...Sliding body, 9'...Sliding surface, 10.12...Pipeline, 1l...Gap, 13.14...Web, 13'...
...Outer surface, l5...Seal.

Claims (1)

Claims: 1. A dry gas seal configured as an axial shaft seal for a rotating shaft (1) guided through a casing wall (2), the sealing surface (6) It is equipped with a shaft bushing (3) that rotates together with the shaft (1) as a support for the seal body (5) with a seal surface (6).
) and is lubricated with gas.
9') and such that a gas-filled gap (S) between the sealing surface (6) and the sliding surface (9') is maintained. In the constructed version, an elastic packing ring (8) is provided between the sealing body (5) and the shaft bushing (3) approximately in the middle of the distance from the shaft (1). The sealing body (5) is supported directly on the inside of the packing ring (8) via a coaxial web (13) on the shaft bushing (3), so that the packing ring (8) directly follows the web. (
13) and is axially movable on the back side of the inner part of the sliding ring (7), the sliding ring (7) and the casing wall (2)
Alternatively, a support ring (4) is provided which is sealed against the structural member (2') connected thereto, and which supports another coaxial web in the inner zone adjacent to the axis (1). (14) against the back side of the sliding ring (7), and the distance of this web (14) from the axis (1) in the support ring (4) is such that the gas pressure (
p_1), which presses the sliding ring (7) toward the sealing body (5), is selected so as to give a resultant force that acts in the direction of increasing the sealing gap (S) as it moves away from the shaft (1). A dry gas seal characterized by: 2. Gas seal according to claim 1, characterized in that the sliding surface (9') is provided on a sliding body (9) supported by a sliding ring (7). 3. Claim 1 or 2, wherein the support ring (4) is provided in an internal recess oriented towards the axis (1) of the sliding ring (7).
Gas seal as described. 4. A sliding ring (7) is fixedly connected to the casing wall (2) and is arranged axially movably in a seal holder (2') as a component forming part thereof. , a gas seal according to any one of claims 1 to 3. 5. Web between shaft bushing (3) and seal body (5) (
5. Gas seal according to claim 1, wherein the seal 13) is configured as a step on the radial surface of the shaft bushing (3) or the sealing body (5). 6. The support ring (4) is attached to the annular web (14) in another position.
) is replaceable with another support ring with a
5. The gas seal according to any one of items 5 to 5.