Labyrinth seal and method for producing a labyrinth seal

Abstract

A labyrinth seal for sealing a sealing region between a rotor and stator of a rotary machine includes, a base, and a plurality of sealing rings. The sealing rings are formed on the base, project into the sealing region and form, between them labyrinth valleys bounded, laterally, by the sealing rings and, in the floor of the valleys, by the base. The sealing rings, in at least one region, include at least one material which is different from that of the base.

Claims

1. A labyrinth seal for sealing a sealing region between a rotor and stator of a rotary machine, comprising: a base, and a plurality of sealing rings which are formed on the base, project into the sealing region and form, between them labyrinth valleys bounded, laterally, by the sealing rings and, in a floor of the valleys, by the base, wherein the sealing rings, in at least one region, comprise at least one material which is different from that of the base, wherein the different material is softer than a rotor material in a region of the labyrinth seal, and where an adhesion-promoting intermediate layer made of a third material is present between the base material and the different material.

2. The labyrinth seal as claimed in claim 1, wherein the sealing rings, in said region, comprise an aluminum alloy and the base comprises steel.

3. The labyrinth seal as claimed in claim 2, wherein the sealing rings, in said region, comprise a polymer material.

4. The labyrinth seal as claimed in claim 1, wherein only a front region of the sealing rings is produced from the different material.

5. The labyrinth seal as claimed in claim 1, wherein the different material contains a solid lubricant.

Description

DETAILED DESCRIPTION OF INVENTION

(1) The invention will be explained in more detail with reference to an exemplary embodiment illustrated in the drawing. The single FIGURE of the drawing shows part of a labyrinth seal 2 configured as a smooth gap seal. The labyrinth seal 2 seals a sealing region in the form of a gap 4 between a rotor 6, of which part of a shaft 8 of a turbocompressor is illustrated, and a fixed location stator 12, sealing here taking place in part, if not in full. The labyrinth seal 2 comprises a seal carrier 12, which bears a sealing insert 14 in the direction of the rotor 6. The seal carrier 12 and sealing insert 14 are constituent parts of the stator 10 and are therefore likewise fixed in location.

(2) The seal carrier 12, together with the sealing insert 14, forms a base 16, which bears six sealing rings 18, which are formed in one piece from the base 16. The base 16 and the sealing rings 18 encircle the shaft 8, wherein the gap 4 between the sealing rings 18 and the shaft 8 remains around the shaft 8. This gap 4 leaves the shaft 8 free space in order to be able to vibrate without rubbing against the sealing rings 18. However, if the vibrations are more pronounced than the width of the gap 4, rubbing nevertheless takes place.

(3) In order to avoid damage to the shaft 8 in the event of rubbing, the sealing rings 18 are produced from a number of materials. The bottom 20 of the sealing rings, at the rear, that is to say oriented away from the shaft, is formed from the material of the sealing insert 14—the base material. This base material is a suitable steel. As can be seen from the FIGURE, this material forms the floors 22 of the labyrinth valleys 24, which are arranged between the sealing rings 18 and are bounded, externally or at the rear in each case, by the floor 22 of the valleys and, laterally, by the flanks 26 of the adjacent sealing rings 18.

(4) At the front, that is to say in the direction of the rotor 6, the sealing rings 18 are formed from different material 28, that is to say from an aluminum alloy. A particularly advantageous material 28 is an aluminum/silicon alloy, in particular with 12%±1% silicon. The silicon means that the coefficient of thermal expansion is around 21×10.sup.−6/K±2×10.sup.−6/K, and thus in the vicinity of that of stainless steel, which is around 18×10.sup.−6/K. This means that thermal stressing between the base material and the different material 28 is kept to a low level, even in the event of pronounced fluctuations in temperature, as may occur, for example, in the case of rubbing. This counteracts breakage of the front part of a sealing ring 18 or of a labyrinth tip.

(5) It is likewise advantageous for the strength of the sealing rings 18 if the boundary surface between the different material 28 and the base material is narrow, that is to say is small. Even with different coefficients of expansion, the level of stressing between the materials remains low, even in the event of pronounced fluctuations in temperature.

(6) The different material 28 comprises two material zones of differing materials. The front part, which is oriented in the direction of the gap 4 and thus in the direction of the sealing region, is the aluminum alloy and the rear part is an intermediate layer 30, which promotes adhesion between the base material and the different material 28, in this exemplary embodiment between the steel and the aluminum alloy. A particularly suitable intermediate layer 30 is a zinc layer, which can be applied to the steel by hot galvanization of the steel. Likewise suitable is a nickel layer, which can be electroplated onto the steel.

(7) In the event of the rotor 6 rubbing the stator 10 in the region of the labyrinth seal 2, the shaft 8 and the front region of the sealing rings 18 made of the aluminum alloy come into contact with one another. The aluminum alloy is considerably softer than the steel of the shaft 8, and therefore material deformation occurs, for the most part, on the sealing rings 18, and there only in the front region made of the aluminum alloy material 28. Damage to the shaft 8 thus remains at a low enough level for repair not to be necessary. Depending on the deformation of the sealing rings 18, and/or on the amount of material removed therefrom, these sealing rings have to be replaced, in which case the sealing insert 14 with the sealing rings 18 is exchanged.

(8) In order, nevertheless, to keep damage to the shaft 8, but also to the labyrinth tips, to an even lower level, the aluminum alloy is provided with the solid lubricant. The latter is present in the form of α-boron nitride (BN), which is present in the surrounding aluminum alloy in the form of small islands measuring a number of μm in size. This solid lubricant reduces the sliding friction between the labyrinth tips and shaft 8, and therefore deformation of the labyrinth tips and removal of material therefrom are reduced.

(9) In order to produce the labyrinth seal 2, in the first instance the base 16 is produced in the form of a bushing. The operation of forming the sealing rings on the base material then takes place in a first step, by the different material being applied in the form of an inner layer of powder to the base material and being retained there, for example with the aid of a shaping enclosure. Subsequent sintering of the powder forms the inner layer into a cohesive layer. Thereafter, hot isostatic pressing compresses at least an outer layer of the aluminium alloy and closes pores.

(10) In a later step, the sealing rings are formed from the compact inner layer by the labyrinth valleys being cut into the inner layer and also, in part, into the base material, the floors 22 of the valleys therefore being positioned in the base material. The completed sealing insert 14 is introduced into the seal carrier 12 and the labyrinth seal 2 is thus transferred to its site of use.

(11) An alternative method comprises the initial processing step of the base 16 being created in the form of a bushing. Then, the different material 28 is introduced as a multi part body into the bushing. The two materials are connected integrally to one another by diffusion welding. The geometry of the base 16 and of the different material 28 here is selected such that the greater coefficient of thermal expansion of the aluminum, which is used in this exemplary embodiment, or of the aluminum alloy results in the different material 28 expanding to a more pronounced extent than the base material, and therefore, when the two materials are heated, the different material is forced into the base material. This promotes the connection, established by diffusion welding, between the two materials, and therefore the connection made as firmer than one which does not involve one material being forced into the other.