GB2331131A - Shaft seal with secondary lip seal - Google Patents

Abstract

A slide ring seal for sealing a rotating shaft 3 against a housing 1 comprises a non-rotating slide ring 11 connected to the housing 3 and a dynamic slide ring 12 connected to the shaft 1. A sealing element 18 is provided between the non-rotating slide ring 11 and the housing, this having a portion 18b sealingly mounted in the housing and an axially spaced sealing lip 18d biassed against the outside of the slide ring 11. The sealing element is arranged such that it is subjected to pressure at its sealing surfaces so that it may be made from materials with little elasticity, yet high chemical resistance such as PTFE.

Description

2331131 1 A slide ring sealing g The present invention refers to a slide

ring sealing for sealing a rotating shaft against a housing, and in particular to a slide ring sealing with replaceable slide rings that may be fastened to the housing or the shaft, respectively, via seals.

A slide ring sealing comprises a stationary slide ring fastened to the housing, and a dynamic slide ring fastened to the rotating shaft. The slide rings abut along a sliding surface where they effect the sealing between the stationary and the dynamic elements of the slide ring sealing. The slide rings are biased towards each other, for example, by means of springs so as to obtain a high pressure force and. thereby. a good sealing effect.

Typically, the slide rings are mounted to slide ring holders for an easyr replacement of the slide rings that wear down with time. At the junctions between the slide rings and the slide ring holders and between the slide ring holders and the housing or the shaft, ring seals are provided that act as a kind of secondary seals. These ring seals seal off the C transition between the dynamic slide ring and the shaft, as well as the transition between the stationary slide ring and the housing, whereas the sliding surface between the two slide rings acts as a kind of primary seal between the stationary and the rotating elements. Usually, slide rings are made of elastomeric materials because of their low costs and because they offer good sealing properties due to their high elasticity. However, when the media to be sealed off are chemically aggressive, very expensive special elastomenc materials have to be used, whereby the costs of the overall slide ring sealing are increased.

United States Patent 3,740,059 discloses a seal for a water pump that forms the basis of the precharacterizing part of claim 1. Here, the holder of the stationary slide ring is formed as a ring with a plurality of steps. In the mounting portion of the slide ring holder, i.e., in that portion in which it is fastened to the housing wall, an Clastomeric 2 is seal element is welded on, enclosing the inner and outer circumferential surfaces of the mounting portionOn the inner side, the sealing element passes into a sealing tongue abutting the stationary slide ring and being pressed against the stationary slide ring by means of a continuous spring ring. Due to the firm connection between the stationary slide ring holder and the sealing element, a replacement of the worn-down sealing elements also requires a replacement of the slide ring holder, thereby increasing the operation costs of the seal. Moreover, the exact orientation of the stationary slide ring holder depends on the material, in particular on the elasticity of the sealing element, since the sealing element fixes the slide ring holder in the housing opening. This is disadvantageous in particular with chemically aggressive media within the housings since this requires the use of very expensive chemically resistant special elastomeric materials. Chemically resistant and less expensive materials such as Teflon cannot be used for lack of elasticity.

It is an object of the present invention to provide a slide ring sealing with a simple structure.

According to the present invention, there is provided a slide ring sealing for sealing a rotating shaft against a housing, the shaft extending through a passage opening of the housing, comprising an annular stationary slide ring holder having a circumferentially extending mounting portion for mounting the holder to the housing, and a stationary slide ring supported by the stationary slide ring holder, a dynamic slide ring holder adapted to be fastened to the shaft, and a dynamic slide ring supported by the holder, the two slide rings being biased towards each other and 3 is providing a sealing effect along their contact surfaces, and an annular sealing element provided between the housing and the stationary slide ring press fitted into the a seat of the housing and having housing sealing portion abutting the seat and a transition axially projecting therefrom, which transition is adjoined by a sealing lip pressed against the stationary slide ring by a spring ring, characterised in that the housing sealing portion of the sealing element is arranged axially separate from the mounting portion of the stationary slide ring holder.

The slide ring sealing of the present invention comprises a stationary slide ring holder for mounting stationary slide ring to a housing from which a rotating shaft extends through a passage opening. A dynamic slide ring adapted to be fastened to the shaft by means of a dynamic slide ring holder abuts the stationary slide ring, the two slide rings; biased towards each other, providing a sealing effect along the contact surfaces. A sealing element is provided between the stationary slide ring and the housing in order to guarantee a sealing effect in this region between the interior of the housing and the environment. A sealing lip of the sealing element is pressed against the stationary slide ring by means of a spring ring, whereas a housing sealing portion of the sealing element is pressed into a seat in the housing. According to the present invention, the housing sealing portion of the sealing element is axially separated from the mounting portion of the stationary slide ring holder. The mounting portion of the stationary slide ring holder corresponds to that part of the slide ring holder by which it is fastened to the housing.

4 Thus, the portion of the slide ring sealing which is mounted to the housing is separated from the portion effecting the sealing against the housing. This is advantageous in that the pressure force of the sealing element can be adjusted independent from the fastening force of the stationary slide ring holder. Further, providing the sealing element and the stationary seal ring holder separately, the slide ring sealing may be of simple structure and the wear-prone sealing element can be replaced more easily. Moreover, the mounting of the slide ring sealing is simplified since the fastening to the housing and the pressing-in of the sealing element may be effected independently. As another aspect, the present slide ring sealing makes it possible to provide the entire sealing element into the interior of the housing, i.e. out of the passage opening in the housing wall. Within the housing, the sealing element finds better protection from outer influences.

Axial displacements of the stationary slide ring, caused, for example, by the wear of the sliding surface and the thrust provided by the spring, are compensated for by the transition portion of the sealing element so that the sealing element remains in sealing contact with the housing and the stationary slide ring even when the latter takes different positions. The use of only a single sealing element between the housing and the stationary slide ring and the abutment of the sealing lip on the stationary slide ring allows for a smooth shape towards the interior of the housing so that no dead zones are present as with conventional ring seals. Therefore, the slide ring sealing may also be used to seal off media containing a high percentage of solids.

The mounting portion of the stationary slide ring can be located in the passage opening of the housing. In this manner, the assembly dimension of the slide ring sealing may be shortened since the respective portion of the housing wall is used to fasten the stationary slide ring holder. The stationary slide ring holder may also be located entirely within the passage opening, the sealing element advantageously directly joining the slide ring holder in the axial direction. It is also possible to have the slide ring holder abut the wall of the passage opening so that no contaminating matter can enter the housing from that place.

Preferably, the axial extension of the housing sealing portion is smaller than the axial extension of the mounting portion. This allows for a facilitated mounting of the slide ring sealing since, upon insertion-of the sealing element, only the clamping effect of the housing sealing portion which is relatively small, but fully sufficient for sealing purposes, has to be overcome.

To secure the slide rings against rotation relative to the slide ring holders, the slide rings advantageously cooperate directly with the associated slide ring holders. This may be realized through a pin and groove connection, for example. This embodiment is advantageous in that the slide rings are always in.a defined position since no deformable elements such as springs are used to secure the slide rings against relative rotation.

Preferably, the sealing lip and the transitional region of the sealing element form a Ushaped receptacle for the spring ring. The receptacle is closed off against the interior of the housing so that the medium inside the housing is kept away from the spring ring.

In a particular embodiment the stationary slide ring holder is provided with a supporting portion axially projecting into the housing for pressing the sealing element in the seat of the housing, the supporting portion preferably being annular and extending circumferentially. When assembling the slide ring sealing, the sealing element is clamped between the seat of the housing and the supporting portion so that a particularly good sealing effect is obtained, in particular for materials with little elasticity such as Teflon.

A conventional ring seal of elastomeric material may be arranged between the supporting portion and the sealing element. Here, the sealing element and the ring seal are complementary to each other. The sealing element protects the ring seal from the 6 influences of the medium, in particular chemically aggressive media, whereas the elastic ring seal supported on the supporting portion of the stationary slide ring holder, presses the sealing element against the seat of the housing due to its elasticity.

Preferably, the sealing element is made of PTFE (polytetrafluor ethylene), such as Teflon, since this material, while being of low cost, has a high resistance against chemically aggressive media and is insensitive to high temperatures (up to about 260' C). Other than elastomeric materials, PTFE materials only have very little elasticity so that the sealing effect usually is limited. P1FE materials may be formed cold and have no memory, i.e. they will adapt to the abutment surface upon little pressure, yet they do not press thereon in a sealing manner. Therefore, movements will create gaps between the sealing element and the abutment surface, through which the medium can escape. Using the present design and arrangement of the sealing element, a good sealing effect may also be obtained with PTFE materials. At all locations where the sealing element abuts the housing or the stationary slide ring, the PTTE material is subjected to pressure so that it is compressed and causes a good sealing effect.

The following is a detailed description of embodiments of the present invention with reference to the accompanying drawings.

In the Figures:

Fig. 1 is a sectional view of a first embodiment, Fig. 2 is a sectional view of a second embodiment.

As illustrated in Fig. 1, a housing 1 filled with a high-pressure medium comprises an inner space 2 and passage opening 2a in the housing wall. A rotating shaft 3 extends through the passage opening 2a. A slide ring sealing 10 arranged in the inner space 2 or the passage opening 2a seals the inner space 2 of the housing from the outer end of the 7 shaft 3 and against the environment. The slide ring sealing may also be mounted in spaces corresponding to the DIN standard L, K, The slide ring sealing 10 comprises a stationary slide ring 11 and a dynamic slide ring 12; the two slide rings 11, 12 meet at a sliding surface 13 forming the sealing surface between the stationary and the rotating parts.

The stationary slide ring 11 is secured to the housing 1 through a stationary slide ring holder 14 located in the passage opening 2a. Means (not illustrated) such as pin and groove connections, fix the stationary slide ring holder 14 in the axial direction along an external mounting portion 14a to the housing 1 and secure it against rotation. On its inner end, i.e. the side facing toward the inner space of the housing, the stationary slide ring holder 14 has one or a plurality of bolts 15 engaging axial grooves 16 in the stationary slide ring 11 to secure the same against rotation. Further, the stationary slide ring holder 14 comprises one or a plurality of circumferentially distributed pressure springs 17 pressing the stationary slide ring 11 against the dynamic slide ring 12.

A sealing element 18 is fit into a seat 4 of the housing 1, which adjoins the inner end of the passage opening 2a and projects backward radially, the sealing element being adapted to the outer circumference of the stationary slide ring 11 in a sealing manner. The sealing element 18 is made of a PTFE material or a similar material or from a base member 18a of reinforced PTFE material to which PTFE seal segments of a softer PTFE material are sintered. Thus, a mushroom-shaped housing sealing portion 18b of the sealing element 18 abuts the seat 4 of the housing 1 in the form of a ring. The housing sealing portion 18b has a diameter larger than the seat 4 so that the housing sealing portion 18b is press fitted and has a good sealing effect. Extending axially into the housing 1, a transition 18c adjoins the base member 18a. The transition 18c passes into a scaling lip 18d which rests in parallel on an outer circumferential surface of the stationary slide ring 11. Here, the transition 18c and the sealing lip 18d form a Ushaped recess open towards the outer surface of the housing, into which recess a 8 continuous spring ring 19 is inserted. The spring ring 19 firmly presses the sealing lip 18d onto the stationary slide ring 11 so that a good sealing effect is guaranteed.

The sealing element 18 is located only wid-iin the inner space 2 of the housing 1; it directly adjoins the stationary slide ring holder 14 fastened in the passage opening 2a to which it may be fastened, for example, by the bolts 15.

The dynamic slide ring 12 is secured by a dynamic slide ring holder 20 fastened to the shaft 3 by means of one or a plurality of locking screws. The dynamic slide ring holder 20 comprises one or a plurality of radially extending pins 22 engaging axially extending grooves 23 in the dynamic slide ring 12 to secure the same against rotation.

The dynamic slide ring holder 20 further comprises a continuous circumferential groove 24 open towards the shaft 3, which is provided between the locking screws 21 and the pins 22. The circumferential surface 25 of the groove 24 is beveled such that its radial distance from the shaft 3 decreases towards the outside of the housing 1. The circumferential surface 25 is always beveled towards the portion where lower pressure prevails. Located in the groove 24 is a ring seals 26 of PTFE material. The pressure of the medium inside the housing 2, which also builds up in the inward portion of the groove 24, urges the ring seal 26 towards the outside of the housing whereby the ring seal is progressively compressed by the beveled circumferential surface 25 of the groove 24 so that a good sealing effect is ensured.

A second ring seal 27 of PTFE material is provided between the dynamic slide ring 12 and the dynamic slide ring holder 20. The pressure springs 17 compress the second ring seal 27 in the axial direction and the medium pressure within the housing 1 compresses it radially so that also at this location a good sealing effect is obtained.

All secondary seals, namely the sealing element 18 and the two ring seals 26, 27, consist of low-cost, chemically resistant PTFE materials or similar materials of little 9 elasticity. By their design and arrangement, the secondary seals are subjected to pressure at their contact surfaces so that even the PTFE material has a sealing effect.

Fig. 2 illustrates a slide ring sealing 110 according a second embodiment of the invention; elements of the slide ring sealing 110 identical to the first embodiment are represented by the same reference numerals. The two embodiments differ in the structure of the stationary slide ring holder and the sealing element.

The outer circumference of the stationary slide ring holder 114 is provided with a mounting portion 114a for mounting the stationary slide ring holder 114 within the passage opening 2a of the housing 1. The stationary slide ring holder 114 is secured against rotation by means not illustrated. The inner end of the mounting portion 1 14a, i.e. the end averted from the housing wall, is adjoined by a continuous annular supporting portion 1 14b of a tongue-like shape and projecting into the inner space 2 of the housing. The diameter of the inner circumferential surface of the supporting portion 1 14b is dimensioned such that it embraces the outer circumference of the stationary slide ring 11 at least at the outer end portion thereof, leaving a gap therebetween, so that the stationary slide ring 11 can move without interference by the supporting portion 114b.

The outer circumferential surface of the supporting region 114b has its inward end provided with a ramp that, at the outward end of the supporting portion 114b, passes into an annular surface via a step.

A sealing element 118 is arranged between the outer circumferential surface of the stationary slide ring 11 and a seat 4 of the housing 1 to seal the inner space 2 of the housing off against the environment at this location. A scaling lip 11 8d of the sealing element 118 lies plane on a part of the outer circumferential surface of the stationary slide fing 11. The axial extension of the sealing lip 11 8d is smaller than the axial extension of the abutment surface of the stationary slide ring 11 on which the sealing lip 11 8d abuts so that even when the stationary slide ring 11 moves, e.g. due to wear or adjusting movements, the sealing lip 11 8d always abuts the stationary slide ring 11 in a sealing manner. The outer circumference of the sealing lip 11 8d is provided with a groove for receiving a continuous spring ring 19 firmly pressing the sealing lip 11 8d against the stationary slide ring 11 so that a good sealing effect is ensured at all times even with materials that have little elasticity, such as Teflon. When the inner space 2 of the housing holds chemically aggressive media the spring ring 19 may be made of Hasteloy C since this material is chemically indifferent.

Adjoining the sealing lip 11 8d is an axially extending transition 11 8c of the sealing element 118. The axial length of the transition 11 8c is dimensioned such that an axial distance exists between the abutment surface or the point of abutment of the scaling lip 1 18d on the stationary slide ring 11 and the inward end of the supporting portion 1 14b of the stationary slide ring holder 114 so that upon an axial movement of the stationary slide ring 11, an finpairment of the sealing effect of the sealing lip 11 8d by the inward end of the supporting portion 1 14b is avoided.

Further radially outward, the transition 1 18c is adjoined by a housing sealing portion 1 18b of the sealing element 118. The outside circumferential surface of the housing sealing portion 11 8b abuts the seat 4 of the housing 1 in a sealing manner. The inside circumferential surface is provided with a recess for an elastomeric ring seal 128. The ring seal 128 is supported on the annular surface of the supporting portion 1 14b of the stationary slide ring holder 114 and presses housing sealing portion 11 8b of the sealing element 118 into the seat 4 of the housing 1. The diameter of the scat 4 and of the supporting portion 1 14b, as well as the thickness of the housing sealing portion 11 8b and the ring seal 128 are dimensioned such that the ring seal 128 is mounted in a compressed state so that, due to its elasticity, it presses the housing sealing portion 11 8b against the scat 4 of the housing 1.

1 1 In the second embodiment, the sealing element 118 features a separation of the sealing effect and the contact pressure. The sealing element 118 provides the sealing effect and protects the ring seal 128, while the same presses the sealing element 118 into the seat 4 of the housing 1 from the inside, as it were. Instead of a ring seal, one may also use other pressure means such as springs. Also in the second embodiment, a sealing lip as shown in the first embodiment illustrated in Fig. 1, may be used which has a spring ring 19 separate from the inner space 2 of the housing. Furthermore, it is possible to drop the ring seal 128 and to make the housing sealing portion 11 8b correspondingly thicker so that the latter is compressed between the seat 4 of the housing 1 and the supporting portion 1 14b of the stationary slide ring holder 114, thereby to seal off the inner space 2 of the housing against the environment.

Although the present invention has been described and illustrated with reference to particular embodiments, the foregoing description is not to be understood as restricting the invention to the specific embodiments discussed. An expert in the field will readily see various possible modifications which all fall within the scope of the present invention as defined by the appended claims.

12

Claims (1)

1. Claims:

   1. A slide ring sealing for sealing a rotating shaft (3) against a housing (1), the shaft (3) extending through a passage opening (2a) of the housing (1), comprising an annular stationary slide ring holder (14; 114) having a circumferentially extending mounting portion for mounting the holder to the housing (1), and a stationary slide ring (11) supported by the stationary slide ring holder (14), a dynamic slide ring holder (20) adapted to be fastened to the shaft (3), and a dynamic slide ring (12) supported by the holder, the two slide rings (11, 12) being biased towards each other and providing a sealing effect along their contact surfaces, and an annular sealing element (18; 118) provided between the housing (1) and the stationary slide ring (11) press fitted into the a seat (4) of the housing (1) and having housing sealing portion (1 8b; 11 8b) abutting the seat (4) and a transition (1 8c; 11 8c) axially projecting therefrom, which transition is adjoined by a sealing lip (1 8d; 11 8d) pressed against the stationary slide ring (11) by a spring ring (19), characterized in that the housing sealing portion (1 8b; 1 18b) of the sealing element (18; 118) is arranged axially separate from the mounting portion (14a; 114a) of the stationary slide ring holder (14; 114).

   2. The slide ring sealing of claim 1, wherein the mounting portion (14a; 114a) of the stationary slide ring (14; 114) is provided in the passage opening (2a) of the housing (1).

   1 3 3. The slide ring sealing of claim 1, wherein the housing sealing portion (1 8b; 18b) has a larger diameter than the mounting portion (1 4a; 1 14a).

   4. The slide ring sealing of claim 1, wherein the axial extension of the housing scaling portion (1 8b; 11 8b) is smaller than that of the mounting portion (1 4a; 1 14a).

   5. The slide ring sealing of claim 1, wherein the slide rings (11, 12) directly cooperate with the associated slide ring holders so as to be secured against relative rotation.

   6. The slide ring sealing, of claim 1, wherein the seat (4) of the housing (1) has a larger diameter than the passage opening (2a).

   7. The slide ring sealing of claim 6, wherein the end of the seat (4) averted from the pasage opening (2a) has a ramp.

   8. The slide ring sealing of claim 1, wherein the seat (4) is provided separate from the passage opening (2a).

   9. The slide ring scaling of claim 1, wherein the sealing lip (18d) and the transition (1 8c) together form a Ushaped open receptacle for the spring ring (19) to protect the spring ring (19) from a medium contained in the housing (1).

   10. The slide ring sealing of claim 1, wherein the stationary slide ring holder (114) has a supporting portion (1 14b) projecting axially into the housing (1) for pressing the sealing element (118) into the seat (4) of the housing (1).

   11. The slide fing scaling of claim 10, wherein the supporting portion (1 14b) is annular in shape.

   14.

   12. The slide ring sealing of one of claims 10 or 11, wherein a ring seal (128) of elastomeric material is arranged between the supporting portion (1 14b) and the sealing element (118) so as to press the sealing element (118) into the seat (4) of the housing (I).

   13. The slide ring sealing of claim 1, wherein the sealing element (18; 118) is made of PTFE or a similar material.

   14.The slide ring sealing of claim 1, substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.