WO1989007726A1

WO1989007726A1 - Mechanical face seals

Info

Publication number: WO1989007726A1
Application number: PCT/GB1989/000143
Authority: WO
Inventors: Paul Martin
Original assignee: John Crane Uk Limited
Priority date: 1988-02-18
Filing date: 1989-02-13
Publication date: 1989-08-24
Also published as: GB8803832D0; AU3195289A; ZA891147B

Abstract

Elastomeric bellows unit (16) includes a tubular element (17) made of elastomeric material and reinforcing means (21), the reinforcing means comprising a pair of cylindrical formations (22, 23) by means of which the ends (18, 19) of the tubular element (17) are clamped to the seal face member (15) and component (10) to provide a seal and transmit drive therebetween, a divergent, axially compliant intermediate portion (24) of the reinforcing means (21) acts between the cylindrical formations (22, 23) to provide torsional reinforcement.

Description

MECHANICAL FACE SEALS

The present invention relates to mechanical face seals and in particular to mechanical face seals in which one seal face member is sealed to an associated component by means of an elastomeric bellows unit.

Typically with such seals, means must be provided to clamp the bellows unit to its associated component and to the seal face member. Also separate spring means is required to apply an axial load to the seal face member and means is necessary for location of the spring means. Furthermore means, which may possibly be the spring means, is required to transmit torsional loads from the seal face member to the component with which it is associated in order to prevent torsional stressing of the bellows unit.

With such seals, the axial flexibility of the bellows unit allows for movement of the seal face member as the sealing faces wear, while the spring means maintains an axial load on the sealing faces over the wear range. The bellows unit is however only capable of withstanding low torsional stress without positive drive to the seal face.

It has also been proposed to provide seals in which the bellows unit itself provides the axial load on the seal face members. However, in order to provide sufficient resilience, torsional strength and also to withstand pressure differentials across the seal, such bellows units have been of substantial cross section and will only permit limited axial movement of the seal face member.

According to one aspect of the present invention, a mechanical face seal for producing a seal between a pair of relatively rotatable components comprises a first seal face member mounted in fixed rotational relationship and sealed with respect to one component and a second seal face member mounted in fixed rotational relationship to the other component, said second seal face member being sealed with respect to its associated component by means of an elastomeric bellows unit which permits axial movement of the second seal face member relative to the components, characterised in that said bellows unit comprises a tubular element made of elastomeric material and reinforcing means having cylindrical formations adjacent each end to apply reinforcement to the tubular element to maintain the ends of the tubular element in sealing engagement with the seal face member and its associated component respectively, and a divergent, axially compliant, intermediate portion of the reinforcing means providing torsional reinforcement.

The bellows unit described above provides means for sealing the seal face member to its associated component which avoids the need for additional clamping means and will transmit torsional stresses therebetween without the need for positive drive means.

According to a preferred embodiment the reinforcing means is formed by a single reinforcing element. The end portions of this reinforcing element are preferably of plain cylindrical configuration while the intermediate portion has at least one divergent portion. The end portions may however be formed by separate reinforcing rings in which case the elastomeric tubular element adjacent the ends of the intermediate portion of the reinforcing means must be of sufficient strength to transmit torsional stresses to the intermediate portion of the reinforcing means.

The reinforcing means may be in the form of a helically wound spring element, each end portion being formed by several windings of the same diameter, these windings abutting one another, while the intermediate portion is formed from windings of increasing diameter which are spaced apart so that they may be compressed axially. With this embodiment the resilience of the spring reinforcing element may be used to reinforce the resilience of the elastomeric material to axially load the seal face member into engagement with the seat. Advantageously, the spring element may be wound so that any torsional load applied thereto will tighten the coils of the radial reinforcing portions onto the second seal face member and associated component to reinforce the clamping and sealing effect thereof. However, reinforcing elements of this form may also be used with components which rotate in either direction, the radial reinforcement applied by the cylindrical portions of the reinforcing element being sufficient to maintain sealing and driving engagement between the bellows unit and seal face member and its associated component, even if the torsional load applied thereto tends to unwind the helically wound reinforcing element. The reinforcing means may alternatively be made of, for example, cylindrical metal foil, cylindrical pre-shaped woven metal braid, or resilient plastics material.

The reinforcing means of the present invention may be embedded in the elastomeric material of the tubular element. This is particularly advantageous where the reinforcing means is made of corrodable material.

The invention is now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a part sectional side elevation illustrating a seal formed in accordance with the present invention;

Figure 2 is a perspective view illustrating an alternative form of reinforcing element which may be used in the bellows unit of the seal illustrated in Figure 1;

Figure 3 illustrates in side elevation a further embodiment of the invention;

Figure 4 shows a sectional side elevation of the bellows unit of the embodiment illustrated in Figure 3, in a relaxed condition;

Figure 5 shows a view similar to Figure 4 but with the bellows unit in a compressed condition; and

Figure 6 is a section along the line VI-VI of Figure 3.

The seal illustrated in Figure 1 provides a seal between a shaft 10 and housing 11.

The first seal face member or seat 12 is sealed in a recess 13 of the housing 11 by means of an elastomeric ring 14.

A second seal face member 15 is sealed with respect to the shaft 10 by means of a bellows unit 16. The bellows unit 16 has a tubular elastomeric element 17 with a plain cylindrical portion 18 at one end which is a stretch fit upon the shaft 10 and a plain cylindrical portion 19 at the other end which is a stretch fit on the external diameter of seal face member 15. The cylindrical portions 18 and 19 are interconnected by a divergent portion 20.

A helically wound spring element 21 is embedded in the elastomeric element 17. Said spring element 21 has a pair of plain cylindrical portions 22 and 23, adjacent turns of each of these portions 22 and 23 abutting one another. The portions 22 and 23 compress the underlying elastomeric material against the shaft 10 and seal face member 15 respectively, to seal the bellows unit 16 thereto and to maintain positive drive engagement between the bellows unit 16 and shaft 10 and between the bellows unit 16 and seal face member 15. The cylindrical portions 22 and 23 of spring element 21 are interconnected by a compressable divergent spring portion 24.

The bellows unit 16 is mounted on the shaft 10 such that when seal face member 15 engages seat 12, the divergent portion 24 of spring element 21 is held under compression thereby loading the seal face member 15 axially into engagement with the seat 12. Furthermore, the spring element 21 transmits drive between the shaft 10 and seal face member 15 and also opposes any torsional loads applied to the seal face member 15 by reaction between the sealing face thereof and that of the seat 12.

The reinforcing element 29 illustrated in Figure 2 is made of resilient plastics materials. A pair of plain cylindrical ring formations 30 and 31, formation 30 being of greater diameter than formation 31, are interconnected by a series of angularly spaced axially extending spokes 32. The spokes 32 may be tied together by one or more rings 33 positioned intermediate of formations 30 and 31.

This reinforcing element is embedded in a tubular elastomeric element in similar manner to the spring element 21 of the seal illustrated in Figure 1, so that ring formation 30 will apply radial reinforcement maintaining the tubular elastomeric element in sealing and driving engagement with the seal face member 15, ring formation 31 will apply radial reinforcement maintaining the tubular elastomeric element in sealing and driving engagement with the shaft 10, while the spokes 32 will provide a divergent portion which will transmit torsional stresses from the shaft 10 to the seal face member 15 while permitting axial compression of the bellows unit. In the embodiment illustrated in Figures 3 to 6 the bellows unit 16 has a reinforcing element 40 again made of resilient plastics material. A pair of annular formations 41 and 42 are interconnected by a series of axially extending angularly spaced flat strips 43.

The reinforcing element 40 is mounted externally of an elastomeric tubular element 44. The internal diameter 45 of annular element 41 is contoured to engage a correspondingly contoured end portion 46 of the elastomeric tubular element 44 and radially load the elastomeric tubular element 44 into sealing and driving engagement with a shaft. The other annular formation 42 defines a cylindrical socket in which the seal face member 15* is located, the other end portion 47 of the elastomeric tubular element 44 being interposed between the annular formation 42 and sealing element 15' under compression, to provide a seal and to transmit drive therebetween.

The bellows unit 16 described above is assembled on the shaft so that it is compressed axially as illustrated in Figure 5 and the seal face member 15' will be forced into sealing engagement with seat 12, as illustrated in Figure 1. In this condition the strips 43 are deformed axially and will resiliently load the seal face member 15' into engagement with the seat 12. The flat strips 43 being relatively rigid torsionally due to their width, will also transmit torsional loads from the shaft to the seal face member 15'.

Various modifications may be made without departing from the invention. For example, while in the embodiments described above the axially movable seal face member 15 is sealed with respect to the shaft 10 by means of bellows unit 16, this seal face member 15 may alternatively be sealed by the bellows unit 16 to the housing 11, an axially fixed seat being provided on the shaft 10 in suitable manner. Also while in the above embodiment a single divergent portion is provided on the reinforcing element, any arrangement which will permit axial flexing of the bellows unit may be used. For example, the axially compressable portion of the reinforcing element may define one or more convolutions. The divergent portion of the reinforcing means may contribute substantially to the axial loading of the seal face member, for example as with the spring element described with reference to Figure 1. In such circumstances separate spring means will not be required. Alternatively the reinforcing means may have less effect on the axial loading, in which case the resilience of the elastomeric tubular element itself and/or additional spring means may be used to apply the appropriate axial load to the seal face members.

Claims

1. A mechanical face seal for producing a seal between a pair of relatively rotatable components (10, 11) comprising a first seal face member (12) mounted in fixed rotational relationship and sealed with respect to one component (11) and a second seal face member (15; 15') mounted in fixed rotational relationship to the other component (10), said second seal face member (15; 15') being sealed with respect to its associated component (10) by means of an elastomeric bellows unit (16) which permits axial movement of the second seal face member (15; 15') relative to the components (10, 11), characterised in that said bellows unit (16) comprises a tubular element (17; 44) made of elastomeric material and reinforcing means (21; 29; 40) having cylindrical formations (22, 23; 30, 31; 41, 42) adjacent each end to apply reinforcement to the tubular element (17; 44) to maintain the ends (18, 19; 46, 47) of the tubular element (17; 44) in sealing engagement with the seal face member (15; 15*) and its associated component (10) respectively, and a divergent, axially compliant, intermediate portion (24; 32; 43) of the reinforcing means (21; 29; 40) providing torsional reinforcement.

2. A mechanical face seal according to Claim 1 characterised in that the reinforcing means (21; 29; 40) is a single element.

3. A mechanical face seal according to Claim 1 or 2 characterised in that radial reinforcement adjacent each end (18, 19; 46, 47) of the bellows unit (16) is provided by reinforcing formations (22, 23; 30, 31; 41, 42) of substantially plain cylindrical configuration.

4. A mechanical face seal according to any one of Claims 1 to 3 characterised in that the reinforcing means (21) comprises a helically wound spring element.

5. A mechanical face seal acccording to Claim 4 characterised in that the radial reinforcing portions (22, 23) of the spring element (21) are of substantially plain cylindrical configuration and adjacent turns of these portions abut one another.

6. A mechanical face seal according to Claims 4 or 5 characterised in that the intermediate portion (24) of the reinforcing means (21) is provided by a plurality of increasing diameter axially spaced turns.

7. A mechanical face seal according to any one of Claims 4 to 6 characterised in that the helically wound spring element (21) is wound so that any torsional load applied thereto due to a reaction of the sealing face of the second seal face member (15) against that of the first seal face member (12), will tend to tighten the turns defining the radial reinforcing elements (22, 23) against the second seal face member (15) and associated component (10).

8. A mechanical face seal according to any one of Claims 1 to 3 characterised in that the reinforcing means (29) comprises a pair of ring formations (30, 31) interconnected by a series of angularly spaced axially extending spokes (32), said spokes (32) defining at least one divergent portion.

9. A mechanical face seal according to Claim 8 characterised in that the reinforcing means (29) is formed from a resilient plastics material.

10. A mechanical face seal according to any one of Claims 1 to 3 characterised in that the reinforcing means is formed from shaped tubular elements made of metal foil or woven metal braid.

11. A mechanical face seal according to any one of the preceding claims characterised in that the intermediate portion of the reinforcing means defines one or more convolutions.

12. A mechanical face seal according to any one of the preceding claims characterised in that the reinforcing means (21, 29) is embedded in the elastomeric tubular element (17).

13. A mechanical face seal according to any one of Claims 1 to 3 characterised in that the reinforcing means (40) comprises a pair of annular formations (41, 42) interconnected by a series of axially extending angularly spaced flat strips, the reinforcing means (40) being mounted externally of the tubular element, one annular formation (41) of the reinforcing means (40) engaging an end portion (46) of the tubular element (44) and forcing it into sealing and driving engagement with the associated component (10), the seal face member (15) being mounted in the other annular formation (42) with the other end portion (47) of the tubular element (44) interposed between annular formation (42) and the seal face member (15'), said other end portion (47) of the tubular element (44) being under compression so as to provide a seal and driving connection between the seal face member (15) and reinforcing means (40).

14. A mechanical face seal according to any one of the preceding claims characterised in that the intermediate portion (24; 32; 43) of the reinforcing means (21; 29; 40) is made of resilient material and in operation is held in compression to bias the seal face members (12, 15; 15*) into sealing engagement.