GB2029518A

GB2029518A - Seals

Info

Publication number: GB2029518A
Application number: GB7928355A
Authority: GB
Original assignee: Crane Packing Ltd
Current assignee: Crane Packing Ltd
Priority date: 1978-05-25
Filing date: 1979-08-15
Publication date: 1980-03-19
Also published as: GB2029518B

Abstract

In a rotary mechanical face seal a seat 12 is made of hard material, difficult to machine, such as sintered silicon carbide or tungsten carbide, by arranging that only the rubbing face is machined and the remaining surfaces are left rough, the seat being mounted by means of a graphite backing ring 13 which can be of moulded-on expanded graphite powder or tape. It can be sealed to its associated components by a wedge ring 14, also of moulded or compacted graphite, bearing against a rough unmachined face of the seat. <IMAGE>

Description

SPECIFICATION Rotary mechanical face seals This invention relates to rotary mechanical face seals, such as are used primarily for sealing rotating shafts, for example of pumps or mixing vessels, into housings. The stationary seat is usually sealed into the housing by one of two methods; in one of these the seat has an outer portion clamped between a shoulder on the housing (with the interposition of a gasket) and a shoulder on a clamping ring secured to the housing. In addition to the lapped rubbing face engaged by the rotating seal face member this requires at least four further accurately machined surfaces to be formed on the seat member.

In an alternative known construction the seat is of simple rectangular cross-section and is pushed into a counterbore in the mounting ring, being sealed into it by an elastomeric 0ring, but it still requires at least two accurately machined surfaces in addition to the lapped rubbing face.

As new and improved materials become available for seats, such as tungsten carbide and, more recently, silicon carbide, both in sintered form, it is necessary to keep the geometric form as simple as possible because of the difficulty of shaping these materials.

Also it is desirable to use them if possible in the "as-sintered" state because of the high cost and difficulty of machining them, involving the use of diamond grinding. This puts the clamped version virtually out of the question and even the alternative version described above is of limited use unless a way can be found of avoiding the need to machine the surfaces other than the lapped face.

According to the invention, therefore we propose that a rotary mechanical face seal for a pair of relatively rotatable components should comprise a seal face member and a seat, each associated with a respective one of the components and urged axially into mutual face-to-face rubbing contact and the seat should be an annular body of sintered carbide or other hard material having its rubbing face machined but having at least one other surface left rough, the rough surface having formed thereon a layer of a graphite by which the seat is adapted to be mounted in that component with which it is associated.

Also according to the invention there is proposed a seat for a rotary mechanical face seal for a pair of relatively rotatable components, comprising an annular body of sintered carbide or other hard material, having a machined rubbing face for engagement with a rubbing face of second seal face member and at least one other surface left rough, the rough surface having a layer of graphite formed thereon.

The invention will now be further described by way of example with reference to the accompanying drawings, in which.

Figure 1 is a diagrammatic cross-section through an example of the first of the two known forms of seal mounting mentioned above; Figure 2 is a similar section through the alternative known form mentioned above; Figure 3 shows a section through a ringshaped seat for use in the manner according to the invention; Figure 4 shows the seat of Fig. 3 with a backing ring moulded onto it; Figure 5 shows a separate reinforced seal ing ring that can be used in conjunction with the ring of Figs. 3 and 4; Figure 6 illustrates sections through adaptor rings suitable for use in mounting the sealing rings of Figs. 4 and 5; Figure 7 is a section through an assembled seal employing the components of Figs. 4, 5 and 6; and Figure 8 is a section similar to Fig. 7 but showing an alternative form of assembled seal embodying the invention.

Referring first to Fig. 1, a typical known rotary mechanical face seal assembly for sealing a shaft 1 into a housing 2 comprises a seal face member 3 rotating with, and sealed to, the shaft 1 and urged axially, by means not shown, into face-to-face rubbing contact with a stationary seat 4 mounted in the housing. In the example shown, where the member 3 may for example be of carbon, the seat 4 is of a hard material and is clamped between a shoulder 5 on the housing 2 (with the interposition of a gasket 6) and a shoulder 7 on a clamping ring 8 secured to the housing by studs 9.Obviously the rubbing face of the seat, engaged by the seal face member 3, has to be machined, and is indeed lapped to a very high degree of surface finish and flatness, but in addition four other surfaces, shown at A, B, C and D, have to be accurately machined to fit the co-operating surfaces on the housing 2 and clamping ring 8.

In the alternative known version shown in Fig. 2, where the same reference numberals as in Fig. 1 have been used where applicable, a seat 4' of simple rectangular cross-section fits in a counter bore 10 in a clamping ring 8', being sealed into it by an elastomeric 0ring 11, but it still requires at least two machined surfaces E and F in addition to its lapped rubbing face.

By virtue of the invention we are able to use a seat of simple rectangular section, shown at 12 in Fig. 3, which furthermore has only one lapped and machined face, the other three faces being left rough. This allows the seat to be manufactured economically from a very hard material, difficult to machine, for example sintered tungsten carbide or sintered silicon carbide. Moulded onto the opposite end of the ring-shaped seat from the lapped face is a backing ring 1 3 of graphite powder, as shown in Fig. 4; this backing ring is able to accommodate any irregularities or eccentricity in the rough surface of the seat but can be moulded to form smooth external radial and cylindrical surfaces, accurately parallel to and perpendicular to the lapped face.It will be seen that the moulded backing ring extends over substantially the whole over the end face and part of the external cylindrical surface of the seat 12.

The graphite may be in the form of expanded graphite moulded onto the seat or it could be in the form of compacted graphite and may include fillers and binders. It may be applied in the form of a tape, moulded or compacted to the required shape. The graphite has a certain degree of resilience and flexibility and its functions, at least in the embodiment shown, are twofold. First it provides an accurate and smooth external surface or surfaces allowing the seat to be accurately positioned, in particular radially, and secondly it acts as a flexible cushion at the rear end of the seat, accommodating surface irregularities in the housing as well as in the seat.

The graphite-backed seat of Fig. 4 can be used directly as a replacement for a seat of the kind shown in Fig. 2, with the O-ring 11 engaging the outer cylindrical surface of the backing ring 13, or it can be used with a wedge-type sealing ring, in particular a metalreinforced ring such as that shown in Fig. 5.

Here a wedge-shaped ring 14 is formed by moulding graphite powder under pressure onto a channel-section metal reinforcing ring 15.

Fig. 7 shows the seat of Fig. 4 installed with the use of the sealing ring of Fig. 5. To accommodate the wedge-shaped sealing ring 14 an adaptor ring 1 6 is inserted between the housing 2 and clamping ring 8", these two last-mentioned rings having the internal profiles illustrated in Fig. 6. Although the external cylindrical surface of the seat 1 2 is in the rough "as-sintered" condition, the moulded graphite ring 14 is able to form an adequate seal onto it by virtue of the wedging action when the clamping ring 8" is tightened.

In a modified layout shown in Fig. 8 a sintered seat 12' has an expanded graphite sealing ring 13' forming a cushion only over its end face, opposite to the lapped face, and a wedge-shaped metal-reinforced sealing ring 14, identical with that of Fig. 5, but facing the other way, is urged axially by a ring of hairpin springs 1 7 of the kind disclosed in Patent Specification No. 866 302, held in place by their own resilience against an internal shoulder 18 in a clamping ring 8"'. The pressure of the fluid against which the seal is acting assists the springs in wedging the ring 14 between the clamping ring 8"' and the seat 12', ensuring a fluid-tight seal at this point despite the fact that the outer cylindrical surface of the seat 12' is in its rough assintered state.

In this version the graphite performs only the second of the two functions mentioned earlier, the first (that of accurately locating the seat, especially in a radial direction) being performed by the wedging action in the ring 14.

It will be appreciated that the use of the flexible graphite ring 1 3 or 13' makes it practical to employ, for the seat, a sintered body of simple shape with the minimum of machining and hence to take advantage of materials which would be out of the question on grounds of cost if one were to attempt to use them directly as substitutes for steel or similar seats.

Claims

1. A rotary mechanical face seal for a pair of relatively rotatable components comprising a seal face member and a seat, each associated with a respective one of the components and being urged axially into mutual face-toface rubbing contact and in which the seat is an annular body of sintered carbide or other hard material having its rubbing face machined but having at least one other surface left rough, the rough surface having formed thereon a layer of graphite by which the seat is adapted to be mounted in that component with which it is associated.

2. A rotary mechanical face seal according to claim 1 in which the grahite layer is formed on the rough surface of the seat by moulding graphite powder or tape directly onto that surface.

3. A rotary mechanical face seal according to claim 1 or claim 2 in which the seat is of rectangular cross-section and the graphite body is on the face opposite the rubbing face.

4. A rotary mechanical face seal according to any one of claims 1 to 3 in which the seat is sealed to its associated component by a wedge-section annular seal bearing against a rough surface of the seat.

5. A rotary mechanical face seal according to claim 4 in which the wedge-section annular seal is made of compacted graphite.

6. A rotary mechanical face seal according to any one of claims 1 to 5 in which the only face of the seat that is machined is the rubbing face.

7. A rotary mechanical face seal according to any one of claims 1 to 6 in which the seat is made of sintered tungsten carbide.

8. A rotary mechanical face seal according to any one of claims 1 to 6 in which the seat is made of sintered silicon carbide.

9. A seat for a rotary mechanical face seal for a pair of relatively rotatable components, comprising an annular body of sintered carbide or other hard material, having a machined rubbing face for engagement with a rubbing face of second seal face member and at least one other surface left rough, the rough surface having a layer of graphite formed thereon.

10. A seat according to claim 9 in which the graphite layer is formed on the rough surface by moulding graphite powder or tape directly onto that surface.

11. A seat according to claim 9 or claim 10 which is of rectangular cross-section and in which the layer of graphite is on the face opposite the rubbing face.

1 2. A seat according to any one of claims 9 to 11 of which the only machined face is the rubbing face.

1 3. A seat according to any one of claims 9 to 1 2 made of sintered tungsten carbide.

14. A seat according to any one of claims 9 to 1 2 made of sintered silicon carbide.

1 5. A rotary mechanical face seal according to claim 1, substantially as described with reference to Fig. 7 of the accompanying drawings.

16. A rotary mechanical face seal according to claim 1, substantially as described with reference to Fig. 8 of the accompanying drawings.

1 7. A seat for a rotary mechanical face seal for a pair of relatively rotatable components, substantially as described with reference to Figs. 4 to 7 of the accompanying drawings.

1 8. A seat for a rotary mechanical face seal for a pair of relatively rotatable components, substantially as described with reference to Fig. 8 of the accompanying drawings.