GB2264986A

GB2264986A - Ring seal

Info

Publication number: GB2264986A
Application number: GB9204983A
Authority: GB
Inventors: Alan Henry Organ
Original assignee: Dowty Seals Ltd
Current assignee: Dowty Seals Ltd
Priority date: 1992-03-07
Filing date: 1992-03-07
Publication date: 1993-09-15
Anticipated expiration: 2012-03-07
Also published as: GB2264986B; GB9204983D0

Abstract

A ring seal comprises a ring 1 of elastomeric material protected by a layer of PTFE. The outer diameters of the ring are trimmed by a cutting tool to expose a peripheral sealing contact ring 8 between two supportive shoulders 9 and 10 of PTFE. The exposed elastomeric material 8 provides an efficient sealing contact whilst the less resilient PTFE shoulders 9 and 10 prevent distortion of the elastomeric material. The shoulders also serve to wipe a member against which they seal to resist leakage. The seal is produced by pre-forming two semicircular sectioned PTFE shells. pressing them into intimate contact with the elastomeric ring and bonding in a vulcanising process. <IMAGE>

Description

RING SEAL This invention relates to a ring seal, particularly, but not exclusively, an 'O' ring seal.

It is well known in sealing technology that polytetrafluoroethylene (PTFE) is a material having low friction qualities and good chemical resistance. Because of its good chemical resistance, PTFE has been used to form an outer protective cover on rubber sealing members such as heat exchanger gaskets. The PTFE protects the rubber against chemical attack but is substantially non-resilient compared with the rubber. It is the rubber core which acts as the energising member to maintain the sealing pressure at the interface between the PTFE cover and the members being sealed. The performance of the seal is therefore dependent on the properties of the PTFE at the interface, which may not be adequate for all applications, especially in dynamic applications where PTFE is not sufficiently conformable to restrict fluid film leakage.

According to the invention, there is provided a ring seal comprising a ring of elastomeric material covered by an outer layer of environmentally resistant material except in the region of the inner and/or outer diameter of the ring where the elastomeric material is exposed so as to provide an annular sealing contact area.

Because the elastomeric material rather than the environmentally resistant material forms the major sealing contact area, a more efficient seal is obtained. However, because the elastomeric material is only exposed at the sealing contact area, it is protected elsewhere by the environmentally resistant cover. The environmentally resistant material may be resistant to chemicals or heat present in the environment in which it is used.

Advantageously, the environmentally resistant material is more rigid than the elastomeric material so as to support the exposed portion of the latter, thereby to restrain it.

The thickness of the environmentally resistant material is selected to give the ring seal the required stiffness and resilience for any particular application.

Preferably, the sealing contact area engaging a member in use includes two supporting shoulders of environmentally resistant material either side of the exposed elastomeric material. This is preferred because the shoulders act as secondary sealing elements which are advantageously energised against the dynamic surface by the effort imparted in resistance to the buckling load on the radial section and on the energisation resulting from the systems pressure being transferred through the elastomer. A further advantage is that the shoulders act as wipers cleaning the member to be sealed during movement.

The preferred environmentally resistant material for the seal is PTFE since it is a material which has good chemical resistance, good heat resistance, low resilience and a low coefficient of friction.

According to a second aspect of the invention, there is provided a method of making a ring seal comprising forming a ring of elastomeric material, forming a layer of environmentally resistant material about the elastomeric material and exposing the elastomeric material about an inner or outer diameter of the seal to form a sealing contact area.

In one preferred embodiment, the elastomeric material is exposed by a cutting operation to form the sealing contact area comprising the exposed elastomeric material between two supportive shoulders of environmentally resistant material.

Preferably, the environmentally resistant material is provided as pre-forms which are assembled and bonded together with the elastomeric material by a vulcanisation process.

A specific embodiment of the invention will now be described, by way of example, with reference to the drawing in which: Figure 1 is a plan view of an '0' ring seal in accordance with the invention; Figure 2 is a side view of the seal shown in Figure 1; and Figures 3 & 4 illustrate a method of making a seal in accordance with the invention.

With reference to Figure 1, a seal in accordance with the invention comprises a ring 1 centred about an axis 2. The ring 1 comprises an elastomeric polymer material clad by layers 3 and 4 of PTFE. The elastomeric material is exposed at an inner diameter 6 and an outer diameter 7 to provide respective peripheral annular sealing contact areas, the outer sealing contact area 8 being shown in Figure 2.

As well as shielding the major faces of the seal from chemical attack, the PTFE forms supportive shoulders 9 and 10. The shoulders 9 and 10 being more rigid than the sealing contact area 8, resist forces acting to deflect the elastomeric material and also act to form a secondary seal themselves.

Further, the shoulders 9 and 10 serve to wipe a member against which they seal to resist leakage.

The sealing contact area 8 and the shoulders 9 and 10 form an edge which is parallel to the axis 2 of the ring 1.

The seal is produced by pre-forming two semicircular sectioned PTFE shells 11 and 12 and placing them either side of a circular sectioned elastomer ring 13 as shown in Figure 3. The shells 11 and 12 are then pressed into intimate contact with the elastomer ring 13 and bonded in a vulcanising process by application of pressure and heat. The vulcanised assembly is shown in Figure 4 as a cross-sectional view.

To expose the elastomeric material a trimming operation is carried out in which a cutting tool cuts along the dotted lines in Figure 4 to produce the edge comprising the shoulders 9 and 10 and the inner and outer sealing contact areas. The degree of exposure of the elastomeric element can be varied depending on the degree of squeeze and the requirement of the application.

A comparative test of two PTFE encapsulated '0' ring in accordance with the invention with two existing '0' rings was carried out.

Test Procedure and Results Test 1 The seals were put under a sequenced test cycle in 5 stages consisting of: Stage 1: 4000 cycles at room temperature Stage 2: 2000 cycles at 500C Stage 3: 2000 cycles at 1000C Stage 4: 600 cycles at -200C Stage 5: 600 cycles at -400C at a pressure of 68.9 bar using fluid DTD 585.

PTFE encapsulated '0' rings No leakage from seal 1, seal 2 had 3 cc of recorded leakage, which occurred at the end of the 3rd stage.

Existing '0' rings Steady leakage from both seals until stage 5. The total leakage from seal 1 was 17 cc, with 41 cc recorded from seal 2.

Test 2 The same procedure as test 2 except under a pressure of 137.6 bar.

PTFE encapsulated '0' rings No leakage from seal 1, seal 2 had 4 cc of leakage after stage 1, which increased to 10 cc after stage 3.

Existing '0' rings Steady leakage from both seals until the end of the test. The total leakage from seal 1 was 14 cc, with 61 cc recorded from seal 2.

Test 3 This was a repeat of test 2.

PTFE encapsulated '0' rings No leakage from seal 1, seal 2 had 6 cc of leakage after stage 1, which increased to 11 cc after stage 3.

Existing '0' rings Steady leakage from both seals until stage 5. The total leakage from seal 1 was 8 cc, with 53 cc recorded from seal 2.

Conclusions In general the sealing performance of the two PTFE encapsulated '0' rings was better than the two existing '0' rings.

When put under a 5 stage sequenced test cycle at temperatures of room, 500C, 1000C, -200C and -400C at pressures of 68.9 bar and 137.6 bar, there was only slight leakage from seal 2 of the PTFE encapsulated '0' rings with none from seal 1, in contrast to the steady leakage from both of the existing '0' rings.

Claims

1. A ring seal comprising a ring of elastomeric material covered by an outer layer of environmentally resistant material except in the region of the inner and/or outer diameter of the ring where the elastomeric material is exposed so as to provide an annular sealing contact area.

2. A seal as claimed in claim 1, wherein the environmentally resistant material is more rigid than the elastomeric material so as to support the exposed portion of the latter, thereby to restrain it.

3. A seal as claimed in claim 1 or 2, wherein the sealing contact area engaging a member in use includes two supporting shoulders of environmentally resistant material either side of the exposed elastomeric material.

4. A seal as claimed in claim 3, wherein the sealing contact area is substantially parallel to the axis.

5. A seal as claimed in any preceding claim, wherein the environmentally resistant material is polytetrafluoroethylene.

6. A ring seal substantially as hereinbefore described with reference to and as illustrated by Figures 1 and 2 of the drawing.

7. A method of making a ring seal comprising forming a ring of elastomeric material, forming a layer of environmentally resistant material about the elastomeric material and exposing the elastomeric material about an inner or outer diameter of the seal to form a sealing contact area.

8. A method as claimed in any preceding claim, wherein the elastomeric material is exposed by a cutting operation to form a defining edge comprising the exposed elastomeric material between two supportive shoulders of environmentally resistant material.

9. A method as claimed in any preceding claim wherein the environmentally resistant material and the elastomeric material are provided as preforms which are assembled and bonded together by a vulcanisation process.

10. A method of making a ring seal substantially as hereinbefore described with reference to and as illustrated by Figures 3 and 4 of the accompanying drawing.