GB2083575A

GB2083575A - Seals

Info

Publication number: GB2083575A
Application number: GB8125312A
Authority: GB
Original assignee: General Connectors Corp
Current assignee: Meggitt Simi Valley Inc
Priority date: 1980-08-26
Filing date: 1981-08-19
Publication date: 1982-03-24
Also published as: GB2083575B; FR2489463B1; FR2489463A1

Abstract

A rubber ring-shaped seal is formed by inserting one or more layers 14, 16 of fiberglass cloth against a surface in the mold cavity of a suitable ring-shaped mold. A tubular ring- shaped insert 18 formed from semi- cured silicone rubber with a garter or helical coil spring 22 inside the bore of the tubular insert, is placed in the mold cavity over the fiberglass cloth. The tubular insert is sized so the coil spring inside causes the insert to contract and exert a compressive force on the fiberglass cloth. This holds the cloth against the surface in the mold cavity. A ring of uncured silicone rubber is placed in the mold cavity and the mold cavity is then closed and subjected to heat to cure the rubber. The resulting seal has fiberglass cloth covering a surface of the seal with the helical coil spring inside the seal held in spaced relationship from the inner surface of the fiberglass cloth. <IMAGE>

Description

SPECIFICATION Seal Rubber seals, particularly those used in aircraft connectors and ducts, tend to leak when cold, due to variations between the thermal coefficients of the material composing the seal and the metal ducts. This leakage tends to increase after a period of use, particularly when the seal is used at elevated temperatures because the rubber forming the seal "sets" and becomes less elastic.

One way to prevent this leakage is to provide the seal with a garter spring under tension which embraces the seal. With this arrangement, when the seal is on a duct or connector, the spring exerts a compressive or radially inwardly directed force on the seal, causing the seal to make a sealing engagement with a duct or connector at low temperatures and even after the rubber in the seal has set and become less resilient.

Elastomeric seals which have a spring under tension formed therein are typically formed from a silicone impregnated rubber with one or more laminations of silicone impregnated fiberglass cloth molded to and covering at least the surface of the seai which makes a sealing engagement with a surface on a connector or duct. This cloth covering is used because it is resistant to abrasion so that the life of the seal is prolonged. This is described in the U.S. patents to Kramer, No.

3,918,726, and Greenwald, No. 3,698,727.

Heretofore, however, when o-ring type seals of this kind are being molded, garter or ring shaped coil springs under tension were inserted in the ring shaped cavity of the mold. These springs were sized so they contracted until they pressed against the inner surface of the fiberglass cloth lining the mold cavity. Then the mold cavity was filled with a suitable amount of uncured rubber and the mold was then subjected to heat to cure the rubber and form the seal. With this arrangement, the springs inside the seal abutted the inner surface of the fiberglass cloth. This is shown in the patent to Greenwald, No.

3,698,727. As a consequence, when the seals were used in aircraft, vibration caused the springs to rub against the inner surface of the fiberglass cloth, wearing it through in a comparatively short time, and destroying the surface that makes a sealing engagement with the work, so that the seal had to be replaced.

Since seals in aircraft are positioned at various locations along the ducts in the aircraft, they are often mounted in locations which are hard to get at and which require the disassembly of many aircraft parts to reach when the seals have been replaced. This increases the down-time for the aircraft which greatly increases the cost of aircraft operation.

It is apparent that if the useful life of seals could be increased, a disproportionately large savings in the cost of the aircraft operation would result.

One way to increase the useful life of such seals is to prevent the spring mounted inside the seal from rubbing against the inner surface of the fiberglass cloth. If the spring, although under tension, could be held away from the inner surface of the cloth during the molding process, then when the rubber was cured, the spring would be embedded in the seal, with a thickness of rubber between the spring and the inner surface of the fiberglass cloth. This would greatly prolong the useful life of the seal because, before the spring could rub against and through the fiberglass cloth, it would first have to rub through this thickness of rubber.

Heretofore, as exemplified by the U.S. patent to Weber, No. 3,406,979, efforts were made to solve the problem of centering a spring inside a seal.

The Weber approach had a number of disadvantages. First of all, it required expensive hydraulic equipment. Secondly, it was timeconsuming because it required two separate molding steps and it required the seal half sections to be performed. Thirdly, "flash" formed on the work engaging surfaces of the Weber seal.

"Flash" is that part of the elastomeric material which forms at the junction of the molds and in this instance it appears as irregular clumps of rubber. This "flash" had to be removed in order to form the sealing surface, but it was time consuming and costly to do this. In addition, the work engaging surface in the Weber seal was not surrounded by fiberglass cloth so it did have a sufficiently long useful life.

In accordance with one aspect of the present invention there is provided a ring-shaped seal comprising an inner work-engaging surface formed from at least one layer of material, a resilient ring-shaped insert, and a ring-shaped spring so arranged that at least a part of the insert lies between the spring and the layer or layers of material, whereby, when the seal is mounted on a duct, the spring maintains the work-engaging surface in sealing engagement with the duct.

In accordance with a further aspect of the present invention there is provided a method of constructing a seal comprising forming a tube of semi-cured silicon impregnated rubber, inserting a coil spring in the tube, securing the ends of the spring together to form a semi-cured ring-shaped tubular insert, laying a ring of silicon impregnated fiberglass cloth in a ring-shaped mold cavity in a mold, positioning the ring-shaped insert over the fiberglass cloth, laying a ring of uncured silicone impregnated rubber in the mold cavity along with the semi-cured ring-shaped insert and the fiberglass cloth, closing the mold, and heating the mold to cure the semi-cured rubber insert and the ring of uncured rubber to form the seal.

In the accompanying drawings, by way of example only Figure 1 is a plan view of the seal constructed according to the principles of this invention.

Figure 2 is a sectional view taken on the line 2-2 of Figure 1.

Figure 3 is an enlarged view of the region surrounded by the circular arrow 3-3 in Figure 1.

Figure 4 is an elevational view of the ringshaped tubular insert with a coil spring inserted therein.

Figure 5 is a cross-ectional view of the tubular insert with the coil spring in the tubular bore.

Figure 6 is a cross-sectional view of a modified insert with the coil spring mounted thereon.

Figure 7 discloses a stack of mold sections used to simultaneously form a number of seals.

Figure 8 is an exploded view of the mold sections shown in Figure 8.

Figure 9 illustrates a first step in the construction of a seal.

Figure 10 illustrates a second step in the construction of a seal.

Figure 11 illustrates a third step in the construction of a seal.

Figure 12 illustrates a fourth step in the construction of a seal.

Figure 13 discloses a ring-shaped seal, Jshaped in cross-section, with an elastomeric insert constructed according to the principles of this invention.

Figure 14 discloses an enlarged portion of double seal connectors such as those shown in Figures 15 and 16, wherein the inner ring shaped seal is constructed like the seal shown in Figure 13, and the outer seal is constructed like the seal shown in Figure 2.

Figure 15 discloses an aligned double seal restrained connector utilizing the double seal structure shown in Figure 14.

Figure 16 discloses an offset double seal connector utilizing the double seal structure shown in Figure 14.

Figure 17 discloses an offset single seal restrained connector with the seal shown in Figure 2.

Figure 18 discloses a conduit arrangement employing a single seal bulkhead connector in combination with a restrained connector with the seals shown in Figure 2.

Figure 19 is a perspective view of a connector clamp used in combination with the restrained connector of Figure 18.

Figure 20 discloses a double seal bulkhead connector wherein the inner seal is shown in Figure 13 and the outer seal is shown in Figure 2.

Referring now to Figure 1 of the drawings, a ring-shaped O-ring type seal indicated generally by the reference numeral 10 is formed from an elastomeric material such as silicone impregnated rubber. Referring to Figure 2, the seal 10 has a surface 12 which is covered by two layers or laminations of silicon impregnated fiberglass cloth 14 and 16 to form a continuous work engaging surface which is shaped to make a sealing engagement with a surface on a connector or duct. A ring shaped insert 18 comprising an elastomeric tube having a bore 20 and formed from silicone impregnated rubber is inside the seal and a garter or helical ring shaped coil spring 22 is inside the bore.

The tubular insert 18 is formed by a conventional extruding machine and is cut to the desired length with the rubber in a semi-cured state. Next, the coil spring 22 also cut to the desired length is inserted in the bore 20, see Figure 5. The ends 24 and 26 of the coil spring are shaped so that they can screw into each other to form a ring in a manner well known in the art, see Figure 3. In this way, after the spring 22 is inserted in the bore 20 in the tubing and the ends of the springs are secured together, the ring shaped insert 18 is produced, see Figure 4.

To construct the seal, ring-shaped layers 12 and 14 of fiberglass cloth are inserted in the cavity 28 in mold section 30, see Figure 9. Then the ring shaped insert 18 is inserted in the ring shaped mold cavity 28 in mold section 30 over the cloth, see Figure 10. When the insert 18 is inserted in the mold, the rubber compositing it is in a semi-cured state. This makes the tubular rubber insert strong enough to hold the coil spring 22 away from the inner surface of the fiberglass cloth during the molding process. The diameter of the ring-shaped tubular portions 18 and coil spring 22 in an unstressed condition is smaller than the diameter of the mold cavity. This causes the garter spring 22 in the insert 18 to be under tension when it is mounted in the mold cavity so that it exerts a compressive force on the fiberglass cloth layers 12 and 14 in the mold, see Figure 10.

This gives the insert 18 with the spring inside, the added function of holding the ring-shaped fiberglass cloth in place in the mold cavity 28 during the molding process.

Next, a preferably ring shaped piece of uncured silicone rubber 32 is inserted in the mold cavity 28, see Figure 11. After this, the mold cavity 28 is closed off by mold section 46 and by the mold closing surface 58 on mold section 30, or by surface 64 on closure member 60, see Figures 7, 8 and 12.

Then, the mold is inserted in an oven long enough to cure the rubber. While this is happening, the uncured ring of silicone rubber 32 in mold cavity 28 becomes cured and expands to fill the mold cavity and bonds itself to the insert 1 8 and to the inner surface of the fiberglass cloth.

The silicon impregnated rubber bonds itself to the fiberglass cloth easily and strongly because, the fiberglass cloth itself is impregnated with silicon impregnated rubber. In addition, the semi-cured rubber insert 18 with the spring 22 inside becomes cured and bonds itself to the ring 32 of uncured rubber and to the helical coil spring 22 to form the seal.

As stated above, the semi-cured insert 18 serves as a spacer to hold the coil spring 22 away from the fiberglass cloth during the molding process so that in the finished seal, the spring is embedded in the seal and held in spaced relationship to the inner surface of the fiberglass cloth, see Figure 2. It is noted that other kinds and methods of forming an elastomeric seal having silicone impregnated fiberglass cloth covering the work engaging surface of the seal and with a spring inside the seal held in spaced relationship to the fiberglass cloth are contemplated within the purview of this invention. This is suggested in the modifications shown in Figures 13 and 14 described below.

As seen in Figures 2, 13 and 14, in the finished seal the coil spring 22 is held away from the inner surface 40 of the fiberglass layer 16 by the thickness of the tubular insert 18. Tension in the spring 22 inside the finished seal, causes the seal to contract on and make a sealing engagement with a surface of a metal duct or connector when cold and even after the rubber in the seal has hardened. Of course, aircraft vibration will cause the coil spring 22 in the seal to gradually wear away the silicone impregnated rubber between it and the inner surface 40 of the fiberglass layer 16.However, this will take some time and, finally, when the coil spring has worn away enough rubber so it reaches the inner surface 40 of the fiberglass cloth 14, the useful life remaining in the seal would still be where it is in present seals where the coil spring rubs against the inner surface of the fiberglass cloth from the beginning of its use.

To vary the life of the seal, it would only be necessary to extrude tubular insert 18 with walls which have a different thickness. Alternatively, the composition of the insert and the cloth layers 12 and 14 could be varied to change the ability of the seal to withstand abrasion and rubbing in accordance with special requirements. As will become apparent below, the method of molding the seal described herein is particularly suited for making adjustments in the useful life of the seal, because such adjustments would not involve any important changes in the method of forming the seal.

To this point, the insert 18 is shown in the form of a tube, see Figure 5. However, the insert can have other forms. For example, the insert 18' shown in Figure 6, could be extruded with a spring receiving groove 19 formed therein. Then a coil spring 22 could be inserted in the groove 19, see Figure 6. With this arrangement, after the uncured material 32 in the mold cavity 28 is heated and cured, it would expand to fill the groove 19 in the insert 18' so that the final result would not be much different than the result obtained by using the insert 18 shown in Figure 5.

In both insert 18 and 18' in assembled relation, at least a part of the ring shaped insert is between the garter spring 22 and the inner surface of the fiber glass cloth.

The molds used in the construction of the seal can be used to form a number of seals at the same time. To do this, a base member 42 is provided. An upright, centrally disposed pole or support member 44 extends up from the base and through support receiving bores 45 formed in the molds.

Each mold is formed in two parts, although it is possible to provide molds formed from a single piece. The first part consists of mold section 30.

This section has a generally cylindrical base portion 31 and a centrally disposed cylindrical portion 33 extending up from the base portion.

The upwardly extending cylindrical portion is smaller in diameter than the base portion 31, in this particular embodiment, although other configurations where the opposite is true are contemplated. The periphery 35 of the upwardly extending cylindrical portion 33 is generally concave and in this embodiment serves to completely shape the inner surface of the seal which will ultimately engage a sealing surface on a duct or connector. This arrangement is important because the entire inner work contacting surface 11 of the seal 10 is formed from this surface on mold section 30. This prevents the formation of "flash" on surface 11, of the seal, See Figure 2.

The second part of the mold consists of a ring shaped mold section 46 including a bore 47 and a counter bore 48. Sections 30 and 46 in assembled relation form one complete mold for one seal. In order to assemble mold sections 30 and 46 together, mold section 30 is provided with positioning surfaces 54 and 56 which are disposed on the periphery of a circle, see Figure 8.

Surface 54 in addition to functioning as a positioning surface for mold section 46, also serves as the base of the mold cavity, see Figure 7.

As seen in Figure 12, mold section 46 rests on mold section 30 and cooperates with it to form the mold cavity. This is achieved by counter bore 48, see Figure 8. The counter bore of mold section 46 has locating surfaces 50 and 52 which are on the diameter of a circle and bear against surfaces 54 and 56 of the mold section 30 and embrace them to hold the sections 30 and 46 together. In stacked relationship, the lower surface 58 on one mold section 30 rests on the upper surface 59 on mold section 46 and is shaped so it closes the mold cavity 28. See Figure 7. The periphery 49 of the bore 47 in mold section 46 is, in this embodiment, concave, and completely defines the entire outer work contacting surface 1 3 of the seal remote from the inner work contacting the surface 11, see Figure 7. Consequently, "flash" cannot form on the outer work contacting surface 13.In assembled relation with mold section 46 resting on mold section 30, the concave sufaces 35 and 49 face each other defining the peripheral limits of the mold cavity 28.

A number of molds, each comprising a mold section 46 and a mold section 30 can be stacked on the upright support 44 so a number of seals can be formed at the same time. A closure member 60 having a centrally disposed support receiving bore 62 is provided for the top of the stack of molds, see Figure 8. This section has a lower surface 64 which is shaped like surface 58 on mold section 30 and closes off the top mold cavity in the stack of mold sections.

To this point, the principles of this invention have been applied to the ring-shaped O-ring type seal shown in Figure 1. However, they can also be applied to other kinds of seals and the connectors shown in Figures 13 to 20.

Seal 70 shown in Figure 13 is ring-shaped and generally channel shaped in cross section with leg portions 72 and 74 and a connecting web portion 76. The seal is formed from multiple laminations of silicone impregnated fiberglass cloth. This seal is designed to be used in a connector such as the connector shown in Figure 11 of the Greenwald Patent #3,698,727.

In Figure 14, leg portion 72 of seal 70 bears against the inturned flange of wall 102 in connector 90. This type of seal depends on temperature and the internal pressure in the duct or connector to deform the laminations of fiberglass cloth and force them into a sealing engagement with surfaces on the connector or duct.

Insert 18 or 18' with the garter spring 22 in its bore 20 is mounted against the inner surface 78 of the web or semi-toroidal part 76 of the seal, and is sized so it exerts a compressive force on it.

This causes the outer work contacting surface 80 of the web portion 76 seal to make a better sealing engagement with seal engaging surfaces on a duct independent of temperature over a wide temperature range, see Figure 13 and 14.

It is apparent that the life of this kind of seal is greatly prolonged in comparison to prior seals of this kind because before spring 22 can reach and rub through the laminations 61 and 63 of the fiberglass cloth, it first has to rub through the thickness of the rubber or elastomer insert 1 8 or 18', which is between the spring 22 and the inner surface 78 of the web portion 76. This arrangement is like the structure shown in Figure 2 where the spring has to rub through the thickness of the rubber or elastomeric material in the insert which is between the spring 22 and the inner surface 40 of the fiberglass cloth.

If the seals constructed according to the principles of this invention are to be used in a particularly hot environment, in aircraft, where a seal failure could have very severe consequences, the connector 90 shown in Figure 15 is particularly useful. This connector is provided with three counterbores, 92. 94 and 96, see Figure 14.

In addition, an inwardly open channel shaped divider or seal retaining ring 98 is secured to the counterbore 92 of the end of the connector 90 by welding or any other suitable means.

The ring-shaped seal 10 shown in Figure 2 is mounted inside the channel 100 defined by the seal retaining ring 98. As seen, the seal is sized so a portion of the seal protrudes beyond the channel 100 for engagement with a seal engaging surface on a duct.

The seal retaining ring 98 includes an outer leg or flange 101, an inner leg or flange 102, and a connecting web portion 104, which is secured by welding or any suitable means to the inner surface of the counterbore 22. The inner leg or flange 102 of a seal retaining ring 98 serves as a divider separating the outer seal 10 from the inner seal 70 and provides an additional fire resistant protective surface.

Insert 18 or 18' mounted on seal 70, as shown in Figure 13, causes the seal to exert a radially inwardly directed force on the ducts 106 and 108 mounted on connector 90 as shown in Figure 1 5.

With this arrangement, as the web portion 76 of seal 70 hardens with use, the inwardly directed force exerted by the inserts 18 or 18' on seal 70 maintains a sealing engagement between the web portion 76 of the seal and the outer seal engaging surfaces of ducts 106 and 108.

As seen in Figures 14,15 and 1 6, the base 110 of the counterbored portion 96 is in spaced relation to the inner surface 11 2 of the leg 74 of seal 70. This is important because it permits nondestructive flexing of the legs 72 and 74 of the seal 70 when the end of the ducts 106 or 108 pivots inside connector 90. Without this arrangement, the inner seal would wear rapidly and failure could occur after a comparatively short time. The double seal connector shown in Figures 1 5, 1 6 and 17 provides an additional margin of safety because if the inner seal fails, the outer seal would prevent the hot gases from escaping.

As a further protection for the seals against very high duct temperatures and pressures, the ducts 106 and 108 include sleeves 112 and 114 which are secured by welding or any other suitable means to the ends of the ducts. The seal engaging surfaces of these sleeves are in spaced relationship to the outer surface 11 6 and 11 8 of the ducts defining an insulating air space 120 and 122 between the surfaces 116 and 118 of the ducts, and the seals 10 and 70, see Figure 15.

This also greatly extends the life of the seals because the temperature of the seals is thereby lessened.

The ducts 106 and 108 are provided with ringshaped radially outwardly extending collars 124 and 126 which embrace their outer surfaces 116 and 11 8 and are secured thereto by welding or any other suitable means. These collars are channel shaped in cross section as shown in Figure 15. A number of cables 128, in accordance with the strength required, are connected between the collars, in uniformly angularly spaced relationship around the axis of the collars to hold the ducts inside the connector 90 against high pressure gases inside them. The tightness of these cables can be adjusted by any suitable means mounted on the collars.

The seals 10 and 70 used with connector 68 can also be applied to offset connectors 130 as shown in Figure 16. The offset connectors are used to connect ducts or tubes in aircraft where the axes of these ducts are offset or misaligned from each other. As seen in Figure 16, the opposite ends of connector 130 are not in alignment with each other, but they are designed to be aligned with and receive ducts 132 and 134 as shown. The end portions of the offset connector 130 are like that shown in Figure 14.

Cylindrical sleeves 136 and 138 are secured by any suitable means to the outer surface of the ducts and the inner end of the sleeves are bent radially outwardly to define collars 140 and 142.

Restraining cables 144 are mounted on these collars in uniformly angularly spaced relationship around the axis of the ducts to hold the ducts inside the connector 130. Any suitable means, not shown can be provided to tighten these cables as required.

The offset connector 146 shown in Figure 17 is like that shown in Figure 16, except that it employs a single seal 10 at each end instead of the double seal arrangement shown in Figure 16.

Aircraft have many bulkheads through which ducts must pass. These often require the use of a bulkhead connector. As shown in Figure 18, the single seal bulkhead connector 148 is provided with a radially outwardly extending mounting flange 150 mounted at one end and secured by any suitable means to the outer surface of the inner end of the bulk head connector, see Figure 18. This mounting flange is secured to bulkhead 152 by any suitable means. The bulkhead 152 is provided with a bore 154 sized to permit a duct 156 to pass through. The inner end of the bulkhead connector 148 is sized to permit the entry of the duct. The bulkhead connector is provided with a radially inwardly open seal receiving channel 158 at its inner end. Seal 10 is mounted therein and is sized so it is in sealing engagement with the outer surface of the duct 1 56.The opposite end 160 of the bulkhead connector extends inside one end of a connector 162. This connector is provided with rib-like radially outwardly extending inwardly open seal receiving channels 163 and 165 at each end in which the seals 10 are mounted. Another duct, 164, is mounted in the opposite end of the connector 1 62. In order to hold the duct 164 and the end of the other end of the bulkhead connector 148 inside the connector 162 against the high pressure of the gases therein, a generally cylindrical split clamp ring 166 is mounted on the outer surfaces of the bulkhead connector 148 and the duct 164 and tightened thereon by bolt 168 and nut 170 shown in Figure 19. The clamp ring 166 is provided with three integrally attached claws 172 disposed in uniformly anularly spaced relationship around the periphery of the clamp ring. These claws fit over the radially outwardly extending heat radiating surface of the seal cooling and seal retaining channels 163 and 165 as shown in Figure 18. In this way, when the clamp rings are tightened on duct 164 and the bulkhead connector 198 with the claws 172 extending over the outer surface of the rib-like seal ring receiving channels 163 and 165, the bulkhead connector 148 and the duct 164 are held securely inside connector 162.

In some circumstances where special conditions of high temperature and aircraft vibrations require it, the bulkhead connector 170 shown in Figure 20 may be used. This connector is provided with inner and outer seals 70 and 10 mounted in the seal ring receiving channels 1 72 and 1 74. This portion of the double seal bulkhead connector would be shaped like the portion of the connector shown in Figure 14.

Claims

1. A ring-shaped seal comprising an inner work-engaging surface formed from at least one layer of material, a resilient ring-shaped insert, and a ring-shaped spring so arranged that at least a part of the insert lies between the spring and the layer or layers of material, whereby, when the seal is mounted on a duct, the spring maintains the work-engaging surface in sealing engagement with the duct.

2. A seal according to Claim 1 wherein the material is silicon impregnated fiberglass cloth and the ring-shaped insert is formed from silicon impregnated rubber.

3. A ring-shaped elastomeric seal comprising at least one layer of a reinforcing cloth-like material bonded to an inner surface of an elastomeric ring to form a work engaging surface, a tubular ring-shaped elastomeric insert, a garter spring mounted in the bore of the tubular insert so that the walls of the tubular insert are between the spring and the layer or layers of cloth-like material, whereby, when the seal is mounted on a duct, the spring exerts a compressive force which maintains the work-engaging surface in sealing engagement with the duct.

4. A seal according to Claim 3 wherein the material is silicon impregnated fiberglass cloth and the ring-shaped insert is formed from silicon impregnated rubber.

5. A ring-shaped elastomeric seal comprising at least one layer of a reinforcing cloth-like material bonded to an inner surface of an elastomeric ring to form a work engaging surface, a ring-shaped elastomeric insert concentric with the ring, a garter spring mounted in a retaining groove formed in the insert, the insert being positioned so that the elastomeric material comprising the insert lies between the spring and the layer of cloth-like material, whereby, when the seal is mounted on a duct, the spring exerts a compressive force which maintains the work engaging surface of the seal in sealing engagement with the duct.

6. A seal according to Claim 5 wherein the reinforcing material is silicon impregnated fiberglass cloth and the elastomeric material is silicon impregnated rubber.

7. A method of constructing a seal comprising forming a tube of semi-cured silicon impregnated rubber, inserting a coil spring in the tube, securing the ends of the spring together to form a semi cured ring-shaped tubular insert, laying a ring of silicon impregnated fiberglass cloth on a ring shaped mold cavity in a mold, positioning the ring-shaped insert over the fiberglass cloth, laying a ring of uncured silicone impregnated rubber in the mold cavity along with the semi-cured ring shaped insert and the fiberglass cloth, closing the mold, and heating the mold to cure the semi cured rubber insert and the ring of uncured rubber to form the seal.

8. An apparatus for simultaneously molding a plurality of seals, the apparatus comprising a plurality of molds, each mold having an upper surface and a lower surface, a ring-shaped cavity formed in the upper surface of each mold, each cavity having inner and outer concave surfaces facing each other and defining the inner and outer work engaging surfaces of a seal, a centrally disposed bore formed in each mold, a support rod extending upwardly from a base member through the aligned centrally disposed bores to form a stack of molds, the lower surfaces of all but the lowermost mold resting on the respective upper surfaces of the next mold in the stack and being shaped to close off the respective mold cavities in the upper surfaces of the respective molds.

9. A mold for a seal comprising first and second mold sections, the first mold section having a generally cylindrical portion extending upwards from a baso portion, the periphery of the cylindrical portion being shaped to define the entire inner work engaging surface of a seal and forming part of the walls of the mold cavity; the second mold section being generally ring-shaped with locating surfaces positioned to abut positioning surfaces located on the periphery of a circle on the first mold section when the second mold secthion is mounted on the first mold section to hold the first and second mold sections in proper relationship to each other; the walls of the bore in the second ring-shaped mold section being shaped to define the entire outer work engaging surface of the seal remote from the periphery of the cylindrical portion on the first mold section whereby, with the second section mounted on the first section, the periphery of the cylindrical portion faces the walls of the bore to define the peripheral limits of the mold cavity; and surfaces mounted over the upper and lower surfaces of the mold cavity for closing off the mold cavity.

10. A mold for a seal comprising first and second mold sections, the first mold section having a generally cylindrical portion extending upwards from a base portion, the periphery of the cylindrical portion being concave and forming a wall of the mold cavity; the second mold section being generally ring-shaped and including a bore and a counterbore with locating surfaces on the walls of the counterbore, adapted to embrace positioning surfaces located on the periphery of a circle on the first mold section when the second section rests on the first section, the walls of the bore of the second section being concave and defining another wall of the mold cavity whereby, with the second section resting on the first section, the concave surfaces on the first section face the concave surfaces on the second section to define the inner and outer work contacting surfaces of a seal formed in the mold cavity, and means on the upper and lower surfaces of the first and second mold sections for closing off the mold cavity.

11. A method of making a seal comprising steps of selecting a ring-shaped mold section which has a cylindrical base and a centrally disposed upwardly extending cylindrical portion on the base, where the cylindrical portion is smaller than the diameter of the base, the periphery of the cylindrical portion being concave, inserting at least one ring-shaped layer of fiberglass cloth against said concave periphery of the mold section where the diameter of the fiberglass cloth is generally equal to the diameter of the peripheral portion, so that the fiberglass cloth can lie against the concave periphery, inserting a ring-shaped insert over the cylindrical portion where said ring-shaped insert is formed from semi-cured silicone impregnated rubber, mounting a garter spring thereon so that there is a thickness of said insert between said spring and said fiberglass cloth, the diameter of said garter spring being slightly less than the diameter of said cylindrical portion so that the spring in the insert is under tension when the insert is placed over the fiberglass cloth in the mold section whereby the insert embraces the fiberglass cloth pressing it against the concave peripheral surfaces of the mold section, inserting a ring of uncured silicone impregnated rubber over the ring-shaped insert in the mold cavity, then closing the mold cavity with a suitably shaped mold section and applying heat to the mold to cure the rubber to form the seal.

12. A method making a plurality of seals according to Claim 11 furthercomprising varying the thickness of the insert between the spring and the fiberglass cloth for the respective seals.

13. A method of making a plurality of seals according to Claim 11 further comprising varying the abrasion resistance of the insert for the respective seals.

14. A method of making a seal comprising inserting at least one ring-shaped layer of silicone impregnated fiberglass cloth against a seal defining surface in a ring-shaped mold cavity in a seal mold; inserting in the mold cavity a ringshaped spacer formed from a material which bonds to silicon impregnated rubber and to a garter spring when heat is applied; mounting a garter spring on the ring-shaped spacer so that a thickness of the spacer is between the spring and the fiberglass cloth, the relative sizes of the ringshaped spacer and the spring being such that the spacer contracts against the fiberglass cloth and holds the fiberglass cloth against the seal defining surface in the mold cavity, the spacer also holding the spring in spaced relationship from the inner surface of the fiberglass cloth; inserting a ringshaped piece of uncured silicone impregnated rubber in said mold cavity; closing the mold cavity; and heating the mold to cure the rubber to form a ring-shaped seal with the silicon impregnated fiberglass cloth covering the sealing surface of the seal and with the garter spring embedded in the seal and held in spaced relationship from the fiberglass cloth.

15. A seal comprising a ring formed from at least one layer of an elastomeric fabric and being generally channel-shaped in cross section with leg portions and a connecting web portion, the web portion having an inner surface and an outer work contacting surface; a ring-shaped elastomeric insert mounted on the inner surface of the web, a garter spring mounted on the insert such that a predetermined thickness of the elastomeric material of the insert is disposed between the spring and the inner surface of the web, the garter spring when mounted on the insert causing the insert to exert a compressive radially inwardly directed force on the said web portion to maintain the outer work contacting surface of the web in sealing engagement with a duct.

16. A connector comprising a tubular housing, formations integrally formed on at least one end of the tubular housing for positioning seal rings in the housing in spaced side-by-side relationship, outer and inner seal rings mounted in at least one end of the tubular housing, means in the housing cooperating with the said formations to hold the seal rings in said spaced side-by-side relationship, the outer seal ring comprising a seal according to any one of the claims 1 to 6, and the inner seal comprising a seal according to Claim 15.

17. A connector according to Claim 16 wherein the connector has outer and inner seal rings mounted on each end of the connector, ducts mounted in each end of said connector, sleeves mounted on each end of said ducts surrounding the ends of said ducts but in radially outwardly spaced relationship thereto to provide an insulating air space between the outer surface of the duct and said sleeves, said inner and outer seal rings being mounted on the outer surface of said sleeves and in sealing engagement therewith whereby the seals in said connector are protected against high temperatures in said ducts.

18. A connector according to Claim 16 wherein the opposed ends of the connector are offset from each other to permit misaligned ducts to be connected together.

19. A connector comprising a tubular housing, formations integrally formed on each end of said housing defining seal ring receiving channels shaped to permit a seal ring to be mounted in each end of said housing, a seal ring mounted in each of the channels, each seal ring comprising a seal according to any one of the claims 1 to 6.

20. A connector according to Claim 19 wherein the ends of the seal are offset from each other to permit misaligned ducts to be connected together.

21. A connector according to Claim 19 wherein the connector is a bulkhead connector, the bulkhead connector having means thereon whereby the connector can be secured to a bulkhead.