KNITTED HIGH TEMPERATURE SEAL

Abstract

A high temperature seal is disclosed which is made of knitted expanded graphite. The expanded graphite is knitted into a tube and then the tube is rolled back onto itself to prepare a torus. The torus is then die formed into a U shape. Various materials may be added to the knitted tube to enhance desirable qualities. A spring may be added to the torus to give compression force to the seal surface.

Claims

1. A high temperature seal for use on a valve stem, wellhead casing, pump or turbine shaft, comprising expanded graphite knitted into a tube shape using a stockinette stitch, said knitted tube being rolled onto itself to form a torus and said torus being die formed into a U shape.

2. The high temperature seal according to claim 1 wherein said expanded graphite is in the form of multiple strands.

3. The high temperature seal according to claim 1 further comprising stands of reinforcing material are knitted into said tube along with said expanded graphite.

4. The high temperature seal according to claim 1 wherein a strand of pure polytetrafluoroethylene or a porous material to slowly dispense a lubricant is knitted into the tube along with the expanded graphite.

5. The high temperature seal according to claim 1 further comprising a U shaped spring is added to the torus prior to die forming the torus into a U shape.

6. A high temperature seal for use on a valve stem or pump shaft comprising expanded graphite braided into a tube shape, said braided tube being rolled onto itself to form a torus and said torus being die formed into a U shape.

7. (canceled)

8. (canceled)

9. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWING

[0012] FIG. 1 is a depiction of a the expanded graphite knitted using a basic stockinette stitch.

[0013] FIG. 2 is a depiction of the expanded graphite knitted into a tube using the basic stockinette of FIG. 1.

[0014] FIG. 3 shows the tube being rolled into a torus shape.

[0015] FIG. 4 shows a partial cut away view of the completed torus.

[0016] FIG. 5 shows the completed torus of FIG. 4 after being die formed into a U shape.

[0017] FIG. 6 shows the completed and die formed seal of FIG. 5 with an added spring to provide more elasticity to the seal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] As noted above expanded Graphite is a volume compressible material with limited recovery and low elongation, but it is subject to attack only by oxidizers in the temperature range of −400 to over 4000 Degrees F. The method of production of Expanded Graphite is well documented. See for example U.S. Pat. Nos. 1,137,373 and 3,040,061 for the methods employed to create the base material. One of the most common materials goes by the trademarked name Grafoil®, manufactured by GrafTech Industries

[0019] The strand or strands of the expanded graphite is knitted into a tube 10 of FIG. 2 using a stockinette stitch illustrated in FIG. 1. The strands 1, 2 and 3 are simply interlaced to allow moderate lateral expansion in the direction of the arrows with very little in the vertical direction. This lateral expansion is permitted by a slight bending of the individual strands as opposed to stretching orcopressing lengthwise.

[0020] The knitted tube 10 is then rolled back onto it to form a torus, the beginning of which is shown in FIG. 3 at 12. It will be appreciated that the roll/torus 12 is continued until the tube 10 is completely absorbed into the torus shape. Torus 12 begins with one end 14 of the tube 10 in the middle of the cross section with outer edge 16 exposed as shown in FIG. 4.

[0021] The torus 12 is then die formed into a U shape as shown in FIG. 5. The two ends 14 and 16 are thus encapsulated and kept away from any sealing surface. In addition the U shape produces a slight outward biased to assist in maintaining the seal in contact with the sealing surfaces. In the present incarnation as shown in FIG. 6, the folded preform 12 is die formed with the addition of a “U” shaped spring 18 made out of a high temperature alloy, Inconel X750 for use up to 1100 Deg. F. The spring can be captured within a fold of material encapsulating it if desired. The spring 18 does not have to be U shaped. A spiral O shape will also serve to give a compression force to the inner and outer seal surfaces.

[0022] Although lacking the simplicity of the knitted single strand, the same advantages occur when using a braided tube of suitable diameter. It may be rolled to shield all of the ends from wear or exposure to the media.

[0023] The addition of a reinforcing wire or other stronger material either as a parallel strand being knitted or as a separately braided coaxial sleeve is easily accomplished. Also, it is contemplated that strands of material to enhance other properties of the finished seal can be added, such as a strand of pure polytetrafluoroethylene (TEFLON®) or a porous material to slowly dispense a lubricant.

[0024] Usually, blocking agents are not needed with expanded graphite or boron nitride, but they may aid in sealing for some of the other combinations. In all cases a suitable lubricating oil may be added, if desired, to serve to reduce friction during installation and break in.

[0025] Note that, although the seal is presented as a shaft or piston seal, the concept will work in other geometries such as a face seal. Also, the seal is presented as having one plane of sealing, but there is nothing preventing the knitted material from having multiple branches in 3 dimensions should such a seal be needed. In addition the final shape of the seal may be circular or rectangular in cross section while enjoying the advantages of the concept, as long as the edge of the material is not exposed to a dynamic surface.