WO2002101898A1

WO2002101898A1 - Sealing system

Info

Publication number: WO2002101898A1
Application number: PCT/NL2002/000360
Authority: WO
Inventors: Johannes Alfred Beele
Original assignee: Beele Engineering B.V.
Priority date: 2001-06-12
Filing date: 2002-06-03
Publication date: 2002-12-19
Also published as: EP1407524A1; NL1018262C2

Abstract

A sealing system comprising at least one cable and at least two sealing rings at least in part made of an elastic material, which sealing rings are arranged round the cable in spaced-apart relationship for sealing confinement of the cable by collaring the same in a bushing extending co-axially with the cable, a special feature being the fact that the sealing system comprises an electrically conducting material which is present in a passage formed between the cable and the bushing, and which is in contact with an electrically conducting braiding of said at least one cable in the operative condition, earthing said braiding electrically.

Description

Q . AN80

SEALING SYSTEM

The invention relates to a sealing system comprising at least one cable and at least two sealing rings at least in part made of an elastic material, which sealing rings are arranged round the cable in spaced-apart relationship for sealing confinement of the cable by collaring the same in a bushing extending co-axially with the sa-ble.

Such a sealing system is generally known. In the fitted position of the known system, an air space is present between the sealing rings, which air space is bounded by the bushing and, as already said before, the sealing rings. In the case of a fire, for example on one side of the bushing, the excellent thermal insulation properties of said air space prevent the other side of the bushing becoming (too) hot for some time.

One drawback of the known sealing system is the fact that it is not protected against electromagnetic overtension and electromagnetic interference in practice, so that undesirable electromagnetic fields and pulses can be conducted into electronic equipment by the cable.

The object of the invention is to improve the prior art sealing system in the sense that a high-quality, fire resistant, gas and liquid-tight sealing system is proposed, which system is furthermore optimally protected against electromagnetic overtension and/or interference. In order to accomplish that objective, a sealing system of the kind referred to in the introduction is characterized in that the sealing system comprises an electrically conducting material which is present in a passage formed between the cable and the bushing, and which is in contact with an electrically conducting braiding of said at least one cable in the operative condition, earthing said braiding electrically.

Electric installations and machines, in which highly sensitive components are generally used, for example for control and registration purposes, are liable to interference from various external electromagnetic fields and pulses. Said external electromagnetic fields and pulses may be generated by, for example, radar installations, thunderstorms, nuclear explosions and electric equipment. In practice steel structures, which function as a Faraday cage, are frequently placed round a space intended for accommodating electronic equipment, so as to reduce such interference. Electric cables which are led into such a shielded space, may conduct undesirable electromagnetic fields and pulses into the electronic equipment yet, however. As a rule, this conduction will take place across the electrically conducting braiding of the cables in question that are being led through.

According to the invention, said external, undesirable electromagnetic fields and pulses can flow away to earth via the electrically conducting braiding of a cable being led through.

It is noted that within the framework of the invention the term "cable" is understood to include an electrically conductive conduit, tube, pipe of the like, for example a metallic tube or pipe, with the present electrically conductive material being in electrically conductive contact therewith in the operative condition.

In one preferred embodiment of a sealing system according to the invention, the electrically conductive material comprises an electrically conductive tape. In particular, said electrically conductive tape is-.at least partially wound round the electrically conductive cable braiding in the operative condition.

In another preferred embodiment of a sealing system according to the invention, the electrically conductive tape is wound round the electrically conductive cable braiding near one end, whilst it is attached to the electrically conductive bushing (which is made of a metal, for example) fitted in, for example, an opening in a wall, being in electrically conductive contact therewith, near its other end. In another preferred embodiment, the earthing of the electrically conductive cable braiding by means of the electrically conductive material has been effected by selecting several pieces of electrically conductive tape material, whether or not folded together and/or several electrically conductive sleeve means or hose members arranged in said passage as the electrically conductive material, which sleeve means preferably extend in the same direction as said at least one cable .

In another preferred embodiment of a sealing system according to the invention, the electrically conductive tape and/or the electrically conductive sleeve means is/are at least substantially made of an electrically conductive rubber. Said rubber has been made electrically conductive in particular by chemical means, in particular by the addition thereto of carbon particles, preferably in the form of carbon black. In particular, said rubber is EPDM rubber, whilst said carbon particles are preferably concave shell-shaped, especially of the type "Ketjenblack EC" 300J or 600 JD ™. These types of carbon black, which are known under the commercial name of "Ketjenblack", have a unique moxphology in comparison with conventional types of carbon black, which renders them exceptionally suitable for the present electrically conductive application. The abbreviation EPDM stands for Ethylene/Propylene/Diene/Monomer . It is noted that also other elastomers or plastomers can be used as materials for said tape and said sleeve means.

In another preferred embodiment of a sealing system according to the invention, the electrically conductive tape is a metal tape. Preferably, the electrically conductive (rubber or metal) tape is flexible, that is, deformable, so that it can readily be led along other cables that are being led through the bushing.

In another preferred embodiment of a sealing system according to the invention, the electrically conductive tape has a contact width of at least about 20 mm, preferably about 40 mm. In the latter case, the tape is usually used for civil applications (attenuation factor -30 dB) , whilst a contact width of more than 100 mm (attenuation factor -60 dB) can be used for military applications. By winding the present tape of such width round the electrically conductive cable braiding, an optimum electrically conductive contact is effected so as to prevent electromagnetic overtension and/or interference .

In another preferred embodiment of a sealing system according to the invention, said electrically conductive material comprises a moulding paste, for example in the form of an injectable putty, in which the composition substantially consists of a binding agent and an electrically conductive component, in such an amount that the electromagnetic interference measurement in accordance with the EMC IEC 11.9.1 standard in the range between 30 MHz to 1 GHz will show a signal attenuation of at least >-60 dB .

In another preferred embodiment of a sealing system according to the invention, said binder has been selected from the group of elastomers, preferably silicones, and said electrically conductive material is carbon-based, preferably expandable graphite, since this form of graphite also exhibits fire-resistance. Said binder and said form of carbon are advantageous with a view to achieving low resistance values and a good viscosity. More preferably, oil and/or other agents, such as anti-static agents and viscosity- reducing agents, are added, as a result of which in particular a good workability is obtained.

Further preferred variants with regard to the moulding paste are shown in the appended claims 13-23. Surprisingly, the invention provides a moulding paste which exhibits a suitable viscosity, so that the moulding paste is injectable, thus being suitable for a wide range of applications, and which has a surprisingly low resistance value. The moulding paste according to one preferred embodiment of the invention will be marketed under the name of CONDUCTON ^® , which is a brand name of Beele Engineering B.V. Said CONDUCTON ^Θ moulding paste has additional properties: - specific weight 1.4 ± 0.03 g/cm³ tensile strength 0.8 MPa elongation at break 40% hardness 30 Shore A elasticity approx. 25% and in addition it adheres--well to metal surfaces, such as steel, zinc and copper. The resistance value of CONDUCTON ^® moulding paste is less than 100 ohms, and in addition it is water repellent.

In one preferred embodiment of a sealing system according to the invention, the sealing rings comprise circular outer ribs and circular inner ribs, which outer ribs have an outside diameter which is larger than the inside diameter of the bushing, and in which the inside diameter of the inner ribs is at most at least substantially the same as the outside diameter of the cable. In particular, the sealing rings each comprise at least two shell members, whose abutting boundary surfaces extend at least substantially in axial direction, and the rear flanks, seen in the direction of insertion, of the outer, serrated ribs extend in radial direction whilst the inner ribs are arranged in pairs in the radial area of the outwardly extending tips of the outer serrated ribs. The inner ribs of the sealing rings are preferably trapezoidal in shape, seen in the direction of the axial longitudinal section. The advantages of the above features will be explained in more detail below in the description of the figures . Preferably, the spacing between the sealing rings is less than 25 mm, in which said sealing rings comprise an expandable material, in an amount and of a composition such that the sealing rings will expand in the case of a fire, to such an extent that they will wedge themselves in the bushing. Preferably, the spacing .between the sealing rings is less than 120 mm, in particular about 40 mm.

The invention will be explained--in more detail hereinafter with reference to figures illustrated in a drawing, in which Figures 1-4 successively show in schematic and perspective view various steps for providing a high-quality, fire resistant, gas and liquid-tight sealing system according to the invention, which system is furthermore optimally protected against electromagnetic overtension and/or interference .

Figure 1 shows an opening 1 in a wall 2, in which a steel bushing 3 is fitted. For the sake of simplicity, only three multi-core cables 4, 5, 6 are shown in the drawing, which cables have each been stripped of their plastic sheathing 7 along part of their length, so that their electrically conductive braiding 8 is now exposed. In accordance with the invention, a tape 10 of EPDM rubber on a winding roll 9 is used, which tape has been made electrically conductive by the chemical addition of carbon particles (for example carbon black particles) thereto, which tape is to be wound round the electrically conductive braiding 8. The tape 10 preferably has a width of 40 mm, so that an optimum electrically conductive contact with said electrically conductive braiding 8 is realised. The electrical earthing is ensured by winding the tape 10 to a diameter larger than that of cables 4, 5, 6, as is shown in Figure 1 and as will be explained in more detail yet.

In Figure 2, hose members 11 of an electrically conductive material are placed in the passage formed between the bushing 3 and the cables 4, 5, 6, whilst it is also possible to use folded-together pieces 12 of the tape 10 in addition thereto or instead thereof. Since the hose members 11 are made of the same electrically conductive material as the tape 10, viz. of EPDM rubber which has been made electrically conductive by the addition of carbon particles, the electrically conductive braiding 8 is connected, being earthed electrically, to the steel bushing 3 via the tape 10 and the hose members 11 and/or the pieces of tape 12. As already said before, the tape 10 has been wound to a diameter larger than that of the cables 4, 5, 6 so as to guarantee the electrically conductive contact between the tape 10 and the hose members 11.

Figure 3 corresponds to Figure 2, with this difference that an electrically conductive moulding paste 13 is used instead of the hose members 11 and/or the pieces of tape 12 so as to effect electrical conduction between the (electrically conductive braiding 8 of the) cables 4, 5 and 6 and the electrically conductive (steel) bushing 3.

Possible trade names of the products that are used are:

Silicone putty Rhone Poulenc CAF22

Silicone oil Rhodosil 47/V100

Expandable graphite Callotek 500 CONVEYOR BELT 140E Kynol 0185

Anjay metachem S-15 L120

Antistatic agent Kenstat KS MZ 100 Kenstat KS N100

Viscosity-reducing agent Ken-react KR TTS

Ken-react KR 46B

An example of a formula is given below (percentages are wt ,

Rhone Poulenc CAF 22 100 (75 - 100) Rhodorsil 47/V100 75 (50 - 100) Kenstat KS N100 4 (2 - 4)

Callotec 500 CONVEYOR BELT 140E 175 (150-200)

Experiment

The electrical conductivity of a moulding paste according to the invention was measured by experiment. The electrical resistance was less than 1,000 ohms at all times, and preferably less than 100 ohms. The resistance values were determined in accordance with ISO 2878 standard methods in all cases.

A sample plate dimensioned 100 x 100 x 10 mm was used for determining the resistance value. Square electrodes dimensioned 25 x 25 mm, which were spaced 50 mm apart, were affixed to the surface of the test piece by means of Aquadag (a colloidal suspension of carbon in water) . Resistance values of 80 - 90 Ohms and even lower were recorded. Figure 4 shows how the bushing 3 is sealed, both in the preferred variant of Figure 3 and in the one of Figure 2, by fitting sealing rings 14 round the cable 4 on either side for sealing confinement of the cable through collaring in the bushing 3 that extends co-axially therewith. In order not to complicate Figure 4 unnecessarily, said figure shows one cable 4 being led through, and the electrically conductive material in the form of hose members 11, the pieces of tape 12 and/or the moulding paste 13 are not shown for easy reference, although they will he. present in the passage 15 in practice. In situations in which more cables 4, 5, 6 are led through, the sealing rings 14 will comprise a corresponding number of lead-through holes.

As already said before, the sealing rings 14 are fitted in spaced-apart relationship round the cable 4 in the passage 15 between the cable 4 and the bushing 3, so as to confine the cable 4 in the bushing 3 in a gastight and watertight manner. The bushing 3 is fitted in a steel ship's deck, a wall, a partition, or the like.

Each sealing ring 14 made of a resilient rubber is preferably formed by two identical, shell-shaped ring halves 14', 14'', the abutting boundaries surfaces of which extend in axial direction. The ring halves 14', 14' have ribs 16 of right- angled triangular cross-section on the outer side and trapezoidal ribs 17 on the inner side. When the sealing rings 14 are forced into the passage 5 and around the cable 4, the ribs 15 of the sealing rings 14 are compressed by the bushing 3, as a result of which the diameter of the ribs 17 positioned opposite the ribs 16 will be reduced, causing them to press forcefully and sealingly onto the outer side of the cable 4. The pressure forces thus set up in the rubber furthermore cause the abutting boundary surfaces of the ring halves 14', 14'' of a sealing ring 14 to be pressed together sealingly without external pressure means being required.

It is preferable to use an expandable material for the sealing rings 14, in such an amount and of such a composition that the sealing rings 14 will expand to such an extent in the case of a fire that the sealing rings will wedge themselves in the bushing 3. As- a result, the thermally insulating properties of the air space 18 that may be present will be retained in the case of a fire, whilst the risk of a pressure build-up of such a magnitude that the sealing rings 14 will be forced out of the passage 15 is ruled out under all circumstances. At worst, the sealing rings will be forced out a few millimetres, that is, over a width of one or more ribs 17, but the original position of the sealing rings, and thus their sealing function, will be substantially retained in such a case. The expandable rubber material of the sealing rings 14 in particular comprises expandable graphite. Experiments have shown that said graphite is excellently suitable for causing the sealing rings 14 to expand in the case of a fire.

The invention is not restricted to the above-described variant, but also other embodiments fall within the scope of the invention as defined in the appended claims.

Claims

1. A sealing system comprising at least one cable and at least two sealing rings at least in part made of an elastic material, which sealing rings are arranged round the cable in spaced-apart relationship for sealing confinement of the cable by collaring the same in a bushing extending co-axially with the cable, characterized in that the sealing system comprises an electrically conducting material which is present in a passage formed between the cable and the bushing, and which is in contact with an electrically conducting braiding of said at least one cable in the operative condition, earthing said braiding electrically.

2. A sealing system according to claim 1, wherein the electrically conductive material comprises an electrically conductive tape.

3. A sealing system according to claim 2, wherein said electrically conductive tape is at least partially wound round the electrically conductive cable braiding in the operative condition.

4. A sealing system according to claim 2 or 3, wherein the electrically conductive tape is wound round the electrically conductive cable braiding near one end, whilst it is attached to the electrically conductive bushing, being in electrically conductive contact therewith, near its other end.

5. A sealing system according to any one of the preceding claims 1 - 4, wherein said electrically conductive material comprises several pieces, whether or not folded together, of an electrically conductive tape material.

6. A sealing system according to any one of the preceding claims 1 - 5, wherein said electrically conductive material comprises several electrically conductive sleeve means.

7. A sealing system according to any one of the preceding claims 1 - 6, wherein the electrically conductive tape and/or the electrically conductive sleeve means is/are at least substantially made of an electrically conductive rubber.

8. A sealing system according to claim 7, wherein said rubber has been made electrically conductive by the addition thereto of carbon particles, preferably in the form of carbon black.

9. A sealing system according to claim 8, wherein said carbon particles are concave shell-shaped particles.

10. A sealing system according to claim 8 or 9, wherein said carbon particles are "Ketjenblack EC" 300J or 600 JD ™- type particles.

11. A sealing system according to any one of the preceding claims 7 - 10, wherein said rubber is EPDM rubber.

12. A sealing system according to any one of the preceding claims 1 - 11, wherein said electrically conductive material comprises a moulding paste, for example in the form of an injectable putty, in which the^' composition substantially consists of a binding agent and an electrically conductive component, in such an amount that the electromagnetic interference measurement in accordance with the EMC IEC 11.9.1 standard in the range between 30 MHz to 1 GHz will show a signal attenuation of at least >-60 dB .

13. A sealing system according to claim 12, wherein the signal attenuation exceeds -100 dB.

14. A sealing system according to claim 12 or 13, wherein the moulding paste is electrically conductive, having a resistance value of less than 1,000 ohms, preferably less than 100 ohms.

15. A sealing system according to claim 12, 13 or 14, wherein the moulding paste is electrically conductive, having a resistance value of less than 100 ohms.

16. A sealing system according to any one of the preceding claims 12 - 15, wherein a binder has been selected from the group of elastomers and said electrically conductive material is carbon-based.

17. A sealing system according to any one of the preceding claims 12 - 16, wherein said binder is a silicone rubber and said electrically conductive material is graphite, preferably expandable graphite.

18. A sealing system according to claim 17, wherein the electrically conductive material constitutes 40-60 wt . % of the overall composition.

19. A sealing system according to any one of the preceding claims 12 - 18, wherein a plasticizer, such as a silicone oil, has furthermore been added to the composition.

20. A sealing system according—to any one of the preceding claims 12 - 19, wherein an antistatic agent has been added to the paste.

21. A sealing system according to any one of the preceding claims 12 - 20, wherein a viscosity-reducing agent has been added to the moulding paste.

22. A sealing system according to any one of the preceding claims 12 - 21, wherein said silicone rubber and said conductive material are present in the same weight percentages in the moulding paste.

23. A sealing system according to any one of the preceding claims 12 - 22, wherein the composition of the moulding paste, expressed in weight percentages, is as follows:

- silicones + silicone oil - 40-60 wt . %

- graphite - 60-40 wt . %

- antistatic agents - 0-3 wt . %

- viscosity-reducing agents - 0-3 wt . %.

24. A sealing system according to any one of the preceding claims 12 - 23, wherein the sealing rings comprise circular outer ribs and circular inner ribs, which outer ribs have an outside diameter which is larger than the inside diameter of the bushing, and wherein the inside diameter of the inner ribs is at most at least substantially the same as the outside diameter of the cable .

25. A sealing system according to any one of the preceding claims 12 - 24, wherein the sealing rings each comprise at least two shell members-,- whose abutting boundary surfaces extend at least substantially in axial direction, and the rear flanks, seen in the direction of insertion, of the outer, serrated ribs extend in radial direction whilst the inner ribs are arranged in pairs in the radial area of the outwardly extending tips of the outer serrated ribs.

26. A sealing system according to any one of the preceding claims 12 - 25, wherein the inner ribs of the sealing rings are trapezoidal in shape, seen in the direction of the axial longitudinal section.

27. A sealing ring apparently suitable for use in a sealing system according to any one of the preceding claims 1 - 26.