Electrically insulating locking insert for a seal, corresponding

Details Electrically insulating locking insert for a seal, corresponding Electrically insulating locking insert for a seal, corresponding

1995-03-20

1997-07-08

Cuchlinski, Jr., William A.

Seal for a joint or juncture

Seal between relatively movable parts

Relatively rotatable radially extending sealing face member

277189, 277901, 277233, 285 48, 285 50, 285104, 285105, 156 89, 65 591, 65 595, 65 594, 65 43, F16L 37084, F16L 2502, F16L 2103, F16J 1546

Patent

active

056452853

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to locked joints between metal pipes, especially spheroidal-graphite cast-iron pipes.
The joints between such pipes are subjected to separation forces when fluids under pressure are conveyed.
One particularly economical way of locking these joints consists in incorporating, into the seals made of elastomer or other flexible substance, a ring of locking inserts of planar general shape which are contained in radial planes. Where the joints tend to separate, the inserts are braced against appropriate bearing surfaces and thus prevent the pipes from separating. An example of this technique is described in the Assignee's published Patent Application FR-2,679,622.
When the pipes are metallic, it is sometimes necessary, for reasons of safety, to insulate the pipes electrically from each other. Now, the inserts, being metallic, form electrically conducting pathways.
It has been proposed to produce inserts from insulating materials, but this has turned out to lead to expensive and fragile inserts.
It has also been proposed to coat metal inserts with an insulating layer, at least in a region where these inserts bear against the pipes. However, such coatings are in contact with a relatively rough metal surface, are moved frictionally over this surface and are stressed not only in compression but also in shear. As a consequence, they are quickly damaged and removed.


SUMMARY OF THE INVENTION

The object of the invention is to make it possible to ensure, economically, effective and lasting electrical insulation when using seals which include locking inserts.
For this purpose, the subject of the invention is. a locking insert for a seal, of planar general shape, comprising at least two metal parts fixed to each other by means of an electrically insulating junction layer.
Such an insert may include one or more of the following characteristics:
--the junction layer is approximately perpendicular to the thrust axis of the insert;
--the junction layer extends approximately over a cross-section of maximum area of the insert;
--the junction layer consists of a low-creep insulating organic substance simultaneously ensuring the bonding of and the electrical insulation between the two metal parts, the organic substance being unfilled or filled with particles of non-creeping insulating materials;
--the junction layer comprises a fabric, fibrous bed or mat, which is dense and non-creeping, especially made of an inorganic substance, connected on each side to one of the metal parts by means of a bonding layer made of an organic substance;
--the junction layer comprises a non-creeping insulating coating, especially made of an inorganic substance, deposited on one of the metal parts, and a bonding layer, especially made of an organic substance, connecting this coating to the other metal part;
--the junction layer consists of a non-creeping insulating bonding substance, especially of a refractory material such as enamel, connected directly to the facing surfaces of the two metal parts;
--the junction surfaces have, in cross-section, at least in one direction, a non-rectilinear profile, especially a U-shaped, V-shaped or sinuous profile;
--the junction surfaces have a planar or pseudo-planar profile interrupted by facing recesses which are intended to house an insulating member for the relative positioning of the metal parts.
The subjects of the invention are also:
--a seal made of a flexible substance into which is incorporated at least one locking insert as defined hereinabove;
--a method of manufacturing an insert as defined above, this method being characterized in that:
--a mixture of bonding-substance particles with an agglomerating agent is produced;
--the metal parts are produced;
--the metal parts are arranged in their desired relative positions, with a layer of the mixture between them; and
--the assembly is raised to a temperature suitable for carrying out both the firing of the mixture and a heat treatment of the metal parts.
In one mode of operation, the said mixtu

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Introduction to Materials Science for Engineers, Shackelford, James, F., MacMillan Publishing Co., New York, 1985, p. 235.

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