Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Lowe
The present invention relates to an insulting coating conserving
its dielectric characteristics over a very wide range of temperatures.
Safety imperatives require that, in certain cases of use such
as are encountered in the nuclear, oft, aeronautic, space, naval, chemical,
etc.. industries, the circuits conveying energy or transmitting monitoring
or control signals, withstand for a sufficient time the high temperatures
due for example to a fire or, for the electrical circuits, to an abnormal
rise in intensity of the electric current which passes through them,
so as to enable the staff to be evacuated and equipment to be saved.
In the case of short circuits or over intensity, It is desired that the
considerable increase in temperature of the conductor, or even the
fusion thereof, does not provoke a fire by combustion of the coating.
To respond wholly or partly to these requirements, ceramic
coatings, associated or not Vito glass fires, are already usual Further-
more, coatings exist, particularly for electrical cables, which result
from the association of fabrics of glass fires and metallic oxide.
The electrical cables intended for these uses exist in reinforced
or non-reinforced form, depending on whether they are protected, at
manufacture, from the risks of deterioration of mechanical origin by
a rigid metal coating or whether they must be introduced, during asset-
by, into metal tubes intended to ensure protection thereof. The rein-
forced cables are constituted by one or more conductors insulated by
a substance with low carbon content, protected by a cylindrical shell
obtained by winding a metal ribbon or by a metal tube. The non-reinEorced
cables are also constituted by conductors insulated by substances with
low carbon content, but are sheathed by a complex of glass fire and
silicone rubber or any other noncombustible material.
Among the insulating coatings presenting considerable resistance
to high temperatures, those described in the following patents may
be cited:
- FRY 381 377 which describes a coating constituted by
a metal tube packed with magnesia.
- FRY 257 555 which describes a coating composed of a
layer of inorganic noncombustible fires constituting a heat insulator
and of a layer of halogen bonded to non-combustible fires by a resin.
-Aye 462 771 which describes a coating constitu~e(l by
g78
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a b akocl insul;ltin~, malarial matter hl~l~r~ lad with Solon oil, Ire eta
by a metal sheath.
- FRY 482 769 which describes a heat-resistant, flexible,
refractory, insulating coating composed of a porous basic material,
a refractory coating capable of melting with the basic porous material
at high temperature.
- FRY 206 563 which describes a high temperature insulation
composed of a borosilicate glass and silica, which is melted at high
temperature to form a mass having a viscosity greater than the viscosity
of the glass and the silica at -the same temperature.
- FRY 360 530 which describes a frilled, vitrifiable body
based on glass and quartz.
- USE 602 636 which describes a coating constituted by
a helical covering with a glass malarial, with open weave, bearing a
coating of synthetic rubber, flame-resistant, protected by a shc~th
of polyvinylchlorkle.
- USE 632 412 which describes a self-adhesive tape constituted
by an inter polymer lined with a glass cloth.
- US-f\.3 013 902 which describes materials coated with colloidal
alum Noah.
- USE 0~5 336 which describes the preparation of lo in;ltcd
ceramic products with glass cloth.
- European 8û.107217.4 which describes an insulating coaxing of ceramics
constituted by polyamide and mica.
In an attempt to respond to the particularly severe requirements
of certain uses, particularly on oil platforms, in the mining industries
and nuclear power stations, installations in explosion- and fire-proof
conduits have been imposed. This type of installation, although limiting
the effects of self-propagation and the disengagement of fumes, presents
the drawback of confining the heat to inside the conduit, which has
for its effect to destroy the insulator and to create ruptures of cables
or short circuits.
Furthermore, the majority of the above-mentioned coatings,
although they ensure protection of the electrical cables and maintain
tile insulation indispensable for a determined duration, do not allow
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the installations to be subsequently reused without all
the wirings having been previously replaced. The destructive
effect is further accentuated when extinction means such
as the projection of sea water of immersion are used.
Not to mention the fluid conduits which supply
compressed gas or hydraulic liquid to the remote equipment
which is vital to maintain in operation. The supply pipes
which are generally used are only very imperfectly protected
from direct heat and their constitution is not designed
to resist for a sufficiently long time a considerable rise
in temperature.
It is an object of the coating according to the
invention to overcome the previously described drawbacks,
as with this coating, in fact, when a temperature of about
1000C is attained, the glass fires which come into its
composition are converted into a gel which is presented
in the form of a pasty foam which constitutes a continuous
dielectric and thermal barrier which reinforces the insular
lion and protection of the conductor or the conduit. After
lowering of the temperature, this protective barrier is
converted into a layer of glass-coated mica, due to the
disappearance, by combustion, of the polytetrafluoroethylene.
More particularly, this invention provides an
insulating coating comprising a first layer comprised of
mica, a second layer comprised of polytetrafluoroethylene
on said first layer and a third layer comprised of glass
fabric on said second layer, said coating maintaining its
dielectric and thermal properties between -200C and 1,000C,
and being converted to a gel at high temperature, wherein
said gel maintains insulating properties at such high temperature
and upon cooling from such high temperatures.
In consequence, this coating conserves its in-
sulfating characteristics and its tightness, even after
destruction of the combustible elements which are included
in its basic composition (PTFE); this conserves for the
installation its operational value even after a fire. This
particular feature is of capital importance for the remote
control of nuclear reactors after an incident having brought
about a considerable increase in temperature in the hot
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part, and for maintaining in operation the equipment directly
acting for the survival of persons or for continuing a
mission, as is the case in particular in aeronautics, the
navy, aerospati.al operations and on drilling platforms.
Moreover, this coating may be obtained by ribboning,
which makes it possible to envisage use thereof as desired,
to protect certain fluid conduits passing through particularly
exposed zones.
This coating is mainly characterized in that it
conserves its dielectric and thermal properties between
-~00C and 1000C and in that it is converted into a gel
which maintains the insulation at high--------------------
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temperatures and ensures insulation and tightness during cooling.
It is constituted by a layer of mica, a glass fabric end a layer of polytetrafluorethylene (PTFE). The layer of mica is obtained by win-
ding, in one or more layers, a ribbon constituted by a lass tire fabric
impregnated with a binding agent supporting particles of mica; the
layer of polytetrafluoroethylene which is superposed on the layer of
mica, is obtained by winding in one or more layers or by extrusion;
the lass fabric which is superposed on the layer of polytetrafluorethylene
is obtained by winding a ribbon or by weaving elementary fires directly
above the preceding layer.
The layer of mica is turned towards the conductor or the mom-
bier to be protected and this protection is completed by a polymerization
of the polytetrafluorethylene which ensures adherence between the
layers.
The ribbons, of which the thickness is 0.06 mm to 0.12 mm,
are wound with overlapping, for example by 50%, so as to double the
thickness of the layer.
The gel obtained a high temperature vitrifies during drop
in temperature to constitute, with the particles of mica which coat
the element to be protected, a dielectric, tight insulating coating connect
tying all the components of the circulate.
his coating may be produced as desired, from a ribbon obtained
by superposition and adhesion of the different layers of materials entering
in the composition of the complex; this enables protection to be ensured
of elements or components other than electrical conductors or reinforce-
mint of the protection against fire of existing installations.
his coating is in two forms, depending on whether it is question
of protecting a supple conductor, a rigid conductor, a connecting combo-
next or an equipment of particular form.
In the case of conductors, the ideal solution consists in superpo-
sing a ribbon of mica, a polytetrafluorethylene protection and a glass
fabric.
In the case of insulation of elements other than wires, the
solution consists in superposing a ribbon of mica, a glass fabric and
a polytetrafluorethylene insulation.
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Other characteristics end a Ivanta~es will appear in the following
description of a coating made according to the invention, intended for
to row Sheehan of electrical Jon l l lyres, Levine by Wily of Ryan ill
example.
Protection, at manufacture, of the conductors is effected as
lot lows:
- A ribbon constituted by a glass fire fabric impregnated
with a binding agent, generally silicon, supports the particles of mica
and is preferably wound so that the particles of mica are turned towards
the conductor, in one or more layers.
- layer of polytetrafluorcthylene is obtained by winclin~,
above the preceding layer, of a ribbon or by extrusion.
- glass fire fabric is superposed on the layer of polytetrafluor-
ethylene by ribboning or weaving elementary fires directly around
the conductor.
This protection is completed by a polymerization of to poultry
fluorethylene, which is presented in the form of impregnation in the
case ox the glass fabric or of the covering of the fires in the case
of direct weaving, and of the continuous layer obtained by ribboning
or by extrusion. The effect of this polymerization is to obtain the ache-
fence of the two upper layers and a certain adherence of the layer
of polytetrafluorethylene with the ribbon supporting the particles ox
mica, when the latter are turned towards the conductor.
According to a variant, protection of the flexible conductors
may be obtained by superposition of a ribbon of mica, as defined previous-
lye of a glass fabric the form of a braid or a ribbon, and of an insular
lion of polytetrafluorethylene obtained by ribboning or extrusion.
This protection is completed by a treatment of connection
similar to that described in the preceding case.
Ribboning operations are effected with an overlapping chosen
so that at all points of the periphery of the cable, there are one or
more thicknesses of each of the ribbons of which the width and thickness
are defined as a function of the diameter of the wire.
The mica is turned towards the conductor so as to facilitate
the laying bare which precedes the connecting operations and to obtain
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a film of mica coaled with glass altar solidification of the Mel obtained
at very high temperature, in order to facilitate disconnection of the
colonial! if nccss;lry.
Conversion of the coating, by heating to about 1000(~ than
cooling, may be sought a priori on rigid installations on which a perfect
tightness is necessary, in order for example to shelter the components
coming within their constitution from an aggressive or damp ambience.
In fact, the coating of the conductors according to the invention
may be extended, by ribboning, to the other elements of the circuit
so that, after fusion and solidification of the coating, the whole of
the installation is coated with glass continuously and consequently
in tight manner.
The coating according to the invention is mainly intended ion
protection against fire, of electrical conductors, fluid conduits, connecting
components or equipment.
It is more particularly applied to the protection of the electrical
control, illuminating or safety circuits in the nuclear, chemical, oil,
aeronautic, naval and space industries.
Of course, the invention is not limited to the embodiments
described liereinabove, from which other forms and other embodiments
may be provided without dcpartin~ from the scope of the invention.
