Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
B~l~ 1338111
A PAIR OF SEAL MEMBERS OF HARD MATERIAL
HAVING A LOW FRICTION COEFFICIENT
Background Of The Invention
I. Field of the Invention
The present invention relates to the seal members of
hard material of the type in which the seal is a result of
the precise finishing of the seal members. These seal
members are movable and are in direct mutual contact
without the interposition of a pliable gasket.
II. Description of the Prior Art
The small plates of hard material used in the
regulation of the fluid flow in faucets are usually made
with oxide or silicates of sintered aluminum and then
finished until reflective with a roughness of
approximately 0.2 to 0.4 microns. Because of this precise
surfacing treatment, such small plates are suitable for
the efficient regulation of the flow of water. In
addition, because of their hardness, which is on the order
of 23,000 N/mm, they last a long time and are able to
withstand foreign material, even hard material such as
granules of sand, which come in contact with them, without
causing damages. However, it is because of the very
precise processing that, in the absence of lubrication,
these small plates have the tendency to adhere to each
other giving rise to a large sliding friction - even
greater than the normal friction coefficient of this
material which is relatively high (near 0.12). In order
to achieve smooth functioning of the faucets having
similar small plates of hard material, they are smeared
with a light layer of silicon grease which reduces the
sliding friction. However, with the passing of time and
the recipr~cal rubbing of the small plates, this grease is
gradually expelled and friction is increased to an
unacceptable value. In extreme cases, the faucet may lock
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Attempts have been made to manufacture these small
plates of hard material using tungsten carbide, but the
cost of production and processing were found to be
prohibitive. It has also been proposed to manufacture the
pairs of small plates for the faucets with a material made
from silicon carbide (SiC) and by using this same material
to make both small plates. The silicon carbide has in its
various known crystallographic forms, a hardness between
28,000 and 35,000 N/mm and a friction coefficient close to
0.05 which is superior to those materials currently used
for this purpose. Further, this material reduces the
tendency of adhesion between the highly finished surfaces
so that initially this permits the reduction, within
certain limits, of the friction between the fluid control
plates that are working together in the faucet. However,
it was found that with continued use, the friction between
the small plates made of silicon carbide with similar
characteristics increases greatly until reaching
unacceptable values.
It has also been proposed to make a pair of fluid
plates for a faucet from a hard material having various
characteristics, but with at least one of the small plates
being made of silicon carbide (SiC). The two small plates
can differ in their level of hardness and/or their surface
finish. With this process, a considerable reduction in
the friction between the small plates of hard material can
be verified. Finally, it has been proposed to make a pair
of seal members of hard material in which both members are
made from at least moderately hard material of the type
which is able to receive precise finishing in which at
least one of these is covered with a thin layer of
material of greater hardness by means of physical
deposition or chemical deposition by vapor, and in which
the two members have cooperative surfaces having a
different nature and a different finishing.
~ owever, it has also been determined that when the
seal members are exposed for a certain time to heat, the
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frlction coefficlent increases by a considerable increment
until an excessive value for the friction of initial
separation is reached.
Analogous requirements to those stated for the fluid
control plates for faucets can also be found in other uses for
the seal members made from hard material sliding in direct
mutual contact.
Description Of The Present Inventlon
The present invention overcomés the disadvantages of
the prior known cooperatlng seal members of the type used in
faucets by developing a seal in which an increase in the
friction coefficient between the seal members is prevented
even after extended exposure to heat.
This invention relates to a pair of seal members for
use in a valve to control fluid flow characterized by the fact
that the first seal member is made from a silicon carbide
material and the second seal member is formed of a different
material having a base made of a moderately hard material
coated with a layer of material of greater hardness than the
base material, the coating layer applied through a vapor
deposition whereby static friction between the pair of seal
members is reduced.
The cooperating seal members embodying the present
invention generally comprises one seal member made of a
silicon carbide and the other seal member made of a base
material which has a moderate hardness and then coated with a
thin layer of material of greater hardness applied through
physical or chemical vapor deposition. The first seal member
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made from silicon carbide can be manufactured through a
sinterization process, an inflltration process and/or a
chemical reaction process. A particularly advantageous
process of manufacturing the first seal ls the Lagan process
ln which the silicon carbide member ls obtained by submitting
a semi-finished form of carbonaceous material to siliconizing
at high temperatures. Precislon configurations for the plates
can be obtained economlcally since the carbonaceous semi-
finished form is easy to work with and the sillconization does
not deform or alter the member.
Several materials of elevated hardness can be used
to make the second seal member including silicon carbide,
metalllc carbldes and nitrides, and carbon with a cubic
crystallographic lattice. Various processes are known for
physical and chemlcal vapor deposition adaptable to silicon
carbide and the other materials. Thus, because of
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the resulting precisional configuration and the economy of
production, the second seal member is made with a material
of moderate hardness and coated with a material of
increased hardness through chemical or physical vapor
deposition.
Although an accurate and fine finish of the seal
members is necessary to effectuate the seal for faucet
applications, it has been found that the second seal for
faucet applications, it has been found that the second
seal member need not be as resistant to erosion and wear.
In the second seal member which is coated through the
deposition of material of greater hardness, the material
which forms the body of the seal forms only a support
while the ability of the seal to cooperate with the other
seal member is a result of the harder coating material.
Accordingly, the second seal member may be made of a
material which although adequate to receive the necessary
finish and retain its shape during use would be
unacceptable by itself to form a seal member. Examples of
such a material include soapstone, ceramic materials of
modest quality, metals and certain synthetic materials.
The second plate which receives the deposition material of
elevated hardness can be ground or finished to a high
grade of finish before the coating layer. Thus, a base
material should be chosen which is hard enough to receive
the finishing operation but not so hard as to make this
operation difficult or expensive or such that special
equipment and technologies are required.
An advantage of covering the seal members with
silicon carbide is the chemical stability of the compound
and the ability to resist corrosion and wear caused by the
water. Silicon carbide also shows exceptional resistance
to oxidation. Similar characteristics can also be found
in alternative materials such as titanium carbide and
carbon with a cubic crystallographic lattice. The latter
material, which is not suitable to form the body of the
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seal member, is advantageous because of its reduced
friction coefficient (appr. 0.02).
The application of the invention assures the free and
smooth movement of an apparatus utilizing ~uch seal
members without the need for lubricants. The smooth
operation will last over extended periods of time and is
not affected by high temperatures. Moreover, the cost of
manufacturing the seals described herein is equivalent to
other known processes. This invention is particularly
useful in faucets and valves of the type having a pair of
cooperating seal plates, of the type having three
cooperating discs, or of the type having a single plate
cooperating with cylindrical seal members. Nevertheless,
the application of the present invention is not limited to
faucets and valves and alternatively the seal members can
be used in industrial valves, the valves and small plates
for fuel injection pumps of diesel engines and so on.
The foregoing description has been given for
clearness of understanding only and no unnecessary
limitations should be understood therefrom as some
modifications will be obvious to those skilled in the art.
I claim:
