WO1989004433A1

WO1989004433A1 - A pair of seal members of hard material having a low friction coefficient

Info

Publication number: WO1989004433A1
Application number: PCT/US1988/003559
Authority: WO
Inventors: Alfons Knapp
Original assignee: Masco Corporation
Priority date: 1987-11-10
Filing date: 1988-10-13
Publication date: 1989-05-18
Also published as: FI892959A; GB2232458B; CA1338111C; FI892959A0; IT1211509B; CH674556A5; JPH02502749A; EP0339083A4; GB8913616D0; EP0339083A1; GB2232458A; DE3890961C2; DK302489D0; IT8767954A0; ES2011692A6; JP2568712B2; DK302489A

Abstract

A pair of seal members of hard material such as a pair of small plates which control the fluid flow through a faucet. The first seal member is made of silicon carbide, preferably formed by a process of siliconizing a carbonaceous semi-finished form. The second seal member is made from a material which is at least moderately hard, capable of receiving a precise finish, and is covered by a thin layer of harder material - silicon carbide or another carbide, a nitride, or carbon with a cubic crystallographic lattice structure - applied by physical or chemical deposition by vapor. This configuration results in a low friction coefficient even in the absence of lubrication, prevents excessive adhesion among the parts with highly polished surfaces, it assures smooth operation over long periods of time even if the seal members are subjected to high temperatures, and an excessive amount of friction is prevented upon initial separation.

Description

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 reciprocal 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 up. 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.

However, it has also been determined that when the seal members are exposed for a certain time to heat, the friction coefficient 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 Invention The present invention overcomes the disadvantages of the prior known cooperating 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.

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 made from silicon carbide can be manufactured through a sinterization process, an infiltration process and/or a chemical reaction process. A particularly advantageous process of manufacturing the first seal is the Lagan process in which the silicon carbide member is obtained by submitting a semi-finished form of carbonaceous material to siliconizing at high temperatures. Precision configurations for the plates can be obtained economically since the carbonaceous semi-finished form is easy to work with and the siliconization does not deform or alter the member.

Several materials of elevated hardness can be used to make the second seal member including silicon carbide, metallic carbides and nitrides, and carbon with a cubic crystallographic lattice. Various processes are known for physical and chemical vapor deposition adaptable to silicon carbide and the other materials. Thus, because of 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 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 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 such 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.

Claims

1. 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 form a silicon carbide material and the second seal member 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 vapor deposition.

2. The pair of seal members as defined in claim 1 wherein said first seal member is made by siliconizing at high temperature a semi-finished form made of a carbonaceous material.

3. The pair of seal members as defined in claim 2 wherein said first seal member is made using the Lagan process.

4. The pair of seal members as defined in claim 1 wherein the base of the second seal member is made of a moderately hard material selected from the group consisting of soapstone, a ceramic material, a metal, and a synthetic material.

5. The pair of seal members as defined in claim 4 wherein the coating material of the second seal member is selected from the group consisting of silicon carbide, metallic carbides, metallic nitrides, and carbon with a cubic crystallographic lattice.

6. A pair of seal members as defined in claim 5 wherein the first and second seal members are used in cooperating relationship in a faucet valve to control the flow rate, the interruption and the fluid mixing of the water flowing through the faucet.