Sealing element, particularly for shut-off and regulating valves

Details Sealing element, particularly for shut-off and regulating valves Sealing element, particularly for shut-off and regulating valves

1997-05-20

1999-03-30

Krynski, William

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

428212, 428213, 428214, 428361, 428367, 428375, 428380, 251368, 21912137, 21912154, 20424831, 118719, B32B 900

Patent

active

058886389

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention relates to a sealing element, particularly for shut-off and regulating valves. It comprises a disc-shaped, piston-shaped or spherical shut-off body. The shut-off body can comprise a metallic or nonmetallic material. This material can be, for example, a ceramic material, including aluminium oxide and the various silicon carbides SiC, Si.sub.2 C and silicon nitride Si.sub.3 N.sub.4.
On a working surface (sealing surface) of the shut-off body, a hard material layer containing carbon and silicon is applied by plasma CVD or plasma polymerization in a coating chamber. The hard material layer here comprises a bonding layer component applied to the working surface of the shut-off body and a subsequent covering layer (sliding layer) component. The bonding layer component has a first silicon content favouring adhesion to the working surface of the shut-off body, and the subsequent carbon-containing covering layer component has a second silicon content lower than that of the bonding layer component, or is silicon-free, to achieve low coefficients of sliding friction and static friction.
The deposition from the plasma is carried out by ion bombardment, e.g. by means of a glow discharge or by means of an additional ion gun. From a hydro-carbon-containing atmosphere a wear-resistant, carbon-containing layer having sufficiently low coefficients of sliding friction and static friction can be deposited in this way.
A sealing element of the above type and the associated plasma CVD coating process is known from DE-A 38 32 692.
According to this document, shut-off bodies are, to coat their working surfaces, placed in the coating chamber on a specimen holder having a negative potential relative to the plasma. For initial physical etching of the working surfaces of the shut-off bodies with argon, the coating unit is first operated as cathode atomization (sputtering) unit. For subsequent deposition of the bonding layer component of the hard material layer on the etched working surface, the same unit is then operated under certain first process parameters as high-frequency plasma CVD unit, with the argon gas in the coating chamber being replaced, for example by tetramethylsilane. Under altered second process parameters, the covering or sliding layer component is then deposited from a gas mixture of tetramethylsilane and hexane after deposition of the bonding layer component.
The sealing elements obtained by this method (these can advantageously be coated ceramic plates for water valves, e.g. single-hand mixers) have, thanks to the hard material layer applied, sufficiently low coefficients of sliding friction and static friction when sliding over one another, even in the presence of water, so that greasing of the sealing surfaces as has hitherto been required for uncoated ceramic plates is no longer necessary.
A disadvantage of the known sealing plates is that their hot-water resistance is in many cases unsatisfactory. This is the case particularly when a hot-water resistance of more than 1000 operating hours is to be achieved without the hard material layer applied becoming detached from the shut-off body.


SUMMARY OF THE INVENTION

It is an object of the invention to provide a sealing plate of the type mentioned in the introduction which has both sufficiently low coefficients of static friction and sliding friction on the sliding layer surface and a high hot-water resistance. Preferred sealing plates, in particular in the form of discs, should have a hot-water resistance at 95.degree. C. over an operating period of at least 1000 hours without, in particular, the adhesion of the hard material layer to the shut-off body being significantly impaired.
It was surprising that an optimized thickness ratio of bonding and sliding layer components by selection of the deposition times in the coating chamber was able to improve significantly the adhesion properties of the bonding layer component to the shut-off body under hot water conditions and that, in addition, these adhesion properties of the

REFERENCES:
patent: 4856785 (1989-08-01), Knapp
patent: 4991822 (1991-02-01), Enke

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