Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1999-04-01
2001-03-20
Speer, Timothy M. (Department: 1775)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S457000, C428S698000, C384S907100, C384S913000
Reexamination Certificate
active
06203895
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to parts for process valves, provided with a thermally sprayed coating to protect them from wear. The process valves are components of larger technical apparatuses used in the chemical and petrochemical industry, in the mining industry and in other processing industries.
The invention is thus particularly advantageous when used in these fields.
It is important that the process valves do not have any or have extremely few leakages, and that no deposits occur under any operating conditions between the waiting intervals. This requires good adhesive wear resistance from the sealing faces of the valves.
The valve surfaces in contact with the process media (e.g. liquids, sludge and solids) are generally exposed to aggressive, particularly corrosive effects of the media. The high rate of the process media also causes erosive and/or abrasive wear. Further, a prerequisite for the control and reliability of all adjusting motions is that the sealing faces of the valves, which rub against each other, must have a low friction coefficient.
Coating is an effective way of achieving the required low friction coefficients on the surfaces of the parts for process valve and simultaneously reliably protecting the surfaces from wear and corrosion. Different coating techniques, such as hard chrome plating, non-conductive nickel plating, coating with stellite using powder plasma dot welding, thermal spraying and sintering of free-flowing alloys, such as NiCrBSi, are used to protect the surfaces of the valve parts. Thin electrolytically or non-conductively applied coatings tend to wear under heavy load (e.g. high pressure exerted on the surface) and have an operating temperature not higher than 400° C. In the powder plasma dot welding and the sintering of the free-flowing alloys, the process valve parts, subjected to high thermal load during the coating process, tend to distort. Further, the sintering of the coatings in the furnace is time consuming and expensive.
The thermal spraying methods, such as plasma spraying, detonation spraying and high-rate flame spraying (HVOF), are the most effective methods of applying thick and wear resistant coatings that are able to resist high surface pressure even at high temperatures and at the same time, exhibit good wear resistance. Different thermally sprayed coating systems are used to coat process valve parts. Such coatings are used in particular on the bearing and sealing faces of the valves. The function of the coatings is to reduce adhesive wear, generally together with abrasive wear, and to reduce the friction coefficients of the surfaces rubbed against each other. In addition, high moist corrosion and temperature stability are simultaneously required in many cases.
DESCRIPTION OF RELATED ART
DE OS 42 29 006 teaches the use of universal metal carbide in a metal matrix as a thermally sprayed coating to protect a pair of components subjected to friction, but the solution of the publication is, however, restricted to WC—Co.
The prior art relating to the use of thermally sprayed coatings in process valves is described in detail in two publications (1. R. Manuel, E. Yung, Proc. 7
th
National Thermal Spray Conference 1994, Boston, ASM International, p. 111-114; and 2. E. J. Barrette, Proc. 8
th
National Thermal Spray Conference 1995, Houston, ASM International, p. 699-704). In particular, the publications describe the use of commercially available standard cemented carbide systems as coating systems to coat process valve parts. These include in particular WC—Co and WC—Ni, usually alloyed with Cr, and Cr
3
C
2
—NiCr coatings.
When the above coating systems are used in the above way, their typical defects are apparent. The use of WC—Co is restricted by its poor corrosion resistance and low operating temperature. The alternative Ni binder phases or the alloying with chrome can solve the problems only in part. Cr
3
C
2
NiCr has essentially better corrosion resistance, but poorer wear resistance.
The friction coefficient of all these coating systems is acceptable at low operating temperatures, but within the temperature range 200 to 600° C. the coefficients are too high.
The systems also have a restricted alloying capacity, and so the alloy compositions for the coatings can be adapted to a particular use only to a very restricted extent.
Another alternative is to use TiC as hard material with a suitable binder matrix, as described in U.S. Pat. No. 4,233,072 and WO 87/04732 A1. However, the use of TiC as the only hard material phase and, moreover, in a lower concentration does not suffice to improve the coating characteristics over the prior art cited above. Further, the use of the coating powders described in DD OS 224 057 and DE OS 4 134 144 does not solve the problem, either, since the pulverized raw material in these two publications does not show any particular hard material structures that would enable the production of thermally sprayed coatings with improved characteristics.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide parts of the above type for process valves, the parts being better suited to extreme operating conditions than the prior art solutions are and are also cost-effective and simple to manufacture.
It is another object of the invention to provide a coating system for parts that is easily adaptable to different operating conditions by changing the alloy like composition.
It is yet another object of the invention to provide a coating system for parts that ensures a low friction coefficient and high wear and corrosion resistance.
It is thus the object of the present invention to provide a cost-effective wear resistant coating for process valves, the coating having a low friction coefficient and being adaptable to the operating requirements of the process valves by the change of the alloy composition and having high wear resistance.
REFERENCES:
patent: 3859057 (1975-01-01), Stoll et al.
patent: 4806394 (1989-02-01), Steine
patent: 1174997 (1964-07-01), None
patent: 224 057 (1985-06-01), None
patent: 224057 (1985-06-01), None
patent: 4134144 (1993-06-01), None
patent: 41 34 144 (1993-06-01), None
patent: 42 29 006 (1994-03-01), None
patent: 1433399 (1976-04-01), None
Johner et al: Verschleissschutz Durch Thermisches Spritzen Wolframkarbidhaltiger Metallschichten: vol. 44, No. 9, Sep. 1990 pp. 451-454 XP000176368.
P. Vuoristo et al: “Properties of TIC-N1 and (Ti, Mo)C-NiCo coatings sprayed from agglomerated and sintered powders” Thermal Spraying Conference, International DVS-Conference, Mar. 6-8, 1996, Essen, pp. 58-61, XP002056407.
S. Economou et al: “Tribological behavior of TiC/TaC-reinforced cermet plasma sprayed coatings tested against sapphire” Wear, vol. 185, 1995, pp. 93-110, XP002056408 (no month).
Berger Lutz-Michael
Laitinen Kai
Mäntylä Tapio
Vuoristo Petri
Neles Controls Oy
Pillsbury & Winthrop
Speer Timothy M.
Young Bryant
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