Oven rack having an integral lubricious, dry porcelain surface

Abstract

A lubricious porcelain coated steel wire oven rack. The preferred coated steel wire oven rack includes a plurality of elongated steel wire members joined together to form an oven rack having an outer surface. The plurality of elongated steel wire members are made from a cold drawn steel rod material containing from about 80 to about 99.9% by weight of iron, up to about 0.08% by weight of carbon and from about 0.001 to about 0.2% by weight of a carbon stabilizing transition metal, preferably selected from the group consisting of Vanadium, Tantalum, Titanium and Niobium. In a preferred embodiment, the porcelain surface of the oven rack includes a dry lubricant selected from carbon; graphite; boron nitride; cubic boron nitride; molybdenum (IV) sulfide; molybdenum disulfide; molybdenum sulfide; molybdenum (IV) selenide; molybdenum selenide; tungsten (IV) sulfide; tungsten disulfide; tungsten sulfide; silicon nitride (Si3N4); TiN; TiC; TiCN; TiO2; TiAlN; CrN; SiC; diamond-like carbon; tungsten carbide (WC); zirconium oxide (ZrO2); zirconium oxide and 0.1 to 40 weight % aluminum oxide; alumina-zirconia; antimony; antimony oxide; antimony trioxide; and mixtures thereof.

Description

FIELD OF THE DISCLOSURE [0001] The present disclosure is directed to glass, ceramic or porcelain coated metal products wherein the porcelain coating has a lubricious surface such that repeated sliding contact against another porcelain surface does not cause noticeable deterioration in the form of marring, chipping or flaking of the porcelain of either porcelain surface. In the preferred embodiment, these products are porcelain-enameled steel oven racks that are subjected to temperatures above 500° F., usually above 900° F., as in self-cleaning, pyrolytic ovens, and the metal is steel wire that has the composition disclosed in this assignee's U.S. Pat. Nos. 6,837,235 and 6,915,552, both hereby incorporated by reference. Alternately, the product can be formed of cast iron, such as a burner grate. The preferred combination of the steel wire together with the lubricious porcelain coating provides oven racks which do not discolor during cooking or during self-cleaning cycles when the ove...

AI Technical Summary

Benefits of technology

[0007] Described herein is a lubricious porcelain-coated metal oven rack designed to be received within an oven cavity. In the preferred embodiment, the coated metal oven rack includes a plurality of elongated steel wire members formed of a special steel composition and joined together to form an oven rack having an outer surface; wherein the diameter of the steel rod material is reduced by at least about 20% when the steel rod material is drawn to form the steel wire; the outer surface of the oven rack being coated by a glass material having a lubricious, integral, dry outer surface, the glass material preferably being porcelain. The amount of carbon in the steel rod material, the amount of carbon stabilizing transition metal in the steel rod material and the degree to which the cross-sectional area of the steel rod material, is reduced, when the steel wire is drawn from the steel rod material is selected, i.e., balanced, so as to prevent chipping of the glass material away from the outer surface due to the release of hydrogen gas from the steel wire members when the steel wire is either heated or cooled.

[0010] The plurality of elongated steel wire members are made from steel rod material containing from about 80 to about 99.9% by weight of iron, up to about 0.08% by weight carbon, e.g., from about 0.001 to about 0.08% by weight of carbon, and from about 0.001 to about 0.2% by weight of a transition metal that will have a stabilizing effect on the carbon in the elongated steel wire members such that the carbon absorbs less hydrogen gas when the steel wire member is heated to temperatures above 500° F. than it would in the absence of the carbon stabilizing transition metal. In preferred embodiments, the transition metal is selected from the group consisting of Vanadium, Tantalum, Titanium and Niobium, and in the most preferred embodiment, the transition metal is Vanadium. The plurality of elongated steel wire members are preferably made from steel rod material by a cold drawing process to reduce the diameter of the steel wire. In the preferred process, the steel rod is pulled through a cold die that gradually reduces in diameter so that the rod is drawn repeatedly through the die and the cross-sectional area of the rod is reduced to form a steel wire having a cross-sectional area of diminished diameter. In preferred embodiments, the diameter of the steel wire is diminished at least about 20%, preferably at least about 30%, more preferably at least about 40%, even more preferably at least about 45%, and most preferably at least about 50%. It will be appreciated that the diameter reduction creates voids in the steel wire which are desirable to provide cavities into which hydrogen gas can be received and, perhaps, compress, without creating pressure to be released from the surface of the steel wire once the steel wire is coated with porcelain. It will be appreciated, that the diameter reduction, which creates cavities in the steel wire, and the inclusion of carbon stabilizing transition metal elements so that the steel absorbs hydrogen, will diminish the degree to which hydrogen gas out-gassing causes cracking, spalling and chipping of the porcelain surface of the elongated steel wire members of the oven rack which are coated by the glass material.

Problems solved by technology

In addition to the hydrogen out-gassing problem experienced at high temperatures with porcelain-encapsulated steel oven racks, another very significant problem has more recently been discovered during the manufacture, testing and use of the porcelain-coated oven racks.

It has been found that the porcelain can deteriorate by marring, flaking or chipping off of the porcelain material from the oven racks as a result of the normal periodic sliding contact between the oven rack porcelain surface and a contacting porcelain wall surface of the oven cavity.

That is, over the 13 to 15 year normal life expectancy of an oven, the repeated sliding porcelain-to-porcelain contact upon insertion and removal of the porcelain-coated oven racks, particularly when the oven racks are supporting a relatively heavy cooking load, can cause unwanted abrasion, chipping and squeaking of the sliding porcelain surface (of one type) against and across a porcelain surface (of the same or another type) on the oven wall.

Prior to this assignee's out-gassing solution, as described in the '235 and '522 patents, commercially satisfactory porcelain-coated oven racks to be used in self-cleaning pyrolytic ovens were non-existent so that assistance in attempting to solve the porcelain-to-porcelain abrasion and flaking problem in porcelain materials that are regularly subjected to temperatures above 900° F. was not forthcoming from the prior art.

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