Easy-clean ceramic coating for ovens

SWEDEN

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PATENTS AND REGISTRATION OFFICE

PUBLISHING LETTER No. 367 661 intci C 23 d 5/02

Patent Application. No. 5354/70 Received 17 IV 197 0 Validity Date 17 IV 1970

Ans. generally available on 18 X 1970

Ans. published and the publication document published on 4 VI 1974

Priority requested from 17 IV 1969 (US, 817 128)

SCM CORPORATION, NEW YORK, NY US

Inventor: RE Ott, Bet Air, Md.

Agent: L Brann

Process for the preparation of an adhesive self-cleaning ceramic coating on a metal substrate intended for use in a cooking device

The term self-cleaning surfaces is used as a term and, in the present case, refers to surfaces which require a temperature of at least about 400 ° C to effect pyrolytic removal of accumulated carbonaceous material, such as residues or burnt material when cooking foods. The term continuous cleaning surfaces is used as a trade term and in the present context to denote surfaces which, when heated to 175-290 ° C, reduce and counteract the accumulation of carbonaceous residues derived from burnt material and the like, for example fat, derived from the preparation of foods. .

Previously used ovens or other self-cleaning appliances have been based on pyrolysis to remove grease splashes and burnt material from the surface of the oven wall. The evaporated products could then be oxidized over a platinum network. Very high temperature, long time and unpleasant air often characterize these methods. Later, continuously cleaned ovens have been developed, such as those described in U.S. Patent 3,266,477. The latter devices, which often exhibited poor abrasion resistance, utilized strongly oxidizing catalysts, for example, platinum or oxides of chromium, manganese, nickel and the like in the furnace, these catalysts being embedded on the surface of the wall, the catalysts being disposed in surface-mounted materials which were supported in surface materials. , for example, alumina or silica.

As advantages of the present invention over prior art devices, it may be mentioned that the invention enables continuous cleaning properties.

Dupl.kl. C 03 c 7/00 with a high degree of efficiency for reducing and counteracting the accumulation of splash and burnt material on the surface at temperatures between 175 and 290 ° C and that the surface is resistant to at least the moderate abrasive effect that arises when the surface is washed by hand , rubbed or scraped. Furthermore, the present invention offers lower costs than similar devices containing surface-embedded oxidation catalysts, significant impact strength, use of only one coating, the possibility of directly re-coating defective parts without having to scrap them, and the possibility of avoiding incorporation of heavy metal compounds in such coating. this can become toxic or have other unwanted effects.

The present invention relates to a method of producing an adherent ceramic coating on a metal substrate intended for use in a cooking or similar device, the coating being capable of reducing the accumulation of carbonaceous residues obtained by the action of frying grease or the like. This method is characterized by applying (a) to the substrate in intimate contact with each other an enamel composition containing particles of alkali-containing glass frit, about 0.5 - 25 $ halide calculated on the weight of the glass-free and about 2 - 75 parts by weight per 100 parts by weight solid material content of the enameling composition, of particulate elemental metal, which is aluminum, magnesium, high or predominant alloys of either or both of these metals and mixtures of these materials;

(b) heating the coated substrate in a heating zone until the enamel composition and the particulate metal, by mutual influence, form a coherent, porous, sorptive surface coating containing crystalline glazing products;

(c) interrupting this mutual reaction in a cooling zone before significant confluence or coalescence of the structure has occurred.

The invention enables improved devices for heating foodstuffs (preparation of food with heating, cooking, frying, etc.) with means for heating the food preparation area and means for supporting food when cooked and a wall at least partially connects or encloses the food heating, is provided with an adhesive ceramic coating which is applied in the manner stated above.

Oven walls or oven surfaces and other wall surfaces can also be treated with the above-mentioned method, as well as broiler pan and grill or similar.

Examples of parts of cooking appliances that have been treated can be mentioned internal stoves, broiler racks, grills, trays, reflectors, burners and such equipment parts as trays, grills, pans and the like.

₃ 367641

It is well known that fat splashes when cooking often form carbonaceous deposits or deposits when heating food. These deposits are difficult to remove from the surface of parts or objects in or on an oven during surface washing or in grinding. Continuously cleaned parts according to the present invention, upon heating to a temperature of about 175-290 ° C, remove such splashes or deposits of carbonaceous material. The mechanism that causes the disintegration or removal is not fully understood. The carbonaceous products can be chemically altered, for example, by decomposition into lower molecular weight compounds which evaporate and pass to the surrounding gas phase.

It is believed that the porous, extended (sorptive) surface obtained by the process of the invention prevents the grease splash from being burnt to a lacquer-like residue to prevent such splashes from collapsing during the stage of heating at which presumably polymerization and confluence ( coalescence) of the fat would normally take place on a normal non-sorptive or less sorptive surface. It is known that cooking fat has a relatively low vapor pressure and does not evaporate easily at normal cooking temperature. As a result, grease splashes, in particular grease-carbon unsaturation grease, tend to decompose and burn to a lacquer-like residue at the temperature used in cooking rather than vaporizing. The sorptive surface obtained according to the invention is conceivable to prevent confluence or coalescence of grease splash at the cooking temperature and therefore prevent formation of such varnish-like residues. The sorptive surface obtained according to the invention can also give improved evaporation effect through a large exposed surface. The fat can thereby more easily evaporate at relatively high temperature without corresponding risk of forming a lacquer-like carbonaceous residue.

The invention will now be described in more detail with reference to the accompanying drawing.

The first 16 figures are photomicrographs of coatings according to the invention on steel substrates. Figs. 5.8, 11 and 14 are taken with direct light. Figures 1, 3, 6,

9, 12 and 15 are occupied with oblique incident light. Figures 2, 4, 7, 10, 12 and 16 are cross sections of the coating on a steel support. Areas of elemental metal such as white irregular particles appear on the photomicrographs. The steel substrate appears in the photomicrographs showing the cross-section, such as brightly colored material with clear rope or grinding marks. The mounting material above the cross-section and the cavities in the coating appear on all microphotographs such as the darkest, irregular spots. '!

Fig. 1 is a photomicrograph with magnification 340X of a steel plate support provided with an adhesive chemical sorptive coating prepared by the procedure of Example 6 below, the surface being viewed from above and oblique The plate is baked in a plastic mounting material to facilitate micro shooting. The assembled specimen was then ground to obtain a smooth surface. Mellax. the mounting material and the substrate are the ceramic matrix material applied by the method of the invention and bond the metal particles and indicate the cavities. The solid particulate material used in preparing this coating had a grain size such that 18% of the material was retained on a sieve of 0.074 mm mesh.

Fig. 2 is a photomicrograph with the magnification 610X of a cross-section of the steel plate and coating used as shown in Fig. 1.

Fig. 3 is a photomicrograph of magnitude 340X seen from above and with oblique illumination of a steel plate support, which is provided with the adherent ceramic sorptive coating prepared by the method described in Example 6. The specimen was prepared and ground in the same manner as the specimen shown in Fig. 1. The particles used in making this coating had a particle size such that only trace amounts were retained on a 0.037 mm mesh screen. This coating has particularly good properties.

Fig. 4 is a photomicrograph of the first degree 610X of a cross-section of the steel plate used as a substrate and the coating shown in Fig. 3. The coating appears to be more porous than the coating shown in Figure 2, the pores being smaller and more uniformly distributed than in the material of Figure 2.

Figures 5, 6 and 7 are photomicrographs of the composition described in Example 10 hereinafter, which were burned at 7S0 ° C for 4 minutes to a good, continuous, self-cleaning surface. Fig. 5 is a direct shot at first degree 100X. Fig. 6 shows the same surface with oblique illumination at first degree 100X. Fig. 7 is a cross section through the same surface at magnification 200X.

Figs. 8, 9 and 10 correspond to Figs. 5, 6 and 7 and show a coating according to Example 10, except that the coating was burned at 815 ° C for 4 minutes. The resulting coating had very poor performance in terms of continuous cleaning. The coating was clearly burnt. It can be observed that the coating of FIG.

contains significantly more voids than the coating of Fig. 10 and that the coating shown in Fig. 10 has evidently volatilized the sauna or coalesced considerably so that the voids are removed.

Figs. 11, 12 and 13 correspond to Figs. 5.6 and 7, except that the coating was the one described in Example 5, which was burned at 815 ° C for 3 minutes. This coating proved to be one of the best tested in terms of the ability to continuously clean,

Figures 14, 15 and 16 correspond to Figs. 5, 6 and 7 and refer to the same composition as Figs. 11, 12 and 13 except that the firing was carried out at 926 ° C for 3 minutes. The continuous cleaning effect of the resulting ceramic coating is still moderate to good, but the coating shows a tendency to burn.

One can observe the smaller number of voids in Fig. 16 compared to Fig. 13 and the larger size of the voids. The cavities in the more efficient coating (Fig. 13) are smaller and considerably more numerous in the entire coating.

Fig. 17 is a view of a stove with an oven in which the oven walls and the interior wall of the oven are coated with the ceramic coating of Example 5. Fig. 18 is a view of an oven wall plate of the oven of Fig. 17 provided with a coating according to example. 5 and showing the ridges which act as support for oven grids or the like.

As a summary of the first 16 figures, the following conclusions can be drawn. Figures 1 and 2 show a useful coating with nocturnal to good effect, but this coating is less effective than the coating shown in Figures 3 and 4, in which the starting material was ground. to much finer particle size so that the material appears to undergo a solid phase reaction during an initial stage. 5, 6 and 7 show a useful coating with good efficiency heat-treated appropriately, while Figs. 8, 9 and 10 show the same coating in the burnt state so that the effect of the coating for continuous cleaning is substantially destroyed. Figs. 11, 12 and 13 show a coating with very good properties in terms of the ability to continuously clean and the burning of this coating is almost optimal for this particular material. FIG. 14, 15 and 16 show how the same coating can be burnt somewhat and lose a certain degree of efficiency and shows a tendency to deteriorate to marginal utility. The firing of this coating at temperatures up to 1038 ° C for 4 minutes essentially destroys the effect of the coating in terms of its continuous cleaning ability.

Overburning entails a certain degree of collapse of at least the highest points of the porous surface (a kind of flame polishing) and gradual confluence of the matrix phase in the coating. The confluence or coalescence and the gradual elimination of the pores becomes more pronounced to the extent that the combustion increases. A large part of the porous structure is eliminated or collapses. In addition, a pronounced coalescence or clumping of the particulate material appears to have taken place when viewed under optical microscope. In a highly efficient coating, when viewed under a microscope, the different particles of gray, black and light color are relatively evenly distributed and dispersed. If the same coating is burned more vigorously at higher temperatures, the gray particles appear to coalesce or become more agglomerated so that isolated black particles and a lighter background appear more, -. also marked at 100X magnification,

In general, a markedly darkening reaction occurs when elemental metal reacts with the pits in the presence of the halide component. For a given composition, in many cases, the darkest color corresponds to the most effective heat treatment reaction, but this relationship does not in all cases apply accurately to all types of compositions.

Each useful square exhibits a conversion or transition zone which can be determined by plotting, in a graph whose vertical axis indicates increasing linear expansion of the glass in the upward direction and along the horizontal axis, increasing temperature to the right. Ife receives an approximately straight line from the intersection point of the axles367661 up to a weak inflection point scm. Has been called equivalent rate temperature (Andrews Porcelain Enamels, second edition, p. 59, Girard Press, Champaign, Illinois, Afs 1961). At this point, the linear expansion increases with increasing temperature up to a maximum, at which further increase of the temperature causes a decrease in the linear expansion. This second point of inflection is referred to in the same article by Andrews, p. 59 fusion temperature. Other authors have different names for these two points. Thus, Volf in Technical Glasses (Sir Isaac Pitman &amp; Sons Ltd., London, UK, 1966) designates the lower point of annealing temperature and the upper point of incipient deformation point. This initial deformation point corresponds approximately to a low value for the viscosity of about 8. The initial deformation temperature can be determined according to ASTM-Test Method C-539-66 - Linear Thermal Expansion of Porcelain Enamel Frits by the Interferometer Method. The area between these two temperatures is called the transformation or transition range. above the initial deformation point, the metal present in elemental form begins to react significantly with the frit for the purpose of the invention and sintering can usually be observed along with gradual darkening. At this point, the continuous cleaning action may be acceptable but the coating is soft. The cleaning effect decreases slightly as the heat treatment reaction passes this point and then increases as the coating burns harder. Studies have shown that the useful frit (glass) has an initial deformation point which does not significantly exceed about 685 ° C, preferably 370-650 ° C and especially 410-500 ° C.

From the experimental work on which the present invention is based, it has been found that the most effective surfaces for continuous cleaning are those in the preparation of which the temperature range between the initial deformation point and the optimum burning temperature is passed during the burning within a period of less than about 7 minutes, and preferably less than about 5 minutes, and especially for about 2 minutes or less. After this interval is passed (between the initial deformation point and the optimum firing temperature), the heat treatment reaction (a type of through-heating, soak) between the elemental metal and free-particle particles is continued for a maximum of about 6 minutes and preferably about 0.5-5 minutes, and more preferably about 1 minute. , 5-2 minutes time at the optimum firing temperature. Approximately 10 minutes of reaction at temperatures above the initial deformation point is generally too long and entails excessive collapse or collapse of the porous structure to obtain a surface of fully usable continuous cleaning capability.

Crystalline glazing products have been observed in the pre-treated coating by X-ray diffraction examination. Thus, for example, with aluminum such as elemental metal alumina, sodium aluminosilicate and other crystal phases are not yet identified. The firing can be adjusted for a particular composition or for a particular plant using more or less refractory frying, changing the treatment line or conveyor speed and / or adjusting the firing temperature. The chemical and physical interaction between the glass, the formation of pores or cavities and the formation of new crystalline phases are of course complicated. The reaction is stopped by cooling, most simply by removing the coated metal substrate from the firing zone and introducing it into a room with air of room temperature so that the heated object is allowed to cool to room temperature. Other types of cooling or shock cooling can be carried out with forced circulation of gas or the like if required or desirable.

For a given composition, the elemental metal will gradually decrease on the surface, as measured by X-ray diffraction, when identically the same sample material is burned over the same period of time (for example, a total of 3 hours) but at increasing temperature. The bright color of the elemental metal is initially very clear in the coating. What is presumed to be oxide interference prevents accurate measurement of the metal if the firing is interrupted or kept very low in the temperature range between the initial deformation point and the optimum burning temperature, and the coating often becomes somewhat soft even if the coating is capable of continuous cleaning. is less suitable than coatings that are burnt harder.

A typical coating, such as that described in Example 5, after burning for 3 minutes at 705 ° C on a steel plate as a substrate is capable of continuous cleaning but is still soft. At 732 ° C, the coating darkens and the Moh hardness amounts to about 4. At 760 ° C and at the same time during firing, the Moh hardness amounts to between 5 and 6 and the coating becomes clearly dark. At 815 ° C, the typical Moh hardness is between 8 and 9 and the firing is optimal. This surface is, of course, considerably porous and raw in texture and is quite unlike the smooth, continuous surfaces, which are normally hardness measured with Moh hardness testing. In correlation with this, the level of elemental metal in the surface (measured by X-ray diffraction measurement) has clearly dropped from the same material burned at 705 ° C for 3 minutes. From this temperature, successive specimens burned at 871 ° C, 926 ° C and 982 ° C for 3 minutes show essentially the same Moh hardness and usually, upon visual examination, appear to be gradually somewhat lighter than the deepest color of that at 815 ° C. the burnt sample material. The coating's operations for continuous cleaning gradually decrease with increasing firing temperature, and the material burned at 982 ° C can be considered useful but has marginal utility and is considerably less suitable than the material burned at 815 ° C. When the same kind of material is burned at 1038 ° C for 3 minutes, slightly higher hardness is obtained, the amount of elemental metal in the surface, as measured by X-ray diffraction, is smaller and fat deposits are not removed very efficiently but rather form a lacquer-like or varnish-like coating, which glazes the surface. and is very difficult to remove.

In general, it can be stated that most of the compositions are burned within the relatively narrow range of firing conditions which would be used for direct firing of the corresponding flutter on a metal plate sauce substrate in the absence of elemental metal to obtain a matured (maturation) coating, i.e. film and develop optimum properties regarding chemical resistance, hardness of the surface finish and the like. In such conventional firing directly on a metal substrate, a desirable microbubble structure is formed in a primer coating, and such primer is designated by those skilled in the art as burnt in that microbubble structure is missing or not clearly developed, the ripening temperature or the optimum firing temperature (temperature range) as the present invention may be. be the optimum ripening temperature for the frit, generally plus or minus up to about 110 ° C (200 ° F). This generally corresponds to a range of about 220-385 ° C above the initial deformation point.

The best way to determine the coating's operation and burning conditions to achieve continuous purification action is possibly as follows. A coated steel sheet (20 gauge sheet steel with approximately 160 g / m burnt coating in a single layer directly on the sheet steel or on a pre-applied porcelain enamel primer coating) is heated to 190 ° C, applying a coating of refined corn oil. . 2 brush at an amount of about 15 mg per cm, the sheet is then returned to a heating zone and heated for 1 hour to 190 ° C, then the temperature is raised to 275 ° C, while heating is continued for an additional 2 hours.

A surface with very good continuous purification effect does not show any residue but at its most a slight veil or discoloration is almost impossible to distinguish from a dark coating. An acceptable quality coating exhibits a much clearer visible residue but is still not coated with a lacquer-like coating and the residue is burned over time. A poor-quality coating exhibits adjacent coatings where the corn oil is applied, and this coating is visible to the unarmed eye if you look obliquely at the surface. This simple test makes it possible to determine the operation of the method according to the invention.

The particulate metal used in the preparation of the adherent ceramic coating is in elemental form unlike oxides or other chemical compounds of the metal and is used in atomized state, for example as flakes or powders. The metals suitable for use in the process of the invention are aluminum, magnesium, high alloys of these metals, and mixtures of such metals and alloys. The aluminum and magnesium alloys used should exhibit at least predominantly aluminum or magnesium content. Aluminum can be alloyed with magnesium. The sauce examples of elements which are suitable for alloy with aluminum or magnesium can be mentioned silicon, zinc, nickel, iron, manganese, chromium, copper and cobalt. Typical examples of high-alloy aluminum and magnesium alloys can be found in the third edition of Perry's Chemical Engineering Handbook, published by McGraw-Hill Book Company, Inc., Afs 1950, p. 1527, 1529 and 1531. It is also possible to use mixtures of the indicated two metals and / or the indicated alloys. In view of the activity, non-alloyed metal, especially aluminum, is preferred to provide the continuous described; the purification effect of the coatings.

For best effect, the particles of the elemental metal or alloy used should pass at least through a mesh of 0.250 mm mesh. Usually, the metal or alloy is in the form of flakes or atomized powder. Larger particles can be used in the preparation of the coating, but this often results in a deterioration of the ability for continuous cleaning. In addition, if a grinder is prepared prior to application to the substrate, large particles cause problems regarding the stability and handling properties of the grinder. The particle size of the elemental metal is not of critical importance for the ability of the coating to be continuously cleaned compared to the size of the free particles since firing is normally carried out at a temperature above the melting point of the elemental metal. However, it is desirable that the metal particles be so fine that 95¾ of the particles pass through a screen of 0.053 mm mesh or preferably 0.044 mm.

When preparing a coating with practically useful ability for continuous cleaning, at least about 2 parts of elemental metal per 100 parts of solid or non-volatile material is used in the enamel composition when preparing the applied coating before firing. When using less amount of metal than this, insufficient reaction is obtained during firing, so that a sufficiently porous, sorptive surface is not obtained, Frittan in that case is prone to glass formation or to fill the many pores formed in the surface, and As regards the ability to provide continuous cleaning can be significantly reduced. When the amount of elemental metal exceeds about 75 parts per 100 parts of solid or non-volatile material in the enamel composition, the coating may be less adherent and is probably not as practically useful or effective in the ability of continuous cleaning as a coating made with use. 'of lesser amount of metal. If the coating is made from an aqueous slurry composition containing the metal, high metal content can also give rise to excessive gas formation and consequent problems in preparing the slurry and the resulting sludge often exhibits unsuitable spray properties. Most effective coatings are obtained if the non-burnt coating contains about 15-35 parts of metal per 100 parts of solids in the enamel composition, and this amount ratio is thus preferred.

For reasons of activity and for financial reasons, aluminum metal as elemental metal is preferred in carrying out the invention. Aluminum metal is cheaper than most of the other useful particulate metals listed and also allows preparation of a coating with very good ability for continuous cleaning, and aluminum and reaction products of this metal are generally free from toxic effects when used in processing equipment. or the processing of foods. It is convenient that the used aluminum metal or particulate metals, of other kinds, be in the form of a finely divided metal paste. When the steel is added to the sauce stabilized paste when preparing an aqueous slurry, gas formation caused by the reaction between the metal and alkaline water is easier to control than when the metal is added to sludge in the form of dry powder. A paste that has been found to be suitable is sold under the term hydropaste 830 "by Aluminum Company of America, Afs, and is a blend containing 70% aluminum flakes, based on the weight of the paste, with 95% of the aluminum flakes passing a sieve down the mesh size of 0.044 mm, volatile organic solvent and stearic acid such as leafing agent. Stabilized aluminum pastes of this type are disclosed in U.S. Patents 2,587,266, 2,587,267, 2,587,268, 3,244,542 and, in particular, 2,848,344, and the disclosures in these patents form part of the present disclosure.

In the present case, the term enamel composition is intended to be alkali-containing

O · «.» »» In glass fryers conventionally produced by quenching and consequent decomposition of molten glassy materials, and the term includes, if necessary, conventional and conventional porcelain enamel additives (mill additives) for the application to the surface of pretreated enamel metal or such metal already coated with a preparative coating of the type encompassed by the invention, or on an ordinary porcelain enamel coating such as preparatory primer coating.

A slicker is a type of enamel composition and refers to a dispersion, slurry, paste or spreadable or sprayable blend suspension suspended in a volatile liquid carrier medium. An enamel coating composition for a dry process is an enamel coating composition which is sprayed or applied as particles directly onto a hot substrate.

In preparing the lime, ordinary mill additives, such as refractory oxides, clays, stains, binders, surfactants, thickeners, plant mucus (gums), suspending and peptizing agents, resins and other organic additives, etc. can be used. to achieve the desired stability and texture for the application and improved adhesion to the deposit on the metal substrate. In the process of the invention, it is convenient that the weight content of such refractory oxides and other additives (other than halides) be less than about 15% by weight and preferably less than about 10% by weight of the amount of phase material or non-volatile material, and in particular not more than about 5% of this amount.

The content of solid or non-volatile material in enameling compositions used in accordance with the invention refers to the proportion of enamel composition remaining in the coating after normal or regular drying to remove free carriers. A considerable proportion of the non-volatile material in the sugars is free from, i.e., alkaline glass particles. Typically, the percentage of free sludge is more than 30% and generally amounts to 40-80% and in particular about 55-75% by weight of non-volatile or solid material, or even more than this stated percentage.

In order to achieve good cleaning performance, it is essential that the enamel composition comes into intimate contact with a source of halide in an amount of at least about 0.5% and up to about 25% calculated as the amount of halogen based on the glass frit. In order to make intimate contact, it is preferred that the halide be melted freely, but it may also be added to the enamel composition as an additive in the preparation and alternatively may also be added from a primer coating which gives off the halide during firing. The most active halide for the desired action is fluoride, and a decreasing effect on the ability to continuously clean using chlorine, bromine and iodine is observed, in the order indicated, such as replacement for fluoride. For practical use of the halide in the enamel composition is mainly fluoride. It is difficult and generally accompanied by losses to introduce more than about 25% (based on the weight of the glass particles) into a free composition, and greater amount can also impair the desired ability to clean. According to the invention, the use of fluoride alone such as halide is preferred, wherein the fluoride is melted into the glass and amounts to about 3-4% by weight of the weight of the glass-free tank.

The halide can be melted into the frit by the addition of fluorospate, sodium silicofluoride, cryolite, sodium fluoride or other alkali metal halides. It is convenient for the halide to be melted in this way in the frit to give the best control of the composition. Fluorides in particular and halides in general appear to produce a desired and desired interplay between the metal particles and the frit.

However, the halide can also be incorporated into the enamel composition as well as additives at the time of addition by the addition of fluoride, alkali metal chloride, eto. to frittai before painting it. Halides other than fluorides are difficult to incorporate into the frit through melting.

The glass frits suitable for the present invention are generally of two basic types, alkali borosilicates and alkali aluminophosphates. Alkali metal oxide, in particular sodium and / or lithium oxide appears to be a necessary ingredient. Generally, the alkali borosilicates contain about 25-65% by weight SiC₂, 10-25% 1 0 alk (alkali metal including lithium oxide and preferably also some sodium oxide for better activity ), 2-20% and 5-40% modifiers (the modifiers) wherein the modifiers are typically oxides of alkaline earth metals and / or metals belonging to Group IIB of the Periodic Table, for example, magnesium oxide, calcium oxide, strontium oxide, barium oxide, zinc oxide, etc. In addition, even very small proportions of adhesion-enhancing oxides (e.g. cobalt oxide), colorant oxides (e.g. manganese oxide, cobalt oxide, iron oxide, etc.) and opacifying oxides can be found in conventional ways. .

In general, alkali aluminum phosphates have the following composition: 10-50% by weight ·. ²2θ5 'alkali metal oxide (R₂O), 10-35% Al₂Og and 10-30% modifier, which are typically B₂°3» ^s^2 ^{and T}2 ° Adhesion promoter materials, colorant materials, and oxide-inducing materials can also be incorporated as indicated for the previous type of glass frit. Conventional methods are used for the composition of the glass coating or bulk for the preparation of the free-tank, wherein silica can be supplied in the form of such mineral silica quartzite ground to grain size less than 0.074 mm, alkali metal silicofluorides, and zirconia, B₂O₃ can be added in the form of borax, boric acid or rasorite, P₂Og can be supplied in the form of sodium tripolyphosphate, alkali metal and alkaline earth metal can be supplied in the form of carbonate, fluorides, nitrates and various kinds of minerals used in the charge, alumina can be supplied directly in the form of this oxide, in the form of feldspar, and / or in in the form of cryolite, zirconia can be supplied in the form of ground zirconium, titanium oxide can be added such as the oxide in question or rutile ore, and fluoride as well as other halo genides can be added in the manner stated above.

The best deep fryers contain the sodium oxide and / or lithium oxide combined or bonded in the fryer with regard to the ability to continuously clean, the lithium oxide presumably lowering the optimum firing temperature when lithium oxide is added instead of some or all of the sodium oxide. If potassium oxide is used to replace the entire amount of sodium oxide or lithium oxide, the effect on the ability to continuous cleaning appears to be somewhat disadvantageous. Addition of a certain amount of BgOg as a substitute for silica seems to improve the demand for continuous cleaning. Changes or adjustments in the content of oxides of alkaline earth metals or metals belonging to Group IIB do not appear to have any major effect on the continuous cleaning requirement. Adhesive promoting and coloring oxides, for example oxides of cobalt, manganese and the like, can be used as is conventional in primer coatings. If these substances are excluded from the enamel composition either from use as additives in painting or from the glass, this does not appear to have any effect on the quality of the coating produced for continuous cleaning. However, some impairment of the adhesion ability has been observed if the low cobalt content of conventional basic coating fryers is omitted. Refractory oxides, for example titanium dioxide, zirconium dioxide, clays, silica, zirconium, alumina and calcium zirconate added as milling additives to the free composition can help to extend the burning interval to some extent, but it is appropriate for reasons of operation and for financial reasons not to exceed about 5% of the world dry weight for most effective use.

Experiences regarding the composition of alkali borosilicate frit can be summarized in the form of the following table. Minimum levels, practically usable maximum levels and preferred by weight, of the various oxides and elements used in the preparation of coatings according to the invention, one with the ability to continuously clean (which has not left significant varnish-like coatings in testing) , which refers to weight percentages:

<td></td><td>Minimum</td><td>Maximum</td><td>preferred</td>

<td>SiO?</td><td> 24</td><td> 66</td><td> 42</td>

<td>^B2°3</td><td> 2</td><td> 23</td><td> 8</td>

<td>Na₂0</td><td> 3</td><td> 20</td><td> 18</td>

<td>F</td><td> 0</td><td> 20</td><td> 3,5</td>

<td>^Co.3°4</td><td> 0</td><td> 1</td><td> 1</td>

<td>ai₂O₃</td><td> 0</td><td> 10</td><td> 0,5</td>

<td>ZrO₂</td><td> 0</td><td> 15</td><td> 15</td>

<td>CaO</td><td> 0</td><td> 10</td><td> 3</td>

<td>BaO</td><td> 0</td><td> 14</td><td> 0,7</td>

<td>^Ti02</td><td> 0</td><td> 21</td><td> 3</td>

<td>ZnO</td><td> 0</td><td> 29</td><td> 2</td>

<td>Li₂0</td><td> 0</td><td> 6</td><td> 2</td>

<td>^V2°5</td><td> 0</td><td> 0,2</td><td></td>

<td>Moog</td><td> 0</td><td> 4</td><td></td>

<td>k₂O</td><td> 0</td><td> 22</td><td></td>

<td>MgO</td><td> 0</td><td> 1</td><td></td>

<td>SrO</td><td> 0</td><td> 0,2</td><td></td>

<td>PbO</td><td> 0</td><td> 17</td><td></td>

<td>Nine</td><td> 0</td><td> 2</td><td></td>

<td>CuO</td><td> 0</td><td> 0,5</td><td></td>

<td>MnO₂</td><td> 0</td><td> 2</td><td></td>

<td>^P2°5</td><td> 0</td><td> 3</td><td></td>

<td>CdO</td><td> 0</td><td> 2,5</td><td></td>

<td>^Sb2°3</td><td> 0</td><td> 2</td><td></td>

<td>^pe2°3</td><td> 0</td><td> 0,2</td><td></td>

<td>^As2°3</td><td> 0</td><td> -</td><td></td>

<td>Cl</td><td> 0</td><td> -</td><td></td>

<td>IN</td><td> 0</td><td> -</td><td></td>

<td>Br</td><td> 0</td><td> -</td><td></td>

<td>Cr "0"</td><td> 0</td><td></td><td></td>

<td> 2 3</td><td></td><td></td><td></td>

<td>Twist</td><td> 0</td><td> -</td><td></td>

It will be obvious to those skilled in the art that chlorine, bromine and iodine cannot be easily blended into a frit in the same way as fluorine. These substances can be added as mill additives in the form of metal halides. It is also apparent that certain materials which can be incorporated into the frit by themselves may not necessarily be useful in view of inappropriate properties in treating foods such as lead, arsenic and other optional materials.

The frit is generally milled so that at least about 95% of the material passes through a sieve of 0.074 mm mesh, and in order to achieve good capacity for continuous cleaning and to facilitate production for a maximum of about 0.2% is retained in a sieve with a mesh size P, 044 mm. The frit is ground into a ball mill and the particulate elemental metal can then be mixed with the milled frit with a low-power working slurry (lcw shear bling), for example, a pony crank or with a stirrer fitted to the atmosphere. In general, the finer the paint used, the better the ability to continuously clean the coating, but in some cases it has been found that if the entire amount of grit is ground to a finer grain size than 0.037 mm, some deterioration of the coating's operation occurs.

In preparing the sorptive coating, a dried coating is applied to the substrate in the form of a coating containing a halide content enamel composition (either in the glass fryer or sauce grinding additive or added: with ^oneundercoating, as described below), and 2-75 parts of elemental metal per 100 parts of solids in the enamel composition. The enamel composition may be applied in a dry state or as a lick containing volatile liquid carrier.

One way to apply a coating to the dry method is to mix the enamel composition, add metal to the preparation of intimate powdery mixture and apply this mixture over and on the substrate. This mixture of the free composition and metal to form the specified mixture should be carried out in a relatively inert environment to prevent significant oxidation of the elemental metal. However, satisfactory results can be obtained and the mixing, application of the mixture to the substrate and firing are carried out rapidly. Another method is to apply a first layer of powdered aluminum metal to the substrate and then a layer of the enamel composition. Bias formation in the coating can often occur during firing if aluminum is applied after the enamel composition is applied. Because of this bias formation, the latter methods are less suitable for both aesthetic and practical reasons.

The preferred method of applying a coating to a substrate is to perform simultaneous deposition of seeds. an aqueous slurry containing volatile liquid carrier, non-volatile material or solid comprising the frit (containing halide additive) and particulate elemental metal (as well as usually volatile adhesive, suspending agent, thickening agent and other conventional grinding additives). Simultaneous application is preferred because thereby ensuring intimate mixing of free tan and the elemental metal without significant conversion of the metal to oxide. Sludge is usually prepared by mixing carriers, ferrets, suspending agents, painting additives and particulate elemental metal in e.g. a pony mill, a stirring tank or an equivalent low shear slurry.

By the term volatile liquid carrier is meant a liquid which acts as a medium for dispersing the frit and the particulate elemental metal and is volatile at normal drying temperature up to one or several hundred ° C. For efficiency and for economic reasons, water is a preferred carrier. Furthermore, slightly better coatings with continuous cleaning action can be obtained when using water than when using organic carriers. However, as examples of other useful volatile liquid carriers may also be mentioned lower aliphatic alcohols, ketones, alkyl esters of aliphatic alcohols, aliphatic and aromatic hydrocarbon solvents such as xylene, toluene, benzene, heptane, decane and the like. Volatile Carrier Ratio: Non-volatile material in the lick is usually kept between 0.5: 1 at. about 10: 1. Lower and higher ratios of carrier to non-volatile material usually cause difficulties in applying the sludge to the substrate. The amount ratio of carrier to non-volatile or solid material is therefore usually controlled so as to obtain a sludge having the desired spraying or dipping properties.

Another method of applying an enamelling composition to the substrate to apply a first layer of a primer coating of licks containing a frit without the addition of elemental metal in particulate form but with the addition of halide to the substrate and then applying an enameling composition such as an overcoat in the form of a slicker composition containing a second frit with little or no halide addition but with elemental metal in the amount indicated above primer coating. The halide in the primer coating appears to diffuse sufficiently to the cover layer upon firing and contributes to the reaction between the glass and the elemental metal. A primer coating may consist of porcelain enamel applied directly to the base metal to act as an intermediate layer between the metal and the cover layer. By cover layer is meant a coating that is applied to a primer coating or undercoat.

After the coating is applied to the substrate, the coating is usually dried before burning. Drying of the slicker coating is usually carried out at atmospheric pressure and at a temperature of up to cal75 ° C. Drying should be carried out in a relatively short period of time to reduce the oxidation of the elemental metal. The intention is to remove the volatile liquid carrier medium prior to firing, but without causing significant reaction between elemental aluminum and present water or causing the coating to form flakes or otherwise fall off the substrate. Wet coatings are more difficult to burn in a satisfactory manner than dry coatings. The drying step is therefore carried out to improve efficiency.

The apparently dry coating is transformed into an adherent ceramic coating capable of continuous cleaning by heating the deposited coating containing the frit and particulate elemental metal, as stated above.

One point of view in connection with the firing process is that the firing is carried out at a temperature and for a period sufficient to form a cohesive, porous, sorptive surface but insufficient for significant and gradual reduction of porosity and final fusing of the resulting complex ceramic composition. as a result of the heat treatment. If the coating is burnt, the matrix shows a tendency to sink, become shiny at peaks or raised places, and the efficiency of the coating with regard to the ability to continuously clean rapidly decreases with the degree of burn. Underburning caused by burning at too low a temperature or for too short a time does not cause a sufficient reaction between the fryer and the elemental metal so as to mar. obtains a sufficiently hard (e.g. Moh 4+), porous, sorptive surface. Optimum for best results, burning should be carried out at such temperature and for such a long period that the coating provides the normal, strongly adherent bond to the metal substrate and the mutual influence or reaction between elemental metal and glass takes place to form the highly porous structure. The burning is usually carried out in air, but relatively good burning results can be obtained if most or almost all of the oxygen is removed.

During firing, a halogen-activated reaction is assumed to take place between the elemental metal and the glass, probably with some amount of water or hydroxyl groups adhering, so that gaseous materials are formed and released. The formed gases cause small pores, voids, cracks and the like so that a porous matrix is ​​formed in the ceramic coating. In addition, projections are formed on the surface which increases the surface area. The activity of the coating with regard to the ability for continuous cleaning seems to depend on the appearance of a very large specific surface of both external and internal kind which is achieved during the burning and is retained thereafter by the cooling. The porous and windy structure of the burnt coating appears to become deformed and collapse so that the specific surface reduces the similar porosity of the coating.

To show this, a free-pitch position which was practically identical to the composition as set out in column 2, rows 14-22 of U.S. Patent No. 2,898,253 was mixed and mixed with 25% aluminum flakes, after which the mixture was applied to steel plate and three. specimens were burned at a temperature and for a period of 30 minutes at 926 ° C, 4 minutes at 805 ° C, respectively. 4 minutes at 750 ° C, The coating's ability to continuously clean was 0 for the first treatment, poor for the second treatment and good for the third treatment while the gloss of the burnt coating diminished in the same order, the burn; appear to have been desirable for the same kind of materials in previously used heat treatment methods, while the present invention is characterized by avoiding overburning and considering that even moderate temperature rise can cause overburning. Λιχ. Examples hereinafter show that a moderate reduction in firing temperature and duration of firing often provides much better coating in terms of the ability to continuously clean a cooking surface when using a particulate mixture of enamel composition and metal powder;

In general, useful ready-made coatings can be obtained by burning at normal temperature and during the period of time. used for optimum maturation of the particulate frite used if the elemental metal was not present. For the deep fryers best suited to the present invention, firing is normally carried out at a temperature slightly above the sintering temperature of the composition (455-760 ° C, depending on the viscosity-temperature relationship of the glass composition) up to about 926 ° C. Typically, this optimum firing temperature is within a range of 220-385 ° C above the initial deformation point. When used. of a free take with the composition set forth in Example 1, a firing temperature is between about 705 ° C and about 87Ö⁶C and burning time between about 2.5 minutes and no more than about 20 minutes suitable. Preferably, the firing temperature is maintained between 760 ° C and 815 ° C for a period of about 3-8 minutes.

Another point of view of the burn is that the best coatings in terms of the ability for continuous cleaning are obtained if the heating during the burning is carried out quickly. This is shown in Example 7. When using a muffle-type oven for firing, the thickness of a metal substrate whose turning capacity is equivalent to steel should in this respect not exceed about 10 mm and preferably below 5 mm. Thicker metal substrates have a lower heating rate in muffle-type furnaces and often provide coatings with poorer use characteristics in terms of drying capacity for continuous cleaning. However, thicker sections that are heated or preheated very rapidly, for example by electrical induction, can be used for coatings with good efficiency in terms of continuous cleaning ability. Sheet material of. common type (steel, aluminum, copper, etc.) for household purposes, such as ovens, frying pans, and the like, have a thickness of about 16-22 B&amp;S gauge and preferably 20 gauge, and this thickness is preferred for the present invention. These metal materials are prepared for enamelling in a conventional manner for best adhesion between enamel and substrate. As an example, steel can often be cleaned, machined and provided with a thin nickel (flash of nickel) coating for best adhesion between the enamel and the substrate. ,

A thickness of about 0.1 mm after firing is preferred in the burnt top coating or single ceramic coating of the invention. This corresponds

2 about 160 g per m. A burnt coating having a weight of less than about 53 g / m on a clean metal surface usually allows metal oxide (e.g. iron oxide) to color through, while a burnt coating having a thickness exceeding about 265 g / m

...

m often exhibit spontaneous splitting. To obtain thicker coatings, it is possible to use successive application and firing of the applied coating in accordance with the invention, for example, to obtain a thickness of about 0.3 mm in three successive application and firing steps without splitting due to gas formation.

The examples below show ways of applying the present invention. All temperatures refer to ° C and all percentages are by weight unless otherwise stated. All quantities are by weight.

Example 1

A preferred fryer for use in preparing a coating according to the invention was prepared by fusing the materials listed in Table A at a temperature of 1177 °. Table B indicates the calculated oxide composition of the frit. After melting, the total weight of the batch was 1556 parts by weight.

Table A

Parts by weight

<td>silica</td><td> 520</td>

<td>fetriumhydroxid</td><td> 328</td>

<td>Fluorspar</td><td> 60</td>

<td>Zinc oxide</td><td> 26</td>

<td>sodium fluorosilicate</td><td> 105</td>

<td>litiunikarbonat</td><td> 90</td>

<td>zirconium</td><td> 364</td>

<td>barium carbonate</td><td> 15</td>

<td>Rasorit</td><td> 195</td>

<td>rutile</td><td> 53</td>

<td>cobalt oxide</td><td> 17</td>

1773 parts by weight

Table B

<td>Na +</td><td>oxide Composition weight Percent 17.87</td><td>mole percent 18.61</td>

<td>CaO</td><td> 2,75</td><td> 3,16</td>

<td>Fluorine</td><td> 3,77</td><td> 6,41</td>

<td>^B2°3</td><td> 8,02</td><td> 7,43</td>

<td>SiO₂</td><td> 42,56</td><td> 45,75</td>

<td>Al ^ Og</td><td> 0,40</td><td> 0,25</td>

<td>MgO</td><td> 0,08</td><td> 0,14</td>

<td>ZnO</td><td> 1,64</td><td> 1,29</td>

<td>Li₂0</td><td> 2,29</td><td> 4,96</td>

<td>ZrO₂</td><td> 15,49</td><td> 8,12</td>

<td>BaO</td><td> 0,74</td><td> 0,31</td>

<td>CoO</td><td> 1,02</td><td> 0,88</td>

<td>Ten₂</td><td> 3,27</td><td> 2,64</td>

<td>^V2°5</td><td> 0,03</td><td> 0,01</td>

The frit produced after melting was pre-milled in the ball mill so that essentially the entire amount of frit passed through a sieve with a mesh size of 0.044 mm. The frit had an initial deformation point of about 455-482 °,

Example 2,

It is prepared by mixing 1000 parts of the frit prepared according to Example 1 with 70 parts of conventional porcelain enamel, 50 parts of finely divided silica with a particle size of about 0.044 mm, 3.75 parts of hydrated borax, 1.25 parts of bentonite clay, 1.25 parts parts magnesium carbonate, 0.5 parts sodium nitrite and 483 parts water. These materials were loaded into a ball mill and ground for 1.5 hours to a sludge.

104 parts of the lick containing about 80 parts of non-volatile material were mixed with 20 parts of atomized elemental aluminum powder with a particle size less than 0.074 mm and milled in a ventilated ball mill to form a coating / layering lick. The resulting coating lick was sprayed onto a 20 gauge steel plate conventionally prepared for porcelain enameling, in an amount of about 160 g of dry solid material per m (about 430 g of moist) of the substrate. The coated substrate was dried at about 150 ° for about 10 minutes until most of the water on the surface was removed from the coating. No reaction of the elemental aluminum metal with the atmosphere during the drying was observed. The coated substrate was then burned in the presence of air in a muffle furnace at a temperature of about 805 ° for 4 minutes, removed and cooled in a cooling zone to room temperature.

It was estimated that heating the coated substrate from room temperature to the firing temperature required about 1 minute. It was also estimated that the fries were kept at the burning temperature for an additional 3 minutes for throughput. This is the period of time during which the sorptive surface is optimally formed by the mutual interaction of aluminum and the fryer. porous, sorptive coating on the substrate, which was designated disk X, after air cooling. The adhesive coating on the substrate of disc X, after burning and cooling to room temperature, had a thickness of 0.076-0.1 mm and had dark color and a weight 2 of about 160 g per m coating on the substrate.

Example 3.

A number of similar 20 gauge steel sheets described hereinafter are coated, burned and cooled in the manner set forth in Example 2 except as set forth herein and subsequently assessed for continuous continuous operation 367661 ο

For cleaning as follows: bacon grease (about 15 mg per cm of the coated sheet surface) was brushed on the coated surface of a sheet heated to 175 ° in the form of intersecting strips or a plurality of strips. The plate was heated for 1 hour to a temperature of 175 °, after which the temperature was raised to 275 ° for 2 hours. This heat treatment constituted a test cycle, The assessment system used in the assessment of the continuous cleaning effect of the coating on the sheet was based on an arbitrary scale between 0 and 10, the latter being the best result. The test value 10 was indicated if any residual fat or lacquer-like material formed therein and little or no visible discoloration could be detected with the unarmed eye on the tested coating after a test cycle. The test value 0, corresponding to the fact that most of the fat initially greased surface was covered with a darkened or charcoal varnish-like gloss, remained after a single test cycle,

Sample Test value

1) Sample plate X according to Example 2

2) Sample plate prepared in the same way as sample plate X except that enamel clay is not used in the slicer composition. 10

3) Sample plate prepared in the same way as sample plate X, except that 20% of finely divided magnesium powder of which substantially the entire amount had a particle size of 0.074 mm or less was used instead of 20% aluminum powder.

4) Sample plate prepared in the same manner as sample plate X except that 20% of finely divided iron powder of which almost the entire amount had a particle size of 0.074 mm or less was used instead of 20% aluminum powder 6

5) Sample plate prepared as Sample plate X except that 20% of finely divided silicon, which is so; almost the whole amount had a particle size less than

0.074 mm was used instead of 20% aluminum powder 5

6) Sample plate made as sample plate X except that 20% of finely divided copper, almost entirely of particle size 0.074 mm or less, is used instead of 20% aluminum powder 5

7) Sample plate made from the sauce sample plate X, except that 20% of finely divided nickel powder of almost only particle size less than 0.074 mm was used instead of 20% aluminum powder 3

8) Sample plate made from the sauce sample plate X, except that 20% finely divided zinc, almost only with particle size 0.074 mm or less, was used instead of 20% aluminum powder 1

9) Sample plate made of the sauce sample plate X except that finely divided metallic tin, almost only down to particle size 0.074 nm or less, was used instead of 20% aluminum powder 1

10) Sample plate prepared as sample plate X except that 20% finely divided nickel oxide, almost only with particle size 0.074 mm or less, is used instead of 20% aluminum powder

11) Rough plate made as test plate X except that 40% fine-grained aluminum powder, almost only particle size 0.074 mm or less, is used instead of 20% aluminum powder

6, the sheet was also brightly colored and discoloration could therefore be more easily observed

12) Sample plate prepared as sample plate X except that 5% fine-grained aluminum powder, used almost only with a particle size of 0.074 mm or less, is used instead of 20% aluminum powder

Example 4

A series of surfaces was tested for the ability to continuously clean with the test set forth in Example 3. The same valuation system used in the experiment of Example 3.

Tested surface

1) Aluminum sheet

2) Sample plate prepared as Sample plate X of Example 2 except that aluminum powder is not used

3) Conventional hydrocarbon decomposition catalyst consisting of 25% alumina and the residual silica ground to particle size less than 0.044 mm and deposited on glass plate

4) Prepared with aluminum powder of Example 2, mixed into a bacon grease paste, applied to a glass plate and subjected to a test cycle, the grease disappearing and the aluminum metal forming a continuous, apparently continuous coating. This aluminum coating surface was tested.

Testing Safety

Example 5,

A plate with the best properties obtained in the test in terms of continuous cleaning ability was prepared as follows:

Step 1: Preparation of licks was prepared by mixing 100 parts of pre-milled frit prepared in the manner set forth in Example 1, 2 parts of conventional porcelain enamel, 0.25 parts of bentonite clay, 3/64 parts of barium chloride, 5/64 parts of sodium alumirate and 50 parts of water. These materials were ground in a ball mill for a period of about 6 hours until only traces of the particulate material in the enamel lick were retained on a sieve mec 0.044 mm mesh. The resulting lick had a density of about 1.75

Step 2: The solution of the Fai binder was prepared by mixing 25 parts of a component alkyl phenoxy polyethoxy ethanol sold under the trade name Triton X-100 and produced by Rohm% Haas Company, Afs, 110 parts of a component made up of an ammonia neutralized acrylic acid resin water, the water constituting 75% by weight of this component and the material being marketed under the name Acrysol P6N by Rohm &amp; Haas Company, Afs, and 1975 sharing water.

The heating of the mixture to about 38 ° C or slightly higher was found to facilitate the dispersion of the components in water.

Step 3: A premix was prepared by mixing 25 parts of the binder solution according to steps 2 and 43 parts of a paste, which was 69% elemental aluminum flake powder, which was coated with fatty acid lubricant and had a particle size of about 0.044 mm, in a carrier of 13% mineral turpentine (predominantly aliphatic hydrocarbons down boiling point between 150 and 200 °), 12% 1-nitropropane and 6% of an alkyl arylsulfonate wetting agent. This paste is marketed under the designation Hydropaste by Aluminum Dompany of America, Afs. Other aluminum pastes of this type which are particularly suitable for carrying out the present invention are described in U.S. Patent No. 2,848,344. After the material Hydropaste is substantially mixed, an additional 25 parts of the binder solution is added to form a premix.

Step 4: 175 portions of the lick prepared at the step were mixed with slurry in an open stirred vessel together with the entire amount of a pre-mix prepared according to step 3. The mixture was reapplied until substantially all of the slioker-prepared slurry was free of lumps. The slurry core density after mixing was approximately 1.45.

It has been found that by the addition of finely divided elemental aluminum metal in the manner so specified, a substantial improvement of the slab core storage life or service life is obtained. It is previously known that about unstabilized finely divided elemental; Aluminum metal is mixed with the enamel composition and water results in considerable gas formation and licks show a tendency to instability if the slioker core is allowed to stand. Step 5: The lime prepared according to step 4 was sprayed onto a conventional 20 gauge steel sheet which was conventionally pretreated for and commonly used for the preparation of walls in ovens in kitchen stoves, applying about 2 to 270-350 g wet coating per m of substrate and about 160-220 g of dry coating 2 per m of substrate.

Step 6: The wet coating was dried at about 150 ° for a period of about 10 minutes to form a coating which felt dry upon contact.

Step 7: After drying, test plates were introduced. in a muffle oven for burning. The firing was carried out at a temperature of 815 ° for a period of 3 minutes. It was estimated that approximately 1 minute time was required for heating the coated substrate to 815 ° firing temperatures and that approximately 2 minutes of heat treatment at 815 ° was performed there. the mutual reaction between aluminum and the frit. At the end of this 3-minute firing period, the substrate was removed from the muffle furnace to a room-temperature cooling zone and allowed to cool to room temperature. The coating on the burnt substrate had a thickness of about 0.076-0.1 mn and exhibited very good properties. the ability for continuous cleaning. Microphotographs of these coatings are shown in Figures 11, 12 and 13.

The procedure summarized in Process Steps 1-7 is performed except that the coating is applied as a cover layer to a porcelain enamel primer coating. The resulting cover layer exhibited very good properties in terms of the need for continuous cleaning.

Another coated substrate having substantially the same ability for continuous cleaning was prepared in the manner specified in steps 1-7, except that the pre-milled frit did not contain cobalt.

Kitchen stoves with ovens were made in a factory as follows: The metal walls of the oven were prepared mainly in the manner indicated in steps 1-7 and mounted in the stoves so that the walls enclosed the oven area. The walls showed very good properties in terms of the need for continuous cleaning.

Example 6

Three test plates A, B and C were prepared in the manner set forth in Example 2, with the exception that the frit used in preparing the coating was pre-molded as follows:

(a) Sample plate A frit was ground in a ball mill for 2 1/2 hours. 18.7% of this frit was retained on a 0.074 mm mesh screen;

(b) the frit for sample plate B was ground for the same 6 hours as the fry of (a). 1.4% of this clearance was retained on a 0.044 mm mesh screen;

(c) the plate for C plate C was ground for 11 hours in the same equipment as the two previous frites, after which 600 g of the resultant milled product was further ground in a 1000 g ball mill for 60 minutes. Only 0.2% of this frit was retained on a 0.037 mm mesh screen.

Sample plate A is shown in Figures 1 and 2. Sample plate C is shown in Figures 3 and 4.

Figures 1 and 2 show a surface with highly irregular matrix containing relatively large cavities or pores. Upon critical inspection, it can be observed that the coating of Figures 3 and 4 appears to have a more uniform and more porous structure than the coating of Figures 1 and 2.

Figures 2 and 4 show cross sections through the sample plates A and 2 respectively. C and show that cavities, cracks, sore pores, etc. exist under the top surface of the coating and in most cases these cavities below the surface are connected to the surface through small pores and cracks or cavities. Furthermore, the coating of FIG. 4 exhibits significantly more and smaller voids than the coating of FIG. 2, and these voids are more uniformly distributed in the coating. It can also be seen that the coating of FIG. 2 contains greater amount of elemental aluminum (light areas) than the coating of Fig. 4, but in both cases at least a certain amount of elemental aluminum is present in the fired ceramic coating.

Sample plates A, B and C were soiled with thin strips of bacon grease and refined corn oil in a manner similar to that of Example 3 and tested and evaluated in the manner set forth in Example 3, the effectiveness of the coating in terms of continuous cleaning ability and residual discoloration or the coating is given in the following table using the valuation system specified in

<td>Example 3. sample plate</td><td>Frittans Sight Analysis</td><td>Testing Safety</td><td>Remaining coatings.</td>

<td>A</td><td>18.7% on the mesh size 0.074 mm</td><td> 6</td><td>Some coating remains (moderate grooves)</td>

<td>B</td><td>1.4% on the mesh size 0.044 mm</td><td> 8</td><td>Weak tracks</td>

<td>C</td><td>0.2% in mesh size 0.037 mm</td><td> 10</td><td>No visible coating</td>

This experiment shows that the ability for continuous cleaning increases with increasing degree of fineness of the milled frit (decreasing particle size).

Example 7

The relative activity in terms of the ability to continuously clean the otherwise identical test plates produced with rapid burning and resp. slow firing was investigated in the manner set forth in Example 2. The substrate and preparation of the coating up to the firing were in accordance with Example 2. Sample plate A was subjected to a hot spot burn test (rapid burn), sample plate B was subjected to a cold point burn test (slow burn). Hot-point firing tests were carried out by placing coated 20-gauge steel test plates 10 cm wide and 15 cm long and fired at points in a muffle furnace in the presence of air at a temperature of 805 ° for 4 minutes. The cold point burn test was performed by placing the test plates on a cast iron plate of identical width and length of 6.4 mm thickness and being burned for 10 minutes in the same oven when kept at the same temperature. The second sample plate was held during firing approximately 1.5 mm from the surface of the cast iron plate with wire support. The results of the continuous cleaning performance of the two test plates are given in the following table:

Sheet A Sheet B

Hot-spot testing Cold-point testing

Efficiency Remaining coatings. Efficiency Remaining coating, 10 None 7 Moderate

Example 8.

The operation for the continuous cleaning performance of the plates prepared in the experiment of Example 5 was compared with a conventional commercial plate designed to provide continuous cleaning provided with an oxidation catalyst embedded in the surface. Each plate is coated with bacon fat and corn oil and tested in the manner set forth in Example 3. At the end of a test cycle, the sample plate of Example 5 did not show any visible coating and gave an efficiency value of 10. The commercial plate exhibited a slight to moderate coating remaining on the surface, showing that not all of the corn oil and bacon fat was removed. This coating received the efficiency value 8,

Example 9,

Another glass frit suitable for the preparation of sheets capable of continuous cleaning was prepared by melting the materials listed in Table A in weight percent at a temperature of 1150 ° and rapidly cooling the molten material in water. The frit had the calculated oxide analysis listed in Table B. The frit had an initial deformation point of about 482-510 °.

Table A

weight Percent

<td>Quartz</td><td> • · ; 34,7</td>

<td>Borax</td><td> 21,8</td>

<td>Feldspar</td><td> 19,9</td>

<td>sodium hydroxide</td><td> 11,2</td>

<td>Fluorspar</td><td> 5,4</td>

<td>sodium nitrate</td><td> 4,9</td>

<td>Litiummanganit</td><td></td>

100,0

Table B

Calculated oxide analysis (%)

<td>Si0₂</td><td> 53,11</td>

<td>^B2°3</td><td> 16,49</td>

<td>Na₂0</td><td> 15,10</td>

<td>of K₂O</td><td> 2,23</td>

<td>Li₂0</td><td> 0,59</td>

<td>CaO</td><td> 4,30</td>

<td>al₂°3</td><td> 3,64</td>

<td>MnO₂</td><td> 1,73</td>

<td>F</td><td> 2,81</td>

Example 10.

Two coated test plates were prepared using the frit of Example 9, one plate being burned at a temperature of 750 ° for 4 minutes and the other being burned at 805 ° for 4 minutes. Both plates were prepared except for the firing in the same manner as indicated in steps 1-6 of Example 5. Microphotos of the 750 ° burnt plate are shown in Figures 5, 6 and 7, and end photographs of the 805 ° burnt plate are shown. in Figs. 8, 9 and 10. The plate burned at 750 ° exhibited good properties in terms of the ability to continuously clean while the plate burned at 805 ° C appeared to be burnt and had worse properties than the plate burned at 750 ° in terms of the ability to continuously clean. Part can be observed that fewer and even larger cavities and slits can be observed in the plate burned at 805 ° than the plate burned at 750 °.

Example 11.

A test plate was prepared in substantially the manner set forth in Example 5, step 16, except for the burn, in order to compare the effect of the burning temperature on the ability for continuous cleaning. In this case, the firing was carried out at a temperature of 927 ° for 3 minutes. Microphotographs of the burnt plate are shown in Figs. 14, 15 and 16. The plate exhibited acceptable properties in terms of its continuous cleaning ability but was inferior to that. The sheet produced according to Example 5, while the sheet burnt at 815 ° for 3 minutes, as indicated in Example 5, exhibited an efficiency value of 10. This test showed that for this particular composition, the burning tended to slight low burn.

Example 12.

One-fryer, through melting of conventional bulk materials, was prepared under substantially the same conditions as those of Example 1, and this release proved useful in place of Example 5. The frit had the oxide assay listed in Table A.

Table A

Oxide Analysis (%)

<td>Silica -</td><td> 26,8</td>

<td>Boron oxide</td><td> 17,3</td>

<td>phosphorus pentoxide</td><td> 1,0.</td>

<td>calcium oxide</td><td> 6,6</td>

<td>barium</td><td> 13,1</td>

<td>sodium oxide</td><td> 14,5</td>

<td>potassium oxide</td><td> 0,8</td>

<td>alumina</td><td> 4^0</td>

<td>zirconium</td><td> 3,4</td>

<td>Fluorine</td><td> 4,3</td>

<td>Zinc oxide</td><td> 6,4</td>

<td>molybdenum oxide</td><td> 2,3</td>

The frit showed an initial deformation point of about 482 °.

Example 13.

Another frit was used instead of the frit specified in Example 12 in preparing a coating and proved to be suitable for preparing a coating with good continuous cleaning ability. Freeze the oxide assay indicated in Table A. The temperature for initial deformation was about 510-540 °.

Table A

Oxide Analysis (%)

33,1 17,3 0,8

Silica. Boron oxide

phosphorus pentoxide

<td>calcium oxide</td><td> 6,7</td>

<td>magnesium oxide</td><td> 0,2</td>

<td>barium</td><td> 13,2</td>

<td>sodium oxide</td><td> 15,3</td>

<td>potassium oxide</td><td> 0,9</td>

<td>alumina</td><td> 4,7</td>

<td>Fluorine</td><td> 4,3</td>

<td>nickel oxide</td><td> 1,4</td>

<td>cobalt oxide</td><td> 0,5</td>

<td>magnesium oxide</td><td> 1,2</td>

<td>Strontium</td><td> 0,2</td>

<td>ferric oxide Example 14,</td><td> 0,1</td>

<td colspan="2">Yet another frit was used instead of the frit of Example 12</td>

<td>when preparing a coating,</td><td>and this frit proved to be suitable for making</td>

<td colspan="2">application of a coating with very good drying capacity for continuous cleaning. Frittan ha-</td>

<td colspan="2">they are the oxide analysis listed in Table A below. The fryer had an initial deformation point of 482 °. Table A Oxide Analysis (%)</td>

<td>silica</td><td> 27,1</td>

<td>Boron oxide</td><td> 16,8</td>

<td>phosphorus pentoxide</td><td> 1,0</td>

<td>calcium oxide</td><td> 6,8</td>

<td>barium</td><td> 13,9</td>

<td>Eitiumoxid</td><td> 0,6</td>

<td>sodium oxide</td><td> 13,5</td>

<td>potassium oxide</td><td> 1,8</td>

<td>alumina</td><td> 4,5</td>

<td>Fluorine</td><td> 5,4</td>

<td>Zinc oxide</td><td> 3,2</td>

<td>molybdenum oxide</td><td> 4,21</td>

<td>antimony</td><td> 1,1'</td>

Example 15,

A different frit was used instead of the frit of Example 12 in the preparation of a coating, obtaining a coating with good ability for continuous cleaning. The frit had the oxide analysis set forth in Table A below.

Table A

Oxide Analysis (%)

<td>silica</td><td> 1,3</td>

<td>Boron oxide</td><td> 7,0</td>

<td>phosphorus pentoxide</td><td> 44,5</td>

<td>sodium oxide</td><td> 22,8</td>

<td>alumina</td><td> 20,5</td>

<td>Fluorine</td><td> 4,7</td>

The fryer had an initial deformation point of about 400-427 °,

The coated substrates with the porous, sorptive surface have been found to be effective in removing and reducing decomposable or decomposable carbonaceous products formed in cooking appliances, such as kitchen stoves, but it is obvious that these coatings are also useful for reducing the amount of decomposable or decomposable carbonaceous products in other devices. In addition, carbonaceous products may be contained in gases or be gases, such as carbon monoxide and light hydrocarbons. Examples of such devices are exhaust systems and silencers for cars and other devices, heat exchangers, turbine blades, burner grilles, burner bowls, prefabricated fireplaces (fireplaces), grills, charcoal chambers, carburetor chambers, burner chambers, combustion chambers, combustion chambers, combustion chambers, combustion chambers similar. The porous ceramic coating of the present invention may also be suitable for the sauce surface for application of polymer coatings, for example poly · tetrafluoroethylene. The coating may also be useful in fuel burners and fat collectors and eliminators.