NO130579B - - Google Patents

Description

Ferrous porcelain enamel for self-cleaning stoves.

This invention relates to covers for stove construction, and

more particularly, the invention relates to an improved porcelain enamel frit of such a composition that when it is incorporated into a porcelain enamel coating and a suitable substrate is applied, when heated to a critical temperature range, food residues, which usually splash on the hob when baking or frying, will easily and is completely oxidized to a fine ash residue, which can be easily removed from the enclosed stove room.

While previously self-cleaning cookers have been of the electric type, according to this invention the enamel represents a means by which gas cookers can be made self-cleaning. When it comes to electric stoves, with the help of appropriate design, self-cleaning parts can be made that can be heated to high oxidation temperatures directly by means of elements that are placed along the backs of the surfaces to be cleaned. on the other hand, it is not easy and practical to construct a gas stove, whereby it self-cleanses by controllably raising the temperature of the stove walls to the oxidation temperatures by means of gas nozzles along the backs of the surfaces.

To provide an appropriate self-cleaning gas stove,

it is therefore important that the inner surface becomes effective at relatively low oxidation temperatures, and that these temperatures can be reached with the help of the ambient temperatures by using standard cookers with conventionally placed burners for baking or frying.

It is well known that an increase in the oxygen content of an atmosphere effectively reduces the temperature at which a material oxidizes. This can be observed in particular when organic materials are exposed to an atmosphere with a high content of oxygen. It has been found that certain porcelain enamels, made from frit (glass), are effectively supplied with oxygen when organic materials, such as e.g. food stains, come into contact with the enamel surface, and that oxygen from a normal atmosphere is absorbed by the coating, and that, according to the theory, the oxygen is either stored by or diffuses through the enamel coating and thereby contributes to a sufficient excess of oxygen, which thereby causes an oxidation of food stains when the cover is finally heated in accordance with this invention.

This oxygen absorption phenomenon seems to occur at approx. the same surface temperatures as are required for oxidation of a contaminant of organic material, which comes into contact with the surface, and this oxidation is greatly enhanced by the presence of enamel frit of iron oxide.

An examination of U.S. Patent No. 3,266,477 to Stiles will make apparent and increase the understanding of the unexpected and surprising results obtained according to the present invention.

Stiles uses a number of catalyst materials, which are dispersed on the stove surface using a number of different materials, with the intention of supporting the oxidation of stove contaminants.

From the general part of Stiles' patent it appears that it is important according to his invention to distribute the catalyst materials in a thin layer on the stove surface.

One of the methods that Stiles uses to achieve a sparing distribution of his catalyst in a stove liner is to

stick the catalyst material on the surface. Stiles expressly states, see bottom of column 2, lines 70-72, that even

if he can distribute the catalyst material on the surface of the enamel coating and then reheat the coating to "partially" bake the catalyst into the ceramic layer, then the catalyst should not be baked in so deeply that contact with the catalyst distributed on the surface is prevented. See also column 5, lines 25, etc., where Stiles again emphasizes that it is absolutely necessary that his catalyst particles not be baked too deeply into the enamel coating as this will result in an inactivity with regard to the purification.

Examples 4 and 10-18 in the said patent are special embodiments whereby porcelain enamel is used as the base material for Stiles's catalyst particles. In particular, attention is directed to the number of intricate steps in each work operation, and which can be attributed to the efforts to achieve

a workable catalyst surface layer on porcelain enamel.

It is in the nature of the matter that the catalyst layer according to Stiles's patent, i.e. the so-called catalyst particles, are very difficult to remove by wear, whereby their effect is significantly reduced after a certain period of use.

Surprisingly and in direct contrast to what was described by Stiles, however, the searcher has found that a completely unexpected improvement is achieved by incorporating a larger amount of iron oxide into the frit, whereby this is homogeneously fused into the fritted glass matrix, which is later ground into porcelain enamel and apply a stove liner, requiring only step 1 of Stiles's enamel examples, thereby allowing me to completely eliminate steps 2-5 of Stiles' examples 4, and 11-18

and steps 2-6 of Stiles's example 10.

By incorporating iron oxide into the glass matrix of my frit, this is fixed in the enamel coating in a permanent way so that wear and tear cannot remove it. This means that if the enamel coating is exposed to wear, the homogeneous dispersion of oxidation-promoting iron oxide throughout the enamel coating, and which will always be present in the coating at or near its surface, ensures the presence of oxidation-inhibiting oxide for the oxidation of food residues.

Both of the foregoing advantages, which are unexpected and contrary to what is known in the art, are achieved by precise melting and a completely homogeneous mixing of jemok.vyd into the matrix of glass frit, which forms the base component of porcelain enamel for stoves. cover.

Another advantage of incorporating iron oxide directly into the frit,

is that, because oxide is melted directly into the glass,

there is no need to use high-quality glass, and standard-quality ceramics are therefore sufficient.

For effective oxidation of vegetable oil stains on the stove surface, temperatures of 425°c have previously been necessary. The glass, porcelain enamel or glaze produced according to the present invention will effectively oxidize and remove stains at 260°C, whereby the oxidation time at this temperature is the same as the oxidation time at 425°C. The oxidation at lower temperatures, i.e. in the vicinity of 175°^, can be carried out with the aid of fritters according to the invention, but oxide as ion sv; takes place at a reduced speed.

This invention relates to a highly improved frit and method by which said frit is used for the production of a porcelain enamel cover for stoves, whereby the vitreous frit component makes up a total of preferably 25 - 55% by weight. However, this amount can vary depending on the frit properties and can thus contain from 15% by weight to approx. 70% iron oxide by weight. The said frit is finally ground into a porcelain-enamel slurry for coating and firing onto the metal substrate, which thereby forms a stove construction. The usually box-shaped stove or roasting room is so well known that it is unnecessary to describe them, and they are usually made of steel coated with porcelain enamel. However, as is well known, the porcelain enamel can be coated with a number of metallic materials, such as e.g. aluminium, stainless steel, etc. The invention thus includes oven bearings which are manufactured on

any metal capable of withstanding actual stove temperatures, whereby the coating of enamel contains frits according to this invention.

In the practical production according to the invention, enamel frits are weighed in batches, mixed, melted and rapidly cooled to form flakes or frits, whereby conventional dosing materials and processes are used, except for new amounts of iron oxide, which will be described later.

As will be seen below, the base composition for the frit, apart from the content of iron oxide which is appropriate according to the present invention, is not critical, and it is only required that the frit, when it is fused with a specified percentage amount of iron oxide, must be fusible and have the necessary physical properties that make it applicable for burning on metal substrates as a firmly adhering porcelain enamel coating raea preferably matt to semi-matt surface.

The expressions "matt" and "semi-matt" are well known among professionals, and these expressions therefore need no further definition.

To be completely precise and to make it easier to understand the description and requirements, "matt" and "semi-matt" refer to a surface that shows a 45° specular gloss value of less than 5 when using a Photovolt Corporation glossmeter model 610, according to AS TM standard method for testing 45° mirror gloss for ceramic materials fASTM Designation C-346-

59 (Reapproved 1967)], whereby the preferred value is approx.

3 or less.

Although the composition as such is not important, table I shows below, as a general guide, the oxide components which may be relevant for the production of a frit according to the invention. The table should be understood in such a way that when the weight % of a component is varied, this must be balanced with other components so that you always get a total of 100%.

Moreover, one or more of the indicated components can be completely excluded in a particular frit, whereby e.g. other well-known oxides, even if these are not indicated in the table, may be added in special cases.

The sum of the above-mentioned components must be a total of 100 when the components vary within the specified range.

The amount of iron oxide used depends on the other elements included in the glass, only to the extent that at higher limits for iron oxide, the fusibility of a particular glass can vary and thereby change the processing properties, whereby the amount of iron oxide must be adjusted so that processing can take place .

As previously mentioned and although the preferred range for iron oxide lies in the range from 25 - 55% by weight of the frit, measurable oxidation properties can also be achieved, either alone or in combination, with a content as low as 15% by weight and as high as 70 % by weight, and which depends on the properties of a particular frit, such as meltability etc.

There is no upper measurable limit for the oxidation-promoting oxide, and the only requirement is that there be enough other glass-forming components to provide a workable glass that has the usual properties of porcelain enamel at conventional firing temperatures.

Examples of special vitreous enamel compositions, which are applicable according to this invention, can be seen from the following special working examples.

EXAMPLE 1

The following composition was weighed and mixed in a suitable raw-batch mixer.

The aforementioned mixture was then melted at 1400°c. quenched (fried) in cold water and dried in a dryer at 93°C. The resulting frit has the following composition of oxides in % by weight:

Oskyd wt%

The resulting frit was then ground in a conventional ball mill with the addition of the following:

^OLYTRAN FS is a water-soluble bio-polymer compound containing scleroglucan, i.e. a polysaccharide

with high molecular weight produced by fermentation.

The polymeric structure consists mainly of straight-chain anhydroglucose units linked together beta 1-3. 30 - 35% of the straight-chain units exhibit single-linked anhydroglucose units linked beta 1-6.

This enamel was ground to a fineness of 10 grams/400 mesh/50 cc, then sprayed onto a suitably prepared substrate at an application weight of 30 g/square foot. The enamel was then fired at 783°C for three minutes to a matte finish. The enamels according to the invention will normally burn in at temperatures lower than 870°C.

The above-mentioned paint additive is, as will be seen later, assumed to be "kaolin-free", and is applicable when a layer is applied to a metallic substrate or by a 'direct-on' process, whereby a suitable prepared metal substrate is used.

The frit, which contains the above-mentioned oxidation-promoting iron oxide, was compared with a similar frit which did not contain iron oxide as well as with conventional stove enamel in the following experiment. In this and all subsequent examples, the comparison standard was a blank enamel of essentially the same composition as the enamel according to the invention, except for the oxidation-promoting iron oxide together with a conventional stove enamel from hitherto known stoves, and which does not contain any oxidation-promoting iron oxide in such quantities as is included in the frit according to the invention.

This and the following examples were assessed by heating to 199°C, and at this temperature a drop consisting of different types of food scraps, lard, meat scraps and sugar water was placed on the hot test piece using an eye drop counter. The sample plates were then heated for 2 hours at 288°C

After this two-hour period, the sample was dressed and judged. The coating according to the invention with iron dioxide fused in showed no residue, while the two comparison standards, which contained no oxidation-promoting iron oxides, had a well-decreasing, black residue where the food sample was placed.

EXAMPLE 2

The following composition was weighed out and mixed in a mixer.

The aforementioned mixture was melted at 1400°C, quenched (fried) in cold water and dried in a dryer at 93°C. The frit obtained had the following oxide composition in % by weight:

The frit was ground in a conventional ball mill with the addition of the following substances:

This enamel was ground to a fineness of 10 g/400 >.v\esh/50cc.,

and sprayed directly onto a suitable metallic substrate with a

application weight of 30 g/square foot5 the firing was carried out at 760°C in three trays, whereby a matt surface was obtained.

The above-mentioned frit was assessed in relation to a blank standard and a conventional stove enamel according to the methods described in example 1. After a two-hour test period, the sample was cooled and compared. The glass with the fused iron oxide showed no residue, while the sample with the conventional enamel and the standard sample without iron showed an adherent black residue.

EKS EMPEL 3

A glass with the following raw-batch composition was weighed in batches

and mixed in a blender:

The mixture was then melted at 1400°C for 40 minutes, quenched in cold water and dried in a drier at 93°C. The resulting frit had the following oxide composition in % by weight:

The frit was then ground in a conventional ball mill and the following substances were added:

This enamel was ground to a fineness of 10 g/400 mesh/50 cc.,

and then sprayed onto a suitably prepared substrate with an application weight of 30 g/square foot. The burn-in was carried out at 783°C for three minutes.

The samples were assessed by following the same procedure as described in example 1. After a two-hour test period, the samples were cooled and assessed. The glass with the fused iron oxide showed no residue, while the sample with the conventional enamel and the glossy standard showed adherent black residue where the food stains had been applied.

EXAMPLE 4

The following composition was weighed out and mixed in a mixer.

This glass was then melted at 1400°C for 50 minutes, quenched in cold water and dried in a dryer at 93°C. The resulting frit had the following oxide composition in % by weight.

The frit was then ground with the addition of the following substances:

This enamel was ground to a fineness of 10 g/400 mesh/50 cc, then sprayed (directly on, no intermediate primer) onto a suitably prepared substrate at an application weight of 30 g/sq.ft. The burn-in was carried out at 816°C for two minutes to achieve a matte surface.

These samples were judged using the same procedure as described in Example 1. After a cleaning cycle, the glass with fused iron oxide was essentially free of residue, while samples with conventional enamel and the glossy standard showed an adherent black residue.

EXAMPLE 5

A glass with the following composition was weighed out and mixed in a mixer.

The mixture was then melted at 1400°C for 40 minutes, quenched in cold water and dried in a drier at 94°C. The frit obtained had the following oxide composition in % by weight:

The frit was then ground in a conventional ball mill by adding the following substances:

This enamel was ground to a fineness of 10 g/400 mesh/50 cc., then sprayed onto a suitably prepared substrate at an application weight of 30 g/sq.ft. The cremation was done with wood

o

760 C for three minutes to achieve a matt surface.

The samples were assessed using the same procedure as described in example 1. After the two-hour 1-hour test period, the samples were cooled and assessed. Thereby, the glass with 17% fused iron showed no remaining residue, while the sample with conventional enamel showed an adherent black residue. As previously established, the composition of the frits according to the invention is not particularly critical, and this fact is the basis for Table II below, whereby the quantity ratios of the various oxides correspond to examples 1-5.

The total quantity is always 100.

While I have shown the utility of this class of vitreous coatings in connection with self-cleaning stoves, it is clear that the utility of a vitreous coating such as mine, which is capable of oxidizing organic compounds, may also be applied to other areas. , e.g., as enamels in connection with the exhaust system of kilns, whereby the fumes, which have hitherto been discharged into the free atmosphere, may be supplied to a series of hot surfaces, which may be coated with my porcelain enamel for' oxidation to compounds which can be accepted as air pollutants. The same theory can be applied to car exhaust systems, where the interior could be coated with mine enamel and thereby obtain combustion products that are less toxic and more acceptable as air pollutants. The ability of these coatings to oxidize organic materials is a function of time, temperature and the type of organic material to be oxidized. Generally, little or no effective oxidation can be achieved below a temperature of 177°C. It can be expected that the upper temperature limit for the oxidation, and by which my overcoat is used, will lie in the area of approx. 316°C. This further means the advantage that extensive safety and locking devices are not necessary at these temperatures as the probability of an explosion, which may be the result of a sudden excess of oxygen due to the opening of the stove door, can be considered to be greatly reduced within this temperature range, while, on the other hand, at higher temperatures according to previously known methods for heat oxidation of stove stains, there was always a certain danger of such explosions, and consequently a safety lock device was required for the stove door.

Of the above-mentioned practical examples, apart from the percentage of oxidation-promoting oxide in the frit which can be reduced by means of added components in the paint, such as e.g. aluminum in example 4, the percentage by weight of oxidation-promoting oxide in the finished, baked-in enamel coating will essentially be the same as in the frit.

Claims (2)

1. Porcelain enamel which is essentially produced from amorphous frit for application to an iron substrate, and which is applied to the substrate at a temperature below 871°C, and which is in the form of a matte or semi-matte porcelain enamel coating which can oxidize organic residues which settles on the coating, at a temperature from 177°C to 316°C, characterized in that iron oxide is homogeneously fused in the frit in a quantity ratio corresponding to 15 - 70% by weight expressed as Fe2O^, and that the rest of the frit is essentially published whereby the sum of the aforementioned components always becomes loo when the component amount varies within the specified ranges. 2. Frit or enamel according to claim 1, characterized in that it contains 25 - 55% by weight of iron oxide.