US3178323A - Enameling composition and method of application - Google Patents

Description

April 13, 1965 w. w. BROWN l-:TAL 3,178,323

ENAMELING COMPOSITION AND METHOD OF APPLICATION Filed Jan. 17, 1962 2 Sheets-Sheet l www/WM 60% AAAAAAAA o AAAAMAAAA/vvm YO/QAMAMAAAAAACAA 07 O/ a 0/ol 20% `30% 40% 50% 60% 70% 80% 90% [00% INVENTORS W. WIL AM BROWN MERR E. GOTTFREDSON BY ROLAND O. PABST April 13, 1965 w. w. BROWN ETAL 3,178,323

ENAMELING COMPOSITION AND METHOD OF APPLICATION INVENTORS W. WILLIAM BROWN MERRILLE. GOTTFREDSON BY ROLAND O. PABST A Homey United States Patent O 3,178,323 ENAMEHNG CMPOSTEN AND METHB 0F APPLICATIN Walter Wiiliam Brown and Merrill E. Gottfredson, Provo,

and Roland 0. Pabst, Springviile, Utah, assignors to Pacific States Cast iron Pipe Company, Provo, Utah, a

corporation of Nevada Filed Jan. 17, i962, Ser. No. 166,839 10 Claims. (Cl. 148-134) This invention relates to a composition suitable for the formation of porcelain enamel coatings on metallic surfaces and to the methods of forming such enamel coatings. More particularly, this invention relates to an enameling composition which will form tightly adherent coatings on ferrous metal surfaces, particularly cast iron pipe, eg., gray iron or ductile iron pipe, without prior cleaning of the surfaces.

Heretofore, it has been essential to have a clean metallic surface as a base for the formation of a porcelain enamel coating. Unless the base surface was free from contaminants, such as scale, oxides, etc., enamel coatings would not satisfactorily adhere thereto. For good results, the metal base surface is usually subjected to one or more cleaning operations, such as pickling, Sandblasting, grinding or other cleaning operations.

The pre-cleaning of ferrous metal surfaces such as cast iron was particularly troublesome because of the roughness of the surface, which made it more difficult to completely remove scale and oxides. These ditiiculties were compounded in the cleaning of the interior of cast iron pipe, particularly long sections of pipe, because of the obvious difficulty in inspecting the inside surface for cleanness prior to coating.

in View of the above diliiculties, heretofore cast iron pipe has conventionally been lined with cement rather than enamel where a relatively low cost interior coated pipe was required. Cement-lined pipes were considered to be superior to unlined pipes because there was less tendency for the lined pipe to build up mineral deposits, nodular growths and the like. Also, it was found that the cement-lined pipe may have a lower coefficient of friction, thus promoting higher flow rates.

The use of cement-lined pipe, however, was not considered completely satisfactory for a number of reasons. For example, the application of the cement involved extra operations after the pipe had been made. Also, in order to achieve the desired results, it was necessary -to form a coating of substantial thickness, that is, 1/s to 1A inch, depending on the diameter of the pipe. Such a coating thickness reduces the etfectve diameter of the pipe, thereby minimizing any increase in flow rate normally expected to result from the lower coefficient of friction.

The present invention is the result of a discovery of an enameling composition which will form tightly adherent porcelain enamel coatings on metal surfaces without the pre-cleaning of the surfaces as heretofore has been considered necessary. Moreover, the enameling composition of the invention may be applied to and become adherent on oxidized metal surfaces such as, for example, scaled or rusted ferrous metals. Furthermore, the present invention includes a novel method for rapidly and economically forming such tightly adherent coatings, particularly on cast iron surfaces without pre-cleaning of the surfaces.

The employment of the enameling composition of the present invention in the formation of coatings on cast iron pipe, fittings, valves, hydrants, and other cast iron articles, provides a number of additional benefits. For example, the enamel coatings are substantially thinner than cement linings and have a lower coeficient of friction.

These factors together result in the enamel-coated cast.

iron pipe having a substantially higher flow rate than a cement-lined pipe. Moreover, our porcelain coating has a very smooth surface, which reduces the tendency for foreign materials to adhere thereto.

Since the porcelain coating is substantially impervious, the rate of corrosion of the cast iron, e.g., ductile or gray 1ron, is appreciably reduced. This reduction in the rate of corrosion, particularly when both the interior and the exterior of the pipe are coated, permits the use of pipe having thinner walls since the customary allowance for corrosion of the pipe is minimized. An obvious advantage is a saving in weight of the iron with a corresponding reduction of the cost.

Furthermore, since the enameling composition of the invention permits the formation of tightly adherent coatings without pre-cleaning of the base surface, the cost of producing enamel-lined pipe is less than that for cement-lined pipe. An additional reduction in cost is achieved by the employment of the method of this invention, whereby the steps of coating the pipe may be carried out during those of the annealing operation, thereby eliminating subsequent processing of the pipe as is required in the lining of pipe with cement.

The enameling composition of the present invention comprises essentially a furnace slag, borax, and an aluminosilicate material, such as the feldspars or clays previously employed in enamel formulations. In addition to the borax which functions in part as a fluxing agent, the enameling composition advantageously also contains one or more conventional uxing agents such as various inorganic salts, for example, carbonates, fluorides, nitrates, etc.

The furnace slag employed in the enameling composition of the invention preferably is a slag from either an acid or basic cupola furnace. Generally, the slag from an acid cupola furnace contains more oxides of silicon than oxides of calcium, Whereas the slag from a basic furnace will contain a higher proportion of calcium oxides. As a result, the silicon oxides in the slag will comprise between about 1/2 to 2 times by weight the amount of the calcium oxides with the higher proportion of the Silicon oxides being present in the slag from an acid cupola furnace. Preferably, such cupola slag contains only relatively minor amounts of iron oxides, for example, `less than about l0 or 15% or so.

The slag is generally formed by the reaction of coke and limestone with pig iron or other ferrous material. In some cases, a portion or all of the pig iron may be replaced by iron or steel scrap. Also, a portion or all of the limestone may be replaced by dolomite, a calcium magnesium carbonate. In such cases, the slag will be termed a basic slag if the total amount of the oxides of calcium and magnesium is greater than the proportion of the silicon oxides.

In addition to the above-mentioned slags from acid and basic cupola furnaces, slags containing at least a major proportion by weight of oxides of aluminum, calcium, iron, magnesium and silicon also may be employed. For example, the slag from a blast furnace for the making of pig iron from iron ore is quite similar to a basic cupola slag and may be used in carrying out this invention. Therefore, slags within the above characterization will be termed furnace slags for the purpose of the present invention.

Among the aluminosilicate materials employed in combination with the slag in formulating the enameling composition of the invention are various feldspars and clays commonly employed in enameling formulations. While feld spars and clays are dilerent in their physical form, their chemical composition is generally quite similar since many clays are products of the decomposition and degradation of the feldspathic rocks. The feldspars and clays, when used in finely divided condition, are believed to iniiuence the fusing temperature and firing range of the enameling composition, and, in some cases, function as suspending. agents for the various'enamel constitutents. Also, these aluminosilicate materials may affect the opacity, brilliance, a-nd surface characteristics of the fused enamel coating. Advantageously, a plastic or fatty clay, i.e., a lowPCE (Pyrometric Cone Equivalent) clay is employed. 'Othersuitable clays include china clays, `ball clays, stoneware clays, activated clays, dusting clays, bleaching clays, calcined clays, colloidal clays, and filler clays. Bentonite and fullers earth also may be employed as an aluminosilicate material for the purposes of the invention.

As pointed out above, while borax is generally. considered a .fiuxing agent, it is desirable to include in the enameling composition of the invention small amounts of other fluxing materials such as sodium nitrate, the 11u0- rides of calcium and sodium, and various forms of sodium carbonate, e.g., soda ash and trona.

Among the metal oxides which may be present in the enameling composition, in addition to the various oxides present in the above principal constituents, are the oxides of manganese, cobalt, titanium, chromium, copper, nickel, lead, tin, zinc, andthe like. In the case of the oxides of manganese and cobalt, it is believed that they assist in making the enamel coating more tightly adherent to the basesurface while other oxides generally function as coloring materials. Oxides of manganese are particularly preferred in the present composition because of their ability to i-ncrease adherence of the enamel coating to cast iron without greatly increasing costs. The proportion of the furnace slag employed in the enameling composition is preferably between about or 1.0% and to 40% by weight of the composition. Generally, if less than about 5% of the slag is present, the enameling composition is too fluid and tends to burn more easily. In addition, if insufficient slag is present, the fired coating may be dough-like and not adherent to the base surface. When the proportion of the slag is greater than about 40%, the coating has a tendency to craze, that is,'has many fine cracks, and is less tightly adherent to the base surface.

The proportion of the other aluminosilicate materials, e.g., clay or -feldspar, in the enameling composition is preferably between about 20% and 40 or 45% by weight. If less than about 20% is present, the enamel coating tends to blister and burn, whereas, if` the proportion of the aluminosilicate istoo large,the composition tends to thicken and'become lumpy so that it becomes. extremely difficult to form smooth, uniform coatings.

The proportion of borax in the enameling composition is preferably between about 15 or 18% and 37 to 40% by Weight of theicomposition. If the proportion of borax is reduced below this range, the enameling composition generally does not melt and flow uniformly so that uneven coatings are formed. If the proportion of borax is greater than this range, excessive uxing of the composition may take place, with the result that the coatings are thin and tend to blister and burn.

Advantageously, the relative proportions of the three principal constituents of the enameling composition, namely, cupola slag, borax, and the aluminosilicate material, are within the area -ABCDEF shown in the ternary diagram set forth in FIGURE 1, and preferably together constitute at least about 78% by weight of the composition.

As pointed out above, additional tiuxing agents advantageously are employed in minor amounts, e.g., less than about 22% and preferably between about 15 to 22%, to assist in the fluxingfunction and in the reduction of the melting temperature of the slag. Preferably, the proportion of sodium carbonate is about 8 to 12% by approaching ambient temperature.

Weight, while the proportions of the iiuorides, sodium nitrate and any other liuxing agents employed are each below about 5%, and preferably in the range of about 2 to 4%.

The oxides are preferably employed in amounts from about 0.5% to 3% with the larger amounts being used when the oxide selected is one `which contributes to the formation of a tightly adherent coating, as discussed above.

Another advantage of the enameling composition of the invention is that it is not necessary to form a frit Yrom the ingredients prior to the application of the enameling composition to the base surface, although frits may be formed first, if desired. Thus, the time and expense required in the formation of the frit may be eliminated.

Advantageously, the ingredients of the enameling composition are reduced toa particle size of about or 200 mesh or finer to minimize the time required to evenly coat the base surface.

The following are typical enameling composition formulations:

The enameling composition maybe applied to the base metal surface by either ythe Wet or dry coating method. In some cases, the application of the enameling composition as a slurry in water or another suitable liquid may be less advantageous because the slurry should be applied to a relatively cool surface. Even when the ,slurry is applied to a relatively warm surface, the cooling effect which occurs whenfthe liquid is eliminated by vaporization becomes significant. On the other hand, when a finely-divided enameling composition is dusted or blown as a dry powder. onto a hot metal surface, it is important that the powder be carefully distributed over the base surfaces to insure an even coating.

The temperature of the base metal surface during the application of the enameling composition Vto a large eX- tent will depend upon the method of application. Generally, with wet coating methods, the temperature .during application will be below about 1100 F. and preferably With dry coating methods, the application temperature may vary from ambient temperature to the firing temperature, with temperatures in the range `of about 1400-1800o F. being preferred since the spreading and flowing of the composition is facilitated at higher temperatures. Also, at these higher temperatures, the proportion ofthe uxmaterials in the composition may advantageously be reduced during application.

The temperature at which the venamel coating is tired will depend primarily upon the particular constituents and proportions thereof in the composition. Advantageously, the tiring temperature will be in the range of about 1100"- lt300f1 F. Also, as discussed above, Where minimum proportions of the various constituents are employed, there is a tendency for the coatings to blister and burn; how ever, by employing the lower range of' temperatures, this tendency may be Ysignificantly reduced.

In the drawings:

FIGURE 1 shows a ternary diagram setting forth, the proportions of the essential constituents of the enameling compositions of the invention;

FIGURE. 2Vis a diagrammatic illustration of an apparatus for the coating of the interior of cast iron pipe; and

FIGURE 3 is a diagrammatic illustration of an apparatus for the coating of the exterior of lengths of cast iron pipe.

The application of the enameling composition of the invention will be more fully described with reference to the drawings. As shown in FIGURE 2, a length of pipe i2 to be coated is positioned in a heated furnace 1i. The pipe 12 is rotated on supporting rollers 13. A long tube or lance 14 having a conical dellector 16 positioned at one end of the pipe and a supply hose or conduit 17 is attached to the opposite end.

The interior of the pipe 12 is coated with porcelain enamel by inserting the lance 14 into the pipe 12 until the end of the lance with the deector is positioned adjacent to the far end of the pipe. Powdered enameling composition is forced through the lance 14 and out the end thereof, being deflected against the interior of the pipe 12 by deflector 16. The lance 14 is maintained in proper position near the axis of the pipe by a suitable support 1S. As the powder is forced against the inside wall of the rotating pipe, the lance 14 is slowly withdrawn so that a thin coating of the enameling composition will be applied by the end of the lance throughout the entire inside wall of the pipe.

The thickness of the coating will depend on the particular use, although generally, with cast iron pipe, coatings about 8 mils or more thick are considered satisfactory, with coatings of about 8 to 50 mils being particularly useful.

As shown in FIGURE 3, an enamel coating may be applied to the exterior of a length of pipe 21 in a furnace 22. The pipe 21 is maintained in proper position within the furnace by inserting a pair of supporting cones 23 in the ends of the pipe. The supporting cones are driven by a power source (not shown) so that the pipe is rotated slowly on its axis. The euameling composition is applied to the rotating pipe 21 by means of a lance 25 suspended within the furnace above the rotating pipe 21. The end 26 of the lance 25 is turned upward and has a suitable detlector 27 suspended above it by a bracket 28. As the powdered enameling composition is forced from the end 25 of the lance 25, the powder strikes the deflector 27 and drops down onto the upper surface of the pipe. As the pipe is rotated and the lance 25' is slowly withdrawn, the entire exterior of the pipe 21 is completely coated with the powder.

Since the enameling powder, as shown in FIGURES 2 and 3, has been applied to the pipe While it is in a heated condition, the enameling powder will begin to fuse immediately and form a tightly adherent porcelain coating on the pipe without the necessity of pre-cleaning the pipe prior to the application and tiling of the coating on the pipe.

In a similar manner, the apparatus shown in FIG- URES 2 and 3 may be employed to apply slurries of an enameling coating composition or an enameling composition which has been formed into a frit prior to the coating operation.

When coating cast iron pipe, the enameling composition of the invention is preferably applied while the pipe is advancing through an annealing furnace. Generally, after the molded pipe has cooled sufficiently, it is transferred from the mold to an annealing furnace, wherein it is slowly heated to a temperature of about 1500-1800 F. and thereafter permitted to cool slowly. Since the application of the coating composition is advantageously carried out while the pipe is at a temperature between about 1l00l80 F., the coating may be readily performed in the annealing furnace, thereby providing a convenient, low cost method for forming tightly adherent enamel coatings.

In the normal operation of a pipe-making plant, pipe may be stored for an extended period prior to application of the enamel coating, thereby acquiring an increased amount of rust, scale and other oxides prior to coating. However, in accordance with the invention, the stored pipe advantageously may be passed through an annealing furnace during Which time it is heated to the desired temperature and the enameling composition applied and fired.

The period of time necessary to complete the coating and firing of the enameling compositions of the invention is generally relatively short, for example, less than about 1/2 hour and usually less than about 15 minutes. Since molded pipe generally remains in an annealing furnace for an hour or so, the coating and firing may be accomplished simultaneously with the annealing operation Without increasing the annealing time.

The above detailed description shows that the enameling composition and method of application of the present invention may be employed to successfully produce tightly adherent porcelain enamel coatings on contaminated or oxidized metallic surfaces and particularly on the surface of cast iron and cast iron pipe. Furthermore, employment of the method and composition of the invention permit the formation of such tightly adherent porcelain enamel coatings economically and simply without requiring expensive pre-cleaning or multiple coating operations.

It will be apparent that various modifications and variations in the enameling composition and method of application described in detail above may be made within the scope of the invention. For example, while the above discussion describes the employment of the enameling composition of the invention in single coat applications, this composition also may be used successfully in multiple coating applications. Therefore, the invention is not intended to be limited to the particular formulations and procedures described in detail herein except as may be required by the appended claims.

What is claimed is:

1. A single coat enameling composition for the coating of cast iron consisting essentially of a powdered admixture of a furnace slag from the manufacture of iron, borax and an aluminosilicate material selected from the group consisting of clays and feldspar, the proportions of these constituents being within the area ABCDEF of the ternary diagram of FIGURE 1.

2. In the process of enameling an iron body, the improvement which comprises applying to the body a porcelain enameling composition consisting essentially of a furnace slag from the manufacture of iron, borax, and an aluminosilicate selected from the group consisting of clays and feldspare in proportions Within the area ABCDEF of the ternary diagram of FIGURE 1, heating to fuse the composition into a porcelain coating, and permitting the resultant coated body to cool, whereby said coating becomes tightly adherent to said body.

3. A process of enameling an article having a metallic surface without pre-cleaning the surface comprising applying to said surface an enameling composition consisting essentially of a furnace Slag from the manufacture of iron, borax, and an aluminosilicate selected from the group consisting of clays and feldspar in proportions within the area ABCDEF of the ternary diagram of FIGURE 1, and fusing the composition to form an enamel coat on said surface, said resulting coat being tightly adherent to the metal surface even in the absence of a preliminary cleaning thereof.

4. A process of enameling a surface of an iron body without pre-cleaning said surface comprising the steps of applying directly to the uncleaned surface an enameling composition consisting essentially of a furnace slag from the manufacture of iron, borax, and an aluminosilicate selected from the group consisting of clays and feldspar in proportions within the area ABCDEF of the ternary diagram of FIGURE l, heating to fuse the composition to form an enamel coat on said surface, and then cooling the body, whereby said enamel coat tightly adheres to said surface notwithstanding the lack of a precleaning thereof.

5. A process of directly enameling a cast iron pipe having an exposed oxidized surface portion without initially removing such oxidized surface portion comprising the steps of applying directly to the pipe surface` including the oxidized portion a powdered admixture consisting essentially of a furnace slag from the manufacture of iron, borax, and an aluminosilicate selected from the group consisting of clays and feldspar in proportions within the area ABCDEF of the ternary diagram of FIG- URE 1, and heating the pipe to fuse the admixture and form an enamel coat on said oxidized surface portion of the pipe, whereby, upon cooling, said coat tightly adheres to the oxidized surface portion of said pipe.

6. In the process of `enaxneling successive pieces of surface-oxidized cast iron pipe being conveyed through an annealing furnace, the improvement of avoiding any surface preparation of removing the oxidized portion to reach bare iron metal while nevertheless obtaining a tightly adherent enamel coat,.said process comprising the steps of applying to the pipe a porcelain enameling cornposition consisting essentially of about 10 to about 35 percent by weight of finely divided furnace slag from the manufacture of iron, about 15 percent to about 40 percent by weight of borax, and about 20 percent to about 45 percent by weight of clay, fusing said composition from the heat of the furnace while simultaneously car, rying out annealing of the pipe to form from said fusion a porcelain coat on the pipe, and then discharging the pipe from the annealing furnace.

7. A single coat enameling composition adapted for the direct enameling of an oxidized iron body without removal of the oxidized portion to reach bare iron metal, said compositionbeing in powdered admixture and consisting essentially of about 10 percent to about 35 Ipercent by weight of a cupola slag from the manufacture of iron, about 15 percent to about 40 percent by weight of borax, and about 20 percent to about 45 percent by weight of an aluminosilicate selected from the group consisting of y clays and feldspar.

8. An enameled article comprising an iron body having an oxidized surface, and an enamel coat overlying and tightly adhered to said oxidized surface, said enamel coat being formed by fusing while in contact with said oxidized surface a composition consisting essentially of a furnace slag from the manufacture of iron, borax, and an aluminosilicate selected from the group consisting of clays and feldspar, the proportions of said constituents being within the area ABCDEF of the ternary diagram of FIGURE 1.

9. The enameling composition of claim 1 further including up to 3 percent by weight ofmanganese dioxide.

10. The process of claim 2 wherein said porcelain enameling composition further includes up to 3 percent by weight of manganese dioxide.

References Cited by the Examiner UNITED STATES PATENTS 1,017,360 2 /12 York et al. 117-129 1,763,937 6/30 Stievator 106-51 2,475,469 7/49 Bennett et al. 117-129 2,612,457 9/52 Davis 106-48 2,662,020 12/53 Schofield 10G-48 2,785,091 3/57 Rex 117-129 `FOREIGN PATENTS 340 1875 Great Britain.

411,380 6/34 Great Britain.

1,835 1854r Great Britain.

OTHER REFERENCES Howe et al.: Effect of Manganese, Nickel and Cobalt Oxide Upon the Adherence and Reboiiing Properties of a Ground-Coat Enamel, presented March 23, 1937, at Thirty-Ninth Annual Mtg. of American Ceramic Soc., New York City.

TOBIAS E. LEVOW, Primary Examiner.

JOHN R. SPECK, Examiner.

Claims (2)

1. A SINGLE COAT ENAMELING COMPOSITION FOR THE COATING OF CAST IRONCONSISTING ESSENTIALLY OF A POWDERED ADMIXTURE OF A FURNACE SLAG FROM THE MANUFACTURE OF IRON, BORAX AND AN ALUMINOSILICATE MATERIAL SELECTED FROM THE GROUP CONSISTING OF CLAYS AND FELDSPAR, THE PROPORTIONS OF THESE CONSTITUENTS BEING WITHIN THE AREA ABCDEF OF THE TERNARY DIAGRAM OF FIGURE 1.

6. IN THE PROCESS OF ENAMELING SUCCESSIVE PIECES OF SURFACE-OXIDIZED CAST IRON PIPE BEING CONVEYED THROUGH AN ANNEALING FURNACE, THE IMPROVEMENT OF AVOIDING ANY SURFACE PREPARATION OF REMOVING THE OXIDIZED PORTION TO REACH BARE IRON METAL WHILE NEVERTHELESS OBRTAINING A

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