EFFECTS OF COMPOSITION ON THE PROPERTIES OF GROUND COAT ENAMELS FOR SHEET STEEL1

A series of ground coats was developed about each of three refractory bases, one of which consisted of flint and feldspar in a ratio frequently used commercially, another consisting of feldspar only, and the third of flint only. In each case the refractory portion was 58.5 parts of the whole. Besides the refractory, a “fixed addition” of 11.5 parts, comprised of 0.5 cobalt oxide, 1.0 manganese oxide, 5.0 boric oxide and 5.0 sodium oxide, was used in every enamel, bringing the basic constant portion for each series to 70 parts of the whole. The variable portion in each series was made up of equal parts of three constituents commonly used in enameling, chosen from a total of six in such a way that every possible combination was employed, making a total of twenty enamels in each series. All were given two cover coats of a standard white and tested for resistance to mechanical and thermal shock. In general the ingredients which were most conducive to resistance to the test treatments were flint in the refractory portion, and sodium oxide in the variable portion, constituted of fluxes. Also, boric oxide favorably influenced resistance to mechanical shock in the series containing both flint and feldspar. Resistance to mechanical and thermal shock in ground coats was considerably less affected by variations in expansivity than is the case in cover coats, the influence of that factor appearing to be partially obscured by other factors.     

THE MELTING RELATIONS OF POTASH FELDSPAR,SODA FELDSPAR,AND FLINT MIXTURES1

P.C.E. values of ternary mixtures of potash feldspar, soda feldspar, and flint were determined and results shown on a solid phase diagram. No eutectics were developed with either of the binary series of feldspar and flint. The soda feldspar-flint mixtures were more refractory than were those of the potash feldspar series. At least 20% flint variation with potash feldspar will show no change in P.C.E. values and at least 10% with the soda feldspar showing the unreliability of P.C.E. to indicate the amount of the quartz content.     

WET PROCESS ENAMELS FOR CAST IRON1

Wet process enameling of cast iron is becoming of importance because of its application to the enameling of stove parts, sanitary fittings and hardware. This paper is a report of an extended investigation of wet process enamels for cast iron, in connection with the use of a ground coat. Compositions used in dry process enameling have served as a basis for the work, which includes a study of ground coats and white cover enamels. The effect of varying methods of preparing the frits, mill additions, and the relation of composition of the enamels to such properties as adherence, texture and opacity have been carefully studied. Ground Coats. —Sintering of most ground coat frits has been found desirable in order to develop best adherence on the castings. Clay gave best results as a mill addition for the groundvt and feldspar were found to be less satisfactory. Excessive additions of clay or flint produced flaking of the ground coat while feldspar tended to develop blistering. About 15 per cent of clay or 10 per cent each of clay and flint are recommended as mill additions for the ground coats. Excessive additions of any one flux were not desirable, and best results were obtained when sodium, lead and boric oxides were combined in more or less definite pro-portions. Sodium oxide in excess of about 10 per cent gave rise to blistering. Boric oxide increased the firing range of the ground coats and was preferable to lead oxide on this account, although it tended to promote crawling of ground coats high in boric oxide if they were applied somewhat heavily. The best ground coats developed are Rg-26, 17, 1, 25 and 18. Cover Enamels. —Cover enamels were smelted in the usual manner. The mill additions consisted of 5 per cent of clay, 8 per cent of tin oxide, and 45 per cent of water, all based on the weight of the dry frit. For best results, the cover enamel must he adapted to the ground coat in refractoriness. Boric acid increased the firing range of the enamels but tended to promote crawling, although this was less pronounced in the case of the more fusible compositions. Boric oxide improved the opacity when suhsituted for such fluxes as sodium and lead oxides. Cryolite increased opacity but additions above 10 per cent, based on the melted weight, tended to promote crawling. Considering all factors, cover enamels R-14 11, 28, 1 and 18 gave best results.     

THE EFFECT OF GLAZE COMPOSITION ON THE CRAZING OF TERRA COTTA1

Comparing the effects of equal molecular additions of the various components of the glazes in this study, it was found that ZnO and feldspar overcome crazing, ZnO being the more effective. MgO, BaO and CaO tend to produce crazing, MgO having the greatest tendency and the effect of BaO being somewhat greater than that of CaO. SnO₂ has no effect on the crazing. Increase of clay is more effective in overcoming crazing than any other changes that can be made in the glaze formula. Addition of small amounts of clay are more effective in overcoming crazing than much larger additions or substitutions of the other components. Increase of flint (per molecular equivalent) is less effective in overcoming crazing than increase of either clay, ZnO or feldspar, although, generally, considerable more flint than clay or ZnO can be added without appreciably changing the maturing point of the glaze. In many cases, increase of flint will not overcome crazing in a glaze.     

SOME PARTICULATE CHARACTERISTICS OF COMMERCIAL FLINT AND FELDSPAR *

The particle-size variations of eleven shipments of commercial flint and of fifteen shipments of feldspar have been investigated as a possible cause of production variations in electrical porcelain. A correlation of sieve data with specific surface calculations based on sedimentation determinations was made on six grades of commercial flint. The Andreasen pipette sedimentation method was used for all tests except those in which the hydrometer method was employed for comparison purposes. Either of these sedimentation methods had adequate accuracy to control particle size. The percentage remaining on the 325-mesh sieve, however, could not be correlated with the specific surface values. Particle-size distribution was determined for each sample. To facilitate comparisons, specific surface values were calculated from a plot of the distribution data on log-probability graph paper. The investigation included the effect of various liquid suspending media and electrolytes on the settling characteristics of flint and feldspar. Neither flint nor feldspar could be adequately dispersed in non-polar liquids. Feldspar apparently has surface-active characteristics that permit it to be flocculated or deflocculated, depending on the nature of the ions present in solution. An anomalous peptizability of some feldspar samples in the particle-size range below 3 microns is discussed.     

EFFECT OF COEFFICIENT OF EXPANSION OF GROUND- AND COVER-COAT ENAMELS ON THERMAL-SHOCK AND IMPACT RESISTANCE *

Four antimony cover-coat enamels, four fluoride cover-coat enamels, and four ground-coat enamels were formulated to give varying coefficients of expansion. The calculated values were 250, 275, 300, and 325 × 10^–7. The observed coefficients of expansion are included in the paper. The enamels were applied to standard 2-quart pudding pans and were tested for thermal shock and impact resistance using the standard methods of the Enameled Utensil Manufacturers’Council. The results show that thermal-shock resistance is controlled chiefly by the coefficient of expansion of the ground-coat and cover-coat enamels. The best results were obtained by using a cover-coat enamel with a low coefficient of expansion and a ground coat with a high coefficient of expansion. No conclusive evidence was found to indicate any effect of the coefficient of expansion of the ground- and cover-coat enamels on impact resistance. The solubility resistance and reflectance curves for the enamels are also included.     

THE THERMAL EXPANSION OF SHEET-IRON GROUND-COAT ENAMELS*

The thermal expansions of sheet-iron ground-coat enamels were determined by use of the interferometer. The results showed that the calculated expansions based on the factors of Mayer and Havas were close to the actual expansions. It was also shown that variations of borax, feldspar, and quartz resulted in a fairly uniform change in the expansion. It was possible to interpolate between values for these constituents. The softening of the enamels in the interferometer test proved to be a characteristic change depending on the fusibility of the enamel. These data showed promise as a test for fusibility.     

THE BEHAVIOR OF FELDSPAR AND FLINT WITH ACIDS AND BASES1

On addition of acids and bases to fine-ground feldspar or flint, the same phenomena are observed as with clays, Le., flocculation, deflocculation, and absorption. The effects are less sharp than with clays, the zone of deflocculation covering a wider range of PH and flocculation occurring at lower pH (greater acidity). The sensitiveness of flint and feldspar to reagents increases with fineness of grinding.     

THE EFFECT OF LEPIDOLITE IN A HIGH TENSION ELECTRICAL PORCELAIN BODY1

Lepidolite is a lithium mica which has had considerable commercial application in glass and enamels. Its use in porcelain has not been tried to any great extent. This work covers the replacement by lepidolite of the feldspar in a high tension electrical porcelain. The results show that changing the RO of the standard body by molecularly replacing K₂O by Li₂O raises the vitrification temperature of the body, but that replacing feldspar directly pound for pound by lepidolite greatly lowers the vitrification temperature of the body. Lepidolite gives porcelains having a fine appearance and extreme whiteness. The most important property noted is an improvement of the bodies containing lepidolite in resistance to thermal shocks. Owing to its higher cost it is unlikely that lepidolite will be used in porcelains except in small proportions with feldspar to produce bodies having special properties. As hitherto the most important applications of lepidolite will doubtless be in glasses and enamels where full benefit can be secured from its fluorine content and low fusion temperature.     

EFFECT OF OPACIFIERS ON FUSED VISCOSITY OF FELDSPATHIC GLAZES*

A study has been made of the fusion characteristics of feldspar, flint, kaolin, and whiting used in glaze compositions with zine oxide and various opacifiers. The fusion characteristics of tin oxide, Opax, Zircopax, and various combinations of opacifiers are given. All heat-treatments mentioned are at cone 12. Isoviscosity triaxial diagrams show the fields of good glazes in each series, and the rclative effects of composition changes on the physical properties are outlined.     

STUDY OF EUTECTIC FLUXES IN SEMIVITREOUS AND VITREOUS WHITEWARE BODIES*

Frits of oxides of lithium, barium, calcium, and magnesium combined with calcined alumina and pulverized flint were substituted for feldspar in a dry-press whiteware body. Three series of bodies were studied which contained (1) about one half the normal RO content, (2) the normal RO content, and (3) about three times the normal RO content. Firing behavior and mechanical properties of the various bodies in the vitreous and semi-vitreous range were determined, and the results are reported in this paper.     

SHEET STEEL COOKING WARE WHITE ENAMELS ECONOMICALLY SUITABLE FOR USE IN CHINA1

The research was carried on to develop data on sheet steel enamels which would be good enough and cheap enough for use in China. Substitutes for tin oxide were tested. An efficient and cheaply constructed kerosene fired enameling furnace was designed and built. Little could be gained by work on the ground coats. Sodium antimonate and calcined alumina yielded the cheapest enamels with quality almost equal to enamels made with tin oxide. Zirconium oxide yielded the best results when tested with acids. Cryolite could be reduced to the minimum and with benefit to the resulting product. High feldspar enamels proved to be most satisfactory. High zinc oxide content greatly increased the gloss but lowered the opacity. Calcined alumina failed when used alone.     

EFFECT OF ZIRCONIA IN ENAMELS FOR SHEET STEEL1

This paper deals with the results obtained from a study of the effect of additions of zirconium oxide to enamels for sheet iron and steel. The work includes additions of the zirconia to the raw smelter batch of both the ground and cover enamels, also the substitution of the zirconia for tin oxide in the mill batch. Several tests were used to determine its effect on some of the properties of the enamels, such as resistance to impact, thermal shock and acid.     

EFFECT OF FIRING TREATMENT ON PHYSICAL PROPERTIES OF DRY-PROCESS ENAMELS *

The relations between the firing treatment and physical properties of some commercial, antimony-bearing dry-process enamels for cast iron were studied. These properties include opacity and resistance to surface abrasion for both acid-resistant and regular enamels and acid resistance of the acid-resistant types. In contrast to wetprocess enamels for sheet steel, these dry-process enamels were found to be little affected by the extreme variations in firing which might be encountered in ordinary practice.     

A STUDY OF DRY-PROCESS CAST-IRON GROUND-COAT ENAMELS*

This investigation covers a study of varying firing treatment of ground coats for cast iron and the resulting effect on the quality of adherence and the tendency to blister of dry-process enamels. Five ground coats have been used, composed of one and two frits and with varying clay and flint additions at the mill. Data on the impact resistance of the enameled specimens obtained with a pendulum-type impact tester are included. Conclusions are noted on some of the factors affecting firing range, and plans for further studies are outlined.     

THE RELATIONS BETWEEN COMPOSITION AND PROPERTIES OF ENAMELS FOR SHEET STEEL1

Very little has been reported on the relations existing between enamel composition and the properties except the resistance to acids. In this investigation a study was made of the relation between enamel composition and such properties of the enamel as expansion, strength and acid resistance, as well as the effect of the relative “fit” of the ground and cover coats on resistance of the enameled ware to impact and to thermal shock. The work was done on fourteen ground coats and white cover enamels applied to eight-inch dinner plates. The latter were tested for resistance to impact, to thermal shock, and to acetic acid. Determinations were made of the expansion and compression strength of the enamels before application to the steel. Conclusions.—1. The replacement of boric oxide by sodium oxide in the enamels increased the coefficient of expansion. Fish-scaling decreased with increase of ex- pansion, due to increases of sodium oxide. 2. The compressive strength of the ground coats appeared to decrease with re- placement of boric oxide by sodium oxide, although the reverse conditions occurred in the case of the cover enamels. 3. Impact on the parts of enameled ware not free to deflect, such as the curved corners at the bottom, gives a measure of the toughness of the enamel as applied on the steel. The resistance of the enamel on corners to impact apparently is a function of the inherent strength of the enamel rather than its “fit” on the ware. 4. For greatest resistance to thermal shock, the ware should be coated with a ground coat having a coefficient of expansion equal to or preferably greater than that for the cover enamel. 5. Acid resistance, while dependent on the enamel composition, is not affected in the same way for all enamels. For these particular cover enamels, resistance to acids decreased with replacements of boric oxide by sodium oxide.     

EARTHENWARE BODIES AND GLAZES1

Effect of body composition on crazing .—-Six bodies of each of 2 standard clay compositions were prepared with variable clay and flint content and after biscuiting at cone 8 were glazed with 21 earthenware glazes and glost fired at cones 4 and 6. The results indicated that the variability of the silica content of clays would not be great enough to produce crazing in a well-balanced glaze. Effect of proportion and composition of frit .—-A standard whiteware glaze was compounded in 6 different ways and several other glazes in 2 ways. It was found that the method of compounding had no effect on crazing but it affected the gloss and fusibility. Increase in the percentage of material fritted increased the gloss and fusibility. With the same percentage of frit the best glost and highest fusibility were obtained when the flint and part of the clay were included in the frit. Effect of some variations in glaze composition .—-Substitution of CaO by Na₂O, pound for pound, as well as direct addition of Na₂O, increased crazing, improved gloss and increased the fusibility. Direct addition of feldspar increased crazing slightly and diminished gloss, but did not noticeably affect the fusibility. Substitution of 1½1/2 parts of feldspar for one part of flint to maintain the same fusibility increased crazing and diminished gloss. Direct addition of CaO improved gloss, increased fusibility and slightly reduced crazing.     

USE OF A HIGH SERICITE PYROPHYLLITE IN VITREOUS BODIES*

A pyrophyllite containing approximately 15% of sericite is being produced at Hemp, North Carolina. When it is substituted in vitreous bodies for all of the flint or all of the flint and some feldspar, a marked increase in fired strength results, and the shrinkage and absorption properties are not affected by this substitution. The types of bodies studied include electrical porcelain, made by the dry and plastic processes, sanitary ware, vitreous floor tile, and hotel china ware.     

USE OF SPECIAL OXIDES IN PORCELAIN BODIES1

Substitution of special oxides for flint.—The oxides of thorium, titanium and zirconium and the silicate of zirconium were used. Variations in composition were based on batch weights, the percentage of oxide (or silicate) increasing from 27 to 49% with a corresponding decrease in feldspar content. A similar series using flint was also made a basis for comparison. Effect of special oxides on drying and burning behavior, dielectric strength and resistance to spang.—(1) Rutile causes high drying and burning shrinkage. The burning range is long but softening in every case results above cone 12. Resistance to spalling is above normal. (2) Thoria produces a body with a long burning range and great refractoriness. Drying shrinkage is normal, burning shrinkage very high, resistance to spalling very low, and the bodies warp badly. (3) Zirconia bodies have a normal drying shrinkage and a high burning shrinkage, no warping, long firing range, and the highest resistance to spalling. (4) Zircon.—The zirconium silicate bodies soften at temperatures below cone 18 and the firing range is short. Drying and burning shrinkage are similar to flint bodies but resistance to spalling is above normal. Effect of oxides on dielectric resistance.—No effect on dielectric resistance is obtained through the use of the special oxides mentioned.     

Effect of Wollastonite Substitutions in a Semivitreous Dinnerware Body

A study was made of a series of typical semivitreous dinnerware bodies in which increasing amounts of wollastonite were substituted for flint and for equal portions of flint and feldspar. Wollastonite in amounts up to 8% improved the body by greatly reducing the moisture expansion, reducing the firing shrinkage, reducing the maturing temperature, and increasing the modulus of rupture. Three bodies were selected from this study and four additional bodies were formulated on the basis of a commercial composition. These bodies were used in a plant trial. The findings from a number of tests agreed with those of the laboratory and in addition showed that wollastonite improved dry strength and impact strength. On the basis of the entire investigation, the best bodies were obtained when wollastonite was used in the range 1 to 4%.