GOUGE RESISTANCE OF PORCELAIN ENAMELS*

An exploratory study was made to determine possibilities of the Porcelain Enamel Institute rolling-ball gouge test as well as to discover some of the factors influencing the gouge resistance of enamels as shown by the test. The test results compare favorably with deep-scratch and gouge defects encountered in actual enamel practice. The accuracy of test results, moreover, compares favorably with other such physical tests designed for use with porcelain enamel. The gouge resistance is shown to be a function of enamel thickness and of bubble structure. Factors which increase or decrease bubble structure, such as mill additions, frit compositions, and firing treatment, are shown to affect gouge resistance.     

RELATION OF COEFFICIENT OF EXPANSION TO IMPACT RESISTANCE OF PORCELAIN ENAMELS*

The tentative standard impact test procedure, adopted by the Porcelain Enamel Institute, was used to test and compare cylinders coated with several experimental and commercial enamels. The important facts noted were (1) the effect of cubic thermal expansion on the impact resistance, (2) the importance of the ground coat to the resistance of any one cover enamel, and (3) the wide variation between cover enamels in resistance to impact.     

ELECTROSTATIC SPRAYING OF PORCELAIN ENAMELS *

The application of the process of electrostatic spraying to the porcelain enamel industry is described. The equipment which is used and the method of using it are discussed in detail. Particular emphasis is placed on the preparation of enamel for electrostatic spraying and on theoretical considerations which have a direct bearing on the spraying process. The applicability and limitations on the use of the equipment in the porcelain enamel industry are considered.     

CHEMICAL DURABILITY OF PORCELAIN ENAMELS *

The resistance of representative porcelain enamel surfaces to the chemical attack of different concentrations of various solutions was investigated in considerable detail. Cylindrical cup-shaped samples were coated with (1) a ground coat, (2) a white fluoride cover enamel, (3) a white antimony cover enamel, (4) a white zirconium cover enamel, (5) an acid-resistant white cover enamel, (6) a sign blue cover enamel, (7) a blue zirconium enamel, and (8) a chemical acidproof blue cover enamel. The loss in weight of these enamel surfaces, after exposure to chemical attack, was determined at definite time intervals. The solutions studied consisted of different concentrations of the inorganic acids, alkalis, several organic acids, as well as selected salt solutions at both room and boiling temperatures. Numerous curves are presented showing the comparative chemical durability of the various porcelain enamel surfaces in which the cumulative loss in weight is plotted against time. Several photomicrographs show the nature and type of chemical attack on the different surfaces. The porcelain enamel surfaces showed considerable variation in their resistance to the chemical attack of the various solutions. All of the porcelain enamels were, in general, resistant to attack at room temperature by the alkali and salt solutions. The acid-resistant and acidproof enamels were resistant to the action of both inorganic and organic acids at room and at boiling temperatures; a wide variance, however, was shown in the comparative acid resistance of the non-acid-resisting enamel to the attack of either organic acids or inorganic acids at room temperature. AU porcelain enamels showed equally low resistance to boiling alkali solutions, but some of the enamel surfaces were attacked markedly by the boiling salt solutions.     

RESISTANCE OF ENAMELS TO THERMAL SHOCK*

Thermal-shock resistance tests were made on enamels of varying thermal expansions applied on test pans. Increased weight of application and high expansion of the cover coat decreased the thermal-shock resistance, whereas high expansion of the ground coat increased the resistance.     

FUNDAMENTAL STUDY OF FACTORS INFLUENCING COLOR OF PORCELAIN ENAMELS*

The fundamental basis of color specification, namely, brilliance, purity, and dominant wave length, has been determined from spectrophotometric curves by means of an integrating calculator. The effect of variations in the particle size of the frit and the coloring agents on the purity, brilliance, and dominant wave length has also been studied.     

INVESTIGATION OF ABRASION RESISTANCE OF VARIOUS REFRACTORIES*

This paper describes a new abrasion test for re-fractories consisting of a controlled sandblasting operation wherein various brands of brick were tested. Graphs show correlations for abrasion loss per hour against other properties for the brands tested. Data and charts which compare this abrasion test with the A.S.T.M. rattler test for paving brick are also included.     

TESTS FOR HOT-WATER RESISTANCE OF TANK ENAMELS*

The resistance to attack by hot water of a representative group of commercial enamels, designed especially for use on hot-water tanks, and of several nontank enamels was measured by the following three types of test: (A) loss of gloss after periods up to several hours in a conventional autoclave with distilled water, (B) loss of gloss after one day to two weeks in apparatus which kept the specimens in contact with constantly changing, boiling distilled water, and (C) loss in thickness after periods up to 5000 hours (208 days) in a modified autoclave with circulating aerated tap water under pressure. The tests are described in detail, comparisons are made, and the loss-of-gloss test with boiling distilled water as used in Commercial Standard CS115–44 is discussed.     

RELATION OF THICKNESS TO IMPACT RESISTANCE OF PORCELAIN ENAMEL*

Chipping of porcelain enamel on the flanges of table tops as a result of impact was studied and compared with the results obtained from the Porcelain Enamel Institute tentative standard impact test. A correlation was found to exist between the results using the P.E.I, test on standard 1-in. tubes and those obtained on the corner of a table-top flange. The impact resistance of enamels applied over a radius also increased as the thickness of the enamel was increased.     

EXPERIMENTS WITH AN ACCELERATED WEATHERING TEST FOR PORCELAIN ENAMELS*

Experiments were conducted on porcelain enamels using the accelerated weather test developed at the National Bureau of Standards. A comparison of results indicates this test to be a promising solution to the problem of the rapid determination of the weather resistance of porcelain enamel.     

TESTING RESISTANCE OF ENAMELED SURFACES TO SCRATCHING GOUGING,AND ABRASION*

Seven types of cover-coat enamels were tested for resistance to scratching, gouging, and abrasion by various methods. These methods were (a) P.E.I. abrasion test, (b) P.E.I. gouge test, (c) variations of the gouge test, (d) Taber Abraser, and (e) a scratch test. Chemical durability and reflectance were found to have little or no correlation with the resistance of the enamels to abrasion. The bubble structure of the enamel layer seemed to have the greatest effect on abrasion and scratch resistance of the enamel layer.     

EFFECT OF SIZE AND SHAPE OF TITANIUM OXIDE CRYSTALS ON SPECTROPHOTOMETRIC PROPERTIES OF TITANIUM-BEARING PORCELAIN ENAMELS*

Color changes of three titanium enamels given varied firing treatment were investigated. The size and shape of titanium oxide particles were studied with the electron microscope, the relative amounts of anatase and rutile were determined from X-ray analyses, and spectrophotometric curves of the fired panels were made. Electron micrographs showed that rutile particles recrystallized as needles or “sticks,” whereas anatase appeared as ill-defined, irregularly shaped, rounded particles. With increasing firing temperature or firing time (1) rutile particles showed a greater increase in size than anatase particles, (2) the amount (by weight or volume) of anatase crystals decreased and the amount of rutile crystals increased, and (3) a color change from blue-white to cream-white was observed. The change in color seemed to be related to the scattering of blue light by small particles at lower temperatures or shorter periods of firing. As the size of opacifying particles increased, the scattering of blue light decreased, and the characteristic absorption of visible light in the shorter wave lengths was more apparent. In enamels containing both anatase and rutile, the smaller anatase crystals were predominant at lower and the larger rutile crystals at higher temperatures, so that sharp changes of color were observed as the firing temperature was increased.     

EFFECT OF VARIATIONS IN COLOR STAINS AND FRITS ON COLORS PRODUCED IN PORCELAIN ENAMELS*

A representative series of colors, blue, brown, green, red, and yellow, was selected for this investigation. Variations of the constituents for these five stains were made and the resulting colors produced in the enamels were measured by means of spectrophotometric curves. The influence of additions of barium oxide, lead oxide, and zinc oxide to the frit was also studied. The addition of lead oxide to the frit tended to give greater solution of the blue stains. The barium oxide additions dissolved the lead antimonate yellow the most, while the lead oxide had the least effect on the yellow stains. Variations in calcination temperatures of the red stains produced decided changes in color. The additions of lead oxide darkened the color produced with the red stains.     

EFFECT OF SODIUM ALUMINATE ON CONSISTENCY AND ACID RESISTANCE OF SOME ACID-RESISTANT ENAMELS*

This paper includes consistency studies and shows variations in acid resistance occurring with concentration and the method of using sodium aluminate as a setting-up agent.     

EFFECT OF ZIRCOPAX ADDITIONS ON ABRASION RESISTANCE AND VARIOUS PROPERTIES OF SEVERAL GLAZES*

A test method is described and the results of four series of experiments are given for the empirical evaluation of the effect of Zircopax in improving the resistance to abrasion of glazes. Simultaneous resistance to crazing and the effect on gloss, color, and opacity are noted.     

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.     

RELATION OF THE PARTICLE SIZES OF THE FRIT AND COLOR OXIDES TO THE COLOR PROPERTIES OF PORCELAIN ENAMELS*

The effect of variations in the particle size of typical green and blue color stains in sized fractions of a representative clear frit was studied. Microscopic examinations were made of the sized fractions, and photomicrographs of the respective fields are presented. The color characteristics of the enameled panels were determined on a continuously recording spectrophotometer. Frit particles of 45 to 75 μ, combined with color particles of less than 5μ, were found to give the optimum or most efficient color characteristics, and color particles larger than 5 μ, seriously impaired the resulting color.     

A METHOD FOR TESTING THE FINENESS OF PORCELAIN ENAMELS1

The sieve-shaker method of testing is described and recommended for use as a means of testing the fineness of porcelain enamels. The initial expense of equipment is offset by the economy of having the enamels leave the mill room in proper condition.