RELATION OF METAL THICKNESS,ENAMEL THICKNESS,AND BOTTOM RADIUS TO IMPACT RESISTANCE OF PORCELAIN ENAMELED UTENSILS*

Three series of standard two-quart pudding pans of different metal thicknesses, coated with one, two, and three coats, respectively, of enamel were tested for impact resistance, using the Enameled Utensil Manufacturers' Council standard impact test. The impact resistance of the pans was increased with increase (1) in metal thickness of the pans, (2) of the enamel thickness, and (3) in the size of the bottom radius. The size of the chip formed on impact also increased with increase in enamel thickness. The literature dealing with the fracture of glass and enamels is reviewed, and the factors influencing spontaneous chipping and chipping caused by bending and impact are discussed.     

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.     

THE RELATION OF FINENESS OF FELDSPAR USED IN COMPOUNDING A PORCELAIN ENAMEL TO RESISTANCE TO DEFLECTION1

The effect of changing the fineness OF the feldspar in an enamel was investigated, from which test it was concluded that resistance to deflection is lowered about 9% with a slight increase in fusion temperature when substituting 40-mesh (glassmakers') feldspar for 120-mesh feldspar, both of the same chemical composition.     

RELATION OF PARTICLE SIZE AND CHARACTERISTICS OF LIGHT REFLECTED FROM PORCELAIN ENAMEL SURFACES*

Various opacifiers were added in increasing percentages to clear, regular white, very opaque white, and acid-resisting enamels. These were ground to various degrees of fineness from coarse down to a few microns or finer; they were applied to sample plates and their reflectances were measured. Increased opacity is obtained by extremely fine milling because of the excellent dispersion of the opacifiers.     

ABRASION RESISTANCE OF PORCELAIN ENAMELS*

The abrasion resistances of enamels, differing in composition and properties, were determined by the test for resistance of porcelain enamels to surface abrasion (a standard of the Porcelain Enamel Institute, March, 1942). Four to five classes of abrasion resistance were obtained, but for the most part, the results fell within relatively narrow limits. Differences in abrasion index, in general, were not distinguishable by visual inspection. No one class or kind of enamel was superior. While changes in abrasion index were affected by changes in frit formula, it seems that many compositions will give comparable results.     

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.     

PRACTICAL THICKNESS OF PARTIAL COATINGS OF ACID-RESISTANT ENAMEL*

The effect of the firing cycle, fluidity of enamel glasses, water content of enamel slips, method of application, fineness of grind, and opacifiers on the actual thickness of partial acid-resistant enamel coatings, measured by the Shartsis and Harrison method, is discussed. The results of this study appear to explain the failure of highly acid-resistant enamels to produce satisfactory acid resistance in some enameling plants.     

NICKEL FLASHING AND ITS RELATION TO ENAMEL ADHERENCE*

Nickel flashing as applied to enameling stock is shown to be primarily metallic nickel. The role of nickel in developing enamel adherence is apparently bound up with the retardation of oxidation which the nickel flash imparts in the enameling cycle. The problem of adherence may be considered to be a corrosion phenomenon of the base iron developed by the action of gases and other agents which may be present at enameling temperatures. As such, the degree of adherence is a function of oxygen pressure at the interface when the glass is fused. The equilibria developed are strongly affected by the presence of nickel. Using cover coats directly on iron, the amount of nickel required will vary with each particular enamel composition. Şome evidence as to the nature of the adherence-promoting oxide is presented.     

THE RELATION OF DEFECTS IN ENAMEL COATINGS TO HYDROGEN IN STEEL*

The effects of hydrogen as functions of time, temperature, and impurities in steel are described and experimentally demonstrated. Experimental evidence is presented to show that the blistering and boiling action over carbide areas in steel are due principally to hydrogen that associates with the carbon. Steel enameling stock contains quantities of hydrogen which may effuse during firing to cause or aggravate such phenomena as “boiling,”“primary boiling,”“rebelling,”“blistering,” and “bubbling.” Low-temperature effusion of hydrogen contributes to other defects, including “fishscaling,”“delayed fishscaling,” and possibly “pop-offs,”“jumping,”“shiners,” and some cases of “chipping” and, perhaps, “bursting” of enamel on cooking utensils. These defects have seldom been identified with hydrogen evolution. An indirect effect of hydrogen on “copperheads” and “black specks” is also identified. An exhaustive review of both English and German literature on enameling defects is included. Many observations recorded in the literature are shown to agree with the hydrogen theory. Certain types of inclusions in steel are shown to react with occluded hydrogen to form compounds that will not dissociate appreciably at some enamel-firing temperatures, and critical quantities of the hydrogen are therefore prevented from reaching the enamel coating during firing to cause blistering and related defects.     

EFFECT OF RESIDUAL COLOR ON CONSUMER ACCEPTANCE OF PORCELAIN ENAMEL WHITES*

Reflectometers are widely used to give a numerical rating for the comparative whiteness of porcelain enamels, but these instruments occasionally show values in disagreement with a careful visual comparison. To find the reason for this disagreement, a survey was made to determine the effect of residual color on the consumer rating of porcelain enamel whites. A series of 12 white plaques was made ranging from 67 to 75% in reflectance, from 478 to 485 m/x in dominant wave length, and from 1.6 to 5.6% in residual color. These specifications were determined from curves run on a Hardy G. E. recording spectrophotometer. The 12 plaques were submitted to 36 persons who arranged them in order of whiteness. The order of arrangement was compared statistically, and the whites were rated in their order of acceptance. Residual color was found to have an important effect on apparent whiteness, and of these typical porcelain enamel whites, those most highly colored (blue) were preferred.     

DETERMINATION OF COMPRESSIVE STRESS PRESENT IN PORCELAIN ENAMEL ON SHEET IRON*

A method for determining comparative compressive stress produced in porcelain enamel on sheet iron is described. The method consists of preparation of laboratory samples under carefully selected and controlled conditions and measurement of the warpage produced in the sample due to application of enamel on one side. Data obtained by the above method are compared with expansion curves. Several methods of analyzing the curves fail to produce correlation between expansion as determined on frit samples and compression in the porcelain enamel as indicated by the warp of sample plates. It is concluded that expansion curves on frit samples are not a satisfactory means of evaluating compressive stress in the porcelain enamel coating on sheet iron.     

PORCELAIN ENAMEL AS A PROTECTIVE COATING FOR HOT-WATER TANKS*

The suitability of zinc and porcelain enamel as protective surfaces for water-storage tanks is discussed. The test methods are given in detail as well as the results of the simulated service tests.     

FRIT SOLUBILITY: II,CONTROLLED VARIABLES OF FRIT COMPOSITION AND THEIR RELATION TO ENAMEL CONSISTENCY *

The sodium carbonate and borax of a sheet-steel ground-coat composition were varied to give variable frit solubility. Definite relationships between enamel consistency and Na₂O and B₂O₃ content of the mill liquor are shown. The ratio of soluble Na₂O to B₂O₃ is of more importance than their total solubility.     

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.     

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.     

RESISTANCE OF GLASS TO THERMAL STRESSES*

The theory of stresses introduced in glass by thermal shocks is a matter of fundamental interest to the glass manufacturer. Analysis is complicated by the existence in many cases of unknown degrees of stress relief or transference by flexure. General treatment of these cases is extremely difficult because of irregular or variable shapes. There is, however, a large group of thermal-shock phenomena in which flexure of the piece is not a factor. Complete immersion shocks fall in this category; so also do thermal shocks administered to tubes and pipes, since the cylindrical shape prevents flexure. (There is a small end effect accompanied by flexure, but in practice only a small fraction of breaks originate in the end region.) Many examples of breakage from shocking one side only of a piece are also of this simple type, since maximum tension occurs immediately from pure “stretch” and is greater than subsequent stresses accompanied by flexure. Analysis of the stresses resulting from stretch incurred by thermal gradients has been carried out by many writers for plates and cylinders, and various applications have been made of the results.¹ The calculation of maximum fiber tension, however, is not in itself enough to determine thermal endurance. The duration of the stress also plays an important role. The simplest example of this is the well-known fact that in immersion tests breakage frequently does not occur for an appreciable interval, sometimes several seconds. Yet maximum tension on the cooled surface is almost immediate and falls off rapidly. The importance of duration is pointed out by Schönborn,^1(c) but he does not attempt any quantitative treatment. It is the purpose of the subsequent analysis to incorporate the time of stressing into the discussion of thermal endurance.     

纤维增强摩阻材料的冲击性能研究

主要研究了丁腈橡胶形态、粘结剂含量及混杂纤维含量对混杂纤维增强摩阻材料冲击性能的影响。结果表明，酚醛树脂中混入丁腈橡胶可大大提高摩阻材料的冲击性能，其中，液态丁腈橡胶与树脂混合制作的纤维增强摩阻材料的冲击性能较高；用质量分数为28％－29％的粘结剂与28％的混杂纤维制得的摩阻材料的冲击性能最佳。     

浅谈唐英对珐琅瓷的贡献

从唐英在清宫内务府造办处时期对珐琅瓷的贡献、雍正时期时期"唐窑"对珐琅瓷的贡献、乾隆时期时期"唐窑"对珐琅瓷的贡献,三方面介绍了唐英对清宫瓷胎画珐琅的特殊贡献,展现了清代宫廷珐琅瓷产生、发展和消亡的过程。