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.