A new method for measuring the glost-warpage of refractory coating caused by the internal stress developing during the heating was described. The apparatus was designed so that it satisfies the following three conditions:(1) Easy and stable setting of the specimen, (2) Preventive measure against the oxidation during the heating, (3) Accurate measurement of slight strain.The specimen was prepared by applying the coating to one side of a piece of a Steel plate (0.8×20×80mm). It was inserted into the silica tube of the heating furnace to rest horizontally on the saddles of silica glass (Fig. 3). To avoid the oxidation nitrogen or argon was introduced from one end of the silica tube to which a small hole was provided at a proper position as a gas-outlet. For easy setting of the specimen the upper part of the furnace was cut off to form a longitudinal groove of 5mm in width. The deflection was measured by the displacement of the thin silica tube standing vertically at the middle point of the specimen.Transition point, Pt, and softening point, Ps, of the thin coated layer could easily be evaluated from the deflection-temperature curve. A linear relation between Pt, Ps, and the content of alumina in mill addition was confirmed when the specimen was fired in nitrogen atmosphere. Moreover, the possibilities of evaluating the expansivity of coating layer and the internal stress developed in it were discussed making use of the examples of the actual deflection curves.Deflection of warpage, δ, can be expressed byδ=K⋅Δα⋅Δθ⋅l2/hK=3pq(1+2p)/(4pq+1), p2<<1, q<1, where, Δα stands for the difference of the thermal expansion coefficients between the coating layer and the base metal. Δθ the temperature difference, l the span, and h the total thickness of the specimen, p=hc/hs and q=Ec/Es, where hc, Es and Ec are respectively, the thickness and the elastic constant of the base metal, that of the coating layer as indicated in Fig. 8.It was established experimentally that the relation between the coefficients of glost-warpage and the thickness of coating is expressed by a non-linear function.
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Jan 1, 1963
Masanobu Hamasaki 
Open Access
