Electric Hot Plate with a Cast-In Element: Jordan & Schneider, 1935

In a cast cooking plate the heating coils sit, insulated, inside tubes, and the tubes are cast into the plate. Friedrich Jordan and Paul Schneider of Voigt & Haeffner, Frankfurt, patented a better way in 1935, US 1,998,764: embed each tube only to about half its circumference, or a little more. Casting metal round the whole tube needs core models, costs material and spreads the heat unevenly, while the exposed underside loses little heat because air conducts far worse than metal. To hold the coil firmly while the iron is poured, holding strips or notched webs are fixed to its turns and cast into the plate with it. The centre of the plate may be made thicker to even out the heat.