Electric heating plate

Abstract

Claims

A ril 30, 1940. E. CHALLET 2,198,761 ' ELECTRIC HEATING PLATE Filed March 29, .1937 ' JFVVEA/T0/P .555 mg izaZZeZ Patented Apr. 30, 1940 UNITED STATES PATENT OFFICE ELECTRIC HEATING PLATE Etienne Challet, Paris, France, assignor of onefourth to Entreprises Electriques Fribourgeoises, Fribourg, Switzerland, a company of Switzerland ApplicationiMarch 29, 1937, Serial No. 133,708 In' Switzerland April 6, 1936 3 Claims. (01. 219-37) always comes into contact with said elevation of high calorific density. g It hasbeen found by experiments that the zone of highest calorific density in the heating plate enclosing an electric heating element of annular shape is immediately above a median circle which divides the zone of the heating plate above the annular heating element into equal halves. It is therefore of advantage to have a circular elevation directly above this zone of highest calorific density in order to insure the contact of a vessel with curved or deformed bottom with the plate along a substantially unbroken line which, furthermore, lies on or near said zone of calorific density. In the more particular case of electric plates, these will be made, according to the invention, of pressed metal sheet so that the plate can expand freely by an extension of the prominence of the annular peak which returns to its original position on cooling. The heating resistance will be mounted in anyv suitable manner, but preferably said resistance will be constructed in the shape of an annulus of which the mean circumference will coincide as far as possible with the most prominent part of the annular elevation; this is so that the heat produced in particular at the periphery and at the inside of the annulus, shall have the same distance to travel by conduction in the metal, to reach the annular elevation, where it is carried away by the saucepan. According to the invention, the plate may have an annular elevation which is formed by the domed surface of the plate which is of annular shape. This ring can be solid and the heating element can be contained in the body of same, according to the known methods of mounting. It can also be hollow and obtained by pressing, the hollow forming a housing for the heating element. Said ring can expand freely along its diameter, so that its expansion in height, in particular opposite the annular elevation, will be very slight. The accompanying drawing shows examples of construction of plates according to the invention. Fig. 1 shows a cross section through a solid plate according to the present invention. , wherein themedial portion of the ring I3 is Fig.2 shows a top view of the plate shown in Fig. 1. The heating plate I has an annular elevation 2 against which can be appliedthe deformed bottom of a thin bottom receptacle, whether said 5 bottom be convex as shown at 3, or concave as at 3. The elevation" 2 is located along the line of maximum calorific density. Fig. 2 shows the theoretical position of the line of maximum, calorific density, the radius of which is substantially m said line dividing the surface of the plate into two substantially equal parts. Contrary to solid plates, the plate illustrated and described herein can be deformed, either owing to the fact that it has been suddenly cooled, or that it is heavily electrically loaded, or owing to the two above causes together, without impairing its thermic efficiency. Fig. 3 shows a sectional view of a plate formed of pressed sheet metal 4 having an annular elevation forming a housing 5 for the heating element. Fig. 4 shows a sectional view of a similar plate wherein the zone of maximum density is of slightly greater thickness at 6 to drain off the heat better at this part where it will be collected by-the saucepan. Fig. 5 is a sectional view of a modification wherein the lower face is flat at 1, whereas the upper face has an annular elevation 8. Fig. 6 shows a sectional view of an annular plate 9 having a domed upper surface Ill, the heating element, not shown, being embedded in the body; In Fig. 'l, the plate is a hollow annular part II which is pressed with the housing i2 for-the resistance. Fig. 8 is a sectional view of a modification 40 thicker to collect the heat better at this place of maximum heating density. Fig. 9 is a sectional View of a modification having a flat lower face l4 forming an extra thickness I5 at the medial portion of the ring. In every figure of the drawing, l6 denotes the electric resistance wire and I1 denotes the material insulating said resistance wire. In Figures 3 to 9, the heating element may be mounted improvement comprising said heating plate having a substantially circular circumference, the upper surface of said heating plate being convexly curved and having a single annular elevation, said elevation being positioned substantially directly above a median circular line between the outermost and innermost circumference of said annular heating element, said annularelevation thereby being positioned directly above the zone of highest calorific density on the surface of said plate, the position of said zone of highest calorific density depending on the position of said annular heating element; whereby a vessel placed on said plate is supported by said' elevation and comes in' contact with the zone of highestcalorific density of said plate along a substantially unbroken line regardless of irregularitiesain: the. shape in the bottom of said vessel. 2. An electric heating device, comprising an electric heating element of annular shape and a heating plate in which said heating element is embedded; said heating plate having a substantially circular circumference, the upper'surface of said heating plate being convexly curved and having a single annular elevation, said elevation being positioned substantially directly above a median circular linebetween the outermost and innermost circumference of said annular heating element, said annular elevation thereby being positioned directly above the zone of highest calorific density on the surface of said plate, the position of said zone of highest calorific density depending on the position of said annular heating element; whereby a vessel placed on said plate is supported by said elevation and comes in contact with the zone of highest calorific density of said plate along a substantially unbroken line regardless of irregularities in the shape in the bottom of said vessel. 3. An electric heating device comprising an electric heating element of annular shape and a relatively thin metal sheet pressed into the shape of a hollow heating plate for housing said electric heating element and having a substantially circular and convexly curved upper face with a single annular elevation, said elevation being positioned substantially directly above a median circular line between the outermost and innermost-circumference of said annular heating element, said annular elevation thereby being positioned directly above the zone of highest calorific density on said upper face, the position of said zone .of highest calorific density depending on the position of said annular heating element; whereby a vesselplaced on said upper face is supported by said elevation and comes in contact with the zone of highest calorific density of said upper facelalong a substantially unbroken line regardless of irregularities in vthe shape in the bottom of said vessel. ETIENNE CHAILET. so

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