Composite metal plate surface heating unit

Claim 1

A low thermal mass, solid plate surface heating unit comprising a lightweight plate of composite metal with a center core selected from the group of high thermal conductivity metals or alloys such as copper, silver and aluminum, and an outer skin selected from the group of strong and oxidation and corrosion resisting metals or alloys such as stainless steel, nickel and chromium, a metal sheathed electrical resistance heating element of coiled configuration covering a large expanse of the underside of the composite plate, and an embossed back-up plate underlying the composite plate and attached at a plurality of spaced points to the underside of the composite plate along a major extent of the heating element while allowing for limited relative sliding movement of the heating element witH respect to the composite plate under heating conditions without causing warpage of the composite plate, the said back-up plate including a spiral recess for receiving the coiled heating element therein, the area of the back-up plate at either side of the outermost turn of the heating element being attached to the composite plate at a plurality of spaced points that are remote from the heating element.