Abstract A smooth surface heating apparatus is provided having a heat spreader plate of high thermal conductivity coated, at least on its upper surface, with a thermochromic glass-ceramic material containing a predominant crystalline phase of lithium disilicate in a glassy matrix and having a coefficient of expansion in the range of 80-120 X 10 7 per *C. The thermochromic property is obtained by the presence of basic lead chromate in the glassceramic coating. An insulated electrical resistance heating element and a reinforcing member are attached to the underside of the heat spreader plate. A reflector pan is provided beneath the heating element to direct the heat in an upward direction.
The heating apparatus of claim 1, comprising additionally a reinforcing member attached to the underside of said plate to prevent warpage and a reflector pan beneath the heating element to direct the heat in an upward direction.
Claim 2
Dependent Claim
19 words
The heating apparatus of claim 1, wherein said glass-ceramic coating has a thickness of about 3 to 12 mils.
Claim 3
Dependent Claim
21 words
The heating apparatus of claim 2, wherein said coating covers both sides of the heat spreader plate and the heating element.
Claim 4
Dependent Claim
20 words
The heating apparatus of claim 1, wherein the glass-ceramic coating contains up to about 50 percent of a crystalline phase.
Claim 5
Dependent Claim
39 words
The heating apparatus of claim 1, wherein said glass-ceramic coating consists essentially as calculated from the batch on the oxide basis in weight percent of about 73.0% SiO2, 13.7% Li2O, 5.6% K2O, 4.9% Al2O3, 2.8% P2O5 and 5% PbO.PbCrO4.
Claim 6
Dependent Claim
54 words
The heating apparatus of claim 1, wherein said heat spreader plate is a composite metal sheet material having a core selected from the group consisting of copper, silver and aluminum placed between two integral outer layers of a metal or alloy selected from the group consisting of carbon steel, stainless steel, nickel and chromium.