Alternating current electrically resistive heating element having intrinsic temperature control
US4256945A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Aug 31, 1979 |
| Grant date | Mar 17, 1981 |
| Priority date | — |
| Expiry date | Aug 31, 1999 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH05B3/12
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
The heating element consists of a substrate or core of a non-magnetic material having high thermal and electrical conductivity, clad with a surface layer of a ferromagnetic material of relatively low electrical conductivity. When the heating element is energized by a source of high frequency alternating current, the skin effect initially confines current flow principally to the surface layer of ferromagnetic material. As temperature rises into the region of the Curie temperature of the ferromagnetic material, however, the decline in magnetic permeability of the ferromagnetic material causes a significant lessening of the skin effect, permitting migration of current into the high conductivity non-magnetic core, thereby simultaneously enlarging the cross-sectional area of the current flow path and expanding it into the highly conductive material; the resistance of the heating element becomes less due to both causes. By selecting the proper frequency for energization, by regulating the source to produce constant current, and by selecting dimensions and material parameters for the heating element, temperature regulation in a narrow range around the Curie temperature of the ferromagneti…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.