Electric heating – Heating devices – With heating unit structure
Patent
1996-03-15
2000-05-02
Walberg, Teresa
Electric heating
Heating devices
With heating unit structure
313331, H05B 310, H01J 550
Patent
active
060575328
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to infra-red radiation sources and in particular to those sources comprising an electrically conductive element formed of a plurality of carbon fibres.
Infra-red radiation sources are used as heat sources in commercial process ovens, domestic cooker hot plates and ovens, and radiant energy electrical heaters.
In each of the aforementioned applications there is a requirement for a higher degree of control of the heat output by such sources. To attain this higher degree of control the heat output from the source should rapidly reach an equilibrium value for a predetermined and constant electrical power input. Furthermore, the electrical resistence of the source should not vary to any great extent as it heats from room temperature to its maximum operating temperature. It is also desired that the source be capable of operating effectively through a wide range of power outputs which in turn necessitates a wide range of element temperatures such as, for example, between 600.degree. C. and 1800.degree. C.
There is in addition a further requirement for the processing of varied pigmented surfaces such that the source should have an enhanced emissivity at wavelengths much longer than those of the visible spectrum.
In the past a number of designs of infra-red radiation source have been proposed in which various starting materials are used for forming the or each electrically conductive element. Most of these starting materials have, after processing, yielded brittle elements which are difficult to handle. It has been found however that the use of carbon fibre fabrics and linear tapes impregnated with certain resins and thermoplastics such as epoxy allow the fabrication of elements having the required degree of flexibility.
Within the designs that use carbon fibre the or each carbon fibre element is supported at opposite ends between two members which are adapted so as to facilitate the connection of the element across an electrical power supply. Typically these supporting members have been formed of metals such as tungsten, molybdenum, nickel or steel. However, one of the problems associated with carbon fibre infra-red radiation sources is the tendency for the element to become sufficiently degraded within the region of the metal supporting members as to result in the failure of the radiation source after only a few tens of hours of operation. This degradation comes about as a result of either migration of carbon atoms from the conductive element into the metal of the or each supporting member or as a result of a reaction between the carbon and the metal to form the apropriate metal carbide. In either event carbon atoms are removed from the element resulting in its eventual collapse. As the carbon atoms are removed there is a tendency for the temperature of the element to increase which in turn only serves to exacerbate the mechanisms by which the carbon is lost.
According to a first aspect of the present invention there is provided an infra-red radiation source comprising an electrically conductive element formed of a plurality of carbon fibres and connection means for connecting the electrically conductive element across an electrical power supply, the connection means including at least one support member formed of carbon and secured to one end of the electrically conductive element.
According to a second aspect of the present invention there is provided an infra-red radiation source comprising an electrically conductive element formed of a plurality of carbon fibres and connection means for connecting the electrically conductive element across an electrical power supply, said connection means including at least one support member secured to one end of the electrically conductive element and formed of or coated with a metal through which carbon does not diffuse.
According to a third aspect of the present invention there is provided an infra-red radiation source comprising a housing formed of a material transparent to infra-red radiation, an electrically conductive element located with
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Dexter Amos Christopher
Jones William
Paik Sam
Walberg Teresa
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