Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
1999-11-23
2001-03-13
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C338S279000
Reexamination Certificate
active
06201220
ABSTRACT:
The present invention relates to an electrical heating element structurally coupled to an insulating support base and especially adapted for a cooking hob.
PRIOR ART
Electrical cooking hobs are known whose heating element is made from a fine flat alloy strip, the element first being wound and then attached supported at the edge on the horizontal insulating base of the hob. The means of attachment used are either lugs or feet forming part of the element, emerging from one edge at regular intervals along the length, or removable clamps fitted over the element. The tips of the feet or clamps are inserted in the porous insulating base to attach the element. The attachment feet create an uneven conductive section along the element causing differences of temperature which increase the effect of fatigue due to cyclic heat stresses, particularly in non-ductile alloys such as chrome or nickel.
EP-612199 describes an electrical element of the above sort. To limit the mean conductive section of the element and make it more even, the strip is pressed with cuts in the feet in the form o openings or grooves to remove material. This also reduces heat dissipation toward the attachment feet. Heating element solutions with integral feet require a change of matrix to die-cut the element, when a different spacing is required between feet.
U.S. Pat. No. 4,161,648 (DE-2551137) describes another design for a flat element with attachment feet inserted in the insulating base.
The conductive length of the heating element is increased in relation to its overall length by cutting slits alternately from each edge of the flat strip, to form a zig-zag conductor of smaller conductive cross-section than the width of the strip. The strip slitting reduces the rigidity of the element in all directions and particularly vertically. The rigidity of the heating element and the tendency to bend have the adverse effect of warping the insulating base.
ES-2079293 (P9302122) describes a system for attaching the flat element to the insulating base. The element does not have attachment feet and its lower edge fits into a vertical groove in the base in spiral form. The element is attached to the base after fitting, by inserting inverted U-shaped attachment clamps spaced evenly on the element, which press it against the bottom of the housing groove. Because there are no integral attachment feet, the full width and material of the original strip are employed as the element's conductive section. The drawback of this known solution is the insertion of the clamps, after the element has been fitted on the groove in the insulating base, which is laborious and susceptible of errors which cause partial shearing of the conductive section and undesired local curving.
DISCLOSURE OF THE INVENTION
The object of the invention is a flat electrical heating element fitted to a porous insulating base of a cooking hob heater, as defined in claim
1
.
The invention provides the combined advantages of the disclosed prior art designs. In the absence of integral attachment feet, the heating element according to the invention can be employed as an element throughout the entire width of the strip, the conductive section of the element is even throughout its length, heat stresses caused by uneven temperatures are reduce, at the same time as having the advantage of the consistency of bending offered, by attachment clamps together with the secure attachment of the element to the base. A further advantage over the examples cited in the Prior Art is, the variety of intervals of the length of the strip or spacing between two attachment points, for adaptation to any cooking hob. Moreover, the spacing between feet conditions the element's placement upon the insulating base throughout the cooking hob's life.
The attachment feet are preferably an inverted U-shape and their flat walls remain in contact with the element around the bending line so that, in relation to the mass of the feet, a moment of force is permitted for insertion which is greater that admitted by integral feet in the Prior Art solution, so that the housing groove in the insulating base can be done away with.
The feet are made of an alloy similar to those of the element, so that heat expansion in terms of volume does not have effects of deformation, displacement or transversal curving different from that of the element.
REFERENCES:
patent: 600057 (1898-03-01), Ball
patent: 3833793 (1974-09-01), McWilliams et al.
patent: 4296311 (1981-10-01), Hagglund et al.
patent: 5181312 (1993-01-01), Gross
patent: 5977524 (1999-11-01), Deo et al.
Eika S. Coop.
Paik Sang
The Kline Law Firm
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