Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2000-12-01
2001-10-02
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S392000, C219S402000, C219S409000, C219S544000, C219S548000
Reexamination Certificate
active
06297477
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electric element and to a toaster or other cooking apparatus (which term includes apparatus for reheating already cooked food) incorporating a plurality of such elements.
BACKGROUND OF THE INVENTION
Conventionally an element for an upright toaster comprises a former of an electrically non conductive material and an electrically conductive tape wound continuously round the former with each run thereof extending between grooves in the opposite side edges of the board or each half of the board. The conductive tape is exposed except that one or more narrow strips of non-electrically conductive material are frequently located outside the tape running from top to bottom of the former, and spaced from the side edges, to limit the amount of outward bowing of the tape and to prevent the tape flying outwards if it breaks.
A toaster comprises a plurality of such elements which could be connected in parallel or in series. Because the conductive tape is exposed and can be easily touched by anything inserted into the toaster slots it is a requirement that the toaster must be double pole switched. This increases the cost of the toaster particularly if any electronics are incorporated in the toaster. It is also a requirement for upright toasters that an array of guard bars to prevent toast contacting the elements and which define the toaster slot are spaced at least 4 mm from the tape (since this is likely to bow outwardly when hot).
Conveyor toasters or other cooking apparatus in which elements are located horizontally conventionally also have live conducting tape or strip exposed, and suffer from uneven heating across the width of the apparatus.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides an electric element in which electrically conductive tape is wound on a non-electrically conductive former and the tape is completely covered by cover means of electrically non conductive but heat conductive material.
Preferably the or each cover is secured to the former by channel sectioned strips extending over the edges of the former and cover or covers on at least two opposite sides and by fastening means extending through the cover or covers at at least two positions intermediate those sides and not contacting the tape. This provides a particularly easy method of construction.
The cover on each side of the former may be formed by a single piece of material or has two pieces or more (up to ten) pieces of material overlapping at their adjacent edges.
Using such elements in a toaster or other cooking apparatus is safer because the electrically conductive tape cannot be touched so as to make electrical contact by a knife or finger or other object inserted into the toaster or the like. This allows the apparatus to be single pole switched. In addition the number of guard bars in an upright toaster can be reduced because the toast in the slot cannot touch the conductive tape. In addition the arrangement increases the life of the element considerably because most failures are caused by bits of bread, toast, currants or other ingredients falling off and touching the tape. This causes a burn-out which may be explosive. Also instruments inserted can no longer break the tape. In addition because the tape cannot bow outwardly the space between the element and the guard bars in an upright toaster can be reduced.
Preferably the cover material is either mica or mica paper (a combination of mica and silicon resin), particularly that known as Micanite, either Moscovite or Phologopite, depending on the temperature requirements. We have found that with covers made of this material in a toasting apparatus, the toasting performance is improved for a particular heat input and is more even over the area of the toast. The former may be made of mica or Micanite so that the heat generated in the tape is absorbed by the former and cover material and then radiated evenly towards the toast.
The channel-sectioned strips located along the side edges of the former serve to stabilise the former and hold the edges of the covers to the former. The channel-sectioned strips are not otherwise connected so that they do not prevent expansion of the former on heating. The fastening means, such as eyelets, reduce bowing of the cover away from the former. The eyelets may hold in place washers of electrically insulating but heat conductive material to increase the area over which the covers are held to the former.
The or each cover may be formed with slots at positions between the runs of tape but so that the cover still covers the tape to increase the heat output.
In one preferred form, where the former is made from a single piece of material, the tape starts adjacent one end of the former, is wound spirally towards the other end using alternate grooves, passes through a slot in the other end of the former to change direction, is wound spirally towards said one end using the remaining grooves and ends adjacent said one end of the former.
The former may be made in two parts, each with grooved upright edges with the tape wound first round one part, then the other part and the parts then secured together with abutting edges before connection of the covers. Each part may itself be preformed from one or more pieces connected along horizontal overlapping edges.
In a preferred form for an upright toaster, the former has a dimension in the range 130 to 150×160 to 180 mm (preferably 140×171 mm) and a thickness in the range 0.3 to 0.7 mm. Preferably each cover has a thickness in the range 0.1 to 0.3 mm.
Preferably the former and covers have convex rounded or sloped top edge corners corresponding to the shape of many loaves of bread, and to the end profile of the toaster. This allows the height of the former in the central portion to be greater.
The invention extends to an electric toaster or other apparatus including a plurality of such elements and which is preferably single pole switched. Preferably the elements are connected in parallel to an electrical supply. With such an arrangement, even if one element fails the remaining elements will continue to function. In addition each element can have a greater (or lesser) length of tape to produce the required watt density and thus produce more heat, giving faster toasting or heating.
For toasting the tape should be selected to produce a watt density equal to or less than 3 watts per cm
2
or within the operating band of the tape. With conventional 80/20 nickel chrome alloy tape, and with parallel connection of the elements to a 230 volt supply, the tape for each element can have a length in the range 5 to 10 meters, preferably 7 to 9 meters, in order to achieve this.
In another aspect the invention provides an electrical element for an upright toaster comprising a former of electrically insulating but heat conductive material and electrically conductive tape wound spirally on the former in a plurality of runs extending between grooves in opposite side edges of the former or each part of the former, the runs in the upper portion being spaced from one another by 4.6 to 7 mm for a 200 to 250 volt supply and twice this for a 100-125 volt supply, while the runs in the lower portion of the former are spaced from one another by a smaller distance in the range 3.6 to 5 mm for a 200-250 volt supply and twice this distance for a 100 to 125 volt supply, the length of the tape being in the range 5 to 10 meters for a 200 to 250 volt supply and half this length for a 100 to 125 volt supply and the watt density being equal to or less than 3 watts per cm
2
or in accordance with tape tolerances.
With advantage the spacing of the grooves in the lower part is in the range 3.6 to 4.5 mm for a 200 to 250 volt supply while the spacing in the upper part is in the range 4.6 to 6 mm for a 200-250 volt supply. One or more adjacent grooves may be spaced more widely apart to accommodate fastening means extending through the former and not contacting the tape. Alternatively where the former is formed in two parts, with their adjacent vertical
Gort-Barten Leslie Alexander
Milton Brian
Bacon & Thomas PLLC
Dualit Limited
Pelham Joseph
LandOfFree
Electric cooking and toasting apparatus and electric... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric cooking and toasting apparatus and electric..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric cooking and toasting apparatus and electric... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2611926