IE42534B1 - Heater unit for a toaster - Google Patents

Abstract

1490684 Resistance heating unit WESTFALISCHE KUPFER - UND MESSING- WERKE AG 26 March 1976 [27 March 1975] 12377/76 Heading H5H A heating unit for a two slice toaster comprises a central heating element 1 between two lateral heating elements 5, wherein the central element 1 consists of a notched mica plate around which is wound a wire resistor 2 in the form of a double helix, terminals 3 provided at one end of the plate and a slot 4 provided in the opposite end of the plate through which the wire resistor 2 passes from one surface of the plate to the other, wherein each lateral element 5 consists of a mica plate formed at opposed edges with notches, the notches 6 in one edge being deeper than the first and last notches 6a and 6b in that edge and deeper than the notches in the other edge, a resistor wire 2 wound in serpentine fashion about the notches to extend on one side of the plate, terminals 3 at one end of the plate, and a return portion 8 of the wire 2 extending down said one edge of the plate and passing alternately in front of and behind the teeth between notches 6a, 6b; and wherein the central element 1 is provided on each side and the lateral elements 5 are provided on the said one side with a narrow fixing strip 10 to prevent displacement of the resistance wire convolutions, each fixing strip 10 being formed by a cut-out portion 11 removed from the lateral plates. The four fixing strips 10 required are provided by two cut-outs 11 in each lateral plate. The fixing strips 10 are secured to the mica plates by rivets.

Description

This invention relates to a heater unit for an electric toaster, of the kind comprising a central heating element and two lateral heating elements each consisting of a mica plate wound with resistor wire, the central heating element comprising a resistor wire which extends through edge notches of a mica plate and is helically wound around both sides and each of the lateral heating elements comprising a resistance wire which extends through edge notches and is wound in the form of a meander substantially only on one side, and the terminals of the heating elements being arranged on corresponding edges.

Electric toasters are usually provided with two slots for receiving two slices of bread which are to be simultaneously toasted. A plate-like heating element is disposed between the two slots and has a resistor wire which is so wound that it can deliver heat to both slots, while a lateral heating element, which is also plate-like is disposed on the outside of each slot. 7 As each such lateral heating element must deliver heat only on one side, it has a resistor wire which is wound accordingly.

Various regulations and requirements must be observed in the design of such heating elements. For instance, the heating resistor material, its dimension and its arrangement must be selected so that tlse required heat output can be produced within the space available. Care must be taken to maintain the required minimum distance between the individual convolutions. On the other hand, it is obviously desirable to use not more material in such a mass-produced article than is essentially required. This requirement applies to the resistor wire as well as to the mica plate which must be electrically insulating, heat-resisting and of adequate strength. In addition to these more basic requirements some special problems arise in connection with heater units for toasters of the kind defined hereinbefore. These problems will now be explained more fully with reference to previously proposed embodiments.

German Utility Model No. 72 13 852 discloses a heating element in which a resistor wire is wound in serpentine manner substantially on one side only of a mica plate and extends through edge notches of the plate from said one side to the opposite side of the mica plate, A return conductor consisting of a metal strip, is disposed on the opposite side of the mica plate and is provided with a contact tag at its upper end while its lower end is secured to the resistor wire, which extends to the opposite side through a bore in the plate. The mecal strip is secured by lugs, which extend through slots in the mica plate and are then reversely bent. This return conductor is relatively expensive because an additional metal strip is required, which must be so dimensioned that it does not involve unnecessary power losses because this strip is disposed on the opposite side of the mica plate so that any temperature rise of the strip would not contribute to the useful heat output of this lateral heating element.

In such heating elements, care must also be taken to ensure that the wound heating resistor wire engages the mica plate as closely as possible during operation and does not festoon due to thermal expansion so that the wire may contact adjacent convolutions or parts of the toaster which must not carry current. It has often been attempted to solve this problem by the provision of narrow cover strips, which are disposed in the middle of the mica plate, so that the convolutions of the heating resistor are clamped between the mica plate and cover strip and are thus held in the intended position. Such a cover strip is also provided on the lateral heating element disclosed in German Utility Model NO: 72 13 852.

The German Offenlegungsschrift No. 22 53 293 discloses a flat heating element, particularly a lateral heating element for toasters. This heating element comprises a flat plate of insula20 ting material which is provided at its mutually opposite longitudinal edges with notches and intervening teeth. A heating resistor wire is wound in loops on the frontside of this insulating material plate and extends on the rear side of the plate around the teeth and extends back to one of the two terminals provided at a transverse edge of the plate. A feature of this element is that; the notches at the longitudinal edges of the insulating material plate differ in depth and the heating resistor extends forth and back on the front side of the insulating material plate with portions of the resistor extending on the rear side of the - 4 4 3 53 4 plate around the teeth, the resistor extending from one o£ a pair of terminals at one end of the plate to the other end of the plate and then being connected to the other terminal by a return conductor. In this element the problem related to the return conductor has been solved in that notches differing in depth are provided so that the wire can be wound in the described manner.

The winding technology disclosed in the aforesaid German Offenlegungsschrift in conjunction with edge notches differing in depth is relatively complicated and may easily involve defects in the manufacture of the heating element. Because the heating resistor and the return conductor of the winding overlap, the winding is not clearly arranged so that winding defects cannot easily be detected and defective plate heating elements may pass an inspection and be delivered.

According to the present invention there is provided a heater unit for an electric toaster comprising a central heating element and two lateral heating elements spaced from and lying in planes parallel to that of the central heating element, wherein the central heating element consists of a mica plate formed at oppo20 site edges with notches and a resistor wire wound around the plate in the form of a double helix and engaging in said notches so as to lie on both sides of the plate, terminals for the resistor wire being provided at one end of the plate and the opposite end of the plate being formed with a slot through which the resistor wire passes from one side of the plate to the other, wherein each lateral heating element consists of a mica plate formed at opposite edges with notches, the notches at one edge, except for the first. and the last, being deeper than those at the other edge, and a resistor wire wound in a serpentine manner substantially on one si.de only of said plate from the notches of one edge to those of the other, terminals for the resistor wire being provided at one end of the p'late· and a return portion of the resistor wire running down said one fedge of the plate alternately in front of and behind the portions defined between the notches, and wherein the central heating element is provided on each side, and each lateral heating element is provided on the side carrying the resistor wire with a narrow fixing strip extending across the convolutions of the resistor wire and consisting of a cut-out portion removed from a plate of the lateral heating elements, there being two such portions removed from each such plate.

The present heating unit can easily be manufactured,has a clearly arranged winding and involves a low expenditure of materia1. ( in order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example an erribodi ment thereof, and in which:Fig. 1 shows a central heating element for an electric toaster, and Fig. 2 shows a lateral heating element for an electric toaster.

Referring now to Fig. 1 there is shown a central heating element 1 for an electric toaster, the element comprising a resis· tor wire 2 wound around a substantially rectangular mica plate, the opposite edges of which are formed with notches. The wire is wound in the form of a double helix and, as shown, extends from I the left-hand terminal 3 to the lowermost notch at the left-hand edge of the mica plate. The wire then proceeding on the rear side of the plate to the lowest but one notch at the right-hand edge of the plate; on the front side fo the lowest but two notch at the left-hand edge and so forth. In this way the winding formed by the resistor wire 2 extends on the rear side of the mica plate to the uppermost notch at the right-hand edge of the mica plate and from there on the front side approximately to the centre of the mica plate, where it extends through a slot 4 to the rear side of the mica plate and now extends back through the notches which are not occupied by the upward winding and finally terminates at the right-hand terminal 3 on the rear side of the mica plate.

As the resistor wire winding expands strongly at the operating temperatures it may sag to a very large extent particularly in the middle portion of the mica plate or may contact other parts of the toaster. In order to avoid this, the central heating element is provided on each of its front and rear sides with a fixing strip 10. These fixing strips consist of the same material as the base plate of the central heating element and are secured to the base plate by rivets or other suitable means.

The winding formed by the heating resistor wire 2 is clamped between the fixing strips and the base plate in the central portion thereof.

Referring now to Pig. 2, there is shown a lateral heating element 5, which, like the central heating element comprises a substantially rectangular mica plate which is formed at its lefthand edge with a series of notches of equal depth. At the righthand edge, only the first and last notches 6a_ and 6b are shallow and the intervening notches 6 are deeper than the first and last notches and the notches at the left-hand edge of the lateral . 42534 . heating.element 5, Because lateral heating elements of toaster must deliver heat only on one side, the same winding technology as with the central heating element cannot be used here. The resistor wire 2 must extend substantially only on one side of the lateral heating element 5 and the winding formed by the resistor wire 2 extends in a substantially serpentine manner as follows: From the left-hand terminal 3, the resistor wire extends first on the rear side of the plate to the lowermost notch at the left-hand edge, then on the front side of the lowermost deep notch at the right-hand edge, then on the rear side to the next upper deep notch a’t the right-hand edge, then on the front side to the lowest but one notch at the left-hand edge and then on the rear side to the lowest but two notch at the left-hand edge and on the front side to the right-hand edge and so forth.

The last convolution extends on the front side from the upper most left-hand notch to the shallow uppermost notch 6a^ at the right-hand edge and extends from there as a straight return condue tor 8 alternately on the forward and rear sides of the outer portions 9 defined between the deeper edge notches 6 to the shallow lowermost notch 6b and then to the right-hand tertnihal 3.

The lateral heating element also comprises a fixing strip 10 but differs from the central heating element in that this fixing strip is provided only on one side. In other respects the fixing strip has the same function as the central heating element. The fixing strip may be fixed also by rivets or other suitable means. Each of the fixing strips 10 required for a heater unit consisting of a central heating element and two lateral heating elements consists of two cut-out portions 11 of one of the lateral heating elements 5 so that additional material is not required for the - 8 fixing strips 10. The portions 11 cut out from the lateral heating elements 5 do not adversely affect the strength and dimensional stability of the lateral heating elements 5. Because the material of the plate accounts for a relatively large part of the cost of a heating unit and the fixing strips lo consist of the same material, the heater unit according to the invention can be manufactured economically. In conjunction with the described configurations of the windings, particularly of the lateral heating elements, considerable economical advantages may be obtained which are sig10 nificant when the elements are mass produced.

Claims (3)

1. CLAIMS ' - _

1. A heater unit for an electric toaster comprising a central heating element and two lateral heating elements spaced from and lying in planes parallel to that of the central heating element, 5 wherein, the central heating element consists of a mica plate formed at opposite edges with notches and a resistor wire wound around the plate in the form of a double helix and engaging in said notches so as to lie on both sides of the plate, terminals for the resistor wire being provided at one end of the plate and 10 the opposite end of the plate being formed with a slot through which the resistor wire passes from one side of the plate to the other, wherein each lateral heating element consists of a mica plate formed at opposite edges with notches, the notches at one edge, except for the first and the last, being deeper than those 15 at the other edge, and a resistor wire wound in a serpentine manner substantially on one side only of said plate from the notches of one edge to those of the other, terminals for the resistor wire being provided at one end of the plate and a return portion of the resistor wire running down said one edge of the plate 20 alternately in front of and behind the portions defined between the notches, and wherein the central heating element is provided on each side, and each lateral heating element is provided on the side carrying the resistor wire with a narrow fixing strip extending across the convolutions of the resistor wire and consisting 25 of a cut-out portion removed from a plate of the lateral heating elements, there being two such portions removed from each such plate.

2. A heater unit for an electric toaster substantially as 10 42534 hereinbefore described with reference to the accompanying drawings.

3. An electric toaster having a heater unit as claimed in Claim 1 or 2.