US3668599A

US3668599A - Electrical resistance element

Info

Publication number: US3668599A
Application number: US72454A
Authority: US
Inventors: Nils Gustav Schrewelius
Original assignee: Kanthal AB
Current assignee: Kanthal AB
Priority date: 1969-09-16
Filing date: 1970-09-15
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: DE2045357A1

Abstract

An electrical resistance element formed of an array of parallel MoSi2 rods coupled in series by connecting adjacent rod ends together in pairs at one end of the array and at the other end connecting adjacent rod ends together in pairs staggered with respect to those at the first end. The connection is made by means of a flame-sprayed layer of MoSiAl or MoSi2 and the array is supported by an elastic cross bar in a ceramic frame.

Description

United States Patent [151 3,668,599

Schrewelius. 1 June 6, 1972 [54] ELECTRICAL RESISTANCE ELEMENT 737,689 9/1903 Win ..33s 2s9 1,657,507 1/1928 Keene... ..338/295 [72] Inventor. lSQilsdGustav Schrewelius, Hallstahammar, 1,719,179 7/1929 Haydenm" "338,3 1 8 x we 1,861,434 6/1932 'CampbelL. .....338/318 x 73 Assignee; Akfiebolgge' m Hansgahammar, 2,992,959 7/1961 Schrewelius. .....338/330 X Sweden I 3,144,545 8/1964 Shrimplin ..219/532 X 1 3,321,727 5/1967 Schrewelius ..338/330 [22] Filed: Sept. 15, 1970 v [21] APPL No; 72,454 Primary Examiner-E. A. Goldberg Anorney--Brumbaugh, Graves, Donohue & Raymond [30] Foreign Application Priority beta I l t [57] ABSTRACT Sept. 16, 1969 Sweden 12710/69 A le tri l re i tance element formed of an array of parallel MoSi rods coupled in series by connecting adjacent rod ends [52] U.S. Cl. ..338/289, 338/318, 219/532 together in pairs at one end of the array and at the other end [51] Int. CL... H010 1/02 connecting adjacent rod ends together in pairs staggered with [58] Field of Search ..338/295, 289, 318, 330, 332, respect to those at the first end. The connection is made by 338/315, 316, 317, 319, 320; 219/532 means of a flame-sprayed layer of MoSiAl or MoSi and the array is supported by an elastic cross bar in a ceramic frame. [56] References Cited v UNITED STATESPATENTS v I 5 Claims, 1 Drawing Figure 497,795 5/1893 Jenkins ......338 /295 i 4 l ELEc'rRrcAL RESISTANCE ELEMENT .The present invention relates to an electrical resistance element of the kind having a resistance conductor of a material brittle in cold condition, particularly molybdenum disilicide.

Electrical resistance elements, particularly intended for translucent cooking plates have been previously proposed, comprising resistance conductors of a material brittle in cold condition, e.g., the material sold under the registered trade mark KANTHAL Super. Said material consists essentially of molybdenum disilicide. In these known elements spirals, meanders or other shapes have been used in which a long, rather thin wire of said material has been shaped in heated condition to a disc-like element. The disc-like resistance element has been placed on a fire resistant support, such as a mineral fiber plate. However, it has been found that the support hascaused corrosive attacks on the resistance material, and particularly the shaping, the transportation and the mounting of the disc-like resistance elements have involved great problems. i

. The object of the present invention is to provide an electrical resistance element in which said problems have been avoided and for this purpose the resistance element according to theinvention is characterized in that the resistance conductor consists of a plurality of substantially straight elements disposed in a common plane and connected in series by having their ends connected to each other in pairs at staggered positions on respective ends of the element to form a resistance conductor of the required length.

; .The invention will be described below with reference to the accompanying drawing which shows a top view of a resistance element chosen as anexample only. g

'In the embodiment shown,'the resistance element consists I of'a plurality of substantially straight parallel element rods connected in series by having their ends connected in pairs at one end and,'at the other end, in pairs staggered with respect In the example, the element rods 10 are connected elastically or resiliently to a rigid support, which in this case consists to thepairs on the first end so as to form a resistance conduc- 1 tor of the required length. The ends of the element rods are connected with each other by means of a flame sprayed layer 11 of MoSiAl or Mosi for example, The element rods 10 are interconnected mechanically, but not electrically by means of two transverse bars l2, e.g., ofAl O The two transverse bars 12'also resilient connect the element rods 10 to a rigid sup-' port,in this case a frame 13 enclosing the element and consisting of A1 0 The ends of the two outermost rods are connected to rather thick lead-in

wires

14, 15 of metal, said leadin, wires being connected with the ends of the element rods by means of flame sprayed layers of Mosi for instance.

K In the example shown, the-element rods 10 are arranged in a parallel and rather closely spaced array. in most cases this arrangement will be preferable, but it is also possible to arrange the essentially straight element rods in some other configuration to form a plate. Further, all the element rods are interconnected in that the ends of pairs of adjacent rods 10 are connected with each other and with the ends of adjacent rods,

respectively, in such a way that the element rods connected in series fonn a continuous resistance conductor. Of course, it is also possible to make the connection in such a way that on each separate occasion only a portion of the disc-like element is switched on and the connection may also be made such that when using three-phase current the element is operated either in Y-connection or in A-connection.

In the embodiment shown, all the element rods 10 are equal length so that a square resistance element (as seen in top view) is obtained. However, for some practical applications it will of course be possible to chose rods with a length progressively increasing from one side of the element towards the middle and then progressively decreasing so that the shape of the element plate as'a whole is approximately circular, as seen from above. i

in the example, the connecting layers 11' which are staggered from one end to the other are created by masking spaces 16 between the rod ends, when flame spraying.

of a frame 13 of, e.g., Al o -ceramics enclosing the element. In this case, the connection has been provided by extending the sprayed-on thin cross connections 12 between the element rods to the enclosing frame. Of course, it is also possible to use some other kind of rigid support, such as a supporting plate which may also be designed as a reflector, if required.

As in the example shown, the lead-in

wires

14, 15 may be drawn through the frame at one side of the element. However, it is equally well possible to draw the lead-in wires through the bottom of a plate-shaped support, for instance, and to supplement said plate-shaped support by a translucent casing, for example, of some suitable material so that the unit thus formed is useful as a cooking plate of approximately the conventional kind. In the embodiment shown, the intention is that it should be possible to place the element under a glass plate at an appropriate distance therefrom, in which case no separate support or bottom insulation under the cooking plate is required.

Conveniently, an element according to the invention may have the outside dimensions 150 X 200 X 2 mm, and the resistance element rods may have a diameter of 0.5 mm.

Of course, the cross connection material is chosen such that the material does not react with the resistance material of the element rods, and further the cross connections must be such that the element'is sufficiently resistant to high temperatures so that it does not become deformed when used. In case the element rods consist of molybdenum disilicide, as is particularly preferred according to the invention, it is advisable to use aluminum oxide for the sprayed-on cross connection beads, as the aluminum oxide does not react with the resistance material mentioned. Owing to the design of the element,'the individual element rods 10 can, to a considerable extent, move freely at variations in temperature. i-lowever,also in cold condition the element is surprisingly insensitive to impacts which is probably due to the fact that-the element is flat andthin so that it becomes surprisingly elastic.

It should be apparent that the costs of manufacture for elements of the kind now proposed become very low, as all the steps in the production of the element can be automatized.

A great many modifications and alterations of details are possible within the scope of the inventive idea.

What is claimed is:

l. Anelectrical resistance element, comprising:

a plurality of elongated resistance rods formed of a resistance material which is brittle in cold condition;

. electrical interconnection means between said rods for connecting said rods in a continuous series circuit; and

- resilient support means for resiliently holding said rods in a spaced array, said support means including a resilient cross bar formed of dielectric material interconnecting all of said rods intermediate the ends thereof.

2. An electrical resistance element as claimed in claim 1, further comprising:

frame means surrounding said resistance rods, said resilient cross bar connected at opposite ends thereof to said frame means.

3. An electrical resistance element as claimed in claim 2, wherein said spaced array of said rods includes a plurality of substantially straight mutually parallel element rods connected in series by having their first ends connected in pairs and their other ends connected in pairs staggered by one rod with respect to the pairs at said first ends.

4. An electrical resistance element as claimed in claim 3 wherein said resilient support means includes two spaced parallel resilient cross bars supporting all of said rods at symmetrical positions spaced from the ends of said rod, approxiflame sprayed layer of a material including molybenum disilicide.

t in s t s

Claims

2. An electrical resistance element as claimed in claim 1, further comprising: frame means surrounding said resistance rods, said resilient cross bar connected at opposite ends thereof to said frame means.
3. An electrical resistance element as claimed in claim 2, wherein said spaced array of said rods includes a plurality of substantially straight mutually parallel element rods connected in series by having their first ends connected in pairs and their other ends connected in pairs staggered by one rod with respect to the pairs at said first ends.
4. An electrical resistance element as claimed in claim 3 wherein said resilient support means includes two spaced parallel resilient cross bars supporting all of said rods at symmetrical positions spaced from the ends of said rod, approximately one-fourth the length thereof.
5. An electrical resistance element as claimed in claim 3, wherein said electrical interconnection means comprises a flame sprayed layer of a material including molybenum disilicide.