GB2261351A

GB2261351A - Electric heating appliance having a temperature-compensated heating element made from enamelled sheet metal with a resistive track

Info

Publication number: GB2261351A
Application number: GB9221546A
Authority: GB
Inventors: Claude Perrin
Original assignee: AIRELEC IND
Current assignee: AIRELEC IND
Priority date: 1991-10-23
Filing date: 1992-10-14
Publication date: 1993-05-12
Also published as: ES2037622B1; FR2683026B1; ES2037622A1; FR2683026A1; CA2081158A1; GB9221546D0

Abstract

Electric heating appliance comprising a heating element (1) constituted by at least one enamelled metal sheet having on one of its faces a resistive track (2) produced by silk-screen printing and which heating element is mounted in an enclosure comprising, in the vicinity of the heating element, a cool-air inlet (30) at its lower part and a hot-air outlet (31) at its upper part, the heating element being mounted in the enclosure by means of supports (28, 29), at least one (29) of these supports being placed in the path of the hot-air outflow and creating temperature peaks in the air outflow which goes around this support, characterised in that the heating element includes, in line with each perturbative support, a reduced-heating zone (7) for compensating for the temperature peaks caused by the presence of the support (29). <IMAGE>

Description

ELECTRIC HEATING APPLIANCE HAVING A TEMPERATURE-COMPENSATED HEATING ELEMENT MADE FROM ENAMELLED SHEET METAL WITH A RESISTIVE TRACK.

The present invention relates to electric heating appliances and relates more particularly to electric heating appliances comprising an enclosure in which at least one heating element, constituted by an enamelled metal sheet on which a resistive track is formed by silkscreen printing, is mounted.

In accordance with the new standards concerning electrical heating appliances, a heating element of the aforementioned type made from enamelled sheet metal has to have, when it is disposed vertically, a uniform temperature at every point of the surface of the metal sheet.

This temperature uniformity is generally obtained by a variation in the spacing between the horizontal parallel sections of the resistive track enabling a temperature homogeneity to be obtained over the vertically disposed plate.

Moreover, it is necessary for an electric convector, provided with a heating element made from enamelled sheet metal with a resistive track obtained by silkscreen printing, to have a uniform temperature rise over the entire extent of the air outlet of the appliance.

In known appliances having heating elements made from enamelled sheet metal with resistive tracks obtained by silk-screen printing, the enamelled metal sheets are mounted in the bodywork of the appliances by means of supports, some of which are located in the path of the air leaving the appliance and thereby create perturbations in the flow from the air outlet.

These perturbations are manifested by temperature peaks which detract from the uniformity of the temperature of the air outflow from the appliance.

The invention aims to remedy the drawbacks of the known appliances by creating an electric heating appliance which, whilst being of a relatively simple construction, satisfies the conditions of temperature uniformity at the surface of the heating element and of uniformity of the temperature of the air outflow from the apparatus which are imposed by the aforementioned standards.

The subject of the invention is therefore an electric heating appliance comprising a heating element constituted by at least one enamelled metal sheet having on one of its faces a resistive track produced by silkscreen printing and which heating element is mounted in an enclosure comprising, in the vicinity of the heating element, a cool-air inlet at its lower part and a hot-air outlet at its upper part, the heating element being mounted in the enclosure by means of supports, at least one of these supports being placed in the path of the hot-air outflow and creating temperature peaks in the air outflow which goes around this support, characterised in that the heating element includes, in line with each perturbative support, a reduced-heating zone for compensating for the temperature peaks caused by the presence of the support.

The invention will be better understood with the aid of the description which follows, given solely by way of example and made with reference to the attached drawings, in which: - Fig. 1 is a view in elevation of a conventional enamelled sheet-metal heating element for an electric heating appliance; - Fig. 2 is a plan view of a first embodiment of enamelled sheet-metal heating elements according to the invention; - Fig. 3 is a plan view of a second embodiment of enamelled sheet-metal heating elements according to the invention; - Fig. 4 is a plan view of a variant of the enamelled sheet-metal heating element of Fig. 3; - Fig. 5 is a diagrammatic sectional view of an electric heating appliance comprising an enamelled sheetmetal heating element according to the invention;; - Figs. 6 and 7 show, diagrammatically, enamelled sheet-metal heating elements designed respectively to be supported by two and three intermediate supports; - Fig. 8 is a curve showing the air-outflow temperature of a conventional electric heating appliance having an enamelled sheet-metal heating element; and - Fig. 9 is a curve corresponding to that of Fig. 8 for an electric heating appliance, the heating element of which is provided with compensation means according to the invention.

The conventional heating element shown in Fig. 1 essentially includes a metal sheet 1 made from enamelled sheet metal, on one of the faces of which a resistive track 2, formed from a silver and lead alloy or from aluminium for example, is formed by silk-screen printing, the successive sections 3 of which extend horizontally along the large dimension of the metal sheet 1 and are connected together via short vertical sections 4 disposed at the two ends of the metal sheet 1.

In Figure 1, in the lower left-hand corner of the metal sheet 1 are provided at least two terminals 5 for connecting the heating element thus constituted to terminals for supplying the heating electric appliance.

Along the long sides of the metal sheet 1 markers 6 indicate locations of supports intended for mounting the metal sheet in the bodywork of an electric heating appliance.

In order for the temperature supplied by the heating element of Fig. 1 to be uniform over its entire height when it is mounted vertically, the distance or spacing between the track sections 3 can be varied. It may be seen from Fig. 1, starting from the bottom of the heating element, that the density of the track sections 3 decreases from the bottom of the heating element to the top.

Thus, the highest zones of the metal sheet which benefit from the heating they receive from the zones of the metal sheet located below them, receive less heat from their own track sections on account of the greater distances which separate them.

The heating element according to the invention shown in Fig. 2 also comprises an enamelled metal sheet 1 on which a resistive track 2, the successive sections 3 of which extend horizontally and have a decreasing density from the bottom of the element to the top, is deposited by silk-screen printing.

On this element, the support locations for mounting the element inside the bodywork of an electric heating appliance have also been indicated by the reference numbers 6.

It may be seen in Fig. 2 that these locations are six in number, two locations for support elements at each end of the metal sheet 1 and two intermediate locations 6, one at the lower part of the element and the other at its upper part. At the upper intermediate location 6, an attachment support is to be placed which will be situated in the path of the outflow air from the electric heating appliance and which will create temperature peaks at this location.

In order to compensate for these temperature peaks, the heating element 1 according to the invention includes, in line with the intermediate location 6, a zone 7 free of resistive track, obtained by the resistive track 2 skirting round its perimeter.

For this purpose, the resistive track 2 of the heating element includes a first lower part 8 in which the horizontal sections 3 of the resistive track extend approximately over the entire large dimension of the heating element 1. This lower part 8 is extended upwards by a first upper part 9, the resistive-track sections 10 of which also extend horizontally but only between one edge of the zone 7 free of resistive track and a first end edge 11 of the metal sheet 1.

A third upper part 12 disposed on the other side of the zone 7 free of resistive tracks includes horizontal track sections 13 extending between the other edge of the track-free zone 7 and the end edge 14 of the metal sheet 1 opposite the edge 11.

It may therefore be seen that such an arrangement makes it possible to obtain a zone 7 free of resistive track, surrounded by the resistive track 2 of the heating element.

In order to prevent the upper horizontal section 3 of the heating element from heating too much, on account of its local resistance, in the region of the track-free zone 7, this upper section 3 has, in line with the zone 7, a portion 15 of increased surface and consequently of reduced resistance permitting the connection between the first and second upper track portions 9 and 12, whilst keeping the zone 7 at a lower temperature than the remainder of the heating element.

In the example which has just been described, the transverse cross-section of the resistive track is constant with the exception of the region 15 of reduced resistance.

The heating element shown in Fig. 3 has a similar structure to that of the heating element of Fig. 1.

Its resistive track 16 also has horizontal sections 17 of decreasing density from the bottom of the element to the top.

However, this resistive track differs from that of the heating element of Fig. 1 in that each horizontal track section 17 includes two lateral parts 17a, 17b of increasing cross-section from each end edge of the heating element to the middle of the latter and which parts are joined together by a zone 18 of increased cross-section which defines, with the zones 18 of increased cross-section of the other track sections 17, a reduced-heating region 19 located in line with the locations 6 intended for receiving top and bottom intermediate supports (which are not shown).

By virtue of such an arrangement, there is, on the one hand, a progressive decrease in the resistance, and consequently in the heating capacity, from the end edges of the heating element towards its centre and, on the other hand, a rapid decrease in the heating at the location of the zones 18 of increased cross-section.

The heating element shown in Fig. 4 has a very similar construction to that of the heating element of Fig. 3. It indeed includes a resistive track 20 formed by silk-screen printing on one of its faces and which has, like the track 16 of the heating element of Fig. 3, horizontal track sections 21 formed from lateral portions 21a, 21b of increasing cross-section from the end edges of the heating element towards the middle of the latter.

However, the heating element of Fig. 4 differs from that of Fig. 3 in that the lateral portions 21a, 21b of each of the sections 21 of the resistive track are joined together without interposition of a zone of increased cross-section.

Thus, the temperature compensation is obtained in a central zone 22 of the heating element simply by a progressive reduction in the resistance, and consequently in the heating capacity, from the ends of the heating element towards its middle.

Fig. 5 shows, diagrammatically and in crosssection, an electric heating appliance according to the invention, comprising a body 25 made from sheet metal constituted by a double-wall hollow element facing the flat core 26 of which is mounted a heating element 1 according to the invention, which element is attached to inclined parts 27 of the body 25 extending on either side of the core 26 by means of lower supports 28 and of upper supports 29 made from electrically and thermally insulating material.

The electric heating appliance presented diagrammatically in Fig. 5 is seen in the region of the locations of the supports 28, 29 disposed in the intermediate zone of a heating element such as that of Fig. 2. The electric heating appliance furthermore includes a coolair inlet 30 at its lower part and a hot-air outlet 31 at its upper part. The resistive-track sections 3 are shown, for more clarity, as raised features of exaggerated thickness. The zone 7 free of resistive track thus appears clearly underneath the support 29.

A grille 32 is also fastened to the upper supports 29.

It may therefore be seen that the upper support disposed in the intermediate zone of the heating element 29 is situated in the path of the air outflow from the heating appliance shown by arrows F. The body of the support 29 forms an obstacle to the free circulation of air towards the outlet of the appliance.

The rising hot air tends to accumulate at the base of the support 29 and to create a zone of increased temperature. The air which goes around the support is heated more than the air which leaves directly via the air outlet 31 without encountering an obstacle, and therefore forms temperature peaks at the outlet which detract from the uniformity of the temperature of the air outflow (Fig. 8).

The zone 7 free of resistive track of the heating element of Fig. 3 disposed in line with the support 29 makes it possible, by virtue of a localised reduction in the heating, to avoid the formation of an overheated pocket at the base of the support located above this zone 7 and thus provides a temperature compensation for the air which goes around the support.

An approximately uniform temperature is thus obtained over the entire horizontal extent of the hot-air outlet 31 (Fig. 9).

Figs. 6 and 7 show diagrammatically two heating elements having resistive tracks 32 and 33 respectively, longer than the heating elements of Figs. 2 to 4 and which are intended to be attached at the locations designated by the reference numbers 6, in longer electric heating appliance bodies, by means of four lower supports and four upper supports for the element of Fig. 6 and of five lower supports and five upper supports for the element of Fig. 7.

The heating element of Fig. 6 is therefore intended to be attached to the body of the electric heating appliance to be equipped therewith by two supports disposed at each of its lateral ends and by four intermediate supports. In order to compensate for the overheating of the air outflow due to the presence of the intermediate supports, the heating element of Fig. 6 includes, in line with the locations 6 of the two upper intermediate supports, two reduced-heating zones 35, 36 which are produced by the resistive track skirting round them, in a similar manner to that described with reference to Fig. 2.

The heating element of Fig. 7 is intended to be supported by three sets of intermediate supports, the upper locations 6 of which are associated with reducedheating zones 37, 38, 39 produced by skirting round in a similar manner to that described in reference to Figs. 2 and 6.

The heating element of Fig. 6 includes, in the reduced-heating zone 35, a region 40 of larger crosssection intended for connecting the right-hand part of the resistive track with its intermediate part without causing a temperature rise.

The heating element of Fig. 7 includes a first zone 41 of increased cross-section intended to connect the right-hand part of the resistive track with one end of the intermediate part of the latter located on one side of the central reduced-heating zone 38 and a second zone 42 of increased cross-section for connecting the left-hand part of the resistive track with the other end of the intermediate part of the latter located on the other side of the central zone 38.

Fig. 8 shows the curve of the temperature of the air outflow from an electric heating appliance equipped with a heating element having three intermediate supports but lacking means for compensating for the localised overheating due to the presence of the intermediate supports.

In the graph of Fig. 8, the length L of the heating element is plotted as abscissae and the temperature t as ordinates.

It may be seen that at the locations of the supports, such as the support 29 of the appliance shown diagrammatically in Fig. 5, the curve of the temperature of the air outflow, the maximum value of which is slightly less than 125 , has temperature peaks C1, C2 which result from the excessive heating of the air which goes around each of the supports 29.

Fig. 9 shows a curve of the temperature of the air outflow from an appliance having three intermediate supports, but temperature-compensated by the presence on the heating element of reduced-heating regions, such as the regions 37, 38, 39 of the element shown diagrammatically in Fig. 7.

It may be seen that the outflow temperature of the air is established approximately uniformly, slightly below 124 C and that the presence of the reduced-heating zones in line with the supports 29 has suppressed the temperature peaks and has thus provided a virtually complete compensation for the irregularities of the temperature of the air outflow from the electric heating appliance.

It may be seen that, by virtue of the arrangement which has just been described, electric heating appliances having heating elements made from enamelled sheet metal having resistive tracks are obtained which meet, virtually perfectly, the standards imposed on the manufacturers.

Such appliances not only have a constant temperature over their entire surface when they are disposed vertically, but also have a temperature of their air outflow which is practically uniform over their entire length.

In the examples which have just been described, the electric heating appliances were considered as comprising a single heating element made from enamelled sheet metal and resistive track obtained by silk-screen printing, and provided with temperature-compensation zones.

It is also possible to envisage producing such appliances by combining two or more enamelled metal sheets each having a resistive track, which are disposed on either side of intermediate supports, so that the temperature compensation for the overheating due to the presence of these supports in the path of the air outflow is ensured purely and simply by the absence of the heating element in line with the support in question.

It thus suffices to interconnect consecutive heating elemets by single electrical conductors of suitable size, in order to prevent any overheating.

Claims

1. Electric heating appliance comprising a heating element (1) constituted by at least one enamelled metal sheet having on one of its faces a resistive track (2; 16; 20; 32; 33) produced by silk-screen printing and which heating element is mounted in an enclosure comprising, in the vicinity of the heating element, a cool-air inlet (30) at its lower part and a hot-air outlet (31) at its upper part, the heating element being mounted in the enclosure by means of supports (28, 29), at least one (29) of these supports being placed in the path of the hot-air outflow and creating temperature peaks in the air outflow which goes around this support, characterised in that the heating element includes, in line with each perturbative support, a reduced-heating zone (7; 19; 22; 35, 36; 37, 38, 39) for compensating for the temperature peaks caused by the presence of the support (29).

2. Electric heating appliance according to Claim 1, characterised in that the reduced-heating zone (7; 35, 36; 37, 38, 39) of the heating element is a zone free of resistive track, obtained by the resistive track skirting round its perimeter (2; 32; 33).

3. Electric heating appliance according to Claim 2, characterised in that the resistive track (2; 32; 33) includes track portions (9, 12) located on either side of each reduced-heating zone (7; 35; 36; 37, 38, 39), at least some of which are connected together via a reducedresistance track portion (15; 40; 41, 42) located in line with the corresponding zone (7; 35; 37, 39).

4. Electric heating appliance according to Claim 1, characterised in that the reduced-heating zone (19) is constituted by zones (18) of increased cross-section of the resistive track which join together the lateral parts (17a, 17b) of horizontal sections (17) of the resistive track.

5. Electric heating appliance according to Claim 4, characterised in that the lateral parts (17a, 17b) of the horizontal track sections (17) have a cross-section which Increases from each end edge of the heating element towards its middle.

6. Electric heating appliances according to Claim 1, characterised in that the reduced-heating zone (22) is constituted by the direct junction of lateral portions (21a, 21b), of increasing cross-section from the end edges of the heating element towards its middle, of sections (21) of the relevant track of the said heating element.

7. Electric heating appliance according to Claim 1, characterised in that the heating element consists of at least two enamelled metal sheets each having a resistive track and disposed on either side of a corresponding perturbative support.

8. Electric heating appliance comprising a heating element substantially as hereinbefore described with reference to and as shown in any of figures 2 to 4, 6 and 7 of the accompanying drawings.

9. Electric heating appliance substantially as hereinbefore described with reference to and as shown in figure 5 of the accompanying drawings.