WO2015101889A1

WO2015101889A1 - Method for fastening a resistor to a muffle and oven made according thereto

Info

Publication number: WO2015101889A1
Application number: PCT/IB2014/067069
Authority: WO
Inventors: Matteo Scoponi; Fabio Gambardella
Original assignee: Indesit Company S.P.A.
Priority date: 2013-12-31
Filing date: 2014-12-18
Publication date: 2015-07-09
Also published as: ITTO20131098A1

Abstract

The invention relates to a method for fastening an electric resistor to a muffle of an oven for household use. The method provides to fasten the resistor through support structural elements that are applied at the bottom of the muffle. To this end, the resistor is configured according to a linear, polygonal, circular, or other shape extending in a peripheral region with respect to the bottom of the muffle. The invention also relates to an oven made according to this method.

Description

METHOD FOR FASTENING A RESISTOR TO A MU X<B AND OVEW MADE ACCORDING THERETO

DESCRI S?IOH

A ording to a sain aspect, the present invention relates to a tnethod for applying an electric heating resistor to a muffle of an oven, in particula , but: not exclusively, ·.: : oven for household use.

The latter may be a bui it-in oven, i.e., a separate househol appliance which is: inserted in a piece of fnrni.i.uri! , or part of a large;: appliance such as a gas; c ok r; ho e e the p esent i n ve n t i o n a 1 so may be applied to hobs, hotplates and similar products, i.e., not. ne c e s s a r i 1y mu f f les .

The latter have, as is Known, a hollow body, substantiall of cubic sha or, in any case, of paral lelapiped or similar shapes, which surrounds the cavity wherein the food to foe he t ad is inserted, whic is fronta!iy closed by the Ooor of the oven. The muffle is in turn inserted in a comp rtment, which is defined within a piece of furniture in the case of built-in ovens, or within, a coating appliance depending on the applica ions within said compartment the muffle ma be thermally insulated (i.e. , with mineral wool) and its heat: emo e by venti 1 a t n .

For the heating o he muffles there are used electric resistors, which can be arranged curls ide and/or inside; the present invention is directed in particular to the first ones, although, it roight be applied also to the latter.

Usually, the electric resistance applied outside the muffle is a coil, 'Wh ch i supported below the bottom of the muffle itself. With reference to Figure l_s whe ein a substantially cubic shaped muffle I is shown, comprising an upper wall 2 at the top and a foottora wall 3 at the bottom, witb a series of side walls , 5 end 6, the resistor 3 is const tinted b a coil suppor ed by a tray 3. The latter is made o metallic material, generally sheet metal, and is applied on the bottom of the •ruffle 1 through screws and brackets in a sirapia way. The coil 8 is kept slightly lifted from the bottom of the tray 3 through spacers 10: in. this way t e tray 9 can serve as a resistor support and also as a surface for reflecting heat radia ion to the bottom wail 3 of the Eiiuf fie .

However, the realisation of an oven according to is technique has some drawbacks .

The firs one is that the ma o.fa oi u.r i g of a tray like that of the support 10 is costly, given that it is made of wo ked sheet metal; thi entails a waste of materials and proces ing which ma adversely affect the final cost or^" the component .

Furthermore from a strictly thermal and operating point of view, it should be noted that the support tray 10 cannot be mounted close to the bottom of the muffle, when there are deep drawings or ribs on the bott m, wa l itself.

These deep drawings, or ribs a e sometimes made in order to stiffen the bottom wall of trie muffle 3 and they car have different shapes, i.e. circular, linear or concave snoh as that shown in fig, 1, wherein the wall 3 has a truncated pyramidal configuration.

In these cases, the tray must be applied in. s ch a manner as to av id a y int rfe ence with the most downwardly projecting porti n of the bottom wall 3 of the muffle, so thai;, in fact:, it is spaced f oro. i wi h the result hat heat t r. a :r s fe :ε: car! not o pt ima 11 y a ccoai fi hed.

f The saiae app es to the elect ic resistor 9 contained in t e t cay 10 indeed; in othe words it ma be said that although having a resistor 9 with a serpentine shaped development, throughout the whole bottom wall 3 of the ran trie, th heading effac produced by it is not satisfactory in ase of a concave c torn, a ... or of a wall with r bs, where t e bottom wall is concave or presents seas ribs, which inevitably requires rise mounting of the resistor 3 and of the corresponding support tray 10, at a certain distance from the bo tom wall of the muffle.

The t chni l roblem underly ng the p es nt invent.! or: is he efore to raake avail ble a me hod for fastening an electric heating resistor to a !tuffle of an oven, that allows to overcome the above- in ers t i o ned 1 imi t a t ions w11h r e f e r a nc e to the p r i. o r a r t .

The idea for solving this problem is that of ap lying the res i si: ance near he muffle, o s s i b 1 y juxtaposed to it, regardless of the shape of the wall o which it is applied.

In this context, i should be rioted thai: the method of the invention is particularly suitable for resistors that are fi:;.ed outside the bottom wail of the muffle; however, it can be ad an ageousl applied lso to the ether alls of the latter, either ide and upper walls.

Furthermore, as will be apparent: her after, this e tho d ita y also be a plied j. n c a s e o f he a t: i o.g resistors ar anaed inside the riuf ie. The features of the invention as a whole, including the implementa ion phases of the method and. the elements of the oven iaade in accordance with the invention, are s a i. out specifically i the ci alias appended to this descri tion ,

hese features will became more appa ent, i view of the following description of a preferred, but iioi: exclusi e, embodiment thereof sho n in the attached drawl n g s , wh e^■: sin:

- Fig. 1 shows an axcnometri.c exploded view of a muffle and a resis r ccording to the prior art;

- Fig. 2 is an axonoraet ric bottom view of a muffle e ·:: e o r. d i n g o the i n v e n f i o n ;

- Fig. 3 shows an enlarged detail of the muffle of fig. 2;

- Fig. s a axonometrie view from ar other angle of the muffle o 3;

- Fig. 5 shows an enlarged detail of the muffle of fig. 4;

- ig, 6 is a bottom view of the muffle of fig. 2--o

- Pig. ^"I is an _::i¾.onoaEtric view of a muffle according to a -variant of the invention;

- Fig. 8 is a bottom, view of the muffle f fig. 7. With reference to the above listed drawing.* and, in particular, to fig res from 2 to 6, with refer ed number 11 id: is generally indicated a muffle of an oven in accordance with the present invention.

The muffle car; be manufactured with any appropriate system known in. the art., preferably with parts made in drawn, metal sheet arid assembled as it is c stomaril done by the applicants for its products. he mu fle 11 is shaped substantially as a paralleiepi pedon, with an upper wall or sky 12 at the top, a bottom wall 13 at the bottom, two opposite side walls 1-1 and 15, a rear back 16, which surrou d a c ooking cavit y 17.

The muffle 11 has a iron;: aperture 18 to have access to the cavity 17 , on e edge of which a gasket 1 can be applied, preferably as those applied by the applicant in the evens that it raanufactures-;- .

n connection with ::he bottom wall 13 of the muffle 11, an electric resistor 20 is a ranged in accordance i t n the i n en 11 n .

The resistor is coniigured as a 5-10 m di arret er conduct: itsg wire and extends p i he ally with respect to the bo tom wall 13, in this; case following a ubstantiall quadrangular long i tud in a 1 extension , between two ends 21, 2 of power s pply,

la accordance wi h this mbodiment, the vertices 23, 2 and 25 o th q ua dr a.n g al r ex1: eo s i o n o f he resistor 20 are configured as lobes and link, the straight sections 26, 27, 23 and 29 of the resistor

20, l ing p a. t: a 11 si to the ed e o f t he h o 1 t om wa 11 13 of the muffle.

In particular, as can be better understood from the bottom views of the latter, the bottom wall 13 of the muffle 11 is deep-drawn into a circular downwardly projecting imprint 30, in order to give it a sub tantially concave configuration .

The resistor 20 extends around the deep-drawn form

30 and is j u¾taposed t o the ortion of t he bottom wail 13 surrounding the prospecting imp int 30: in this way, the close distance between the resistor 20 arid the wall 13 ro.a κ i.mi z e s the t r an sm1 s s i on of the heat generated by the resistor 20 to the wail itself 13 , th u s to the mu f £ 1 e 11. la this ccntsx;t, it should be noted thai: the resistor is supported i n the position close to he bot om wail 13 by a pair of structural elements 33, that are fastened at the bottom ; t the muffle.

The structural elements 32, 33 are identical each other and are arranged syianie<^': r i ca 1 with respect to a median a.Kis line X-X of the bctloa wall 1 {fig. 6 } end have s ab s t ant i a 11 y an "L" cross-section, with, a portion thereof applied to the wa l 1 and another perpendicular it: .

For fastening the struc u al elements 32, 33 several solutions are possible; in the a sam le shown i the figures, the front end 32a, 33a, is enga ed through a shape-locking fit with the edge of the aperture 18 of the muffle 11, while the rear end 32b, 33b is folded and fastened to h muffle by means of screws (not shown in the drawings; ith through holes 35, This solution, according to which one end of the s t r uo t u r a 1 elements 32 , 33, in his case the rear end 13b, 3Sb, t it might also be the front one, is fastened with screws whereas the other one is engaged with a shap e-locking fit, allows the s ructur l eieiaenos to support, the thermal expansions of the muffle 11, so as to avoid being damaged, or ca using d amag e .

In this context it should foe noted that the folded shape of the rear ends 32b, 33b of the structural elements 32 and 33, rovides for flexibility so that ^■the can adapt to the thermal deformations of the muffle, as mentioned above.

In order to uppo t the esistor 20 along the structural eien;ents 32, 33, they are equipped vrl.fh tangs 36 protcudi ug f ron; thei e pendicular po 11 (5n o the bottom wall 13 of the muffle; said tangs are a άv a n t a g e o u a 1 y ade solid i t h t he structural elements, through machining such as blanking, punching cr s i m i i a v. processes .

Howsvsr, they could be applied by welding o t replaced by brackets or other support eleme ts.

The resistor 20 rests with its side straight lines 2 ? , 29 o r: t he tangs 36 protiud i. n g ·: r o m the portio n of the structural elements' section, which is p pendicular to the bottosi wail 13.

In accordance with a preferred embodiment, the resistor is held ermanently esting o the tangs 36; to this end, it is advantageously and resiiiently held pressed against them by a series of second tangs 38, which are similar to the previous ones but formed in the ort i o n o f t h ii s t ructural e 1 e ::· e n I: s 2, 33 juxtaposed to the ot om wail 13 of the muffle ii . I this way the resistor 20 is held in a preset position with respect to the bottom wail 13 of the muffle, to ensure optimal radiation and convection heating .

he mounting of the resistor 20 by resting^" on the ti ts:: tangs 36, p r o v i d e s sufficient freedoiii of •novens!Qt for supporting f s thermal expansions {and contractions) due to heating and cooling thermal c cles .

This also applies to the second tangs 38. i.e. , the ripper tangs working e 1 a s t i.ca 11 y on the resistor 20, si nee their action is elastic and therefore does not sti ). y fasten the resistor 20.

In the light of the bove. it is possible to understand that the fastening method of the resistor 20 solves the technical problem underlying the invention .

Indeed, as it can be easily appreciated from the attached figures, the resistor 20 is supported without the need of any tra , pan, or similar fiat elements with a surface corresponding to trie one of the bottom wall 13 of the mu fle .

This has a twofold beneficial effect: the one hand, it constructively simplifies the manufacturing of the oven, given that now the support of the resistor 20 is obtained by two structural elements, while on the ether, and .ft. si l ws; to plac the resistor in a position closer to the bet cot;; wail 13 of the ttu f f1 e , in order to im rove heat traftsmiss ion .

As a consequence, it may be stated that the presence of the two structural elements 32, 33 in pi. ace of t e tr 9 of the prior art, allows ad ntageous! t reduce the costs not only bec use of a dec res sed use of mate ials for the support, elements {i.e., the structural elements 32, 33 in place of the tray 9) , but also because of a reduced length required for the resistor 20, which now is no more coil sh d but .id:, is polygon l, ci cula , or o f h e r .

In othe words, the met.hod of the 1 ;rv en t i o n. allows to ap ly the elect rule resistor 20 to an ideal d.i. stance from the muff e, which can be chosen on the basis of the design parameters (for example, the thermal power of ' he oven, :he size of ^'the muf le 11 and of i t a wails 12-16, the materials with which, it: is realised, etc,} , i ord r to chieve opt i m.a 1 he a f t r a n s i s s i o tr , and therefore an improved thermal efficiency of the ove .

This applies notably when the wall 13 of the muffle

S to which the resistor 20 is associated,- is; deep-drawn or ;: e s e at s sosis ribs, protruding areas or the like, as usually happens (the attached figures show s ortie possible examples of these d;?¾p-;ii:av;ings, ribs end protruding areas, whict can however be d.i. I ·: e r. e tit from them.) .

In this context 1 s should be noted that the structural e l eiRsa t e ^"s 2 , 33 support the resistor 20 in a peripheral region of the cor espondi g wall (in the drawings the bottom wall 13, but. .id: may also be the upper wail 12 or a side via 11. 14-16; of the muffle and, itio e generally, in a position surrounded by a possible deep-drawing on the wail, as in the ezample above .

¾s a result, t he resis t a r 20 can be positioned close to the muffle wall, unlike the prior art; where the tray 9 is spaced f r ora the correspondi g well when there are deep-drawings, ribs, etc. on it..

This; allows to have a resistor 20 o f a snorter le g h with respect, to the length; of the serpentine 10, given that the closer' position to the vjaii 13 of the muffle allows, all oth r- co no it: .ions b ing equal, to improve heat transmission.

Of course, ether variants of the invention d i f ': e r e t t: from the o ne described heretofore, a r e also p o s s i b l e■

Indeed, in addition to what is ^'mentioned above, in relation to the possible appl ication o r the resistor 20 to the upper wail 12, or to one side wall 14-16 of the tcuffie (in place of the bottom wall 11; , it s h o r; 1d b e n ot ed t he functional versatility o f t h e su ort met od of the heating resistor in accordance with. she present. invent:! on, that car, be easily applied to muffles a ad /or resistors with a configuration other than that already mentioned.

To this aim, please refer to the variant of the invention shown in figure;; 7 and S wherein, for s i ;n p 1 i o i t y , t.h e i: u uc: f i n a 11 y r. s t r u c tu r a i 1 y e 1 em ents equivalent to the ones already^' seen h v bean, indicated with the same reference numerals, characterised by an apex.

For the sake of brevity, unless otherwise indicated, r ference is made to the explanations already provided on t e above mentioned parts of the muffle and the resistor, while, he re a iter, focus wi ll he on the structural elements 32'^' , 33' that, as shown in the figures 7 and 8, extend along one side and a part of the adjacent ones t the bottom wail 13' of the ma fie, so s o have subs antiall a " C" c o n f i g ur at i e n .

For fastening the structural elements 33' , 33^r _f brackets 32' a, 33'^' a are provided arid fastened to the muffle 11' through screws.

For greater safety, the structural elements are also r^■·· :: ··· r. a : y warded to the muffle 11' in some points. T o t his a i m , ao tc es 40' (i .e. , r e E;^■ o v e <:I a reas) a r e provided in the structural el ments 32' , 33' _f so as to allow the passage o a welding electrode.

In this variant of the invention, the structural elements have ubstantially a ^WC" cross-section, so a a to be corf i gated, in fact, as a duct..

This solution is h re none particular iy indicated for large diameter electric resistors, or for more resistors arranged in the structural elements 32', 33', such as electric cables in a cable duct or also single resistors but of double or multiple length, which can be configured into coils. In this context, it should bo noted that the electric resistor 20' supported by the structural elements 32' , 33' , is configured as that of the previous xample, namely ex tended in a peripheral region with respect to- e bottom we 11 13' of the ma fie 11' with a substantially polygonal longitudinal ex I;en-sion; it should only be noted thai, as^; in this ease, the ends 21', 22' are projecting centrally with respect to the bottom wall 13' of the muffle.

In the example of the resistor shown in the figures 7 and 8, the lobes; in the ver ices of trie pol gonal extension are tb.ssing, since the square shaped st ructura 1 elements 33', 33' do not allow it.

However, it is worth to note that such form ioay be different, for example with rounded or opened vertices, so as to allow having resistors equipped with lobes.

With regard to the functional aspects and the advantages of this embodiment, of the invention, reference can be made to what has been explained above for the firs on®.

It should only be noted that, in this- case as well, the resistor is arranged at a preset distance with respect to the bottom wall 13' of the muffle, so as to ensure optimal heat- transmission conditions, depending on size and other design features .

However, this v riant is not the only possible; indeed, in general, it ma be said that th applications in which a heating electric resistor is fastened to a wall of the muffle, at a preset distance, along one or more portions of its longitudinal range, re included in the invention.

In the exam les above, the structural elements 32, 33, 32', 33' support the resistors 20, 20' along respective sections of their length: this raakes it possible to hold the resistors closer to the corresponding wail of the muffle, given that this support mode is easily adaptable arid applicable. wh ever the form of the resistor, na ely oly n::;!, ci r. onlar, carved, and also serpentine.

ΐχ) this; context, it should, be noted indeed that it could be possible to apply the str.¾ iqht support structural elements 32, 33 or also with a -^'(." section stch :^■ :^■ 32' , 33', for supporting a coil resistor like that seen with reference t o t h p r i r a t ,

Claims

1. Method for fastening an electric heating resistor (20; 20' ) to a muf le (.1.1; 11' } of an oven, in which a plurality cf alls (12-16; 12' -16'} surround a cooking cavity (17; 17' ) , comprising the foll wing steps :

- arranging a resistor (20; 20^! } extended substantially in a line between at least one pair of power supply ends {21, 22; 21' , 22');

- supporting the resistor (20; 20') at a preset distance f om a wall ⁽12-16; 12' -.16' · of the muffle (11; 11' j , in connection with portions (26, 27, 28, 29· of the longitudinal extension thereof,

2. Method according to claim 1, wherein the resistor (20; 20' } Is supported in connection with portions (26, 27, 28, 29; which are -substan ially peripheral with respect to the wall (12-16; 12' -16' J of the muffle (11; 11/ ) .

3. Method according to clsrca 2, wherein the portions (26, 27, 23, 29; are substantially straight.

4. Method according to any one of claims i to 3, wherein the resistor (20, 20' } is applied to the bottom wail (13; 1 ' ) of the muffle.

5. Oven cornp;: isi ng a :muflie (11; in which a plurality of wails {12--16; 12' --IS' ) surround a cooking cavity (.17; 17' ), at least one electric resistor (20; 20' ) extending substanti ll along a line between at least one pair of power supply ends (21, 22; 21', 22' ) and associated with art least one of said walls (12-16; 12'-16' ) for heating it, characte ised in that it. comprises at least one structural element (32, 33; 32', 33' ! supporting a respective longitudinal portion of the electric resistor (20^; 20' } .

6. Over; according to claim 5, wherein the electric resistor (20; 20' ;· is held urged ag.ain.st said at least one structural eleven f (32, 33; 32' , 33' } .

"' . Oven according to claim 6, wherein the str cturai l m nt [32, 33; 32', 33' ; c mpris s first and second tangs (36, 385 , which respectivel act as a support for the electric resistor (20. 20' ) and as an element: applying an elastic force thereto, in order to hold it finely in position.

8. Oven according to any one of claims 5 to 2, wherein the electric resistor (20; 20' · and the structural elements (32, 33; 32' , 33' } extend substantially in a peripheral- region of the corresponding wall {1.2-16; 12'-1δ' } of the muffle with which they are associated.

9. Oven according to any one of claims 2 to 3, wherein the wail (13; 13') with which the electric resistor (20; 20') is associated, is the bottom wail of the muffle.

I.0. Oven according to any one of claims 5 to 9, wherein the structural eletienf (32,- 335 is substantially straight and has an ^ΛΙ," cross-section .

II. Oven according to any one of claims 5 to 9, wherein the structural, element (32', 33') subsr.an i lly has a "C" cross- section, arid wherein the resistor (20') is housed in the structural element. (32', 33' } like a cable in a raceway,

12. Oven according to any one of claims 5 to 11, wherein the structural elemen (32' , 33') extends along on side of the wail !I3'1 of the muffle (11' 5 and at least alone a part of the ad acent sides.

13. Overs according to any one of claims 2 to 12, wh rein the wall (13; 13') of the muffle (11; 11') with wnich the electric resistor (20; 20') is associated comprises a deep- drawing, a rib or another raised, -element (30; 30';, and wherein the electric resistor (20; 20' 5 axid the structural elements (32, 33; 32', 33' ) that support it are arranged in a region or the wall (13; 13'} which is circumscribed around the dishing, rib or other raised element (30; 30').