GB2266651A - An insulating side wall for baking ovens - Google Patents

Abstract

Heat insulating wall elements (9) are disposed on a frame of a baking oven to form a heat insulating wall (1b) of the oven. Each side wall element (9) has a front face (10) exposed to ambient temperature, a rear face (11) exposed to the elevated temperature in the interior (7) of the oven, and top and bottom edges (13, 12). The wall elements (9) each have at least one fresh air passage (25) which leads into the interior (7) of the baking oven, and which is adjacent to the front (10) of the wall element. The air passage (25) is separated from the back (11) of the wall element (9) by heat insulation (18). At least one air inlet aperture is provided at the bottom edge (12) of the wall element and communicates with the air passage. Furthermore, the wall element (9) has at least one connecting passage (32) which traverses the heat insulation and has an inlet connected to the fresh air passage (25) and an outlet connected to at least one air outlet 3 orifice provided at the back (11) of the wall element (9). <IMAGE>

Description

2266651 AN INSULATING SIDE WALL FOR BAKING OVIKNS The present invention

relates to heat insulating walls for baking ovens. 5 For example, the heat insulating walls may form side walls of wafer baking ovens, wafer baking machines and the like. Each side wall has a front face exposed to ambient temperature, a rear face exposed to the elevated temperature in the interior of the baking oven and fresh air passages leading into the interior of the baking oven. In particular, the present invention relates to heat insulating wall elements for such side walls.

Automatic wafer baking equipment as described in DE-PS 33 46 970, GB-A 2 142 517, and US-PS 4 648.314 has a baking space sub-divided by interior partitions into an internal heating zone provided with heating burners and external flushing zones through which flushing air flows. The outer cladding of the baking space is formed by the heat insulating side walls of the housing of the automatic wafer baking oven. These housing side walls are provided on their interior or rear face, which is directed towards the baking space and which is exposed to the elevated temperature in the interior of the wafer baking oven, with downwardly and upwardly open fresh air shafts. These fresh air shafts commence only at a short distance from the bottom edge of the side wall and end far from its upper edge. Substantially centrally between the upper shaft end and the upper edge of the side wall and on the inside thereof there is an air baffle which deflects inwardly into the interior of the baking space air which flows out from the top end of the shaft. In such prior art constructions, whilst the wafer baking oven is in operation, there is increasing dirtying of the upwardly open ends of the interior air shafts and of the air baffles disposed above them. A further drawback resides in the inadequate cooling of the upper marginal portions of the side wall.

From DE-AS 24 48 902, it is known for the housing of a wafer baking oven to be of double-walled construction with column-like intermediate spaces to form a heat exchanger. Provided on the outside of the housing are inlet and outlet apertures which lead to the intermediate spaces. In the case of this wafer baking oven, the fresh air needed for combustion is pre-heated in the column-like intermediate spaces of the housing and is extracted from the housing in the region of the baking space extractor on the outside of the housing. The housing has neither individual wall elements nor fresh air ducts leading into the interior of the baking space. The column-like intermediate spaces are disposed in the middle of the housing wall and provide for only moderate cooling of the outside of the housing.

Furthermore, it is known for instance from AT-PS 350 989 and/or GB-PS 1 542 066, for the outer heat insulating cladding on the long sides of an oven space in an automatic wafer baking oven to be constructed from just seamless doors of which the lateral edges are directly adjacent one another. These doors consist of a frame of heat insulating material on the front and rear faces of which are panels of heat insulating material and the interiors of which are filled with a heat insulating filling. The body of the door is on the outwardly pointing front face clad with stainless steel sheet and is provided on the top edge with a handle strip while the hinge pins for the pivot mounting of the door are provided on the rear surface on which there is no cladding.

It is an object of the invention to provide a heat insulating wall for baking ovens, for example, for wafer baking ovens, wafer baking machines and the like, with heat insulating wall elements which permit of improved cooling of the wall.

According to a first aspect of the present invention there is provided a heat insulating wall for a baking oven, said heat insulating wall comprising an exterior face exposed to ambient temperature, and an interior face exposed to the elevated temperature in the interior of the baking oven, wherein said heat insulating wall is formed of at least one insulating wall element comprising spaced front and rear faces, air passages defined within said wall element and disposed adjacent the front face thereof, and heat insulating means disposed within said wall element and separating said air passages from said rear face, and is further comprising air inlet apertures provided in said wall element and communicating with said air passages, connecting passages extending through said heat insulation and in communication with said air passages, and air outlet apertures at the interior side of said wall element in communication with said connecting passages.

In an embodiment, a plurality of wall elements are adjacently arranged, and the air passages are provided adjacent the front face thereof, and separated from the rear face by the heat insulation. The air passages are connected to the air inlet apertures which are provided at least at the bottom edge of the wall elements, and via the connecting passages to the air outlet orifices which are provided on the rear face of the wall elements.

The present invention enables even cooling of the outwardly facing front of the insulating wall and of the wall element, the temperature on the front of the wall elements being approximately 10 OC below that of equivalent wall elements provided with the cooling passage on the interior face.

In an embodiment, a fresh air passage extending in and along the front face of the side wall element may extend from the edge which is provided with the air inlet apertures as far as the region of the upper edge of the side wall element and it is possible to provide, communicating with this fresh air passage, a connecting passage the outlet of which is on the rear face of the side wall element more remote from the top edge than the end of the fresh air passage which is adjacent the top edge. This construction permits of an intensive cooling of the front faces of the side wall elements right into the upper marginal areas with which they engage over the horizontally adjacent roof element of the outer cladding of the baking oven in question.

Preferably, at least one by-pass passage is provided in the air passage to bridge an inlet of the connecting passage. This enables an increased flow through the parts of the fresh air passage which are close to the edge and which extend beyond the entrance from the connecting passage while at the same time it prevents the outer skin on the front face of the side wall element becoming heated because the radiated heat striking the side wall elements and which passes through the connecting passage and into the fresh air passage, strikes there the rear face of the by-pass passage and not the outer skin of the side wall element. Furthermore, a side wall element may have, composed from hollow sections, a supporting frame which is constructed as an additional ventilation passage which has at least one air inlet aperture in the region of the bottom edge of the side wall element and at least one outlet orifice which discharges into the fresh air passage. This enables additional cooling of the supporting frame of the side wall element and prevents a deformation of the supporting frame under high temperature loading on the rear face of the side wall element.

In order to regulate the flow of cooling air passing through the side wall elements, it is proposed to provide additional air intake gaps on the bottom edges of the side wall elements and to adjust the volume of air passing through the respective air intake gap by providing an adjustable strip along the bottom edge of each side wall element.

Preferably, sealing strips are provided on the side wall elements, which can be brought into engagement with the frame carrying the side wall, and between the sealing strips and the side wall element there are cooling gaps which open out into the interior of the baking oven. This enables additional cooling of the sealing strips of the side wall element and prevents deformation of the supporting structure of the side wall element when the rear face thereof is subjected to a high temperature loading.

According to a further aspect of the invention there is provided a heat insulating wall for baking ovens having an oven frame along which heat insulating wall elements are adjacently disposed, each said wall element comprising: a front surface arranged to be exposed to ambient temperature, and a back surface arranged to be exposed to an elevated temperature in the interior of the baking oven; at least one air passage for communicating with the interior of the baking oven, said air passage being disposed adjacent the front surface of the wall element and being separated from the back of the wall element by heat insulation, and said air passage being in communication with at least one air inlet aperture of said wall element; and at least one connecting passage which passes through the heat insulation, said connecting passage having an inlet connected to said air passage and an outlet connected to at least one air outlet orifice provided at the back of 5 the wall element.

Embodiments of the present invention will hereinafter be described by way of example, with reference to the accompanying drawings, in which:10 Figure 1 shows a side view of a wafer baking oven, Figure 2 shows a plan view of the wafer baking oven in Figure 1, Figure 3 shows a section through the outer cladding of the is wafer baking oven of Figure 1, Figure 4 shows an enlarged view of the upper marginal portion of the wafer baking oven shown in Figure 3, Figure 5 shows a plan view of the rear face of the side 20 wall element shown in Figure 3, Figure 6 shows a horizontal section through the side wall element taken on the line V-V of Figure 5, Figure 7 shows an enlarged view of the detail A of Figure 6, Figure 8 shows a vertical section through a further embodiment of a side wall element, Figure 9 shows an enlarged view of the upper marginal area of the side wall element shown in Figure 8, Figure 10 shows a plan view of the rear face of the side wall element shown in Figure 8, Figure 11 shows a section through the side wall element taken along the line X-X on Figure 10, Figure 12 shows a section through the outer cladding of a baking oven having an additional air intake gap provided at the bottom edge of the side wall, and Figure 13 shows in an enlarged view the sealingstrips of two adjacently disposed side wall elements which bear on the oven frame supporting the side wall.

Examples of embodiments of heat insulating side walls or side wall elements of the invention are described hereinafter with reference to baking ovens of the type used in the wafer production industry for the production of wafers, cornets, wafer baskets and the like on an industrial scale. It is characteristic of such baking ovens that fresh air is induced along the under side of the oven side walls. The volume of air which is drawn in is to ensure the extraction of a quantity of used gases which is normally a multiple of the quantity of gas which is composed of the quantity of baking gases created by the baking process and the quantity of waste gas created by the heating of the baking oven.

Of course, the heat insulating side walls or side wall elements of the invention can also be used in other ovens, for example, in ovens in which it is intended to avoid any substantial heating of the environment at the installation site.

Figures 1 to 3 show a wafer baking oven which is outwardly screened by a heat insulating cladding. This cladding comprises a horizontal top wall la and vertical side walls lb which are fixed to an oven frame 2. In the interior of the wafer baking oven 1, which is enclosed by the heat insulating cladding, there is contained wafer baking moulds and an encircling chain of baking grips. The wafer baking moulds are in the so-called pre-head lc and are first opened to allow the withdrawal of ready baked wafers therefrom, and the subsequent incorporation therein of wafer dough. once the dough has been introduced, the wafer baking moulds are closed again for the subsequent baking process. During the baking process, the closed wafer baking moulds pass through part ld of the interior of the.wafer baking oven 1 which is defined as a baking space. The moulds are heated in the baking space to approx. 150 OC to 200 OC. 5 Figure 3 illustrates a marginal zone of the wafer baking oven 1 in which wafer baking jaws revolve in the oven frame 2 in two horizontal, superposed planes. In Figure 3, only wheels 5, 6 of the wafer baking jaws are shown. These wheels 5, 6 rest on rails 3, 4 fixed on the oven frame 2 to extend laterally. The interior 7 of the wafer baking oven 1 is screened outwardly by a heat insulating cladding which consists of upper, substantially horizontally disposed, wall elements 8 which form the ceiling of the interior 7, and substantially vertically disposed lateral wall elements 9. The lateral wall elements 9 are constructed as doors which are pivotally disposed on the oven frame 2 and which form the side walls 1b of the wafer baking oven 1.

Each lateral wall element 9 has a front face 10 directed outwardly from the interior 7 of the wafer baking oven 1, a rear face 11 directed towards the interior 7, a bottom end 12, and diametrically opposite to the bottom end 12, an upper edge 13. Each wall element 9 also has two spaced lateral edges 14 and 15. The wall element 9 is substantially panel-shaped and comprises a box-like outer sheet metal cladding 16 having a substantially vertically extending end portion which constitutes the front 10 of the wall element 9. Marginal portions of the cladding 16 are bent over at a right-angle and form the two lateral edges 14, 15, and the bottom and top edges 12, 13 of the wall element 9. Furthermore, the wall element 9 comprises a supporting frame 17 of hollow sections which is connected to the marginal portions of the sheet metal cladding 16 and of which the front face is disposed at a distance from the vertical bottom member of the sheet metal cladding 16 and of which the rear face constitutes the rear face 11 of the wall element. The wall element 9 also incorporates heat insulation. In the illustrated embodiment, the heat insulation comprises two panels 18, 19 disposed inside the supporting frame 17, and marginal strips 20, 21, 22, 23 of a heat insulating material. The marginal strips 20 - 23 are disposed outwardly of and adjacent to the supporting frame 17 and on the two lateral edges 14, 15 and on the upper edge 13 between the relevant marginal portions of the sheet metal cladding 16 and the supporting frame 17.

The vertical end member of the outer sheet metal cladding 16 is covered on its inside with a metallic stiffening 24 (e.g. Metawell produced by Messrs. Metawell), which resembles a corrugated cardboard. Between this vertical end member and the front face of the supporting frame 17, which is filled with the two heat insulating panels 18, 19, there is a fresh air passage 25. The inside clearance W of this passage 25 substantially corresponds to the thickness D of the supporting frame 17 or of the two heat insulating panels 18, 19. The passage 25 extends substantially over the entire surface of the wall element 9 which is parallel with the front face 10. The fresh air passage 25 commences at the bottom edge 12 of the wall element 9 at the bottom marginal portion of the outer sheet metal cladding 16 which is provided with air inlet apertures 26. The passage 25 extends along the inner face of the sheet metal cladding 16 upwardly as far as the upper heat insulating marginal strip 22 which bears on the upper edge 13 of the wall element 9 on the inside of the upper marginal portion of the outer sheet metal cladding 16.

The supporting frame 17 extends substantially parallel to the fresh air passage 25 over the major part of the height of the wall element 9 and ends below the upper end 25' of the fresh air passage 25 which is adjacent the upper edge 13 of the wall element. The supporting frame 17 is comprised of cross-sectionally rectangular hollow sections, and comprises a lower transverse bearer member 17a which is connected by two laterally disposed substantially vertical columns 17b, 17c to a first upper transverse bearer member 17d. The substantially vertically disposed heat insulating marginal strip 23 is upwardly adjacent to the first upper bearer member 17d. Between the two lateral, substantially vertical columns 17b and 17c, the supporting frame 17 is comprised of a second upper transverse member 17e which is spaced below the first upper transverse member 17d and which is laterally connected to the two lateral columns 17b and 17c. The centre of the second transverse member 17e is connected to the top end of a substantially vertical central column 17f which is at its bottom end connected to the bottom transverse member 17a. On the rear face of the middle column 17f there is, in the region of its bottom end, a lower hinge pin 27 for engagement with a pivoting device (not shown) for the wall element 9. A corresponding upper hinge pin 28 is fixed on the second upper cross member 17e at an extension of the central column 17f.

The two cavities bounded by the bottom cross-member 17a, the second upper cross-member 17e and the three vertical or upstanding columns 17b, 17c, 17f and situated within the supporting frame 17 are filled by the heat insulating panels 18, 19 which are placed loosely therein. These cavities are, at the back of the wall element 9, covered by a thin sheet metal plate 29 which is rigidly clamped against the back of the supporting frame 17 by means of clamping strips 30 riveted to the supporting frame 17. On the front face of the supporting frame 17, there are for the two panels 18, 19 retaining strips 31 which span these cavities.

The cavity defined between the two upper cross-members 17d and 17e and bounded laterally by the upper end portions of the lateral vertical columns 17b and 17c, is open to both the front and the back of supporting frame 17, and forms a communicating passage 32. This passage 32 communicates the fresh air passage 25 and the back of the wall element 8 by way of a connecting passage aperture 33 disposed on the front of the supporting frame and communicating with the fresh air passage 25, and a connecting passage outlet 34 situated on the back of the supporting frame and communicating with the exterior of the wall element 9.

Provided in the fresh air passage 25 and bridging the connecting passage mouth 33 is a by-pass passage 35 which is is open at its top and bottom. At its front face, the by pass passage 35 is bounded by the inside of the vertical end member of the outer sheet metal cladding 16, and on its rear side it is bounded by an air baffle 36 extending substantially parallel to the end member of the sheet metal cladding. This air baffle 36 is disposed substantially in the centre of the clearance W of the fresh air passage 25 and is fixed via spacing members 37 on the two upper transverse members 17d and 17e of the supporting frame 17, beyond which it extends upwardly and downwardly. The baffle 36 also projects laterally beyond two lateral edges 32'of the connecting passage 32.

The supporting frame 17 is constructed as an additional ventilation passage for the wall element 9. At the junctions between the cross-members 17a, 17d, 17e and the lateral upstanding columns 17b, 17c of the supporting frame 17, and at the junctions between the central column 17f and the lower cross-member 17a and the second upper cross member 17e, are provided respective apertures 38. These apertures 38 are formed in the side walls of the hollow profiles of the frame members 17a - 17f which connect to one another whereby cavities in the abutting frame members are communicated (Figures 4, 6). The lower cross-member 17a has in the region of its connection with the middle column 17f both communicating apertures 38 on its upper face which communicate with the interior cavity in the central column 17f, and also apertures on its under side which are aligned therewith. These additional apertures on the under side of the cross member 17a discharge directly into an air inlet aperture 38' provided for ventilation of the central column 17f in the lower marginal portion of the outer sheet metal cladding 16. Also provided in this marginal portion are air inlet apertures 38' which discharge into the downwardly open vertical columns 17b and - 17c. On its front face, the supporting frame 17 has outlet orifices 39 which open out into the fresh air passage 25 and are disposed in the lower transverse member 17a and in the second upper transverse member 17e.

As a result of the ventilation of the hollow profiles in the supporting frame 17, and of the flow connection thereof to the fresh air passage 25, deformation of the supporting frame 17 under the effect of the temperature loading acting on the back 11 of the wall element 9 is prevented. In addition, the cover plate 29, for the heat insulating panels 18, 19 disposed on the back 11 of the supporting frame 17, is clamped only onto the supporting frame 17 and cannot therefore induce into the supporting frame 17 any stresses resulting from a temperature loading.

Fixed to the top edge 13 of the wall element 9 is a handle strip 40. This handle strip 40 has a portion resting on the edge 13 of the wall element 9 and which is angled over in respect thereto, and a portion engaging over the upper marginal portion of the front 10 of the wall element 9 and which is fixed to the outer sheet metal cladding 16 by way of spacing means 41.

For sealing the wall element 9 with respect to the oven frame 2 two vertical lateral sealing strips 43 and a horizontal sealing strip 44 are provided on the back 11 of the wall element 9 disposed in the region of the first upper cross member 17d of the supporting frame 17. Between these sealing strips 43, 44 and the wall element 9 are narrow ventilation gaps (Figure 7) so that fresh air is able to flow around the sealing strips 43, 44 when a negative pressure with respect to the ambient pressure occurs in the interior 7. This might occur, for example, with a baking or wafer baking oven in which the atmosphere prevailing in the interior 7 is drawn off continuously via an oven extraction means so that fresh air is drawn into the interior 7 through the fresh air passage 25 in the wall elements 9. Thus, the pressure in the interior 7 will be lower than that adjacent the front 10 of the wall element 9.

By way of illustration, the flows of air in the fresh air passage 36, in the connecting passage 32 and in the by-pass passage 35, in the supporting frame 17, and occurring around the sealing strips 43 are indicated diagrammatically by arrows.

Figures 8 to 11 show a further embodiment of a wall element 50 of the invention which is likewise constructed as a baking oven door intended to be hung in a pivoting device provided on the oven frame.

The wall element 50 is comprised of two outer profiled sheet metal shells 51, 52 having hollow interiors arranged to face towards each other and which are at their edges fixed to a common frame 53. In their interior the metal shells 51, 52 enclose a fresh air passage 54 and a heat insulation 55.

The rear sheet metal shell 52 has a substantially vertically disposed flat bottom member 56 which forms the back of the wall element 50, is directed towards the baking space, and bears on the back of the frame 53. The rear sheet metal shell 52 has forwardly directed marginal portions 57 engaging over outer end faces of the frame 53.

The cavity defined by the frame 53 and the bottom member 56 of the rear sheet metal shell 52 extends substantially over half the thickness of the wall element 50 and is filled by a loosely inserted heat insulation 55.

The vertically disposed end member 58 of the front sheet metal shell 51 forms the front of the wall element 50 and it has on its marginal portions 59, which extend rearwardly at a right-angle, fixing portions 60 which project at a distance from the bottom member 58 inwardly to the middle of the wall element 50 and through which the front sheet metal shell 51 bears on the front face of the frame 53 and is fixed to the frame 53. A sheet metal strengthening member 61 is mounted on the inside of the bottom member 58 of the front sheet metal shell 51.

Between the back of the sheet metal reinforcement 61 and the front of the heat insulating layer of insulating material 55 is the fresh air passage 54. This passage 54 extends over the entire height and width of the wall element 50 and is bounded only at the edges of the wall element 50 by the rearwardly extending marginal portions 59 of the front sheet metal shell 51. Between the sheet metal reinforcement 61 and the layer of insulating material there is a bracing grid 63 which has, parallel with the lateral edges of the wall element 50 and disposed at a distance from one another, vertical sheet metal plates 62 defining vertical air passages, and which fixes the position of the layer 55 of insulating material. The plates 62 of the bracing grid 63 are connected to one another by two longitudinal metal plates 64, 65 extending substantially parallel to the wall element 50. These metal plates 64, 65 are disposed substantially centrally of the clearance W in the fresh air passage 54, and, at the side edges of the wall element 50, are connected to the rearwardly extending marginal portions 59 of the front sheet metal shell 51. The upper longitudinal plate 65 of the supporting grid 63 forms together with the inside of the sheet metal reinforcing member 61 a by-pass passage 66. This by-pass passage 66 bridges, over the total width of the wall element, a connecting passage 67 extending from the fresh air passage 54 through the heat insulation 55. By reason of the vertical plates 62 in the supporting grid 63, the fresh air passage 54 together with the by-pass passage 66 is sub-divided into a plurality of adjacently disposed vertically extending individual passages for which in each case two air inlet apertures 68 are constructed in the lower marginal portion 59 of the front sheet metal shell 51. The individual passages discharge downstream of the upper longitudinal plate 65 rearwardly into the single connecting passage 67 which is provided for its part with outlet orifices 69 disposed in the bottom or end member 56 of the rear sheet metal shell 52 and which in their position are aligned with the individual passages.

Figure 12 shows the outer cladding of a baking oven 70 in which at the bottom edge of the side wall 71 or at the bottom edge of the side wall element 72 which is constructed as a door there is an additional air intake gap. This air intake gap is bounded by a horizontal lower cross-member 73 of the oven frame 74, on which there is fixed an end member 75 which closes off the bottom of the interior 76 of the baking oven, and also by a strip 77 which is constructed as an angled sheet metal member and is adjustably fixed to the bottom edge of the side wall element 72. The current of air drawn in through the additional air intake gap into the interior 75 of the baking oven 70 between the cross-member 73 and the strip 77 is indicated by the arrow 78. The side wall element 72 in Figure 12 corresponds substantially to the lateral wall element 9 of Figure 3 as far as its other features of construction and design are concerned.

The volume of fresh air drawn in along the side wall 71 of the baking oven 70 is composed of the stream of air drawn in through the fresh air passages of the side wall element 72 and the air stream 78 drawn in through the additional air intake gaps. By the adjustment of the position of the strip 77 in relation to the side wall 72, it is possible to vary the width of the additional air intake gap and thus of the volume of air 78 flowing through it. This leads to a variation in the sub-division of the volumes of air flowing through the side wall elements and the air intake gaps and subsequently to a variation in the cooling of the front of the side wall elements.

Figure 13 illustrates a detail of the baking oven 70 showing a horizontal section through a vertical bearer 79 of the oven frame and through thelateral marginal portions of two mutually adjacent side wall elements 80, 90.

Provided on the back of the side wall elements 80, 90 are sealing strips 81, 91 which bear on the outside face of the vertical member 79. Each sealing strip 81, 91 has fixed to the back of the relevant side wall element 80, 90 fixing strips 82, 92 which have a short arm 83, 93 engaging over the end 84, 94 of the respective side wall element 80, 90.

The sealing strips 81, 91 define between themselves and the side wall elements 80, 90 a cooling gap which opens out into the interior 75 of the baking oven 70.

The present invention has been explained with reference to examples of embodiments in which the heat insulating wall elements provided with back ventilation adjacent the front face are constructed as seamlessly adjacently disposed doors and which have profiled and sheet metal parts consisting of aluminium or stainless steel and heat 5 insulating means produced from rock wool.

Of course, wall elements according to the invention can be suspended in supporting means provided on the oven frame or can be fixed on the oven frame. In addition, the present invention is by no means restricted to planar, panel-like wall elements but also extends to angular arrangements or curved wall elements.

Other variations and modifications may be made to the is embodiments of the invention described and illustrated in accordance with the appended claims.

Claims (14)

1. A heat insulating wall for a baking oven, said heat insulating wall comprising an exterior face exposed to ambient temperature, and an interior face exposed to the elevated temperature in the interior of the baking oven, wherein said heat insulating wall is formed of at least one insulating wall element comprising spaced front and rear faces, air passages defined within said wall element and disposed adjacent the front face thereof, and heat insulating means disposed within said wall element and separating said air passages from said rear face, and further comprising air inlet apertures provided in said wall element and communicating with said air passages, is connecting passages extending through said heat insulation and in communication with said air passages, and air outlet apertures at the interior side of said wall element in communication with said connecting passages.

2. An insulating wall as claimed in Claim 1, wherein a said air passage extending in and along the front face of the wall element extends from an edge thereof in which said air inlet apertures are provided to the region of an upper edge of the wall element, and wherein a connecting passage is provided which communicates with said air passage and has a said air outlet aperture disposed at the rear of the wall element, said outlet aperture being situated further from the upper edge of said wall element than the end of the air passage which is adjacent the upper edge.

3. An insulating wall as claimed in Claim 1 or Claim 2, wherein at least one by-pass passage is provided in said air passage which bridges an inlet to the connecting passages.

4. An insulating wall as claimed in any of Claims 1 to 3, wherein the wall element has a supporting frame comprised of hollow sections, said supporting frame being constructed as an additional ventilating passage and having at least one air inlet aperture and at least one air outlet aperture which opens into said air passages.

5. An insulating wall as claimed in any of Claims 1 to 4, wherein additional air intake gaps are provided at bottom edges of the wall element, and wherein a strip is adjustably fitted to the bottom edge of the wall element to enable adjustment of the volume of air passing through said air intake gaps.

6. An insulating wall as claimed in any of Claims 1 to 5, wherein sealing strips are provided on the side wall elements and can be brought into engagement with the frame carrying the side wall and in that in each case between the sealing strips and the side wall element there are cooling gaps which open out into the interior of the baking oven.

7. A heat insulating wall for baking ovens having an oven frame along which heat insulating wall elements are adjacently disposed, each said wall element comprising: 25 a front surface arranged to be exposed to ambient temperature, and a back surface arranged to be exposed to an elevated temperature in the interior of the baking oven; at least one air passage for communicating with the interior of the baking oven, said air passage being disposed adjacent the front surface of the wall element and being separated from the back of the wall element by heat insulation, and said air passage being in communication with at least one air inlet aperture of said wall element;, and at least one connecting passage which passes through the heat insulation, said connecting passage having an inlet connected to said air passage and an outlet connected to at least one air outlet orifice provided at the back of the wall element.

8. An insulating wall as claimed in Claim 7, wherein at least one by-pass passage is provided in said air passage and bridges the inlet to the connecting passage.

9. An insulating wall as claimed in Claim 7 or Claim 8, wherein a said air passage extends in the wall element along its front surface from an edge in which said air inlet aperture is provided to the region of an upper edge thereof, and wherein a said connecting passage communicates with said air passage, the outlet of said connecting passage being at the back of said wall element and being more remote from the upper edge thereof than an end of the air passage which is adjacent the upper edge.

10. An insulating wall as claimed in any of Claims 7 to 9, wherein the or each said wall has a supporting frame comprised of hollow sections, said supporting frame being constructed as an additional ventilation passage and having at least one air inlet aperture in the region of a lower edge of the wall element and at least one outlet orifice which opens into said air passage.

11. An insulating wall as claimed in any of Claims 7 to 10, wherein additional air intake gaps are provided on lower edges of the wall elements, and wherein a strip is adjustably fixed at a bottom edge of each said wall element for setting the volume of air flowing through the respective air intake gap.

12. An insulating wall as claimed in any of Claims 7 to 11, wherein sealing strips which can be brought into engagement with the oven frame carrying the wall element are provided on the wall element, cooling gaps being provided in each case between the sealing strips and the wall element, said cooling gaps opening into the interior of the baking oven. 5

13. A heat insulating wall for a baking oven substantially as hereinbefore described with reference to the accompanying drawings.

14. A baking oven comprised of a plurality of walls. at least one of said walls comprising a heat insulating wall as claimed in any preceding claim.