Field of application of the invention

The present invention is applied to the field of utensils for cooking food in an oven. Namely, the present invention relates to baking trays for baking breadsticks.

Overview of the prior art

The current baking trays for baking breadsticks comprise a wavy sheet made of steel and integrally connected, by electric spot welding, to a tubular peripheral frame substantially shaped like a rectangular frame and made of steel as well.

When the temperature of the tray significantly increases (for example, following the introduction thereof into an oven), the steel from which it is made expands. However, the sheet and the frame expand at different speeds due to the effect both of the different mass and the different geometry thereof. The differences in thermal expansion between the sheet and the frame generate relatively intense stresses at the weld points. Given that the latter are highly rigid, the differences in thermal expansion deform the tray in a non-homothetic manner, causing the yielding of one or more weld points (and the subsequent at least partial disconnection of the sheet from the frame) or the cracking of the sheet over time.

The possibility of mutually connecting the sheet and the frame by means of rivets rather than by welding was considered in an attempt to obviate the above problem. Although the rivets allow partially compensating for the differences in thermal expansion between the sheet and the frame, they however tend to loosen and detach from the sheet, with the risk of contaminating the breadsticks baking on the tray.

Purposes of the invention

It is the object of the present invention to overcome the aforesaid drawbacks by indicating a baking tray for baking breadsticks in which the connection between the sheet and the frame is obtained so as to allow an at least partial compensation for the differences in thermal expansion between said two components of the tray (i.e. between the sheet and the frame), without using rivets.

Summary and advantages of the invention

The present invention relates to a baking tray for baking breadsticks, said tray comprising:

• a metal sheet, preferably made of at least partially wavy AISI 304 steel, said sheet having a cross section including a plurality of ridges alternated by a plurality of depressions, said ridges and said depressions extending, as a whole, in said sheet in a same direction, said sheet being delimited by an edge comprising a first and a second stretch opposite to each other, said edge further comprising a third and a fourth stretch opposite to each other and each of which being interposed between said first and second stretches, said sheet:

- being at least partially flat at said first and second stretches of said edge, and

- including said ridges alternated by said depressions at said third and fourth stretches of said edge;

• a frame for supporting said sheet, said frame comprising a plurality of metal tubular elements, each of which preferably made of AISI 304 steel, each of said tubular elements including a first flat wall extending in length, said tubular elements lying on the same side as said sheet and being con- nected to one another so that said first walls face said sheet, a first and a second tubular element of said plurality being opposite to each other, a third and a fourth tubular element of said plurality being opposite to each other, each of said third and fourth tubular elements being interposed between said first and second tubular elements;

• first means for connecting said sheet, at said first and second stretches of said edge, to said frame at said first and second tubular elements, respectively;

• second means for connecting said sheet, at two portions of the latter including said third and fourth stretches of said edge, respectively, to said frame, at said third and fourth tubular elements, respectively, wherein, according to the invention:

• said sheet, at each of said first and second stretches of said edge, is folded over itself, preferably in a "U" shape, on the side of said tubular elements so as to comprise a flat upper strip and a lower strip which are at least partially mutually opposed at a given distance from each other, for each of said first and second stretches of said edge, said upper strip and said first wall of said first or second tubular element to which said stretch of edge is connected by said first connection means, lying on opposite sides with respect to said lower strip, for each of said first and second stretches of said edge, the assembly consisting of said upper strip, said lower strip and a mutually connecting fold thereof facing the assembly formed by said upper strip, said lower strip and a mutually connecting fold thereof of said other first or second stretch of said edge, on the side of the concavity thereof;

• said first connection means, for each of said first and second tubular elements, comprising a first metal bar, preferably made of AISI 304 steel, including at least a second flat wall extending in length, for each of said first and second tubular elements, said first bar being connected, by means of one or more welds, preferably by electric spot welding, to said first or second tubular element so that said second wall is at least partially opposed to said first wall of said first or second tubular element at a given distance from the latter, for each of said first and second tubular elements:

- said lower strip of said first or second stretch of said edge to which said first or second tubular element is connected by said first connection means being at least partially interposed between: said first wall of said first or second tubular element and said second wall of said first bar connected to said first or second tubular element, so that said second wall of said first bar connected to said first or second tubular element at least partially opposes said first wall of said first or second tubular element with the at least partial interposition of said lower strip of said first or second stretch of said edge to which said first or second tubular element is connected by said first connection means, and

- said second wall of said first bar connected to said first or second tubular element being at least partially interposed between said upper strip and said lower strip of said first or second stretch of said edge to which said first or second tubular element is connected by said first connection means, so that said upper strip and said lower strip of said first or second stretch of said edge to which said first or second tubular element is connected by said first connection means are at least partially mutually opposed with the at least partial interposition of said second wall of said first bar connected to said first or second tubular element, moreover, for each of said first and second tubular elements:

- said lower strip of said first or second stretch of said edge to which said first or second tubular element is connected by said first connection means being sandwiched between: said first wall of said first or second tubular element and said second wall of said first bar connected to said first or second tubular element, and/or

- said second wall of said first bar connected to said first or second tubular element being sandwiched between said upper strip and said lower strip of said first or second stretch of said edge to which said first or second tubular element is connected by said first connection means, so that said sheet is connected to said first or second tubular element;

• said second connection means, for each of said third and fourth tubular elements, comprising a second metal bar, preferably made of AISI 304 steel, including at least a third, a fourth, a fifth and a sixth wall, each of which being flat and extending in length, for each of said third and fourth tubular elements, said second bar being connected, at said third wall, by means of one or more welds, preferably by electric spot welding, to said third or fourth tubular element at said first wall thereof, in each of said second bars:

- said fourth and fifth walls being at least partially mutually opposed and being connected to each other by at least one fold at a first edge thereof;

- said fourth wall being connected, at a second edge thereof opposite to said first edge thereof, to said third wall, at an edge of the latter, by at least one fold;

- said fourth wall being connected to said third wall so that the assembly consisting of said fourth and fifth walls and of said fold mutually connecting them faces said sheet on the side of the concavity thereof;

- said fifth wall being connected, at a second edge thereof opposite to said first edge thereof, to said sixth wall, at an edge of the latter, by at least one fold, for each of said third and fourth tubular elements, said second bar being connected, at said sixth wall, by means of one or more welds, preferably by electric spot welding, to said portion of said sheet including said third or fourth stretch of said edge to which said third or fourth tubular element is connected by said second connection means at one or more of said depressions, respectively, so that said sheet is connected to said third or fourth tubular element.

In the tray of the invention, the connection between the sheet and the frame is such as to allow these two components to thermally expand without generating stresses, thus resulting in a disconnection of the sheet from the tray or cracking of the sheet, with the use of the tray. This result is achieved by virtue of the first and second connection means which couple the sheet to the frame, allowing a freedom of movement therebetween. The lower strips of the first and second stretches of the edge of the sheet, although sandwiched between the first wall of the first and second tubular elements and the second wall of the first bars or tighteners, in conjunction with the upper strips, the second wall of the first bars, may indeed slide, in conjunction with the upper strips, with respect to the frame. The aforesaid portions of sheet including the third and fourth stretches of the edge thereof, respectively, may move away from or close to the third and fourth tubular elements, respectively, elastically deforming the folds between the walls of the second bars. Although it is limited, said freedom of movement is sufficient to at least partially compensate for the differences in thermal expansion between the sheet and the frame of the tray. This not only increases the operating life of the tray, but also ensures an increased planarity upon a heating in an oven thereof, with subsequent decrease of "non conforming" product rejects.

A further advantage associated with the use of the tray of the invention consists of the first and second bars acting as ribs which allow reducing the cross section of the tubular elements of the frame, rigidity being equal. Said reduction of the cross section results in a decrease in the overall weight of the frame, with the following benefits:

• less wear of the mechanical components of the system moving the tray (given that said mechanical components support and move a smaller load);

• reduction of the calories required to cook the breadsticks (because the smaller mass of the tray results in a lesser absorption of heat, with subsequent reduction of energy consumption of the oven); • reduction of the duration of the complete production cycle (in many cases, the temperature is to indeed be at room temperature when the raw product is put on it and a tray having smaller mass cools down more quickly, allowing a quicker re-use thereof, and therefore increasing the hourly production of the system);

• increase of the usable area of the tray ((the product deposited close to the frame indeed does not cook in optimal manner due to the heat absorbed by the latter. This effect is such as to force the breadsticks produced in the first and last channels of the tray (i.e. the two which are closest to the frame) to be entirely rejected in certain cases. The reduction of cross section of the tubular elements of the frame reduces this "non optimal" area of the tray, thus increasing the usable surface thereof)).

Other innovative features of the present invention are disclosed in the description below and referred to in the dependent claims.

According to an aspect of the invention, each of said first and second tubular elements has a rectangular-shaped cross section with a side of said rectangle corresponding to said first wall of said first or second tubular element, for each of said first and second tubular elements, said first bar of said first connection means of said first or second tubular element:

• having an "L"-shaped cross section with an arm of said L corresponding to said second wall of said first bar,

• being connected, by means of one or more welds, preferably by electric spot welding, at a wall corresponding to the other arm of said L, to said first or second tubular element at a wall of the latter corresponding to a side of said rectangle orthogonal to said side corresponding to said first wall of said first or second tubular element.

According to another aspect of the invention, said first and second tubular elements and said first and second stretches of said edge of said sheet extend in respective directions parallel both to each other and to said direction in which said ridges and said depressions extend in said sheet.

According to another aspect of the invention, in each of said second bars:

• said third and sixth walls are coplanar, • said fourth and fifth walls are parallel to each other and

• each of said fourth and fifth walls is orthogonal to said third and sixth walls. According to another aspect of the invention, each of said third and fourth tubular elements has a rectangular-shaped cross section with a side of said rectangle corresponding to said first wall of said third or fourth tubular element, for each of said third and fourth tubular elements, said fourth wall of said second bar of said second connection means of said third or fourth tubular element being parallel to a wall of the latter corresponding to a side of said rectangle orthogonal to said side corresponding to said first wall of said third or fourth tubular element.

According to another aspect of the invention, for each of said third and fourth tubular elements, said fourth wall of said second bar of said second connection means of said third or fourth tubular element being in contact with said wall of the latter corresponding to said side of said rectangle orthogonal to said side corresponding to said first wall of said third or fourth tubular element.

According to another aspect of the invention, said third and fourth tubular elements and said third and fourth stretches of said edge of said sheet extend in respective directions parallel to each other and orthogonal to said direction in which said ridges and said depressions extend in said sheet.

According to another aspect of the invention, said frame comprises one or more third metal bars, preferably made of AISI 304 steel, each of said third bars being interposed between said first and second tubular elements, each of said third bars including at least a seventh, eighth, ninth and tenth wall, each of which being flat and extending in length, each of said third bars being connected, at both said seventh wall and said tenth wall, by means of one or more welds, preferably by electric spot welding, to said sheet at one or more of said depressions, respectively, so that said sheet is connected to said third bar, in each of said third bars:

• said eighth and ninth walls being at least partially mutually opposed and con- nected to each other by at least one fold at a first edge thereof;

• said eighth wall being connected, at a second edge thereof opposite to said first edge thereof, to said seventh wall, at an edge of the latter, by at least one fold;

• said eighth wall being connected to said seventh wall so that the assembly consisting of said eighth and ninth walls and of said fold mutually connecting them faces said sheet on the side of the concavity thereof;

• said ninth wall being connected, at a second edge thereof opposite to said first edge thereof, to said tenth wall, at an edge of the latter, by at least one fold.

According to this aspect of the invention, the frame includes one or more reinforcing bars (i.e. the aforesaid one or more "third bars"), they also being shaped and connected to the sheet so as to allow the latter and the frame to thermally expand without generating stresses resulting in a disconnection of the sheet from the tray or cracking of the sheet, with the use of the tray.

According to another aspect of the invention, each of said third bars includes at least an eleventh and a twelfth wall, each of which being flat and extending in length, in each of said third bars:

• said eleventh and twelfth walls being at least partially mutually opposed and being connected to each other by at least one fold at a first edge thereof;

• said eleventh wall being connected, at a second edge thereof opposite to said first edge thereof, to said eighth wall, at said first edge of the latter, by at least one fold;

• said eleventh wall being connected to said eighth wall so that the assembly consisting of said eleventh and twelfth walls and of said fold mutually connecting them faces said sheet on the side of the convexity thereof;

• said twelfth wall being connected, at a second edge thereof opposite to said first edge thereof, to said ninth wall, at said first edge of the latter, by at least one fold, so that in each of said third bars, said eighth and ninth walls are at least partially mutually opposed with the at least partial interposition of said eleventh and twelfth walls.

According to this aspect of the invention, the eighth and ninth wall are not connected to each other by a single fold but by two walls (the eleventh and the twelfth) and by three folds.

According to another aspect of the invention, said third bars extend in respective directions parallel to each other and orthogonal to said direction in which said ridges and said depressions extend in said sheet.

Brief description of the figures

Further objects and advantages of the present invention will become apparent from the following detailed description of embodiments thereof and from the accompanying drawings, given by mere way of non-limiting example, in which:

- Figure 1 shows a top plan view of a tray according to the present invention;

- Figure 2 shows a diagrammatic cross section of the tray in Figure 1 , along a plane A-A indicated in Figure 1 ;

- Figure 3 shows a diagrammatic cross section of the tray in Figure 1 , along a plane B-B indicated in Figure 1 and orthogonal to the aforesaid plane A-A;

- Figure 4 shows a top plan view of a variant of the tray in Figure 1 ;

- Figure 5 shows a diagrammatic cross section of the tray in Figure 4, along a plane C-C indicated in Figure 4 and corresponding to plane B-B in Figure 1 .

Detailed description of preferred embodiments of the invention

Hereinafter in the present description, a figure may be illustrated also with reference to elements not expressly indicated therein but indicated on other figures instead. The scale and proportions of the various illustrated elements do not necessarily correspond to the real values.

Figures 1 to 3 show a tray 1 of the invention of the "baking" type, namely for baking breadsticks.

Tray 1 preferably is substantially rectangular and comprises an at least partially wavy sheet 2. Like tray 1 , sheet 2 preferably is substantially shaped like a rectangle, preferably with the vertexes rounded, and is made of metal, preferably of AISI 304 steel. As shown in Figure 2, the cross section of sheet 2 includes a plurality of ridges 3 alternated by a plurality of depressions 4. The ridges 3 and the depressions 4 extend, as a whole, in a same direction, preferably parallel to two opposite sides, preferably the short ones, of the rectangle as sheet 2 is substantially shaped. In other words, the ridges 3 and the depressions 4 preferably extend vertically in Figure 1 .

Sheet 2 is delimited by an edge comprising an opposite first stretch 5 and a second stretch 6, which are preferably mutually parallel, and more preferably corresponding to the short sides of the rectangle as sheet 2 is substantially shaped. The edge delimiting sheet 2 further comprises a third stretch 7 and a fourth stretch 8, they also opposite each other and each of which being interposed between the above-mentioned stretches 5 and 6. The stretches 7 and 8 are preferably mutually parallel, and more preferably corresponding to the long sides of the rectangle as sheet 2 is substantially shaped. The stretches 7 and 8, which are arranged horizontally in Figure 1 , therefore are preferably orthogonal to the stretches 5 and 6, which are arranged vertically Figure 1 . In light of the foregoing, the stretches 5 and 6 of the edge of sheet 2 extend in respective directions which preferably are parallel both to each other and to the direction in which the ridges 3 and the depressions 4 extend in sheet 2. The stretches 7 and 8 of the edge of sheet 2 extend in respective directions which preferably are parallel to each other and orthogonal to the direction in which the ridges 3 and the depressions 4 extend in sheet 2.

As shown in Figure 2, sheet 2 is at least partially flat at the stretches 5 and 6 of the edge thereof, and includes the ridges 3 alternated by the depressions 4 at the stretches 7 and 8 of the edge thereof. The stretches 5 and 6 of the edge of sheet 2 preferably are coplanar.

Sheet 2 is supported by a frame 9 comprising a plurality of metal tubular elements, each of which preferably made of AISI 304 steel. Namely, frame 9 preferably comprises four preferably rectilinear tubular elements 10, 11 , 12 and 13 connected to one another at the respective ends preferably so as to form, overall, a frame which is substantially shaped like the perimeter of a rectangle. A first tubular element 10 and a second tubular element 11 are opposite to each other, preferably mutually parallel, and more preferably corresponding to the short sides of the rectangle as the perimeter of which frame 9 is substantially shaped. A third element tubular 12 and a fourth tubular element 13 are also op- posite to each other and each of them is interposed between the above- mentioned tubular elements 10 and 11. The tubular elements 12 and 13 are preferably mutually parallel and more preferably, corresponding to the long sides of the rectangle as the perimeter of which frame 9 is substantially shaped. The tubular elements 12 and 13 are therefore preferably orthogonal to the tubular elements 10 and 11 .

The tubular elements 10, 11 , 12 and 13 lie on the same side as sheet 2. In particular, they lie below the latter in Figure 1 . The tubular elements 10 and 11 are preferably arranged so as to extend in respective directions which not only are parallel to each other but also to the direction in which the ridges 3 and the depressions 4 extend in sheet 2. The tubular elements 12 and 13 are preferably arranged so as to extend in respective directions which not only are parallel to each other but also orthogonal to the direction in which the ridges 3 and the depressions 4 extend in sheet 2. In light of the foregoing, the tubular elements 10 and 11 are preferably arranged so as to extend in respective directions which are parallel to the directions in which the stretches 5 and 6, respectively, of the edge of sheet 2 extend. Similarly, the tubular elements 12 and 13 are preferably arranged so as to extend in respective directions which are parallel to the directions in which the stretches 7 and 8, respectively, of the edge of sheet 2 extend. As shown in Figure 2, the rectangle as sheet 2 is substantially shaped has almost the same dimensions as the rectangle like which peripheral frame 9 is substantially shaped. More preferably, sheet 2 and frame 9 overlap each other and are mutually connected so that stretch 5 overlaps and is connected to the tubular element 10, stretch 6 overlaps and is connected to the tubular element 11 , stretch 7 overlaps and is connected to the tubular element 12, stretch 8 overlaps and is connected to the tubular element 13, and the vertexes of the rectangle as sheet 2 is substantially shaped almost overlap the rectangle, respectively, like which peripheral frame 9 is substantially shaped.

Each of the tubular elements 10, 11 , 12 and 13 has a preferably rectangular cross section. As shown in Figures 2 and 3, each of the tubular elements 10, 11 , 12 and 13 is preferably arranged with the short sides of the rectangle as the perimeter of which the cross section of said tubular element 10, 11 , 12 or 13 is substantially shaped, which are parallel to the plane on which the stretches 5 and 6 of sheet 2 preferably lie. Each of the tubular elements 10, 11 , 12 and 13 therefore is preferably arranged with the long sides of the rectangle as the perimeter of which the cross section of said tubular element 10, 11 , 12 or 13 is substantially shaped, which are orthogonal to the plane on which the stretches 5 and 6 of sheet 2 preferably lie. The wall of each of the tubular elements 10, 11 , 12 and 13 corresponding to the short side of the aforesaid rectangle (as the perimeter of which the cross section of said tubular element 10, 11 , 12 or 13 is substantially shaped) closest to sheet 2 was previously indicated by the expression "first wall" and is marked by numeral 14 in the drawings. In addition to lying on the same side as sheet 2 (as mentioned above), the tubular elements 10, 11 , 12 and 13 are thus connected to one another so that the walls 14 - each of which is flat and extending in length - face sheet 2.

As shown in Figure 2, sheet 2, at each of the stretches 5 and 6, is folded over itself, preferably in a "U", on the side of said tubular elements 10 and 11 (i.e. downwards in Figure 2), respectively, so as to comprise a flat upper strip 15 and a lower strip 16 which are at least partially mutually opposed at a given distance from each other. Again as shown in Figure 2, in each of the stretches 5 and 6 of the edge of sheet 2, the assembly consisting of the strips 15 and 16 and of the fold mutually connecting them faces the assembly consisting of the strips 15 and 16 and the fold mutually connecting the other of said stretches 5 and 6 on the side of the concavity thereof. Additionally, for each of the stretches 5 and 6, strip 15 and wall 14 of the tubular element on which said stretch 5 or 6 or edge is superimposed, lie on opposite sides with respect to strip 16.

For each of the tubular elements 10 and 11 , tray 1 comprises a metal bar 17, preferably made of AISI 304 steel and identified above by the expression "first bar". Each bar (17) preferably has an "L" cross section. Each bar 17 therefore preferably comprises a flat wall 18, extending in length and identified above by the expression "second wall", which is orthogonally connected, at an edge thereof, to the edge of a further wall 19, it also flat and extending in length. The arms of the aforesaid "L" of each bar 17 therefore correspond to the walls 18 and 19, respectively. Each of the walls 18 and 19 preferably is rectangular and the walls 18 and 19 in each bar 17 are preferably connected to each other by a fold at a long edge thereof.

As indicated above, tray 1 comprises one of the bars 17 for each of the tubular elements 10 and 1 1. Namely, for each of the tubular elements 10 and 1 1 , the corresponding bar 17 is connected to said tubular element 10 or 1 1 so that wall 18 at least partially opposes wall 14 of said tubular element 10 or 11 at a given distance from the latter. For this purpose, for each of the tubular elements 10 and 1 1 , wall 19 of the corresponding bar 17 is connected to said tubular element 10 or 1 1 by means of one or more welds 21 , preferably by electric spot welding, at a wall 20 of said tubular element 10 or 11 orthogonal to wall 14 of the latter and facing the other of said tubular elements 10 and 1 1 (i.e. at a wall of said tubular element 10 or 1 1 corresponding to a side of the rectangle as the perimeter of which the cross section of said tubular element 10 or 11 is substantially shaped, orthogonal to the side of said rectangle corresponding to wall 14 of said tubular element 10 or 1 1 ).

As shown in Figure 2, in each bar 17, wall 18 is preferably parallel to wall 14 of the tubular element 10 or 1 1 to which bar 17 to which wall 18 belongs, is connected. Similarly, wall 19 is preferably parallel to and at least partially matches wall 20 of the tubular element 10 or 1 1 to which bar 17 to which wall 19 belongs, is connected.

The walls 18 and 19 of each bar 17 have a length (intended as dimension in the direction in which bar 17 extends) which is preferably almost equal to the one of the tubular element 10 or 1 1 to which said bar 17 is connected. The walls 18 and 19 of each bar 17 further have a width (intended as third dimension of said walls in addition to length and thickness) which is preferably less than the one of the walls 14 and 20 (of the tubular element 10 or 1 1 to which said bar 17 is connected), respectively, to which said walls 18 and 19 are opposed, respectively.

Again as shown in Figure 2, for each of the tubular elements 10 and 1 1 , the strip 16 of stretch 5 or 6 of the edge of sheet 2 overlapping said tubular element 10 or 1 1 is at least partially interposed between wall 14 of said tubular element 10 or 1 1 and the wall 18 of bar 17 connected to said tubular element 10 or 11 (so that the wall 18 of bar 17 connected to said tubular element 10 or 11 at least partially opposes wall 14 of said tubular element 10 or 11 with the at least partial interposition of the strip 16 of stretch 5 or 6 of the edge of sheet 2 overlapping said tubular element 10 or 11 ).

For each of the tubular elements 10 and 11 , the wall 18 of bar 17 connected to said tubular element 10 or 11 is also at least partially interposed between the strips 15 and 16 of stretch 5 or 6 of the edge of sheet 2 overlapping said tubular element 10 or 11 (so that the strips 15 and 16 of stretch 5 or 6 of the edge of sheet 2 overlapping said tubular element 10 or 11 are at least partially mutually opposed with the at least partial interposition of the wall 18 of bar 17 connected to said tubular element 10 or 11 ).

For each of the tubular elements 10 and 11 , the strip 16 of stretch 5 or 6 of the edge of sheet 2 overlapping said tubular element 10 or 11 is sandwiched between wall 14 of said tubular element 10 or 11 and the wall 18 of bar 17 connected to said tubular element 10 or 11 . Additionally or alternatively, the wall 18 of bar 17 connected to said tubular element 10 or 11 is sandwiched between the strips 15 and 16 of stretch 5 or 6 of the overlapping edge of sheet 2 and said tubular element 10 or 11 so that sheet 2 is connected to the tubular elements 10 and 11 .

In light of the foregoing, the bars 17, belonging to the previously mentioned "first connection means", connect sheet 2, at the stretches 5 and 6 of the edge itself, to frame 9 at the tubular elements 10 and 11 , respectively.

For each of the tubular elements 12 and 13, tray 1 comprises a metal bar 25, preferably made of AISI 304 steel and identified above by the expression "second bar". Each bar 25 has a cross section, which is preferably almost a "U" (i.e. almost like the symbol in the international phonetic alphabet of the "rounded almost rear almost closed vowel"). Namely, each bar 25 preferably comprises four walls 26, 27, 28 and 29 (previously identified by the expressions "third wall", "fourth wall", "fifth wall" and "sixth wall", respectively), each of which being flat and extending in length. In each bar 25, the walls 26 and 29 are preferably coplanar and the walls 27 and 28 are preferably mutually parallel and at least partially opposed, at a given distance from each other. In each bar 25, each of the walls 27 and 28 is also preferably orthogonal to the walls 26 and 29. In each bar 25, the walls 27 and 28 are preferably connected to each other by at least one fold at an edge 30 thereof (identified above by the expression "first edge") so that the assembly consisting of the walls 27 and 28 and of the fold mutually connecting them has a concave cross section (corresponding to the bulge in the U). In each bar 25, wall 27 is connected, at a second edge thereof opposite to edge 30 thereof, to wall 26, at an edge of the latter, by at least one fold. Similarly, in each bar 25, wall 28 is connected, at a second edge thereof opposite to edge 30 thereof, to wall 29, at an edge of the latter, by at least one fold. Each of the walls 26, 27, 28 and 29 preferably is rectangular and, in each bar 25, the walls 26, 27, 28 and 29 are preferably connected to one another by a fold at long edges thereof.

As indicated above, tray 1 comprises one of the bars 25 for each of the tubular elements 12 and 13. Namely, for each of the tubular elements 12 and 13, the corresponding bar 25 is connected to said tubular element 12 and 13 so that the assembly consisting of the walls 27 and 28 and the fold mutually connecting them faces towards sheet 2 on the side of the concavity thereof. For this purpose, for each of the tubular elements 12 and 13, wall 26 of the corresponding bar 25 is connected to said tubular element 12 or 13 by means of one or more welds 22, preferably by electric spot welding, at wall 14 of said tubular element 12 or 13. Additionally, for each of the tubular elements 12 and 13, the wall 29 of bar 25 connected to said tubular element 12 or 13 is connected by means of one or more welds 23, preferably by electric spot welding, to a portion of sheet 2 including stretch 7 or 8 of the edge thereof overlapping said tubular element 12 or 13, at one or more depressions 4, respectively, so that sheet 2 is connected to the tubular elements 12 and 13.

In light of the foregoing, the bars 25, belonging to the previously mentioned "second connection means", connect sheet 2, at two portions of the latter including the stretches 7 and 8, respectively, of the edge itself, to frame 9 at the tubular elements 12 and 13, respectively.

As shown in Figure 3, in each bar 25, wall 27 is preferably parallel to wall of the tubular element 12 or 13 to which bar 25 to which wall 27 belongs is connected, previously indicated by reference numeral 20, i.e. the wall of said tubular element 12 or 13 orthogonal to wall 14 of the latter and facing the other of said tubular elements 12 and 13 (i.e. at a wall of said tubular element 12 or 13 corresponding to a side of the rectangle as the perimeter of which the cross section of said tubular element 12 or 13 is substantially shaped, orthogonal to the side of said rectangle corresponding to wall 14 of said tubular element 12 or 13). More preferably, in each bar 25, wall 27 is preferably in contact with wall 20 of the tubular element 12 or 13 to which bar 25 to which wall 27 belongs is connected, and even more preferably, so as to at least partially match with the latter.

The walls 26, 27, 28 and 29 of each bar 25 have a length (intended as dimension in the direction in which bar 25 extends) which is preferably almost equal to the one of the tubular element 12 or 13 to which said bar 25 is connected. The walls 27 and 28 of each bar 25 further have a width (intended as third dimension of said walls in addition to length and thickness), which is preferably less than the one of wall 20 (of the tubular element 12 or 13 to which said bar 25 is connected), to which wall 27 is preferably opposed.

In tray 1 , the connection between sheet 2 and frame 9 is such as to allow these two components to thermally expand without generating stresses resulting in a disconnection of sheet 2 from frame 9 or cracking of sheet 2 with the use of tray 1. Although they are sandwiched between wall 14 of the tubular elements 10 and 11 and wall 18 of the bars 17 or tighteners, the strips 16 of the stretches 5 and 6 of the edge of sheet 2, in conjunction with the strips 15, wall 18 of the bars 17, may indeed slide, in conjunction with the strips 15, with respect to frame 9. The aforesaid portions of sheet 2 including the stretches 7 and 8, respectively, of the edge of sheet 2 may move away from or close to the tubular elements 12 and 13, respectively, thus elastically deforming the folds between the walls 26, 27, 28 and 29 of the bars 25. Although it is limited, said freedom of movement is sufficient to at least partially compensate for the differences in thermal expansion between sheet 2 and frame 9.

Figures 4 and 5 show a tray 35 which differs from tray 1 in that frame 9 also comprises one or more metal bars 36 preferably made of AISI 304 steel. Each of the bars 36, identified above by the expression "third bars", includes a first end and a second end, opposite to said first end. Each of the bars 36 is interposed between the tubular elements 10 and 11 so that, in each bar 36, the first end is closer to the tubular element 10 than the tubular element 11 , and the second end is closer to the tubular element 11 than the tubular element 10. Each of the bars 36 preferably extends from the tubular element 10 to the tubular element 11 , more preferably at a given distance from the latter. Alternatively, one or more bars 36 could be connected to the tubular element 10 at the first end thereof, and to the tubular element 11 at the second end thereof. The bars 36 are preferably arranged so that the directions in which the bars 36 extend, respectively, are mutually parallel and orthogonal to the directions in which the tubular elements 10 and 11 extend, respectively (and therefore preferably orthogonal to the direction in which the ridges 3 and the depressions 4 extend in sheet 2).

Each bar 36 preferably has an almost "co" cross section (i.e. "lower case omega"). Namely, each bar 36 preferably comprises six walls 37, 38, 39, 40, 41 and 42 (previously identified by the expressions "seventh wall", "eighth wall", "eleventh wall" "twelfth wall", "ninth wall" and "tenth wall", respectively), each of which being flat and extending in length. In each bar 36, the walls 37 and 42 are preferably coplanar, and the walls 38, 39, 40 and 41 are preferably mutually parallel and at least partially opposed to one another, mutually spaced apart. In each bar 36, each of the walls 38, 39, 40 and 41 is also preferably orthogonal to the walls 37 and 42. In each bar 36, the walls 39 and 40 are preferably connected to each other by at least one fold at an edge 45 thereof (identified above by the expression "first edge") so that the assembly consisting of the walls 39 and 40 and the fold mutually connecting them has a concave cross section. In each bar 36, wall 39 is connected, at a second edge 43 thereof opposite to edge 45 thereof, to wall 38, at an edge of the latter, by at least one fold. Similarly, in each bar 36, wall 40 is connected, at a second edge 44 thereof opposite to edge 45 thereof, to wall 41 , at an edge of the latter, by at least one fold. In addition to the foregoing, in each bar 36, wall 38 is connected, at an edge thereof opposite to edge 43 thereof, to wall 37, at an edge of the latter, by at least one fold. Similarly, in each bar 36, wall 41 is connected, at an edge thereof opposite to edge 44 thereof, to wall 42, at an edge of the latter, by at least one fold. Each of the walls 37, 38, 39, 40, 41 and 42 preferably is rectangular and, in each bar 36, the walls 37, 38, 39, 40, 41 and 42 are preferably connected to one another by a fold at long edges thereof.

If one of the bars 36 is connected to the tubular elements 10 and 11 , said connection is preferably obtained by means of welds, preferably by electric spot welding, between each of the tubular elements 10 and 11 and the two ends, respectively, of said bar 36, more preferably at the fold mutually joining the walls

38 and 39 and/or at the fold mutually joining the walls 40 and 41 .

Each bar 36 is connected to sheet 2 so that the assembly consisting of the walls

39 and 40 and the fold mutually connecting them faces towards sheet 2 on the side of the convexity thereof. For this purpose, each bar 36, at both wall 37 and wall 42, is connected by means of one or more welds 31 , preferably of the TIG type with the addition of material, to sheet 2 at one or more depressions 4, respectively, so that sheet 2 is connected to said bar 36.

The walls 39 and 40 of each bar 36 further have a width (intended as third dimension of said walls in addition to length and thickness) which is preferably less than the one of the walls 38 and 41 between which they are interposed, so as not to be in contact with sheet 2 (at edge 45).

The bars 36 serve as reinforcing bars of frame 9 and, like the bars 17 and 25, are shaped and connected to sheet 2 so as to allow the latter and frame 9 to thermally expand without generating stresses resulting in a disconnection of sheet 2 from the frame 9 or cracking of sheet 2, with the use of tray 35. As mentioned above, the bars 36 have a length which is preferably less than the distance between the tubular elements 10 and 11 in order to allow the latter to thermally expand by bending towards the inside of frame 9 (i.e. one approaching the other).

According to a variant of tray 35, the bars 36 are substantially shaped as the bars 25. According to this variant, the bars 36 no not have the walls 39 and 40. The walls 38 and 41 of each bar therefore are not connected to one another by two walls and three folds, rather by one fold alone. Incidentally, according to this variant, each bar 36 is connected to sheet 2 so that the assembly consisting of the walls 38 and 41 and the fold mutually connecting them faces towards sheet 2 on the side of the concavity thereof. Additionally, according to this variant, in each bar 37, the walls 38 and 41 are at least partially mutually opposed with the at least partial interposition of the walls 39 and 40.

According to the description provided for a preferred embodiment, it is obvious that certain changes may be introduced by those skilled in the art without departing from the scope of the invention as defined by the following claims.