In particular, the present invention relates to the production of head elements used for supporting and connecting the tubular heating elements, which form the heater.

DESCRIPTION OF THE PRIOR ART According to known methods, heaters for e. g. civil and industrial use are produced by joining tubular elements using head elements, which support and. join the tubular elements with each other.

The groups, composed of two or more tubular elements joined one to another by head elements, are connected to each other by liquid-tight connection applied between each pair of head elements, thus forming a heater.

There are different methods for producing the head elements.

The Patent Publication FR 1.201.614 describes the preparation of the head element by fusion technique and subsequent working of the so obtained workpiece.

The obtained head element is composed of a hollow body with four parallel holes situated on a narrow and long side of the body and communicating with the inside, and of two opposite apertures made on the two wider surfaces of the body.

The four parallel holes are machined inside while the opposite apertures are threaded internally.

Subsequently, two head elements are applied to the opposite extremities of four tubular elements by introducing and fastening, by welding, the tubular elements ends into the four parallel holes.

Threaded joints are inserted into the opposite and threaded apertures of the head elements so as to connect the thus obtained groups to each other.

According to the document FR 1.425.677, the tubular elements are joined to the head elements by an adhesive.

The drawbacks of the head elements obtained in this way derive from the difficulty in producing, by fusion, a head element which is hollow and'features holes of small diameter conducting to the cavity.

This constructive feature imposes the use of cores, which must be crumbled in order to be removed from the piece obtained by fusion, thus increasing the number of working steps and production costs.

Moreover, it is difficult to make the fused material flow appropriately in the dies to avoid a high number of wastes.

This problem imposes also the choice of those materials which feature good flowability when fused, in place of other materials, which would be cheaper, but are more difficult to be treated by fusion.

The publication EP-A-0854347 describes a method for obtaining head elements, which have an aperture on their narrow side, opposite to the side with holes for connection with the tubular elements.

This conformation allows insertion of a suitably shaped core into the die during the fusion, to support easily the core and to remove it without the necessity of subsequent operations for cleaning and finishing of the inner cavity.

However, it is necessary to close the aperture before assembling the tubular elements.

According to another known method, the head elements are obtained by pressing two semi-shells of e. g. sheet metal, and welding the two semi-shells along their whole contour.

In this way, the head element is produced from a cheap material, e. g. a ferrous material, using a procedure that is not particularly complicated, such as fusion.

Nevertheless, the welding of the two semi-shells is very difficult, because of the welding length and critical position, as it extends along the matching line of the two curved surfaces and must pass across further curved sections.

Since the head element must be liquid-tight, so the welding must be performed correctly, thus increasing the difficulty and costs of this working operation.

Moreover, after the welding had been finished, it is necessary to finishing the whole welded area, in order to make it shapely.

This step increases again the production time and costs.

SUMMARY OF THE INVENTION The object of the present invention is to propose a method for producing a head element composed of one

single body, by more pressing steps, without the drawbacks resulting from the fusion procedure and without the necessity to weld other closing elements of the head element.

Another object of the present invention is to propose a method, which allows a reduction of time and costs of the head element production.

A further object of the present invention is to propose a method, which allows using ferrous material, which is cheap and easy to work.

A still further object of the present invention is to propose a head element obtained by the above mentioned method, whose production is cheap and does not require extensive time, and which is shapely, so as to reduce as much as possible other finishing operations.

In particular, the proposed head element is produced in such a way that it does not require grinding of extended surfaces, which have been welded in critical points.

The above-mentioned objects are obtained by a method for producing head elements for heaters, characterized in that it includes: preparing of a piece of a sheet metal; deep drawing said sheet metal piece to obtain a hollow molded piece, defined by a base wall, sides joined to and surrounding the base wall and forming an open side; cutting the sides along the open side, to define a hollow body with an edge, which is uniform and extends around said open side; making a lateral through aperture on two opposite sides to obtain apertured opposite sides;

providing connection means around each lateral through aperture; making of at least one notch, on the apertured opposite sides, along said edge; introducing at least two cores into said edge matching areas without said at least one notch; stamping a flange extending around each of said at least one notch and included between said cores, so as to close the sheet metal around said cores and in the area of said edge, thus widening said notches; removing said cores from the hollow body; welding of said edge along said flange of said widened at least one notch, so as to obtain a series of holes separated from each other.

According to a different embodiment of the method for producing the head elements after the hollow body is obtained the following steps are performed: making a lateral through aperture on each two opposite sides to obtain two apertured opposite sides; making at least one notch, on each of said apertured opposite sides, along said edge; introducing at least two cores into said edge in areas without said at least one notch ; pressing a flange extending around said notches and included between said cores, so as to close the sheet metal around said cores and in the area of said edge, thus widening said notches; removing said cores from the hollow body;

welding said edge along said flange of said widened at least one notch, so as to obtain holes separated from each other; providing fastening means on each lateral through aperture on each of said apertured opposite sides.

From the method a head element for heaters is obtained, which is made in a single hollow body, defined by a base wall, sides joined to and surrounding the base wall, at least two holes turned toward the inside of said hollow body, with at least one lateral through aperture made on two opposite sides defining two apertured sides, characterized in that: said body is obtained from a single part of a deep-drawn metal sheet; said holes are delimited by a press-shaped edge of an open side, opposite to said base wall of said hollow body, with notches made on said edge and widened by pressing, so as to define pressed flanges, which surround the notches and are welded to each other to separate said holes; and fastening means are provided on each lateral through aperture.

BRIEF DESCRIPTION OF THE DRAWINGS In accordance with the invention, the head elements and the method of its production are defined by the characteristic features reported in independent claims concerning the product and the method, respectively, and other preferred characteristic features reported in additional claims'.

In the following, the invention'is described in a more detailed way with reference to particular, but not only embodiments and with reference to the enclosed drawings, in which: Figure 1 is a lateral section view of the body of a head element during its forming by pressing, according to the present method; Figure 2 is a top view of the body of Figure 1; Figure 3 is a lateral view of the body of Figure 1; Figure 4 is a perspective view of the body of Figure 1; Figure 5 is a view of the body of Figure 1 in a subsequent working step; Figure 6 is a section view of the body along the line VI-VI of Figure 5; Figure 7 is a view of the body of Figure 5 in another working step of the present method; Figure 8 is the body of Figure 7 along the line VIII-VIII; Figure 9 is a section view of the finished head element; Figure 10 is a view of constructive variant of the body forming the head element; Figures from 11 to 13 show three working steps necessary to complete the head element according to the above mentioned constructive variant; Figure 14 is a view of the finished head element, according to the above mentioned constructive variant;

- Figure 15 is a view of two finished head elements, according to the above-mentioned constructive variant; joined to each other.

BEST MODES OF CARRYING OUT THE INVENTION According to the present method, with reference to Figures from 1 to 4, head elements for heaters are produced beginning from a piece of sheet metal 1.

The piece of sheet metal 1 is first deep-drawn to obtain a hollow molded piece 2 defined by a base wall 3, two opposite larger sides 4,5 joined to the base wall 3, two narrower sides 14,15, joined to the base wall 3 and integral with the two opposite large sides 4,5, and an open side 6, situated opposite with respect to the base wall 2.

It is assumed that there will be always two larger sides and two narrower sides, as this is the common practice in manufacturing these fittings. It is self evident that the method can be equally applied to a head having equally extending sides, this being also part of the claimed invention.

The deep drawing of the sheet metal 1 to obtain the hollow molded piece 2, is performed according to a series of subsequent steps, e. g. three steps.

The intermediate forms assumed by the hollow molded piece 2 during the drawing step are indicated with dotted line and broken ling in Figure 1.

According to particular materials and dimensions of the head element to be formed, it is possible to obtain the hollow molded piece by only one drawing step, without leaving the inventive scope of the present invention.

The deep-drawing step can be performed by using a mechanical press or a fluid-pressing device (hydro- forming), or any other suitable apparatus.

The base wall 3 and the narrow sides 14,15 can be curved, as shown in Figures 2 and 3, or they can have more or less rounded corners and edges, so that the head element can show a squared form.

Later, the opposite large sided 4,5 and the narrow sides 14,15 are cut near the open side 6, along the broken line T of Figure 3, so as to define a hollow body 8 (Figure 4), with an edge 9 uniform and oblong, extending around the open side 6.

A lateral through aperture 12, e. g. circular, is made on each of the opposite large sides 4,5 (Figure 5).

The aperture 12 can be made by punching or drilling, the choice of the technique depending on the materials used and thickness obtained.

As shown in Figure 9, fastening means 25 are made on each lateral through aperture 12 of each of the opposite large sides 4,5, so as to allow mutual fastening of the adjacent hollow bodies to assemble groups formed by the head elements and the tubular elements, thus building a heater.

According to a first embodiment, shown'in Figure 9, the fastening means 25 on each lateral through aperture 12 are obtained by welding a threaded ring 26 around the lateral through aperture 12.

A threaded joint (not shown) is then screwed into the inner threading 36 of the ring 26 during the heater assembly.

According to another embodiment of the fastening means 25, shown in Figures from 11 to 15, a circular crown 27, extending around each lateral through aperture 12, is obtained by applying a pressure directed outwards, thus deforming plastically the hollow body 8 and forming a protruding edge 31.

The protruding edge 31 is obtained by introducing a flat core 28 into the hollow body 8 through the open side 6, before the holes 13 are made (Figure 11).

The flat core 28 is equipped with a floating element 29, which is situated in a position matching each lateral through aperture 12 and is pushed outwards alternately in opposite directions, thus forming the protruding edge 31 on the circular crown 27.

A die 30 is situated on the outer part of the hollow body 8 during the pressing on the circular crown 27, to strike as a stop against the hollow ; body 8 and form the protruding edge 31 from outside (Figures 12 and 13).

The protruding edge can be obtained by using a mechanical press or a fluid-pressing device (hydro-forming).

At this point the apertures 12 can be finished, e. g. by boring or other suitable known technique.

A threaded ring 38 can be inserted into the seat defined by the protruding edge 31.

The ring 38 fulfills the same function as the ring 26, fastened externally in the previously described embodiment, as shown in Figure 14.

Otherwise, the adjacent head elements can be joined by welding spots 37 of the circular crowns touching each other, as shown in Figure 15, using the apertures 12 arranged in a sequence, to enter this area.

Independently from the used embodiment of the fastening means 25, two notches 16, suitably spaced apart, are made on each of said opposite large sides 4,5, along said edge 9, so as to leave three areas 19 of the edge 9 unvaried and without the notches.

The depth of the notches must be determined by the dimensions of the head elements to be obtained and of the holes to be obtained for coupling with the tubular elements 23.

In the example case, there are three holes for tubular elements.

However, the method can be advantageously carried out also with a smaller number of holes, e. g. two, or a bigger number of holes, e. g. four holes.

The number of the notches 16 to be made on each opposite surface 4,5 depends substantially on the number of the holes and is smaller to it by one.

Therefore, with two holes to be obtained, it is necessary to make only one notch 16 on each surface, while with three holes to be obtained, two notches 16 must be made on each surface.

Cylindrical cores 18 are introduced into the edge 9, in the region of to the intact areas 19 (Figure 7).

The number of cylindrical cores 18 corresponds to the number of the holes 13 to be made.

In the shown example, three cylindrical cores 18 have been introduced.

The depth of introduction of the cylindrical cores 18 into the hollow body 8 depends substantially on the depth of the notches, and is at least identical thereto.

A flange 17, extending around each notch 16 and situated between the two cylindrical cores 18, is pressed to close the sheet metal around the cores in the area of the edge 9, and at the same time the notches 16 are widened.

Therefore, the sheet metal in the area of the notches is pushed against the cores 18 and deformed plastically, thus assuming the curved shape of the cores, as well seen in Figure 8.

Afterwards, the cores 18 are withdrawn and the edge 9 is welded along the flange 17 of the widened notches 16, so as to obtain three holes 21 separated from each other.

Possible finishing operations, moreover not necessary, will be performed only on the flanges 17, slightly protruding due to the material brought by the welding.

At this point, it is possible to postpone the application of the fastening means 25 to the surfaces 3,4 of the hollow body 8, only if the fastening means are formed by the outer threaded ring 26, and consequently it is possible to treat a piece which is lighter and structurally less rigid.

The holes 13 are coupled with the tubular elements 23 by a small cylinder 24, introduced into each hole 13 and featuring a groove along its circumference, into which a ring 34 of fusible material is inserted.

Then, the head of each tubular element 23 to be coupled is fitted onto the part of the small cylinder 24 protruding from the relative hole 13.

The connection area between the tubular elements 23 and the head element at the corresponding holes 13 and the ring 34 of the fusible material, is heated by a flame carried rotating around the connection area.

The heat causes the fusion of the ring 34, thus welding the head element to the tubular elements 23 by brazing.

The above described method allows the production of a head element for heaters comprising only one hollow body 8 composed of a base wall 3, two opposite large sides 4, 5, joined to the base wall 3, two narrow sides 14,15, joined to the base wall 3 and integral with the two opposite large sides 4,5 and of holes 13, e. g. three, turned toward the inside of the hollow body 8.

A lateral through aperture 12, equipped with fastening means 25, is made on each of the opposite large sides 4, 5.

The hollow body 8 is obtained from one piece of sheet metal by deep-drawing.

The holes 13 are delimited by an edge 9, shaped by cold stamping, which defines an open side 6, opposite to the base wall 3 of the hollow body 8, with notches 16 made on the edge 9 and widened by cold stamping, so as to define the pressed flanges 17, which surround the notches 16 and are welded to each other to separate the holes 13.

In the shown example, there are three holes 13, which need two notches 16.

The fastening means 25 on each lateral through aperture 12 can be made according to two embodiments.

According to a first embodiment, the fastening means 25 include a threaded ring fastened to the relative surface 4,5.

According to the second embodiment, the fastening means 25 on each lateral through aperture 12 are obtained by a circular crown 27 surrounding'the lateral through

aperture 12, which has been plastically deformed by pressing outwards, so as to form a protruding edge 31.

A threaded ring 38 is introduced into the seat defined by the protruding edge 31 and fixed therein either by welding spot or by slight deformations made in the material of the head. Any other means can be used to fix the threaded ring and avoid rotation thereof.

Otherwise, the circular crown 27 is left free to be fastened to an adjacent head element by welding.

Consequently, the objects listed in the introduction have been obtained by the method for producing head elements and the head element described above.

The head element is produced in a single body, by more pressing steps, without the drawbacks resulting from the fusion procedure and without the necessity to weld two semi-shells to each other, or other elements of considerable dimensions for the head element closing.

This feature allows to reduce the production time and costs and to obtain a product of high quality, yet using ferrous material, which is cheap and easy to work.

The head element obtained by the above mentioned method is aesthetically pleasant, which allows to reduce as much as possible other finishing operations.