Method for manufacturing a vacuum solar thermal panel and related vacuum solar thermal panel

Abstract

A method for manufacturing a vacuum-tight envelope for a vacuum solar thermal panel includes: joining edge to edge a first metal strip to a second metal strip in order to form a bi-metal strip, and then joining together the opposite ends of said bi-metal strip in order to form a closed loop; after said joining step, forming said first metal strip into a peripheral frame and said second metal strip into a peripheral belt; after said joining and forming steps, sealing the free edge of the peripheral belt to a glass front plate; after said joining and forming steps, joining a metal bottom plate to the peripheral frame.

Claims

1. A method for manufacturing a vacuum-tight envelope for a vacuum solar thermal panel, said vacuum-tight envelope being defined by a glass front plate transparent to solar radiation, a metal bottom plate, a peripheral frame joined to the metal bottom plate, and a peripheral belt connecting said peripheral frame to the glass front plate; said method comprising the following steps: providing a first metal strip having a shape peripherally defined by: a first metal strip upper edge, a first metal strip lower edge opposed to said first metal strip upper edge, a first metal strip first end, a first metal strip second end opposed to said first metal strip first end; providing a second metal strip having a shape peripherally defined by: a second metal strip upper edge, a second metal strip lower edge opposed to said second metal strip upper edge, a second metal strip first end, a second metal strip second end opposed to said second metal strip first end; joining the first metal strip upper edge to the second metal strip lower edge in order to form a bi-metal strip, said first metal strip first end and said second metal strip first end thus defining a bi-metal strip first end, said first metal strip second end and said second metal strip second end thus defining a bi-metal strip second end opposed to said bi-metal strip first end; joining together the bi-metal strip first end and the bi-metal strip second end with each other in order to form a closed loop; after said joining steps, forming said first metal strip into the peripheral frame and said second metal strip into the peripheral belt; after said joining and forming steps, sealing a free edge of the peripheral belt to the glass front plate; after said joining and forming steps, joining the metal bottom plate to the peripheral frame.

2. The method according to claim 1, wherein the peripheral frame is more rigid than the peripheral belt.

3. The method according to claim 1, wherein the first metal strip is thicker than the second metal strip, sides of the first and second metal strips corresponding to an outer side of the resulting vacuum-tight envelope being aligned during the step of joining the first metal strip upper edge and the second metal strip lower edge.

4. The method according to claim 1, wherein the forming step comprises a step of shaping a first longitudinal rib in the peripheral frame.

5. The method according to claim 1, wherein the forming step comprises a step of shaping a second longitudinal rib in the peripheral belt.

6. The method according to claim 1, wherein the sealing step is performed by a thermal process determining fusion and subsequent solidification of glass material forming a vacuum-tight seal.

7. The method according to claim 1, wherein the first metal strip has a thermal expansion coefficient matching that of the glass front plate.

8. The method according to claim 7, wherein the first metal strip is made out of a controlled expansion alloy.

9. The method according to claim 1, wherein during the forming step a resulting free edge of the peripheral frame is inclined with respect to a peripheral plane, on which the peripheral belt and frame lie, in order to define a peripheral frame joining edge; the method comprising a step of forming the metal bottom plate, in order to determine a metal bottom plate joining edge inclined to match the inclination of the peripheral frame joining edge; the step of joining the metal bottom plate to the peripheral frame being performed after the sealing step and comprises joining the metal bottom plate joining edge to the peripheral frame joining edge.

10. The method according to claim 9, wherein said peripheral frame joining edge and said metal bottom plate joining edge are inclined outwards with respect to the resulting vacuum-tight envelope.

11. The method according to claim 10, wherein said peripheral frame joining edge and said metal bottom plate joining edge are inclined at an angle comprised between 5 degrees and 45 degrees with respect to the peripheral plane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 schematically shows a first step of the manufacturing method according to the present invention;

(3) FIG. 2 schematically shows a perspective view of a detail of a vacuum solar thermal panel manufactured according to the method of the present invention;

(4) FIG. 3 schematically shows a cross-section of the detail in FIG. 2;

(5) FIG. 4 shows an enlarged detail of the cross-section in FIG. 3.

DETAILED DESCRIPTION

(6) A vacuum solar thermal panel according to the present invention comprises a substantially flat box-like vacuum-tight envelope defining a sealed volume and able to withstand atmospheric pressure when evacuated.

(7) The vacuum-tight envelope comprise heat absorbing means, a pipe, a glass plate support structure and possibly other functional elements which do not pertain to the present invention, and therefore are not represented in the enclosed drawings.

(8) The vacuum-tight envelope is defined by a front glass plate 1, substantially rectangular in shape, and a metal bottom plate 2 of roughly the same size parallel to it. Said two plates 1, 2 are kept in a spaced apart relationship by a peripheral frame 3 welded to the metal bottom plate 2, and by a peripheral belt 4 connecting the peripheral frame 3 to the glass front plate 1.

(9) The peripheral frame 3 and belt 4 define a peripheral plane x preferably orthogonal with respect to the front glass plate 1.

(10) The peripheral frame 3 has a thickness comprised between 0.5 and 5 mm, preferably 1.5 mm and exhibits a rigid behaviour, while the peripheral belt 4 is thinner (its thickness being comprised between 0.1 and 1 mm) and exhibits an elastic behaviour.

(11) An upper edge 33 of the peripheral frame 3 pointing toward the front glass plate 1 is welded to a corresponding lower edge 43 of the peripheral belt 4 along a longitudinal seam L. As it may be seen in FIG. 4, the outer sides of the two peripheral elements are aligned, so that the outer surface of the vacuum-tight envelope is smooth at the longitudinal seam L. On the inside, the surface of the envelope features a step at the longitudinal seam L given the different thickness of the two peripheral elements.

(12) The opposite edge of the peripheral frame 3, which will be named joining edge 32 in the following, is slightly inclined with respect to the previously defined peripheral plane x. In particular, the joining edge 32 is inclined outwards with respect to the interior of the vacuum-tight envelope, at an angle of about 30 degrees.

(13) The joining edge 32 of the peripheral frame 3 is welded to a corresponding joining edge 22 of the metal bottom plate 2. In fact, the metal bottom plate 2 is flat, said peripheral joining edge 22 being inclined with respect to a main portion of the plate. The inclination of the joining edge 22 of the metal bottom plate 2 matches the inclination of the joining edge 32 of the peripheral frame 3, i.e. the joining edge 22 is inclined at an angle of about 60 degrees with respect to the main portion of the metal bottom plate 2. The term matching the inclination of the joining edge means that the angle formed by the plane identified by peripheral frame 3 and the one identified by the metal bottom plate 2 is approximately orthogonal. This explain why, at an angle of 30 degrees of the joining edge 32 corresponds a matching angle for the joining edge 22 of the metal bottom plate 2 of 60 degrees.

(14) The peripheral frame 3 features a first longitudinal rib 31, semi-circular in cross-section, projecting toward the outside of the vacuum-tight envelope with respect to the peripheral plane x.

(15) The peripheral belt features a second longitudinal rib 41, semi-circular in cross-section, projecting toward the outside of the vacuum-tight envelope with respect to the peripheral plane x.

(16) The vacuum-tight envelope is manufactured according to a manufacturing step herein described.

(17) Preliminarily, a first metal strip 3 and a second metal strip 4 are provided. The first metal strip 3 is taken from a thicker steel sheet with a thickness comprised between 0.5 and 5 mm, while the second strip 4 is taken from a thinner sheet (its thickness being comprised between 0.1 and 1 mm) of a controlled expansion alloy (preferably NiFe alloy 48) having substantially the same thermal expansion coefficient of the soda-lime glass employed for the glass front plate 1.

(18) In a first step of the manufacturing method, the first metal strip 3 is in line welded edge to edge with the second metal strip 4 in order to form a pre-welded bi-metal strip, i.e. the upper edge 33 of the peripheral frame 3 is in line welded with the lower edge 43 of the peripheral belt 4. Preferably said operation is performed by arc welding at a speed of at least 0.5 m per minute or laser and electron-beam welding at a speed of 5 m per minute. Said welding step is preferably carried out taking care of aligning the outer surfaces (i.e. the surfaces that will eventually face the outside of the resulting vacuum-tight envelope) of the first and second metal strips 3, 4.

(19) The two opposite ends of the resulting bi-metal strip are then joined together and welded along a transverse seam z, in order to form a closed loop.

(20) In a second step, the looped bi-metal strip is formed in the desired rectangular shape through known metal forming techniques. In such a step, the first metal strip 3 is shaped in the form of the peripheral frame 3 described above, while the second metal strip 4 takes the shape of the peripheral belt 4. In particular, the joining edge 32 of the peripheral frame 3 is bent into its final position and the first and second longitudinal ribs 31, 41 are obtained.

(21) After the welding step, the resulting peripheral belt 4 is attached to the inner side of the glass front plate 1, at a short distance from the outer perimeter of the plate. In such a step, a vacuum-tight glass-metal seal 11 is obtained in a known manner. In particular, the vacuum-tight seal 11 is formed by local heating determining fusion and subsequent solidification of glass material; the fused glass material may be part of the glass front plate 1 itself or else a different frit material.

(22) Meanwhile, the perimeter of a rectangular steel plate is bent through metal forming in order to obtain the metal bottom plate 2 with the inclined joining edge 22.

(23) All other panel components like heat absorbing means, a pipe, a glass plate support structure and all other functional elements which do not pertain to the present invention are then attached to the metal bottom plate 2.

(24) In a final step, the joining edges 22, 32 of the metal bottom plate 2 and of the peripheral frame 3 are pressed one against the other and welded in order to complete the structure of the vacuum-tight envelope.

(25) Obviously, the afore-described finding may be subjected to numerous modifications and variantsby a man skilled in the art with the aim of meeting the possible and specific requirementsall falling within the scope of protection of the invention as defined by the following claims.