ES2360876T3 - GLASS AND METAL UNION, APPROPRIATE IN PARTICULAR FOR A SOLAR VACUUM TUBULAR COLLECTOR. - Google Patents

Abstract

Glass and metal junction, in particular for a vacuum tubular solar collector, with a metal junction piece (1), which joins a heat efferent tube (3) and a glass casing tube (2) vacuum-proof, one end (5) of the casing tube (2) being formed inwardly in the manner of a flange, so that by fusion it encloses a vacuum edge section (7) of the metal joint piece (1) by vacuum proof.

Description

The invention relates to a union of glass and metal with an inorganic glass casing tube, particularly suitable for a vacuum tubular solar collector.

In tubular solar collectors of this type, an absorbing surface of the solar radiation which is thermally integrated with the tube or with several tubes by means of a suitable joining technique is arranged inside the evacuated casing tube. Said tube or the tubes serve to transport the solar heat absorbed by means of a conveying liquid that acts as a thermal carrier. Both ends of the casing must be closed against vacuum.

Usually, one end of the casing tube is closed vacuum-proof by means of glass melting.

It is known to close the other end of the casing tube by means of a glass and metal joint by vacuum-proofing, a metal junction piece passing through an efferent heat pipe or several heat-effector tubes and being connected with this vacuum-proof tube by a joint by welding or welding. The outer edge of the glass and metal junction of the vacuum tubular solar collector forms, in turn, a vacuum-proof junction with the glass envelope tube. The metal joint piece and the vacuum-proof joint on the outer edge of the joint piece together form the glass and metal joint.

The technical problem of a vacuum-proof joint between a glass and a metal is that the expansion coefficients of glass and metals are normally very different and, consequently, temperature changes produce stress cracks and, therefore, Therefore, loss of vacuum.

To solve the problem there are a number of technical achievements.

According to "Werkstoffkunde der Hochvakuumtechnik", Berlin, Verlag Julius Springer, 1936, solutions are known in which glass and metal joints are produced for glass with a very low coefficient of expansion, such as quartz glass or borosilicate glass, fusing with each other a series of intermediate glasses with increasing expansion coefficients, so that the difference between the expansion coefficients of the fused glass in each case is such that it does not exceed a certain magnitude. If the difference in expansion from the metal is small enough, the metal is fused to the last piece of glass.

A disadvantage in this solution is its complication and the very high costs necessary for the fusion fusion of the intermediate glass or intermediate glasses (horsetail). The automation of such a procedure is virtually impossible.

Document US 2005 / 0181925A1 describes a technical solution in which the objective is to enable an automatic production technology. In this solution, a suitable metal alloy in the expansion coefficient is indicated for two different borosilicate glasses, which has an expansion coefficient of 5 E-6 / K and with which a fusion joint of a tube is possible in the which glass tube is vacuum-fused with a metal tube, the thin-walled metal tube penetrating axially at the edge of the thick-walled glass tube.

A disadvantage is that the proposed solution is suitable only for borosilicate glasses to be manufactured from expensive and energy-efficient raw materials and that the manufacture of glass and metal joints is a multi-stage process, because the metal tube, on the other hand , it must be connected to the heat effector vacuum tube by means of a connecting piece.

According to "Technologie der Glasverschmelzungen" Leipzig 1961, Akademische Verlagsgesellschaft Geest & Portig KG, the so-called fusion joints of metal tubes to glass tubes are known. Such pipe fusion joints have in common that the metal tube axially penetrates the edge of heated glass or is joined by fusion unilaterally. If there is a greater difference in the coefficients of expansion between the metal and the glass, the metal must be shaped like a knife. The thickness of the metal blade, the gradient of the blade and the width of the fusion joints depend on the diameter of the metal tube to be joined by fusion and vacuum-proof and are not disclosed in the above-mentioned letter for copper tubes .

From GB 222 510 a glass and metal joint arises whose outer edge section has a blade in which a separate piece of glass is axially joined by fusion. It is a typical glass knife welding with metal materials.

GB 452 558 discloses a technology for glass welding with machined metal. Through the edge section of a metal tube made as a blade a piece of glass is formed from the inside out and fuses with the edge section.

By another technological step, both in the technical solution according to GB 222 510 and also GB 452 558, a glass tube is joined by fusion, axially, to a glass part by means of a so-called "end to" joint. end ".

US 4 231 353 discloses a solution in which one or two metal lids, which wrap the casing tube symmetrically by rotation, are molded so that the vitreous glass casing tube to the sodium-sodium bicarbonate of a Tubular solar collector vacuum gears in annular grooves on the outer edge of the caps. In this, the casing tube penetrates a liquid material initially, usually lead glass dust, which merges into the groove and solidifies there. This results in a vacuum-proof connection between the metal cover and the casing. The caps are made of a Ni-Cr-Fe alloy. The efferent heat pipe (s) to transfer the heat pass through the center of the covers. The heat efferent tubes are vacuum-bound with the covers by means of welding or welding.

The disadvantage of this process is the significant process times due to the application and fusion fusion of the lead glass dust and the complicated handling of caps and casing, so that the proposed procedure is only automatable with the greatest technical efforts.

In addition, glass and metal joints are also known according to "Werkstoffkunde der Hochvakuumtechnik", Berlin, Verlag Julius Springer, 1936. Also in this case, the tubes to be joined by fusion and vacuum-proof are equipped with corresponding blades, to compensate for the different glass and metal dilations produced with temperature changes. The disadvantages are those described above.

It is the object of the invention to provide a glass and metal joint, in particular for a vacuum tubular solar collector that remains vacuum-proof for a very long time, that resists mechanical stresses due to expansion, steam impacts and pressure of the wind, technologically simple, in particular automatic to manufacture and that requires reduced material costs.

The objective is achieved in accordance with the invention by means of a union of glass and metal with the characteristics of claim 1.

The invention relates to the preference that the glass and metal junction can be manufactured mechanically in a simple way and, therefore, easily automatable and, therefore, also cost-effective. The special shape of the glass beading and the configuration of the connecting piece have the particular advantage that both inherent stresses and stresses under load can be absorbed by the glass, which guarantees the vacuum tightness of the joint for a long time. period, even with a significant action of forces, for example, expansion, wind and cavitation forces.

A special embodiment of the invention provides that the metal junction piece is vacuum connected to an efferent heat tube or several heat efferent tubes.

According to another embodiment of the invention, the metal joint piece and the glass of the casing have approximately a linear expansion coefficient of equal magnitude.

According to a preferred embodiment of the object according to the invention, the linear expansion coefficient α of the glass of the casing tube is 9.5 x E -6 / K to 10.1 x E -6 / K.

Another embodiment of the invention provides that the metal joint part is composed of a metal alloy containing a nickel component of ≥ 50%, a manganese component of ≤ 0.6%, an aluminum component of ≤ 0, 1%, a chromium component of ≤ 0.25% and a silicon component of ≤ 0.3%, in each case supplemented with an iron component.

According to an advantageous configuration of the glass and metal joint, the outer edge section of the metal joint piece has a thickness of 0.1 mm to 0.5 mm, preferably 0.2 mm and, over a length of 2 mm to 8 mm, preferably 4.2 mm, is vacuum-wrapped around the end of the casing tube.

According to a particularly preferred embodiment of the invention, an oxide layer obtained by means of a heat treatment or several heat treatments has been applied to the surrounding edge section of the metal joint piece, preferably , 800 ° C ± 100 ° C, particularly preferably at 800 ° C ± 20 ° C.

Next, the invention is explained in detail by drawing. Sample

Figure 1, the tubular solar collector of vacuum with the union of glass and metal, partially in section.

As can be seen in figure 1, the collector presents the casing tube 2 and the efferent heat tube 3 which also supports the absorption plate 4.

The metal junction piece 1 is vacuum connected to the heat effector tube 3 by welding or welding. Its outer edge section 7 is joined by the beading technique to the end 5 of the wrapping tube 2, such that the end 5 of the wrapping tube 2 is formed from the outside inwards above the outer edge section 7 of the piece of metallic union 1 and, in a fused state, it directly wraps it on both sides in a vacuum-proof manner.

5

10

fifteen

twenty

25

30

35

An annular groove 6 that extends around the efferent heat pipe 3 serves to reinforce the metal connecting piece 1. The groove 6 reinforces the connecting element 1 axially and serves, at the same time, to absorb forces orthogonal to the tube axis and acting on the heat efferent tube 3. Such a configuration places the connecting piece 1 in position to resist the air pressure without major deformations. At the same time, the groove 6 contributes to the transition from glass to metal being very little requested mechanically.

The metal joint 1 has the expansion coefficient equal to or almost equal to the glass of the casing tube 2 of the vacuum tubular solar collector.

In order to produce the union of glass and metal according to the invention, the heat efferent tube 3, which holds the absorption plate 4 and at which end the connection piece 1 is connected to the heat effector tube 3, is vacuum-proof, is inserted in the wrapping tube 2 in such a way that the glass of the wrapping tube 2 is projected a few millimeters above the edge of the metal joining piece 1. Now, the glass of the wrapping tube 2 is heated to the point of deformation, so that the glass can be pressed by internal and external molding tools in such a way against the outer and inner surface of the edge section 7 of the connecting piece 1, that a vacuum-proof joint is produced in the manner of a beading and mechanically stable.

For the connection piece 1, preferably a metal with low thermal conductivity should be chosen so as to thermally stress as little as possible the connection of the connection piece 1 with the casing tube 2 and, if possible, cause low heat losses.

When using a material for the connecting piece 1, which with its expansion coefficient broadly matches that of the glass of the wrapping tube 2, the edge section 7, wrapped by the glass, of the connecting piece 1 must present a radius of 0.1 mm

If a ductile material, for example, copper, is chosen as connection piece 1, the blade indications of the aforementioned literature must be observed with respect to its thickness, length and blade angle.

For a vacuum tubular solar collector, a glass tube 2 of calcium-sodium bicarbonate glass of the following chemical composition (in mass%) can be used:

SiO2

71.41%

Al2O3

2.20%

Fe2O3

0.03%

TiO2

0.05%

CaO

4.90%

Mg0

3.40%

Beam

0.03%

Na2O

16.10%

K2O

1.50%

SO3

0.30%

In this composition it has a coefficient of expansion of (9.8 ± 0.2) E-6 / K). The following alloy is chosen as the starting material for connection piece 1:

Ni = 50%

Cr ≤ 25%

Yes ≤ 0.3%

At ≤ 0.1%

Mn ≤ 0.6%

Fe = 100% difference

In this alloy composition of the connection piece 1, the expansion coefficient is in the range of the expansion coefficient of the glass of the casing tube 2. In addition, the material of the connection piece 1 has a very low thermal conductivity, so that the thermal stresses of the melting point of the glass and metal junction according to the invention are relatively reduced, even when the stagnation temperature has been reached.

The connecting piece 1 is deeply embedded in a sheet of approximately 0.2 mm thick. The edge section 7 of the connecting piece 1, enclosed later by the end 5 of the casing 2, is rounded to avoid tensions in the glass. The radius of said rounded is close to 0.1 mm. Depending on the type of subsequent melting process with the glass of the casing tube 2, the connecting piece 1 can be pre-oxidized. After said previous treatments, the connecting piece 1 is vacuum-proof connected with the heat efferent tube 3 which supports the absorption plate 4, preferably by welding.

After introducing the heat efferent tube 3, with absorption plate 4 and connecting piece 1, so that the surrounding tube 2 protrudes approximately 4 mm, a gradual or continuous heating of the glass of the surrounding tube 2 is carried out, until Reach your plasticity. Now, in multiple stages of treatment the glass of the casing tube 2 is deformed inwardly by means of tools, so that an intimate union is produced, both internally and externally in the manner of a flange with the surrounding edge section 7 of the connection piece 1. Finally, to ensure the elimination of stresses in the glass of the casing tube 2, slow cooling of the connection element 1 occurs.

To improve its anti-reflective efficiency and its corrosion and impact resistance properties, the wrapping tube 2 has a layer or multiple layers of nanoparticles, preferably silicon dioxide, arranged on its inner and / or outer boundary surface. in a thickness of 40 nm to 330 nm, preferably 150 nm. Said nanoparticles have a grain size of 5 nm to 50 nm, preferably 12 nm.

The coating of the wrapping tube can be carried out by a single or repeated immersion and a slow extraction of the tube into a suspension containing SiO2, a binder, a humectant and a dispersant, such as deionized water. After extraction, the resulting layers are air dried on the inner and outer surface and then tempered to a temperature of approximately 450 ° C.

Although a specific embodiment of the invention has been shown and described for the explanation, the invention is not limited to the illustrated embodiment. The invention also encompasses all embodiments and modifications of the application of glass and metal joints, in particular for vacuum-proof containers that are within the range of protection of the claims.

List of references

one

Union piece

2

wrap tube

3

heat efferent tube

4

absorption plate

5

beaded end shaped

6

groove

7

edge section

Claims (5)

1. Union of glass and metal, in particular for a vacuum tubular solar collector, with a metal junction piece (1), which joins a heat efferent tube (3) and a casing tube (2) of vacuum proof glass, one end (5) of the casing tube (2) being shaped inwardly as a flange, so that by fusion it encloses 5 Vacuum-proof an outer edge section (7) of the metal joint piece (1).

2.

Glass and metal junction according to claim 1, characterized in that the connecting piece (1) is vacuum-connected with a heat efferent tube (3) or several heat efferent tubes (3).

3.

Glass and metal joint according to one of claims 1 to 2, characterized in that the joint piece (1) and the glass of the casing tube (2) have approximately a linear expansion coefficient of equal magnitude.

4. Glass and metal joint according to claim 3, characterized in that the linear expansion coefficient α of the glass of the casing tube (2) is 9.5 x E -6 / K to 10.1 x E -6 / K . 5. Glass and metal joint according to one of claims 1 to 4, characterized in that the metal joint (1) is composed of a metal alloy that contains a nickel component of ≥ 50%, a component of manganese of ≤ 0.6%, an aluminum component of ≤ 0.1%, a chromium component of ≤ 0.25% and a silicon component of ≤ 0.3%, in each case supplemented with a component of iron. 6. Union of glass and metal according to one of claims 1 to 5, characterized in that the outer edge section (7) of the connecting piece (1) has a thickness of 0.1 mm to 0.5 mm, preferably 0.2 mm, and, over a length of 2 mm to 8 mm, preferably 4.2 mm, It is wrapped in vacuum proof by the end (5) of the casing tube (2). Glass and metal joint according to one of claims 1 to 6, characterized in that, prior to the fusion joining of the casing tube (2), it has been applied on the surrounding edge section (7) of the connecting piece ( 1) an oxide layer obtained by heat treatment or several heat treatments.