MX2008003742A - Glass-metal connection, in particular for a vacuum-tube solar collector - Google Patents

Abstract

The invention relates to a glass-metal connection, in particular for a vacuum-tube solar collector, comprising a metallic connecting part (1), which connects a heat recovery tube (3) and a enclosing tube (2) of glass in a vacuum-tight manner, one end (5) of the enclosing tube (2) being inwardly deformed in a flange-like manner in such a way that it encloses an outer edge portion (7) of the metallic connecting part (1) in a vacuum-tight manner on both sides by fusing. This edge portion (7) is expediently formed in a rotationally symmetrical manner and/or the enclosing tube (2) is produced from a soda-lime glass. The connecting part (1) is connected in a vacuum-tight manner to one or more heat recovery tubes (3). The connecting part (1) and the glass of the enclosing tube (2) have approximately the same coefficient of expansion.

Description

GLASS-METAL JOINT, IN PARTICULAR FOR A SOLAR VACUUM TUBE COLLECTOR DESCRIPTION OF THE INVENTION The invention relates to a glass-metal connection comprising an inorganic glass tube which is suitable, in particular, for a vacuum tube solar collector. In solar vacuum tube collectors of this type, a surface which absorbs solar radiation, which is thermally connected to the tube, respectively, with several tubes, is disposed within the evacuated jacket tube by means of an appropriate joining technique. This tube, respectively, these tubes serve to transport the solar heat absorbed by a carrier liquid as a heat carrier. Both ends of the enclosing tube must be closed under vacuum. In general, one of the ends of the enclosing tube is closed to vacuum proof by glass melting. It is also known to vacuum close the other end of the shell tube with a glass-metal joint, where a heat recovery pipe or several heat recovery pipes penetrate a metal connecting element and are vacuum-proofed therewith. by a direct or indirect welding union. The outer edge of the glass-metal junction of the vacuum tube solar collector in turn forms a vacuum-proof connection with the glass tube. The metal connection element and the vacuum-proof connection on the outer edge of the connection element together form the glass-metal connection. The technical problem of a vacuum-proof connection between a glass and a metal is that the coefficients of glass and metal expansion are normally considerably different and that, therefore, voltage breaks occur when the temperature changes, and it, the loss of emptiness. To solve the problem there is a series of technical upgrades. They are known, according to "Werkstoffkunde der Hochvakuumtechnik", Berlin, Verlag Julius Springer, 1936, solutions in which glass-metal joints are produced for glasses with a very small coefficient of expansion, such as quartz or borosilicate glass, fusing a sequence of intermediate glasses with an incremental coefficient of expansion, in each case, in such a way that the difference between the coefficients of expansion between the molten glasses, in each case, does not exceed a certain measure. If the expansion difference to the metal is sufficiently small, then the metal is fused with the last part of glass. The disadvantages of this solution are its complexity and the very large investment for fusion bonding of the intermediate glass, respectively, of the intermediate glasses (boxed stem). Such a method is practically not amenable to automation. US 2005/0181925 A1 discloses a technical solution that has the objective of enabling an automatic production technology. In this solution, a corresponding metallic alloy is indicated for two different borosilicate glasses in terms of coefficient of expansion which has an expansion coefficient of 5 E-6 / K and which allows a melting connection with the tube, melting the glass tube with a vacuum-proof metal tube by immersing the thin-walled metal tube axially in the edge of the thick-walled glass tube. It turns out to be a disadvantage that the proposed solution is suitable only for borosilicate glass that can be produced only with high energy and expensive raw materials investment, and that the production of the glass-metal bond is a multi-stage process, since the The metal tube, in turn, must be connected by means of a connection element to the vacuum-proof heat recovery tube. It is known, according to "Technologien der Glasverschmelzung ", Leipzig 1961, Akademische Verlagsgesellschaft Geest & Portig KG, some so-called fusion joints of tube for metal tubes with glass tubes. The common thing about these fusion joints for pipes is that the metal pipe is inserted axially into the heated glass edgerespectively, merged unilaterally. If there is a greater difference in the coefficients of expansion between the metal and the glass, the metal should have a sharp outline. The thickness of the metal edge, the inclination of the edge and the width of the fusion depend on the diameter of the metal tube, which must be fused under a vacuum test, and they do not appear for copper tubes in the referred publication. GB 222 510 discloses a glass-metal junction with a metal tube whose outer marginal section has a cutting edge in which a separate glass part is fused. It is a typical glass-edge welding of materials. GB 452 558 discloses a technology for welding machined glass. Through the edge section, also configured as a cutting edge, a part of glass is molded from inside to outside and merged with the edge section.

By means of another technological step, a glass tube is axially fused to the molded glass part, both in the technical solution according to GB 222 510 and also according to GB 452 558, by means of a so-called "end-to-end" connection. US Pat. No. 4,231,353 shows a solution in which one or two metal caps with rotational symmetry, which wrap around the tube, are molded in such a way that the tube of soda and lime glass of a vacuum tube solar collector fits in slots stamped in an annular shape on the outer edge of the lid. The wrapping tube is initially introduced into it in a liquid material, usually lead glass powder, which is melted in the groove, and which then solidifies there. In this way, a vacuum-proof joint is produced between the metal lid and the enclosing tube. The caps consist of a Ni-Cr-Fe alloy. The heat recovery tube (s) for the transport of heat output pass through the center of the caps. The heat recovery tubes are vacuum-proofed with the lids by direct or indirect welding. The disadvantages of these methods are the considerable process times due to the necessary introduction and casting of the lead glass powder and the complicated handling of the lid and the casing tube, so that the proposed method can be automated only with maximum technical investments. Glass-metal connections are also known according to "Werkstoffkunde der Hochvakuumtechnik", Berlin, Verlag Julius Springer, 1936. Also here the tubes to be fused under vacuum are equipped with corresponding edges to compensate for the different expansion of glass and metal in the case of temperature changes. The disadvantages correspond to those described in the foregoing. The object of the invention is, therefore, to offer a glass-metal connection, in particular for a vacuum tube solar collector, which remains vacuum tight for a very long period without an end-to-end connection, which withstands loads mechanical due to thermal expansions, steam collisions and wind loads and that can be produced technologically in a simple, particularly automatic way, and that requires less investment in raw material. The objective is achieved inventively by means of a glass-metal connection, in particular for a vacuum tube solar collector, comprising a metallic connection element and a heat recovery tube, vacuum-proofed with the metallic connecting element, in the that a circumferential edge section of the metal connecting element is flanged with a separate glass part, formed in the manner of a cap, and in which a vacuum-proof connection is thus produced and, in the separated glass part, a tube of glass is axially fused, the separated glass part and the glass tube being formed in one piece, without fusion bonding, as a jacket tube, and one end of the jacket tube being molded directly on the circumferential outer edge section of the connecting element metal from outside to inside, which encloses by fusion, vacuum-proof, the outer edge section of the metal connecting element. The invention is associated with the advantage that the glass-metal bond is easy to produce mechanically and with this easy to automate and - in this sense - also economical. The particular shape of flanging the glass and the configuration of the connection element exhibit the particular advantage that both the inherent and load stresses of the glass can be absorbed, which guarantees the vacuum tightness of the connection even with considerable force action, for example, the forces of expansion, wind and cavitation, during an extended period. A particular embodiment of the invention provides that the metallic connection element is vacuum-proofed with a heat recovery tube or several heat recovery tubes. According to another embodiment of the invention, the metallic connection element and the glass of the enclosing tube have an approximately equal linear expansion coefficient. According to another preferred embodiment of the inventive solution, the coefficient of linear expansion a of the glass of the shell tube amounts to 9.5 x E -6 / K at 10.1 x E -6 / K. Another embodiment of the invention provides that the metal connecting element It consists of a metallic alloy, containing a proportion of nickel >; 50%, a proportion of manganese < 0.6%, a proportion of aluminum < 0.1%, a proportion of chromium < 0.25% and a proportion of silicon < 0.3%, supplemented in each case by a proportion of iron. According to an advantageous conditioning of the glass-metal connection, the outer edge section of the metal connecting element has a thickness of 0.1 mm to 0.5 mm, preferably 0.2 mm, and is vacuum-proofed in a length of 2 mm to 8 mm. mm, preferably 4.2 mm from the end of the jacket tube. According to a particularly preferred embodiment of the invention, in the circumferential edge section of the metal connecting element, an oxide layer has been applied, before melt-bonding, by a heat treatment or various heat treatments to, preferably, 800 ° C. ± 100 ° C, with particular preference to 800 ° C ± 20 ° C. The invention is explained in more detail below by means of a drawing. The solar collector of vacuum tube with a glass-metal connection, partially sectioned, is shown in FIG. As seen in Fig. 1, the collector has a tube 2 and the heat recovery tube 2 also carrying the absorption plate 4. The metallic connection element 1 is joined by direct or indirect welding with the heat recovery tube 3. Its outer edge section 7 is joined by flanging 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 inwardly above the edge section 7 of the element 1 of connection and encloses it in the fused state directly on both sides vacuum proof. An annular groove 6 extending around the heat recovery tube 3 serves to stiffen the connecting element 1. The groove 6 confers rigidity to the connecting element 1 in the axial direction with respect to the axis of the tube and simultaneously serves to absorb the forces acting perpendicular to the axis of the tube on the heat recovery tube 3. This design allows the connection element 1 to withstand atmospheric pressure without significant deformation. Simultaneously, the groove 6 contributes to the glass-metal transition receiving little mechanical load. The metallic connection element 1 has the same, or approximately the same, expansion coefficient as the glass of the tube 2 surrounding the vacuum tube solar collector. To produce the inventive glass-metal connection, the heat recovery tube 3, which carries the absorption plate 4 and at one end of which the connection element 1 is vacuum-proofed with the heat recovery tube 3, it is inserted in the casing tube 2 in such a way that the glass of the casing tube 2 projects beyond, by a few millimeters, the edge of the metal connection element 1. The glass of the envelope tube 2 is now heated to soften it, so that the glass can be pushed, with the help of internal and external molding tools, in such a manner to the external and internal surface of the edge section 7 of the element 1 of connection that generates a fusion to vacuum proof and mechanically stable as a flange. For the connection element 1, preferably a metal having a lower thermal conductivity must be selected in order to thermally stress as little as possible the fusion of the connection element 1 with the casing tube 2 and to cause the least possible heat losses. By using a material for the connecting element 1 which broadly coincides in its coefficients of expansion with that of the glass of the envelope tube 2, the edge section 7 of the connecting element 1, wrapped by the glass, must possess a radius of 0.1 mm . If a ductile material, such as copper, is selected as connection element 1, then the edges noted in the literature referred to in terms of thickness, length and edge angle must be respected. For the vacuum tube solar collector a soda-lime glass tube 2 can be used having the following chemical composition (% mass indications): Si02 71.41% A1203 2 20% F3203 0 03% Ti02 0 05% CaO 90 % MgO 3 40% BaO 0.03% Na20 16.10% K20 1.50% S03 0.30% The glass has an expansion coefficient of (9.8 ± 0.2) E-6 / K in this composition. As a raw material for the connection element 1, it is selected The following alloy: Ni = 50% Cr <; 25% Yes < 0.3% Al < 0.1% Mn < 0.6% Fe = difference to complete 100% The coefficient of expansion of the connecting element 1 is located in this alloy composition in the area of the coefficient of expansion of the glass of the jacket tube 2. In addition, the material of the connection element 1 has a very low thermal conductivity, so that the thermal load of the melting point of the inventive glass-metal bond is relatively low, even when the temperature of stagnation is reached. The connection element 1 is produced by deep-drawing sheet metal with a thickness of approximately 0.2 mm. The edge section 7 of the element 1 of connection that is subsequently enclosed by the end 5 of the tube 2 envelope is rounded to avoid tensions in the glass. The radius of this rounded is located at 0.1 mm. Depending on the type of the subsequent melting process with the glass of the envelope tube 2, the connection element 1 can be pre-oxidated. After these preparative treatments, the connecting element 1 is vacuum-proofed with the absorption plate 4 carrying the heat recovery tube 3, preferably by indirect welding. After inserting the heat recovery tube 3, with the absorption plate 4 and the connection element 1 in such a way that the enclosing tube 2 protrudes by approximately 4 mm, stepwise or continuous heating of the glass of the tube 2 is carried out. enveloping, until achieving its deformability. In several processing steps, the glass of the casing tube 2 is now deformed by tools in such a manner that it contracts an intimate connection both inside and outside with the circumferential edge section 7 of the connection element 1 in the manner of a flange . Finally, a hardening of the connecting element 1 is carried out to ensure the freedom of the glass tube 2 surrounding voltages. To improve its anti-reflective effect, as well as its characteristics of corrosion and shock resistance, the envelope tube 2 is provided on its internal and / or external boundary surface, in a thickness of 40 nm to 330 nm -preferably 150 nm-, with a layer or several layers of nanoparticles, preferably of silicon dioxide. These nanoparticles have a grain size of 5 nm to 50 nm, preferably 12 nm. The shell of the jacket tube can be made by immersion, once or several times, and slow extraction of the tube from a suspension containing Si02, a binder, a humidifying agent and a dispersing agent, such as deionized water. After removing the tube, the coating generated on the internal and external surface is air-dried and then tempered at a temperature of approximately 450 ° C. However, a specific embodiment of the invention was shown and described to explain it, the invention is not restricted to the represented embodiment example. The invention also includes all the modalities and modifications of the application of glass-metal joints, in particular for vacuum-proof containers, which are within the scope of the protection of the claims. List of reference symbols 1 Connection element 2 Surround tube 3 Heat recovery tube Absorption plate End formed as flange Groove Edge section

Claims (7)

1. Glass-metal connection, in particular for a vacuum tube solar collector, comprising a metallic connection element and a heat recovery tube vacuum-proofed with the metallic connecting element, a circumferential edge section of the element being flanged of metal connection with a separate glass part, formed in the manner of a cap, and thus generating a vacuum proof connection and a glass tube being axially fused with the separated glass part, characterized in that the separated glass part and the tube of glass are formed in one piece, without joining fusion as a sheath tube, and one end of the sheath tube is molded in such a manner, directly above the circumferential outer edge section of the metal connecting element, from the outside in, which encloses the outer edge section of the metallic connection element vacuum proof by fusion. Metal-glass connection according to claim 1, characterized in that the connection element is vacuum-proofed with a heat recovery tube or with several heat recovery tubes. Glass-metal connection according to one of claims 1 to 2, characterized in that the connection element and the glass of the jacket tube have an approximately identical linear expansion coefficient. Glass-metal connection according to claim 3, characterized in that the coefficient of linear expansion a of the glass of the enclosing tube is 9.5 x E -6 / K at 10.1 x E -6 / K. 5. Glass-metal connection according to one of claims 1 to 4, characterized in that the connecting element consists of a metallic alloy containing a nickel proportion > 50%, a proportion of manganese < 0.6%, a proportion of aluminum < 0.1%, a proportion of chromium < 0.25% and a proportion of silicon < 0.3%, supplemented in each case by a proportion of iron. Glass-metal connection according to one of Claims 1 to 5, characterized in that the outer edge section of the connection element has a thickness of 0.1 mm to 0.5 mm, preferably 0.2 mm, and is vacuum-sealed on a length from 2 mm to 8 mm, preferably 4.2 mm, from the end of the jacket tube. The glass-metal joint according to one of claims 1 to 6, characterized in that an oxide layer, produced by a heat treatment or by several thermal treatments, is applied to the circumferential edge section of the connection element before the melting connection. of the enclosing tube.