Abstract
This disclosure relates to a method and an apparatus for sealing a double-walled glass tube in a vacuum-tight manner, in particular a production method for manufacturing of solar collectors. By means of a vacuum chamber, inside of which a holding element is fixed and inside of which a heating conductor is arranged, an electro-conductively heating and a subsequent deforming of the double-walled glass tube can be achieved. No additional materials, such as metallic auxiliary element, solders are required. A simple installation inside the vacuum chamber is possible and a minimum vacuum feedthrough for the power supply of a heating conductor is required. The direct heat transfer onto the double walled glass tube and a resulting quick process control allows to reliably seal a double-walled glass tube of a thermal solar collector under vacuum with simple means.
Claims
1. A method for sealing a double-walled glass tube in a vacuum-tight manner, the glass tube having an inner glass tube and an outer glass tube, the method comprising the steps of: providing the double-walled glass tube inside a vacuum chamber at a desired negative pressure inside the vacuum chamber; electro-conductively heating the outer and/or inner glass tube at a first end of the double-walled glass tube by means of at least one heating conductor; and deforming the electro-conductively heated glass tube at the first end such that the outer glass tube and the inner glass tube touch each other and such that the first end of the double-walled glass tube is sealed in a gas-tight manner.
2. The method according to claim 1, wherein the electro-conductively heating and the deforming are conducted through the at least one heating conductor within the vacuum chamber.
3. The method according to claim 1, further comprising the step of: creating a relative motion between the double-walled glass tube and the heating conductor, through which the deforming of the double-walled glass tube at the first end is caused.
4. The method according to claim 1, wherein at least two heating conductors are used, and wherein the method further comprises the steps of: at least partially covering the outer glass tube by means of the first heating conductor; at least partially covering the outer glass tube by means of the second heating conductor; and displacing both heating conductors perpendicular to a longitudinal axis of the double-walled glass tube for deforming and air-tight sealing of the electro-conductively heated glass tube.
5. The method according to claim 1, wherein the heating conductor comprises a ceramic material.
6. The method according to claim 5, wherein the heating conductor comprises silicon infiltrated silicon carbide (SiSiC).
7. The method according to claim 1, wherein the electro-conductively heating is accomplished through direct application of the heating conductor onto a surface of the double-walled glass tube and after an evacuation process of the vacuum chamber.
8. The method according to claim 1, further comprising the step of: evacuating a volume, which is arranged between the inner glass tube and the outer glass tube.
9. The method according to claim 1, further comprising the step of: creating a rotational movement of the inner and outer glass tube during the electro-conductively heating relative to the heating conductor.
10. The method according to claim 1, further comprising the step of: vapor depositioning of an extra layer onto an outer surface of the double-walled glass tube before deforming and air-tight sealing of the glass tube.
11. The method according to claim 10, wherein the extra layer comprises an antireflection coating.
12. An apparatus for vacuum-tight sealing of a double-walled glass tube having an inner glass tube and an outer glass tube, the apparatus comprising: a vacuum chamber for providing a desired negative pressure inside the vacuum chamber; a holding element for fixing a double-walled glass tube inside the vacuum chamber; and at least one heating conductor for electro-conductively heating the double-walled glass tube; wherein the apparatus is configured to deform a double-walled glass tube, that is fixated at the holding element and electro-conductively heated through the heating conductor, at an end of the glass tube, such that the first end of the double-walled glass tube is sealable in an air-tight manner.
13. The apparatus according to claim 12, further comprising: a first partial cylinder barrel as a first heating conductor; and a second partial cylinder barrel as a second heating conductor; wherein both partial cylinder barrels are designed for a direct and form-fitting contacting and covering an outer glass tube of a double-walled glass tube fixated by the holding element.
14. The apparatus according to claim 13, further comprising: a first pneumatic device; and a second pneumatic device; wherein the first pneumatic device is configured to move the first heating conductor in the direction of the second heating conductor; and wherein the second pneumatic device is configured to move the second heating conductor in the direction of the first heating conductor.
15. The apparatus according to claim 12, wherein the heating conductor is designed for conducting a motion during the electro-conductive heating to deform and seal the double-walled glass tube.
16. The apparatus according to claim 12, wherein the holding element is provided by the at least one heating conductor, in a form of a second partial cylinder barrel.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] The various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and:
[0051] FIG. 1 shows a schematic illustration of a flow-chart of a method for vacuum-tightly sealing a double-walled glass tube according to an exemplary embodiment of the invention.
[0052] FIG. 2 shows a cross-section through a part of an apparatus for vacuum-tightly sealing a double-walled glass tube according to an exemplary embodiment of the invention.
[0053] FIG. 3 shows an apparatus for vacuum-tightly sealing a double-walled glass tube according to an exemplary embodiment of the invention.
[0054] FIG. 4 shows a further exemplary embodiment of an apparatus for vacuum-tightly sealing a double-walled glass tube.
[0055] Embodiments of the invention will be explained in more detail once again under reference to the attached figures based on schematic illustrations of preferred exemplary embodiments. Here, further details and advantages of the invention are apparent.
[0056] The illustrations in the figures are only schematic and not to scale. In the figure descriptions, same reference numerals are used for identical or similar elements.
DETAILED DESCRIPTION
[0057] The following detailed description is merely exemplary in nature and is not intended to limit the disclosed embodiments or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background detailed description.
[0058] The method of FIG. 1 is a method for vacuum-tightly sealing of a double-walled glass tube and may particularly be considered as a manufacturing method or a part of a manufacturing method for manufacturing of solar collectors. In FIG. 1 the providing of the double-walled glass tube within a vacuum chamber at a desired negative pressure inside the vacuum chamber is shown with step S1. Such a glass tube may be considered as a solar collector. In step S2, the outer and/or the inner glass tube may be heated electro-conductively, namely at a first end of the double-walled glass tube. This is accomplished by means of at least one heating conductor. The deforming of the electro-conductively heated glass tube at the first end of the double-walled glass tube is accomplished in a manner that the outer glass tube and the inner glass tube touch each other and thereby the first end of the double-walled glass tube is sealed in an air-tight manner. This step of deforming and sealing is shown in FIG. 1 as step S3.
[0059] In this regard it is to be noted that this exemplary embodiment may be supplemented by different steps explained before and in the following. For example, a relative motion between the double-walled glass tube and the heating conductor may be created, by means of which the double-walled glass tube is deformed and sealed at the first end. Likewise, a volume arranged between the inner and the outer glass tube, may be evacuated. Additionally or alternatively, a rotational motion of the double-walled glass tube relative to the heating conductor may be created. For example, this may be accomplished through a roller device, which is also part of a respective vacuum chamber of an apparatus according to the invention. The method according to FIG. 1 allows heating and sealing of both glass tubes through direct application of the heating conductor, in particular of a ceramics heating conductor and allows a direct heat transfer onto the surface of the glass tubes directly after the evacuation process. For example, the deformation may be accomplished through shifting the respective heating conductors relative to each other. Furthermore, it is possible to vapor deposit absorption layers in a separated chamber section. Hereby, the method of FIG. 1 allows reduction of evacuation times and resultantly a more economic production course. Furthermore, a simple installation in the vacuum chamber is possible. Merely the power supply of the heating conductor into the vacuum zone is required. A direct heat transfer onto the double-walled glass tube and thus a quick process control is enabled by the method of FIG. 1.
[0060] FIG. 2 shows a part of an apparatus 200 for vacuum-tightly sealing a double-walled glass tube 206. In this regard, FIG. 2 in an upper part shows the state of the double-walled glass tube 206 and the respective contacting with the heating conductor 202, 204 before a deforming and before the sealing of the double-walled glass tube. Contrary thereto in the lower part of FIG. 2, the double-walled glass tube 206 is shown after the deforming and after the air-tight sealing of the glass tube. Both heating conductors 202, 204 of the example of FIG. 2 are designed in a manner that their contour receives the glass tube 206 to be sealed, in particular the outer partial tube 201 in a form-fit manner. The double-walled glass tube is partially enclosed in its circumference by both heating conductors; and at the contacting surface the desired heat transfer is accomplished. Hence, hereby a form-fit between both heating conductors and the outer glass tube of the double-walled glass tube is created, such that a particularly good heat conduction from the heating conductor onto the glass tube is possible. FIG. 2 shows the outer glass tube 201 and the inner glass tube 203 in a cross-section. Also, a first heating conductor 202 and a second heating conductor 204 are shown in the upper part of FIG. 2 in a heating position each, i.e. in contact with the double-walled glass tube 206. Hereby, arrow 205 indicates that a relative motion, in particular a relative rotation between the heating conductors 202, 204 and the double-walled glass tube 206 is created.
[0061] In the lower part of FIG. 2, the outer glass tube 201 is shown after the deforming and also the inner glass tube 203 is shown after the deforming. Also, in the lower part of FIG. 2, the first heating conductor 202 is shown in a deforming position and also the second heating conductor 204 is shown in a deforming position in FIG. 2. In other words, this apparatus is designed for deforming an electro-conductively heated, double-walled glass tube 206 at an end of the glass tube, which glass tube is fixed at the holding element (not shown in FIG. 2), by means of the heating conductors 202, 204, such that the first end of the double-walled glass tube is sealed in an air-tight manner. This state is shown in the lower part of FIG. 2. In this regard it is to be noted, that the first heating conductor 202 in its position in the upper part of FIG. 2 is identical with the heating conductor 202 in the deforming position in the lower part of FIG. 2. The same applies for the second heating conductor 204 shown in the upper picture and the second heating conductor 204 shown in the lower picture of FIG. 2. The apparatus 200 is designed for creating a relative motion between the double-walled glass tube and the heating conductors 202, 204, by means of which the deforming of the double-walled glass tube at the first end is caused. Hereby, in the lower part of FIG. 2 it is shown with reference numeral 207, that due to the shifting of both heating conductors at the end of the method, these are positioned closer to each other in comparison to the beginning of the method as shown in the upper part of FIG. 2. In this example of FIG. 2, both heating conductors are moved to each other in a radial direction each. These may exemplarily be realized through a hydraulic or pneumatic mechanics for creating the motion. An exemplary embodiment is discussed in conjunction with FIG. 3.
[0062] FIG. 3 shows a further exemplary embodiment of an apparatus 300 for vacuum-tightly sealing of a double-walled glass tube. Hereby, the apparatus 300 is described by means of its components and functionalities with the double-walled glass tube, by means of which structural and functional features and characteristics of the apparatus 300 are given. Hereby, the apparatus 300 comprises a first upper heating conductor 301 for the outer tube and is shown in a heating position in FIG. 3. Likewise, the apparatus 300 comprises a lower heating conductor for the outer tube, which is also shown in a heating position. The apparatus comprises an upper pneumatic cylinder 303, by means of which a vertical motion of the upper heating conductor is creatable. This translational motion is indicated with the arrow 311 in FIG. 3. The outer glass tube is shown with 304 and the inner glass tube is shown with 305 in FIG. 3. Also, electric connectors 306 and 307 are arranged on the right and left side of the apparatus 300. As can be gathered from FIG. 3, the lower heating conductor 302 is realized in form of a partial cylinder jacket and provides a holding element for the double-walled glass tube. Also, the upper heating conductor 301 fixes the position of the double-walled glass tube. The lower pneumatic cylinder 309 enables a translational motion of the lower heating conductor in analogy to the upper pneumatic cylinder 303. Thereby, a base plate 308 is present in the apparatus 300, on which guide poles 310 are arranged laterally, which guide the translational motions of the heating conductors, which are created by the pneumatic cylinders 303 and 309. According to a further formed exemplary embodiment of the apparatus of FIG. 3, a roller guide is present in the apparatus 300, which is able to create a rotation of the double-walled glass tube during the heating. A respective electrical control of all components, in particular the pneumatic cylinder and the rotation device, may also be included. Furthermore, it can be gathered from FIG. 3 that both partial cylinder jackets in form of the first and the second heating conductors are in a direct and form-fitting contact and are covering of the outer glass tube. Altogether, the apparatus enables the reduction of evacuation time during the manufacturing of solar collectors, in particular of the vacuum-tight sealing of the double-walled glass tube, which is used as a solar collector.
[0063] FIG. 4 shows a further exemplary embodiment of an apparatus 400 for vacuum-tightly sealing of a double-walled glass tube. The apparatus 400 comprises an upper heating conductor 401 for the outer tube and a heating conductor 402 for the inner tube. Hereby, the outer tube is referred to with 403 and the inner tube is referred to with 404. Likewise, the lower heating conductor 405 for the outer tube 403 is shown in FIG. 4. Bushing 406 is used for insulation. The bushing 406 has the function of an electrical insulator. The user of the invention may choose the material of the bushing 406 according to the requirements. Due to the relatively high process temperatures, insulators exemplarily made of a plastics material are mostly not to be considered. Oxide ceramics materials are very suitable, such as aluminum oxide, zirconium oxide, yttrium oxide, silicon dioxide or mixtures thereof. In addition to that, the substance class of aluminosilicates are to be considered, e.g. mullite and cordierite. The power supply unit 407 is preferably realized as DC power source/DC current process. Due to possible plasma arcs about 800 V should not be exceeded. In some cases, voltages higher than 800 V are possible. Working voltages suitable for the process are in a range of 20 to 400 V depending on the specific resistance of the heating conductor, the cross-sectional surface and the length. The realization as an AC power unit is also possible and suggested in case of higher desired voltage levels. Hereby, possible plasma arcings may be reduced.
[0064] The apparatus 400 of FIG. 4 comprises a console 408 made of a mineral material, which is electrically insulating up to 1400 C. Thereby, different materials may be used. In this regard, the upper, previously described part of FIG. 4 is the state of the apparatus according to the invention within the heating phase. In the lower part of FIG. 4, the state of the apparatus 400 according to the invention within the deforming phase is shown. Hereby, the outer tube 409 is illustrated in its deformed configuration. Also, the upper heating conductor is illustrated for the outer tube 401 in a position moved downward. The heating conductor for the inner tube 402 is also illustrated in the lower part as well as the inner tube 404 and the lower heating conductor 405 for the outer tube. The console 408 is also illustrated in the lower part of FIG. 4. The same applies for the bushings 406 and system 407.
[0065] The present invention is applicable for different kinds of methods for vacuum-tightly sealing of a double-walled glass tube in general and is not limited to the given combination of features of claim 1 and the dependent claims. In addition to this, further options arise, to combine single features, if they are derivable from the patent claims, the description of the exemplary embodiments or directly from the drawing.
[0066] In addition, it should be pointed out that comprising does not exclude other elements or steps, and a or an does not exclude a plural number. Furthermore, it should be pointed out that characteristics or steps which have been described with reference to one of the above exemplary embodiments may also be used in combination with other characteristics or steps of other exemplary embodiments described above. Reference characters in the claims are not to be interpreted as limitations.
[0067] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the embodiment in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the embodiment as set forth in the appended claims and their legal equivalents.
