METHOD OF APPLYING ELECTRICALLY CONDUCTIVE BUS BARS ONTO LOW-EMISSIVITY GLASS COATING

Abstract

The invention relates to the application of electrically conductive bus bars onto a low-emissivity coating of glass. A method of applying electrically conductive bus bars onto a low-emissivity surface of glass is performed by gas dynamic cold spray method with the aid of a spraying nozzle of a gas dynamic spraying apparatus. The method comprises: providing in the gas dynamic spraying apparatus an estimated bulk weight of a powder, sufficient for spraying the powder over the entire length of the bus bar; moving the spraying nozzle to a beginning point of the bus bar without supplying the sprayed powder into the nozzle, and upon positioning the moving nozzle at the beginning point of the bus bar, supplying the sprayed powder into the spraying nozzle and moving the spraying nozzle with a constant speed from the beginning point to an end point of the bus bar. Upon reaching the end point of the bus bar, the movement of the nozzle is reversed towards the beginning point of the bus bar with a speed greater than the speed of the nozzle from the beginning point to the end point of the bus bar.

Claims

1. A method of applying electrically conductive bus bars onto a low-emissivity surface of glass by gas dynamic cold spray method with the aid of a spraying nozzle of a gas dynamic spraying apparatus, the method comprising: providing in the gas dynamic spraying apparatus an estimated bulk weight of a powder, sufficient for spraying the powder over the entire length of the bus bar; moving the spraying nozzle to a beginning point of the bus bar without supplying the sprayed powder into the nozzle, and upon positioning the moved nozzle at the beginning point of the bus bar, supplying the sprayed powder into the spraying nozzle and moving the spraying nozzle with a constant speed from the beginning point to an end point of the bus bar; wherein upon reaching the end point of the bus bar, the movement of the nozzle is reversed towards the beginning point of the bus bar with a speed greater than the speed of the nozzle moving from the beginning point to the end point of the bus bar.

2. A method according to claim 1, wherein said reversed movement of the nozzle is effected over a distance of about 2-3 cm.

3. A method according to claim 1, wherein said providing of an estimated bulk weight of the powder, sufficient for spraying the powder over the entire length of the bus bar, upon reaching a specified point of the path is effected by cutting off an estimated part of a feed pipe from a feeder by means of air valves provided in the gas dynamic spraying apparatus.

4. A method according to claim 3, wherein the bulk weight of the powder, formed in the cut off part of the feed pipe, is determined with account of the length of the applied area of the bus bar, its section and geometry, and is calculated based on process parameters accepted in the process, such as temperature, powder flow rate, compressed air pressure, and speed of the nozzle.

5. A method according to claim 1, wherein the sprayed powder is a fine powder, such as a homogeneous powder or a mixture of powders, the size of the applied fine powder being 5-5.0 mμ.

6. A method according to claim 1 or 5, wherein a single-layer bus bar is applied using a two-component powder, for example, Al+Zn, at a temperature of about 240° C., and after said applying a second layer of powdered copper (Cu) is applied onto the edge of the bus bar to form thereon a contact pad for soldering.

7. A method according to claim 1 or 5, wherein said applying of the bus bar is effected in two stages, where the first stage comprises applying a powder to form an underlayer of the bus bar, and the second stage comprises applying the fine powder to form the final bus bar.

8. A method according to claim 1, wherein the process of applying the powder is controlled through a computer with software, into which delay functions are introduced, taking into account the delayed action of the gas dynamic spraying apparatus.

9. A method according to claim 1, wherein before applying the powder onto the glass surface, a part of the surface along the path, onto which the bus bar is to be applied, is treated with an abrasive powder, e.g. Al.sub.2O.sub.3, to partially remove the low-emissivity layer, and the bus bar material is then disposed with an offset of 2-3 mm from the axis of the application path to ensure electrical contact of the bus bar with the low-emissivity glass surface around said part with removed low-emissivity layer.

10. A method according to claim 9, wherein said beginning and/or end points of the bus bar are disposed on the low-emissivity surface or on said part of the surface with removed low-emissivity layer.

11. A method according to claim 1, further comprising withdrawing dust and gas mass from the powder application area with the aid of a gas dynamic dust and gas ejection valve mounted on the spraying apparatus coaxially with the nozzle; wherein the ejecting jet in the dust and gas ejection valve is the jet of sprayed powder as such, which provides aspiration of the powder mass non adherent to the surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Hereinafter the invention will be explained in more detail by describing a particular embodiment in conjunction with the accompanying drawings, where:

[0062] FIG. 1 shows schematically a gas dynamic spraying apparatus used for implementing the present method;

[0063] FIG. 2 shows two projections of an external view of the used gas dynamic spraying apparatus;

[0064] FIG. 3 shows a flow chart of the method; and

[0065] FIG. 4 illustrates the arrangement of electrically conductive bus bars on the surface of a low-emissivity glass.

DETAILED DESCRIPTION OF THE INVENTION

[0066] FIG. 1 shows schematically a gas dynamic spraying apparatus used in this method, which comprises a spray gun 1, two feeders 2 with powders 13, connected to the spray gun 1 via feed pipes 5. In addition, the design of the conventional gas dynamic spraying apparatus has been modified by installation of additional air valves 3, 4 on the feed pipes 5, which, as will be shown, enable applying bus bars 11 onto any place of glass surface 10 without masks and templates.

[0067] The spray gun 1 comprises an air heater 14, a Laval nozzle 6 and an outlet variable cross-section nozzle 7. Each of the feeders 2 is connected alternately using a tee 12 via the pipes 5 to the outlet nozzle 7.

[0068] Furthermore, in one embodiment, a dust and gas ejection valve 8 can be mounted on the outlet nozzle 7, in which the ejecting jet is the jet of sprayed powder per se.

[0069] As also shown in FIG. 2, the apparatus includes a three-axis table comprising a table frame 16, stops 17 for positioning glass 10 on the table, a bridge 15, and a bridge carriage 19. The plan view also shows a casing 18 of the valve 8 and injectors 20 to provide air support to the glass 10, the injectors being connected to an air blower 22; and the side view shows an aspiration channel 21 connected at one end to the casing 18 of the valve 8, which is connected with a hose 9 of the aspiration system.

[0070] The apparatus further comprises a control stand with power supplies and industrial PC (not shown in FIGS. 1 and 2).

[0071] A method according to the present invention is performed as follows.

[0072] As explained above, the gas dynamic cold spray technique used in the method involves heating a compressed gas (air), supplying it into a supersonic nozzle and forming a supersonic flow therein, and supplying a powder material into the flow, increasing the speed of the material by the supersonic flow and directing it through an outlet variable cross section nozzle onto the workpiece surface.

[0073] The process of applying bus bars is carried out using LDesigner software product (ATEKO Company), to which a delay function is added to take into account the delayed response of the equipment and to adapt it to the process.

[0074] LDesigner 5.0 software product consists of two parts:

[0075] (a) Graphic editor (LDesigner 5.0 Graphic Editor), which provides wide opportunities for creating, editing and processing images. Its main features include a modern, easy to use graphical interface (including detailed menus, toolbars, hotkeys, image editing using the mouse) and the ability to work with vector and raster graphics created using popular graphics editors (such as CorelDraw or AutoCAD); and

[0076] (b) Marker (LDesigner 5.0 Marking Program), which controls the three-axis table and process equipment.

[0077] The marker implements the algorithm of applying bus bars onto the glass, created in the LDesigner.

[0078] The process is carried out in the following sequence: [0079] a graphic file of contour of the glass product with applied bus bars is generated in the graphic editor; furthermore, process conditions are specified for each object: [0080] speed of movement of the nozzle, v mm/s; [0081] number of working feeder 2 (FIG. 1); [0082] temperature corresponding to the sprayed powder contained in the feeder; [0083] process (program) delays for the beginning of the application process, Δt (ms), and the end of the application process, Δt (s); [0084] powder mass flow rate Q (g/s) (to provide an estimated bulk weight of the powder in the gas dynamic spraying apparatus, sufficient for applying the powder over the entire length of the bus bar); [0085] working air pressure (atm); [0086] sequence of processing the objects.

[0087] Operator starts the “Marker” program at the control stand, thereby providing implementation of the specified project and carrying out the process of applying bus bars.

[0088] With that, a spraying nozzle of the spray gun 1 is moved to beginning point B of the bus bar 11 without supplying the sprayed powder therein, and upon positioning the moved nozzle at the beginning point B of the bus bars 11 the sprayed powder is admitted into the nozzle, and the spraying nozzle is moved with a constant speed from the beginning point B towards end point D of the bus bar (see FIG. 3). Upon reaching the end point D of the bus bar, the nozzle movement is reversed towards the beginning point B of the bus bar with a speed greater than the speed of the nozzle from the beginning point B to the end point D of the bus bar.

[0089] The process of applying bus bars can be either single-stage or multi-stage, where an underlayer is pre-applied of a powder exhibiting better “wettability” to the glass to increase the adhesion of the bus bar to the low-emissivity surface of the glass.

[0090] The gas dynamic cold spray process is carried out using powders with a fraction of 5 to 50 μm; it is generally a mixture of powders of several components, one of which exhibits a better “wettability” to the surface, and the other exhibits adhesion and cohesion. This combination of powders is typical for the underlayer, while the second and subsequent layers generally consist of components that enhance the electrical and process properties. For example, a mixture of copper and zinc (or pure copper) reduces the electrical resistance and simplifies the process of soldering current-carrying wires. Using the above combination of compositions of powders and alternating the layers a bus bar can be produced that is capable of conducting high currents without temperature gradient between the bus bar and the electrically heated surface.

[0091] Bulk weight of the powder, formed in the cut-off part of the feed pipes, is calculated using known formulas and adjusted at experimental weighing and experimental sputtering of these bulk volumes on a sample of the bulk weight at the process parameters accepted in the process: [0092] temperature, t ° C.; [0093] powder flow rate, Q g/s; [0094] compressed air pressure, P atm; [0095] speed of the nozzle, v mm/s;

[0096] with determining the length of the applied area of the bus bar, its cross section and geometry.

[0097] Owing to the properly chosen exposure time (τ=d/v(sec), where d is the diameter of the spraying nozzle, v is the speed of its movement relative to the low-emissivity surface) and the powder flow rate, a bus bar is formed that has an equal cross-section throughout its length, including the beginning of the bus bar and its end.

[0098] The use of an air dynamic dust and gas ejection valve 8, in which, as mentioned, the ejecting jet is the working spraying jet, and which is mounted coaxially on the spraying nozzle 7, enables the process to be implemented without a special aspiration chambers, therefore the method and the equipment developed on its basis can be integrated in the existing process of manufacturing electrically heated glass to replace low efficient and costly processes and construct fully automated lines.

Example of Implementing the Method

[0099] To carry out the present method, the described above apparatus was used with “DIMET” gas dynamic spraying system (Model 423) supplied from the aforementioned Obninsk Center for Powder Spraying, which was supplemented with required additions relating to installation of additional air valves and the air dynamic dust and gas ejection valve.

[0100] An example will be described for a two-stage method of applying bus bars, wherein: [0101] the first stage comprises applying a bus bar underlayer of a composition of Al+Zn powders in the ratio of 50/50 to provide maximum adhesion of powders to the low-emissivity surface (not less than 100 MPa); and [0102] the second stage comprises applying a composition of Cu+Zn powders in the ratio of 70/30 to improve electrical characteristics of the bus bar (decrease the electrical resistance) and to facilitate the process of soldering current-carrying wires from the power supply to the bus bar.

[0103] Process engineer creates in the LDesigner graphic editor a graphic file of the project with applied electrically conductive bus bars and specifies process parameters for each object: [0104] number of feeder 2; [0105] temperature of spraying jets, T, degrees C. (200-300° C.); [0106] mass flow rate of powder, Q, g/s (0.6 g/s); [0107] speed of the nozzle when spraying the bus bar, v, mm/s (40 mm/s); [0108] thickness of glass to be processed; [0109] process delay, t, (C), for powder supply when forming the beginning of the bus bar; [0110] process delay for cutting off the currently running feeder 2 from feed pipe 5 (FIG. 1);

[0111] Next, the process engineer generates the algorithm for applying bus bars, determines the processing sequence and imports the generated project in LDesigner “Marker” program.

[0112] The apparatus operator performs the following actions: [0113] puts glass on the surface of a three-axis table in an air layer created by the blower 22 and the injectors 20 for air support, and positions it by stops 17 (FIG. 2); [0114] provides suction clamp by switching a gate (not shown); [0115] enables the supply of compressed air at a pressure of 5 to 6 atm; [0116] actuates the aspiration system; [0117] starts the “Marker” program.

[0118] Further, the process of applying bus bars runs automatically on the specified algorithm and the predetermined parameters.

[0119] A solenoid valve (not shown) of the gas dynamic spraying apparatus opens, and compressed air enters the spray gun 1 and is heated there through the Laval nozzle 6 and increases its speed, and flows to the variable cross section nozzle 7 and further to the air dynamic dust and gas ejection valve 8 (FIG. 1).

[0120] At the same time the air valve 3 opens and connects the first feeder 2 with the feed pipe 5 (FIG. 1). Al+Zn powder enters from the feeder 2 due to ejection into the jet of heated compressed air, mixes with it and passes into the variable cross section outlet nozzle 7, which is currently above zero aspiration point A (FIG. 3; in FIG. 2 the point is under the valve casing 18). The feed pipe is blown through by the powder from the first feeder 2 and is filled with it.

[0121] Next, the compressed air supply is shut off by closing a solenoid valve included in the system. With this, powder supply into the nozzle does not occur, and the nozzle moves from zero aspiration point A (FIG. 2) to the beginning point B of the bus bar at the estimated time set by the delay in the program. At the instant when the nozzle 7 is moving above the point B, the solenoid valve opens, and compressed air is admitted, with the powder material spray exposure time of T=d/v (sec), to form the bus bar beginning. Then, the nozzle 7 is moving with a constant speed, v mm/s, along the path of the sprayed bus bar towards the end point D of the bus bar. Upon reaching point C at the software set time a command is received to close the air valve 3 for cutting off the pipe 5 from the feeder 2. The estimated bulk weight of powder is formed in the pipe, which is sufficient to apply the bus bar length between points C and D. Upon reaching the point D with exposure time τ≧d/v (s) and at a greater speed than the constant speed, the movement of the nozzle along the path of the applied bus bar is reversed towards the beginning point A of the bus bar, preferably at 20-30 mm. The air valve 3 opens, the built-in solenoid valve shuts off the supply of compressed air, and the nozzle 7 is then moved to the beginning of the next bus bar, point K (FIG. 4). Then, the same algorithm is run as in the case of the first bus bar. This is the procedure of the first stage—the stage of applying an underlayer of Al+Zn on all bus bars of the project (shown in FIG. 4).

[0122] Then, the second stage, application of Cu+Zn powder composition, is carried out. Here, the spraying nozzle 7 is moved at idling speed to the zero aspiration point A (buil-in solenoid valve is closed). At the zero aspiration point A the solenoid valve opens, the air valve 3 closes and the air valve 4 opens. Thereby the second feeder 2 is operated, and the feed pipe and the spray gun are blown off from the Al+Zn powder and filled with Cu+Zn powder.

[0123] The process proceeds for 1.5-2 seconds. The spraying nozzle 7 is then moved from the point A to the point B according to the same algorithm as during the application of the bus bar underlayer, and the main layer of Cu+Zn powder is applied. The process parameters are the same, except that the temperature of the spraying jet is set in the range of from 240 to 400° C.

[0124] At that the process of forming a conductive bus bar on the low-emissivity glass surface is completed.

[0125] As will be apparent to persons skilled in the art based on the described invention, many changes and modifications may be made in the above-described and other embodiments of the present invention, not going beyond its scope defined in the appended claims.

[0126] For example, the provision of the estimated bulk weight of the powder, sufficient for applying the powder over the entire length of the bus bar, is not obligatory carried out by cutting off a part of the pipe upon reaching a specified point of the bus bar, but can also be calculated before moving the nozzle along the entire bus bar length.

[0127] Furthermore, although reference was made to some types of powders and their mixtures, it should be clear to those skilled in the art that other types of powders can be also used. Therefore, the above detailed description of a preferred embodiment should be taken as illustrative and not restrictive.