EP0704249B1 - Device for distributing pulverulent solids on the surface of a substrate for coating this substrate - Google Patents

Description

The present invention relates to a device for distributing pulverulent solids on the surface of a substrate, especially glass, in order to coat it with thin layers likely to give it optical, thermal or electrical properties.

This device allows in particular to deposit these thin layers by a technique so-called powder pyrolysis consisting in spraying said pulverulent solids (generally organo-metallic compounds), suspended in a gas, towards a substrate heated to a high temperature, so that they decompose (usually in the form metal oxide) on contact. The substrate can take the form of a glass ribbon continuous said float, leaving the glass float enclosure, the device then comprising usually a nozzle having a cavity which passes right through it and which ends in a distribution slot above the ribbon and transversely to its axis of scrolling, the nozzle being equipped with suitable powder supply means.

It is thus possible to obtain, continuously, thin layers generally having high adhesion to the substrate and satisfactory quality and durability.

However, the float glass ribbon to be covered (or any other substrate of large dimensions that one would seek to cover) usually has a width of at least 2 meters, in particular of the order of three to four meters. So it's on this width, which is considerable, that the nozzles have to distribute the gas / powder suspension in the most homogeneous possible to ensure, at least transversely to the axis of travel of the tape, a certain consistency in the quality and / or thickness of the coating deposited. Many studies have already been carried out, aiming either at the design of the nozzle itself, or its powder supply mode, to best guarantee this homogeneity.

Thus, patent EP-B-0 130 919 has developed an efficient distribution means allowing a fairly uniform subdivision of a vein of powder in suspension conveyed in a single supply duct in a plurality of powder veins conveyed in as many secondary conduits coming to feed the nozzle over its entire width by through feeders called injectors into which they open. he however, it is difficult to guarantee that each of the veins has a perfect identity with all the others, in terms of flow rate of powder transported, and that all of the veins will be able to “melt” into a perfectly homogeneous powder flow at the level from the nozzle distribution slot.

This is why patents EP-B-0 125 153 and EP-B-0 374 023 have proposed complete this mode of supply by providing each means of supplying gas under pressure in the cavity to facilitate, homogenize the flow of the suspension powder-gas from the injectors through the nozzle, without yet managing to remove all risk of irregularity in thickness in the deposited layer and to truly "correct" the possible slight disparities between the different gas streams arriving in the injectors.

Patent EP-B-0 392 902 then proposed a device making it possible to modify automatically the relative positions of the injectors arranged in line at the inlet of the nozzle, removing or moving the injectors concerned as soon as a variation is detected of local thickness in the coating deposited “downstream” from the nozzle. This solution gives interesting results, but is not yet fully optimal, firstly because it may seem a little complicated to implement, then and above all because it tries to compensate for any disparities in flow from the secondary veins without correcting them truly.

The object of the invention is therefore to further improve the operating mode of the powder distribution devices of this type, and in particular to optimize the homogeneity of the flow of the powder-gas suspension in the nozzle without sacrificing too much simplicity of implementation, in order to obtain quality coatings, particularly in terms of thickness consistency.

The subject of the invention is a device for distributing powdered solid in suspension in a gas, in order to deposit a coating, in particular by pyrolysis, on a moving substrate, in particular of the float glass ribbon type. This device includes on the one hand, a dispensing nozzle whose walls define a cavity which ends in a longitudinal distribution slot. It also includes a main duct powder feed provided with a distribution means. A plurality of conduits secondary powder supply connected to this main conduit using the means of distribution allows the nozzle cavity to be supplied with powder over its entire length. According to the invention, at least part of the secondary conduits is equipped with at least one means pneumatic capable of modulating the flow rate of the powder-gas suspension that each of the conduits secondary concerned is intended to convey. Preferably, each of the conduits is equipped of such pneumatic means. This solution has two major advantages: on the one hand, being able to modulate the flow in each of the conduits will make it possible to truly correct and directly any differences in flow between the gas-powder mixture streams that they carry into the nozzle, and thus ensure a very even distribution in the powder supply at the nozzle, over the entire length of its cavity. Else on the other hand, use a pneumatic and non-mechanical means to operate these modulations debit is very advantageous. Indeed, a mechanical means of the valve type operates on the principle of partial obturation of the duct, obturation which, in the case of a flow of powder, causes untimely local accumulations of powder, clogging or engorgement which can cause sudden and uncontrolled high loss of load in flow.

A pneumatic means, on the contrary, allows to modulate a mixing flow powder-gas in a fine and controlled manner and can be adjusted with very short response times short, with appropriate adjustment means, which can be manual or automated. These means, if chosen automated, can advantageously be part of a regulation loop, under control of a control unit connected to at least one means of measuring quality or thickness on the coating deposited on the substrate, using the dispensing nozzle. If it is a float glass ribbon, the regulation in the powder flow rates from secondary conduits can be carried out continuously, adjusting very quickly the flow of the appropriate secondary conduit (s) using their means tires as soon as a change in transverse thickness in the coating is detected deposited on the tape just downstream of the nozzle. Using, for example, preset charts indicating the correspondence between a given local thickness variation and a adjustment variation of the appropriate pneumatic means of the secondary duct concerned for rectify it, so we don't even need to measure the mixing rates precisely powder-gas of the conduits and their possible deviations, one can only carry out a correlation between the variations in thickness which are the consequence of these differences and the pneumatic means to be adjusted.

These pneumatic means can be presented simply in the form of auxiliary supply conduits opening into the secondary conduits, supplied auxiliaries which are advantageously provided with a manual regulation means or automated gas flow or pressure, using for example valves. Insofar where they only carry gas, this type of mechanical adjustment means does not problem. These feeds thus introduce into the flow of the powder-gas mixture secondary conduits a jet of gas whose characteristics are controlled in order to create there a controlled pressure drop then allowing the flow to be more or less reduced when this is necessary. Thanks to an appropriate distribution means, the quantity of powder which is no longer carried by the conduit due to this induced reduction in flow will be able to distribute homogeneously on all the other secondary conduits.

These secondary conduits can advantageously include pipes, preferably flexible, connected by means of distribution of the main supply duct, pipes whose ends opening out at the entrance to the nozzle cavity are constituted by rigid supply members called “injectors”, and preferably metallic. The means for supplying auxiliary gases can then lead into the secondary conduits at any point, either at the level of these (flexible) pipes, downstream means for distributing the main duct, either near or in the nozzle, in particular at the pipe-injector junction or at the injector itself. It is this latter configuration which is more favorable, because the rigid injector allows Easy and safe "connection" of the auxiliary gas supply.

A preferred embodiment of the invention thus consists of a device for distribution, where each of the secondary conduits intended to carry the suspensions powder-gas is fitted at its end with an injector, the injectors being regularly arranged in line in the inlet opening of the nozzle cavity over its entire length and all having an auxiliary gas supply with variable flow. In addition, the cavity of the nozzle is also provided with means for injecting pressurized gas to drive the powder-gas suspension emitted by the injectors in the cavity, means for injecting preferably arranged symmetrically on either side of the injector line. So, the powder supply of the nozzle is doubly optimized. We fix it first "At the source", thanks to the pneumatic means of the invention making it possible to eliminate or at the very least attenuate very significantly all the disparities in flow between the jets of powder-gas mixture emitted into the nozzle by the injectors. We then homogenize it, in the nozzle, thanks to pressurized gases which will “transform” the plurality of individualized mixing jets flowing in the nozzle in a "curtain" of uniform powder at the outlet of the transverse slot.

The invention also relates to the method for implementing the device. previously described, and in particular the various ways of controlling and regulating pneumatic means equipping the secondary conduits. When these pneumatic means are in the form of auxiliary gas inlets opening into the conduits, can thus adjust each of the auxiliary gas jet flow rates separately for each of them, and this in a range of flow rates which can range for example between 0 and 100% of a predetermined flow value. These jets of gas must indeed have an action of "Braking" of the flow of powder in the duct, in order to create a pressure drop there and not a depression which would cause an acceleration of the flow. Debits, speeds and directions of injection of these jets of auxiliary gas compared to those of the flow of powder-gas mixture must therefore be carefully selected.

A first possibility is to operate "all or nothing". If no disparity local duct flow rates, resulting in a local variation in thickness of the coating, is detected, the flow rate of these auxiliary gas jets is zero. If a disparity appears, locally causing excess thickness in the coating, the means pneumatic of the secondary duct (s) involved intervenes to deliver a jet of auxiliary gas of suitable flow rate which cannot exceed a certain value, in order to decrease the powder flow rate of the duct (s) sufficiently to eliminate this excess thickness.

A second possibility is to permanently operate all of the pneumatic means, which all emit, when no disparity is detected, a jet of auxiliary gas of given flow. They therefore all exert a certain “braking” effect. permanent on the powder-gas mixture flows in the conduits, which can be compensate if necessary by adapting the flow rate of powder-gas mixture in the main supply duct. It is thus possible to regulate the flow rate of the gas jets auxiliary around this given flow value. This operating mode is more flexible and leaves more room for maneuver, since we can also correct local coating thicknesses (by increasing the gas jet emission rate suitable auxiliary) than local decreases in thickness of said coating (in this time decreasing the emission rate of the appropriate auxiliary gas jet).

In this operating mode, it is advantageous that the flow value around which regulates the flow rate of each of the auxiliary gas jets is approximately 20 to 60% of the average gas flow rate of the powder-gas suspension carried by each of the conduits secondary. Preferably, a value of around 50% is chosen, with regulation of the flow rate of each of the auxiliary gas jets of ± 50% around this value. We hear by "average" flow, their theoretical flow, if no disparity of flow between conduits could to exist.

As previously mentioned, the simplest and most effective is to regulate these auxiliary gas jet flow rates not as a function of the quantitatively evaluated differences between the flow rates of the secondary conduits, which would be difficult to do, but directly in as a function of the thickness variations detected in the coating “downstream” from the nozzle distribution. This corrects the flow differences indirectly.

The device and method for implementing the latter can be advantageously used in view of depositing coatings based on metal oxide, by pyrolysis on a strip of hot float glass, in particular coatings of doped oxides of SnO ₂ type: F, for example from a powder of dibutyltin difluoride (DBTF) or of the ITO type from powder of indium formate and tin dibutyloxide.

• figure 1 : une vue schématique d'ensemble d'une installation de dépôt d'un revêtement par pyrolyse de poudre sur un substrat,
• figure 2 : une vue en coupe transversale de la buse de distribution de l'installation selon la figure 1.

The details and advantageous characteristics of the dispensing device according to the invention will now emerge from a nonlimiting embodiment illustrated with the aid of the following figures:

• FIG. 1: an overall schematic view of an installation for depositing a coating by powder pyrolysis on a substrate,
• FIG. 2: a cross-sectional view of the dispensing nozzle of the installation according to FIG. 1.

The installation as shown as a whole in FIG. 1 makes it possible to distribute regularly powdery solids of all kinds on various substrates, especially large dimensions. In the context of this nonlimiting example, it is used to distribute a powder of organo-metallic compounds on a ribbon 1 of float glass hot out of the floating bath enclosure, ribbon running on a bed of rollers 2 according to a given axis at a uniform speed. The powder thus brought into contact with the glass surface hot decomposes there to leave a coating based on metal oxide (s).

This installation is an optimization of that described in the European patent EP-B-0 130 919 cited above insofar as it additionally includes pneumatic means 22 specific to the present invention.

The nozzle 24 of the installation shown in FIG. 2 is likewise a optimization of that described in patent EP-0 374 023. The following is to describe more particularly the characteristics relating specifically to the invention. For more of information concerning the operation of the installation in general and of the nozzle in particular, one will therefore advantageously relate to these two patents, as well as to other previously cited patents.

The installation according to FIG. 1 therefore represents a hopper 3 for storing powder 4 to be dispensed, a mixer 5 in which the powder-gas mixture is produced, generally of air in order to constitute a suspension as homogeneous as possible of the powder in the gas using an air inlet 25 and a worm screw 26 supplied with powder by the hopper 3. A main intake duct 6 conveys the powder-gas suspension at the outlet of the mixer 5, a distribution means 7 subdividing the single stream of powder-gas suspension brought through line 6 into a plurality of secondary veins as uniform as possible, a plurality of flexible secondary conduits 8 conveying these up to the dispensing nozzle 24. This nozzle is arranged transversely to the axis of travel of the glass ribbon 2 and defines a transverse cavity whose length corresponds to the width tape to be coated. The secondary conduits 8 open into metal injectors 9 arranged in line at the entrance of this cavity.

If we refer to Figure 2, we actually see one of these injectors 9 coming project a gas-powder mixture stream at the inlet 10 of the cavity 11 defined by the walls 12 interior of the nozzle, flat walls and slightly convergent to the slot of distribution 13 located a few millimeters from the surface of the glass ribbon 1. Means pressure gas injection pipes are also provided on either side of the line of injectors 9, in order to facilitate the “curtain” distribution of powder and the training of the jets of powder-gas suspension from the injectors 9. These means are formed by a series of chambers 14 located symmetrically in the nozzle body and connected by a ramp 15 to a source of gas, air in general. These rooms are interconnected by a partition 16 forming a spacer, provided with a gas passage means for example using porous materials and through orifices 17. The chambers 18 located in the upper part of the nozzle open into the cavity 11 through slots 19 near the injectors 9, so as to inject the gas under pressure substantially parallel to the walls 12, slots limited by lips 20, of suitable configuration.

According to the invention, each of the injectors 9 consists schematically of a hollow metal cylinder into which each of the secondary conduits 8 of waterproof way. These injectors further include an air type gas inlet under form of an auxiliary conduit 22 coming into it, preferably with a configuration such between injector 9 and line 22 that the jet of powder-gas mixture in the injector and the gas jet that can emit the conduit 22 in the injector 9 make an angle between them a between 5 and 90 °, preferably around 30 °. It is indeed preferable that this angle remains below 90 ° to avoid any risk of traces of powder seeping into the conduit 22, traces which can in particular disrupt the proper functioning of the means of flow adjustment that equip it. Each auxiliary conduit 22 is supplied by a source of suitable gas not shown.

We can modulate the gas jet flow conveyed by each of the conduits 22 in the powder-gas flow of each of the injectors, individually, using regulation loop. Each of the conduits connected to a source of gas, in particular air, external to the nozzle, is provided with a flow control means of the solenoid valve type. This means of adjustment (for example of the flow meter type associated with a magnetic valve) is controlled by a control unit according to the thickness variations detected in downstream of the nozzle on the coating 23. This detection can be carried out continuously or by time interval given using one or more thickness measurement means of the type reflectometers (a reflectometer mounted mobile above the glass ribbon in order to "Sweep" the width of the coating, ie several reflectometers arranged in line above ribbon.

The mode of operation of the nozzle 24 is explained with the aid of an implementation example, consisting in depositing a layer of SnO ₂ : F 200 nm thick from a tin dibutyldifluoride powder. (DBTF). The mass flow rate of DBTF powder conveyed in the main supply conduit 6 is between 3 and 10 kg / hour / linear meter of nozzle. The volume flow rate of the gas in which it is suspended is between 3 and 80 m ³ / hour / linear meter of nozzle. The flow of pressurized gas injected through the slots 19 into the cavity is between 200 and 500 m ³ / h / linear meter of nozzle.

If the distribution means 7 and the design of the conduits 6 and 8 were perfect, each secondary duct would carry a gaseous vein whose mass flow rates D.B.T.F. and gas volume would be exactly equal to the ratio of those of the suspension conveyed in the main supply duct on the number of ducts secondary. However it turns out that differences in flow can appear between the jets of powder-gas mixture from each of the injectors 9, deviations leading to extra thicknesses or on the contrary local decreases in the thickness of coating deposited compared to the average thickness of 200 nm sought. These transverse variations in thickness of the coating are detrimental to its quality, because they can, in particular, cause optical defects, of the iridescent type, unattractive.

In normal operation, in the absence of detection by the reflectometer (s) of a local variation in coating thickness exceeding a given tolerance threshold, for example not more than 3% deviation from the desired average thickness of 200 nm, a powder-gas flow from the secondary conduit 8 is continuously passing through each of the injectors 9, presenting a gas flow rate of approximately 2 m ³ / h and a gas jet emitted by the auxiliary conduit 22 d ' a given gas volume flow rate, in particular around 1 m ³ / h.

As soon as a reflectometer detects a local reduction in thickness crossing the predefined threshold of 3%, the control unit controls the valve of the line (s) 22 of the injectors 9 concerned to reduce the flow rate of the auxiliary gas jet . In the case where it is an additional thickness, it will then on the contrary be necessary to increase this flow rate. Thus, starting from an average value of 1 m ³ / h, the flow rate of each of the auxiliary gas jets can vary between for example 0.5 and 1.5 m ³ / h. The more the auxiliary gas jet flow increases, the more it will decrease that of the powder-gas flow, and therefore locally decrease the thickness of the coating deposited. The control unit (or the operator) can use charts giving direct correspondences between variation in thickness in the coating and variation in flow rate in conduits 22, without even having to measure precisely the flow rates of powder passing in the conduits 8 then the injectors 9.

Note that it is important that these auxiliary gas jets, in view of the envisaged flow rates and diameters of the conduits 22, maintain a sufficiently low speed by compared to that of the powder-gas flow in the injectors 9 to avoid creating a aspiration which would brutally drive it instead of modulating the flow.

Any irregularity in the thickness of the coating can thus be quickly corrected, remotely, manually, automatically or semi-automatically. The regulation flow rate of the powder-gas suspension coming from each of the conduits secondary 8 is carried out by the auxiliary gas jet of each of the conduits 22, without any clogged or clogged secondary duct problem or detrimental impact on the supply of the other secondary conduits. Thus, if, thanks to the adjustment of the gas jet auxiliary the powder flow in the secondary duct 8 adhoc is reduced to rectify an excess thickness in the coating, the “excess powder” not delivered by the conduit of which we reduced the flow will be distributed regularly on all the other conduits at the level means of distribution.

Furthermore, it appears from the preceding description that the mode of supply of powder uses the pneumatic means of the invention to improve uniformity in the thickness of the coating deposited. But we could just as well, without leaving the framework of the invention, use these pneumatic means to create, this time so voluntary and controlled, gradients in the thickness of the coating deposited, at all less transversely to the axis of travel of the substrate, if this proved useful or advantageous to manufacture coatings having such characteristics.

Claims (13)

1. Device for the distribution of pulverulent solid suspended in a gas for the deposition of a coating (23), particularly by pyrolysis, on a moving substrate, more particularly a float glass ribbon (1), said device comprising a distributing nozzle (24), whose walls (12) define a cavity (11) terminated by a longitudinal distribution slot (13), and a system for supplying powder to said nozzle having a main, powder supply pipe (6) equipped with an apportioning means (7) and a plurality of secondary, powder supply pipes (8) connected to said main pipe with the aid of said apportioning means and making it possible to supply powder to the cavity (11) over the entire length thereof, characterized in that at least part of the secondary pipes (8) is equipped with at least one pneumatic means (22) able to modulate the powder-gas suspension flow rate to be transported by each of the secondary pipes in question.
2. Device according to claim 1, characterized in that the pneumatic means is able to produce a pressure drop controlled by manual or automated regulating means of said pneumatic means.
3. Device according to claim 2, characterized in that the regulating means of the pneumatic means form part of a regulating loop, under the control of a control unit connected to at least one means for measuring the quality or thickness of the coating deposited on the substrate.
4. Device according to one of the preceding claims, characterized in that the pneumatic means equipping the secondary pipes (8) has at least one auxiliary gas supply pipe (22) issuing into each of said pipes.
5. Device according to claim 4, characterized in that each auxiliary gas supply pipe (22) is equipped with a means for regulating the gas flow rate or pressure.
6. Device according to one of the preceding claims, characterized in that the secondary pipes (8) incorporate preferably flexible ducts, whose ends issuing at the intake of the cavity of the nozzle are constituted by rigid injectors (9), particularly metallic injectors.
7. Device according to claim 6, characterized in that the pneumatic means incorporate auxiliary gas inlets (22) issuing into the secondary pipes (8) at any point of the duct or at the level of the duct-injector junction or at the level of the injector (9).
8. Device according to one of the preceding claims, characterized in that each of the secondary pipes (8) for transporting the powder-gas suspension is equipped at its end with an injector (9), the injectors of the pipes being regularly arranged in line in the intake orifice of the nozzle cavity (11) over the entire length thereof and all are provided with an auxiliary gas intake (22) having a variable gas flow rate and in that the cavity (11) of the nozzle (24) is also equipped with pressurized gas injection means (19) for transporting the powder-gas suspension discharged by the injectors (9), the injection means preferably being arranged symmetrically on either side of the line of injectors.
9. Process for using the device according to one of the preceding claims, characterized in that the pneumatic means introduce a gas jet into each of the secondary pipes (8) and in that the flow rate of each of the jets is regulated separately and said rate can assume any value between 0 and 100% of a given flow rate.
10. Process according to claim 9, characterized in that the pneumatic means permanently discharge a gas jet, whereof the flow rate is regulated around a given flow rate value.
11. Process according to claim 10, characterized in that the flow rate value around which the flow rate of each of the gas jets discharged by the pneumatic means is regulated is approximately 20 to 60%, particularly 50% of the mean gas flow rate of the powder-air suspension transported by each secondary pipe (8).
12. Process according to one of the claims 9 to 11, characterized in that the flow rate value for each of the jets discharged by the pneumatic means is regulated as a function of thickness variations detected in the coating (23) deposited downstream of the distributing nozzle (24).
13. Use of the device according to one of the claims 1 to 8 or the process according to one of the claims 9 to 12 for depositing metal oxide coatings (23) by pyrolysis on a hot float glass ribbon (1), particularly doped oxide coatings of the SnO₂:F type, based on dibutyl tin difluoride powder, or of the ITO type based on tin dibutyl oxide and indium formate powder.

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