DE202004021819U1 - Device for producing units for the production of flat screens u. like. - Google Patents

Abstract

Device for the production of two glass panels which are connected to one another via a connecting medium, in particular a glass frit and have an intermediate space, for the production of flat screens, flat discharge lamps and the like. Like. With facilities for performing the following steps: a. Applying the connecting medium to at least one glass panel, at least partially curing the connecting medium and forming a border which varies in height from the connecting medium; b. Placing the other glass panel on the border, forming a natural interrupted gap and mechanically fastening the two glass panels together; c. Preheating the formed unit to a first temperature; d. Evacuating the intermediate space while the unit is heated further to the temperature of the connecting medium required for the connection through the naturally interrupted gap and thus gas-tight connection of the glass panels; and e. Cool the unit down to room temperature and loosen the mechanical attachment if necessary.

Description

The present invention relates to an apparatus for producing from two via a connecting medium, in particular a glass frit interconnected glass panels having a gap, existing units for the production of flat screens, flat discharge lamps u. like.

It is known to produce such units by gluing two glass panels together with a glass frit under normal pressure and air. As a glass frit here usually a lead dioxide glass is used. For gluing, the glass frit is heated until it reaches a molten state. During melting and subsequent hardening, outgassing takes place, whereby, inter alia, oxygen is formed which collects in the intermediate space between the two glass panels.

The gap formed between the glass panels must then be evacuated to fill it with a process gas, which is usually a noble gas mixture, such as a neon / xenon mixture. The evacuation must be carried out very carefully, since no gas contaminants may remain, which may affect the operation of the flat screen, etc. manufactured. For evacuation, a so-called exhaust tube is attached to a glass panel, which encloses a hole provided in the glass panel. The exhaust tube is connected to a conduit through which the space between the two glass panels is evacuated, whereby the frit gas that has entered into the interspace is also removed. As mentioned, this evacuation must be done very carefully and therefore usually takes about 4-10 h. After filling with the process gas attached to the exhaust tube glass tube is melted, so that a characteristic nipple remains on the product.

This known method has the disadvantage that it takes a very long time, since the evacuation can be done only over the small cross section of the bore and the exhaust tube. Furthermore, there is the danger in this method that despite the long-lasting evacuation by the outgassing of the glass frit formed gaseous impurities remain in the space, so that no error-free product is formed. Finally, the energy costs are high in this known method, since the evacuation is carried out for a relatively long time in a chamber furnace under heating to achieve an acceleration of the evacuation.

The present invention has for its object to provide a device of the type specified, with which the units can be made particularly quickly and safely.

• a. Aufbringen des Verbindungsmediums auf mindestens ein Glaspaneel, zumindest teilweises Aushärten desselben und Bilden einer in der Höhe variierenden Umrandung aus dem Verbindungsmedium;
• b. Auflegen des anderen Glaspaneels auf die Umrandung unter Ausbildung eines natürlichen unterbrochenen Spaltes und mechanisches Aneinanderbefestigen der beiden Glaspaneele;
• c. Vorerhitzen der gebildeten Einheit auf eine erste Temperatur;
• d. Evakuieren des Zwischenraumes während weiterem Erhitzen der Einheit auf die zur Verbindung notwendige Temperatur des Verbindungsmediums durch den natürlichen unterbrochenen Spalt und damit gasdichtes Verbinden der Glaspaneele; und
• e. Abkühlen der Einheit auf Raumtemperatur und ggf. Lösen der mechanischen Befestigung.

This object is achieved according to the invention by a device which has devices for carrying out the following steps:

• a. Applying the bonding medium to at least one glass panel, at least partially curing it, and forming a height varying border from the bonding medium;
• b. Placing the other glass panel on the border to form a natural broken gap and mechanically securing the two glass panels together;
• c. Preheating the formed unit to a first temperature;
• d. Evacuating the gap during further heating of the unit to the temperature required for the connection of the connection medium through the natural gap interrupted and thus gas-tight connection of the glass panels; and
• e. Cool the unit to room temperature and if necessary release the mechanical fastening.

The device described above and the invention is characterized over the prior art essentially in that is not evacuated via the relatively low cross-section having exhaust tube, but on the natural gap formed between glass frit and glass panel, so that the actual evacuation process substantially run faster than in the prior art. In this evacuation process, the gaseous contaminants formed by the outgassing of the bonding medium (the glass frit) are removed from the gap. The evacuation of the gap is carried out during further heating of the unit to the necessary connection temperature of the connecting medium through the natural gap interrupted until by reaching the bonding temperature (melting of the glass frit) both glass panels are connected (glued). It is to be assumed that the gaseous impurities formed by the outgassing of the connecting medium (the glass frit) have been completely removed with the space. To be on the safe side, one can switch before the subsequent filling of the gap with the process gas through the opening in the glass panel another evacuation step to remove said impurities, but this step can be handled relatively quickly.

In a further development of the device according to the invention, which ensures a particularly good removal of the gaseous impurities of the connection medium (the glass frit), the procedure is as follows:
During or prior to evacuation of the gap, the formed unit is heated to a second temperature that is below the bonding temperature of the bonding medium (glass frit temperature) and an equilibrium temperature at which the outgassing of the bonding medium (the glass frit) has substantially come to a standstill , This equilibrium temperature depends, in particular, on the bonding medium used (on the glass frit used), but also on the glass of the glass panels used, and must be determined empirically on a case-by-case basis.

Prior to subsequently heating the unit to the bonding temperature (glass frit melting temperature) to bond the panels, the space of the unit is then flooded with an inert gas to build up a partial pressure in the system which acts. that no further outgassing of the connecting medium (the glass frit) takes place. Such outgassing would be harmful because the resulting impurities would be trapped in the space and would have to be removed in a very expensive way again from this over the provided in the panel opening with a small cross-section. Anyway, further outgassing of the connecting medium is prevented by the introduced into the space inert gas, so that without substantial contamination of the gap of the connecting process (bonding process) of both panels can take place.

As the gas for flooding the gap, the process gas or a part of the process gas is preferably used, so that a subsequent removal of the inert gas used for flooding is no longer required, at least to the full extent. If, for example, a neon-xenon gas mixture is used as the process gas, neon is preferably used as the gas for flooding the intermediate space, which is relatively inexpensive. This neon is then later partially withdrawn and replaced by the desired xenon / neon mixture.

Since the flooding of the intermediate space takes place via the interrupted gap formed between glass frit and glass panel, this process takes place very rapidly, so that there is no significant delay in the process. The inert gas used for flooding is then enclosed by the bonding in the gap, wherein, as mentioned, due to the built-up in the intermediate space partial pressure no further outgassing of the connecting medium (the glass frit) takes place more. The introduction of the process gas in the exchange or partial replacement of the inert gas in the space then takes place either in the same or a separate process through an opening in a glass panel, which is opened to introduce the process gas and closed after completion of the introduction. After cooling, the mechanical attachment of the glass panels is released, so that a finished unit for the production of flat screens, flat discharge lamps u. Like. Is available.

In the device according to the invention, one or more chambers are used to carry out the respective method steps. Thus, the step of preheating the formed unit to a first temperature takes place in a chamber filled with air or inert gas. The step of evacuating the interspace of the unit preferably takes place in a next chamber, wherein evacuation is preferably to a negative pressure of about 10 ^-5 -10 ^-6 mbar. The subsequent further heating to the bonding temperature of the bonding medium (the melting temperature of the glass frit) while flowing with an inert gas is preferably carried out in another chamber. For filling with the process gas, the unit is preferably transferred again into another chamber.

With the device according to the invention, a significant gain in time is achieved over the known method, since the evacuation is not carried out over the relatively small cross-section of the opening provided in the panel, but over the interrupted gap between glass panel and glass frit. Further, since the gas used for flooding is introduced via this gap, this process also takes place very quickly. If the later used process gas is used for flooding, a later gas exchange is no longer required, so that the process is particularly rapid. In most cases, however, it will replace for economic reasons, at least part of the inert gas used for flooding by the process gas, so that only this replacement process must be performed on the provided in the panel opening with a small cross-section. For example, if the process gas consists of a neon-xenon mixture with a much higher proportion of neon, the relatively cheap neon is used for flooding and later only a small amount of neon replaced by the desired gas mixture to obtain the process gas. This procedure has the advantage that the expensive xenon does not have to be used to flood the gas chamber.

In addition, can be reduced with the device according to the invention of the Committee, since the likelihood of whereabouts of gaseous contaminants within the gap is particularly low. The evacuation step removes the outgassing of the bonding medium (glass frit) from the gap. This is preferably done until a state of equilibrium is reached and the compound medium no longer outgassed. In this state, all outgassing are thus removed from the intermediate space. By the subsequent flooding of the intermediate space with an inert gas, a further outgassing is prevented during bonding (bonding), so that no more gaseous impurities are trapped in the intermediate space. The process thus guarantees with great certainty a contamination-free intermediate space.

Further advantages of the device according to the invention arise in terms of energy costs, since the very long and energy-consuming heating cycles of the chamber furnace processes omitted.

As mentioned, the temperature to which the unit is heated before or during the evacuation of the gap (equilibrium temperature) depends on the glass panels used and the bonding medium used. The corresponding temperature is to be determined empirically. The lead oxide glasses commonly used as a glass frit are in a range of about 350 ° C-400 ° C, with a common value being about 390 ° C, that is, about 390 ° C. H. considerably below the sticking temperature of the glass frit.

After the bonding (bonding) of the unit (preferably at about 390 ° C), it is cooled to room temperature. If the gap has already been flooded with the process gas, a further process gas filling or gas exchange is no longer necessary. However, as mentioned above, this will usually be the case, so that the inert gas used for flooding is then preferably removed via the opening provided in a glass panel and replaced by the process gas mixture. The opening provided for this purpose in a glass panel was preferably closed during the preceding steps and is now opened to carry out this step. After completion of the filling process, the opening is permanently closed. The mechanical attachment (clamping device) used to put the two glass panels together can now or already be cooled to room temperature after the unit has cooled.

Since in the device according to the invention the opening provided in a glass panel is neither needed for evacuation nor for the inert gas to be flooded, the opening is kept closed during these method steps. This preferably ensues with the aid of a closed exhaust tube which covers such an opening. The exhaust tube is preferably affixed to the glass panel over the opening with a glass frit, particularly along with the application of the bonding medium (glass frit) to at least one glass panel to form the border and cure or bond the panels thereof. But he may also have been attached to the panel before the start of the process. For carrying out the method according to the invention, therefore, a glass panel is preferably provided with a glued-on exhaust tube for filling the intermediate space with the process gas. For gas pumping and / or filling the intermediate space of the unit, this, over the opening disposed to the opening facing the region closed pumping stem can be opened, namely at the provided in the exhaust tube predetermined breaking point by heating, mechanical stress and / or the The pulse exerted by the gas to be introduced is destroyed. After completion of the filling process with the process gas, the exhaust tube is closed by melting.

The device according to the invention can be used for the production of any units which consist of two glass panels interconnected by a glass frit, the interspace of which can be filled or filled with a gas (process gas). Such units are used, for example, for the production of flat screens, flat discharge lamps, backlights u. Like. Used. In any case, the invention covers all possible fields of application.

As mentioned, the exhaust tube is glued to the glass panel having the opening, preferably during the formation of the border. The closing of the exhaust tube is done by merging the same or the connected glass line, this is done in particular by a localized heating.

The bonding medium (the glass frit) for forming the border is preferably applied in a mountain and valley shape in order to achieve the natural discontinuous gap after the second glass panel has been stuck, which is used for evacuation and introduction of the gas used for flooding. This gap is formed by the respective spaces between the valleys of the border and the glass panel.

The device according to the invention has a device for heating, evacuating and cooling the unit and, according to a particular embodiment, a downstream station for evacuation and filling with process gas. The device is preferably designed as a furnace, which in the conveying direction a plurality of successively arranged and mutually sealed treatment chambers. The unit to be produced is successively passed through the respective treatment chambers and subjected to the appropriate treatments. In this case, the conveying means of the furnace on which the units are arranged and transported, not critical, so that various types of funding can be used. For example, these may be roles. It is essential, of course, that the funding is not affected by the various treatment steps (heating, evacuation, etc.).

In general, it is possible to work with a suitable device in a continuous or discontinuous manner. As a continuous furnace, a pass-through furnace is suitable. As a batch furnace, a chamber furnace, hood furnace, Hubherdofen, rotary kiln is suitable.

Several units to be treated can be stacked to form respective treatment packages. The treatment packages may then be treated continuously or discontinuously, for example in a special oven, which may comprise a plurality of shuttle kilns on which a retort (bell) is placed, in which a package to be treated of superimposed units is located. These shuttle kilns move in succession through a tunnel in which the corresponding heating and cooling steps are carried out. Each individual shuttle kiln is already provided with corresponding connections in order to be able to carry out the evacuation step and / or flooding step within the retort. Thus, evacuation and gas flooding within the retort occurs in this device, while heating and cooling occur indirectly within the tunnel through which the individual shuttle kilns pass.

The station downstream of the unit for heating, evacuating and cooling the unit preferably has an evacuating / filling device which is sealed against a glass panel of the unit and has a tubular body embracing the panel ovens or the exhaust tube and an evacuation port and a process gas port connected to communicate with the tubular body. This evacuating / filling device is used to evacuate the gap of the unit via the opening and the exhaust tube and to fill the gap with process gas. It preferably has a heater for heating the exhaust tube in order to destroy in this way the provided on the exhaust tube predetermined breaking point and thereby open the exhaust tube. This does not exclude that the opening of the exhaust tube can also be done in other ways, as indicated above.

As a bonding medium, a suitable glass frit is preferably used, as it is known for example from the prior art. The mentioned "bonding temperature" is the temperature necessary for bonding the glass panels (bonding temperature, melting temperature, etc.). The formed edge of the bonding medium is, for example, a closed strand of the glass frit, etc. It is essential that the glass panels are connected to one another in a gas-tight manner.

The interspace of the unit can be subjected to one or more rinses and then evacuated and filled with inert gas or process gas. This can be done as a pressure swing rinse.

As mentioned, the connection medium (the glass frit) can be applied in a mountain and valley shape to form the border, so that (after curing) the desired natural interrupted gap results. However, it is also possible to produce a desired gap by subsequent grinding of the hardened border.

It should also be added that quasi-continuously operating furnaces, for example stovepipe continuous furnaces, are suitable for the process according to the invention.

It is understood that the present invention with respect to the furnaces used for carrying out the invention corresponding loading and unloading, infeed and Ausschleuseeinrichtungen, gas circulation means, drive means for the pumped medium, etc. covers. The downstream station may further comprise an auxiliary heater for heating the glass panels.

The invention will now be explained in detail with reference to an embodiment in conjunction with the drawings. Show it:

1 a schematic longitudinal section through a continuous furnace;

2 a schematic cross section through the antechamber of the continuous furnace;

3 a schematic cross section through an evacuation chamber of the continuous furnace;

4 a schematic representation of the continuous furnace downstream station for evacuation and filling with process gas;

5 a vertical section through a part of the station for evacuation and filling on an enlarged scale; and

6 five vertical sectional views through various embodiments of exhaust stems, which are arranged on a glass panel.

In the 1 shown device comprises a device for heating, evacuation and cooling of the unit and a downstream station for evacuating and filling the unit with process gas. The device is as a continuous furnace 1 formed, which has a plurality of successively arranged and mutually sealed treatment chambers in the conveying direction. From left to right in the figure, the continuous furnace has a heating chamber 2 , three evacuation chambers 3 , a flooding chamber 4 , a Verkiebungskammer 5 , an atmospheric separation chamber 6 and a cooling chamber 7 , As a conveyor, the continuous furnace 1 a roller conveyor made up of a variety of rollers 8th composed and passes through all the chambers, wherein the respective inlet and outlet openings of the respective chamber are sealed against the surrounding atmosphere or with respect to the adjacent chamber. In 1 is shown as several units to be treated 9 on the rollers 8th move.

The units 9 can go through the continuous furnace continuously or discontinuously. The control of the running movement can be done via the roller drive of the individual chambers.

2 shows a cross section through the heating chamber or pre-chamber 2 , In the interior enclosed by the chamber walls 10 is a radiation and / or convection heating a suitable atmosphere for preheating the unit to be treated 9 generated.

3 shows a cross section through an evacuation chamber 3 , With the help of cables 11 is via a vacuum pump 12 in the interior 13 the chamber generates a suitable negative pressure to evacuate the unit located in the chamber.

The procedure is such that a suitable glass frit is applied to a glass panel and cured so that a variable in height glass frit ring is formed. On this glass frit ring another glass panel is placed so that an interrupted gap is formed between the glass frit ring and the second glass panel. Both glass panels are mechanically attached to each other and then into the in 1 introduced continuous furnace introduced. The educated unit 9 enters the heating chamber 2 of the furnace where it is preheated in an atmosphere of air or nitrogen, for example at a temperature between 250 ° C and 350 ° C. The preheating takes place over a suitable period. The preheated unit is then placed in the first evacuation chamber 3 introduced and evacuated, which takes place over the gap formed between the glass panel and frit ring. During evacuation, the unit is heated to 350-390 ° C (equilibrium temperature). At this temperature, no outgassing of the glass frit takes place more, but both glass panels are not yet glued together. The in 1 illustrated continuous furnace 1 has three evacuation chambers connected in series 3 , for example, evacuate the gap of the unit to 10 ^-5 mbar.

In the following downstream chamber 4 The space of the unit is flooded with a suitable inert gas, which may be, for example, a part of the gas mixture used later as a process gas. In the present case, a flooding with neon takes place. In the following bonding chamber 5 The unit is heated to the sticking temperature of the glass frit from 350 ° C-430 ° C, so that the actual bonding process takes place here. By previously filling the gap with the inert gas, further outgassing of the glass frit is suppressed.

The bonded unit then travels through a subsequent atmosphere separation chamber 6 and one of these subsequent cooling chambers 7 and then leave the in 1 shown continuous furnace.

The continuous furnace 1 Downstream is a station 15 for evacuating and filling the unit with process gas. The glued unit 9 enters the in 5 dotted position shown and is with a suitable clamping device 24 clamped. The clamping device can be raised and lowered, further formed pivotable, as shown. Furthermore, the station points 15 an evacuating / filling device 17 on, which is likewise raised and lowered as well as pivotally arranged and in 5 illustrated state against the upper panel of the unit 9 is pressed. The evacuation / filling device 17 , which is arranged, moreover, movable back and forth, is in detail in 5 shown. It has a tubular body 22 that of a heater 21 surrounded, which in turn by a suitable insulation 35 is protected. heater 21 and insulation 35 form an annular unit that forms the tubular body 22 surrounds and at the top and bottom of each a suitable water cooling 30 . 31 having corresponding sealing rings. Below the lower water cooling 30 There are one or more sealing rings 23 , about which the device on the upper glass panel 25 supports the unit to be treated. In 5 is the unit to be treated 9 shown schematically next to the upper glass panel 25 a lower glass panel 26 and the space to be filled with the process gas 27 having. In the upper glass panel 25 there is an opening 36 that from a pumping stem 28 surrounded by a glass frit 29 with the upper glass panel 25 is glued. The sticking of the exhaust tube 28 to the upper glass panel 25 can be done for example during the gluing of the two glass panels.

When the device 17 is placed on the unit, as in 5 shown, extends the exhaust tube 28 in the tubular body 22 , From the tubular body 22 , which is preferably made of glass, extends up a main line leading to a branching point, from the left to a terminal 19 for supplying a process gas, right a connection 20 leading to the vacuum pump, and up a port 21 lead to a sight glass. Corresponding valve devices, with which the respective terminals or connecting lines can be opened or locked, are not shown.

6 shows five different embodiments of the exhaust tube in vertical section. As already mentioned, this pumping stem is 28 provided with a predetermined breaking point, which is used to evacuate the gap 27 the unit is opened. This breaking point is in 6 With 40 and is formed by a thinner wall portion of the exhaust tube.

If a unit to be treated in the station 15 it passes through the clamping device 24 and the evacuating / filling device 17 clamped. The sealing rings 23 Make a tight connection between the interior of the pipe body 22 and the atmosphere. About the heater 21 now takes place heating the interior of the tubular body 22 to the glass of the exhaust hose 28 bring to melting temperature. As a result of the resulting differential pressure between the interior of the tubular body 22 and the interior of the exhaust tube 28 the breaking point is broken up 40 , so that now the gap 27 the unit 9 can be further evacuated by pressing the vacuum pump, not shown. After sufficient evacuation, the filling of the gap takes place 27 with the part of the still missing process gas. After the filling process is completed with the help of the heater 21 the pump stem closed by fusing the breaking point again. After proper cooling, the clamp can be released and the unit removed from the station.

Claims (23)

Apparatus for producing glass units which are interconnected by means of a connection medium, in particular a glass frit, and which have a gap, existing units for the production of flat screens, flat discharge lamps and the like; with the facilities for performing the following steps: a. Applying the bonding medium to at least one glass panel, at least partially curing the bonding medium and forming a height varying border from the bonding medium; b. Placing the other glass panel on the border to form a natural broken gap and mechanically securing the two glass panels together; c. Preheating the formed unit to a first temperature; d. Evacuating the gap during further heating of the unit to the temperature required for the connection of the connection medium through the natural gap interrupted and thus gas-tight connection of the glass panels; and e. Cool the unit to room temperature and if necessary release the mechanical fastening. Device according to claim 1 with means for carrying out the following further steps: f. Filling the gap with the process gas via an opening in a glass panel; and G. Close the panel opening and, if necessary, release the mechanical fastening. Apparatus according to claim 2, comprising means for obtaining, prior to step f. the space is evacuated through the opening in the glass panel. Device according to one of the preceding claims, in which a glass frit is used as the connecting medium. Device according to one of the preceding claims, having means with which the gap in step d. after or during further evacuation of the unit to a second temperature (equilibrium temperature) below the bonding temperature of the bonding medium, in particular melting temperature of the glass frit at which outgassing of the bonding medium has substantially ceased, is evacuated through the natural discontinuous gap and with an inert gas during or flooding to the bonding temperature of the bonding medium before further heating the unit. Apparatus according to claim 5, wherein the inert gas used is the process gas or a part thereof. Device according to one of the preceding claims, with devices with which the Gap of the formed unit before step d. evacuated and filled with inert gas. Device according to one of the preceding claims with means by which the intermediate space is subjected to one or more flushing operations with inert gas or process gas and then evacuated and filled with inert gas or process gas (pressure swing flushing). Devices according to one of the preceding claims, in which, for the gas removal and / or filling of the space of the unit with the process gas, a pump stem with a predetermined breaking point, which is arranged above the opening in a panel and faces the opening, is used, which by heating, mechanical Stress and / or impulsed by the gas to be introduced pulse is destroyed. Apparatus according to claim 9 with means by which the exhaust tube is glued to the glass panel having the opening. Apparatus according to claim 10, wherein the bonding of the exhaust tube during the formation of the border or connecting the glass panels takes place. Device according to one of claims 9-11, comprising means with which the exhaust tube is closed by fusing. Device according to one of the preceding claims, comprising means with which the connecting medium is applied to form the border mountain and valley. Device according to one of claims 1-13, characterized in that it comprises means for heating, evacuating and cooling the unit ( 9 ). Device according to claim 14, characterized in that it comprises a downstream station ( 15 ) for evacuation and filling with process gas. Apparatus according to claim 14 or 15, characterized in that the device is used as a furnace ( 1 ) is formed, in the conveying direction a plurality of successively arranged and mutually sealed treatment chambers ( 2 - 7 ) having. Apparatus according to claim 16, characterized in that the furnace ( 1 ) in the conveying direction at least one heating chamber ( 2 ), at least one evacuation chamber ( 3 ), at least one flooding chamber ( 4 ), at least one connecting chamber ( 5 ) and at least one cooling chamber ( 7 ) having. Device according to one of claims 14-17, characterized in that the furnace ( 1 ) is designed as a continuous furnace, in particular pass / pusher furnace. Device according to one of claims 14-17, characterized in that the furnace is designed as a discontinuously operating furnace, in particular chamber furnace, hood furnace, Hubherdofen, Drehringofen. Apparatus according to any one of claims 14-19, characterized in that the apparatus comprises a plurality of shuttle kilns on each of which a retort receiving one or more units to be treated is disposed, and a tunnel for heating and / or cooling which is from the shuttle kilns is passed through. Device according to one of Claims 15-20, characterized in that the downstream station ( 15 ) an evacuating / filling device ( 17 ), which in a sealed manner against a glass panel ( 25 ) the unit ( 9 ) is pressed and a the panel opening or the pump stem ( 28 ) encompassing tubular body ( 22 ) and an evacuation port ( 20 ) and a process gas connection ( 19 ) which is connected to the tubular body ( 22 ) keep in touch. Apparatus according to claim 21, characterized in that the evacuating / filling device ( 17 ) a heater ( 21 ) for heating the exhaust tube ( 28 ) owns. Device according to one of claims 15-23, characterized in that the downstream station has an additional heating for heating the glass panels.

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