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217293 <br><br>
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No.. Date: <br><br>
Priority Date's): <br><br>
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Complete Specification F.ted- . • Cass: CP5&55/.«H^?. <br><br>
. nt 3 OMAR 1953.... <br><br>
Publication Date i <br><br>
P.O. Journal, No: •.. • * ;NEW ZEALAND ;PATENTS ACT. 1953 ;COMPLETE SPECIFICATION ;\ 20 AUG 1986 ;DEVICE FOR GRIPPING AND TRANSFERRING SHEETS OF GLASS AFTER THEY ;u. ;HAVE BEEN HEAT TEMPERED ;o ;1/We. SAIOT-GOBAIN VITRAGE, a French company of Les Miroirs, 18, Avenue d'Alsace, 92400 Courbevoie, France hereby declare the invention for which ( / we pray that a patent may be granted to me/us, and the method by which it is to be performed, ;to be particularly described in and by the following statement:- ;- 1 - ;I ;(followed by page la) ;N—I ;217293 ;- la - ;DEVICE FOR GRIPPING AND TRANSFERRING SHEETS OF GLASS AFTER THEY HAVE BEEN HEAT TEMPERED ;The invention relates to the manufacture of sheets of curved and tempered glass, used particularly in motor vehicles as windscreens, side windows, rear windows or even as opening roof lights. More precisely, the invention relates to a device for gripping tempered sheets of glass, removing them from a tempering frame and transferring them to a cooling station. ;It is known to manufacture such motor vehicle window elements in line-based plants comprising in succession a horizontal heating furnace, a glass bending cell and an apparatus for tempering on a frame sheets which have already been bent. In such installations, known for instance from Patent Specification EPO 003 391 (available on request), the sheets of glass are charged into the furnace one by one and are conveyed through it. for instance on a bed of rollers which extends as far as the bending cell. In this latter, the sheet of glass, which is heated beyond its softening point, is raised above the conveyor and then bent to shape. As described hereinafter, the bent sheet is then deposited on a frame and routed to a tempering apparatus. ;Such tempering and forming installations are widely used, because in particular they make for high rates of output, while respecting the visual qualities demanded by motor vehicle manufacturers. As the other treatment stations are close by, the passage from one station to another is carried out with a minimum of heat loss. Moreover, these line-based installations provide for a high rate of output with a low level of tooling; for —s instance, one frame or at most one pair of frames, is used for a series of v—' windows. ;To ensure a high rate of output, the time the sheets of glass spend in the various treatment cells and particularly the tempering chamber is reduced to the minimum. Well, although the stresses created in the glass —- are finally established only after complete cooling to room temperature, ;^ it is established experimentally that when the temperature of the glass falls below 300°C, the risk of the glass breaking when handled is very small. ;hXPATEHTOfflCa ;I 27 OCT 1937 ;217293 ;therefore one chooses to discontinue the blowing of cooling medium as soon as the temperature of the glass is around 300°C, which makes it possible more quickly to clear the tempering station. However, the glass has to undergo a secondary cooling stage until it reaches ambient temperature before undergoing any further operations and it must be monitored. ;The cooling of the glass down to ambient temperature, generally carried out in free air. takes a certain time which is in particular a function of the temperature of the piece of glass immediately after tempering and the thickness of the glass. Ordinarily, the period of secondary cooling is never less than a few minutes. Well, with forming and tempering units such as those previously mentioned, the rate of output attained is of the order of only 3 to u pieces of glass per minute. From ■—n the evidence, it is not possible to let the tempered and curved sheet of glass cool on the tempering frame unless one uses a large number of tempering frames, which on the one hand increases the number of regulating and servicing units and on the other singularly complicates the mechanics of the frame conveying apparatus. What is more, this situation would be highly paradoxical if one were to bear in mind the fact that the horizontal heating furnaces through which the sheets of glass are conveyed on a roller bed until they reach their softening point have been properly developed to reduce tooling and particularly the number of bending and tempering frames required. ;It is necessary therefore to remove every curved and tempered sheet of glass from its frame as soon as tempering is completed and to transfer the sheet to a conveyor for secondary cooling, the length and speed of which are such that the tempered and curved sheet is completely cooled when it reaches the end. This operation requires means of transferring ;L » ;pieces of glass at averagely high temperature and capable of moving the glass from the tempering frame and depositing it on the secondary cooling conveyor. ;The simplest solution is to have unloading carried out manually by several workers provided with the individual protective gear rendered necessary by the temperature of the glass. These workers are compelled to perform repetitive and, due to the noise level, tiring tasks resulting from the presence of the blowing apparatus in the tempering unit. Furthermore such manual unloading does not really go hand-in-hand with an ™rwise totally automated production unit. ;27 ocrm? ;217293 ;- 3 - ;Financial considerations are likewise against the transfer means used for handling flat and cold sheets of glass, particularly the suction cup devices used in stacking and unstacking machines. Indeed, the conventional rubber suction cups deteriorate very quickly at the temperatures involved here, necessitating their frequent replacement and a risk of dirtying the glass. It is therefore necessary to resort to suction cups made from new. ultra-resistant materials, the prime cost of which would be too high. ;A solution to the technical problem of quickly and economically removing the sheet of tempered and curved glass from the tempering frame is provided by Patent specification EP 0 003 391 (available on request}. According to its teachings, the tempering frame carrying the curved and tempered sheet is carried over a subpositioned blowing means. The sheet is raised abruptly by the gas. the amount by which it rises being limited by upper supports. When the sheet of glass is in the raised position, the tempering frame is freed and can return to the forming cell to pick up the next sheet. At the same time, a removing frame is positioned underneath the first sheet which drops down onto it as soon as the blowing is discontinued. ;In this way, unloading is very fast, but it does have its drawbacks. First of all, the two sides of the glass are not identically cooled. Furthermore, as the sheet is not supported laterally while it is being raised nor while it is in the raised position, it does have a tendency to slip directly the blower gases fail to support in a perfectly symmetrical way the various points on the underside, that is to say directly the sheet of glass has been asymmetrically bent. This risk of slipping leads to uncertainty as to the position of the sheet and its recovery. Finally, ;this blowing action has to penetrate substantial amounts of cold air inside the forming cell because when the tempering frame enters the cell, the blowing operation is still in progress. ;PA7iarrt>F!303 ;' 27 CCT.W : ;RECeVED ;The object of the present invention is a novel device which does not suffer from the aforementioned drawbacks and which makes it possible very quickly to withdraw the sheets of glass from the tempering frame »i;d then convey them to a cooling station. ;According to the invention, the tempered and profiled glass sheet is raised above the tempering frame by a negative pressure created on the upper surface of the glass, said gripping device essentially comprising suction means connected to a suction chamber having a rigid metal bottom against which the sheet of glass can bear. The bottom consists of a preferably flat or even slightly convex stainless steel plate, facilitating gripping of the glass sheets which feature pronounced curvature. ;After takeover of the sheet of glass, the chamber is raised to permit removal of the tempering frame. The glass can then be conveyed to a secondary cooling station. " " ;According to one form of embodiment, the bottom is not perforated but in its dimensions is slightly smaller than the chamber which allows the indrawn air to pass around the periphery of the bottom. ;Other characteristic features and advantages of the invention are described in the ensuing detailed description in which reference is made to the accompanying drawings, in which: ;Fig. 1 is a general perspective view of a forming and tempering unit for the production of motor vehicle windows and comprising a device for removing the sheets of glass once they have been tempered. ;Figs. 2a and 2b show two embodiments of a gripping and transfer device according to the invention. ;Fig. 1 is a perspective view of a unit for forming and tempering motor icle windows, such as rear windows, side windows, opening roofs and also ;"i'it J. ;-5- ;o tempered windscreens. This unit comprises, from left to right, a furnace charging unit 1 in which the sheets of glass are deposited one by one on a conveyor 2, preferably consisting of a roller bed. The charging unit shown here does not comprise automatic loading means but such means, for instance those described in published Patent specification US 4634329, can of course be used to improve the rate at which the furnace is loaded. The conveyor 2 extends into the furnace 3. ;Such a horizontal so-called tunnel furnace 3 makes it possible progressively to heat the sheets of glass beyond their softening point, that is to say up to a temperature such that the sheet is sufficiently soft to be bent. Heating Is provided by electrical resistors carried in the floor and roof of the furnace. No tools other than the conveyor 2 are used. The sheet of glass is simply carried on the bed of rollers 2 which extends into a forming cell 4. This latter is likewise provided with heating elements such as electrical resistors which make it possible to maintain the temperature of the glass equal to the temperature at the outlet from the furnace, in other words generally around 650°C. The forming cell 4 comprises a bending device, for instance of the type described in published Patent Specification GB 1254410. The sheet of glass is thus raised above the roller bed, matches a shape which is above it by being applied against it so that the glass becomes bent to shape, after which it is carried to the raised position and is recovered by a tempering frame which assumes a position underneath, and then carries the profiled glass sheet to the tempering station 5. The tempering station 5 comprises in known manner two mutually facing blower chambers 6, 7, each of which comprises a series of blower jets aimed at the glass, through which jets of cold gas are passed at high pressure. Thus, the sheet of glass is cooled ;-5FEB19B8*!) <br><br>
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very abruptly, its two faces becoming superficially solidified simultaneously, that is to say reaching the glass solidification point, which in the case of the glass compositions generally used is close to 550°C, and before the cores of the glass attains that temperature. Therefore, the surface is subjected to compression stresses and the core of the glass to extension stresses. When the glass reaches a temperature close to 300°C, these stresses are for the most part established. Therefore, the blowing of cold gases is discontinued in order to free the tempering frame which can go to pick up the next sheet of glass which is-already in the forming cell, isolated from the tempering station by a sliding door in order to prevent the blowing part of the tempering operation causing any cooling of the subsequent sheet before it is bent to shape. To avoid any slowing of the output rate and to stop the glass sheets staying too long in forming cell, it is essential to clear the tempering frame very quickly so that it can collect the next sheet of glass for a fresh cycle"! " <br><br>
However, at the exit from the tempering chamber, the glass is still at a temperature close to 300°C. this temperature depending more precisely on the thickness of the glass and the intensity of the cooling operation. The glass must therefore undergo secondary cooling in order perfectly to stabilise the stress situation. For this, the glass is conveyed to a secondary cooling s"~/ station, but in view of the fact that it is still at a high temperature, it cannot be handled with the tools normally used for handling cold glass. This all the more so since the tools are above all designed for handling flat sheets of glass whereas here the glass to be moved may be considerably bent. <br><br>
According to the invention, removal of the curved sheet of glass from the tempering frame and its transfer to a secondary cooling station 8 are carried ^out by the gripping and transfer means 9 described more precisely with the help rigs. 2a and 2b. <br><br>
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The device for gripping and transferring tempered and curved sheets of glass and shown in Fig. 2 in a cross-sectional view comprises a suction chamber 10 communicating with suction means 11, for instance of the Bertin horn type, <br><br>
or better still a type based on a fan and a bottom 12, preferably of stainless " > steel. The bottom 12 is provided with a series of perforations 13 through which the indrawn air can pass. <br><br>
As soon as a tempering frame 14 carrying a profiled and tempered sheet of glass IS is located underneath the transferring and gripping means lowered by raising-and-lowering mains into the immediate vicinity of the glass, the sheet of glass 15 is attracted by suction and applied against the bottom 12. <br><br>
Preferably, the bottom is covered with a woven material, possibly of refractory fibres, for a more gentle contact between the glass and the bottom, avoiding any surface defects. <br><br>
To allow rapid withdrawal of the tempering frame 14 as soon as the sheet "' of glass 15 has been taken over by the chamber, the suction chamber 10 consists of a bellows made from reinforced plastics material. In this way, as soon as the glass comes in contact with the bottom 12, as shown here, the chamber has its lower part completely closed off and the suction produces a contraction of the bellows, preferably limited by abutments, and consequently the raising of the glass sheet. For sheets with minor concavities, the chamber at rest may be placed sufficiently close to the glass that one can dispense with j raising-lowering means. • <br><br>
Another alternative embodiment of gripping and transfer device according to the invention is shown in Fig. 2b. In this case, the chamber 16 is closed r <br><br>
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The plate 17 is of dimensions which are slightly smaller than those of the chamber and of the sheet of glass which has to be raised, a fact which allows air to pass between the chamber 16 and the plate 17, as indicated by the arrows 18. Here, the glass is lifted by the negative pressure created at its ^ periphery. <br><br>
If the installation turns out glass sheets of different types, then the respective dimensions of the chamber and its shape will be chosen according to those of the glass element which has the smallest surface area, which makes it possible co have standard tooling. The bottom 12 and the plate 17 are slightly convex in the embodiment described, which facilitates the gripping of glazing elements having a quite pronounced curvature. The radius of curvature of the bottom is preferably greater than that of the glass and must therefore be chosen as a function of the overall outline of the least curved glass element which the plant produces. For glass sheets which are slightly concave, it is advantageous to work with a flat bottom or plate. <br><br>
The vertical walls of the chamber 16 consist of metal plates, in which case the gripping and transfer device comprises means to ensure the raising and lowering of the suction chamber. However, it is also possible to construct a chamber 16 which consists of a reinforced plastics bellows unit. <br><br>
It should be noted that whatever embodiment of gripping and transfer means according to the invention is involved, the suction effect is virtually instantaneous. In practice, the duration does not exceed 1.5 seconds and is perfectly compatible with the forming and tempering rate. <br><br>
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As an indication, for a 3mm glass sheet, the rate achieved is of the order of 4 panes per minute, the sheet remaining in the forming cell for about 10 -.-.—seconds and in the tempering station for about 6 seconds, which makes it <br><br>
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possible to lower its temperature to around 300°C. <br><br>
The gripping device according to the invention makes it possible to stop the cooling blowing at the end of the 6 seconds required for tempering and to iimiobilise a frame for only 1.5 seconds for removal of glass. <br><br>
With regard to the transfer of the glass after it has been gripped and in particular after it has been set down on a secondary cooling conveyor, the gripping and transfer device according to the invention is advantageously provided with supplementary translatory and/or rotating means for imparting to it varying degrees of freedom of movement. In this way, it is possible to feed various secondary cooling conveyors in accordance with a specific programme or as dictated by supervisory personnel for example. <br><br>
Thus, according to the invention, gripping of a sheet of glass which is resting on a tempering frame and which has a high surface temperature and transferring it to a secondary cooling station are performed by a very simple " device which calls for no adaptation of the other apparatus but which permits of a high degree of automation of the tempering-bending line. <br><br></p>
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