SI9011125A - Procedure and device for cambering and hardening by contact - Google Patents

Abstract

The invention relates to the manufacture of automotive glass. According to the invention, the glass is preformed before being cast undergoes tempering by touch. In a preferred embodiment touch quenching only affects the center region of the glass (1) and the edge band is tempered by blowing cold air (40.41).

Description

SAINT-GOBAIN VITRAGE INTERNATIONAL

The process and preparation for touch bombing and tempering

The present invention relates to the bombing and tempering of glass panels, especially for the manufacture of glasses intended for e.g. for motor vehicles which must have a very high precision in shape and, in the case of refraction, fragmentation in accordance with safety standards and optical quality, which also meets the very demanding standards.

From patent application EP-A-277 074, e.g. known to simultaneously bombard and toughen glass panes previously heated above its plastic deformation temperature and brought between two cooling and compression plates whose outline corresponds to the curvature desired to be given to the glass plate. The glass panes are sandwiched between the panes until their temperature is low enough that their shape becomes permanent. Such a process is particularly preferred for small glasses, e.g. at least 3 mm thick, which is difficult to bring to a sufficiently high temperature after thermal bombardment; this is due to the speed of their cooling with air, as soon as the tiny glass panels leave the heating furnace.

The second reason for developing such methods of bombing and toughening by touch is because of the complete control of the curvature of the glass, mainly because of the reduction of defects called double-bombing, that is, unwanted curvatures, mainly because of the action of gravity when the glass panel is not supported at all points of its lower plot.

However, the inventors of the present invention have observed a slight deviation from the glass plate profile relative to the profile of the cooling and compression plates, the origin of which is partly due to incomplete loosening of the design stresses, and more specifically due to bending stresses. These bending stresses are greatest near the surfaces of the glass, that is, they are greatest at the places which are most rapidly cooled, and therefore are the shortest time during which the stress relaxation can be effected effectively. The absence of stress relaxation can locally cause stresses greater than the resistance of the glass and break the glass.

It is possible to extend this period during which this relaxation can be effected by treating glass panes whose temperature is initially higher and which, therefore, enter cooling with much higher intensity. However, due to the optical quality, there are limits to the initial warming of the glass panel. Indeed, when glass panes are transported flat on rollers - which is at the same time the simplest mode of transport, the most economical and largely least susceptible to marking or enamel contamination - the glass is too prone to drop between rollers, causing corrugated sheet metal defects , whose trace remains even after squeezing during the level of bombardment and tempering by touch.

Of course, it is practically impossible to prolong the formation phase by the process of touch-bombing and quenching, for example. it was a gradual bending of the bomber forms - this is because the time of the bombing is considered to the extent that the glass is simultaneously subjected to strong cooling with the cooling and compression plates. The use of material swabs that are suitable provides a solution to this problem, but uniformly if left to the standard compression speeds for touch hardening. In fact, if the design time allowed is too long, there will be refraction at the end of the design, because the glass is then too cold to withstand such a deformation. This limitation of the formation time causes a limitation of the acceptable curvatures to be awarded for this process. In addition, the absolute extension of the design phase reduces the cadence of the production line, which is always a disadvantage for industrial use.

On the other hand, there are numerous processes for making bombed and tempered glass, by which these two operations are carried out at different times and places, in particular the processes by which the glass panes are heated horizontally in a furnace, which is crossed by e.g. transported by means of a roller-driven conveyor and raised above the conveyor by mechanical or pneumatic means - in particular by suction or by blowing hot air - and pressed against a top element that is level or forms a bomb shape, and they are then dropped to the bottom element, e.g. a ring which is open at its center and guides the glass plate right up to the preparation for thermal quenching by blowing cold air with the help of quenching caissons. Depending on the case, the formation of the glass pane is performed exclusively on the lower element, partially or already definitively, when the glass is deposited on the lower element. Also known are methods that do not use the element below - or only for the bombing stage - and by which the transport of the glass bombardment is performed right up to the germination device on the top form, which is then movable, or on a conveyor derived from a rolling mill with possibly curved rollers. To these bombardment and tempering processes, the common feature of which is the use of the upper element and the vertical movement of the glass pane, it is necessary to add the bombardment processes whereby the glass pane is allowed to travel on a molding bed, e.g. consisting of curved bars or straight bars, which are arranged along a curved path. All of the above processes are well known in the art and can be found in patent documents US-A-3527589, EP-A-3391, EP-A-5306, FR-A-2085464, FRA-2312463, FR-A -2442219, FR-A-2549464, FR-A-2549465, FR-A-2554436, FR-A2567508, FR-A-2596750, FR-A-2596751.

These procedures allow very high cadences to be achieved even in glass forms that are relatively complex, but when systematically given to optical quality, it is practically impossible to achieve perfect outline consistency and, above all, to avoid the double-bombing error. It should be noted that the outline deviations are all the more sensitive as the thickness of the glass pane is smaller; this explains the increased interest in touch screening and quenching processes for fine glass.

The object of the present invention is primarily to improve the processes of touch and toughening by touch, so that, in conditions which are sufficiently industrial, glass can be obtained which can have all kinds of curvatures, especially those with small curvature radii, with very high precision in outline.

The solution to this proposed problem is provided by the invention and exists in the use of preforming in a hot ambient before the process of bombardment and tempering by touch is initiated. The hot ambient here is that preforming must be carried out under conditions such that the temperature of the glass panes is equal to their temperature of bombardment and tempering when brought between the cooling and compression plates.

Preferably, in all directions of the glass pane, the distance between the desired specific curvature for the glass pane and its initial curvature obtained by preforming at all points of the pane is less than 1 m '¹; recall that the curvature at a given point of the glass pane is by definition equal to the inverse radius of curvature at that point. In other words, whatever form is to be chosen, the operation of the bomber and the tempering by touch can be carried out at the same speed as the operation of the bombardment and tempering for a flat glass panel, which is given a curvature of at least one meter radius. The preforming is therefore intended to roughly approximate the final curvature, especially in places where small curvature radii are localized. This can be done in a very fast way without being overwhelmed by the possible formation of parasitic curvatures, which will be recovered during the compression phase of the bombardment and tempering operations with the touch, and care will be taken not to produce optical defects at all. during the preforming phase or during the transfer phase to the touch and toughening device.

This next phase of recovering a given curvature confers a very high degree of agility on the processes of the invention. If the difference between the curvatures remains smaller, e.g. of 1 m ' ¹ , it does not matter whether the glass pane loses some of the curvature conferred during preformation during transport, or gains additional curvature. Therefore, the transport can be carried out by means of an air cushion conveyor (which cannot cause optical defects), a roller conveyor which may be formed, or a metal carpet made with a flexible strip in the form of a metal fiber cloth. , which are heat resistant and have a heat transfer resistance perpendicular to the plane of the strip between 0.25 χ 10 ' ³ and 5 x 10 ³ m ² .KW ⁴ , said flexible strip extending between the glass plate and the lower compression plate, and cooling.

Replacing these conveyors can also directly use preform molding elements, be it a molding bed that gradually conveys curvature to the glass or any elements that are pressed against the glass plate, in particular male or female compression molds, full or composed of rings that are open at its center. In general, compression members associated with forces of mechanical or pneumatic nature are preferred according to the invention, as they are well suited to achieving small radii of curvature. Compression with rising hot air flow is particularly preferred, but suction compression may also be advantageous, that is, pressing the glass plate against the upper molded element by suction caused by e.g. near the perimeter of the glass pane or near the surface of said upper element.

Of all the above procedures, particular attention should be paid to those which, in the final stage of the bombardment, and thus preforming here, bring the glass plate to the annular support on which the edges of the glass plate rest. In this case, there is no danger of the center of the glass panel being marked - the center of the panel is usually the only visible part after mounting the glass on the vehicle. In addition, it is known that when the windows are coated with an enamel layer, the side is less exposed to the weather, less exposed to the weather; in other words, the enamels - which, when molten in part in the molten state, are highly exposed to the risk of contamination - are on the concave side of the glass and not on its convex side resting on the annular support. Otherwise, this annular frame can be very well used to transport glass panes from preforming apparatus to touch and toughening apparatus, as is known in the thermal quenching processes of cold air blowers, all the more so in the particular case of the invention that gives very high precision in the position of the glass plate relative to the cooling and compression plates, this precision being one of the conditions for obtaining glasses which are very well aligned in outline.

As previously stated, an essential aspect of preforming before bombing and quenching is the ability to reduce in all cases the deformation to which the glass is subjected between the cooling and compression plates to a deformation corresponding to a curvature of less than 1 m ' ¹ . Therefore, it is possible to obtain glasses of any curvature radius, while in the absence of preforming, curvature radii are close to 0.85 m - or even larger for greater optical quality.

As a consequence, this preforming allows for a significant reduction in the design time between the cooling and compression plates and the increase in production cadence, in particular by causing an increase in the compression rate as long as the bombing phase may be short.

Another important advantage is that it is possible to approach the bombardment and germination phase by touching glass panes whose initial temperature is relatively low, which minimizes the risk of optical defects. Below the low temperature, a temperature below 650 ° C and preferably above 630 ° C is expected here, but certainly above the temperature of plastic deformation of the glass pane so that the glass pane can bend.

The process according to the invention, in particular, corresponds to the modes of operation described in the aforementioned patent file EP-A-277 074, that is to say, in order to achieve bombing and tempering by means of cooling plates smaller than glass panes. The choice of this method of operation is particularly preferred in the case of large-sized glasses, because with the increasing dimensions of glass, the construction of cooling plates that are of suitable outline causes greater and greater difficulty. In addition, it becomes more and more difficult to produce pressure with the necessary even compression and to remove the amount of heat that passes through the cooling of said plate. It should be borne in mind that, in addition, this priority process permits the use of a portable frame for glass that rests in place during tempering by touch.

Another well-known problem in which cooling and compression plates smaller than a glass plate can be satisfactorily assisted is that which occurs with glasses whose edges are covered with enamels intended to form an opaque layer , which forms a frame and conceals e.g. adhesive used with glass mounting on the vehicle. It should be borne in mind that the problems described above, in connection with preforming, appear in the same way and the advantage is to treat the cooling and compression plates which do not cover the enameled edge areas from this point of view is quite obvious.

A major disadvantage of the embodiment explained in EP-A-277 074 is, of course, that the outer part of the glass is not subjected to compression and therefore is not directly bombarded, although the condition that the outer parts represent only a very small part of the surface and that the viscosity the glass should not be too small, the stiffness of the glass is sufficient that these areas partly follow at least the curvature given to the central part. With the preliminary design phase of the process according to the invention, it becomes possible to give even the edges the desired curvature, without the risk of damaging the enameled areas and / or contaminating the enamel cooling plate.

It may be advantageous to preform such enameled glass using annular support in a form which, in the form of compression and / or transport tool, is right up to the bombardment and tempering device comprising smaller than glass cooling and pressing plates panels - and in conjunction with this preparation, preparation for blowing cold air to the edge regions of the glass. It can be operated with a frame that is a support surface for the glass pane and is continuous - which increases the quality of the toughening - or with a continuous frame - which is synonymous with better optical quality, in that case it avoids the errors that can be caused by possible compression between the preforming phase, and the frame is thus removed immediately before blowing along the edge regions.

In the strict sense, the doctrine of the invention for preforming, of course, is only applicable in the case of the manufacture of glasses which exhibit non-zero curvature. However, one of the many advantages of preforming is that it allows optimizing the glass surface temperatures. In fact, the authors of the present invention have found that this cognition could be used to some extent even in the case of flat glasses. In fact, it has been found that any asymmetry, even small, at temperatures on both opposite sides of the glass pane is sufficient to cause a certain deviation after quenching with respect to the expected outline, with the colder side initially corresponding to the convex side of the glass. From this point of view, preforming is very interesting, either to give the sample an inverse curvature that will be compensated during the operation of touch-quenching, or more simply to exist only from a single stage of thermal adjustment of the glass plate. Commonly used ovens have e.g. the tendency to heat the top of the glass panel more than the underside, which is partially obscured by the rollers supporting the glass panel; it may therefore be attempted to compensate for the difference in temperature between the sides by supplying a certain amount of heat to the underside, a heat that can be e.g. it gets with a stream of hot air that rises and produces steady dynamic pressure. Therefore, a single production line can be used for all types of glass.

As explained above, most of the known bombardments are suitable for carrying out the process of the invention. The production line designed for the process according to the invention is thus essentially a furnace, a hot-tempered, non-tempering bombing place from a touch-bombing and a glass-transport means between the two bombing devices.

In certain cases, it is certainly preferable to use the specific preparation described below with the help of the accompanying figures, which represent:

FIG. 1 is a schematic view of an assembly of a bombardment and tempering apparatus, FIG. 2 is a perspective view of the essential elements of a compression and tempering site, FIG. 3 is a view of the compression and tempering position at the moment of positioning of the pre-bombed glass; 4 is a view of a compression and hardening location at the time of compression and hardening, FIG. 5 is a cross-sectional view showing the structure of the cooled bomber tool; FIG. 6 is an enlarged view of the part of FIG. 5.

The apparatus for carrying out the process of the invention comprises, as schematically shown in FIG. 1, essentially three sites, namely site A for bombing, site B for compression and tempering and site C for disposal.

The glasses 1 to be bombed are heated to the bombing temperature in a continuous furnace 2 of the known type. By means of a conveyor which is e.g. consisting of engines 3, the heated glass is transported through the furnace 2 and straight to the A-bomb site where preforming is started.

In the present case, the bombing process is carried out in a hot air bombing site A known in US-A-4682997. To this end, Bomb A comprises a fully convex upper bumper form 6 mounted above the rollers 3. Bomb form 6 is attached to the frame 7, which is fixed in its side to the masts 8, which can be moved vertically by means of suitable drive 9 so that the bomber form 6 can be brought into the lowered position shown in the figures and in the raised position. Below the rollers 3, a supply line 12 is provided to supply hot air with a predetermined volume flow and at a predetermined pressure so that the rising hot air is directed toward the upper form 6. After the hot air has crossed the bomber chamber, it drains through channel 13 and then recycled to conduit 12.

With the help of hot air flow, the glass 1 is pressed against the molding surface of the bomber mold 6 and thus takes on a shape defined in advance by the mold. The bomber chamber itself is added by a fence 14. The wall 15 of the fence 14 has an opening 16 which is closed by a door 17 during the bombing process.

The compression and hardening site B comprises an upper convex mold 20 cooled e.g. with water, and the lower concave mold 30, which is also cooled. Both molds 20 and 30 define an area smaller than the glass surface Γ. Both molds are surrounded by annular leads, which are marked with 40 or. 41, for cold air distribution. Water 40 oz. 41 comprise blowing nozzles 42, 43 directed toward the edge regions of the glass Γ. Water 40 and 41 are supplied with air by means of hoses 44 and 45 for blowing cold air.

The upper mold 20 is fitted together with the annular conduit to a frame 46, the vertical position of which is adjusted by means of a pneumatic or hydraulic lifting device 47. Also, the lower mold 30 is mounted together with the annular conduit 41 to a common frame 48, the vertical position of which is adjusted by by means of a pneumatic or hydraulic lifting device 49.

The transport point C comprises essentially a trolley 52 which moves along rails parallel to the axis in the direction of transport of the glass panes. The trolley 52 carries a pneumatic thrust device 53; on the pole 54 of the piston of the displacement device 53, a frame 55 is attached to which the caps 56 are hung. With the aid of this transport device, the glass is grabbed after hardening by means of the cap 56, is raised and deposited on the conveyor on rollers 58. This conveyor 58 transports glasses to rollers for such a distance of post-cooling that the glasses are at ambient temperature at the end of the conveyor 58.

The transfer of the glass Γ behind the bombing point A and to the transport point C is carried out by means of an annular frame 60 corresponding to the shape of the bombed glass. The frame 60 is mounted on a trolley 61, which is provided with wheels 62 which roll on the rails 63 parallel to the rails 51.

The construction of the compression and tempering tools and their method of operation are detailed in FIG. 2 to 6. The upper mold 20, which simultaneously compresses and abruptly cools the center portion to melt the glass 1 ', consists of a metal body which is provided with channels 21 through which cooling water flows. It can also be used to produce cooling plates, any material with a low value of linear dilation ratio and thermal conductivity, especially of graphite, as mentioned in patent application EP-A-312 441. Cooling water is supplied via a flexible hose 22 and drains down the hose

23. On the surface of the mold in the narrower sense, the mold 20 is provided with a layer 24. The layer 24 is made of a material that is slightly elastically deformable, which allows it to be used in the best way throughout its surface on the glass surface and which on the other hand, it has good thermal conductivity properties. Layer 24 may be e.g. derived from a laminated graphite board about 1 to 2 mm thick, available under the commercial mark SIGRAFLEX (trademark of SIGRA GMBH, operating under the law of the Federal Republic of Germany). As FIG. 5 and 6, the graphite lamellae plate 25 is covered and surrounded by a fine metal sheet 26, which in turn is fixed to the side walls of the mold 20. The metal plate 26 is also composed of metal having a thermal conductivity, - as indicated EPA-312 441, previously cited, and having a thickness of between 0.1 and 0.3 mm.

The bottom mold 30 is made in an analogous manner. It is also equipped with channels 31 through which cooling water flows. Cooling water is supplied through flexible pipe 32 and discharged through flexible pipe 33. The surface of the metal body of the compression mold 30 is also provided with an elastic bending layer 34, which is covered with a metal sheet 36 from the lamellar graphite plate 35.

The molds 20 and 30 have a surface area smaller than that of the glass Γ, so that the dimension L of the edge area of the glass beyond the molding should be 1 to 10 cm. In this edge region the glass is tempered by cold air jets protruding from the nozzles 42 and 43.

In order to avoid deformation of the glass 1 'at the level of the edge of the molds 20 and 30, the molding surfaces of the molds each time form a curved radius different from the curved radius of the glass Γ, as clearly shown in Figs. 5 and 6. The compression pressure is therefore always reduced to zero in the region of passage R, which eliminates any risk of deformation of the glass at this location. Moreover, it follows very precisely from FIG. 4, while performing compression and tempering in the narrow sense, the glass is slightly lifted from the molding frame 60 so that the molding frame 60 does not exert any force, possibly disturbing, on the glass during this operation.

The glass 1 'is lifted from the molding frame 60 by means of a lower mold 30, which is lifted by a lifting device 49. In a variant embodiment, wherein in addition the molding frame 60 may also be movable up and down so that the glass 1' may be deposited to the lower mold 30 by lowering the molding frame 60, and separating the molding frame 60 from the glass 1 by lowering it further when the glass 1 'has been grabbed by the lower recompression mold 30.

The process performed using the preparation described above is as follows.

The glass 1, heated to the temperature of the bombardment, penetrates the bombardment chamber 14. During this time, the opening 16 closes with the door 17. The bombardment mold 6 occupies its extreme lower position, which lies slightly above the plane of transport of the glass panes. The glass is installed under the bomb mold 6. The hot air flow that presses the glass against the bomb surface of the bomb mold 6 is then switched on.

While hot air is flowing, the bomber mold retracts to its upper position with the glass 1 '. At the same time, door 17 opens, freeing the way to the ring frame 60, which had been outside the bomber chamber right up to this point. The trolley 61, which kinos the annular frame, moves in the direction of the bomber chamber until the frame 60 is located exactly below the glass Γ pressed against the bomber mold 60 with a stream of hot glass. The bomber mold is now moving in the direction of the annular frame 60 and the hot air volume flow is reduced to the point where the glass Γ peels off from the bomber mold 6 and is deposited on the annular frame 60.

As soon as the glass 1 'is separated from the framing frame 6, it again travels upwards, and the annular frame, which carries the "bombed" glass, is introduced into the compression and tempering position B. A weak deformation of the glass 1 ", which inevitably occurred during transport of hot bombed glass, which, due to the lowering of the glass in the center of gravity, is now eliminated at the compression and tempering point. Immediately after positioning the frame 60 between the cooling and compression molds 20 and 30, this mold moves one against the other so that the glass is slightly lifted from the molding frame 60 with the lower mold. By pressing under pressure with two chilled molds 20 and 30, the glass 1 'has its final shape in its central region and is simultaneously thermally tempered by rapid cooling. At the same time, cool air is supplied to the air distribution ducts 40 and 41, so that the edge region is also rapidly cooled and so tempered.

As soon as the cooling process is complete, both the cooling and compression molds 20 and 30 are brought back to their initial position. This way the glass is released. The trolley 61 with the glass sedaj is now brought to the transfer point C, where the glass is lifted from the molding frame 60 and deposited on the conveyor 58 onto the rollers.

Claims (20)

A method of bombarding and tempering by touching glass panes, characterized by preforming the glass panes in a hot environment. 2. The method of touch bombing and tempering according to claim 1, characterized in that all operations are performed while the glass panes are in horizontal or substantially horizontal position. 3. The method of touch and toughening according to claim 1 or 2, characterized in that in all directions of the glass pane, the initial curvature given to the glass pane during preforming is such that the difference between its final curvature and said initial curvature curvature less than 1 m ' ¹ . 4. Touch-tapping and tempering method according to one of Claims 1 to 3, characterized in that the glass plate temperature after preforming is lower than 650 ° C and preferably above 630 ° C. Touch and toughening process according to one of the preceding claims, characterized in that the preformed glass panes are transferred from the preforming station to the tapping and toughening station by means of one of the forming elements for preforming. 6. A method for touch-bombing and tempering according to claim 4, characterized in that said molding element is an annular molding frame. A touch-bombing and tempering method according to any one of the preceding claims, characterized in that preforming is achieved by pressing. 8. The method of touch bombing and tempering according to claim 7, characterized in that the pressing is carried out by a rising flow of hot air. 9. A method of touch bombardment and tempering according to claim 7, characterized in that the pressing is achieved by suction. 10. A method of touch-tapping and tempering according to any one of claims 1 to 5, characterized in that the preforming is achieved by allowing the glass plate to travel on the forming bed. 11. A method of tapping and quenching according to one or more of the preceding claims, characterized in that the tapping and quenching operation of the glass panes is carried out by leaving the edge regions of the glass extending over the compression and cooling molds, wherein said edge regions are tempered by blowing cold air jets. A method according to claim 11, characterized in that the edge area or edge band of the circumference to be germinated by blowing with air jets represents a width (L) of 1 to 10 cm. Use of a method according to any one of claims 1 to 12 for the bombing and tempering of glasses equipped with a decorative edge embossed in a firing enamel. A device for carrying out the process according to any one of claims 1 to 12, characterized by a furnace, a hot-air bombardment point (A), a bombardment and tempering spot (B) and glass plate transport means between the two bombardment devices. A device for carrying out the process according to claim 11 or 12, characterized by a preforming spot (A), a annular frame (60) receiving a bombarded glass (Γ) and mounted on a movable trolley (61), and a spot (B ) for bombardment and tempering following a preforming site in which there is a compression and cooling tool made up of two cooled molds (20, 30) forming dimensions smaller than those for glass (1 ') and blowing nozzles (42, 43) mounted on the side of the molds (20, 30) and acting on the edge regions of the glass (1 ') extending beyond the molds and supplied by cold air through the air distribution duct (40, 41). Apparatus according to claim 15, characterized in that the cooled molds (20, 30) are provided with channels (21, 31) and are provided with an elastically flexible layer (24) on their side facing the glass (Γ). 34) with high thermal conductivity. Device according to claim 16, characterized in that the elastically flexible layer (24, 34) with high thermal conductivity is made of a plate (25, 35) of 1 to 2 mm thickness of laminar graphite and of a metal sheet (26, 36) , which covers the graphite. Device according to any one of the preceding claims 15 to 17, characterized in that the molds (20, 30) have a curvature radius in their extreme regions that is different from the curvature radius of the glass (Γ) in these areas, such that they are compressive forces, performed on glass (1 ') always remain zero in the transition region (R). Device according to any one of claims 15 to 18, characterized in that the dimension of the surface of the compression molds (20, 30) is smaller than the dimension of the glass (1 ') such that an edge band 1 to 10 cm wide extends laterally over the compression molds. Use of a process according to any one of claims 1 to 12 for the manufacture of flat glasses.