HRP940865A2 - Method and apparatus for bending and tempering by contact - Google Patents

Description

The invention relates to the bending and tempering of glass panels, primarily for the production of glasses intended for cars, which must have a very high accuracy of shape, and in case of breakage, the crushing must be in accordance with safety standards, and the optical quality also in accordance with very demanding standards .

From the patent application EP-A-277 074 it is known, for example, that glass plates are simultaneously bent and tempered above their plastic deformation temperature, and are brought between two plates for cooling and pressing, the contour of which corresponds to the curvature that is to be given to the glass plate. The glass sheets are pressed between the plates until their temperature becomes low enough to permanently retain their shape. Such a procedure is useful above all for thin glass, for example at least 3 mm thick, which after bending is difficult to bring to a high enough temperature for thermal tempering due to the speed of their air cooling as soon as the thin glass sheets leave the heating furnace.

Another reason for such bending and tempering procedures by touch is to completely overcome the curvature of the glass, primarily due to the reduction of the error called double bending, that is, undesirable curvature, primarily due to the effect of weight when the glass plate is not supported at all points of its lower surface.

Although the creators of the proposed invention noticed a small deviation from the profile of the glass plate in relation to the profile of the cooled and pressure plates, and the cause of this is partial and incomplete yielding of the molding stress, or more precisely due to bending stress. These bending stresses are closest to the surface of the glass, which means that they are the greatest in the places that cool the fastest, and for them the time during which stress relief can be effectively carried out is the shortest. The absence of stress relaxation can locally cause stresses higher than the resistance of the glass and glass breakage occurs.

This period can be extended, during which the softening can be carried out by working with glass panels whose initial temperature is higher, and which therefore come to be cooled with a much greater intensity. However, due to the optical quality, there is a limit to the initial heating of the glass panel. Indeed, if glass sheets are transported flat on rollers - this is at the same time the simplest method of transport, the most economical and to a large extent the least exposed to the formation of external or enamel contamination - the overheated glass shows a tendency to descend between the rollers, which causes errors of the "wavy plate" type, whose the mark remains even after pressing between the bending and touch hardening stages.

Understandably, with the process of bending and tempering by touch, it is practically not possible to prolong the forming stages so that, for example, one would go to the gradual bending of bent shapes - this is of course because the bending time is calculated if the glass is simultaneously subjected to strong cooling with cooling and pressing plates. The use of suitable material buffers contributes to the solution of this problem, and only if it remains in the case of normal press speeds for touch hardening. Actually, if the extended molding time is too long, breakage occurs at the end of the molding, because the glass is then too cold to transfer that much deformation. This limitation in molding time causes a limitation in the amount of curvature to be given by this process. In addition, the absolute prolongation of the molding phase shortens the rhythm of the production line, which is still a disadvantage for industrial applications.

On the other hand, numerous methods of manufacturing bent and toughened glass are known, according to which these two processes are carried out at different times and in different places, first of all, processes by which the glass plate is heated in a horizontal position in the furnace, and then transported, for example, by conveyor made on rollers and is raised above the conveyor by means of mechanical or pneumatic means - primarily by suction or blowing hot air - and is pressed against the upper element, which is flat or forms a bending shape, and then descends on the lower element, e.g. .the ring is open in its center and the glass plate is guided to the device for thermal tempering by blowing cold air using a tempering caisson.

According to the example, the shaping of the glass panel is done exclusively on the lower element, partially or even to the end; when the glass is placed on the lower element. Procedures are also known that do not use the lower element - or only for the bending phase - and by which the bombed glass sheet is also transported to the tempering device on the upper form, which is then movable, or else on a conveyor derived from a roller track with possibly curved rollers. To this process of bending and tempering, the overall feature of which is the use of the upper element and the vertical movement of the glass plate, should also be added the bending procedures by which the glass plate is allowed to travel on the forming base, which is composed, for example, of curved rods or straight rods located at curved path. All of the above-mentioned methods are well known according to the state of the art and examples can be found in patent documents US-A-3527589, EP-A-3391, EP-A-5306, FR-A2085464, FR-A-2312463, FR-A- 2442219, FR-A-2549464, FR-A2549465, FR-A-2554436, FR-A-2567508, FR-A-2596750, FR-A2596751.

These procedures allow achieving a very high rate of work even with relatively complex glass shapes, although, if priority is systematically given to optical quality, it is practically impossible to achieve complete contour harmony and above all to avoid the double bending error. It should be said that contour deviations are all the more sensitive the smaller the thickness of the glass panel; this explains the increased interest in bending and touch tempering processes for thin glass.

The proposed invention aims first of all to improve the process of bending and tempering by touch so that, under sufficiently industrial conditions, glasses can be obtained that can have all kinds of curvature, above all those with smaller radii of curvature, and with very high contour accuracy.

The solution to this problem is provided by the invention and consists in the application of pre-forming in a hot environment, before the beginning of the bending and contact hardening process. The hot medium achieves here that the pre-forming can be carried out under such conditions that the temperature of the glass sheets will be equal to their bending and tempering temperature when they are brought between the cooling and pressing plates.

First of all, in all directions of the glass panel, the difference between the desired specific curvature of the glass panel and its initial curvature, which was obtained with reshaping, in all points of the glass panel is less than 1 m-1; let's remember that the curvature at a certain point of the glass plate is by definition equal to the reciprocal value of the radius of curvature at the flow point. In other words, any shape can be chosen, bending and tempering by touch can be done at the same speed as bending and tempering a flat glass plate given a curvature with a radius of at least one meter. Pre-shaping therefore has the goal of roughly approaching the ultimate curvature, primarily in places where smaller radii of curvature are localized. This can be done also very quickly, without overloading with the eventual creation of parasitic curvatures, which will again be obtained during the pressing phase during bending and touch hardening, and care will be taken to absolutely not cause optical errors during the preforming phase or during the transfer phase to devices for bending and tempering by touch.

This next phase of regaining the given curvature gives a very high agility of the process according to the invention. If the difference between the curvatures still remains smaller, for example nd 1 m-1, it is not significant if the glass plate loses some of the curvature during transport, which was given to it during reshaping, or if it nevertheless gains additional curvature. Therefore, the transport can be carried out using an air cushion conveyor (which does not have to cause optical errors), a conveyor with rollers that are possibly adapted in shape or with a metal mat made with a flexible belt in the form of a fabric made of heat-resistant metal fibers, with resistance to the passage of heat perpendicular to the plane of the strip between 0.25x10-3 and 5x10-3 m2.K.W-1, the said flexible strip coming between the glass plate and the lower pressing and cooling plate.

To replace these conveyors, molding elements that serve for pre-shaping can also be used directly, and if it is a molding base, which gradually gives the glass a curvature, or any elements against which the glass plate is pressed, above all pressure molds of male or female shape , full or composed of rings open in their center. The pressure elements are generally connected to mechanical forces or are of pneumatic design, primarily according to the invention, which are very suitable for achieving smaller radii of curvature. First of all, pressing with a current of rising hot air is preferred, and "suction pressing" can also be carried out, that is, by pressing the glass sheet onto the upper molding element by suction caused, for example, near the periphery of the glass sheet or near the surface of the said upper element.

During all the above-mentioned procedures, special attention should be paid to how, in the last phase of bending and also pre-shaping, the glass plate is brought to the ring base, on which the edges of the glass plate rest. In this case, there is no danger of marking the middle part of the glass panel - the central part of the panel is usually the only visible part after mounting the glass on the vehicle. In addition, it is known that if the windows are covered with a layer of enamel, the side facing the interior of the vehicle is always less exposed to the weather; in other words, the enamels - which have partially melted by bending, and are very exposed to the danger of contamination - are on the concave side of the glass, and not on its convex side, which rests on the ring support. Otherwise, that ring frame can very well be used to transport glass sheets from the pre-forming device to the bending and touch-tempering device, as is known for heat-tempering processes with cold air blowing caissons, even better in a particular example of the invention it is useful to give a very high accuracy in the position of the glass plate with respect to the cooling and pressing plate, whereby this accuracy is one of the conditions for obtaining glass with very well-aligned contours.

As previously stated, an important aspect of pre-shaping before bending and tempering is the possibility in all cases to reduce the deformation to which the glass is subjected between the cooling and pressing plates to a deformation corresponding to a curvature of less than 1 m-1. It is also possible to obtain glasses of any radius of curvature, while without pre-forming, for higher optical quality, curvature radii close to 0.85 m - or even larger - are required.

The consequence of this pre-forming is the possibility of significantly reducing the forming time between the cooling and pressing plates and increasing the production rhythm, primarily by increasing the pressing speed if the bending phase can be short.

Another significant advantage is that it is possible to approach the bombardment and tempering phase by touching the glass plates with a relatively low initial temperature, because the risk of creating optical errors is limited to a minimum. Under low temperature here, a temperature lower than 650°C is expected, preferably 630°C, although certainly above the plastic deformation temperature of the glass plate, so that the glass plate can be framed.

The process according to the invention otherwise first of all corresponds to the method of operation described in the already mentioned patent document EP-A-277 074, that is, the one by which it is desired to achieve bending and tempering by contact using cooled plates smaller than a glass plate. The choice of such a procedure is useful above all in the case of large-sized glasses, because with the growing dimensions of the glass, the construction of cooled panels with suitable contours causes increasing difficulties. In addition, it is increasingly difficult to produce the pressure required for uniform pressing and to remove the amount of heat when cooling the mentioned plates. It should be noted that, in addition, the preferred process allows the use of a portable glass frame, which remains in place during touch hardening.

Another known difficulty with cooling and pressing plates smaller than the glass plate, which can be solved satisfactorily, is the one that appears with glasses with edge areas covered with enamel intended to form an opaque layer of the frame and obscures, for example, the glue used when mounting the glass on vehicle. It should be said that the pre-forming difficulties enumerated above appear in an identical way and it is useful to work with cooling and pressing plates that do not cover the marginal enameled areas from this point of view completely obvious.

The major disadvantage of the performance disclosed in EP-A-277 074 is understandable in that the outer part of the glass is not subjected to pressing and it is therefore directly bombarded, although on the condition that the outer part represents only a very small part of the surface and that the viscosity of the glass will not change , the stiffness of the glass is sufficient for that area to partially follow at least the curvature given to the central part. With the previous shaping phase in accordance with the process according to the invention, it is possible to give the charm and the desired curvature to that edge area without the risk of damaging the enameled parts and/or contaminating the cooled plates with enamel.

It may be advantageous to pre-shape such enamelled glasses using a ring support into shapes which go by pressing dies and/or transport tool to a bending and tempering device, which includes a cooling and pressing plate, and which is smaller than the glass plates - and in this device is connected a device for blowing cold air on the edge areas of the glass.

It is possible to work with a frame that represents a support surface for the glass plate and is interrupted - which increases the quality of tempering - or with a continuous frame - which is synonymous with better optical quality, if then errors that can easily occur due to possible pressure during the pre-shaping phase are avoided, and the frame is also removed just before blowing along the edge areas.

In the strict sense, the idea according to the invention for pre-forming is understood to be used only in the case of production of glasses that do not have a curvature of the zero line. Although one of the many advantages of pre-forming is that it enables optimizing the surface temperature of glass panels. Actually, the authors of the proposed invention determined that this knowledge could be used to some extent even in the case of flat glasses. It was actually determined that any asymmetry, even a small one, in the temperatures of both opposite sides of the glass plate is sufficient to obtain a certain deviation from the expected outline after tempering, whereby the side, which was initially colder, corresponds to the conventional side of the glass. From this point of view, pre-shaping is very interesting if you want to give the sample an inverse curvature that will be compensated during touch hardening, or more simply, if the process consists of only one phase of thermal adjustment of the glass plate. Furnaces, which are often used, for example, tend to heat the upper side of the glass plate more strongly than the lower side, which is partially hidden by the rollers that support the glass plate; you can also try to compensate for the temperature difference between the sides by bringing a certain heat to the lower side, which can be obtained, for example, with a stream of hot air that rises and creates an even dynamic pressure. Therefore, only one production line can be used for all types of glass.

As explained above, most of the known bending devices are suitable for carrying out the method according to the invention.

The production line for the process according to the invention therefore consists of a furnace, a "hot" bending place without cooling for tempering, a bending and contact tempering place and means for transporting glass sheets between two bending devices.

In certain cases it is definitely useful to use the special device described below using the attached images of which

Figure 1 schematically shows a view of the composition of the bending and hardening device,

figure 2 shows a perspective view of the main elements of the pressing and tempering site,

Figure 3 shows a view of the pressing and tempering place at the time of installation of the pre-bent glass,

Figure 4 shows a view of the place of pressing and tempering at the time of pressing and tempering,

Figure 5 shows a section of the construction of the cooled bending tool,

Figure 6 shows an enlarged part from Figure 5.

The device for carrying out the process according to the invention comprises, as shown schematically in Figure 1, mainly three places, namely place A for bending, place B for pressing and touch hardening and place C for removal.

The glasses 1 to be bombarded are heated to the bending temperature in a continuous furnace 2 of a known type. By means of a conveyor consisting, for example, of a motor 3, the heated glass is transported through the furnace 2 to the place A for bending, where pre-shaping is performed.

In the case shown, the bending process is performed at the bending point A by the hot air bending process known from US-A-4682997. The bending place A for this purpose comprises a full convex upper bending shape 6 located above the rollers 3. The shape 6 is attached to a frame 7, which in turn is attached to guides 8, which can be moved vertically by means of suitable driving devices 9, so that the bending form 6 can be brought to the lowered position, which is shown in the pictures, and to the raised position. Below the rollers 3 is provided a supply pipe 12 through which hot air is supplied with a predetermined volume flow and under a predetermined pressure, so that the rising hot air is directed towards the upper form 6. Then, when the hot air passes through the bending chamber, it flows out channel 13 and is then recycled into pipe 12.

Using this current of hot air, the glass 1 is pressed against the surface of the bending mold 6 and thus assumes the shape previously defined by the mold. The wall 15 of the fence 14 has an opening 16 closed during the folding process with the door 17.

Place B for pressing and hardening comprises the upper convex mold 20, which is cooled, for example with water, and the lower concave mold 30, which is also cooled. Both mold halves 20 and 30 define an area smaller than the glass area 1'. Both halves of the mold are surrounded by ring tubes marked 40 and 41 respectively for the distribution of cold air. Pipe 40, or 41 includes nozzles 42, 43 for blowing, directed towards the edge areas of the glass 1'. Pipes 40 and 41 are supplied with air using flexible pipes 44 and 45 for blowing cold air.

The upper mold 20 is placed together with the annular or hydraulic lifting devices 47. The lower part of the mold 30 is also placed together with the annular tube 41 on the common frame 48, the vertical position of which is aligned by means of the pneumatic or hydraulic lifting device 49.

Transport site C mainly comprises train 52, which moves on rails parallel to the axis in the direction of transport of glass panels. The train 52 carries a pneumatic pressure device 53; on the column 54 of the piston of the moving device 53, a frame 55 is attached to which the caps 56 are hung. Using this transport device, the glass is caught after tempering by the cap 56, lifted and placed on the roller conveyor 58. This roller conveyor 58 transports the glass to such a distance of subsequent cooling, that the glasses at the end of the conveyor 58 are at ambient temperature.

The transfer of the glass 1' for the place A of bending and to the place C for transport is done by means of the ring frame 60 which corresponds to the shape of the glass to be bombarded. The frame 60 is located on a train 61 equipped with wheels 62 that roll on rails parallel to the rails 51.

The construction of the pressing and tempering tools and their mode of operation can be seen in detail in Figures 2 to 6. The upper mold 20, which simultaneously provides pressing and sudden cooling of the central part, to temper the glass 1, is composed of a metal body equipped with channels 21, through which cooling water flows. For the cooling plates, a variety of materials with a low coefficient of linear expansion and thermal conductivity can also be used, primarily graphite, as mentioned in patent application EP-A-312 441. Cooling water is supplied through a flexible pipe 22 and discharged through a flexible tube 23. On the surface of the mold in the narrower sense, the mold 20 has a layer 24. The layer 24 is made of a material that can be deformed to an insignificant extent, which allows it to be used in the best way over its entire surface on the surface of the glass and which on the other hand it has good thermal conductivity properties. The layer 24 can be made, for example, of a sheet of laminated graphite approximately 1 to 2 mm thick, which is available under the commercial name SIGRAFLEX (product mark of the company SIGRA GMBH, operating under the law of the Federal Republic of Germany). As shown in Figures 5 and 6, the graphite laminated plate 25 is covered and surrounded by a thin metal plate 26, which in turn is attached to the side walls of the mold 20. The metal plate 26 is also composed of a metal of suitable thermal conductivity - as indicated in the previously mentioned patent application EP-A-312 441 - and is of small thickness, between 0.1 and 0.3 mm.

The lower part of the mold 30 is made analogously. It is also equipped with channels 31 through which cold water flows. Cooling water is supplied through flexible pipes 32 and discharged through flexible pipe 33. The surface of the metal body of the pressing mold 30 is also equipped with an elastically flexible layer 34 of laminated graphite plate 35 covered with a metal plate 36.

The size of the surface of the molds 20 and 30 is smaller than the surface of the glass 1ʹ, so the edge area of the glass Z is outside the mold by 1. to 1.0 cm. In this peripheral area, the glass is tempered with a stream of cold air blown from the nozzles for 42 and 43.

To avoid deformations of the glass 1 at the level of the edge of the mold 20 and 30, the edges of the molding surfaces of the mold have a radius of curvature different from the radius of curvature of the glass 1', which is clearly shown in Figures 5 and 6. In the transition area R, the pressing pressure is therefore obviously reduced to zero , which excludes any danger of deformation of the glass in that place. In addition, it is very clear from figure 4 that during the pressing and tempering, in the narrower sense, the glass is slightly raised from the molding frame 60, so that the molding frame does not exert any, possibly disruptive force on the glass 1' during this process.

The glass 1' is lifted from the molding frame 60 by means of the lower mold 30, which is lifted with the lifting device 49. In a version of the embodiment, where in addition the molding frame 60 can also move up and down, so that the glass 1' can be deposited on the lower mold 30 by lowering the mold frame 60, and that the mold frame 60 is separated from the glass 1 by additional lowering when the lower recompression mold 30 grips the glass 1'.

The procedure carried out using the device described above is carried out in the following way.

The glass 1, heated to the bending temperature, enters the bending chamber 14. At that time, the opening 16 is closed with the door 17. The bending mold 6 occupies its bottommost position, where it is slightly above the plane of transport of glass sheets. The glass is located under the bending mold 6. Then a stream of hot air is turned on, which presses the glass onto the surface of the mold 6 for bending.

When the current of hot air is established, the bending mold moves to its upper position with the glass 1. At the same moment, the door 17 is opened, thereby clearing the way for the annular frame 60, which until that moment was outside the bending chamber. The train 61, which carries the ring frame, moves in the direction of the bending chamber just as the frame 60 is just under the glass 1' pressed onto the bending mold 60 with the hot glass stream. The bending die is now moved in the direction of the bending frame 60 and the volume of the hot air stream is reduced to the point where the glass 1' is detached from the bending die 6 and deposited on the ring frame 60.

As soon as the glass 1' is separated from the bending frame 6, it travels up again and the ring frame carrying the bent glass 1' enters the tempering place B. The slight deformation of the glass 1', which inevitably occurred during the transport of the hot bent glass and which is due to the lowering of the glass in the central area under the influence of its own weight, is now corrected at the point of pressing and hardening. Immediately after positioning the frame 60 between the molds 20 and 30 for cooling and pressing, the parts of the mold are moved towards each other, so that the glass 1 with the lower mold is slightly raised from the frame 60 for forming. By pressure contact with the two cooled mold halves 20 and 30, the glass 1 assumes its final shape in its central region, and is simultaneously thermally tempered by rapid cooling. At the same time, cold air is supplied through the air distribution pipes 40 and 41, so that the edge area is also quickly cooled and also tempered.

As soon as the cooling process is completed, both halves of the pressing molds 20 and 30 are brought back to their initial position. In this way, the glass is released. The train 61 of glass 1' is now brought to transfer location C, where the glass is lifted from the forming frame 60 and deposited on the rollers 58 of the conveyor.

Claims (20)

1. Process for bombarding and tempering glass plates by touch, characterized by the fact that the glass plates are previously shaped in a hot environment. 2. Process for blasting and touch hardening according to claim 1, characterized in that the process is carried out while the glass panels are in a horizontal or mostly horizontal position. 3. Process for bombardment and contact hardening according to claim 1 or 2, characterized in that, in all directions of the glass plate, the initial curvature of the glass plate, which the glass plate obtained during pre-forming, is such that the difference between its final curvature and the aforementioned initial curvature is smaller of 1 m-1. 4. Process for bombardment and contact hardening according to one of claims 1 to 3, characterized in that the temperature of the glass plates after pre-forming is lower than 650°C, preferably lower than 630°C. 5. Process for bombardment and touch hardening according to one of the previous claims, characterized in that the preformed glass panels are transferred from the preforming station to the bending and touch hardening station by means of one of the forming elements used for preforming. 6. Process for bombardment and contact hardening according to claim 4, characterized in that said forming element is an annular forming frame. 7. The process for bending and tempering by contact according to any of the previous requirements, characterized in that the pre-shaping is done by pressing. 8. Process for bombardment and contact hardening according to claim 7, characterized in that pressing is done with an upward flow of hot air. 9. Process for bombardment and contact hardening according to claim 7, characterized in that pressing is done by suction. 10. Process for bombardment and touch hardening according to any one of claims 1 to 5, characterized in that the pre-shaping is done by allowing the glass plate to travel on the molding bed. 11. Process for bombardment and contact tempering according to one or more of the previous claims, characterized in that the process of bombardment and contact tempering of glass plates is carried out in such a way that the edge areas of the glass that go over the mold for pressing and cooling are released, whereby said areas are tempered by blowing jets of cold air. 12. The method according to claim 11, characterized in that the edge area or edge strip of the rim to be hardened by blowing air jets has a width (L) of 1 to 10 cm. 13. Application of the process according to any one of claims 1 to 12, characterized in that it is used for bombarding and tempering glasses equipped with a decorative edge pressed into baking enamel. 14. Device for carrying out the process according to any one of claims 1 to 12, characterized in that it includes a furnace, a place (A) for bombarding "hot", a place (B) for bombardment and tempering and means for transporting glass plates between the two devices for bending. 15. Device for carrying out the process according to claim 11 or 12, characterized in that it includes a furnace to include a place (A) for pre-forming, an annular frame (60), which accepts bombed glass (1) and is placed on a moving belt (61), and a place (B) for bombardment and tempering, which follows after the pre-forming place where there is a tool for pressing and cooling two cooled molds (20, 30) whose dimensions are smaller than the dimensions of the glass (1), and the blowing nozzles (42, 43 ) are located on the side of the mold (20, 30) and act on the edge areas of the glass (1) which is laterally larger than the mold, and are supplied with cold air through the distribution tube (40, 41) for air. 16. Device according to claim 15, characterized in that the cooled molds (20, 30) are equipped with channels (21, 31) and on their side facing the glass (1) have an elastically flexible layer (24, 34) of high thermal conductivity. 17. Device according to claim 16, characterized in that the elastically flexible layer (24, 34) of high thermal conductivity is made of a plate (25, 35) of laminated graphite with a wall thickness of 1 to 2 mm and a metal plate (26, 36) that covers graphite. 18. Device according to any of the previous claims 15 to 17, characterized in that the molds (20, 30) in their end areas have a radius of curvature different from the radius of curvature of the glass (1) in these areas, so that the pressing forces in the passing area ( R) do not affect the glass (1ʹ). 19. Device according to any of the preceding claims 15 to 18, characterized in that the size of the surface of the mold (20, 30) is smaller than the size of the glass (1) such that the edge band with a width of 1 to 10 cm goes laterally over the pressing mold. 20. Application of the method according to any one of claims 1 to 12, characterized in that it is used for the production of flat glasses.