Patent Application
20210284565
The invention concerns a method of manufacturing bent, in particular laminated glazing, and proposes an improvement to the step of cooling the glass after bending it with a view to obtaining reduced tension stresses. The invention concerns bending methods involving a step of bending on a gravity bending support termed a gravity support.
The invention concerns in particular the production of laminated glazing of the windshield or roof type for road vehicles (automobiles, trucks, buses), but also any glazing for aeronautics or construction.
In gravity bending processes, the tooling supporting the glass termed a “gravity support”, with a shape adapted to the final geometry of the glass, is in contact with the periphery of the lower face of the glass during all the shaping phases, that is to say rough bending, bending and cooling. Accordingly, for each glazing design it is necessary to have a particular series of gravity supports the number of which is at least equal to the number of different process steps. A gravity support generally has the shape of a frame. It is preferably covered with a refractory fibrous material well known to the person skilled in the art that comes into contact with the glass. The width of its contact track with the glass is generally in the range from 3 to 20 mm, refractory fibrous material included.
When the glass exits the bending step to begin the cooling phase, in the prior art it is usually in contact at its periphery with the last gravity support, in particular between 5 and 10 mm from the edge of the glass. When the glass sets and cools, a physical phenomenon is created generating permanent stresses that correspond to the conversion of the distribution of temperature in the glass into a stress field. This phenomenon is initiated during the setting of the glass and terminates at the end of cooling when a homogeneous temperature distribution is reached. In qualitative terms, the parts where the glass sets first correspond to the parts where the compression stresses are concentrated whereas the parts where the glass sets after a delay concentrate the tension stress zones. The edge stresses described in the context of the present invention are membrane stresses that may be defined at any point in the material and for a given direction as the mean of the stress field at that point and in that direction, the mean being calculated throughout the thickness of the sample. At the sample edge, only the membrane stress component parallel to the edge is pertinent; the perpendicular component has a zero value. Also any method of measurement enabling measurement of the mean stresses along an edge and throughout the thickness of the sample is pertinent. The methods of measuring edge stresses utilize photoelastic techniques. The two methods described in the ASTM standards cited below enable measurement of the edge stress values:
In the context of the present application, the compression stress values are determined by the method described in the standard ASTM F218-2005-01. The tension measurements are effected using the same method in a zone parallel to the edge of the glazing but situated slightly farther toward the interior of its area.
The compression stress values are generally determined between 0.1 and 2 mm from an edge and preferably between 0.1 and 1 mm from an edge. When the measurement is effected in the vicinity of the edge and within the glazing, an edge tension stress zone is generally identified within a peripheral zone situated between 3 and 100 mm from the edge of the glass.
Finally, it must be stated that the tension stresses relate to the membrane stresses of the exterior sheet of glass in the glazing (when mounted on the vehicle), which may be measured either on the exterior sheet of glass alone before lamination or on the exterior sheet of glass after lamination using the commercial apparatus Sharples model S-69 marketed by the company Sharples Stress Engineers, Preston, UK. For the measurement effected after assembly to be pertinent, it is necessary to colorize the interior surface of the exterior sheet of glass of the glazing using black or metallic paint. This sheet in the external position on the vehicle corresponds to the sheet in the lower position during bending by the method according to the invention and in the case of a stack of sheets of glass.
The current specifications on glazing properties require pertinent edge compression values greater than 8 MPa and the lowest possible edge tensions to preserve the mechanical robustness of glazing during mounting and use.
The invention enables prevention of the disturbance to the temperature distribution induced by contact of the periphery of the glass with a gravity support during cooling. Also, the edge compression levels cited above are more easily attained with greater safety margins and the tension stress levels are reduced.
EP2532625 teaches a device for supporting the glass after cooling its surface below its strain point. The central zone of the glass is cooled below the strain point before the edge. This technique is applied to annealing the glass. It is necessary to cool the interior of the glass to be able to lift the glass off its support. This causes compression of this central zone, which must necessarily be counterbalanced by a tension zone at its periphery. The cooling of the central zone therefore risks the creation of higher peripheral tension stresses that can weaken the glass. Moreover, if the annealing step is insufficiently well controlled and the glass remains for too long at too high a temperature during this phase, the surface compression level could be insufficient.
A prior art gravity bending method using a series of gravity supports gives rise to the following problems:
1. the rate of cooling depends on numerous parameters linked to the furnace; there may be cited the cycle time, the mass of the glazing and the onboard cooling, the pressure in the furnace; the latter is difficult to control and necessitates numerous attempts at setting parameters and onboard temperature measurements;
2. even if the rate of cooling is well controlled, it is very difficult to apply fine control of the temperature profile at the edge of the glass when the latter sets over the entire periphery of the glazing; also, stresses departing from the specifications may occur locally; artifice is then required, directly on the tooling, for local correction of these discrepancies, which is costly in testing and maintenance time if the stress level is to be maintained over time;
3. to guard against problems of weakness in use (sensitivity to impact of gravel in the case of automobile glazing for example), automobile manufacturers require that the residual tension stresses be significantly lower than 8 MPa; the cooling of glazing on its gravity support in a simple cooling chamber does not make it possible to achieve values of less than 5 MPa over all the perimeter;
4. a large number of specific tools for each design produced is necessary, because they transport the glass in all steps of the process including the cooling phases, which is reflected in high investment, maintenance and energy costs; each gravity support goes through all the temperature cycle of the process and therefore through very different temperatures, which is costly in terms of energy.
The inventors of the present invention have carried out the following analysis. Problems 2 and 3 above stem from the fact that the glazing is supported by a gravity support at its edge at the time of cooling, and that this support prevents homogeneous cooling of the glass, in particular at the edge. In fact, the contact of the edge of the glass with the support is damaging because the latter cools more slowly than the glass and its contact with the periphery of the glass interferes with its cooling. This phenomenon occurs as a consequence of heat transfer by conduction between the glass and the support and by radiation following the masking of the bed plate of the furnace by the support. This results in high tension stresses.
In the present application, the glass is in the form of a single sheet or more generally in the form of a stack of several sheets, or even more generally a stack of two sheets. In order to simplify the description of the invention, the term “glass” is used to designate a sheet or a stack of sheets. Whether a single sheet or a plurality of stacked sheets is concerned, the glass comprises two external principal faces, here termed the first principal face and the second principal face, gravity bending being effected on a gravity support by supporting the glass on its first principal face, which faces downward. In the case of a stack, the sheets remain stacked throughout the bending and cooling process, in order to guarantee identical shaping of all the sheets intended to be assembled. The association of these sheets of glass in the final laminated glazing is therefore arrived at under better conditions, leading to laminated glazing of better quality.
The invention concerns the method of the independent method claim. The invention also concerns the device of the independent device claim. The method according to the invention may be carried out using the device according to the invention.
The invention more particularly concerns a method of manufacturing bent glass comprising bending and cooling a sheet of glass or of a stack of sheets of glass, termed the glass, comprising a first principal face and a second principal face, said method comprising gravity bending of the glass on a gravity support during which the glass rests on the gravity support through contact with the peripheral zone of its first principal face, said peripheral zone being constituted of the 50 mm from the edge of the first principal face, then separation of the glass from the gravity support while the glass is at a temperature of more than 560° C., then cooling the glass with its first principal face free of any contact in its peripheral zone between a temperature termed the upper homogeneous temperature, of at least 560° C., and a temperature termed the lower homogeneous temperature, of at most 500° C., this range being termed the critical temperature range.
In the context of the present application, the peripheral zone of the first principal face of the glass is without contact in the critical temperature range, which means that this peripheral zone is free of any contact with a solid, that is to say is exclusively in contact with the gaseous atmosphere. During bending on the gravity support, the contact with the gravity support is entirely in the peripheral zone, without contact with the glass beyond the peripheral zone. The separation of the glass from the gravity support then takes place when the latter is at a temperature of more than 560° C., it being understood that the entirety of the glass (peripheral zone and central zone) is at a temperature above that temperature at this time. At the moment of separation, the zone of the first principal face farther than 50 mm from the edge of the glass, termed central zone, is at a temperature higher than that of the peripheral zone. The central region of the first principal face of the glass, in particular the zone of the first principal face of the glass more than 200 mm from the edge and even generally more than 170 mm from the edge and even generally more than 50 mm from the edge is at a temperature at least equal to, and generally greater than, that of the peripheral zone at the moment when the peripheral zone reaches the upper homogeneous temperature and preferably also at the moment when the peripheral zone reaches the lower homogeneous temperature, and more generally between the moment of the separation from the gravity support until at least the moment when the peripheral zone reaches the upper homogeneous temperature and even the lower homogeneous temperature.
The temperature range between the upper homogeneous temperature and the lower homogeneous temperature is termed the critical temperature range and the time to go from the upper homogeneous temperature to the lower homogeneous temperature is termed the critical cooling time. The upper homogeneous temperature is preferably at least 575° C. The lower homogeneous temperature is preferably at most 490° C.
During cooling of the glass in the critical temperature range, the first principal face of the glass is preferably without contact in the 60 mm from the edge and preferably without contact in the 70 mm from the edge. During cooling of the glass in the critical temperature range, the first principal face of the glass is preferably without contact beyond 200 mm from the edge and preferably without contact beyond 170 mm from the edge and preferably without contact beyond 150 mm from the edge. It is therefore possible to define a “contact band” of the first principal face of the glass in which the glass is preferably supported when it is in the critical temperature range:
The absence of contact of any solid with the peripheral zone, even in the 60 mm or even in the 70 mm from the edge, of the first principal face of the glass results in homogenization in temperature of this zone. By homogeneous temperature is meant that the temperature of the glass does not vary by more than 5° C. and preferably by not more than 1° C. and preferably by not more than 0.6° C. over this 50 mm peripheral zone. In practice, the homogeneous temperature of the glass is verified by measurements using a thermal video camera on the first principal face of the glass. This homogeneity is achieved for each of the sections perpendicular to the edge of the glass but one section may have a different temperature to another section. The peripheral zone of the first principal face is homogeneous in temperature on any line at the intersection of a section perpendicular to the edge of the glass in the critical temperature range (between the upper homogeneous temperature and the lower homogeneous temperature).
The glass used in the context of the present invention is a sodacalcic glass. It is conventionally formed by the float process and routinely used for automotive applications. According to the invention, the control of the stresses generated in the glass is improved by separating the latter from its last gravity support and then homogenizing the temperature of its peripheral zone and cooling the glass as far as the end of the critical temperature range whilst preserving temperature homogeneity. It is the first principal face of the glass that must have a particular resistance, in particular impact resistance, because it is usually positioned externally on a vehicle. This first principal face, also termed “face 1” by the person skilled in the art, is usually convex (the face 4 is the face inside the vehicle if the laminated glazing comprises two sheets of glass). It is therefore this face that is in the lower position (and the exterior position in a stack) during bending and in contact with the last gravity support, as well as during the critical cooling time that follows bending.
In the context of the present application, the expression “specific support” designates a support for supporting the glass from below but without contact with the glass in the peripheral zone of its downward-facing first principal face (the 50 mm edge portion of that first principal face). Various types of specific support are described hereinafter. The present application refers to a specific cooling support, a specific preliminary support, a specific offloading support.
According to the invention, the first principal face of the glass is separated from the last gravity support at a temperature greater than the upper homogeneous temperature so as to be able to homogenize the temperature of the peripheral zone of that face. This same face of the glass may be placed on the specific support in at least a part of the critical temperature range to continue the cooling of the glass whilst preserving the temperature homogeneity of the peripheral zone. Once the temperature of this first principal face is homogeneous in its peripheral zone the glass may be cooled more rapidly, even in the critical temperature range.
Thanks to the invention, the edge compression stresses of the finished glass in the sheet comprising the first principal face are greater than 8 MPa, or even greater than 10 MPa and can even range up to 20 MPa, and are more homogeneous along the periphery of the glass. Moreover, the tension levels are significantly reduced, to less than 5 MPa and even to less than 4 MPa, or even to less than 3 MPa. The passage from the compression zone to the tension zone is generally located at a distance from the edge between 1 and 5 mm. The maximum tension stress is generally situated at a distance from the edge between 5 and 40 mm and more generally between 15 and 40 mm.
The mechanical robustness of the glazing obtained may be evaluated by impacting the face 1 of the glazing using Vickers points. A test of this kind enables evaluation of the resistance of windows to impact from gravel when they are installed on a vehicle. The higher the impact energy of the indenter without the glass cracking, the greater is its robustness. The glazing obtained by the method according to the invention is more robust than if their manufacture includes cooling it on its gravity support. This improved robustness is imputed to a reduced edge tension level.
Moreover, as stated above the edge tension stress that, to a first order, determines the fragility of the glazing is a membrane stress, equivalent at every point M of the surface of a sheet of glass to the mean of the stresses within the thickness thereof at that point. This mean is therefore calculated along the segment “S” that is perpendicular to the sheet of glass at the point M and that passes completely through it. Also, different stress profiles may exist along the segment S that correspond to the same tension stress value. Of the various possible stress profiles, profiles in which the first principal face of the glass is in compression are of the greatest benefit for mechanical strength. In fact, the skin of the first principal face in compression then acts like a protection layer that blocks the propagation of surface defects and prevents them from being transformed into cracks both in the thickness of and in directions parallel to the surface of the sheet of glass. In contrast, the stress profiles that it is necessary to attempt to proscribe are those in which the first principal face of the glass is in tension.
During the discussion of the stress generation mechanisms, it was stated that the zones in tension correspond to the locations where the glass has set with a delay. It was also stated that in the prior art the cooling of the glass in contact with its gravity support indeed encourages a delay in cooling in regions situated in the vicinity of the contact zone between the glass and the gravity support.
The cooling of the glass on its gravity support therefore encourages both a mean cooling time (in the thickness of the exterior sheet of the glass) along a zone inside the glass and situated in the vicinity of the edge but also, in that same peripheral zone, a delay in cooling the first principal face of the glass which consequently itself tends to be in tension. The improved robustness of the glass obtained in accordance with the invention is therefore also attributed to a globally higher surface compression level. To achieve temperature homogeneity in the peripheral zone of the first principal face of the glass, that peripheral zone is preferably free of contact with any tool (that is to say in contact exclusively with the gaseous atmosphere) for a sufficient time before reaching the upper homogeneous temperature for homogenization to be obtained. This temperature homogenization time is generally at least 5 seconds and preferably at least 6 seconds and even at least 7 seconds. It is preferably the whole of the first principal face that is totally without contact during this temperature homogenization time. This homogenization is indeed obtained with the glass held by suction on its principal second face and with no contact with its first principal face, thanks to an upper forming mold having a skirt and suction means aspirating air between it and the skirt, termed hereinafter simply the upper forming mold, the suction by the skirt providing the force holding the glass against the forming mold. An upper forming mold of this kind is shown for example in
Although this is not recommended, there is nothing to rule out placing the glass at a temperature above the upper homogeneous temperature on a specific support preserving the temperature homogeneity of the peripheral zone of the first principal face of the glass. If a specific support is used, it is preferable to place the glass on it at a temperature below the upper homogeneous temperature. The glass may be carried by a specific support (or a plurality thereof in succession) at least until the lower homogeneous temperature is reached (end of critical cooling time) and generally also at a lower temperature than the lower homogeneous temperature. If necessary, the glass may be supported by a succession of specific supports between a temperature included in the critical temperature range and a temperature below the critical temperature range.
According to the invention, the bending of the glass may comprise complementary bending against a solid bending forming mold. This complementary bending follows the bending on the gravity support. This complementary bending may notably be carried out on a lower bending mold, notably by suction, termed a suction lower mold. This suction lower mold is a solid forming mold with orifices through which suction is applied to the first principal face of the glass. This solid forming mold is at least as large as the sheet and therefore extends as far as its edge. It does not significantly modify the homogenous or non-homogenous character of the temperature of the peripheral zone of the first principal face of the glass. A suction lower mold of this kind is for example of the type shown in
In the situation where complementary bending is carried out, the latter takes place at a temperature greater than 570° C. and even greater than 580° C. The complementary bending temperature is generally lower than that of gravity bending. After this complementary bending, it is necessary to separate the glass from the suction lower mold and to leave the peripheral zone of the first principal face of the glass free of contact for the time necessary for homogenization of the periphery of the lower face of the glass before it reaches the upper homogeneous temperature.
During the method according to the invention, the first principal face of the glass, generally in the lower position, is in contact with the gravity support, and possibly thereafter with a suction lower mold, and thereafter with at least one specific support.
The passage from the gravity support to the lower suction mold or directly to the specific support can advantageously be achieved by the use of a suction upper forming mold. The passage from the suction lower mold to the specific support may also advantageously be carried out using a suction upper forming mold.
An upper forming mold generally takes charge of the glass by its upper second face and releases it onto a support placed under it and able to support the glass from below, whether this be a suction lower mold or a specific support. The suction means of an upper forming mold are triggered at the moment it has to take charge of the glass and is stopped so that it is able to release it. The supports (gravity support, suction lower mold, specific support) that have to be offloaded or loaded with the glass by an upper forming mold are generally mobile laterally and can pass under the upper forming mold to make it possible to transfer the glass with the upper forming mold. To make this transfer possible, these supports and/or the upper forming mold are driven with a vertical relative movement enabling them to move toward one another or away from one another. After movement toward one another, the upper forming mold can take hold of or release the glass onto one of these supports. This transfer being done, the upper forming mold and the support move apart vertically and the support (whether loaded with glass or not, depending on the type of transfer) is moved laterally. Another support loaded or not with glass depending on the transfer to be carried out can then be placed under the upper forming mold.
If an upper forming mold releases the glass onto a suction lower mold type support, the glass is lightly pressed at its periphery between the upper forming mold and the suction lower mold for the time for which the suction of the suction lower mold is triggered in order to seal the periphery of the first principle face of the glass with the suction lower mold, together with the periphery of any other sheets of glass between them in a stack. The suction by the suction lower mold then acts immediately on the lower face of the glass (with no leaks at the edges), and in the case of a stack the vacuum is communicated to all its sheets. For this pressing to be effective, the suction lower mold and the upper forming mold releasing the glass onto it must have complementary shapes.
An upper forming mold is advantageously placed in a chamber maintained at a substantially constant temperature. The device according to the invention may comprise a plurality of juxtaposed chambers maintained at different and decreasing temperatures on the path of the glass. The first chamber on the path of the glass is termed the separation chamber and comprises a separation upper forming mold responsible for separating the glass from its last gravity support and releasing it onto a specific support or a suction lower mold. The last chamber on the path of the glass is termed the cooling chamber and generally does not comprise any upper forming mold. A specific support carrying the glass termed the cooling specific support may enter therein and the glass may be offloaded from it thanks to a support termed an offloading support, the latter passing under the glass and rising to take charge of it and to exit from the cooling chamber. The device may further comprise a transfer chamber situated between the separation chamber and the cooling chamber, in particular for the situation in which the separation upper forming mold releases the glass onto a preliminary support preceding the cooling specific support. That preliminary support may be a suction lower mold or a specific support different from the cooling specific support and termed a preliminary specific support. The transfer chamber is equipped with an upper forming mold the role of which is to offload the glass from the preliminary support coming from the separation chamber and release it onto the cooling specific support.
The device according to the invention therefore generally comprises two or three chambers each maintained at a substantially constant temperature but the temperatures of which chambers decrease along the path of the glass. In the case of two chambers, the laterally mobile cooling specific support shuttles between the two chambers. It receives the glass in the separation chamber, then enters the cooling chamber in which it is offloaded of the glass, then returns empty into the separation chamber to receive the next glass, and so on. In the case of three chambers, the laterally mobile preliminary support shuttles between the separation chamber in which it receives the glass and the transfer chamber in which it is offloaded of the glass and then returns empty to the separation chamber to receive the next glass, and so on. During this time, the cooling specific support, mobile laterally, shuttles between the transfer chamber in which it receives the glass and the cooling chamber in which it is offloaded of the glass and then returns empty to the transfer chamber to receive the next glass, and so on. In the system with three chambers, the presence of a supplementary chamber enables the reduction of temperature to be staggered more progressively.
Shuttling between two juxtaposed chambers, these supports participate in cooling the glass progressively, without themselves undergoing the whole thermal cycle to which the glass is subjected. These supports therefore always remain hot, which contributes to saving energy, and they are able to pass very rapidly from one chamber to the other. The manufacturing cycle can therefore be very fast. These supports shuttling between two chambers carry turn and turn about all the glass of a production run. They are therefore manufactured only once, which also works toward cost reduction.
Moreover, the temperature of the gravity supports may be higher on entering the bending furnace. In fact, the supports being offloaded at a temperature of more than 560° C., they are able to return relatively hot, in particular at temperatures between 200 and 500° C. at the entry of the furnace, without undergoing strong cooling. Maintaining the gravity supports at high temperatures significantly reduces the quantity of energy necessary to heat them and, moreover, they also serve to heat the glass as soon as it is loaded. The path to be taken by the gravity supports is also shortened. All these elements work toward cost reduction.
The gravity supports each loaded with glass are able to circulate like a train in a tunnel furnace for bending of the glass by gravity generally at a temperature between 590 and 750° C. depending on the composition of the glass. The temperature of the furnace decreases toward the end, producing slow cooling, at between 0.4 and 0.8° C./second, until the glass is at a temperature generally around 585° C. The train passes under the separation upper forming mold, the latter taking charge of the glass from each of the gravity supports one after the other. The separation of the glass from its gravity support occurs at a temperature greater than 560° C. and preferably at a temperature greater than 575° C., or even greater than 590° C. The glass sags under its own weight by virtue of its passage in the tunnel furnace at its plastic deformation temperature before arriving in position under the separation upper forming mold. Each support carrying a bent glass stops under the separation upper forming mold. By vertical relative movement of the separation upper forming mold and the gravity support in position below it, the forming mold is moved sufficiently toward the glass to be able to take charge of it after its suction is triggered. The first upper forming mold then rises so that a support (of the specific support or suction lower mold type) that is laterally mobile can be positioned under it. It then moves toward that support and releases the glass onto it by stopping the suction.
The glass generally passes through the whole of the critical temperature range either supported by at least one specific support or being held by its second principal face by at least one upper forming mold provided with suction means, with the result that the peripheral zone of the first principal face of the glass is never in contact with a solid.
The devices used comprise separation and transfer means able to separate the glass from the gravity support and to deposit it on a so-called cooling specific support. The separation and transfer means comprise a separation upper forming mold provided with suction means, in particular of the skirt type, enabling the glass to be held against it by its second principal face, said separation upper forming mold being able to take charge of the glass and offload it from the gravity support. The suction functions in order for the separation upper forming mold to be able to take charge of the glass and to offload it from the gravity support, and then to move away from the gravity support carrying the glass. The upper forming mold holding the glass against it is then positioned over another support, after which the suction is stopped so that the upper forming mold can release the glass onto that other support. As already explained, this other support may be the cooling specific support itself or a preliminary support preceding the cooling specific support. This preliminary support may be a suction lower mold or a specific support different from the cooling specific support and termed a preliminary specific support. The separation upper forming mold holds the glass by its second principal face which in particular enables the first principal face of the glass to be free of any contact with any solid, which is favorable to the temperature homogenization of this first principal face of the glass in its peripheral zone.
An embodiment is described hereinafter employing two chambers and a cooling specific support shuttling between the two chambers. In this embodiment, the separation and transfer means comprise a separation chamber comprising a separation upper forming mold provided with skirt type suction means enabling the glass to be held against it by its second principal face. The gravity support is mobile laterally and able to be positioned under the separation upper forming mold, the gravity support and the separation upper forming mold are adapted to be moved toward one another or away from one another (by movement of either one or both of them) so that the separation upper forming mold can take charge of the glass and offload it from the gravity support and can then be moved away from the latter on rising into the separation chamber with the glass, the cooling specific support is mobile laterally and able to be positioned under the separation upper forming mold or to be moved away from the latter, and the cooling specific support and the separation upper forming mold are able to be moved toward one another or away from one another (by movement of either one or both of them) so that the separation upper forming mold can release the glass onto the cooling specific support. The gravity support carrying the glass is positioned under the separation upper forming mold, after which the glass separated from the gravity support by the separation upper forming mold and held by the separation upper forming mold in the separation chamber at a temperature lower than the temperature of the glass on the gravity support at the moment of separation, after which the cooling specific support, being mobile laterally and able to enter or exit the separation chamber, is positioned under the glass and the separation upper forming mold releases the glass onto it, after which the cooling specific support carrying the glass exits the separation chamber for continued cooling of the glass.
The glass on its gravity support passes under the separation chamber. The separation upper forming mold and the gravity support are then moved toward one another by vertical relative movement and the separation upper forming mold takes charge of the glass, separates it from the gravity support and raises it substantially high in the separation chamber for the cooling specific support, then empty, to be able to pass under the glass. The temperature of the separation chamber is lower than that of the glass at the moment the separation upper forming mold takes charge of it. In particular, the temperature of the separation chamber may be between 540 and 585° C. The suction serving to hold the glass against the separation upper forming mold by the second principal face of the glass contributes to the homogenization of the temperature of the peripheral zone of the first principal face of the glass. The glass is therefore held for at least 5, and even at least 6 or even at least 7 seconds. The separation upper forming mold and the cooling specific support are then moved toward one another by vertical relative movement and the separation upper forming mold releases the glass onto the cooling specific support, after which the separation upper forming mold and the cooling specific support are separated again. The cooling specific support then carries the glass by lateral movement into a cooling chamber the temperature of which is set to a temperature lower than the temperature of the separation chamber, and in particular may be between 400 and 565° C. The separation upper forming mold can then take charge of the next glass. An offloading support then enters the cooling chamber, passes under the glass and then rises on taking charge of it and exits it from this chamber for its continued cooling. In this variant, the passage of the first principal face of the glass (in the lower face position) below the upper homogeneous temperature may be effected on the cooling specific support but is preferably effected while the glass is held against the separation upper forming mold, the glass thereafter being placed on the cooling specific support in the critical temperature range. On that support, the glass can be cooled relatively rapidly, at a mean rate between 0.8 and 2.5° C./second. The glass may exit the cooling chamber carried by the offloading support while its first principal face is still in the critical temperature range if the offloading support is a support of the specific support type. The offloading support advantageously takes charge of the glass when the latter is at a temperature between 520 and 540° C.
An embodiment is described hereinafter employing three chambers with two specific supports each shuttling between two chambers. According to this variant, the separation and transfer means comprise
The gravity support is mobile laterally and able to be positioned under the separation upper forming mold, the gravity support and the separation upper forming mold are able to move toward one another or away from one another (by movement of either one or both of them) so that the separation upper forming mold can take charge of the glass, offload it from the gravity support and then move it away therefrom, the preliminary specific support is mobile laterally and able to enter the separation chamber, to be positioned under the separation upper forming mold, the preliminary specific support and the separation upper forming mold are able to be moved toward one another or away from one another so that the separation upper forming mold can release the glass onto the preliminary specific support and then move away therefrom, the preliminary specific support is able to exit the separation chamber loaded with glass and then able to enter the transfer chamber (the exit from the separation chamber and the entry of the transfer chamber generally being concomitant during the same lateral movement) and to be positioned under the transfer upper forming mold, the preliminary specific support and the transfer upper forming mold are able to be moved toward one another or away from one another (by movement of either one or both of them) so that the transfer upper forming mold can take charge of the glass, offload it from the preliminary specific support, and the be moved away from the latter, the cooling specific support is mobile laterally and able to enter or to exit the transferred chamber and to be positioned under the transfer upper forming mold or to be moved away from that position, and the cooling specific support and the transfer upper forming mold are able to be moved toward one another or away from one another so that the transfer upper forming mold can release the glass onto the cooling specific support. Compared to the preceding situation, a supplementary chamber, termed the transfer chamber, is located between the separation chamber and the cooling chamber and a preliminary specific support precedes the cooling specific support and shuttles between the separation chamber and the transfer chamber.
The gravity support carrying the glass is positioned under the separation upper forming mold, after which the glass is separated from the gravity support by the separation upper forming mold and held against the separation upper forming mold in a separation chamber at a temperature lower than the temperature of the glass on the gravity support at the moment of separation, after which the preliminary specific support, mobile laterally and able to enter or exit the separation chamber, is positioned under the glass, after which the separation upper forming mold releases the glass onto it, after which the preliminary specific support carrying the glass exits the separation chamber and enters the transfer chamber equipped with the transfer upper forming mold, the temperature of the transfer chamber being lower than the temperature of the separation chamber, after which the glass is separated from the preliminary specific support by the transfer upper forming mold, after which a specific support able to support the glass without contact with the peripheral zone of its first principal face, termed a cooling specific support, is positioned under the glass and the transfer upper forming mold releases the glass onto it, after which the cooling specific support carrying the glass exits the transfer chamber for continued cooling of the glass. For continued cooling of the glass, the cooling specific support carrying the glass can enter a cooling chamber set to a temperature lower than the temperature of the transfer chamber, the cooling chamber being able to be at a temperature between 350 and 520° C.
The beginning of the process starts as in the preceding situation (preceding situation: two chambers and a cooling specific support) up to the point of release of the glass by the separation upper forming mold since for this the separation upper forming mold and the preliminary specific support are moved toward one another by vertical relative movement and the separation upper forming mold releases the glass onto the preliminary specific support, after which the separation upper forming mold and the preliminary specific support are separated again. The preliminary specific support then moves the glass laterally into the transfer chamber. The separation upper forming mold can then take charge of the next glass. In the transfer chamber, the transfer upper forming mold and the preliminary specific support are moved toward one another by vertical relative movement and the transfer upper forming mold takes charge of the glass and rises to allow the empty preliminary specific support to go back into the separation chamber in order to receive the next glass. The cooling specific support (empty at this stage) is positioned under the transfer upper forming mold, after which the cooling specific support and the transfer upper forming mold are moved toward one another and the transfer upper forming mold releases the glass onto the cooling specific support and then rises to allow the cooling specific support carrying the glass to enter the cooling chamber. An offloading support then enters the cooling chamber, passes under the glass and then rises, takes charge of it and exits it from this chamber for continued cooling. In this variant, the passage of the first principal face of the glass (in the lower face position) below the upper homogeneous temperature may occur when the glass is on the preliminary specific support, in the separation chamber or in the transfer chamber, or when the glass is held against the separation upper forming mold, the glass then being placed on the preliminary specific support in the critical temperature range. On that support as well as on the cooling specific support the glass may be cooled relatively rapidly, at a mean rate between 0.8 and 2.5° C./second. The passage of the peripheral zone below the lower homogeneous temperature may occur in the cooling chamber. The glass may also leave the cooling chamber carried by the offloading support while its first principal face is still in the critical temperature range if the offloading support is a support of the specific support type. The presence of three chambers makes it possible to stagger the temperature slightly more progressively. The separation chamber may therefore be in the temperature range 550-590° C., the transfer chamber may be in the temperature range 500-560° C. and the cooling chamber may be in the temperature range 350-520° C., it being understood that the temperature of the cooling chamber is lower than that of the transfer chamber and that the temperature of the transfer chamber is lower than that of the separation chamber. The temperature of the separation chamber is lower than that of the glass at the moment it is taken charge of by the separation upper forming mold. From the separation of the glass from the gravity support and at least until the glass exits the cooling chamber the peripheral zone of the first principal face of the glass is not in contact with any solid.
An embodiment is described hereinafter using three chambers with a shuttle suction lower mold and a shuttle specific support.
This system is substantially identical to the preceding one except that the preliminary specific support is replaced by a suction lower mold serving as a preliminary support. This mold terminates the bending of the glass in the case of relatively complex shapes. The temperature range of the chambers is substantially identical to the preceding situation. However, in this variant, the passage of the first principal face of the glass (in the lower face position) below the upper homogeneous temperature occurs after bending on the suction lower mold, in particular when the glass is held against the transfer upper forming mold. The glass is then placed on the cooling specific support in the critical temperature range.
According to this variant, the separation and transfer means comprise
The gravity support is mobile laterally and able to be positioned under the separation upper forming mold, the gravity support and the separation upper forming mold are able to be moved toward one another or away from one another so that the separation upper forming mold can take charge of the glass, offload it from the gravity support and then be moved away from the latter, the suction lower mold is mobile laterally and able to enter the separation chamber, to be positioned under the separation upper forming mold, the suction lower mold and the separation upper forming mold are able to be moved toward one another or away from one another so that the separation upper forming mold can release and press the glass onto the suction lower mold and then be moved away from the latter, the suction lower mold is able to exit the separation chamber loaded with glass and then able to enter the transfer chamber (the exit of the separation chamber and the entry of the transfer chamber generally being concomitant during the same lateral movement) and to be positioned under the transfer upper forming mold, the suction lower mold and the transfer upper forming mold are able to be moved toward one another or away from one another (by movement of either one or both of them) so that the transfer upper forming mold can take charge of the glass, offload it from the suction lower mold and then be moved away from the latter, the cooling specific support is mobile laterally and able to enter or to exit the transfer chamber and to be positioned under the transfer upper forming mold or to be moved away from that position, and the cooling specific support and the transfer upper forming mold are able to be moved toward one another or away from one another (by movement of either one or both of them) so that the transfer upper forming mold can release the glass onto the cooling specific support.
The gravity support carrying the glass is positioned under the separation upper forming mold, after which the glass is separated from the gravity support by the separation upper forming mold and held against it in the separation chamber at a temperature lower than the temperature of the glass on the gravity support at the moment of separation, after which a bending suction lower mold able to bend the glass by suction on its first principal face, termed a suction lower mold, mobile laterally and able to enter or to exit the separation chamber is positioned under the glass, after which the separation upper forming mold releases the glass onto it, after which the suction lower mold carrying the glass exits the separation chamber and enters the transfer chamber, the temperature of the transfer chamber being lower than the temperature of the separation chamber, the glass being bent on the suction lower mold in the separation chamber and/or the transfer chamber, after which the glass is separated from the suction lower mold by the transfer upper forming mold, after which the cooling specific support is positioned under the glass and the transfer upper forming mold releases the glass onto it, after which the cooling specific support carrying the glass exits the transfer chamber for continued cooling of the glass. For continued cooling of the glass, the cooling specific support carrying the glass can enter a cooling chamber set to a temperature lower than the temperature of the transfer chamber, the cooling chamber being able to be at a temperature between 350 and 520° C.
In the context of the present invention, a so-called specific support is used, with no contact with the peripheral zone of the first principal face of the glass, in at least a part of the critical temperature range. Different types of specific support may be envisaged.
According to one embodiment a specific support comes into contact with the first principal face of the glass through a plurality of contact zones touching the glass only in the “contact band” defined above. The supporting surface of the specific support coming into contact with the glass is therefore discontinuous.
Each contact zone preferably has on its surface a refractory fibrous material well known to the person skilled in the art to reduce the risk of marking of the hot glass by a tool. This fibrous material can be a woven or felt or knitted material and in particular a “tempering knitted material” usually serving to cover the peripheral rings supporting the glazing during annealing and having the advantage of having an open texture. It contains refractory fibers and has a high open porosity that confers on it a property of thermal insulation. A specific support of this kind may comprise 4 to 300 contact zones. The greater the number of contact zones, the smaller the contact area of each zone. The sum of the areas of all the contact zones may represent 0.2 to 5% of the area of the first principal face of the sheet of glass in the lower position. The contact area of each contact zone may be in the range from 50 mm2 to 5500 mm2 and preferably from 500 mm2 to 4000 mm2. The specific support preferably comprises 4 to 20 or even 6 to 20 contact zones each of relatively large area, that is to say an area each in the range from 500 mm2 to 4000 mm2.
A specific support of this kind can have a fixed geometry perfectly complementary to that of the first principal face of the glass with which it has to come into contact. A support of this kind may for example have crenellated support lines.
A specific support of this kind may also feature contact zones connected to supporting elements comprising mobility means of the contact zone driven by the weight of the glass at the moment of its reception by the support, modifying the orientation of the contact zone of the glass and/or damping the reception of the glass by the support. In particular:
According to this embodiment using a specific support touching the glass only in the “contact band” defined above, one feature of the device is that an upper forming mold able to act on the glass (taking charge of it or depositing it) over that specific support has a contact surface for the glass projecting more than 30 mm toward the exterior of the contact zones of the cooling specific support.
According to another embodiment, the specific support is an inclined peripheral track: the glass is deposited cantilever-fashion by the lower border of its edge surface (such as the lower edge of its edge surface) on the track and without contact with the lower face of the glass; the glass is therefore considered to be supported from below but without contact with its lower face and outside the peripheral zone. This support forms a continuous support surface to come into contact with the glass.
A forced convection system can accelerate cooling in the cooling chamber and/or the transfer chamber, if any; a convection system of this kind may be connected to a support or installed in one of these chambers. A convection cooling system may therefore generally be carried by a cooling specific support, a preliminary specific support or an offloading specific support. A convection cooling system may be installed in the transfer chamber, in the cooling chamber and on the final device tasked with conveying the glass to a cooling zone.
The routing of the glass between the cooling chamber and the final offloading zone where the glass is set and cooled sufficiently to be manipulated by operators and stored can be effected in various ways. In particular, an offloading support, in particular one actuated by a robot, may come below the glass, rise to take charge of the glass, and then exit the glass from the cooling chamber. It can then deposit it on a conveyor taking the glass off to a cooler offloading zone. The robot then returns with the same offloading support to take charge of the next glass in the cooling chamber. The method is therefore limited to a single offloading support connected to the robot, which avoids multiple operations of coupling and uncoupling a support and a robot. Given that at the moment the glass is taken charge of by the offloading support the glass is at a temperature close to or greater than the lower homogeneous temperature, the offloading support is advantageously of the “specific support” type (termed an “offloading specific support”) having a plurality of contact zones with the central zone of the first principal face of the glass. The cooling specific support and the offloading specific support are advantageously both of the type having a plurality of zones of contact with the central zone of the first principal face of the glass. They can therefore both come exclusively into contact in the same surface band of the first principal face of the glass, termed the “contact band” and already defined hereinabove. This is made possible by the fact that the contact zones of these two supports are discontinuous and can therefore cross over at the moment of the transfer of the glass from the cooling specific support to the offloading specific support, like the teeth of two combs. It is in fact preferably to avoid contact with the glass in its central zone more than 200 mm and preferably more than 170 mm and preferably more than 150 mm from the edge because in the method according to the invention the glass is hotter in the central zone than at the periphery and is therefore more sensitive to marks in the central zone. Moreover, this “contact band” is sufficiently peripheral for the curvature of the glass to be well maintained, without the peripheral zone collapsing. According to this embodiment, the offloading support and the cooling specific support both comprise support elements comprising contact zones that all come into contact with the glass exclusively in a contact band between an exterior limit and an interior limit, the exterior limit of the band being at least 50 mm and preferably at least 60 mm and preferably at least 70 mm from the edge of the glass, the interior limit of the band being at most 200 mm and preferably at most 170 mm and preferably at most 150 mm from the edge of the glass, the contact zones of the offloading support and of the cooling specific support being at least in part interleaved in the contact band at the moment of loading the glass onto the offloading support. The contact zones of the cooling specific support and the offloading support can therefore all come into contact with the glass exclusively in a contact and substantially parallel to the edge of the glass, said contact band being at most 150 mm wide, or even at most 100 mm wide, or even at most 80 mm wide, the contact zones of the offloading support and of the cooling specific support being at least in part interleaved in the contact band at the moment of loading the glass onto the offloading support. In particular, during the transfer of the glass, there preferably exists, seen from above and in orthogonal projection in a horizontal plane, at least one support element of the cooling support coming to intersect the straight line segment tangential to the exterior edges of two contact zones of a pair of adjacent support elements of the offloading support, that intersection occurring between the two adjacent support elements of the offloading support. This situation generally arises for at least 2 different support elements of the cooling support, or even at least 3, or even at least 4, or even at least 5, or even at least 6 different support elements of the cooling support. This property reflects the fact that the contact zones of the two supports are interleaved in a narrow contact band parallel to the edge of the glass at the moment of the transfer of the glass. The intersection may involve the contact zone of the cooling support or any part of the support element of the cooling support, between the contact zone and the chassis of the cooling support.
During transfer of the glass there may exist, seen from above and in orthogonal projection in a horizontal plane, at least one pair of adjacent support elements of one of the two supports (the cooling one or the offloading one), termed the first support, such that the straight line segment passing through the center of their contact zone comes to intersect a support element of the other support, in particular its contact zone, that intersection occurring between the two adjacent support elements (forming a pair) of the first support. This situation can arise for at least 2, or even at least 3, or even at least 4, or even at least 5 different pairs of support elements of one of the supports, it being understood that a support element may be part of two different pairs. This property also reflects the fact that the contact zones of the two supports are interleaved in a narrow contact band parallel to the edge of the glass at the moment of the transfer of the glass. The intersection may involve the contact zone or any part of the support element of the other support. The center of a contact zone is, seen from above, the barycenter of the orthogonal projection of the contact zone onto a horizontal plane. That barycenter is also the geometrical center or center of mass of the projection of the zone and might be termed the “centroid” or “geometric center”. This is the point on the surface of the projection of the zone corresponding to the barycenter of an object of the same shape, infinitely thin and of homogeneous density.
In the method according to the invention, the overall rate of cooling of the glass generally only rises between the separation of the glass from the gravity support and its exit from the cooling chamber. In the separation chamber, the mean rate of cooling of the glass is generally between 0.5 and 1.2° C. per second. In the cooling chamber, the mean rate of cooling of the glass is generally between 0.8 and 2.5° C. per second. In the transfer chamber, if any, the mean rate of cooling of the glass is generally between 0.8 and 2.5° C. per second.
The mean rate of cooling in a chamber (separation, transfer or cooling chamber) is calculated from the glass temperature difference between the moment it enters the chamber and the moment it exits the chamber, divided by the time spent in the chamber.
The glass cools even more rapidly once it has exited the cooling chamber, at a rate generally between 2 and 5° C. per second at least until the glass reaches a temperature of 400° C.
In the method according to the invention, the cycle time is generally between 10 and 60 seconds, a cycle time being the time elapsed between the passage of two glasses at the same location of the process and at the same stage thereof.
The invention enables the manufacture of a bent sheet of glass the maximum tension stress in which is less than 4 MPa and even less than 3 MPa and the edge compression stress in which is greater than 8 MPa. The passage from the compression zone to the tension zone is generally located at a distance from the edge between 1 and 5 millimeter. The maximum tension stress is generally situated at a distance from the edge between 5 and 40 millimeter, in particular between 15 and 40 millimeter. This sheet is that in the lower position in the stack of sheets that have undergone the method according to the invention. The face of this sheet, in the lower position in this stack (first principal face) is generally convex. This sheet may be placed in laminated glazing, the face that was in the lower position during the method according to the invention forming the face 1 of the glazing. It is then located on the convex side of the glazing.
The invention concerns the manufacture of laminated glazing combining two sheets of glass where the thickness of one of them is in the range from 1.4 to 3.15 mm and the thickness of the other of them is in the range from 0.5 to 3.15 mm. In the situation where the sheets have different thicknesses, the face 1 of the laminated glazing is a face of the thicker or thickest sheet.
Each sheet of glass may be covered before bending it with one or more sheets of enamel or one or more thin anti-solar (low-e) type layers, conductive layers or other layers usually applied to automobile glazing.
The bent glass manufactured in accordance with the invention relates more particularly to the manufacture of glazing, in particular laminated glazing, of the road vehicle windshield or roof type. The area of one of their principal surfaces is generally greater than 0.5 m2, in particular between 0.5 and 4 m2. There may generally be placed in the central region of the glass an imaginary circle with a diameter of least 100 mm and even of at least 200 mm and even of at least 300 mm, all points on which are farther than 200 mm from all the edges of the glass, which characterizes a certain magnitude of the glass. The glass generally has four edges (also termed bands), the distance between two opposite edges generally being greater than 500 mm and more generally greater than 600 mm and more generally greater than 900 mm.
The device comprises a train 130 of gravity supports 131 each carrying a glass. This train circulates at a lower level 134 of the device, in a tunnel furnace heated to the plastic deformation temperature of the glass. During its conveyance (from right to left in the figures), the glass sags under its own weight finally to espouse the contact track of the gravity support 131 under the periphery of the first principal face of the glass. Each support finally arrives under a vertically mobile upper forming mold 233 able to pass from the upper level 135 to the lower level 134 and vice versa. This upper forming mold 233 is in a chamber 236 the atmosphere in which is at a temperature between 550 and 590° C. The contact track of this upper forming mold 233 has a shape complementary to that of the suction mold 200. The upper forming mold 233 can take charge of the glass at the lower level 134 by suction thanks to the skirt 240 surrounding it. At the upper level 135 is located a suction lower mold 200 the face 201 of which in contact with the glass is solid and includes orifices in order to communicate vacuum to the first principal face of the glass in the lower position. This mold 200 shuttles between a position under the upper forming mold 233 in the chamber 236 and a juxtaposed chamber 136 heated to a temperature between 500 and 560° C. This chamber 136 contains a vertically mobile upper forming mold 133 able to take charge of the glass thanks to a skirt 241. At the upper level 135 is also located a laterally mobile cooling specific support 137 shuttling between a position under the upper forming mold 133 in the chamber 136 and a position in the cooling chamber 138, the temperature in which is between 350 and 520° C. A door 139 on the structure carrying the cooling specific support 137 therefore moves with it. This door therefore closes the bulkhead between the chambers 136 and 138 when the cooling specific support is in the chamber 138. It closes the bulkhead between the chambers 136 and 236 when the cooling specific support 137 is in the chamber 136. A door 239 on the structure carrying the suction lower mold 200 therefore moves with it. This door 239 therefore closes the bulkhead between the chambers 136 and 236 when the suction lower mold 200 is in the chamber 136. The support 137 and the mold 200 move simultaneously in translation, as if they were fastened to one another and without modification of the distance that separates them. The glass is offloaded from the cooling specific support 137 by the offloading support 140 held by the arm 142 of a robot 141. The cooling specific support 137 is of the type from
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 1751568 | Feb 2017 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2018/050430 | 2/22/2018 | WO | 00 |
