Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B23/00—Re-forming shaped glass
  • C03B23/02—Re-forming glass sheets
  • C03B23/023—Re-forming glass sheets by bending
  • C03B23/025—Re-forming glass sheets by bending by gravity
  • C03B23/0258—Gravity bending involving applying local or additional heating, cooling or insulating means
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B29/00—Reheating glass products for softening or fusing their surfaces; Fire-polishing; Fusing of margins
  • C03B29/04—Reheating glass products for softening or fusing their surfaces; Fire-polishing; Fusing of margins in a continuous way
  • C03B29/06—Reheating glass products for softening or fusing their surfaces; Fire-polishing; Fusing of margins in a continuous way with horizontal displacement of the products
  • C03B29/08—Glass sheets

Definitions

• the present invention relates to a method and a device for bending glass sheets.
• the glass sheets are brought to high temperature in order to bead them from flat sheets.
• the bending temperature corresponding to a softening of the glass is around 600-700 ° C.
• Various techniques are used to proceed with the bending of the glass sheets, depending on the nature of the glazing to be produced, its dimensions , of its form.
• the most common techniques for the production of glazing with very pronounced curvatures comprise at least partly the shaping of the glass sheet on a frame or bending skeleton which confers its profile on the periphery of the final glazing.
• the forming takes place at least partly by gravity on the frame.
• the bending may be entirely carried out on the frame or may also be subject to a pressing which itself may concern either limited portions of the surface of the sheet or all of it.
• a method includes for example a first training of the glass sheet on the frame, followed by the application of the sheet carried by the frame on a counter mold.
• the bending techniques discussed above are all closely dependent on the thermal conditioning of the sheets.
• the deformation by gravity is obviously directly dependent on the temperature which conditions the softening of the glass, but even when the deformation is partly effected by pressing, the temperature level at which it is carried out is important insofar as it controls the degree of ease of deformation and consequently the efforts to be applied and the resulting stresses in the sheet.
• the distribution of temperatures to bend the leaves in the best conditions is a function of the shape of the glazing products. This distribution and its application over time can be relatively difficult to achieve in traditional ovens.
• the production of complex curvatures is currently preferably carried out by passing the glass sheets into furnaces comprising sections in which the conditions are set in a fixed manner according to each type of glazing concerned.
• the glass sheets pass "step by step” from one section of the oven to the next, and their treatment is well controlled by the stable conditions established in each section.
• the residence time in each section is typically of the order of 20 to 80 seconds, which makes it possible to take advantage of the peculiarities of the thermal conditions implemented in the section in question.
• Different ways of furnishing step-by-step ovens have been proposed previously to best meet the conditioning requirements of glass sheets with complex crowns.
• Conventional bending ovens have, primarily, heating elements distributed above and below the glass sheet. Incidentally heating elements are arranged on the side walls to maintain a great uniformity of temperature at any point of the oven.
• the bending ovens that operate step by step have good possibilities for controlling the thermal conditions, as recalled above, they have the disadvantage of limiting production rates. They also have limitations in terms of both the size of the sheets that can be processed and the flexibility of changing the processed parts. For these reasons, despite being not the most suitable for producing complex bending parts, continuous furnaces are still widely used.
• the object of the invention is to reach continuous furnaces, operating conditions as well controlled as those obtained on the ovens step by step.
• the invention proposes to make sure that the distribution of heat on the surface of the glass sheet follows the progression thereof.
• the production rates being set as high as possible the progression of the leaves is relatively fast. Under these conditions it is not possible to ensure a movement of the heating elements carrying out the heat distribution in the direction of progression of the glass sheets. To a certain extent it is possible to have movable heating elements facing glass sheets, but regardless of the difficulty it may have to have mechanisms for moving the heating elements, the extent of the movements it is It is not possible to arrange a sufficiently long follow-up of the leaves to reach the required temperature gradients.
• the invention proposes to solve this problem by arranging on the path of the glass sheets a set of heating elements, covering at least a portion of the surface of the sheets and which extends over at least part of the path in the oven, the operation of all of these heating elements being controlled in a programmed manner so that the start of these heating elements accompanies the progression of the sheet to be treated.
• the overall heating of the sheets is to a significant extent carried out by means of this set of heating elements so as to control the bending process from the moment it manifests itself. Therefore it is advantageous to have this set of heating elements at least in the part of the oven in which the softening of the glass is achieved, and preferably before it. For ordinary "float" glasses, this corresponds to arranging all these heating elements at a point in the oven where the temperature reaches the value of approximately 400 ° C., and possibly even as soon as it reaches a value of about 300 0 C.
• the speed of progression of the glass sheets in the most successful bending plants reaches and even exceeds 10cm / s. It is most frequently of the order of 5 to 7 cm / s. In practice a non-negligible treatment time to form the desired temperature gradient is necessary. For this reason it is necessary to ensure that several elements located one after the other can successively warm the glass sheet according to the required distribution.
• the location of the zones that must support this properly distributed heating is not generally oriented in a direction parallel to the progression of the leaves, nor does it necessarily extend over the entire height of these sheets. It is therefore necessary to make the implementation of the heating elements ensuring this distribution, on the one hand only heats the areas concerned to the exclusion of neighboring areas (to form the necessary gradient), and on the other hand that the displacement of the sheet is followed by the successive and synchronized intervention of heating elements located on the path of the sheet.
• a particular difficulty to solve is related to the inertia that characterizes the heating devices. It is necessary, in order to ensure a precise distribution, to have elements whose rise in temperature is as fast as possible, and likewise the decrease which follows quickly. Heaters having the first feature are commercially available. On the other hand, these same elements present, as we will see later in detail, a certain thermal inertia so that the descent in temperature is never as fast as it would be desirable to be able to have an adjustable source of heat instantly to follow the most appropriate conditions. For this reason the control of the heating elements must be carried out according to a relatively complex process which integrates this particularity.
• the operation of the heating element (s) used is controlled by the dimensions of the areas of the sheet that are the subject of this particular distribution. It is also a function of the rate of progression of the sheets and the dimensions of the heating element or elements used for this localized heating. It is finally a function of the thermal characteristics of the heating element (s), as well as the distance from it (these) to the glass sheet.
• thermo inertia speed of the sheets, dimension of the treated area, size of the heating elements, etc.
• speed of the sheets does not follow a continuous regime.
• Each element follows a cycle of operation depending on the scrolling of the glass along this element.
• the successive elements when several heating elements are used, reproduce the same cycle with a translation corresponding to the displacement of the glass sheet.
• each heating element is a function of the heat transfer required.
• the heating elements may for example be maintained between a relatively low base power, and increased power to the passage of the zone of the sheet to "overheat".
• the adjacent heating elements in the direction of progression of the glass sheets may operate successively or, at least over part of their operating cycle, simultaneously. Triggering the operation of elements successive ones may also comprise a more or less long time interval during which no element is powered or is powered to deliver a more restricted power.
• elements of dimensions of the order of twenty centimeters, for glass scroll speeds of about 5 cm / s may lead to modulate the operating time of about 1 to 4s for areas to be treated a few tens of centimeters.
• the invention proposes to modulate the distributed heat input using the distance separating heating elements from the glass sheet.
• the implementation of the heating elements is proposed in the context of ovens essentially of the "step-by-step" type.
• the movements of the heating elements that follow the course of the process are controlled by the need to clear the space required for moving the sheets and their support from one section of the oven to the next.
• the movements of the heating elements operate continuously without the progression of the glass sheets being interrupted.
• the simultaneity of the movements of the glass sheet and the operation of the heating element vis-à-vis implied by the implementation of the invention requires means to control rigorously their synchronization. This is achieved for example by means of sensors detecting the presence of the sheets and controlling the selection of the heating elements to be activated.
• the distributed heat input elements must be able to establish momentary differences in temperatures with the remainder of the sheet sufficient to facilitate accentuated bending and / or having radii of curvature which may to be small.
• the target gradient is that which corresponds to the average temperature in the thickness of the glass sheet, it being understood that in practice the heating elements are situated for convenience on one side of the sheet, the gradient will be greater on the face of the sheet directly exposed to the heating elements in question.
• the useful gradient depends on the mode of obtaining the curvatures. It is most important for curvatures that are produced only by sagging under the effect of gravity. When the method used comprises pressing means, the gradient can be much less marked.
• the gradient can be up to 10 ° C / cm.
• Such important values correspond, for example, to the formation of so-called "panoramic" glazings in which the glass sheet generally has a U-shape, the central part of the glazing being flanked by two lateral parts located in planes orthogonal to this central part.
• the gradient can be substantially smaller and can be established for example at values of the order of 5 ° C / cm. or less.
• the area over which the gradient extends depends on the size of the desired curvature and possibly on its radius of curvature. The smaller the radius should be, the higher the gradient and the smaller the distance it focuses on
• FIG. 1 schematically shows a curved glass sheet having a complex shape of the type for which the implementation of the invention is particularly useful
• FIG. 2 schematically shows a bending process to which the invention can be applied
• FIG. 3 is a schematic top view of the part of the process of FIG. 2 relating to the invention.
• FIG. 4 is a schematic view illustrating a mode of operation of the invention.
• FIG. 5 is a view similar to that of Figure 4 of a variant comprising heating elements whose position is adjustable relative to the glass sheet;
• FIG. 6 represents an embodiment of mobile heating elements
• FIG. 7 is a graph illustrating the typical behavior of an insulated heating element
• FIG. 8 is a graph illustrating the temperature distribution of a series of heating elements leading to a particular curvature of the glass sheet
• FIG. 9 is a graph showing the impact of the distance of the heating element on the intensity of the resulting heating, according to the part of the sheet considered.
• the glass sheet (1) shown in FIG. 1 is of the type comprising a central part whose radii of curvature (Rx and RyI) in the X and Y directions are relatively limited, but which comprises on the sides (2,3 ) and in the Y direction, wings forming areas of small radius curvature (Ry2).
• Such a shaping is of the type proposed for example in the process described in US Pat. No. 6,240,746 which is schematically represented in FIG. 2.
• the beading sheet (4) is placed on a frame (5) which supports it at its periphery.
• the frame carrying the sheet passes through a tunnel furnace (6) driven by a conveyor (7) animated with a uniform movement.
• heating is provided homogeneously by traditional means located on the vault (8), the sole (not shown), and possibly the side walls.
• the temperature of the sheet is thus raised for example to about 400 0 C or more, without reaching the softening point of the glass.
• the temperature of the sheet is then modulated in particular by the provision of heating elements located on the vault (9, 10), these elements being supplied specifically according to their position vis-à-vis the glass sheet. Heating is maintained until complete bending by gravity is achieved.
• the gravity bending is combined with pressing elements arranged locally at the periphery of the glass sheet, means that ensure the complete and rapid application of the sheet on the frame.
• the final shaping is obtained by applying the frame carrying the sheet on a counter mold extending over the entire surface of the sheet.
• the sheet (11) carried by the frame (5) is gradually cooled in an annealing step to freeze its shape and give it the desired mechanical properties.
• the difficulty is to ensure that the proper temperature distribution is achieved in a particularly short time even while the sheet is in motion.
• FIG. 3 is a top view of an embodiment of the invention applied for example to the method of which it has been mentioned.
• the path of the sheets (12, 13) preheated substantially uniformly to a temperature close to that of softening in a tunnel-type furnace is continued in this furnace in which the vault is covered with heating elements (H) of dimensions limited, each element being controlled individually in power but also in a cycle in time, according to a preset program.
• heating elements H
• the temperature distribution on the sheet is not generally adapted to the desired bending.
• the use of a set of elements such as those implemented according to the invention makes it possible to restore better conditions.
• the necessary temperature gradient is schematized by the concentric zones (16, 17).
• the leaves in their progression, pass successively under a series of heating elements whose operation is synchronized with the scrolling of the sheets.
• the dimensions of the heating elements shown are for illustrative purposes only. They can vary very significantly. The smaller these elements are, the more the heated zones can be precisely determined. The multiplication of the number of heating elements has the counterpart of a complexification of the system. Moreover, the reduction of the dimensions is of interest only to the extent, as we will see in connection with FIG. 9, where the distance separating these elements from the glass sheet is in proportion to these dimensions.
• the implementation of the invention comprises the localized thermal input, which thermal input is controlled to apply in any limited area both transversely (Y direction) and longitudinally (X direction) of the sheet of glass. Nevertheless, because of the thermal inertia of the heating elements, the "superheated" zones necessarily include a component in the X direction.
• the implementation principle consists in modulating the operation of the heating elements, which modulation is controlled according to the passage in line with the area of the sheet whose temperature must be increased.
• each element is controlled in time to intervene specifically during the passage of the sheet.
• the sequences of the elements implemented move with the sheet, the elements themselves remaining essentially immobile in the direction of progression of the sheets.
• the absence of mobility of the heating elements avoids the presence of complex mechanisms located in parts of the installation brought to high temperature. The realization of these devices is therefore facilitated.
• the heating elements are further advantageously of small dimensions to be able to apply the input as accurately as possible. In practice, however, it is superfluous to seek dimensions that would be smaller than the distance of the heating elements to the glass sheet due to the dispersion of the inevitable thermal contribution that entails this distance. Under these conditions it is advantageous that the heating elements do not have dimensions of more than 60 cm, and preferably not greater than 40 cm. In practice, dimensions of less than 10 cm do not provide additional precision for the treated area, but limit the heat gains in proportion to their dimensions, the power delivered being a function of the resistance and consequently of the surface of these elements facing the glass sheet.
• FIG. 8a An example of control of the heating elements is shown in Figure 8a. This example corresponds to what is shown in FIG. 3.
• the temperatures are measured in direction A-A for a glass sheet whose total height is 830 mm.
• Figure 8a shows the temperature (TH) of the various elements facing the glass sheet in the end of its path in the bending furnace. It can be seen from this example that depending on the temperature of the sheet in question, the temperature of the heating elements varies significantly. In this example the temperature difference can be as high as 150 0 C, to lead to sheet temperature differences (TG) of about 60 0 C. The highest temperatures are those that face the gradient zones the highest.
• the graph of FIG. 7 illustrates the operation over time of a heating element as implemented according to the invention.
• the power applied in the case presented is 60 kW. This power is applied instantaneously to study the degree of speed of response that can be achieved using this heating element.
• the energy supply instantly switches to 60 kW for an interval of one second and is then interrupted.
• the temperature of the heating element during this brief interval progresses extremely rapidly from 720 to 830 ° C. at the moment when the supply of the element is again interrupted.
• the rise in temperature of the element is practically linear. Its speed reflects the low inertia of the active part of the heating element.
• the element cools but with a decrease which accounts for the inertia of the heating element as a whole including its housing and the way the energy is dissipated from the heating element .
• the descent in temperature without further intervention extends in the case envisaged over about ten seconds to recover practically the initial temperature.
• the sheet which continues to move under the heating element thus remains exposed to radiation from this element after the power supply has been interrupted.
• the heating elements are evenly distributed over the vault of the furnace and it is the conduct of each of the elements that locates the additional supply of heat and the time during which this input is maintained. Additional heating is the result of all the heating produced by the various heating elements activated successively to the passage of a glass sheet.
• the diagram of FIG. 4 illustrates this mode of operation in a very simplified way.
• this second embodiment is distinguished by the fact that the heating elements can be approached from the sheet to establish more precisely the desired temperature gradient.
• the movable heating elements (19,20,21) are lowered to the passage of the sheets so as to approach them.
• the movement of these elements must be perfectly synchronized with the progression of the leaves.
• the movements of each element can be conducted individually or in groups of elements.
• the movement is not necessarily identical, in particular to take account of the evolution of the bending. It may be advantageous, as the bending process progresses, to amplify the displacement of the heating elements in order to better follow the amplification of the curvatures. This is shown schematically in FIG. 5, where the elements, or groups of elements, progressively lower.
• the provisions relating to the mobility of the elements are obviously cumulable with those concerning the power delivered cyclically. These two modes of regulation of the heat input can thus reinforce the effect leading to the formation of the temperature gradient. But it is possible to proceed by keeping the heating elements at a constant temperature, and modulate the local supply only by the variation in distance of the heating elements to the glass sheet.
• the graph of Figure 9 shows the energy distribution on the glass sheet as a function of the distance of a heating element. This element is assumed at uniform temperature over its entire surface. In the form presented the element is of relatively large dimensions (width 150mm). Three distances are indicated 400, 150 and 50mm.
• the graph of Figure 9 shows the energy distribution from this element in the transverse direction along an arbitrary scale. The distances in millimeters are indicated on the abscissa starting from the median plane of the element. It can be seen on the distribution curves that for the greater distance the localization effect remains very limited. The energy intake in the center is not twice that obtained on the sides. Conversely, when the heating element is at a distance of 50mm from the sheet, the sides are practically unheated and the part concerned by the heating is well concentrated under the heating element.
• This concentration of the local heat input makes it possible to modulate the contribution by the play of the variation of distance, possibly independently of the supply of the heating element.
• This arrangement makes it possible, if necessary, to overcome at least part of the thermal inertia of the heating elements.
• the heating elements can deliver a constant power, and only the distance of these elements modulates the local heat input.
• Figure 6 shows an embodiment of mobile heating elements, described in detail in the publication WO 2004/099094, incorporated by reference. It schematically shows a movement of mobile heating elements implemented in the bending of a glass sheet on an articulated frame (23).
• the figure shows the arrangement of the elements transversely to the progression of the leaves.
• the overall symmetry of the device takes into account that the glazing itself, for example a windshield, is symmetrical.
• the glazing comprises side portions that are strongly raised relative to the central portion.
• the junction between these lateral parts and the central part of the glazing comprises areas with strong curvatures and small radius. These areas of small radius are at the articulation of the movable side elements (24,25) of the frame (23).
• These lateral elements of the frame are represented firstly in an initial position called “open", position in which the glass sheet is flat, and secondly in a raised position corresponding to an intermediate stage of the bending stage in which the curvature of small radius is initiated.
• the final bending not shown, still leads to an additional raising of the lateral parts of the frame to the final position described as "closed”.
• series of heating elements are arranged symmetrically.
• Heaters (27,28) arranged laterally are fixed. They contribute permanently to the establishment of the overall temperature conditions in the oven.
• a set of heating elements (29) can be moved vertically from a level corresponding to that of the fixed elements (28,29) to approach a few centimeters of the glass sheet.
• the central portion (29) and its articulated power supply means (30) are presented in two distinct positions. The low position allows for increased heating in the center of the sheet. Such heating is advantageous at the end of the bending process for the sheets which have curvatures not only in the transverse direction shown, but also in the longitudinal direction, that of progression of the glass in the oven.
• Two other movable heating elements (31,32) are presented, on the one hand in the raised position, on the other hand in position partially lowered. These elements are located on either side of the central element (29).
• the figure also shows the supply means (33) associated with these movable heating elements in the two positions.
• Each of the moving heating elements is independent of the others. In the case considered symmetry leads to identical and synchronized movements for the heating elements (31) and (32).

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Re-Forming, After-Treatment, Cutting And Transporting Of Glass Products (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=35079406

Family Applications (1)

Country Status (5)

Families Citing this family (23)

Family Cites Families (29)

• 2005
  • 2005-03-10 BE BE2005/0130A patent/BE1016542A3/fr not_active IP Right Cessation
• 2006
  • 2006-03-09 US US11/908,176 patent/US20080134721A1/en not_active Abandoned
  • 2006-03-09 WO PCT/EP2006/060585 patent/WO2006095007A1/fr not_active Ceased
  • 2006-03-09 EP EP06724994A patent/EP1874701A1/de not_active Withdrawn
  • 2006-03-09 JP JP2008500201A patent/JP2008532906A/ja not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events