FR2484398A1 - METHOD FOR FORMING AND ASSEMBLING HINGED GLASS PANELS, IN PARTICULAR FOR WINDSHIELDS OF MOTOR VEHICLES OR THE LIKE - Google Patents

Abstract

IN THIS PROCESS, THE PANEL WHICH HAS THE LOWEST ABILITY FOR BENDING IS PLACED IN DIRECT CONTACT WITH THE BENDING MOLD THE PANEL WHICH HAS THE LOWEST ABILITY FOR BENDING, AND ON THIS PANEL THE ONE WHICH HAS THE GREATEST ABILITY FOR BENDING AND WHICH WILL OCCUPY THE REVERSE POSITION, IS PLACED ON THIS PANEL. A-SAY THE POSITION OF THE EXTERIOR OR CONVEX FACE IN THE FINISHED PRODUCT. IN THIS WAY, THE UPPER PANEL APPLIES THROUGHOUT ITS SURFACE ON THE LOWER PANEL AND EXACTLY COMBINES THE LATTER'S SHAPE. THE DEVIATIONS FROM THE THEORETICAL CURVATURE ARE COMPENSATED DURING THE ASSEMBLY WITH INTERPOSITION OF THE PLASTIC INTERPOSITION SHEET. THE INVENTION APPLIES IN PARTICULAR TO THE MANUFACTURE OF WINDSCREENS AND BOMB WINDOWS FOR AUTOMOBILES.

Description

The present invention relates to a method of

  bending curved and assembled glass panels, parti-

  specifically intended for use as windshields or

  other safety glass objects in self-driving vehicles

  mobile or the like. The invention relates more particularly to a method of manufacturing assembled and curved glass panels which can be used in cases where the physicochemical properties and / or the thicknesses of the glass panels which are to be used. 'assemble and bend

are not identical.

  To fully understand the progress made by the

  according to the invention, it is first necessary to

  consider the operating procedures and limitations of the pro-

  sales of glass panels assembled and

  already known so far. In these processes, two consecutive phases can be distinguished, namely: forming and assembly, these two phases being repeated in the process

in question.

  During the forming phase, the glass panels are bent and cut and this can be done using two different techniques. When these operations are performed in the order indicated above, the process is known as the "expansion" method. These operations can also be executed in the order

  in which case the process is known as

  process "contour". The process according to the invention can be carried out using one or other of

two forming techniques.

  During the assembly phase, a sheet of plastic material is placed between two panels.

  glass to assemble. Then, we press the sandwich thus ob-

  held (glass plus plastic) in tempe-

  given to expel most of the air emm

  caught between the plastic and the glass; final-

  the laminate is placed for a sufficient period of time

  long, in an autoclave where the actual assembly operation

  can be done under controlled temperature conditions.

ture and pressure.

  To obtain good results with the method of

  brication, the glass panels must be bent

  in such a way that the surfaces in contact are suitable for

  each other or, rather, there should not be any

  noticeable difference in local curvature between the two surfaces.

these to assemble.

  Although, in reality, when the manufacturing process

  upstream and downstream of the curvature phase is

  nally implemented, slight differences in curvature

  between the two surfaces to be assembled do not alter the result of

  final state, it is very different, in terms of obtaining this result, when there is a significant difference in local curvature on one of the two surfaces to be assembled. This case could lead to a detachment of the

  laminated after assembly (bad bonding with interrup-

  along the edges of the laminate and / or in areas

interior.

  Even today, one generally obtains

  appropriate curvature of the two surfaces to be assembled by bending simultaneously in the oven, glass panels to be assembled later. For this, during the bending phase, the glass panels are placed on a horizontal mold, the concave surface facing upwards, in a position identical to that they will occupy in the finished product. For example, during the manufacture of a windshield comprising two glass layers that have the same physicochemical properties and the same thickness, the two glass panels are loaded on the horizontal mold, the concave face turned the top, of such

  way that the glass panel which will form the outer part

  windscreen (convex side) is placed in contact with the mold (ie in the lower position) then, the glass panel which will form the inner part (face

  concave) of the windshield is placed on this panel, (ie

  say in upper position). Then, the two glass panels loaded onto the mold are introduced into the heating furnace, in which the glass is progressively raised.

  at the softening temperature. As a result,

  of glass are in the final shape of the mold, under the

  effects of temperature and gravity; more precise-

  the lower surface of the lower panel, which is in direct contact with the mold, tends to take the form of this

  last while the lower surface of the upper panel

  laughter tends in turn, if properly heated,

  to take the form of the upper surface of the panel

  férieur. It has been found that in order to obtain a good pairing of

  surfaces in contact, the glass panel must be

  at a higher average temperature than that of the

  lower panel .; in fact, the lower viscosity

  Aunt attained by the glass of the top panel allows

  this panel to apply on the bottom panel. To obtain

  to keep these temperature conditions, the heating furnaces of glass panels of the same thickness are usually adjusted in such a way that, especially in the zone

  the amount of heat transferred to the upper panel

  which is mainly transmitted by radiation,

  greater than that assigned to the lower panel

  laughing. It should also be noted that, in order to obtain a correct final shape of the glass panel during the bending phase, the mold that gives the shape can be either of rigid type (in that its geometry does not vary).

  not in the oven, apart from the inevitable deformations

  elastic and thermal) or of articulated type (that is to say,

  re appropriate joints can change the geometry of the mold inside the oven). Rigid type molds are mainly used for parts with low curvature, while molds are typical

  articulated are mainly used in other cases.

  After bending, the glass panels undergo a suitable annealing treatment which, by lowering the glass temperature without causing significant tensions in its mass allows the panels to retain the shape they

  have taken before during the bending phase.

  In the case where it is necessary to form two glass panels which have the same physicochemical properties, the bending process described above certainly gives

  good results for glass panels of the same thickness

  (symmetrical assembly), or for glass panels

  having different thicknesses (asymmetric

  that provided that the thinnest panel forms the element

  upper part of the pair of elements to bend, that is to say it is on the concave portion of the finished product. Indeed, in the latter case, the lower heat capacity of the upper panel (thin panel) allows it to reach more

  easily higher average temperatures and by following

  it's easier to stick on the bottom panel.

  The veneer of this panel on the lower panel is also

  facilitated by the greater deformation capacity of the

  thin panel, compared to that of the thick panel.

  it has been found that if, on the contrary, the thin panel is placed at the lower part of the pair of panels, that is to say if this panel constitutes the convex element of the finished product, the greater heat capacity and the greater rigidity of the top panel tend to make more

  difficult to obtain a correct curvature and assem-.

  without risk of subsequent separation. It can be

  similar difficulties in the assemblies

  metric and asymmetrical when the glass panels to

  to assemble have different physicochemical properties.

  More particularly, as mentioned above, if the glass panel on the concave side of the finished product has a higher softening temperature.

  and / or a greater coefficient of transmission of the radii

  which is the main form of heat

  In the bending oven, it is not possible to properly apply this panel to the bottom panel using the conventional technique. Indeed, if we assume that the amounts of heat absorbed by the two panels

  are equal, the panel that has the temperature of

  The highest decrease is subject to a lower degree of bending.

  than the other panel, since, with equal radiant heat flux, the panel with the highest transmittance of radiated heat reaches average temperatures lower than those reached.

by the other panel.

  Because of this, with the classical technique, and unless

  that we maintain a very strict regulation of the flow of heat

  their and the process of heat transfer in the oven,

  if the glass panel has the softening temperature

  the highest and / or the highest

  transmission of radiated heat, is placed at the top

  of the pair (because it must be in the

  concave portion of the finished product) it will be very difficult to

quer on the bottom panel.

  Following appropriate experiments, he noted that the difficulties described above are attributable to

  lower degree of bending of the top panel compared

  relative to the lower panel, so that the degree of Japanese

  bending of a glass panel placed in a bending oven is subjected to the force of its own weight, is considered to be the permanent deformation (viscous) reached by the panel, in a given time and in

  given ambient conditions of the oven.

  The degree of bending ability of a glass parcel is therefore a measure of its ability to marry more or

  less easily limit geometry and depends primarily

  the geometry of the panel and the physical properties of

  the glass of which this panel is made.

  With regard to these last properties, a para-

  meter having a particularly great importance is,

  as already mentioned, the temperature of softening

  of the glass and its overall radiated heat transfer coefficient for the wavelength range of the radiation.

  For a given element (that is, for a configuration

  given profile ration), the dependence of the degree of bending ability of a glass panel vis-à-vis its geometry is also essentially a function of its thickness. More specifically, the degree of bending ability of a glass panel decreases with the increase in its thickness and / or with the increase in its transmission coefficient.

  radiated heat and / or with the increase in temperature

softening of the glass.

  To solve the bending difficulties

  in the cases described above, the inventors

  first of all carried out experiments involving cintra-

  separate ge of glass panels to assemble. However, this system gave only poor qualitative results in the assembly phase and thus resulted in a higher value.

high percentage of waste.

  In cases where the lowering of the degree of

  bending of the glass panel were essentially

  its highest overall transmission coefficient of

  radiated heat (for radiation present in

  in the bending oven), we then tried to improve

  improve this degree of bending ability by modifying the

  cessation of heat transfer inside the oven,

  more particularly by increasing the trans-

  convection heat mission at the expense of

  Radiation transmission saxt. However, this implies

  that important and annoying modifications of the bending oven. With the manufacturing method according to the invention, the difficulties encountered in the cases described above were finally overcome. This process applies more particularly to the manufacture of curved and assembled glass panels whose physico-chemical properties and / or

  the thicknesses are not the same.

  The present invention indeed relates to a .procedure

  in which, during the bending phase, the order in which the glass panels are placed on the mold is the reverse of that adopted during the assembly phase. It has been surprisingly found that this is sufficient to remove the difficulties that were encountered.

  in the previous methods listed above.

  More specifically, in the process according to the invention,

  the glass panel with the lowest

  bending study, that is, one that has the same

  highest softening bandwidth or greatest overall radiated heat transfer coefficient (for radiation predominantly present in the furnace) or thickest panel, in direct contact with the mold during the bending phase when that panel must be subsequently placed in the concave region, that is to say in the inner region of the finished product. Naturally, when the factors influencing the degree of bending ability are found in one of the two defects and the others in the other of these two panels, it will in any case be the panel with the lowest aptitude for bending.

  bending which will be put in direct contact with the mold

  during the bending phase, if this panel is to be placed

  in the concave region, that is to say in the region concerned.

  of the finished product. Likewise, in the case of a product involving the use of more than two glass panels having different bending capabilities, it is the panel with the lowest bending ability, when it is to be placed in position. inner position in the

  finished product, which will be in direct contact with the mold

during the bending phase.

  Benefits that result from the manufacturing process

  curved glass panels assembled according to the invention

  clearly emerge from the examples of applications

given below.

TABLE 1

  (medium composition) Glass panel No glass panel no2 Si0 70-7,% 50-70%

-0 - 70%

  CaO 8 -10% 0.5 - 1.0% MgO 2 - 4% 2 - 4%

A1203 O.1 - 1.5% 5 25%

Fe O

, - 0.10 - 0.60% 0.02 - 0.6%

  2 3 Ti02 0.05 - 0.06% 0.05 - 0.2% bases 1 - 5% 12 - 15%

248 4398

EXAMPLE 1

  A sheet of glass composed mainly of

  and lime, designated by the letter A, must be

  similar to a glass sheet composed mainly of silica and alumina and designated by the letter B. The two initially flat sheets of the same thickness must first undergo a forming phase before the assembly phase, then must be used in

  curved windshield quality for a motor vehicle.

  The sheet (A) of silica-lime glass must form the outer part of the windshield, that is to say, be

  in the convex part of the finished product while the úeuil-

  (B) silica-alumina glass should form the integral part

  windscreen (the concave part of the finished product).

  The two glass sheets have physical properties

  different chemicals. Their average compositions are

  Table 1. Viscosity curves, which cover the range of temperatures of interest for both types of glasses, are given in Figure 1 for illustrative purposes only. We can see on this figure that, tied

  temperature, the sheet (B) has a higher viscosity

  than that of sheet (A) and therefore has a point of

  higher softening. This softening point can be defined as the temperature at which the viscosity

  takes a certain value (for example -L: 108 poises).

  FIG. 2 gives, also for illustrative purposes, the curve of variation of the transmission coefficient of the monochromatic radiated heat of the two glass panels for

  the wavelengths of the radiation of the range concerned.

  The fact that the heat transfer coefficient ra-

  monochromatic diant of leaf B is higher than

  that of sheet A for the different lengths of

  This means that the overall coefficient of transmission of the radiated heat (for radiation predominantly present in the furnace) of the silica-alumina glass sheet is higher than that of the silica-lime glass sheet. In some areas of the glass bending furnaces, the ratio linking the two global transmission coefficients of the

heat is approximately 2.

  The two sheets of glass are placed on a mold which is then circulated along the bending oven;

  according to the invention, the sheet B is placed in contact with

  rect with the mold (whose concave surface is facing upwards) and put the sheet A on the sheet B. The assembly comprising the mold and the pair of sheets then enters the heating tunnel and the sheet A, in Because of its lower coefficient of transmission of radiated heat, reaches its softening point (inter alia, lower than that of sheet B) before the underlying sheet B. In spite of this, sheet A will only begin to bend when sheet B will have it

  also reaches its softening temperature.

  Bending then continues until the

  sheet B marries the shape of the bending mold.

  The bending of the sheet B is favored, not only

  not only because of its own weight but also because of its

  fet of the weight of the sheet A which is superimposed on it and which, having reached the first its softening temperature,

  is supported on the sheet B by all its surface.

  The temperature rise of sheet B is favored

  rised by his contact with sheet A which, being more opaque

  than the radiation of the furnace, tends to absorb this radiation more rapidly. In fact, the contact between the two sheets

  promotes the transmission of heat between them by

duction.

  After having carried out the necessary annealing phase,

  the two leaves are separated and assembled together

  position of a plastic sheet; following the in-

  for this operation, the positions of the two sheets are reversed, in that the sheet A, constituted by the silico-alumina glass, takes the outer position (face

  convex), whereas the B-sheet is composed of silico-aluminum

  ne, takes the inner position (concave face). The operation

  reversal of positions reveals a slight difference

  curvature between the surfaces that will be contacted with the plastic sheet during

assembly phase.

  It has been found that in the case of windshields having a

  slight or medium curvature, this slight difference in

  bure between the leaves is not likely to harm the ob-

  a good result of the assembly operation. Indeed, in these cases, the difference between the radii of curvature and the theoretical radius of curvature is between 0.1 and i%. It was also found that the following procedure

  the invention is not detrimental to the achievement of good quality

  assembly, even in the case of windscreens with appreciable curvature, provided that the shape of the mold is

properly corrected.

  EXAMPLE 2 The same glass panel, mainly composed of

  silica-lime, as in the previous example, which will be de-

  signed by the letter A, must be assembled to a thinner glass panel; mainly composed of silica-alumina, which will be designated by the letter B. Since the panels must be used in a curved windshield of a motor vehicle, these two panels, which are initially flat, must first undergo a phase of putting in form that adds to the phase

assembly.

  Furthermore, the silica-alumina glass panel,

  which will form the inner part of the windscreen (facing

  ve of the finished product) must undergo, before assembly, a

chemical quenching process.

  This treatment is intended to confer on the interested party

  of the windshield a greater mechanical strength and, especially to confer a greater degree of safety

passive in case of shock rupture.

  The physico-chemical properties of the two glass panels correspond to those already indicated

  in Example 1; at most, the coefficient of transmission

  monochromatic radiated heat from panel B may be higher in some areas of the

  wavelengths of radiation, because of its lower

10.ble thickness.

  It has been found experimentally that, despite its lower thickness (which can be, for example, between

  2/3 and 1/4 of the thickness of panel A), panel B pos-

  has a bending capacity which is lower than that of panel A under the usual ambient furnace conditions

  bending glass. This means that, in this case, the

  influence of the softening temperature and the coefficient

  The overall radiative heat transfer

than the thickness.

  In this case, too, it is appropriate to adopt the process according to the invention if a good level of quality

  assembly must be obtained. The process of forming and

  appearance is therefore identical to that of the previous example.

  However, it should be noted that, in this case, if the panel B has a thickness significantly lower than that

  of panel A, its lower curvature stiffness does not

  practically no deformation in the phase

* assembly, even for windshields with a

  relatively strong, and as a result, it is not

  it is essential to give the mold an exactly

form.

EXAMPLE 3

  It involves bending and assembling two glass panels of the same composition (for example silica-alumina)

  which have the same physico-chemical properties but thick

  to the outermost part of the windscreen (convex side), while the thickest one, designated windshield (concave side).

  The two glass panels are then placed on a

  which is then circulated along a furnace of

  tration. According to the invention, the panel B is placed in

  direct contact with the mold and assemble the panel A. on the panel S. The assembly composed of the mold and the two glass panels then enters the heating tunnel and, because of its lower thermal capacity, the panel A reaches its softening temperature before the underlying B-panel. In spite of this, panel A only begins to bend when panel B has also reached its

softening temperature.

  Bending then continues until the

  Neau B marries the shape of the bending mold.

  The bending of the panel B is favored not only by the action of its own weight but also by that of the

  weight of panel A superimposed on it and who, having

  first dyes its softening temperature, takes

  then on panel B on its entire surface.

  After carrying out the necessary annealing phase, the panels are separated and assembled with the interposition of a sheet of plastic material; according to the invention, in this assembly operation, the positions of the two

  panels are inverted compared to those they occupy

  pay in the bending phase, in that the sign

  A takes the outer position (convex side) and that the

  thick water B takes the inner position (concave face).

  It was found that this mode of operation was not harmful to

  able to obtain a high quality of the assembly,

  even in the case of windshields having a relative curvature

  strong shape and without any noticeable change in the shape of the mold, thanks to the fact that the thin

  bending rigidity as the thick panel.

  R I V E N D I C A T I 0 N S 1 - A method of manufacturing, that is forming and assembling, two curved glass panels having

  different physicochemical properties and / or thicknesses

  Different types of lamps are particularly suitable for windscreens and other safety glass objects for motor vehicles or the like, comprising the successive known stages of loading the panels onto a horizontal rigid mold with a concave surface facing upwards. simultaneous bending of the two panels in an oven, adjustment to the final shape and, if necessary,

  quenching, interposing a sheet of plastic material

  between the two paired panels and finally, as

  autoclaving in special conditions

  temperature and pressure, characterized in that,

  in the bending phase, the one of the two glass panes to be assembled which has the lowest

  bending in direct contact with the mold and, during the

  assembly, the positions of the two panels are reversed, so that the panel which was initially in contact with the mold forms the inner part, that is to say the

concave part of the finished product.

  2 - Process according to claim 1, characterized in that that of the two panels to be assembled which has

  the poorer bending ability has this characteristic

  exclusively or mainly because of a

  higher softening temperature.

  3 - Process according to claim 1, characterized in that that of the two panels to be assembled which has the lowest bending aptitude has this characteristic exclusively or mainly because of a higher overall coefficient of transmission of the radiated heat

  (for the radiation present mainly for the oven).

  4 - Process according to claim 1, characterized in that the two panels to assemble which has the most

  low centering ability should be characteristic

  clusively or mainly to a greater thickness.

  Process according to one of the claims 1 to 4, characterized in that an articulated mold is used for forming.

  6 - Process according to one of claims 1 to 5,

  characterized in that a process is used for the forming phase instead of an "expansion" process, that is to say, the shaped glass panels and then

bent in the oven.

  Process according to one of Claims 1 to 6,

  characterized in that the two glass panels have colors. different because of differences in physicochemical properties.

  a8 - Process according to one of claims 1 to 7,

  characterized in that the two glass panels have approximately the following compositions:

TABLE 1I

  (average composition) Glass panel Glass panel nl n02 SiO2 70 74% 50 - 70% CaO 8 - 10% 0.5 - 1; 0% MgO 2 - 4% 2 - 4% = zno_ v - 1.3% 5 - 25% Fe O

2 3 0.10 - 0.60% 0.02 - 0.6%

  2 3 Ti2 0.05 - 0.06% 0.05 - 0.2% 0 bases 12 - 15% 12 - 15% 9 - Process for the manufacture of three or more

  three glass panels intended to form together a

  breeze or other safety glass object for

  the, the physicochemical properties and the thickness of each

  any of these signs being wholly or partly different

  different from those of the other panels, according to one of the

  preceding claims, characterized in that the panel having the lowest bending ability is placed in direct contact with a mold and the other panels of more than

  further from the mold, the order of succession in the distance

  compared to the mold being identical to the order of suc-

  transfer of the skills of increasing bending and that the panels occupy successive positions in

  the reverse order during the assembly phase of the pro-

finished duit.