LU83428A1 - PROCESS FOR MANUFACTURING BOMBED GLASS PANELS - Google Patents

Description

The present invention relates to a process for the manufacture of curved and bonded glass panels, proving to be particularly suitable as windshields and other safety glass objects, in automobiles and others. vehicles. The present invention relates more particularly to a process for manufacturing bonded and curved glass panels which can be used in cases where the physicochemical properties and / or the thickness of the glass panels to be bonded and to bomber do; you are not the same.

- 1 In order to understand the progress made by the method of the present invention, it is first necessary to consider the methods of manufacturing currently bonded and curved glass panels and their limits. In these processes, I can distinguish two consecutive phases, namely: shaping and assembly, these phases being repeated in the process concerned.

During the shaping or forming phase, the glass panels are curved in the oven and equalized or adjusted to the desired shape, and this can be done using two different techniques; that is to say that when these operations are carried out in the order indicated above, the process is called * expansion process, or else when these operations can be carried out in reverse order, in this case the process is called contour process. The process according to the invention can be carried out using one or the other of the two shaping techniques.

During the assembly phase, a plastic sheet is first placed between each pair of glass panels J to be bound; then the sandwich thus formed (glass plus 1/3 plastic) is compressed under given temperature conditions to expel most of the air trapped between the plastic and the glass; finally, the sandwich is placed for a sufficiently long period in an autoclave, where the real bonding operation is carried out under controlled temperature and pressure conditions.

To obtain satisfactory results in the manufacturing process, the glass panels must be curved so that the contacting surfaces suitably coincide with one another, or rather, so that there are no appreciable differences in local curvature between the two surfaces to be bonded.

Although in fact if the manufacturing process is carried out upstream and downstream from the bending or bending phase in an appropriate manner, slight differences in bending or bending. between the two surfaces to be bonded will not change the result; the situation is very different, to achieve such a result, when there is a large local difference in curvature on one of the two surfaces to be bonded. Such a situation would lead to detachment after assembly (weak bond with appearance. , interruptions) along the edges of the sandwich and / or inside it.

Appropriate matching of the curvatures of the two surfaces to be assembled is still generally currently achieved by simultaneous bending in an oven of the glass panels to be bonded together subsequently; to do this, the glass panels are placed, during the curving or bending phase, on a horizontal mold with the concave surface oriented towards lpy / haut, in the same position as that which they will take in the / ! I 4 ί finished product.

? , | For example, in the manufacture of a windshield with tj,. · * Two layers of glass having the same physico-chemical properties and the same thickness, the two panels of bending glass are loaded on the horizontal mold with the concave surface facing upwards, so that the panel glass, which will form the outer part of the windshield (convex part), is placed 'in contact with the mold (which is located below), and that thereafter on this one (i.e. on its upper end) is placed the glass panel which will form the inner part (concave part) of the windshield. The pair of glass panels loaded onto the mold will then be placed in the heating oven where the temperature of the glass will gradually rise to the softening temperature. Consequently, the glass panels take, thanks to the effect of temperature and gravity, the final shape of the mold; more particularly, the lower surface of the lower glass panel in direct contact with the mold, tends to take the shape of the latter, while the lower surface of the upper glass panel tends, in turn, if is heated appropriately, to take the form of the upper surface of the lower glass panel.

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It has been found, in order to achieve good agreement of the surfaces in contact, that the temperature of the upper glass panel must be raised to an average temperature which is higher than that of the lower glass panel; in fact, the resulting lower viscosity achieved by the glass of the upper panel makes it possible to extend this panel on the lower glass panel. In order to achieve these thermal conditions, heating / heating furnaces for glass panels of equal thickness are generally used so that in the bending zone in particular, the quantity of heat transferred to the upper glass panel mainly radiation is greater than the quantity transferred to the lower glass panel.

It will also be noted that in order to give a correct final shape to the glass panel in the bending or bending phase, the bending shaping mold can be either of the * rigid type (in the sense that its geometry does not vary in the oven? by the inevitable elastic and thermal deformations), either of the articulated type (that is to say that suitable articulation arrangements make it possible to modify the geometry of the mold inside the oven). These rigid type molds are mainly used for parts with a low curvature, while the articulated type is mainly used in other cases.

After bending or bending, the glass panels undergo an appropriate annealing treatment which, by lowering the temperature of the glass without creating consistent states of tension in it, allows the panels to retain their shape already reached in the phase bending.

In the case of the shaping of a pair of glass panels having the same physicochemical properties, the bending process described above certainly gives rise to good results on glass panels of the same thickness (symmetrical bond) or even on glass panels of different thickness (asymmetrical connection), provided of course that the thinnest glass panel constitutes the upper part of the pair of panels to be curved, that is to say that it is on the concave part / J / b! of the finished product. In fact, in the latter case, the thermal capacity 6 ï (lower mique of the upper glass panel (thinner panel) favors obtaining higher average temperatures, and consequently its placement on the lower glass panel. the placement of this panel is also facilitated by the greater deformability of the thinner glass panel compared to that of the thicker glass panel.

On the other hand, the Applicant has noted that if w * the thinner glass panel is placed in the lower part of the 3 pair of panels, that is to say in the convex part of the finished product, the higher thermal capacity and greater rigidity of the upper glass panel tend to make correct bending and bonding without subsequent peeling more difficult. Similar difficulties can arise both in the case of symmetrical bonding and in the case of asymmetrical bonding, when the glass panels to be bonded have different physicochemical properties. More particularly, as previously mentioned, if the glass panel placed on the concave part of the finished product has a higher softening temperature and / or a higher coefficient of transmission of the radiation present mainly in the bending furnace, it is not possible to correctly place this panel

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Is on the bottom panel using traditional technology. In fact, by absorbing equal amounts of heat, the glass panel having the highest softening temperature undergoes a lesser degree of bending or curving than that of the other glass panel; similarly, for an equal radiant heat circulation, the panel having the highest trapSy- / mission coefficient of radiant heat reaches lower average temperatures than the other panel.

Therefore, in traditional technology, unless you maintain very strict control over the thermal circulation and the method of heat transfer in the oven, if the glass panel having a higher softening temperature and / or a coefficient of Higher radiant heat transmission is placed in the upper part of the pair of panels (because it must be in the concave part of the finished product), it will be very difficult to place it on the lower glass panel.

The Applicant has found, after having carried out appropriate experiments, that the drawbacks described in the preceding cases must be attributed to the smaller degree of curvature of the upper glass panel relative to the lower panel, so that the degree of ability to bending or bending of a glass panel placed in a bending oven and subjected to the force of its own weight, is noted as being the permanent (viscous) deformation achieved by the panel within a certain period of time under conditions oven ambient „. data.

The degree of bending ability of a glass panel 5 is therefore a measure of its ability to conform more or less easily to the constraining geometry and is highly dependent on the geometry of the panel itself and on the physical properties. chemicals of the glass it is made of.

With regard to the latter properties, the softening temperature of the glass and its coefficient of transmittance of radiant heat ootaDe relative to the wavelength range of the radiation are particularly important, thus I that we have already mentioned.

For a given part (that is to say for a given contour configuration), the dependence of the degree of bending ability of a glass panel on its geometry is also essentially linked to its thickness. More specifically, the degree of bending ability of a glass panel decreases the greater its thickness and / or its coefficient of radiant heat transmission is high and / or the softening temperature of the glass which it is done is high.

In order to overcome the bending difficulties encountered in the cases described above, the Applicant first carried out experiments involving the separate bending of the glass panels to be bound. However, this process gave poor qualitative results in the assembly phase and, consequently, a very large number of rejects.

In cases where the very low degree of bending ability of the glass panel depends essentially on its very high total radiant heat transmission coefficient _ (in relation to the radiation present mainly in the bending oven), tests have then have been made to improve this degree of bending ability by modifying the heat transfer process in the furnace, particularly by increasing the convection heat transfer component at the expense of that by radiation. However, this leads to ap-! valuable and complex in the bending furnace of glass panels, j Thanks to the manufacturing process of the present invention ^ n 'f fi (/ if 9 the Applicant has finally overcome the manufacturing difficulties encountered in the cases described above.

The process in question applies, as already specified above, more particularly to the manufacture of curved and bonded glass panels whose physicochemical properties and / or thickness are not the same.

The method is essentially characterized in that during the bending or bending phase, the order in which the glass panels are placed on the mold is reversed with respect to the order during the d phase. assembly, since it has surprisingly been found that this is sufficient to overcome the difficulties encountered during the above-mentioned prior processes.

Consequently, and more particularly according to the method of the present invention, the glass panel having the lowest degree of bending ability, that is to say the glass panel having the highest softening temperature, or either the glass panel with the highest total radiant heat transmission coefficient (in terms of radiation present mainly in the oven) or the thickest glass panel is placed in direct contact with the mold during the bending phase, when it must subsequently be placed in the concave part, that is to say the lower part of the finished product. If such factors influencing the degree of bending ability are present,. certainly in one of the two glass panels and the others in the other, it will obviously be the panel having the smallest degree of bending ability which must be placed in direct contact with the mold during the j phase bending, when it is to be placed in the concaved part, that is to say the lower part of the finished product. Likewise, in the case of a product involving the use of more than two glass panels having different degrees of bending ability, it also follows that the glass panel having the lowest degree of ability when bending, when it must be placed in an internal position in the finished product, will be placed in direct contact with the mold during the bending or bending phase.

The advantages arising from the process for manufacturing curved and bonded glass panels according to the present invention will become more apparent from the examples described below.

TABLE (Average composition)

Glass panel n ° 1 Glass panel n ° 2

Si02 70 - 74% 50 - 70%

CaO 8 - 10% 0.5 - 1.0%

MgO 2-4% 2 - 4% A1203 0.1 - 1.5% 5 - 25%

Pe 0 0.10 - 0.60% 0.02 - 0.6% 2 3

Ti02 0.05 - 0.06% 0.05 - 0.2%

Alcalis 12 - 15% 12 - 15% - * Example 1

A glass panel consisting mainly of a silica-lime composition, designated by the letter A, must be bonded to a glass panel consisting mainly of a silica-alumina composition, designated by the letter B.

The two glass panels, initially flat and of the same thickness, outside the assembly phase, must first undergo a shaping phase, since they must be used as curved windshields for cars. / Jr î I 11 s! The silica-lime glass panel (A) must form! sea the outer part of the windshield, i.e. it will be j I in the convex part of the finished product, while the glass panel based on silica-alumina (B) must form the inner part of the windshield (the concave part of the finished product).

The two glass panels have different physico-chemical properties. Their average compositions are given in the previous table. The viscosity curves, covering the range concerned for the two types of glass, are given only for explanatory purposes in FIG. 1; it can be seen from this figure that the glass panel B has, at the same temperature, a higher viscosity than that of the glass panel A, and therefore has a higher softening point. The latter can be defined as the temperature at which the viscosity takes a certain given value 8 (for example ^ = 10 poises). FIG. 2 gives, still by way of explanation, the curves of the monochromatic radiant heat transmission coefficient of the two glass panels with respect to the wavelength of the radiation in the range concerned; the coefficient of monochromatic radiant heat transmission? higher of the glass panel B compared to that of the glass panel A for the different wavelengths, means "that the coefficient of transmission of total radiant heat (with regard to the main radiation present in the furnace) of the panel of silica-alumina glass is higher than that of silica-lime glass panel. In certain areas of glass bending furnaces, the ratio of the two coefficients of total heat transmission is of the order of 2. /

The two glass panels are placed on a mold qut 12 will then be advanced along the glass bending furnace; according to the present invention, the panel B will be placed in direct contact with the mold (whose concave surface is oriented upwards), and the glass panel A will be placed on the glass panel B.

The mold-pair assembly of glass panels will then enter the heating tunnel and the glass panel A, approx due to S) n lower radiant heat transmission coefficient, will reach its softening temperature (among other things, more lower than that of the glass panel B) before the underlying glass panel B. Despite this, the glass panel A will begin to bulge only when the panel B has also reached its softening temperature.

The bending will then continue until the panel B conforms to the bending shaping mold.

The bending of the glass panel B, apart from being facilitated by the force of its own weight, will also be facilitated by the weight of the glass panel A covering it, which, once it has reached its temperature of softening, will remain entirely on the glass panel B.

The heating of the glass panel B is favored by scn, - contact with the glass panel A which, being more opaque to the radiation coming from the oven, will tend to pick up the latter · »more quickly; in fact, the contact between the two glass panels promotes heat transfer by conduction between them.

After performing the required annealing phase, the glass panels are separated and bonded together with an interposed plastic sheet; according to the present invention, / the position of the two glass panels will be reversed during this /! i 'x,! J lj' i ji this operation, in the sense that the glass panel of silxce- lime (A) will go towards the external position (convex part) while the panel of silica-alumina glass (B ) will go to the inner position (concave part).

The position reversal operation results in a slight bending difference between the surfaces which, during

The assembly phase will be placed in contact with the plastic sheet.

It has been found that in the case of crisis shields with a small or medium bending, this slight difference in the sheet is such that it does not counteract the satisfactory result of the bonding process. In fact, in such a case, the difference between the radii of curvature is in the region of 0.1 to 1% of the ideal radius of curvature.

It has also been found that the operation according to the invention does not modify the good qualitative standards of connection, even in the case of windshields having an appreciable degree of curvature or bending, provided that the shape of the mold is correct. î age appropriately.

Example 2

The same glass panel composed mainly of silica and lime, as the previous example, which will be designated by the letter A, must be linked to a thinner glass panel, composed mainly of silica and alumina, which will be designated by the letter B.

The two initially flat glass panels, in addition to the assembly phase, must first undergo a swimming phase since they must be used as a curved windscreen / ^ · 14 for a motor vehicle.

In addition, the silica-alumina glass panel, which will form the interior part of the windshield (concave part of the finished product) must undergo, before assembly, a chemical toughening treatment.

This treatment is used to communicate greater mechanical resistance to the interior of the windshield, and above all, to communicate a greater degree of passive safety y ** in the event of an impact breakage.

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The physicochemical properties of the two glass panels correspond to those already given in Example 1 above, with the exception, however, that the coefficient of monochromatic radiant heat transmission of the glass panel B may even be higher in certain ranges of wavelengths of the radiation given its smaller thickness.

It has been found experimentally, despite the smallest thickness (situated, for example, between 2/3 and 1/4 of the thickness of glass panel A), that glass panel B has a degree of bending ability or the bending which, under the usual ambient conditions of the glass bending oven, is smaller than that of the glass panel A. This means that in this case, the influence of the softening temperature and s of the coefficient of total radiant heat transmission is greater than that of thickness.

Likewise, in this case, it proves appropriate to adopt the method of the present invention if good qualitative standards of connection have to be achieved. Consequently, the process / of shaping and assembly is identical to that of the previous example ^ / ^^. {Jf, 15

It will also be noted that in this case, if the panel of! glass B has a thickness substantially smaller than that jj of the glass panel A, the lower bending stiffness does not lead, in practice, to deformations in the assembly phase even for windshields of a relatively large curvature, and therefore the shape of the mold must not be absolutely correct.

Example 3 -, Two glass panels of the same composition (for example of silica-alumina) and having the same physicochemical properties but a different thickness, must be curved and bonded so that the interior glass panel, designated i with the letter A, forms the outer part of the windscreen (convex part), and the thicker glass panel, designated by the letter B, forms the inner part of the windscreen (concave part).

The two glass panels are placed on a mold which will then be advanced along the glass bending oven; according to the present invention, the glass panel B will be placed in direct contact with the mold, and the glass panel A will be applied to the glass panel B.

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j ‘The mold-pair assembly of glass panels will enter; * s

then in the heating tunnel and the glass panel A, given its lower thermal capacity, will reach its softening temperature before the underlying glass panel B. Despite this, the glass panel A will only begin to bulge when the glass panel B has also reached / its softening temperature. i m

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Claims (10)

1. This manufacturing process, namely the process of shaping / and assembling two curved glass panels, having different physicochemical properties and / or a different thickness, particularly suitable as windshields and other objects! in safety glass for motor vehicles, etc., comprising the consecutive stages, already known, of loading the glass panels onto a rigid horizontal mold, with the concave surface facing upwards, of simultaneous bending of the two glass panels in an oven, an adjustment or equalization to the shape, required and, as necessary, subsequent tempering, placement of a plastic sheet between 3 "glass panels in concordance, and finally subsequent bonding in an autoclave under special temperature and pressure conditions, this process being characterized in that around the shaping phase, the glass panel with the lowest degree of bending ability, of the two panels to be bonded, is placed in direct contact with the mold present and in that during the assembly phase the position of the two glass panels is reversed, the glass panel initially placed in direct contact with the mold f thus forming the inner part, that is to say the concave part of the finished product. 2. Method according to claim 1, characterized in * * that the glass panel of the two panels which has' the lowest degree of bending ability is assigned this * characteristic entirely or mainly because of a softening temperature higher. 3. Method according to claim 1, characterized in J! that the glass panel of the two tying panels which has "the least degree of bending ability is given this characteristic 1 entirely or mainly because of a higher coefficient of total radiant heat (in this which concet / ne the main radiation present in the oven). 4. Method according to claim 1, characterized in that the glass panel among the two panels to be bonded, which has the least degree of bending ability, is assigned this characteristic entirely or mainly because of a greater thickness of the glass panel itself. 5. Method according to any one of claims a 1 to 4, characterized in that one uses an articulated mold for 1 shaping. 9 6. Method according to any one of claims 1 to 5, characterized in that a contouring method is used for the shaping phase instead of an expansion phase, that is to say that the glass panels are adjusted or equalized to the desired shape and they are then bent in the oven. 7. Method according to any one of claims 1 to 6, characterized in that the two glass panels have, because of different physicochemical properties, a different color. 8. Method according to any one of claims 1 to 7, characterized in that the two glass panels have one. average composition as given in the previous table, 9. Method of manufacturing two curved glass panels “r” as described above, in particular in the examples given. 10. A method of manufacturing three or more than three curved glass panels together forming a windshield or other safety glass object for motor vehicles, these glass panels having all or part of the properties. physico-chemical and / or a different thickness®, one of the ayi ^ / i 1 "'19 very, according to any one of the preceding claims, this process being characterized in that the glass panel having the lowest degree of suitability for botiïbage is placed in direct contact with the mold and in that the other glass panels are gradually placed thereafter and in a position which is all the more distant from the aforementioned panel the greater the degree of bending, glass panels having to acquire a reverse order during the binding of the finished product M Dessms: A— boards * * __XfL D? -oes of which A— pope are Π · "'-" X rn, - ce ·: ssr: püc: * | psoss v. i revendiest. ..... SX ... st.'v-gé descriptif, ^ j '[_ U>' c * ΓΓ: pp -J ΓΓ * ï P ^ * -y * ^ "1 ^ - Charles München • M i *