FI96598C - Method and apparatus for forming the edge tension in the windshield in a windshield bending furnace - Google Patents

Description

96598

A method and apparatus for generating edge tension on a windshield in a windshield bending furnace. - For the purposes of this Regulation, the provisions of this Regulation shall apply.

The invention relates to a method described in the preamble of appended claim 1 and to a device described in the preamble of claim 2.

The problem to be solved by the invention is as follows. When bending glass with a strong bending radius at the ends of the glass and a long straight section on the sides of the glass, the edge tension remains low, well below 10 MPa. Typically, truck glasses, but also many passenger car glasses, are such. Edge tension requirements are generally greater than 10 MPa.

When using known bending furnaces and edge molds, the temperature of the edge of the glass on the straight sides is not sufficient for the formation of edge stress and the cooling rate of the edge is too low. Applying heat only to a narrow edge area has not been satisfactorily solved. When the center of the glass is heated, too much glass goes into the bag. Enhancing cooling with edge tension fans causes harmful stresses in the center of the glass.

The problem has been alleviated by the method and device presented in FI patent publication 86405, which uses a solid rail parallel to the lower surface of the glass sheet. In the heating phase, the rail operates in such a way that it reflects the radiant heat coming from above and thus heats the glass. However, the rail does not increase the air flow through the angular area between the support rail and the glass plate. In the cooling phase, the rail initially slows down the cooling until the cooling flow reaches such a rate that rapid cooling occurs despite the rail. While this solution works, it is not satisfactory in all circumstances.

96598 2

With the device according to the present invention, the problem is solved by installing a low-mass airflow guide plate inside and / or outside the windscreen edge mold support rail, the upper edge of which is substantially closer to the glass plate than the lower edge and away from the corner plate between the glass plate and the support rail. that of the support rail, whereby the flow around the upper edge of the guide plate enhances the heating and cooling of the glass edge. Characteristic features of the method are set out in the appended claim 1.

Thus, in the present invention, the heating and cooling enhancement is based on an enhanced airflow provided by a low mass flow control plate having a direction substantially different from the glass sheet, allowing flow around the top of the sheet and thus enhancing flow in the angular area between the glass sheet and the support frame.

In the following, the structure and operation of the invention and the embodiment of the method will be described in more detail by means of an exemplary embodiment with reference to the accompanying drawings, in which Fig. 1 shows a vertical section of preheating compartments of a furnace apparatus; Fig. 2 shows a vertical section of the bending section of the same furnace apparatus; Fig. 3 shows a detail in which the glass is supported by an edge mold. Fig. 4 shows the operation of the guide plate 14 in connection with heating the glass to control the warm air flow to enhance the heating of the glass edge; and Fig. 5 shows the operation of the guide plate 14 according to the invention in cooling the cold air flow.

II

3> όΐ: 98 sex to enhance the cooling of the glass edge when the bent glass is lowered by elevator from the bending compartment to the cooling.

The furnace in which the method is used comprises a series of successive heating compartments 1, 2, 3. The glass sheet or pair of glass sheets is introduced into the first furnace compartment 1 supported by the bending mold 11. The "glass sheet pair" may also be referred to as "glass sheet". The mold 11 with its glass plates is moved forward from one compartment to another by a mold carriage 9, the end wall 9a of which separates the successive compartments from each other. In the first compartments 1, the glass sheet is heated mainly by forced convection, the thermal energy of which is obtained in the lower cooling compartments 7 from a cooled bent glass sheet, as further described in the applicant's patent US-4,986,842. In compartments 1, forced convection typically accounts for 90% of the glass plate heating power and radiation for 10%. There may be 3 to 6 heating compartments 1 based on heat recovery and the glass sheet reaches a temperature of 230 ° C to 300 ° C before moving to the next preheating compartment 2. In the preheating compartments 2 the heating takes place partly by by incoming convection heat obtained from the glass sheets cooled in the lower cooling compartments 6. In compartments 2, the share of radiation is, for example, 40% and the share of convection heating is 60%. The number of preheating compartments is typically 3-6. From the preheating compartments 2, the glass sheet moves to the preheating compartment 3 when the glass temperature is e.g. about 530 ° C to 550 ° C. In the pre-bending compartment 3, the temperature is raised by a few tens of degrees, whereby the glass sheet is already slightly bent. Finally, the glass sheet is transferred to the actual bending compartment 4, where its temperature is raised, e.g. in the temperature range of 590 ° C to 635 ° C. At the bending temperature, the glass is very sensitive to temperature changes, so that even a few degrees of change in the temperature of the glass sheet strongly affects its bending sensitivity. In the bending compartment 4, heat is typically transferred to the glass so that the proportion of radiation is 90% and the proportion of convection is 10%.

4 3 6 b 9 8

The periodic transport of the carriages 9 on the upper track 18 thus forms successive compartments 1, 2, 3 and 4. After bending, the carriage 9 and the bent pair of glass sheets are moved from the upper track 18 to the lower track 19, where the carriages 9 are also moved in opposite directions. .

The bending mold is an edge mold formed mainly by a vertical support plate 11. As shown in Figs. 3-5, a low-mass airflow guide plate 14 is mounted inside the support plate 11, which forms an angle α of 30 ° to 60 ° with the vertical plane. In this case, a tapering flow gap is formed between the guide plate 14 and the support plate 11 as it goes upwards. The area adjacent the upper edge of the guide plate 14 is bent substantially vertically. Between this vertical edge part and the support plate 11 there is a narrow flow slot with a width 11 of e.g. 5 to 10 mm. The upper edge of the guide plate 14 is below the upper edge of the support plate 11 by a distance I2 of, for example, 5-20 mm. The guide plates 14 are fixed to the mold support plates 11 at least on the long sides of the mold which are perpendicular to the plane of Fig. 2. If necessary, the guide plates can also be fastened to the support plates 11 supporting the ends of the glass, one of which is shown in Figure 2.

Figure 4 illustrates the operation of the guide plate 14 in the preheating compartments 1-3 and the bending compartment 4 during the heating of the glass. When heating the glass, especially in the preheating compartments 2, the guide plate 14 effectively directs the warm air flow from under the mold inside the carriage base 9 to the support plate 11 and moves air at the corner of the support plate 11 and the glass, enhancing heat transfer to the glass. The upward air flow 15 is caused by the fact that at least at the beginning of each heating cycle the lower track 19 has a warmer glass than the upper track 18.

Without the guide plate 14 according to the invention, an air pocket is created in the corner between the support plate 11 and the glass, which effectively prevents heat transfer to the glass. Heat transfer from the lower track 19

II

96598 5 to the upper track 18 can be further enhanced by air blowing from the blowing pipes 13. The pipes 13 extend across the compartments 2 and have upwardly opening blowing holes with a suitable division.

As the bending elevator 10 moves downward after bending, the guide plate 14 acts as a guide for the cooling air 16, effectively cooling the edge zone of the glass inside the support plate 11. This cooling takes place immediately after bending, when the temperature of the glass is still high enough to create edge stress. The temperature of the elevator 10 downstairs is controlled by edge tension fans.

The heating and cooling output can be adjusted by changing the angle a of the control plate 14 and the distance 1- | from the support plate 11 and by adjusting the temperature of the elevator 10 downstairs and the movement speed of the elevator 10 downwards. Heating and cooling capacity can also be affected by the length and thickness of the guide plate 14 and the height position (distance 12) ·

A guide plate 14 'can also be placed outside the edge mold support plate 11, the shape and position of which are affected by the features described above in connection with the guide plate 14. The guide plate 14 'is like a mirror image of the guide plate 14. If the edge of the glass plate extends far enough beyond the support plate 11, the outer guide plate 14' may alone be sufficient to generate edge tension.

Claims (4)

A method for generating edge tension on a windshield in a windshield bending furnace, wherein the glass sheet is supported on an edge mold (11) and heated in preheating compartments (1-3) and a heating and bending compartment (4), from which the bent glass sheet is lowered against a cooling air stream (16) (19) below said preheating compartments (1-3), characterized in that the low-mass guide plate (14, 14 ') inside and / or outside the edge mold (11) / whose direction differs substantially from the direction of the glass plate is directed to circulate the air flow through the angular area between the glass plate and the support frame, whereby in the heating phase the heating of the glass edge is intensified and in the cooling phase the cooling of the glass edge is intensified. An apparatus for generating edge tension on a windshield in a windshield bending furnace comprising a plurality of successive preheating compartments (1, 2, 3), a heating and bending compartment (4), an elevator device (10) below the heating and bending compartment (4) and a plurality of successive cooling compartments (5, 6, 7) below the preheating compartments (1, 2, 3) and an edge mold (11) for supporting the glass sheet during heating, bending and cooling, characterized in that the edge mold is inside and / or outside the support rail (11) a low-mass airflow guide plate (14, 14 ') is mounted, the upper edge of which is substantially closer to the glass plate than the lower edge and extends away from the angular area between the glass plate and the support rail, away from both the glass plate and the support rail, the guide plate (14, 14') the flow enhances the heating and cooling of the glass edge. Device according to Claim 2, characterized in that the guide plate (14, 14 ') forms an angle of 30 ° to 60 ° with the vertical plane and approaches the support rail (11) of the edge mold. going upwards, whereby a flow-narrowing flow gap is formed between the guide plate (14, 14 ') and the support plate (11). Device according to claim 3, characterized in that the area adjacent to the upper edge of the guide plate (14, 14 ') is bent substantially vertically and in that said upper edge is located a short distance (12) below the level of the upper edge of the support plate (11). 8 96593