FI82676B - FOERFARANDE OCH ANORDNING FOER BOEJNING AV EN GLASSKIVA. - Google Patents

Abstract

Method of bending a glass sheet heated to the shaping temperature employing a hot gas stream of wide cross-section, by means of which the glass sheet is pressed against a bending form. According to this process the velocity of the stream components travelling radially along the glass sheet is decreased at least in chosen regions of the glass sheet by virtue of baffles placed in the path of these stream components and in that the static pressure component of the stream is increased in these regions of the glass sheet. <IMAGE>

Description

82676

Method and apparatus for bending a glass sheet

The invention relates to a method for bending a glass sheet heated to a bending temperature by means of a gas stream of a large cross-sectional mandrel, by means of which the glass sheet is pressed against a bending mold.

One such bending method is described in DE-OS 35 23 675. In this method, glass sheets heated to the bending temperature are moved in a horizontal position along a roller track to a bending station where they are lifted from the conveyor belt by against the mold. The glass sheet assumes the shape of a bending mold and is then placed under a transport ring moved under the bending mold to transport it away from the bending station.

If, by means of this known method, the glass sheets have to be bent into a shape having, for example, strongly curved edge areas in some places, the pressure from the gas flow to the edge area is not sufficient to press this strongly curved edge area of the glass sheet tightly into the bending mold. the mold surface. It has been found that this difficulty cannot be eliminated by raising the pressure of the hot gas, i.e. by increasing the gas flow rate.

The object of the invention is to improve the aforementioned method in such a way that it becomes possible to produce also strongly bent glass sheets or glass sheets with strongly edged or curved edge areas.

h According to the invention, this task is solved in such a way that at least in selected areas of the edge of the glass sheet a beam of hot gas flow. In the 'direction', the flow rate of the partial flows flowing along the surface of the glass plate is reduced by the 2 82676 barriers installed in the path of these partial flows, thus increasing the static partial pressure of the gas flowing in these peripheral areas of the glass plate.

The method according to the invention takes advantage of the fact that the static partial pressure of the flowing gas acts in all directions, whereas the dynamic partial pressure acts only in the flow direction of the gas. However, in the edge regions of the glass sheet, the partial currents perpendicular to the glass sheet meet the glass sheet only in a weakened form, because in the central region the gas facing the glass surface If the edge regions of the bending shape are strongly bent or if the angle of inclination of the edge regions in the direction of gas flow is unfavorable, then the pressure component acting perpendicular to the glass surface of the dynamic sub-pair is too small to achieve the desired bending forces. The invention provides an improvement in this by suitably increasing the static partial pressure in these areas. Since, as is known in a flowing gas or liquid system, the sum of the static and dynamic partial pressures at a given flow line is constant, the static, in this case the partial pressure acting in the bending process, must increase if the flow rate of this flow line decreases. According to the invention, the desired reduction in flow rate is achieved in the areas in question by placing suitable barriers in the path of or at the end of these sub-streams, which impede these sub-streams and thus provide the desired braking effect on these sub-streams of hot gas.

In a preferred further development of the invention, it is simultaneously reduced behind the glass sheet, i.e. between this and the surface of the bending mold, an effective static pressure by connecting this space to the space behind the bending mold.

According to a first preferred embodiment of the method according to the invention, the radially flowing partial streams of hot gas along the respective edge region of the glass sheet are passed at the end of the bending mold past the bending mold and the glass sheet by reducing the flow cross section.

According to another preferred embodiment of the method according to the invention, the path of the hot gas partial flows flowing radially along the edge region of the glass sheet is completely closed by a barrier placed in the bending mold and the static gas pressure between these edge areas on the other side of the bending mold to a space at a lower static pressure.

In carrying out the method according to the invention, suitable devices basically mean that dam plates are placed at the edge of the bending mold, at places where the static partial pressure of the gas flow must be increased, approximately perpendicular to the end tangent of the bending mold.

The invention will now be explained in more detail with reference to the accompanying drawings.

• *

The drawings show

Figure 1 is a vertical section of a bending chamber in which a glass sheet is compressed by a stream of hot gas according to the prior art;

Fig. 2 shows the mode of action of a first embodiment of the method according to the invention, shown in the region of the bending mold of the present sectional view; • * • ·

Fig. 3 shows the mode of action of a second embodiment of the method according to the invention, also shown in the region of the bending mold of the present sectional view; • · • · • · 82676 p

Figure 4 is a perspective view of a car glass bending mold with dam plates for carrying out the method;

Fig. 5 is a partial sectional bottom view of the bending shape shown in Fig. 4;

Fig. 6 is a sectional view taken along line VI-VI of Fig. 5, and

Fig. 7 shows another embodiment for shaping a dam plate, shown in section.

A bending station in which the glass sheet 1 is compressed by means of a hot gas stream, in particular a hot air stream, is placed in connection with a roller-through furnace 2, where the glass sheets are heated to a bending temperature by means of electric heaters 3. The transfer of the glass sheets 1 takes place on a roller conveyor consisting of transfer rollers used in the horizontal direction. The roller conveyor consisting of transfer rollers 4 extends as far as inside the bending station.

The bending station comprises a substantially vertically arranged flow channel 8, the walls 9 of which are provided with a suitable thermal insulation layer (not shown). Through the opening 10 in the wall 9 adjacent to the furnace 2 of the flow channel δ, the glass sheets 1 come from the roll-through furnace 2 to the bending station. In the bending station, they are placed inside the flow channel 8 below the bending mold 12. When moving the glass sheets 1 to the bending station and during positioning, the volume flow and pressure of the vertically upward gas flow are kept low. The volume flow and pressure of the gas flow can be kept at a value suitable for reducing the own weight of the glass sheet 1 in order to prevent the glass sheet from deforming as it bends between the transfer rollers M due to the own weight of the glass sheet. In this case, however, the own weight may only be partially reduced, because the movement of the glass plate 1 by rotating the transfer rollers 4 must be guaranteed.

As soon as the glass sheet 1 has reached its desired position, the pressure and volume flow of the gas stream are raised so high that the glass sheet 1 rises from the transfer rollers 4 and presses against the mold surface of the bending mold 12. A carriage with a support ring corresponding to the shape of the bent glass sheet is then moved under the bent glass sheet 1 'by rails 14 perpendicular to the plane of view. By reducing the gas pressure and volume flow in the flow channel 8, a bent glass sheet is placed on top of this support ring and moved away from the bending station.

The gas flow coming to act on the glass plate 1 has substantially the same pressure profile in its entire cross section. When the glass sheet 1 is lifted up from the transfer rollers 4 and into place in the bending mold 12, the entire surface of the glass sheet is subjected to substantially the same pressure. However, this changes as soon as the glass sheet adheres to the bending mold 12. From that moment on, the gas facing the glass sheet 1 must flow laterally along the surface of the glass sheet and turn upwards at the edge of the bending mold 12. In the edge regions of the glass plate 1 ', the outflowing partial currents of the gas act in two ways: First, they weaken the direct effect of the upward flowing gas, i. the effect of the dynamic partial pressure acting in the perpendicular direction, in these edge regions, since the vertical partial flows turn in the “horizontal direction and the outflowing gas flows in the edge areas multiply the effect of the vertical partial flows encountering these outflowing gas flows. Second, along: · the dynamic partial pressure 1a of the gas radially flowing out of the glass plate 1 'itself has no pressure component in the direction perpendicular to the surface of the glass plate, so the gas flowing out along the glass plate has no part in the actual bending process. The larger the surface area of the glass sheet and the larger the end tangent alpha during the bending phase, the smaller the bending currents formed on the edge areas of the glass sheet. The bending force P obtained in this way is no longer sufficient to press these edge areas of the glass sheet 1 'tightly onto the mold surface of the bending mold 12.

Figure 2 illustrates the first possibility of how to increase bending forces at critical points in an efficient manner at only extremely low cost according to the invention. For this purpose, at points with strong bending, the flow rate of the gas stream flowing along the glass plate 1 'is reduced by the dam plate arrangement 16. The dam plate 16 is then placed approximately perpendicular to the direction of the gas flow. The gas flow is braked and forced to flow from the gap 18 between the edge of the glass sheet 1 'and the dam plate 16 and to flow away upwards through the gap 20 between the top of the dam plate 16 and the bending mold 12. As the flow rate of the partial flows flowing along the glass sheet below the glass sheet 1 'decreases, the static pressure then acts as an increased bending pressure P' on the surface of the glass sheet. At the same time, the static pressure in the space 22 is reduced so that this space 22 remains in direct contact with the space 20 above the space above the bending mold, where a lower static pressure prevails.

The measures according to the invention are particularly effective because the dam plate 16 is shaped and positioned so that the width A of the gap 1δ formed between the glass plate 1 'and the dam plate 16 is smaller than the width B of the gap 20 formed between the dam plate 16 and the bending mold 12. The width B is e.g. -20 mm, and the width of the gap A is preferably 2-10 mm. The height H of the barrier part 16 of the dam plate 16 is, for example, 10-100 mm and preferably 20-50 mm.

In the embodiment shown in Fig. 3, the whole desired effect is achieved in a slightly different way. In this case, the dam plate 24 is placed immediately on the edge of the bending mold 26, so that no gas flows between the dam plate 24 and the bending mold 26. As a result, a gas cycle 28 is formed in front of the dam plate 24, and partial streams of gas flowing to this side are forced to flow around the dam plate 24. There is no radial flow directly along the glass plate 1 '. As the kinetic flow energy is further reduced, the static partial pressure increases substantially because the total pressure energy remains constant, 7 82676 which changes the effective bending force P '. The required relative vacuum at the rear of the glass sheet 1 'is provided by holes 30 in the bending mold 26 which extend through it and connect the bending mold 26 to a space behind the bending mold 26 where a lower static pressure prevails.

A concrete embodiment of a bending mold formed according to the invention for bending the rear window glass of a car is shown in Figures 4-7. The bending mold 31 corresponds exactly to the size and shape of the bent glass sheet in terms of its circumferential shape and the shape of the bending surface 32. The bending mold 31, which is, for example, a ceramic material or a metal, is provided with a cylindrical connecting piece 36 connected to a fastening pipe 40 located inside the bending station above the connecting flange 39.

According to the invention, higher bending forces are required in the edge regions 32 'and 32 "of the bending surface 32, because on the one hand there is a corner region which requires spherical bending at these points and on the other hand the end angle of the mold surface in these regions is larger than in other regions. The plates 32 'and 32 "are therefore located on the edge of the bending mold 31! The dam plates 3 & are fastened to the bending mold 31 by screws 41, whereby the spacer sleeves 42 take care of the necessary distance to the bending mold. The angle of inclination of the beta formed by the dam plate 38 with the vertical is selected depending on the curvature of the bending mold as follows:. that the barrier surface of the dam plate is approximately perpendicular to the direction of flow of gas radially flowing along the glass plate.

• ·. In both cases, it may be advantageous to make the device so that the gap between the dam plate and the edge of the glass sheet remains constant throughout the bending process throughout the edge of the glass sheet. In this case, a design of the β 82676 dam plate 44 corresponding to Fig. 7 is recommended. Here, the dam plate 44 has a curvature corresponding to the curve K depicting the edge of the glass plate 1 'during the bending step. In this way, a very narrow gap 18 can be maintained throughout the bending step, which can mean a further improvement in the pressure conditions during the bending step.

t

Claims (11)

A method of bending a glass plate heated to a bending temperature by a hot gas stream of an extensive cross section with which the glass sheet is pressed against a bend, characterized in that at least in the selected peripheral regions of the glass sheet, the flow rate of the hot gas stream in the radial direction of the the surface of the glass sheet flowing partial streams is reduced by means of latches arranged in the way of these partial streams, so that the static pressure proportion of the gas flowing in these peripheral areas of the glass sheet is increased. Method according to claim 1, characterized in that the static pressure in a space between the peripheral areas of the glass sheet and the upper surface of the bending mold is reduced by connecting this space with a space behind the bending mold. 3. A method according to claims 1 and 2, characterized in that the hot gas partial streams, which flow in a radial direction along said peripheral areas of the glass sheet, are passed at the end of the bending mold while reducing the flow cross-section past the gap formed between the bending mold and the glass sheet. 4. A method according to claim 3, characterized in that for further reduction of the static gas pressure in the space between the peripheral regions of the glass sheet and the bending form, this space is connected by means of the bending form through the heel located on the other side of the bending form. 5. A method according to claims 1 and 2, characterized in that the path of the partial gas streams flowing radially along the said peripheral regions of the glass sheet is completely closed with the curves arranged in the bending form and the static gas pressure between the said peripheral regions of the glass sheet is bent and bent. by means of the bending form through the heel. 82676 12 Apparatus for carrying out the method according to one or more of claims 1 to 5, characterized in that at least at selected points a baffle plate (16; 24; 38; 44) is arranged at least at selected points. toward the end key of the bend shape face surface. Device according to claim 6, characterized in that, when forming the slit (20) between the damper plate (16; 38) and the bending mold (31), the pre-evacuation plates (16; 38; 44) are fixed to a distance (B) of about 5. -20 mm from the bending mold. 8. Apparatus according to claim 7, characterized in that the bending mold has been equipped with circumferential plates in the peripheral areas adjacent the damper plates. Device according to Claim 6, characterized in that the damper plate (24) is arranged immediately at the edge of the bending mold (26) and that the bending mold (26) has in the areas adjacent the damper plate (24) fitted with the bending mold (26) through the heel (30). . Device according to one or more of claims 6-9, characterized in that the height (H) of the damper plates (16; 24; 38; 44) is 10-100 mm and preferably about 20 to 50 mm. Device according to one or more of claims 6-10, characterized in that the damper plates (44) have been bent to correspond to the path defined by the edge of the glass sheet below the bending spoon.