FI91245C - Oven equipment for bending and tempering glass sheets - Google Patents

Description

91245

Oven equipment for bending and tempering glass sheets. -Ugnanordning for bojning och hårdning av glasskiva.

The invention relates to an oven apparatus for bending and tempering a glass sheet, the apparatus comprising an edge mold for supporting the glass sheet in different processing steps, at least two preheating sections, a bending section and a tempering cooling section, the glass sheet being kept supported by the same edge mold.

The invention is particularly well suited for bending relatively easy glass shapes that can be bent by gravity using an edge mold. A large proportion of car side windows and rear windows are such relatively easy shapes that can be bent using the method and device of the invention. Apparently, an apparatus is known for a substantially similar purpose, in which a flat-temperature glass is dropped on top of an edge mold and the glass acquires its correct shape due to the inertia force and the shape of the edge mold. The advantages of this known equipment are high capacity and reliability, but its disadvantages are the high cost, the longer model changeover time (4-5 h), the traces caused by dripping in the edge areas of the glass and the high cost of glass-specific tools.

On the other hand, individual furnaces operating on the edge mold principle are known, in which the glass is only heated from above and the glass bends to its shape, the bending depth of which is determined by adjusting the heating time. The advantages of single furnaces are simplicity and cheapness, but the disadvantages are low capacity, relatively large minimum glass thickness (typically 5 mm, sometimes 4 mm), simple bending shapes and bending accuracy (because the bending depth is only controlled by bending time).

The object of the invention is to provide an improved furnace apparatus which achieves the following advantages: - a low price in terms of capacity - the thickness of the glass is generally less than 4 mm thick, typically 3.2 mm minimum thickness or less thereof - small size of the device - cheap tool costs (eg only four edge molds are required per glass model) - small glass model change time (type less than 0.5 h).

The object of the invention is achieved on the basis of the features set out in the appended claims.

In the following, an embodiment of the invention will be described in more detail with reference to the accompanying drawings, in which Fig. 1 schematically shows a longitudinal vertical section of a furnace according to the invention and Fig. 2 schematically shows a longitudinal horizontal section of the same furnace.

Figure 3 shows a detail in the bending section 8.

In the loading compartment 1, the glass sheet to be bent is placed on top of the edge mold 3. The edge mold 3 is conveyed by a carriage 2 along a lower horizontal track 4 to a preheating compartment 5 with resistors 7 for heating a glass plate from above to a radiant heat. The preheating compartment 5 is located below the bending compartment 8 and the conveying path 4 is located below the tempering cooling compartment 13, whereby the glass entering the preheating has to pass under the tempering compartment 13. The carriage 2 with its molds 3 and glass sheets is then moved below the preheating compartment 6 and lifted by an elevator to the preheating compartment 6, where heating is continued by resistors 7. As is known, preheating can be done 91245 3 relatively quickly because the heat is efficiently transferred to the cold glass. In preheating, the glass sheet typically reaches a temperature of about 500 ° C. Naturally, the final preheating state of the preheating can vary considerably in one direction or another. The preheated glass with its edge molds 3 is transferred to a bending compartment 8, which at the same time acts as an efficient heating chamber with a temperature of about 900 ° C. The temperature of the heating and bending chamber 8 can typically vary in the range of 800-1000 * C. With the efficient resistors 9 in the chamber 8, the glass sheet is heated so rapidly that a 4 mm glass is heated from 500 ° C in about 15-20 seconds to a tempering temperature of 600-630 ° C, typically 615-620 ° C. During this rapid heating, the glass is allowed to bend at the same time. Thus, for example, with a 4 mm glass, the rate of temperature rise is preferably about 6-8'C / s, i.e. generally about 24-32'C / mm / s. In order for the glass sheet to reach the tempering temperature before it bends too much, the rate of temperature rise should be at least about 15 * C / mm / s.

The temperature of the glass is monitored by means of a pyrometer and / or a deflection by means of an optical distance measuring device 10. Thus, the thermal insulation of the furnace roof passes through a tubular observation window 11.

When the pyrometer and / or the deflection measuring device 10 detects that a predetermined temperature and / or deflection of the glass has been reached, the glass is transferred to tempering as quickly as possible. The transfer from the bending compartment 8 to the tempering compartment 13 takes place at the same time in the edge fashion 11a 3 along the path 12. In the tempering compartment 13, cooling air jets are applied to both surfaces of the glass sheet. For this purpose, top and bottom nozzles 14 and 15 can be used, the ends of which can either be in a straight plane or they can be arranged according to a foreseeable compromise bending shape. From the tempering compartment 13, the glass with the molds 3 is transferred to the discharge compartment, where the tempered glass is removed from the edge mold 3. The next glass is then placed on top of the edge mold and the glass with the edge molds is transferred to the preheating compartment.

The edge mold 3 is supported on the outside of the carriage 2 and is coated with a fibrous coating 1a suitable for bending and tempering glass.

The movements of the carriage 2 along the tracks 4 and 12 are provided, for example, by the arrangement described in U.S. Pat. No. 4,497,645, using carriages on top of wheels to be rotated from outside the furnace.

In order to keep the glass plate supported by the same edge mold from loading to unloading, while using a combined loading and unloading compartment, the preheating compartments 5 and 6 are arranged on different levels. In this case, substantial savings in floor space are achieved thanks to the two-layer structure.

The charging section 8, which acts as a power heating chamber, is the heart of the device according to the invention. What's new is the fast heating made possible by a high temperature of about 900 * C. The bending of the glass is effected without aligning the heat with the edge mold to the desired shape. This is the case with easy shaping, but as the degree of difficulty of the shape increases, the thickness of the glass decreases and the size of the glass increases, the difficulty of achieving the desired shape increases. However, precise monitoring of the temperature and / or degree of deflection of the glass and the possibility of transferring the glass rapidly to tempering ensure that the method and device according to the invention can easily and controlled bend conventional shapes of car rear and side windows.

The apparatus according to the invention also makes it possible to bend and temper thin (3-4 mm) glasses, since the bending begins only when the tempering temperature is being exceeded; when the desired shape is reached, the glass can be transferred directly to tempering. In the case of lower temperature furnaces, this is not possible, because the glass has already had time to bend over the desired shape in its central area when the tempering temperature has been reached.

91245 5 If an edge mold is used to support the glass throughout the heating process, this will leave the edge area of the glass colder than the rest of the area. The reason for this is that the edge mold remains colder than the glass due to its mass and heat capacity, which is why it takes heat from the glass. If the glass is tempered, the entire glass must be heated above the tempering temperature, whereby the central area of the glass is heated unnecessarily hot. This, in turn, causes uncontrolled over-bending of the central region of the glass.

If the effect of the edge mold 3 on the slower heating of the edge area of the glass cannot be eliminated to compensate for the tax by additional heating of the edge area, the glass must be heated from the central area of 10-20 ° C unnecessarily hot so that the edge area also hardens. If we take into account the memory input that the bending speed of the glass doubles when the temperature of the glass increases by 8 ° C, the problem caused by the cooling effect of the edge mold can be understood.

To eliminate this, it has been proposed in the invention that in the bending section 8 the heating of the glass sheet is intensified by forced convection at least in the edge areas of the glass sheet supported by the edge mold 3. This is illustrated in Figure 3.

The edge area of the glass is thus heated by the cooling effect of the edge mold more, but only to that extent. The goal is perfectly flat glass.

The technical solution is implemented with compressed air jets blown from pipes 17 and / or 18 adjacent to the edge area. Air jets from the lower pipe 17 are blown perpendicularly upwards (possibly at an angle of 15 °) so that the air jet does not hit the glass, but the edge area and edge mold 3 achieved round. Since the need for additional heat is low, only one of the pipes is probably needed, e.g.

lower pipe 17. In practice, the piping is not a single ring but is divided into several separately controlled zones.

6

Experiments have shown that radiant heating alone does not always make it possible to heat the upper surface of the glass sufficiently, but the lower half is even warmer, even if the underside is not actually heated. This can be compensated by utilizing convection blowing, if necessary, over the entire surface area of the glass sheet, either to compensate for the heating of the upper or lower surface.

As already stated, bent glass heated to its tempering temperature is transferred to tempering as quickly as possible. This is important because the 4 mm glass on the outside of the oven cools to about 5 * C / s before tempering. Every "wasted" second causes the glass to be unnecessarily heated to 5'C. For this reason, the tempering-cooling blowing should be on and the nozzles in the correct position when the glass is tempered or possibly the nozzles are immediately attached when the glass enters the chiller.

If the tempering of all glass shapes cannot be done with one nozzle, the nozzles 14, 15 can be made replaceable. In its simplest form, the nozzles 14, 15 are bent and perforated plates. For example, four nozzles (perforated plates) bent into different shapes are sufficient to cover the entire area. Naturally, an adjustable nozzle could also be used (adjustment can be manual).

As can be seen from the above, the device according to the invention is very simple in technical construction and thus inexpensive. However, in terms of price and size, it reaches a good production capacity (60-120 logs / h).

Claims (7)

91245 A furnace apparatus for bending and tempering a glass sheet, the apparatus comprising an edge mold (3) for supporting the glass sheet in different processing steps, at least two preheating compartments (5, 6), a bending compartment (8) and a tempering cooling section (13), the glass sheet from loading to unloading, characterized in that the preheating compartments (5 and 6) are located in two different height levels, so that one preheating compartment (5) is below the bending compartment (8) and the other preheating compartment (6) is ) next to it. Furnace installation according to Claim 1, characterized in that the loading and unloading station (1), located at one end of the furnace installation, is connected to a preheating compartment (5) below the bending compartment (8) in a horizontal conveying path (4) under Title (13). Furnace system according to Claim 1 or 2, characterized in that the temperature of the bending compartment (8) is at least 100 ° C, preferably more than 200 ° C higher than the highest final temperature of the glass sheet to which the glass sheet is heated during tempering. Furnace apparatus according to claim 3, characterized in that the temperature of the bending compartment is about 800-1000 ° C and the tempering temperature of the glass sheet is about 600-630 ° C, in which temperature the glass sheet is transferred from the bending compartment (8) to the tempering compartment (13). Furnace apparatus according to claim 3 or 4, characterized in that the bending compartment (8) is associated with means (10) for measuring the deflection or temperature of the glass sheet, and said measuring means (10) are arranged to start the edge mold (3) and the glass sheet supported therefrom. ) to the tempering section (13). Furnace installation according to one of Claims 1 to 5, characterized in that the bending compartment (8) has tubes (17 and / or 18) from which air jets are blown in the vicinity of the edge area of the glass sheet. Furnace installation according to Claim 1, characterized in that the heating / bending of the glass is enhanced by blowing gas onto the upper or lower surface of the glass. 91245