FI94234B - Process for bending laminated glass sheets - Google Patents

Description

94234

Method for bending laminated glass sheets.

Förfarande föring bending av laminerade glasskivor.

The invention relates to a method for bending laminated glass sheets, in which the laminated, non-bent glass sheets are placed in an edge fashion, an edge mold and a pair of laminated glass sheets supported thereon are conveyed by

In particular, the invention is suitable for use in a method in which, after bending, the mold carriage and the pair of bent glass sheets are transferred from the upper track to the lower track and the bent pair of glass sheets is cooled in the lower track below said preheating compartments.

The following problem is associated with this known method. In the preheating compartments, a temperature difference of about 100 ° C occurs between the lower and upper glass. This temperature difference has not yet been evened out in the bending section. As a result, the lower glass "resists" the bending of the upper glass and slows down the bending because it is necessary to wait for the anvil to warm up to the bending temperature. In particular, the phenomenon occurs when forming a progressive sag in the middle of the glass or in difficult double bending at corners (complex bend).

The object of the invention is to solve this problem and to smooth out said temperature difference so that heating and bending can be accelerated and thus the production capacity of the furnace can be increased while at the same time making it easier to achieve the desired bending shapes.

This object is achieved by the invention on the basis of the features set out in the appended claim 1. A specific embodiment of the invention 2 94234 is set out in claim 2.

Thus, the invention enhances the transfer of heat from the glass cooled in the lower track by convection to the lower glass in the upper track. In a particular embodiment of the invention, this is accomplished by blowing a small amount of air from the tubes between the upper and lower tracks through the open bottom of the mold carriage.

The solution according to the invention achieves the following advantages: the upper and lower glass are brought to a constant temperature before the actual bending begins, effectively utilizing the temperature difference (about 100 ° C) of the lower and upper glass to heat the upper glass using convection without separate heating.

Homogeneous glass allows fast bending of the glass, because during bending there is no need to wait for the lower glass to heat up to the bending temperature.

Cooling does not result in glass brushing or rising angles due to temperature differences between the upper and lower windows (reverse bend). Glass fits better into the shape required by the edge mold, especially at corners that are difficult to bend (complex Bend).

The bending of a progressive sag is successful with a short bending time.

In the following, one embodiment of the invention will be illustrated with reference to the accompanying drawings, in which Figure 1 shows a vertical section of the central area (preheating compartments) of a furnace apparatus according to the invention; Fig. 2 shows a vertical section of the end (bending compartment) of the same furnace apparatus; Fig. 3 shows a schematic cross-section of the furnace at the preheating section 2 94234; Fig. 4 shows a part of the blowpipe 13 with its perforations seen from above; and Fig. 5 shows test run curves of the deflection of a glass sheet when the blowing according to the invention is applied to the lower surface of a pair of glass sheets and when the bending is performed without blowing. In both cases, the bending time was 200 seconds.

The furnace in which the method is used comprises a plurality of successive heating compartments 1, 2, 3. The laminated glass sheet pair is introduced into the first furnace compartment 1, supported by a bending mold 11. The "laminated glass sheet pair" may hereinafter 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. The preheating compartments 2 are heated partly by heating resistors 12 and partly by the bottom and / or around the edges of the transport carriages 9 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 94234 4 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, for example, in the temperature range 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%.

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 glass plate pair are moved from the upper track 18 to the lower track 19, glass 1pair below the plate pair.

As stated earlier, in preheating purchases 2 there is a temperature difference of about 100 * C between the upper and lower glass. This temperature difference causes the disadvantages mentioned in the introduction. In the preheating compartment 2, the temperature of the lower glass can be e.g. 400 * C. Below this, the temperature of the pair of glass sheets cooled in the lower track 19 can be e.g. 500 * C. In this case, the heat transfer of the glass in the lower track 19 can be enhanced by convection into the lower glass of the upper track 18 by blowing a small amount of air from the pipes 13 between the upper and lower track through the open bottom of the carriage 9.

There may be one or more blow pipes 13. For example, horizontal tubes 13 with a diameter of 20 mm can be used, with 2.0 mm holes 20 all the way at 50 mm intervals. The holes 20 may also be of different sizes in the middle than at the edges. To the pipes. 13 The air to be led can be compressed or blown air, which is preheated in the piping circulating inside the furnace or by a separate heater. The tubes 13 can also be branched.

When using the enhanced convection according to the invention, the upper and lower glass are brought to a uniform temperature before the actual bending 5 94234 is started. Homogeneous glass enables rapid bending, because during bending there is no need to wait for the lower glass to warm up to the bending temperature. The glass fits better into the shape required by the edge mold, especially at corners that are difficult to bend. The bending of a straight arc bag is also possible with a short bending time. This is shown by the test run curves in Figure 5. The bending according to the upper curve is obtained by using enhanced convection according to the invention to raise the temperature of the lower glass. If, instead, convection blowing is not used, a deflection according to a curve lower than 200 seconds is obtained with the same bending time.

Typically, convection air is blown from the tubes 13 throughout the heating step 1 when the glass sheet is stopped in compartment 2. When the glass sheet is moved from one compartment to another, the blowing can be stopped if necessary so that the blowing does not target the edge areas. Although the amount of air to be blown is relatively small and does not require separate heating, the method achieves an increase in production capacity of about 30% to 40% compared to a similar type of furnace without blowing.

The arrangement of the blow tubes 13 as well as the size and arrangement of the holes 20 in the tubes 13 can further influence the temperature distribution of the glass sheet 1 so as to be advantageous for the desired bending shape. The bending form of the glass sheet • is also taken care of in the bending section in the usual way by the radiant heat distribution control program.

When the inflatable air is taken directly from the room surrounding the furnace and it only heats up in the pipes in the furnace, the inflatable air must always be somewhat colder than its surroundings.

Claims (6)

6,94234 A method for bending laminated glass sheets, wherein the laminated, non-bent glass sheets are placed in an edge mold 11e (11), the edge mold (11) and a pair of laminated glass sheets supported thereon are transported by a mold carriage (9) (4), heating the plate pair to a bending temperature and performing bending, characterized in that the heat transfer by convection to the lower glass of the glass plate pair in the preheating compartment (2) is enhanced by blowing a small amount of air on the lower surface of the lower glass. the temperature difference between the glass plates. A method according to claim 1, wherein after bending, the mold carriage (9) and the bent glass sheet pair are transferred from the upper track (18) to the lower track (19) and the bent glass sheet pair is cooled in the lower track (19) below said preheating compartments (2). 19) by convection to the lower glass of the upper track (18) by blowing a small amount of air from the tubes (13) between the upper and lower track (18, 19) through the open part of the bottom of the mold carriage (9). Method according to Claim 1 or 2, characterized in that the convection-enhancing blow is switched off while the mold carriages (9) are being moved from one compartment to another. Method according to one of Claims 1 to 3, characterized in that the convection-enhancing blow is used essentially throughout the period in which the glass sheet is stopped in the preheating compartment (2). 7 94234 Method according to one of Claims 1 to 4, characterized in that the convection-enhancing blow is used when the temperature of the glass is in the range from 300 'to 550 ° C. Method according to one of Claims 1 to 5, characterized in that the bending shape of the glass sheet is taken care of in the bending section by means of a control program for the distribution of radiant heat. «· 1 '* 94234 8