EP1511693A1

EP1511693A1 - Method for tempering glass

Info

Publication number: EP1511693A1
Application number: EP03732601A
Authority: EP
Inventors: Risto Nikander
Original assignee: Feracitas Oy
Current assignee: Feracitas Oy
Priority date: 2002-05-30
Filing date: 2003-05-30
Publication date: 2005-03-09
Also published as: FI20021014A0; WO2003101897A1; AU2003238532A1

Abstract

The method for tempering the glass (G) in furnace, which includes heating section (F) carrying the glass on rollers (Rf), to heat the glass into tempering temperature, further tempering section with cooling blow jets (J), equipped with rollers (R) to transfer the glass from heating section to tempering section. The flow directed towards the furnace and caused by air exiting from the first row tempering nozzles, is stopped or reduced by air flow arrangements (AEup), (AB), above and below the glass, which eliminate or reduce cooling of glass before tempering.

Description

PCT RECD 0 8 SEP 2003

WIPO PCT

INTERNATIONAL SEARCH REPORT

(PCT Article 18 and Rules 43 and 44)

Applicant's or agent's file reference FOR FURTHER see Notification of Transmittal of International Search Report

PCT-175 ACTION (Form PCT/ISA/220) as well as, where applicable, item 5 below.

International application No. International filing date (dayjmonthjyear) (Earliest) Priority Date (dayjmonthjyear)

PCT/FI 03/00427 30 May 2003 30 May 2002

Applicant

FERACITAS QY et al

METHOD FOR TEMPERING GLASS

In glass processing plants, flat glass factories and steel factories plate like pieces are transported on rollers and are blown during processing by gas jets, most often by air. This presentation especially concentrates on flat glass tempering machines, but the invention can be applied to other processes, in which plate like pieces are subjected to blowing, while being moved on rollers.

KNOWN ART

In all cases the air blown has to be conducted away from the blowing area. There are different nozzle arrangements and also different kinds of tempering air production methods. More or less common to all methods is, that when tempering thin glass sheets high cooling rates are required, which results in great number of nozzles and high pressures, leading to large air volumes. When the air exit cross sections are small, counter pressures will be created in tempering or cooling sections. The counter pressure tends to push the air to all directions. Especially harmful is air flow into the direction of the furnace, because cold tempering air disturbs the temperature balance of the furnace. Another reason, which makes the air flow into the direction of the furnace very harmful is, that it cools down the glass entering into tempering. If the glass surface cools down before tempering, it will not be tempered or at least higher cooling power will be required. That is why it is advantageous to ensure, that the glass is in high enough temperature when it comes into the tempering. Overheating of the glass does not help achieving correct degree of tempering, but it would worsen optical quality and waste energy.

Thin glasses cool down especially quickly after exiting from the furnace. Even in still air, the cooling rate is about 6 centigrade per second. If the glass is subjected to convection caused by moving air, the cooling rate is multiplied. Even if the air blown onto the glass is hot, (however cooler than the glass), it would still cool down the glass. Thin glasses require very high cooling power, so especially for them correct choices are important in order to get the best result. The most usual method for elimination of the mentioned disadvantages is that the glass is driven into the tempering section with high speed, normally about 0, 6 m /s. There are different known methods, trying to eliminate the air flow into the direction of the furnace. In these methods the main consideration has been just preventing the air flow into the furnace, so they do not eliminate glass cooling before it arrives into the tempering. In some methods the air flow has been considered necessary only on the top side, because the roller under the glass stops the air flow at least partially. All of them are defective or ineffective for the purpose described in the novel idea.

The advantages of the novel idea are best explained by comparing it with a known method, in which the glass is driven through a special tempering section. Tempering section is normally 1 ,2 metres long and thin glass driving speed is generally 0,6 m/s so the glass remains under tempering 2 seconds, during which time the glass is tempered. After this it has to be cooled down, for which purpose a low pressure blower is sufficient. As an average cooling power for 3 mm glass can be considered 250 kW/m2. If the tempering section is 1 metre wide, 1,2 meters long tempering section would require 1 x 1,2 x 250 kW = 300 kW cooling power.

If the glass driving speed could be reduced to 0, 3 m/s, it would be possible to shorten the tempering section down to 0, 6 m and glass would still remain under the quench the necessary 2 seconds. When using the same tempering pressure, 250 kW/m2, the glass would receive the same cooling with half of the area of known methods and the necessary cooling power would be 1 x 0,6 m x 250 kW = 150 kW.

Thicker glasses are driven into the tempering section normally with lower speed, about 0, 3 m/s, but with thin glasses that has not been possible due to the reasons mentioned earlier. In order to be able to temper thin glasses similarly, with low speed, the remarkable reduction of peak power draw, a very short and effective border between hot section, (furnace) and cold section, (tempering part), would be necessary so that the glass would not cool down during this travel. The border should also have similar characteristics on the top and bottom sides of the glass. Otherwise the result would be different cooling on the top side and on the bottom side and the glass would bend during tempering.

Another necessary thing to make low driving speed possible is related to bending of glass as between the rollers if the speed is too low. This applies especially for thin glass, which bend more easily due to the lower bending resistance and higher tempering temperature compared to thicker glasses. This would require decrease of centre to centre distance of the rollers, especially last rollers just before the tempering section. The other possibility would be to support glass between the rollers by other means. The decrease of centre to centre distance of rollers to be sufficiently small is impossible especially with wide furnaces, because the rollers would bend due to their own weight. The minimum roller diameter is about the furnace width / 30. That is why at least the wider furnaces must have some method to shorten support distances of glass, (roller C-C distance).

When these two things have been resolved, also thin glass can be driven slowly out of the furnace and remarkable peak power reduction can be achieved. This method can be used similarly and advantageously also with tempering machines, in which combined tempering and after cooling section is used.

Of known methods most commonly used system is so called air knife as shown in publication 3,672,861 , Fig 1 , item 57. It partially prevents the tempering air from flowing into the direction of furnace by blowing air into the direction of the glass travel. However, it cools down the glass before the glass will be under the first row of tempering jets and it does not form sudden border of hot and cold.

Publication 4,781,747 describes air nozzle arranged above the glass between the furnace and tempering section, which nozzle sucks the air flow moving into the direction of the furnace and thus prevents the air from entering into the furnace. The disadvantage of this method is the air flow on the top of the glass from the tempering nozzles until the said nozzle and one sided cooling effect of this flow onto the glass before the glass enters into the tempering section. There is not such sucking under the glass and even if there was, it would also cool the glass down before the tempering jets.

Publication 0425998 A1 describes sucking channels arranged between the furnace and the tempering section above and below the glass. The problem caused by them is cooling of glass by air flow flowing along the surfaces of the glass before the glass arrives under the tempering nozzles. Another disadvantage is increased need for the space between the rollers.

Publication 4,886,540 describes pipes, 30, which includes nozzles 32, out of which air is blown against the air pressure arriving from the tempering section. Blowing takes place very much in direction of the glass, 5 - 25 degrees angle between the glass and jets, but quite a distance from the glass. Blowing pipes are quite a distance from the tempering section so glass has certain cooling time before it enters under the quench. The method is suitable only for preventing the tempering air from entering into the furnace and it seems to have been developed mainly for bending and tempering.

Very similar is method described in publication EP 0 882 682 A1 , in which there are similar elements, but picture 1 has air flow preventing device under the glass by air bed 12. The top side has the same method and the same problems as described above. The picture 3 still includes air bed under the glass, but hot air is blown above from inside the furnace, otherwise similarly as cold air is blown in picture 1. This is no better method, because immediately, when the air exits the furnace, it mixes with cold air and thus the air is cooler than the glass and thus it cools down the glass. Additionally it allows cold air to flow up to the furnace exit door so cooling effect of the tempering air starts from this point.

Only with thin glasses it is possible to achieve remarkable peak power reduction by shortening the tempering section length and reduce the manufacturing costs this way especially through smaller blowers, smaller drive motors, reduced electrification costs, but also the tempering section costs would go down.

To obtain the advantages the following characteristics of the invention are required;

1) Also thin glass, 3, 5 mm and thinner, are driven into the tempering section at speed of 0,5 m/s or lower speed.

2) A very short and effective borderline between hot and cold are arranged so that glass cooling is prevented before it enters under the first row of tempering nozzles. 3) The trailing end of the glass will be supported by roller or other means just before the first row of tempering nozzles so that the distance from the last support to the first row of tempering nozzles will be remarkably less that typical roller C-C distance, under 120 mm, preferably something like half of that.

Figure 1 shows side view of a part of the tempering furnace according to the invention.

Figure 2 shows an alternative solution to stop the flow of cooling air.

Figure 1 shows advantageous arrangement to transfer the glass G from furnace F into tempering section. Picture 1 shows hot air jets Jha, furnace roller Rf, hot air return AEha and first or few first ones or even all tempering air exit channel(s) with under pressure Aeup. The tempering section rollers R are smaller ones and cooling blowing is arranged through nozzle blocks NB to the under- and topside of the glass. The air if fed from air supply channel AS.

The cooling of glass prior to tempering and sufficiently long tempering time even with relatively short tempering section is arranged, (low exit speed), can be achieved, when glass temperature just before the first row of tempering nozzles is secured as follows;

The tempering air blown through the first nozzle block(s) is removed from temperi g section by leading on the top and bottom sides of the glass suitable under pressure Aeup at least aside of the first row of tempering nozzles on the direction of the glass travel, on the side of the tempering section. It is also advantageous to aim the first air jets somewhat in the direction of the tempering section. The system shown on the picture also makes it possible to arrange the first row of tempering nozzles close to the last roller or other supporting means of the furnace. Thus it immediately cools down the glass and the trailing end of the glass does not need to stay as completely hot, longish "cantilever" supported by the first roller of tempering section, in which case it would bend more easily. This also offers another advantage as slightly cooled glass surface will not be damaged so easily by the touch of the first roller of the tempering section. Furthermore, in order to assist to maintain the correct glass temperature hot air with temperature the same or higher than glass tempering temperature, is arranged to impinge the last furnace roller Rf and the top side of the glass, Jha. The air returns back into the convection furnace according to the principle of the internal circulation. This method is similarly advantageous also in tempering machines in which tempering and cooling sections are combined.

In the picture 2 the cooling jets are arranged in the similar way as in picture 1. In the end of the furnace there are air beds AB with small clearance, into which hot air, with temperature of glass tempering temperature, is blown. With air beds it is possible to create short and effective border with cold and hot and thus prevent cooling of glass before tempering. The air beds must be located very near to the tempering jets, J.

The air bed AB is advantageous at least under the glass, where it also supports the glass, as the glass exits from the furnace. Under pressure Aeup on the other hand is suitable above the glass. These air flow arrangements, under pressure and air bed together or alone or combined in various ways, prevent the flow of tempering air into the direction of the furnace. The upper air bed has to be made adjustable up and down to facilitate tempering of different glass thicknesses and to close the furnace for the heating period.

Different methods described in patent claims can be used also as combinations so that one type is used on the top side and the other below. For the process a good alternative is to have a method described in patent claim 3 after the last furnace roller at least under the glass and additionally method described in patent claim 2 aside of the first row of tempering nozzles. When the underside air bed (AB) is arranged in such a way, that it supports the glass on the same vertical level as the top of the rollers, it is possible to increase the C-C distance of the last furnace roller and the first tempering section roller and this way it would be easier arrange both blow back barriers in this space.

Claims

1. Method for tempering of glass (G) 3,5 mm and thinner in the furnace, said furnace comprising rollers (Rf) transporting the glass in the heating section (F) for heating the glass into tempering temperature, and further glass tempering section with cooling blow (J) and roller arrangement (R) to transfer the glass from heating section (F) into the tempering section, characterized in that the glass is driven into the tempering with speed of 0,5 m s or slower and air is blown towards the glass (G) by means of nozzles (J) locating at least in one row between the last roller (Rf) of the furnace and the first roller (R) of the tempering section and air stream into the heating section is prevented at least one blow back arrangement (AEup), (AB) locating between said last roller and said first roller, said nozzles and arrangements locating both on the top and bottom sides of the glass (G).

2. The method as claimed in claim 1 characterized in that at least great majority of air flow discharged from the first row of tempering nozzles (J) removed by under pressure suction (Aeup) at least from one side of the first row of tempering nozzles.

3. The method as claimed in claim 1 characterized in that the part of air flow, which is directed towards the furnace and which is caused by the air exhausted from the first row of tempering nozzles (J), is stopped air blow arrangement(s) (AB), having perforated plate(s), through which hot air with temperature of glass tempering temperature or higher is blown and air blow arrangement (AB) is located near to the surface(s) of the glass (G) so that air film, with temperature of at least the glass tempering temperature, is created between them.

4. The method as claimed in claim 1 characterized in that on one side of the glass (G) is used method as described in claim 2 and on the opposite side the method described in claim 3. 8

5. The method as claimed in claim 1 characterized in that the last roller (Rf) of the furnace is subjected to hot air jets (Jha), the temperature of which is at least as high as glass tempering temperature.

6. The method as claimed in claim 1 characterized in that the top surface of the glass at the location or close to the last furnace roller (Rf), is subjected to hot air jets (Jha), the temperature of which is at least as high as glass tempering temperature.

7. The method as claimed in claim 1 characterized in that at least after the last furnace roller (Rf) and before the first tempering section roller (R) the glass (G) is supported by hot air bed (AB), which supports the glass on the same height as the rollers.

8. The method as claimed in claims 1 - 7 characterized in that the hot air bed (AB) supporting the glass is arranged between several or all of the furnace rollers (Rf).

9. The method as claimed in claim 1 characterized in that the degree of opening of the door at discharge end of the furnace is adjustable to be small at for tempering situation according to the thickness of the glass.

0. The method as claimed in claim 9 characterized in that the degree of opening of the door at the discharge end of the furnace is automatic based on glass heating parameters.

11. The/Tiethod as claimed in claim θ characterized in that hot air flow j§ blown along the internal surface of the discharge door towards the cjlass.