GB2181123A

GB2181123A - Heat treating panes of glass

Info

Publication number: GB2181123A
Application number: GB08611548A
Authority: GB
Inventors: Wolfgang Erdmann
Original assignee: Techno Glas Engineering GmbH
Current assignee: Techno Glas Engineering GmbH
Priority date: 1985-10-05
Filing date: 1986-05-12
Publication date: 1987-04-15
Also published as: GB8611548D0; DE3535668A1

Abstract

A method of heat treating panes of glass, particularly panes of glazing glass, in which the pane of glass is first heated under oscillating movements and is then, likewise under oscillating movements, prestressed with a coolant and is then subjected to secondary cooling. In order to permit of energy-saving operation, prestressing of the pane of glass is performed with oscillating movements of smaller amplitude than those during the subsequent secondary cooling and for the secondary cooling under reduced coolant pressure, corresponding to the greater amplitude of movement of the glass pane, an additional cooling be incorporated. To carry out the method, an apparatus is suggested in which a cooling station for prestressing and subsequent secondary cooling of the pane of glass consists of a main cooling station and separate therefrom and lengthening the main cooling station, a secondary cooling station, the two stations being connected to each other.

Description

SPECIFICATION Heat treating panes of glass The invention relates to a method of heat treating panes of glass, particularly panes of glazing glass, in which the pane of glass is first heated under oscillating movements and is then likewise under oscillating movements prestressed with a coolant and is subsequently subjected to secondary cooling, and to an apparatus for carrying out the method.

In order than panes of glass, for example windscreens of motor vehicles or panes of glazing glass, do not shatter into large and sharply-edged fragments when broken, are subjected to a heat treatment in order to create a glass fracture structure which consists of harmless small glass crumbs. For this purpose, the pane of glass is first heated and is then prestressed with a coolant, for example cooling air. By reason of the prestressing, compressive and tensile stresses are created in the glass which generate the special glass fracture structure. Prestressing is followed by a secondary cooling of the still warm but prestressed pane of glass. During the heating and subsequently during the cooling of the pane of glass, this performs oscillating movements so that the heated pane of glass does not become misshapen by reason of gravity.

The oscillating movements during heating should not fall below a specific amplitude of travel in order to avoid damage to the pane of glass. Upon cooling, the pane of glass is less sensitive to damage.

Prestressing the pane of glass calls for a high coolant pressure although the prestressing process takes only a short time. For secondary cooling, on the othe hand, the coolant pressure is substantially lower since the residual heat still present after the prestressing ought to be dissipated gradually. The secondary cooling does not have any effect on the fracture picture of the glass sheet. With constantly long amplitude travel in the cooling station, a correspondingly large quantity of coolant must be generated under high pressure.

A method and an apparatus of this kind are known from U.S. Patent No. 3 994 711. The prior art apparatus for heat treating panes of glass comprises a feed means, a subsequent furnace with a roller conveyor, a cooling station adjacent thereto, likewise with a roller conveyor, and finally a withdrawal means. Both the feed means and also the withdrawal means are likewise provided with a roller conveyor. The feed means and the furnace have a common drive, the feed means additionally having a lifting mechanism. The cooling station and the withdrawal means likewise have a common drive, the roller conveyor of the withdrawal means again being provided with a lifting mechanism. Disposed between the furnace and the cooling station is a coupling which separates the roll trains in the furnace and in the cooling station during the oscillating process and couples them during feeding or withdrawal.

With this state of the art, the need to provide an electronically regulable coupling between the furnace rollers and the cooling station rollers is a disadvantage since it increases the cost of the equipment and makes speed control difficult.

The invention is based on the problem of so further developing the method described at the outset that an energy-saving operation is made possible, combined with a reduced cost of equipment.

In order to resolve this problem, in the case of a method of the type indicated at the outset, it is proposed that the prestressing of the pane of glass is performed with oscillating movements of smaller amplitude than those of the subsequent secondary cooling and in that for the secondary cooling under diminished coolant pressure, corresponding to the greater amplitude of the movements of the pane of glass, an additional cooling is incorporated.

The proposal according to the invention is based on the fundamental thought whereby it is suggested for the prestressing process to carry out the oscillating movements with smaller amplitude travel than during the secondary cooling. This has the advantage that the energyexpensive phase of cooling can by virtue of the lesser amplitude of travel be carried out in a smaller cooling station, which overall economises on energy for blowing in the coolant under high pressure. Only if correspondingly larger amplitude travel on the part of the pane of glass is required for secondary cooling, an additional cooling stage is incorporated in order to achieve optimum secondary cooling in spite of the additional space required. Since secondary cooling is carried out at a lower coolant pressure, the additional cooling stage is unimportant.

According to a further feature of the invention, it is suggested that the oscillating movements of the pane of glass during prestressing and secondary cooling are coupled to the oscillating movements of the pane of glass during heating. At the same time, preferably corresponding oscillating movements can be carried out with identical amplitude of travel and at identical speed. This simplifies the process even more since coupling the oscillating movements during heating and during the subsequent cooling means that the apparatus costs are lower. From the procedural point of view, this has the advantage that this coupling permits of perfect transfer from heating to prestressing at any time.

Finally, it is proposed by the method that coolant for the secondary cooling be branched off from the main cooling system. Thus it is possible to carry out the secondary cooling without any great complication or expense.

On a basis of an apparatus having a horizontal feed means for transporting a pane of glass into an electrically fired horizontal furnace for heating the oscillating pane of glass, with a cooling station in a disposition substantially directly behind the furnace with coolant connections, with a roller conveyor means in the furnace and in the cooling station for transport and for the oscillating movements of the pane of glass and also with the withdrawal means for the heat treated pane of glass, the invention suggests that the cooling station consist of a main cooling station for prestressing the pane of glass and of a secondary cooling station separate therefrom and prolonging the main cooling station according to the greater amplitude of travel and that the two stations be connected to each other.

By sub-dividing the cooling station into a main cooling station and a secondary cooling station, it is possible to realise the energy-saving mode of operation. For prestressing the pane of glass, only the main cooling station is subject to coolant under high pressure. Only when the amplitude of travel for secondary cooling is increased are both stations connected to each other by being lined to the same coolant supply. The station which is then increased in volume is supplied with coolant under lower pressure and volume.

According to a further feature of the invention, it is proposed that the cooling station be provided with an additional coolant connection which can be incorporated by means of a valve, the additional coolant connection being branched. from the main coolant connection for the main cooling station. Since the auxiliary coolant connection is branched from the main coolant connection, the secondary cooling station can easily besupplied with coolant. Control of the valve of the auxiliary coolant connection is easily achieved technically.

Finally, the invention suggests a common roller conveyor means both for the furnace and also for the cooling station. This common roller conveyor means does not require any coupling between the furnace and the cooling station so that synchronism in the movement of transport between the furnace and the cooling station is guaranteed.

It is according to a further expedient development of the invention suggested that the rollers of the roller conveyor means of the cooling station be of slightly larger diameter, or example 2 mm, than those of the roller conveyor means of the furnace. Advantageously, this ensures without complicated control that the transfer of each pane of glass between furnace and cooling station takes place with a certain briskness.

The method of heat treating panes of glass according to the invention and the associated apparatus will be described in greater detail hereinafter with reference to the accompanying drawings, which show a diagrammatic side view of the apparatus.

The overall plant shown in the drawing consists of a feed means 1, a furnace 3 disposed directly after the feed means in the direction of transport of a pane of glass 2 and, likewise directly downstream of the furnace 3 in the direction of transport a cooling station 4 which is followed by a withdrawal means 5. As a horizontal conveyor for the panes of glass 2, a roller conveyor means 6 common to the furnace 3 and the cooling station 4 is used and has driven conveyor rollers 7. The conveyor rollers 7 which may be of ceramic construction in the furnace 3 are driven by a common rotating chain 8 and engines 9. Corresponding roller conveyor means 10, 10' are provided for the feed means 1 and the withdrawal means 5.

The furnace 3 is an electrically fired oscillating operating horizontal roller furnace in which the panes of glass 2 are being continually heated up on the ceramic conveyor rollers 7 and softened so that they can be prestressed in the cooling station 4 and subjected to secondary cooling.

The compressive and tensile stresses created in the pane of glass 2 during prestressing produce upon destruction of the pane of glass 2 a glass fracture structure which consists of harmless small glass crumbs.

The cooling station 4 is sub-divided into a main cooling station 4' and a secondary cooling station 4". Discharging into the main cooling station 4' is a coolant connection 12 and into the secondary cooling station 4" an auxiliary coolant connection 13 which branches off the coolant connection 12. The feed of coolant from the coolant connection 12 into the auxiliary coolant connection 13 takes place via a valve 14.

The method according to the invention will now be explained hereinafter with reference to the described installation: First a pane of glass 2 is placed on the feed means 1 and transported by the roller conveyor means 10 into the furnace 3 where the pane of glass 2 becomes heated. When the pane of glass 2 is transported into the furnace 3, it is located between the two reversal points A and C.

During heating, the pane of glass 2 performs an oscillating movement between the reversal points B and C in order to avoid deformation of.the pane of glass 2 by virtue of the force of gravity. After the short oscillating movements between the reversal points B and C, longer oscillating movements follow between the reversing points B and D which have their cause in the as yet to be described oscillating movements in the cooling station 4.

After the pane of glass 2 has become completely softened in the furnace 3, it is transported over the common roller conveyor means 6 into the cooling station 4 and especially into the main cooling station 4'. At the same time, a fresh pane of glass 2 is transported into the furnace 3 by the feed means 1. In the main cooling station 4', coolant is pumped under high pressure through the coolant connections 12 into the interior of the- main cooling station 4' so that prestressing takes place due to the intensive cooling of the pane of glass 2. During this prestressing process, the pane of glass 2 performs an oscillating movement between the reversal points F and G (corresponding to B and C in the furnace). When prestressing of the pane of glass 2 is completed, the amplitude of travel involed in the oscillating movements of the pane of glass 2 in the cooling station 4 is increased.During this secondary cooling, the air valve 14 is opened so that coolant can also be fed to the secondary cooling station 4" through the auxiliary coolant connection 13. This secondary cooling of the pane of glass 2 takes place at a reduced pressure compared with the prestressing process. Due to the oscillating movement of the pane of glass 2 in the secondary cooling phase between the reversal points F and H, and by reason of the common roller conveyor means 6, the already mentioned oscillating movement is created between reversal points B and D in the furnace 3.

As soon as the pane of glass 2 in the furnace 3 has reached its final temperature, the pane transfer takes place in the plant as a whole.

The advantage of the method according to the invention and of the apparatus corresponding thereto lies in the cooling station 4 which is sub-divided into a main cooling station 4' and a secondary cooling station 4". Associated with these two stations 4', 4" are differing lengths of oscillating movement. During prestressing of the glass pane 2, a high coolant pressure is required for which a relatively considerable amount of energy must be expended. The energy to be expended is thereby proportional to the space to which it is to be applied. The main cooling station 4' is adapted to the oscillating movement between the reversal points E and G. Only after the greater amplitude of travel for secondary cooling is adjusted is the entire cooling station 4 consisting of the main cooling station 4' and the secondary cooling station 4" subjected to the action of coolant.

A further advantage lies in the common roller conveyor means 6 for the furnace 3 and for the cooling station 4. According to the roller diameter, so identical or slightly differing speeds of transport will result, both in the furnace 3 and also in the cooling station 4. The structural design and the control of the movement processes are simplified.

Claims

1. A method for heat treating panes of glass, in particular panes of glazing glass, in which the pane of glass is first heated under oscillating movements and is then, likewise under oscillating movements, prestressed with a coolant and subsequently subjected to secondary cooling, characterised in that the prestressing of the pane of glass is performed with oscillating movements of smaller amplitude than those of the subsequent secondary cooling and in that for the secondary cooling under diminished coolant pressure, corresponding to the greater amplitude of the movements of the pane of glass, an additional cooling is incorporated.

2. A method according to Claim 1, characterised in that the oscillating movements of the pane of glass during prestressing and secondary cooling are coupled to the oscillating movements of the pane of glass during heating.

3. A method according to Claim 2, characterised in that the oscillating movements are performed with identical amplitude and identical speed.

4. A method according to one of Claims 1 to 3, characterised in that, for the secondary cooling, the appropriate coolant is branched off from the main cooling system.

5. Apparatus for carrying out the method according to Claims 1 to 4, with a horizontal feed means (1) for transporting a pane of glass (2) into an electrically heated horizontal furnace (3) for heating the oscillating pane of glass (2), with a cooling station (4, 4', 4") in a disposition substantially directly behind the furnace (3) with coolant connections (12, 13) with a roller conveyor means (6) in the furnace (3) and in the cooling station (4, 4', 4") for transporting and for the oscillating movements of the pane of glass (2) and also with withdrawal means (5) for the heat treated pane of glass (2), characterised in that the cooling station (4) consists of a main cooling station (4') for prestressing the pane of glass (2) and separate therefrom and extending the main cooling station (4') in keeping with the greater amplitude of movement, a secondary cooling station (4") and in that the two stations (4', 4") are connected to each other.

6. Apparatus according to Claim 5, characterised in that the secondary cooling station (4") is provided with an additional coolant connection (13) which can be incorporated by means of a valve (14) and which is branched off the main coolant connection (12) for the main cooling station (4').

7. Apparatus according to one of Claims 5 and 6, characterised by a common roller conveyor mean (6) both for the furnace (3) and also for the cooling station (4, 4', 4").

8. Apparatus according to Claim 7, characterised in that the rollers of the roller conveyor means (6) of the cooling station (4, 4', 4") are slightly larger in diameter, for example half millimetre, than those of the roller conveyor means 96) of the furnace (3).

9. Apparatus for tempering flat glass substantially as herein described with reference to the accompanying drawing.

9. A method for heat treating panes of glass substantially as herein described with reference to the accompanying drawing.

10. Apparatus for heat treating panes of glass substantially as herein described with reference to the accompanying drawing.

CLAIMS Amendments to the claims have been filed, and have the following effect: New or textually amended claims have been filed as follows:

1. A method for tempering flat glass in which the glass is first heated under oscillating movements and is then, likewise under oscillating movements, tempered with a coolant and subsequently subjected to secondary cooling, characterised in that the tempering of the pane of glass is performed with oscillating movements of smaller amplitude than those of the subsequent secondary cooling and in that for the secondary cooling under diminished coolant pressure corresponding to the greater amplitude of the movement of the glass, an additional cooling is incorporated.

2. A method according to claim 1, characterised in that the oscillating movements of the glass during tempering and secondary cooling are coupled to the oscillating movements of the glass during heating.

5. Apparatus for carrying out the method according to claims 1 to 4, with a horizontal feed means (1) for transporting a glass (2) into an electrically heated horizontal furnace (3) for heating the oscillating glass (2), with a cooling station (4, 4', 4") in a disposition substantially directly behind the furnace (3) with coolant connections (12, 13) with a roller conveyor means (6) in the furnace (3) and in the cooling station (4, 4', 4") for transporting and for the oscillating movements of the glass (2) and also with withdrawal means (5) for the heat treated glass (2), characterised in that the cooling station (4) consists of a main cooling station (4') for tempering the glass (2) and separate therefrom and extending the main cooling station (4') in keeping with the greater amplitude of movement a secondary cooling station (4") and in that the two stations (4', 4") are connected to each other.

7. Apparatus according to one of claims 5 and 6, characterised by a common roller conveyor means (6) both for the furnace (3) and also for the cooling station (4, 4', 4").