WO2002051758A2

WO2002051758A2 - Method and device for tempering glass, particularly drinking glasses

Info

Publication number: WO2002051758A2
Application number: PCT/EP2001/014723
Authority: WO
Inventors: Ulrich Fotheringham; Michael Kluge; Eva HÖLZEL; Dirk Weidmann; Andreas Bensberg
Original assignee: Schott Glas; Carl-Zeiss-Stiftung Trading As Schott Glas; Carl-Zeiss-Stiftung
Priority date: 2000-12-22
Filing date: 2001-12-13
Publication date: 2002-07-04
Also published as: WO2002051758A3; AU2002233256A1

Abstract

The invention relates to a method for tempering glass, particularly drinking glasses by means of a heating installation containing an infrared emitter and a cooling device, comprising the following steps: the glass which is to be tempered is rapidly heated from an initial temperature T1 to a maintenance temperature T2 with the aid of the heating installation using infrared rays; the infrared emitter and the cooling device are controlled in a manner which regulates a predetermined temperature gradient from the surface of the glass to the depth of said glass which is to be tempered; the glasses are brought to a temperature T3 which is lower than T2 by means of a predetermined cooling rate independent from the regulated temperature gradient inside the depth of the glass.

Description

Method and device for tempering glasses, in particular drinking glasses

The invention relates to a method for tempering glasses, in particular drinking glasses with a heating system, which comprises IR radiators and a device for tempering glasses, in particular drinking glasses with IR radiators, and a cooling device.

The usual procedure for tempering glasses is, for example, in Alexis G. Pincus: "Annealing and strengthening in the glass industry",

Ashiee Publishing Co., Inc., Books for the glass industry division, New York 1987, pp. 266 ff.

A process for the rapid and homogeneous heating of semi-transparent and / or transparent glasses with the help of

Infrared radiation has become known from WO 00/56675. A targeted use for tempering glasses, in particular drinking glasses with IR emitters, is not known in WO 00/56675.

According to the prior art, glasses are tempered in that a cooling medium flows over their surfaces. The flow rate of the cooling medium determines the cooling rate of the glass on the one hand, and the temperature gradient from the glass surface to the other on the other. The temperature gradient from the glass surface to the depth in turn determines the tempering of the glass. Was a

Glass cooled slowly, ie with a low cooling rate, so there was also a low temperature gradient in the depth and thus a low prestress. If a glass was cooled quickly, there was a high temperature gradient in the depth and thus a high prestress. Because when using conventional heating methods (electrical, gas), both heating and cooling are carried out exclusively via the Glass surface takes place, an independent setting of the cooling rate and temperature gradient in the glass depth was not possible in the prior art.

The object of the invention is to provide a method and a device with which the temperature gradient into the glass depth for setting the prestress and the cooling rate can be set independently of one another.

According to the invention, this object is achieved in that in the method for tempering glasses, in particular drinking glasses, the heating is carried out by means of short-wave IR radiators, which, as disclosed in WO 00/56675, enable deep-effective heating of the entire glass volume while cooling by means of Air remains unchanged over the surface. Both the amount of air and the performance of the IR

Radiators are controlled in such a way that a predetermined temperature gradient is set from the surface into the depth of the glass to be tempered, irrespective of the cooling rate at which the glass is cooled to a temperature T ₃ , which is lower than T ₂ , by means of a predetermined cooling rate.

The infrared radiation is particularly preferably short-wave IR radiation with a color temperature greater than 1500 K, particularly preferably greater than 2000 K, very preferably greater than 2400 K, in particular greater than 2700 K, particularly preferably greater than 3000 K.

The cooling of the glass at a predetermined cooling rate is preferably carried out by blowing the glass to be cooled with compressed air or blown air. In a particularly advantageous embodiment, the heating system with IR radiators is tubular with a large number of IR radiators. In a tubular heating system of this type, for example, a drinking glass to be tempered, which comprises a goblet, can be introduced with the goblet standing upwards.

If the heated glass is cooled by means of compressed air or blown air, in a particularly advantageous embodiment the air can be blown into the cup of the drinking glass by means of a nozzle, which can have a plate at the nozzle outlet.

Advantageously, a nozzle with a plate can be moved to the cup of the drinking glass in such a way that the plate has closed the opening of the cup except for a gap of 1 mm between the rim of the mouth and the plate.

In this way it can be achieved that the flow velocity in the gap between the edge of the mouth and the plate is very high and a high cooling rate is achieved. This in turn results in high prestressing of the rim of the mouth, which leads to a much higher strength of the glass and can greatly reduce the risk of breakage.

In addition to the method, the invention also provides a device for tempering glasses, in particular drinking glasses. The device comprises a container into which the glass to be tempered is introduced, IR emitter and cooling device. According to the invention, the cooling device can be controlled individually, so that the glass can be cooled at a predetermined cooling rate. Irrespective of this, the IR emitters can be controlled in such a way that a predetermined temperature gradient is set in the glass depth independently of the cooling rate, since in contrast to gas burners, for example, the IR emitters allow the glass to be heated in depth. In an advantageous embodiment, the device is further characterized by a container, preferably a tubular container with a longitudinal dimension, for example a preferably water-rich quartz glass tube, into which the glass to be tempered is introduced. In such a device, a plurality of IR radiators can be arranged one after the other in the longitudinal direction around the container.

If the device according to the invention comprises a plurality of IR emitters, these can be designed to be individually controllable, in such a way that, in addition to the temperature gradient, a predetermined depth into the glass

Temperature gradient can be set in the longitudinal direction.

The vertical gradient of the temperature distribution can be influenced not only by manipulation of the heater control, but also by the arrangement of the heater.

It is particularly preferred if the container, which is tubular, consists of two half-shells, which can be pulled apart to open the tubular container, so that the tubular container is easily upright

Drinking glass can be loaded.

The half-shells preferably comprise bores for the passage of the circularly curved IR radiators, which are referred to as so-called omega radiators. The half-shells themselves, which form the container, are preferably on a quartz ring and are closed by a quartz ring.

The cooling means for introducing the air to cool the heated glass in the container with a predetermined one

Cooling rate, include at least one pipe that is in front of the lower end preferably has a plate. This cooling device can be moved into the oven in such a way that the plate is only slightly above the edge of the mouth of the hollow glass. If compressed air is fed into the hollow glass for cooling, cooling can be accelerated considerably at this narrow point. In order to prevent excessive heating of the cooling device by IR radiation acting on it, the cooling device is preferably provided with a coating, for example a gold coating. The method according to the invention is preferably used for prestressing the edge of the mouth of a drinking glass. The invention will be described below by way of example using the exemplary embodiments and the figures. Show it:

Fig. 1: The furnace geometry with the glass to be tempered

2: A detailed side view of a furnace construction according to FIG. 1

3: top view of a furnace construction according to FIG. 1

Fig. 4: The temperature distribution of one without surrounding

Quartz glass tube heated drinking glass Fig. 5: Calculated temperature distribution of a glass to be heated using a water-containing

Quartz glass tube in which the drinking glass to be heated is placed. Fig. 6: The temperature distribution of one without surrounding

Quartz glass tube of heated drinking glass.

The basic structure of the heating unit according to the invention with IR radiators is shown in FIG. The heating device is constructed as a tube furnace which is rotationally symmetrical about the axis A-A. The IR emitters are given the reference number 3. The IR emitter devices are as a circularly curved IR emitter, the short-wave IR radiation with a

Emit wavelength <2.7 μm and an intensity maximum at less than 1.93 m, in particular less than 1.4 μm. Short-wave IR radiation enables homogeneous heating of the glass according to the invention, since most of the radiation is transmitted through the glass and the absorbed energy per volume is almost the same at every point of the glass body. If a glass is cooled at a predetermined cooling rate, for example by air flowing over it on the surface, the glass cooled on the surface can be heated with the aid of the IR radiators inside. It is thus possible to set the cooling rate and temperature gradient in the glass depth, which in turn influences the prestress, independently of one another.

The IR emitters are halogen IR quartz tube emitters. The IR quartz tube emitters are circularly curved and are also referred to as so-called omega emitters. The wall material of the furnace 1 consists of quartzal. The maximum output per radiator is 5 kW per radiator in accordance with the heating furnace shown in exemplary embodiment 1.

The object 5 to be heated shown in the exemplary embodiments is a drinking glass with a goblet 7 and a stem with a base 9. A quartz glass tube 11 is additionally introduced into the furnace 1. The quartz glass tube

11 is optional and not mandatory. The quartz glass tube 11 absorbs part of the radiation and, as the following exemplary embodiments show on the basis of the simulation calculations, ensures a homogenization of a temperature gradient which can develop in the longitudinal direction of the furnace, that is to say along the axis of rotation A-A.

FIG. 1 also shows a special embodiment of a cooling device comprising a supply pipe 12 for the air, an air outlet 13 and a plate-shaped widening 15. The outer wall 20 of the furnace 1 is shown in more detail in FIG. The tube furnace 1 consists of two half-shells made of quartzal, one of which, namely the half-shell 20 shown in FIG. 2, has bores 22 for the passage of the tubes of the IR quartz radiator. FIG. 3 shows a top view of the furnace 1. The two half-shells 20.1 and

20.2, of which the half-shell 20.1 has an opening 22. The half-shells 20.1 and 20.2 stand on a quartz ring and are closed by a quartz ring. The furnace comprises two pneumatic moving devices, not shown in the figures. One of them is located above the oven for moving the cooling device. The cooling device as shown in Figure 1 consists of a tube 12 which has a plate 15 in front of the lower end 13. The plate 15 is about 2 cm from the lower end 13. This cooling device can be moved into the oven in such a way that the plate 15 is about 1 mm above the edge of the mouth 24 of the hollow glass 7. For cooling, compressed air or blower air is injected into the

Hollow glass guided, which accelerates the cooling considerably and is strongest at the narrowest point, which is located on the upper edge of the glass 24. The cooling device is preferably provided with a layer which prevents heating by the IR radiation acting on it. This can be done, for example, by gold-plating the cooling device.

The second pneumatic moving device is located at the lower end of the furnace and moves the quartzal base on which the glass to be cooled can be positioned. The quartz radiators 3 are preferably provided with radiator cooling. This can be done by perforating the gap 26 between the quartzal and the radiators

Base plate air is guided. If the cover plate is also perforated, the air can escape there again.

To prevent the gold coating on the upper cooler from evaporating, additional water cooling was provided on the upper cooler. Carrying out the compressed air through the lower bottom part also has the advantage that the cooling medium is guided to the bottom, the lower edge and on the sides of the glass. To achieve this, the holes in the base plate are usually arranged at an angle.

The invention will be described in more detail below using an exemplary embodiment. In a first embodiment of the invention, a drinking glass was introduced into an oven according to the invention, as shown in FIG. 1. In order to achieve acceptable lamp life, the lamps were only with a performance of almost 60% of their

Maximum power operated. The maximum power per radiator was 5 kW per radiator. With such a supply of heat, the cup rim 24 has already reached the maximum temperature of 423 ° C. after 10 seconds. Due to the temperature gradient, the minimum temperature at the base of the calyx at this point is only 117 ° C

Difference between maximum and minimum temperature within the glass after about 10 seconds is a little over 300 ° C. However, the resulting temperature inhomogeneity is not critical in the case of drinking glasses, since the state of tension in the bottom of the goblet, stem and base is generally not relevant for drinking glasses. Relaxation is not necessary at these points. On the contrary, since most of the load is due to the weight of the drinking glass in this area, a lower temperature and the associated higher dimensional stability are even advantageous here. The chalice wall including the upper edge 24 reach the highest temperatures and can thus be relaxed and subsequently biased. In the case of other products to be heated, however, the stress state in the base area of a glass to be heated can be quite relevant for the product quality. By cleverly arranging the radiator and introducing, for example, a water-containing quartz tube frame, a more homogeneous temperature gradient and thus more homogeneous heating can be achieved. The following model calculations show this.

The geometric dimensions of the model are summarized in Table 1. Table 2 contains a compilation of the material data. Table 3 again lists the radiation-relevant parameters. Finally, Table 4 explains the meaning of the symbols.

Table 1: Model dimensions

Table 2: Material data and equations

Table 3: Parameters relevant to radiation

Table 4: Meaning of the symbols

Symbol meaning

^C P specific heat capacity α absorption coefficient e emission coefficient

K thermal conductivity

Q density λ wavelength μ viscosity

In a first model calculation, the heating up of a drinking glass was calculated for a period of 10 seconds. Figure 4 shows the temperature distribution after a heating time of 10 s, which is between 117 ° C and 423 ° C, the minimum and maximum temperature in the drinking glass. The is in the white areas 100 in the area

Temperature above this interval. This area extends from the area between the spotlights and drinking glass to behind the spotlights. This hot area is particularly close to the lower radiators. If the bottom heater is switched on, its quartz glass tube will be the hottest of all heater tubes.

The temperature maximum 110 in the drinking glass at the upper edge of the goblet 24 can be clearly seen. The temperature level in the goblet wall is approx. 100 ° C below the temperature at the edge of the goblet. In the area of the calyx, stem and foot, the temperature level is another 200 ° C lower. The result of this low temperature is that the area of the stem / chalice bottom is not particularly well reached by either radiation or convection.

In order to reduce the temperature inhomogeneity, the drinking glass was placed in a water-containing quartz glass tube in a calculation shown in FIG posed. The material of the quartz glass tube also absorbs part of the radiation. In the present case, the calculation was only calculated up to a heating-up time of 2.75 s. Figure 5 shows the resulting temperature distribution after a heating time of 2J5 s. In the present calculation, the lower radiator was assumed to be switched off. For comparison, the temperature distribution for the case without water-containing quartz glass tube and a heating-up time of 2.04 s is shown in FIG. It can be clearly seen that after this heating-up time, a temperature level comparable to that in FIG. 5 has been reached. In table 5, the minimum and maximum temperature reached and their respective differences are compared for the case of heating with and without quartz glass tube. A reduction in the temperature inhomogeneity can be seen by adding the water-containing quartz glass tube by about 22%.

Table 5:

The exemplary embodiments show that the temperature gradient in the longitudinal direction of the tubular furnace heated with IR radiators can be set by deliberately switching off radiators, here, for example, the lowest radiator, or by introducing absorbent means, such as water-containing quartz glass. In this respect, vertical temperature gradients can be set in a targeted manner with the help of the tubular device, and thus areas that are specifically toughened in the glass and those that do not. Furthermore, it is possible for the first time that a temperature gradient in the depth of the glass and thus the prestress on the surface is set independently of the cooling rate of the glass. This is made possible by the fact that by means of the short-wave IR radiation of the IR radiators used in the heating system, homogeneous heating in the glass depth is possible, while cooling by blown-in air takes place exclusively via the glass surface.

Claims

claims

1. A method for tempering glasses, in particular drinking glasses, with a heating system comprising IR radiators and a cooling device, with the following steps:

1.1 the glass to be tempered is quickly heated from a starting temperature T. to a holding temperature T ₂ using the heating system with IR radiators;

1.2 the IR radiator and the cooling device are controlled such that a predetermined temperature gradient from the surface into the

Depth of the glass to be tempered is set;

1.3 the glasses are cooled to a temperature T ₃ , which is lower than T ₂ , by means of a predetermined cooling rate, regardless of the temperature gradient set, into the depth of the glass.

2. The method according to claim 1, characterized in that the infrared radiation of the IR emitter short-wave IR radiation with a color temperature greater than 1500 K, particularly preferably greater than 2000 K, very preferably greater than 2400 K, in particular greater than 2700 K. , is particularly preferably greater than 3000 K.

3. The method according to claim 1 or 2, characterized in that the IR radiators are controlled such that in addition to the temperature gradient in the depth of

Glases also gives a lateral temperature gradient.

4. The method according to any one of claims 1 to 3, characterized in that the cooling takes place by means of compressed air or blower air.

5. The method according to any one of claims 1 to 4, characterized in that the heating system is tubular with IR radiators.

6. The method according to claim 5, characterized in that the drinking glass to be tempered comprises a goblet and is placed with the goblet standing upwards in the tubular heating system.

7. The method according to claim 6, characterized in that the cooling according to step 1.3 is carried out by means of compressed air or blown air.

8. The method according to claim 7, characterized in that the air through a nozzle with a plate in the cup of

Drinking glass is blown.

9. The method according to claim 8, characterized in that the nozzle is approached to the cup of the drinking glass that the plate has closed the opening of the cup to a gap of 1 mm or less between the rim of the mouth of the drinking glass and the plate.

10. Device for tempering glasses, especially drinking glasses with

10.1 a container into which the glass to be tempered is placed

10.2 IR emitters

10.3 a cooling device, characterized in that 10.4 the cooling device and the IR radiators can be controlled individually, so that the glass is cooled at a predetermined cooling rate and a predetermined temperature gradient in the glass depth can be set independently of the cooling rate.

11. The device according to claim 10, characterized in that the infrared radiation of the IR emitter short-wave IR radiation with a color temperature greater than 1500 K, particularly preferably greater than 2000 K, very preferably greater than 2400 K, in particular greater than 2700 K. , particularly preferably greater than 3000 K.

12. The apparatus according to claim 10 or 11, characterized in that the container has a longitudinal extent and a plurality of IR radiators arranged one after the other in the longitudinal direction.

13. The apparatus according to claim 12, characterized in that the arranged in the longitudinal direction successively arranged IR emitters can be individually controlled such that a predetermined temperature gradient is adjustable in the longitudinal direction of the container.

14. Device according to one of claims 10 to 13, characterized in that the container is tubular.

15. The apparatus according to claim 14, characterized in that the tubular container comprises two half-shells.

16. The apparatus according to claim 15, characterized in that a half-shell contains holes for the implementation of the IR radiator

17. The device according to one of claims 15 - 16, characterized in that the half-shells stand on quartz rings.

18. Device according to one of claims 15 - 17, characterized in that the half-shells are closed by a quartz ring.

19. Device according to one of claims 10-18, characterized in that the cooling devices comprise at least one tube.

20. Device according to one of claims 10 - 19, characterized in that the cooling devices with a coating for reflecting IR

Radiation are provided.

21. Use of a method according to one of claims 1-9 or a device according to one of claims 10-20 for prestressing a rim of the mouth of a drinking glass.