Field of the invention

The present invention relates to a method for tempering materia! by directing one or more forced tempering gas blasts towards a surface of a hot material for rapidly cooling the hot material and more particularly to method as defined in the preamble of independent claim 1. The present invention further relates to an apparatus for tempering material, the apparatus comprising one or more tempering gas nozzles arranged to direct forced tempering gas blasts towards a surface of a hot material for rapidly cooling the hot material, and more particularly to an apparatus as defined in the preamble of independent claim 9. Further, the present invention relates to the use of a porous element for enhancing cooling of a hot materia! as defined in independent claim 16.

Background of the invention

According to prior art, metal such as steel, glass and other materials are tempered by air or gas cooling. In air tempering a strong flow of air is directed to the material to be tempered or to a surface of a product. The strong flow of air is used with the aim of lowering the temperature of the materia! rapidly, the structure and/or properties of the materia! undergoing changes that provide the material with desired characteristics. Steel tempering, for example, is

understood to mean heating the steel above the temperature of austenite formation and cooling it, after a holding period required for the austenite formation and homogenization, at a rate faster that the critical cooling rate. The aim with the tempering is a specific, predetermined martens!te content in the microstructure of the tempered piece. Glass tempering, in turn, aims at using rapid cooling to produce a compression tension in the surface layer of the glass and a tensile stress into the inner part of the glass.

A problem with the above prior art solution based on air coo!ing is that air cooling in connection with tempering requires an extremely large amount of air and an efficient blow thereof towards the surface of the materia! or product to be tempered. Such a large amount of air and efficient blow consume extremely high amounts of energy. Moreover, in many applications management of rapid and uniform cooling is difficult to control and carry out, particularly when thin pieces, such as thin glass, are being tempered. Hence air cooling and the control thereof for producing an even cooling requires complex hardware solutions.

In a PCT application publication WO2011/004061 , the idea of using atomized droplets to enhance tempering so that at least some of the droplets collide with the surface of the material under tempering is introduced. This publication is silent on the details of the atomization in the context of tempering.

PCT application publication W095/35471 discloses a portable evaporative cooling unit to be used by persons e.g. in sports events. The publication is silent on tempering (or other such extreme cooling effects). In said publication, one way of atomising a coolant is to pass air through a wetted membrane, specifically through the pores or fibrous mesh of the membrane. Such an approach is not feasible in the context of tempering where volumetric flows of the tempering gasses in one tempering unit (measured at the intake of the unit) can be very high, from 10m ³ /minute to 2000m ³ /minute, for example over 50m ³ /minute, over 100m ³ /minute, over 250m ³ /minute, over 500m ³ /minute or even over 1000m ³ /minute. Clearly, such high gas flows dry a flow-through membrane very quickly without a dedicated, powerful wetting arrangement (also making homogeneous wetting very difficult), or worse still, shred the membrane to pieces. These issues are not addressed in said publication in any way.

Clearly, there is a need for a novel solution for combining tempering gas flows with liquid atomization enhancing the tempering power.

Brief disclosure of the invention

An object of the present invention is to provide a method and an apparatus so as to solve the prior art problems. The object of the invention is achieved by a method according to the characterizing part of claim 1 , characterized in that the method comprises adding liquid droplets by means of a porous element into at least one of the tempering gas blasts for enhancing the cooling of the hot material. The object of the invention is further achieved by the apparatus according to the characterising part of claim 9, the apparatus being

characterized in that the apparatus comprises one or more atomization arrangements comprising a porous element for atomizing at least one liquid raw material into liquid droplets and adding the formed liquid droplets into at least one of the tempering gas blasts for enhancing the cooling of the hot material. Further, the object of the invention is achieved by the use of a porous element for enhancing cooling of a hot material according to claim 16. The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea of cooling a material or product in tempering by using at least one tempering gas or air blast directed towards and against the material to be tempered. According to the present invention liquid droplets are further added to the tempering gas blasts for intensifying and homogenizing the cooling of the material to be tempered. The tempering gas blasts convey the liquid droplets towards the surface of the hot material such that the liquid droplets receive thermal energy from the hot material. In an embodiment of the present invention, the liquid droplets are formed and directed towards the surface of the hot material in such a manner that the liquid droplets evaporate before colliding with the surface of the hot material as they receive thermal energy from hot material. This means that the individual droplets evaporate substantially separately from each other. Alternatively, in another embodiment, at least some of the droplets hit the surface of the hot material. In an embodiment of the present invention the tempering gas flow or blast is used for atomizing at least one liquid raw material into liquid droplets and conveying the droplets towards the surface of the hot material. The liquid raw material may be atomized into liquid droplets having average diameter smaller than equal to 30 pm, or preferably smaller than equal to 10 pm, or more preferably smaller than equal to 5 pm. An advantage of the method and apparatus of the invention is that the use of small liquid droplets together with the tempering gas for cooling a hot material in a tempering process enables an energy efficient means for tempering a hot material as the amount of tempering gas may be reduced to achieve the desired cooling efficiency. The small droplets allow a rapid and efficient heat transfer from a hot piece to be achieved. The flux liquid droplets may be controlled such that a uniform concentration of liquid droplets may be provided to the surface of the hot material. Uniform and rapid heat transfer is particularly important when large surfaces and thin products, such as thin glass are tempered. Air or gas based tempering boosted with liquid droplets consumes significantly less energy than prior art air cooling. Said small droplets are readily formed by letting the tempering gas interact with the surface of a wetted porous material.

Brief disclosure of the figures

In the following the invention will be disclosed in greater detail in connection with preferred embodiments, with reference to the enclosed drawings, in which:

Figure 1 is a schematic view of a prior art apparatus for air or gas based tempering;

Figure 2 is a schematic and detailed view of one embodiment of the present invention for adding liquid droplets to the tempering gas;

Figure 3 is a schematic and detailed view of another embodiment of the present invention for adding liquid droplets to the tempering gas;

Figure 4 is a schematic view of one embodiment of a tempering apparatus according to the present invention;

Figure 5 is a schematic view of another embodiment of a tempering apparatus according to the present invention; and

Figure 6 is a schematic view of yet another embodiment of a tempering apparatus according to the present invention.

Detailed disclosure of the invention

Reference is made to Figure 1 , which discloses a conventional apparatus for tempering material by directing one or more air or gas blasts towards and against a surface 4 of a hot material 2. The tempering gas cools the hot material 2 convectively. The apparatus is used for tempering a moving hot material web 2 moved with transport rollers 8 supporting the material web 2 from below. The material 2 to be tempered may be for example metal, such as steel, glass, metal alloy or a ceramic material. Although Figure 1 shows the tempering of a moving material web 2, the method and apparatus of the present invention may also be applied to tempering of any material or product movable in any way. Alternatively, the material or product to be tempered may also be stationary and the apparatus may be moved. In accordance with the invention the apparatus comprises a tempering gas supply 10 having one or more tempering gas nozzles 12. The apparatus may comprise one or more tempering gas nozzles 12 successively in the moving direction A of the hot material 2. Furthermore the apparatus may comprise one or more tempering gas nozzles 12 adjacent to each other in the width direction of the hot material. In a preferred embodiment the tempering gas nozzles 12 are separate holes or openings, but in another embodiment the tempering gas nozzles 12 may also be longitudinal slit, preferably extending perpendicularly to the moving direction A of the hot material 2. Tempering gas is supplied through the tempering gas nozzles 12 towards a surface 4 of the material 2. In figure 1 the apparatus comprises a tempering gas supply only on the upper side of the material, but it should be noted that normally the apparatus for tempering material comprises a tempering gas supply on both the upper and lower side of the material, as shown in figure 6. The tempering gas is typically air, but in some case it may also be some other gas, such as nitrogen. In figure 1 the tempering gas blasts are directed perpendicularly towards the material 2, as shown with arrows B. In preferable embodiments the tempering gas blasts are directed at an angle towards the hot material 2. The apparatus further comprises false rolls 15 the purpose of which is to increase pressure on the top of the material for preventing the material from floating. The tempering gas blasts flowing back from the surface 4 of the hot material 2 conveys heat away from the hot material 2. In the present invention the tempering of the material is carried out with tempering gas blasts directed towards the surface 4, 6 of the hot material 2 for rapidly cooling the hot material 2. In the present invention liquid droplets 14 are further added into at least one of the tempering gas blasts for enhancing and boosting the cooling of the hot material 2. In this embodiment, the liquid droplets 14 are formed and guided towards the surface 4, 8 of the hot material 2 in such a way that the liquid droplets 14 evaporate before colliding with the surface 4, 6 of the hot material 2 as they receive thermal energy from hot material 2, The liquid droplets 14 may be guided towards the hot material 2 with the tempering gas blasts. The formed liquid droplets have to be further small enough such that they evaporate before colliding to the surface 4, 8 of the hot material 2. The liquid droplets 14 are formed preferably in the tempering apparatus with an atomizing arrangement. The liquid droplets 14 are added into at least one of the tempering gas blasts. The liquid raw material may be atomized into liquid droplets 14 having average diameter smaller than equal to 30 μιη, or preferably smaller than equal to 10 pm, or more preferably smaller than equal to 5 pm.

Figure 2 shows a detailed view of one embodiment on the present invention. The tempering apparatus comprises an atomizing arrangement having at least one at least one liquid nozzle 13 for supplying the at least one liquid raw material. The liquid nozzle 13 is arranged such that the tempering gas blasts atomizes the at feast one liquid raw material supplied by the liquid nozzle 13 info liquid droplets 14. This is achieved by arranging the liquid nozzle 13 in connection with a tempering gas nozzle 12 for atomizing the at least one liquid raw material into liquid droplets 14 using the tempering gas and adding the formed liquid droplets 14 info at least one of the tempering gas blasts. As shown in figure 2, the liquid nozzle 13 is arranged to a tempering gas nozzle 12. The liquid nozzle 13 is connected to liquid raw material source (not shown) via conduit 16. The conduit 16 or the liquid nozzle 13 may be provided with a flow meter or flow controller for controlling and adjusting flow of the liquid raw- material to the liquid nozzle 13. Accordingly the tempering gas nozzle 12 and the liquid nozzle 13 form together a two fluid atomizer in which the gas blast is used as atomizing gas. The liquid nozzle 13 supplies liquid raw material through the nozzle head 17 of the liquid nozzle 13. The liquid nozzle 13 is positioned inside the tempering gas nozzle 12 such that the tempering gas blast flowing in direction of arrows 8 flows around and surrounds the liquid nozzle 13 and atomizes the liquid raw materia! discharging from the nozzle head 17 into liquid droplets. The tempering gas blasts further conveys the formed liquid droplets 14 towards the surface 4, 6 of the hot material. The liquid droplets receive thermal energy from the hot material 2 as they move closer to it The liquid droplets 14 further evaporate before they collide with the surface 4, 8 of the hot materia! 2. According to the above mentioned the tempering gas is used for atomizing liquid raw materia! into liquid droplets 14 and adding the liquid droplets 14 to the tempering gas blasts in a process of tempering material 2 by directing one or more forced tempering gas blasts towards a surface 4, 8 of a hot material 2 for rapidly cooling the hot material 2. The liquid raw material to be used in tempering is preferably water, although it may also be an alcohol, such as a mixture of ethanoi, water and alcohol, or some other liquid mixture or emulsion comprising wafer and/or alcohol. Alternatively, it is also possible to use some other liquid suitable for cooling or tempering or a mixture of one or more liquids. Figure 3 shows another embodiment of the atomizing arrangement for atomizing liquid raw materia! into liquid droplets 14 and adding the liquid droplets to the tempering gas blasts. The atomizing arrangement of figure 3 comprises a two fluid atomizer or a two fluid atomization nozzle having a liquid nozzle 13 and an atomizing gas conduit 22 via which separate atomization gas is supplied from a atomization gas source (not shown) to the nozzle head 17. Thus, in the embodiment of figure 3 separate atomization gas is used for atomizing the at ieast one liquid raw material into liquid droplets 14 and adding the formed liquid droplets 14 into at least one of the tempering gas blasts. The nozzle head 7 is positioned flush with the tempering gas nozzle 12 in figure 2 and in figure 3 the nozzle head 17 extends out of the tempering gas nozzle 12, In an alternative embodiment the nozzle head 17 may also be positioned inside the tempering gas nozzle 12 and a predetermined distance from the nozzle head of the tempering gas nozzle 12. According to the above mentioned the two fluid atomizer or the liquid nozzle 13 may be positioned to the tempering gas nozzle 12 in a manner suitable for different applications.

In figure 3 it is shown a simple construction for a two fiuid atomizer. However, the two fluid atomizer may also be constructed in many alternative ways for forming the liquid droplets 14, and especially for forming liquid droplets 14 having an average diameter small enough as discussed above. In one embodiment the two fluid atomizer of figure 2 may be provided with a

distributing chamber extending from the nozzle head 17. The distributing chamber is further provided with flow impediments which alter the

hydrodynamic properties of the aerosol flow discharging from the nozzie head 17. The flow impediments unexpectedly cause the droplet size of the aerosol to change into ultra-small droplets as the hydrodynamic properties change. The mechanism is based on both collision energy and pressure change caused by the flow impediments. In other words, the flow impediments 36 are arranged in such a manner that the droplets of the aerosol discharging from the nozzle head 17 collide into one or more flow impediments and/or each other to reduce the droplet size of the aerosol. In addition or alternatively, the flow impediments are arranged in such a manner that they generate into the aerosol flow discharging from the spray head a pressure change and/or restriction to reduce the droplet size of the aerosol such that the average diameter of the liquid droplets 14 becomes 10 micrometers or less, preferably 3 micrometers or less, and more preferably 1 micrometer or less.

In a yet alternative embodiment two atomizers or nozzles 13 may be directed substantially at each other such that the nozzles 13 are arranged directly toward each other. In other words, the nozzles 13 are preferably arranged essentially coaxially opposite each other in such a manner that their liquid droplets 14 discharging from the nozzles 13 collide essentially directly with each other. The aiomization arrangement may comprise two or more nozzles 13. Preferably, the nozzles 13 are arranged in pairs to form one or more nozzle pairs in such a manner that the nozzles 13 of each nozzie pair are directed essentially directly, preferably coaxially, toward each other, whereby the droplets 14 of each nozzie pair collide directly with each other. The average size of the droplets is further decreased as the droplets 14 of one nozzle 13 collide with droplets 14 of an opposite nozzle 13. The afomization arrangement may also comprise means for directing a gas flow from at least one direction to the collision point of the droplets 14. This is preferably done by furnishing the atomizaiion arrangement with a gas nozzle for supplying gas from at least one direction to the collision point of the droplets. Thus, by means of the gas flow, it is possible to move or transfer the droplets generated at the collision point into a required direction toward the surface 4, 6 of the hot material 2. Any gas may be used in the atomizer as atomization gas or in the gas nozzle. In other words, it may be an inert gas, such as nitrogen, or a gas that reacts with the droplets 14. In one embodiment the gas nozzle may be arranged in such a manner that the gas flow flows and collides substantially perpendicularly in relation to the droplet 14 discharging from the nozzles 13. In another embodiment the liquid droplets 14 may be formed at a distance from the tempering gas nozzle 12 and the formed droplets 14 may be conveyed and added to the tempering gas blasts. Thus, the liquid droplets 14 may be formed with a two fluid atomizer or by ultra sound atomizer.

Figure 4 shows an alternative embodiment of an atomization arrangement according to the present invention in which porous elements (elements comprising one or more porous materials) 24 are used for forming liquid droplets 14 from the liquid raw material. The porous element 24 is provided with a liquid supply connection 26 for supplying the at least one liquid raw material to a porous element 24 such that the surface or surfaces of the porous element 24 become wetted.

As shown in figure 4, the liquid supply connection 26 can provide the liquid raw material inside of the porous element 24 so that the liquid seeps through the porous element towards its surface or surfaces, but alternatively (not shown) some surface of the porous element 24 can also be used to receive the liquid raw material through the liquid supply connection 26, wetting the porous element at least partially through absorption. In figure 4, the liquid supply connection supplies pressurized liquid raw material into the porous element such that the liquid raw material flows through the pores of the porous element 24 and to the surface of the porous element 24. The porous element 24 is further arranged to be subjected to at least one of the tempering gas blasts for removing liquid raw material from the surface of the porous element 24 with the one or more of the tempering gas blasts to form liquid droplets 14 and to atomize the liquid raw material into liquid droplets 14. In figure 4 the porous elements 24 are arranged in connection with the tempering gas nozzles 12 such that the tempering gas flows through the porous element 24 via one or more tempering gas conduits (also called flow channels) 11 before discharging from the tempering gas nozzle 12. The tempering gas removes or rips liquid raw material from the surface of the flow channel 11 arranged into the porous element and atomizes the liquid raw material into liquid droplets 14. The tempering gas does not substantially flow inside the bulk of the porous material of the porous element, but instead e.g. in the flow channels or gas conduits arranged therein, or by the outer surface of the porous element. In other words, the tempering gas flow takes place substantially external to the bulk of the porous material of the porous element. Naturally, tempering gas can flow in the flow channels arranged into the porous element or in flow channels in contact with the porous element.

The porous element together with the tempering gas, through the ripping or removing interaction between the liquid on the porous element's surface (or on the surface of the flow channels arranged into the porous element) and the tempering gas, provides a uniform and homogenized liquid droplet flux towards the hot material 2. The porous element may be a sintered metal element, porous ceramic, glass fibre mesh or the like. The flow speed of the tempering gas blast is high enough for atomizing the liquid raw material into small liquid droplets 14. The flow speed of the tempering gas blast may be 50-250 m/s.

Figure 5 shows an alternative embodiment in which the porous element 24 is arranged in connection in connection with a false roll 15 configured to produce pressure on the top of the material 2. In this embodiment the liquid droplets 14 are formed in similar manner as in the embodiment of figure 4. The tempering gas blasts first flow in direction of arrow B towards the surface 4, 6 of the hot material 2 and then change direction at the surface of the hot material into direction of arrows C. Then the tempering gas blasts are influenced by the false rolls 15. The tempering gas blasts thus remove liquid raw material from the surface of the porous element 24 arranged to the false rolls 15 and atomize the liquid raw material into the liquid droplets 14 which may flow or descend towards the surface 4, 6 of the hot material 2.

Figure 6 shows yet another embodiment in which the tempering apparatus comprises transport rolls 8 or cooling rolls 9. The rolls 8, 9 may be perforated rolls or the like and provided with porous element 24 or porous material. Thus the porous element 24 is arranged in connection with a roll 8, 9 positioned against the hot material 2. The tempering gas blasts flow against or along the rolls 8, 9 such that liquid raw material is removed or ripped from the outer surface of the porous element 24 and the liquid raw material is atomized into small liquid droplets 14 by the tempering gas blasts. Figure 6 shows the tempering apparatus in which the both sides 4, 6 of the hot material 2 are cooled simultaneously. It should be noted that all of the embodiments of the present invention may be configured for both sides of the hot material 2.

The present invention the atomization arrangement can be configured to form and guide the liquid droplets 14 towards the surface 4, 6 of the hot materia] 2 in such a way that the liquid droplets 14 evaporate before colliding with the surface 4, 6 of the hot material 2 as they receive thermal energy from hot material 2 and thus rapidly cooling the hot material. Alternatively, the at least some or all of the liquid droplets 14 hit the surface 4, 6 of the hot material 2 causing even more efficient cooling, but with the increased risk of breaking the surface 2 due to stress forces caused by the very efficient cooling.

In one embodiment, liquid droplets 14 are added into at least one of the tempering gas blasts such that the number concentration of the liquid droplets 14 with a mean diameter of 5 micrometers in the tempering gas blasts is 10 ⁶ 1/cm ³ or approximately 10 ⁶ 1/cm ³ , preferably 10 ⁷ 1/cm ³ or approximately 10 ⁷ 1/cm ³ , and more preferably 10 ⁸ 1/cm ³ or approximately 10 ⁸ 1/cm ³ . The coagulation rate for such droplet concentrations is reasonable low so that most of the droplets stay uncoagulated and the cooling effect is reasonably high compared to the forced convective cooling created by the gas flow alone. The time for the average droplet diameter to double due to coagulation is 140 s for initial droplet concentration of 10 ⁸ 1/cm ³ and four hours for initial droplet concentration of 10 ⁶ 1/cm ³ , showing that the droplets stay essentially

completely uncoagulated in the tempering process. The evaporative cooling power due to the droplet evaporation is roughly 10% from the forced convective cooling power with a heat transfer coefficient of 300 W/m ² K, when the concentration of the 5 μίη droplets is 10 ⁶ 1/cm ³ . The evaporative cooling power due to the droplet evaporation is roughly 100% from the forced convective cooling power when the concentration of the 5 μηι droplets is 10 ⁷ 1/cm ³ . The evaporative cooling power due to the droplet evaporation is roughly 1000% from the forced convective cooling power when the concentration of the 5 μιτι droplets is 10 ⁸ 1/cm ³ . Thus, the range of 10 ⁶ 1/cm ³ - 10 ⁸ 1/cm ³ is advantageous for the number concentration of the liquid droplets.

The material 2 may be heated before the tempering process or alternatively the material 2 may come from another process step in which it is processed or formed at an elevated temperature. The heating of the material 2 to be tempered may take place in process step which may consist of heating, working or a similar process step. In a preferred embodiment the tempering apparatus of the invention is connected to a manufacturing or processing line of a material or product, such as a flat glass manufacturing line, the manufacturing line of some other glass product, the manufacturing line of steel or to the manufacturing or processing line of some other product or material. In the manufacturing line of flat glass the tempering apparatus may be placed after the tin bath in the float line, for example, the temperature of the glass strip rising from the bath being 650°C at the most. The temperature of the hot material arriving at the tempering may be from 450°C to 850°C, for example. However, the temperature depends on the material to be tempered and the desired tempering properties.

It is apparent to a person skilled in the art that as technology advances, the basic idea of the invention may be implemented in many different manners. The invention and its embodiments are, thus, not limited to the examples described above, but may vary within the scope of the claims.