Patent Publication Number: US-2013233847-A1

Title: High frequency heating apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Korean Patent Application Number 10-2012-0022639 filed on Mar. 6, 2012, the entire contents of which application are incorporated herein for all purposes by this reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high frequency heating apparatus, and more particularly, to a high frequency heating apparatus which heats a substrate by applying high frequency waves. 
     2. Description of Related Art 
     The use of glass materials in a variety of industrial fields, specifically, as a cover for a photovoltaic cell, a flat display such as a thin-film transistor liquid crystal display (TFT-LCD), a plasma display panel (PDP) or an organic electroluminescent (EL) device, a variety of mobile electronic devices, and the like, is rapidly increasing. Accordingly, glass materials are required to have lightweight and a thin profile. 
     However, the trend in glass materials towards a light and thin profile leads to a problem of fragility due to its characteristic of high brittleness. Accordingly, a variety of tempering methods is being studied in order to improve the durability of glass. 
     Glass tempering technologies of the related art include chemical strengthening technology that uses an ion exchange between the glass surface and a water solution (molten salt) and thermal strengthening technology that includes heat treatment on glass. 
     The chemical strengthening technology has the drawbacks of poor usability regarding process time necessary for the ion exchange between the glass surface and a water solution, the size of the glass, recycling of the water solution (contamination and concentration control), and the like. 
     In contrast, the thermal strengthening technology is to strengthen glass by increasing the temperature of a plate glass and quenching it while moving the plate glass in a hot horizontal furnace. A variety of methods for applying this technology in the industry are underway since heating using high frequency waves has advantages in that the heat treatment effects are enhanced due to volume heating and rapid heating is enabled. 
     At present, high frequency heating technology applied in mass production facilities is generally used in a low temperature range (about 200° C.) because of the problem of uniform heating or the like. 
     In addition, in the case of heat-treating a plate glass having a large size by applying the high frequency technology of the related art, the use of a single high frequency generator is disadvantageous in that control over electric field distribution inside a chamber is difficult and the temperature growth rate is low. Although the use of a plurality of high frequency generators increases the temperature growth rate to a certain degree, concentration in electric fields due to interference between the high frequency generators leads to localized heating in the glass and the decreased heating efficiency, which is problematic. 
       FIG. 1A  and  FIG. 1B  are pictures of electric field distribution analysis and temperature distribution analysis that are measured after heating a piece of glass using a single high frequency generator in a method of the related art. As shown in  FIG. 1A  and  FIG. 1B , it can be appreciated that, when the glass is heated using a single high frequency generator  10 , nonuniform electric field distribution occurs in the glass, thereby forming a hot spot area  20 . 
       FIG. 2A  and  FIG. 2B  are pictures of electric field distribution analysis and temperature distribution analysis that are measured after heating a piece of glass using a plurality of high frequency generators in a method of the related art. In  FIG. 2A , the apricot area represents the portion where no electric field is formed. In  FIG. 2B , the blue area represents a low temperature, and the red area represents a high temperature. It can be appreciated that the corner areas of the heat-treated plate glass are not heated since no electric fields are formed in these areas. In addition, hot spots are formed in localized areas of the plate glass due to the interference of the electric fields. 
     The information disclosed in the Background of the Invention section is only for the enhancement of understanding of the background of the invention, and should not be taken as an acknowledgment or any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art. 
     BRIEF SUMMARY OF THE INVENTION 
     Various aspects of the present invention provide a high frequency heating apparatus which can prevent a substrate being heated locally and high frequency waves generated by a plurality of rows of high frequency generators from interfering with each other. 
     In an aspect of the present invention, provided is a high frequency heating apparatus including a high frequency generator which generates high frequency to heat a substrate and a reflector which reflects the high frequency generated by the high frequency generator toward the substrate. 
     In an exemplary embodiment, the high frequency generator may be a plurality of high frequency generators, and the reflector may partition the plurality of high frequency generators into groups each including at least one high frequency generator of the plurality of high frequency generators. 
     The reflector may include a first reflecting portion which forms a partition between high frequency generators of the plurality of high frequency generators which are spaced apart from each other. 
     The reflector may include a second reflecting portion which is disposed on a left side and/or a right side of the high frequency generator. 
     The reflector may include a third reflecting portion which is disposed above and/or below the substrate, the main plane of the third reflecting portion facing the main plane of the substrate. 
     The reflector may have a plurality of holes. 
     According to embodiments of the present invention, since the reflector reflects high frequency waves, uniform electric fields are formed over the entire area of the substrate, and the entire area of the substrate can be uniformly heated. 
     In addition, in the high frequency heating apparatus having a plurality of high frequency generators, it is possible to prevent high frequency waves generated by the individual high frequency generators from interfering with each other, thereby preventing electric fields from being concentrated and the substrate from being heated locally. 
     Furthermore, it is possible to increase the temperature growth rate of the substrate and improve the energy efficiency of the high frequency heating apparatus. 
     The methods and apparatuses of the present invention have other features and advantages which will be apparent from, or are set forth in greater detail in the accompanying drawings, which are incorporated herein, and in the following Detailed Description of the Invention, which together serve to explain certain principles of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  and  FIG. 1B  are pictures of electric field distribution analysis and temperature distribution analysis that are measured after heating a piece of glass using a single high frequency generator in a method of the related art; 
         FIG. 2A  and  FIG. 2B  are pictures of electric field distribution analysis and temperature distribution analysis that are measured after heating a piece of glass using a plurality of high frequency generators in a method of the related art; 
         FIG. 3  is a schematic top plan view showing a high frequency heating apparatus according to an embodiment of the present invention; 
         FIG. 4A  and  FIG. 4B  are a schematic top plan view and a side elevation view showing a high frequency heating apparatus according to another embodiment of the present invention; 
         FIG. 5  is a schematic top plan view showing a high frequency heating apparatus according to a further embodiment of the present invention; 
         FIG. 6  is a schematic configuration view of a reflector according to an embodiment of the present invention; 
         FIG. 7A  and  FIG. 8E  are pictures of electric field distribution analysis and temperature distribution analysis that are measured after heating a piece of glass using a high frequency heating apparatus according to an embodiment of the present invention; 
         FIG. 8A  and  FIG. 8B  are pictures of electric field distribution analysis and temperature distribution analysis that are measured after heating a piece of glass using a high frequency heating apparatus according to another embodiment of the present invention; 
         FIG. 9  is a graph showing the temperature growth rate of a substrate which is heated using a high frequency heating apparatus according to another embodiment of the present invention; 
         FIG. 10  is a graph showing surface temperatures of a plate glass that are measured after the plate glass is carried to a high frequency heating apparatus according to a further embodiment of the present invention; and 
         FIG. 11  is a side elevation view showing a high frequency heating apparatus according to a further embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to a high frequency heating apparatus according to the present invention of the present invention, embodiments of which are illustrated in the accompanying drawings and described below, so that a person having ordinary skill in the art to which the present invention relates can easily put the present invention into practice. 
     Throughout this document, reference should be made to the drawings, in which the same reference numerals and signs are used throughout the different drawings to designate the same or similar components. In the following description of the present invention, detailed descriptions of known functions and components incorporated herein will be omitted when they may make the subject matter of the present invention unclear. 
     In addition, in the following description, a direction from the front to the rear is defined as a direction in which a substrate is carried, and a direction from left to right is defined as a direction that intersects the direction in which the substrate is carried. 
       FIG. 3  is a schematic top plan view showing a high frequency heating apparatus according to an embodiment of the present invention. 
     Referring to  FIG. 3 , the high frequency heating apparatus according to this embodiment includes a high frequency generator  200  and a reflector  300 . 
     The high frequency generator  200  generates high frequency waves to heat a substrate  100  by vibrating ions inside the substrate  100  using the high frequency waves. The high frequency generator  200  can generate high frequency waves ranging from 0.98 GHz to 6.0 GHz, preferably, from 2.4 GHz to 5.8 GHz. 
     The substrate  100  is a substrate that is heated by the high frequency generator  200 , and can be implemented as a plate glass that has a variety of thicknesses. 
     The reflector  300  reflects high frequency waves generated by the high frequency generator toward the substrate  100 . 
     The reflector  300  can be made of a conductive metal that can reflect high frequency waves. 
     The reflector  300  can be disposed such that it surrounds the high frequency generator  200  from the front and rear and from left and ride sides, or be disposed at corresponding positions above and below the substrate  100 . When the reflector is disposed in this fashion, it is possible to more efficiently reflect high frequency waves generated by the high frequency generator  200 . 
     Since the reflector  300  creates multiple scattering by reflecting high frequency waves generated by the high frequency generator  200  toward the substrate  100 , it is possible to uniformly heat the entire area of the substrate  100  including the corners by forming uniform electric fields over the entire area of the substrate  100 . In addition, it is possible to increase the temperature growth rate of the substrate  100  and improve the energy efficiency of the high frequency heating apparatus. 
       FIG. 4A  and  FIG. 4B  are a schematic top plan view and a side elevation view showing a high frequency heating apparatus according to another embodiment of the present invention. 
     Referring to  FIG. 4A  and  FIG. 4B , the high frequency heating apparatus according to this embodiment includes a plurality of high frequency generators  210 ,  220  and  230 . The reflector  300  can partition the plurality of high frequency generators  210 ,  220  and  230  into high frequency generator groups each including at least one high frequency generator. 
     The reflector  300  can include first reflecting portions  311  and  312  which form partitions between the high frequency generator groups which are spaced apart from each other. 
     Here, the first reflecting portions  311  and  312  can form the partitions between the high frequency generator groups which are spaced apart from each other in the direction from the front to the rear. The first reflecting portions  311  and  312  can be configured such that they extend in the direction from left to right. 
     In this case, in order to efficiently prevent any interference between high frequency waves generated by the individual high frequency generators, it is preferred that the distance {circle around ( 1 )} from each of the high frequency generators  210 ,  220  and  230  to a corresponding one of the first reflecting portions  311  and  312  be n/2*λ, where n is a natural number ranging from 1 to 12, and λ is the wavelength of high frequency waves generated by the high frequency generators. More preferably, the distance can be 2λ. 
     In addition, the distance {circle around ( 2 )} from the substrate  100  to the first reflecting portions  311  and  312  can be 4 cm, preferably, 2 cm. 
     In addition, as shown in  FIG. 5 , when the plurality of high frequency generators  240 ,  250  and  260  is arranged in a plurality of rows, the first reflecting portions  311  and  312  can partition the rows of the high frequency generators  240 ,  250  and  260 . Here, the rows of the high frequency generators  240 ,  250  and  260  can be formed in the direction from left to right. 
     In this fashion, the first reflecting portions  311  and  312  are respectively formed between the adjacent rows of the high frequency generators  240 ,  250  and  260 . The first reflecting portions  311  and  312  prevent high frequency waves generated by the individual rows from interfering with each other, thereby preventing electric fields from being concentrated, so that the substrate  100  are not locally heated by the concentrated electric fields. 
     The reflector  300  according to this embodiment can include reflecting portions  321  and  322  which are disposed on the left side and/or the right side of the high frequency generators. 
     When the high frequency heating apparatus according to this embodiment includes the plurality of high frequency generators  240 ,  250  and  260  which are arranged in at least one row, the second reflecting portions  321  and  322  can be disposed on the left side and/or the right side of the row of the high frequency generators. 
     In addition, the second reflecting portions  321  and  322  can extend in the direction from the front to the rear. 
     In order to efficiently reflect high frequency waves generated by the plurality of high frequency generators  200 , it is preferred that the distance {circle around ( 3 )} from the plurality of high frequency generators  200  to the second reflector  321  or  322  be 2λ or less. 
     In addition, as shown in  FIG. 11 , in order to more efficiently reflect high frequency waves, the reflector  300  according to this embodiment can include a third reflecting portion ( 331 ) which is disposed above and/or below the substrate  100 . The third reflecting portion ( 331 ) is formed such that the main plane thereof faces the main plane of the substrate  100 . 
     The distance from the third reflecting portion ( 331 ) to the substrate  100  can be n/2*λ, where n is a natural number ranging from 1 to 6. Preferably, the distance can be λ. 
     In addition, as shown in  FIG. 6 , the reflector  300  according to the present invention can have a number of holes in order to facilitate air convection, thereby increasing the heating efficiency. The diameter of the holes can be 3 mm or less in order to prevent high frequency waves from leaking to the outside of the reflector  300  through the holes without being reflected. Preferably, the diameter of the holes can be 2 mm. 
       FIG. 7A  and  FIG. 8B  are pictures of electric field distribution analysis and temperature distribution analysis that are measured after heating a piece of glass using a high frequency heating apparatus which includes a high frequency generators  200  which are disposed in one row and a reflector  300  according to an embodiment of the present invention. Here, the measurement was carried out by setting the distance from the row of frequency generators  200  to the reflector  300  to be 2λ, the distance from the substrate  100  to the reflector  300  to be 2 cm, and the diameter of the holes formed in the reflector  300  to be about 3 mm. As shown in  FIG. 7A  and  FIG. 7B , it can be appreciated that, when the substrate  100  is heated using the high frequency heating apparatus having the reflector  300  according to the present invention, a uniform electric field is formed over the entire area of the substrate  100 , which is then uniformly heated. 
       FIG. 8A  and  FIG. 8B  are pictures of electric field distribution analysis and temperature distribution analysis that are measured after heating a piece of glass using a high frequency heating apparatus which includes a high frequency generators which are disposed in two rows and a reflector according to another embodiment of the present invention, and  FIG. 9  is a graph showing the temperature growth rate of a substrate which is heated using the high frequency heating apparatus. Here, the measurement was carried out by setting the distance from the rows of high frequency generators to the reflector to be 2×, the distance from the substrate to the reflectors to be 2 cm, and the diameter of holes formed in the reflector to be 3 mm. 
     As shown in  FIG. 8A  and  FIG. 8B , it can be appreciated that, when the glass is heated using the high frequency heating apparatus having the two rows of high frequency generators, the reflector prevents high frequency waves generated by the individual rows of high frequency generators from interfering with each other so that the electric field distribution can be maintained to be equal to that of the high frequency heating apparatus having one row of high frequency generators and the substrate can be uniformly heated. 
     In addition, as shown in  FIG. 9 , according to the present invention, it is possible to prevent thermal runaway from occurring due to the nonlinear temperature growth of the substrate by linearly increasing the temperature of the substrate while realizing a high temperature growth rate. 
       FIG. 10  is a graph showing surface temperatures of a plate glass that are measured after the plate glass having a width of 1600 mm is heated to a temperature of 650° C. using a high frequency heating apparatus which includes a plurality of rows of high frequency generators and a reflector according to the present invention. 
     As shown in  FIG. 10 , it can be appreciated that the plate glass was very uniformly heated using the high frequency heating apparatus according to the present invention such that the distribution of the surface temperature thereof is 700° C.±10° C. 
     In addition, the high frequency heating apparatus according to the present invention can also include a heater (not shown) which heats the substrate, in addition to the high frequency generators. 
     The heater (not shown) heats the substrate from outside to inside by generating heat through electrical resistance, and the high frequency generators vibrate ions inside the substrate using high frequency waves and heat the inside and outside of the substrate using resultant frictional heat. In this fashion, the substrate can be more efficiently heated. 
     The foregoing descriptions of specific exemplary embodiments of the present invention have been presented with respect to the certain embodiments and drawings. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible for a person having ordinary skill in the art in light of the above teachings. 
     It is intended therefore that the scope of the present invention not be limited to the foregoing embodiments, but be defined by the Claims appended hereto and their equivalents.