Abstract:
A glass tempering apparatus is capable of selectively delivering increased volumes of tempering medium to designated areas of a moving glass sheet to create desired stresses in such designated areas by the specific arrangement of nozzles in the glass tempering apparatus. A method of tempering glass utilizing the subject apparatus is also provided.

Description:
RELATED APPLICATION 
       [0001]    This application is claiming the benefit, under 35 U.S.C. 119(e), of the provisional application filed Jan. 4, 2008 under 35 U.S.C. 111 (b), which was granted Ser. No. 61/009,974. This provisional application is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to an apparatus for tempering glass sheets and a method of tempering utilizing that apparatus. 
         [0003]    Many methods of treating glass to cause it to break in small, harmless pieces, rather than large, elongated shards which can cause serious injury have been practiced. The goal of early tempering methods to treat relatively small sheets of glass was to uniformly distribute the airflow over the entirety of the surface of the glass sheet. As single glass sheets used, for example, in vehicles became larger, and the analysis of stresses in glass became more sophisticated, methods of differentially treating areas of a glass sheet were devised. One particularly intractable problem has been the elimination of inadequately tempered areas, relatively near the center of large sheets of glass such as automotive backlights. 
         [0004]    Thus, those skilled in the art of glass tempering have continued to search for a way to improve tempering, on a consistent basis, during time-critical automotive glass manufacturing operations. 
         [0005]    As noted, glass tempering or heat treatment is the subject of many patents, for example: 
         [0006]    U.S. Pat. No. 5,094,678 describes a high-convection gas jet nozzle section for sheet-like material guided over rollers, in particular, for the thermal tempering of thin, flat glass sheets comprising a lower nozzle field having nozzle ribs which are arranged centrally and parallel to each other, and an upper nozzle field having nozzle ribs arranged symmetrically to the vertical axis of the lower nozzle ribs such that some gas jets are said to perpendicularly contact the sheet-like material, while others obliquely impinge on the surface of the sheet-like material, wherein the nozzle bottoms of the upper nozzle ribs are said to form a slightly modified cross-section of a letter “M”. 
         [0007]    U.S. Pat. No. 4,662,926 describes a method of toughening glass by heating, then rapidly cooling or quenching the glass, the essential feature of the invention purportedly being that, in the quenching step, the cooling medium is caused to impinge on each side of the glass sheet in such a pattern that the glass sheet is said to be more highly toughened in a generally, circular central region and in a plurality of regions, which are substantially concentric about the center of the glass sheet and radially spaced from one another. 
         [0008]    U.S. Pat. No. 4,402,723 describes an arrangement of quench nozzles in different densities transverse to a path of travel for glass sheets moving through a passthrough quench to facilitate removal of spent tempering medium to both lateral sides of the path of travel. 
         [0009]    U.S. Pat. No. 4,323,385 describes an arrangement of nozzles extending from one, or a pair of opposing plenum chambers of a glass sheet tempering apparatus which arrangement is said to minimize the tendency of a large glass sheet interposed between the plenum chambers to slow the escape of tempering medium that is applied to the central portion of the glass sheet undergoing tempering. 
         [0010]    U.S. Pat. No. 3,294,519 describes a nozzle box construction intended to create a slight pressure gradient in the tempering fluid from the center of the glass sheet outward and purportedly providing uniform tempering for large glass sheets, by increasing the width of the intermediate nozzles in their central portion to increase the percentage of aperture portion facing the central area of the glass sheet compared to other portions of same. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention relates to a glass tempering apparatus capable of selectively delivering increased volumes of a tempering medium to designated areas of a moving glass sheet to create desired stresses in such designated areas, by the specific arrangement of quench nozzles in the glass tempering apparatus. In particular, nozzles arranged in closely adjacent rows parallel to the direction of travel of the glass sheet, spanning a specified distance on either side of the centerline of the glass tempering apparatus, have been found to substantially reduce the incidence of inadequate tempering of, in particular, large sheets of glass. 
         [0012]    A method of tempering utilizing the apparatus of the present invention is also provided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a plan view of a glass tempering line in accordance with the invention. 
           [0014]      FIG. 2  is a plan view of a representative glass sheet showing areas prone to insufficient tempering. 
           [0015]      FIG. 3  is a perspective view of a conventional blasthead assembly. 
           [0016]      FIG. 4  is a perspective view of a blasthead assembly with high density modules in accordance with the invention. 
           [0017]      FIG. 5  is a cross-sectional view of first and second complementary tempering assemblies in accordance with the invention. 
           [0018]      FIG. 6  is a graph/chart of quench air delivered to glass across the width of the blasthead assembly in accordance with a preferred embodiment of the invention. 
           [0019]      FIG. 7  is a graph/chart comparing the occurrence of splines in a glass sheet utilizing the tempering technology of the present invention is conventional tempering apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The present invention relates to a glass tempering apparatus  10  and to a method of tempering glass sheets utilizing such apparatus. More specifically, the invention relates to an apparatus  10  for and method of selectively delivering increased volumes of tempering medium to one or more areas of at least one major surface of a glass sheet  12 . The glass sheet  12  is, for example, a vehicle window. In particular, the apparatus  10  of the present invention allows for significant improvement in tempering of large glass sheets  10 , such as vehicle backlights, by directing increased volumes of tempering medium toward specified areas of the glass sheet  10  where glass quality testing has shown that tempering may have been insufficient. To remedy this situation, applicants utilized the well known principle that tempering is creating stresses in the amorphous glass structure, and that areas where compressive stresses predominate make the glass stronger than in areas where tensile stresses predominate. While not wishing to be bound by any theory, applicants believe that the apparatus of the present invention reduces the undesirable occurrence of splines by as much as 90%, due to the creation of a larger number of areas of desirable stresses, but stresses of a lesser magnitude than has been typical using conventional glass tempering equipment. 
         [0021]    As shown in  FIG. 2 , in large glass sheets  12 , the area found to be most prone to insufficient tempering resulting in deviations from acceptable tempering break patterns, i.e., break patterns of elongated glass shards known as “splines”, rather than small, rounded particles, occurs a relatively consistent distance (distance “A”) transversely from, and on either side of the centerline of the glass tempering apparatus. The width of the area in which the splines typically occur is also relatively consistent, and is sometimes referred to herein as distance “B”. The distance from the outer edge of distance “B” to the outermost edge of the glass sheet, transversely from its centerline is sometimes referred to herein as distance “C”. Tempering apparatus such as the present invention are sometimes referred to as “blastheads”, “quench modules” or “quench boxes.” 
         [0022]    It is an advantage of the present invention that the tempering apparatus  10  can be used as a component of a typical glass tempering line  14 , shown schematically in  FIG. 1 . A conventional blasthead assembly is shown in  FIG. 3 . A tempering apparatus  10  in accordance with the present invention is shown in  FIG. 4 . 
         [0023]    Still with reference to  FIG. 4 , and in the direction denoted therein as the direction of glass travel, there is illustrated a plurality of nozzles from which tempering medium, preferably air, is emitted and directed toward a major surface of the glass sheet. 
         [0024]    In the direction of travel of the glass sheet  12 , in accordance with the invention, the glass sheet  12  first encounters a first zone having a first plurality of nozzles  16 , preferably arranged in staggered rows, sometimes known as a “domino five” pattern, although other nozzle patterns are within the scope of the invention. The length of the nozzles in the first, second and third pluralities of nozzles  16 ,  18 ,  20  are predetermined to substantially conform to the shape of the glass sheet  12  to be tempered. The moving glass sheet  12  then encounters a second zone having a second plurality of nozzles  18  arranged in parallel rows, sometimes known as a “striper” or a modified striper. As can be seen, the density of the nozzles varies in an area on either side transversely of the centerline of the apparatus. Distances “A”, “B” and “C” as designated on the glass sheet  12  of  FIG. 2  are superimposed on the corresponding area of the tempering apparatus  10 , according to the embodiment of the present invention illustrated in  FIG. 4 . Finally, in its route of travel for tempering, the glass sheet  12  encounters a third zone having third plurality of nozzles  20  in a domino five, or modified domino five pattern. 
         [0025]    Still referring to  FIG. 4 , in the modified striper portion  18  of the tempering apparatus  10 , and in a direction transverse to the direction of glass travel, the modified striper, according to the present invention, can be described as parallel rows of nozzles from which cooling air at a temperature of from 50° F. to 150° F. is emitted toward the glass sheet  10 . 
         [0026]    As shown, for example, in  FIG. 5 , the density of the nozzles in the parallel rows transverse distance “A” on either side of the centerline of the glass tempering apparatus can be designated as x, preferably on the order of  816  nozzles per square meter (m 2 ). These nozzles are typically about 6-9 mm in diameter. The density of the nozzles distance “A” from the centerline is typical of conventional striper quench modules. 
         [0027]    Notably, however, in the area designated by transverse distance “B”, the density of the second plurality of nozzles  18  can be expressed as y, where y is greater than x. Preferably, the nozzle density is, essentially, doubled, to on the order of 3,265 nozzles/m 2 . The diameter of the nozzles is typically about 6-9 mm. Thus, the volume of tempering medium that can be delivered to a surface of the glass sheet is substantially increased, namely, on the order of 20% or more over the volume delivered by the conventional striper modules. A graphical representation of the variation in the volume of tempering medium delivered in the modified striper module is shown in  FIG. 6 . The temperature of the tempering medium is from 50° F. to 150° F. 
         [0028]    In the area designated as transverse distance “C” the nozzle density once more is that of a conventional striper module, i.e. on the order of 816 nozzles/m 2 . In accordance with the invention, in a direction transverse to either side of the centerline of the glass tempering assembly, transverse distances A, B, and C will be dependent on the size and geometry of the glass sheet  12  to be tempered. 
         [0029]    As previously alluded to, the compressive stresses formed in the glass in the area of increased nozzle density is thought to be comprised of more numerous areas of stress, but of a lower magnitude than in conventional striper module configurations. The stress levels are on the order of at least 20% lower than observed in conventional striper modules. 
       EXAMPLES 
       [0030]    The benefits of the present invention can be seen by reference to the data presented in Table 1. 
         [0031]    Fifteen vehicle windows (Column 1, 1-15) were tempered utilizing a conventional tempering apparatus which contained nozzles arranged in domino five and striper configurations, but with identical spacing between nozzles in all instances. The occurrence of splines ≧75 mm is summarized at the bottom of Table 1. 
         [0032]    Examples (Column 2, 1-15) were tested utilizing a tempering apparatus according to the present invention, as shown in  FIG. 4 . 
         [0033]    Examples (Column 3, 1-15) were tested utilizing an alternative conventional tempering apparatus as shown in  FIG. 7 . Once again, analysis of the data in Column 3 appears at the bottom of Table 1. 
         [0034]    The air pressure introduced into the plenum beneath the different tampering apparatus modules was at two different levels, namely 54 inches of water column, and 65-68 inches of water column. As previously noted, the tempering apparatus modules of the present invention provides for a selective increase in the volume of tempering medium directed to the surface of the glass being tempered in those areas where the nozzle density is increased. 
         [0035]    As can be seen in Table 1, the tempering in those areas of the glass where splines typically occur is significantly improved over conventional tempering modules both in the occurrence of splines ≧75 mm and the smaller size of the splines which do still occur. A graphical presentation of the data of Table 1 is provided in  FIG. 7  of this application. 
         [0000]    
       
         
               
               
               
             
               
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 54″ WC 
                 65-68″ WC 
               
             
          
           
               
                   
                   
                 TA 
                 Alternative 
                   
                   
                 Alternative 
               
               
                   
                 Conventional 
                 according to 
                 conventional 
                 Conventional 
                 TA according 
                 conventional 
               
               
                 Example 
                 TA 
                 invention 
                 TA 
                 TA 
                 to invention 
                 TA 
               
               
                   
               
               
                 1 
                 64 
                 57 
                 132 
                 68 
                 55 
                 88 
               
               
                 2 
                 72 
                 75 
                 98 
                 65 
                 52 
                 88 
               
               
                 3 
                 61 
                 58 
                 95 
                 60 
                 46 
                 100 
               
               
                 4 
                 66 
                 61 
                 121 
                 86 
                 58 
                 86 
               
               
                 5 
                 59 
                 54 
                 106 
                 61 
                 52 
                 52 
               
               
                 6 
                 66 
                 58 
                 64 
                 88 
                 47 
                 79 
               
               
                 7 
                 68 
                 51 
                 112 
                 72 
                 55 
                 131 
               
               
                 8 
                 88 
                 51 
                 70 
                 52 
                 52 
                 88 
               
               
                 9 
                 54 
                 57 
                 110 
                 57 
                 45 
                 96 
               
               
                 10  
                 54 
                 58 
                 103 
                 49 
                 46 
                 70 
               
               
                 11  
                 62 
                 54 
                 132 
                 62 
                 68 
                 83 
               
               
                 12  
                 48 
                 52 
                 98 
                 60 
                 54 
                 82 
               
               
                 13  
                 83 
                 47 
                 100 
                 70 
                 58 
                 69 
               
               
                 14  
                 62 
                 55 
                 97 
                 51 
                 70 
                 100 
               
               
                 15  
                 70 
                 68 
                 87 
                 64 
                 55 
                 87 
               
               
                   
               
             
          
           
               
                 Analysis of Splines Occurring 
               
               
                   
               
             
          
           
               
                 # ≧75 mm 
                 2 
                 1 
                 13 
                 2 
                 0 
                 12 
               
               
                 % ≧75 mm 
                 13% 
                 7% 
                 87% 
                 13% 
                 0% 
                 80% 
               
               
                   
               
               
                 TA = Tempering Apparatus 
               
             
          
         
       
     
         [0036]    In a preferred configuration, a second tempering apparatus  22 , substantially the same as the first tempering apparatus, but having a shape substantially conforming to the shape of the glass sheet to be tempered, and complementary to the first glass tempering apparatus is spaced opposite and apart from the first tempering apparatus  10  a distance sufficient for the glass sheet  12  to be tempered to pass therebetween, the second glass tempering apparatus  22  being capable of directing substantially the same volumes of tempering medium toward the second surface of the glass sheet. 
         [0037]    Those skilled in the art will appreciate that changes and modifications to the invention are possible in light of the preceding description. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.