Abstract:
A method of cutting a glass sheet is disclosed. The method comprises heating a heating element to a heat temperature, which in turn heats a glass sheet along a desired cutting line, to a separation temperature. The glass sheet is subjected to non-destructive pressure at an edge on the cutting line. The non-destructive pressure may be applied by a tool with opposed sharp edges so long as the edges do not nick or otherwise score the glass sheet. A diagonal cutter may be utilized as the sharp-edged tool. After an adequate amount of heating time, the glass sheet will achieve the separation temperature and spontaneously separate along the heated cutting line.

Description:
[0001]    This application claims the benefit of priority to U.S. Provisional Application 62/043039 filed Aug. 28, 2014 content of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
     1. Field 
       [0002]    The present disclosure generally relates to apparatus and methods for thermal cutting of glass sheets and, more specifically, to apparatus and methods for thermal cutting of glass sheets by applying tool non-destructive pressure. 
       2. Technical Background 
       [0003]    Glass sheets have previously been cut in a number of ways such as scoring followed by breaking and diamond saw cutting. Such mechanical methods can be expensive due to costs of the mechanical cutting devices. 
         [0004]    Another method includes thermally severing glass and involves nicking one edge of the glass sheet and then subjecting the glass sheet to radiant heat to propagate the crack. Such a method can result in an inaccurate cutting line. Another method of thermally severing glass requires continuous contact between the glass sheet and the heat source. Such a method can be expensive due to the equipment required to ensure continuous contact along the cutting line. 
       SUMMARY 
       [0005]    According to one embodiment, a method of cutting a glass sheet comprises heating a heating element to a heat temperature, which in turn heats a glass sheet along a desired cutting line to a separation temperature. The heat temperature is greater than the separation temperature. The glass sheet is subjected to non-destructive pressure at an edge on the cutting line. The non-destructive pressure may be applied by a tool with opposed sharp edges so long as the edges do not nick or otherwise score the glass sheet. A diagonal cutter may be utilized as the sharp-edged tool. After an adequate amount of heating time, the glass sheet will spontaneously separate along the heated cutting line. 
         [0006]    Additional features and advantages of the methods for cutting laminate strengthened glass sheets described herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
         [0007]    It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate one or more embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  depicts one embodiment of a glass cutting apparatus for use in the method of the present disclosure. 
           [0009]      FIG. 2  is a perspective view of one embodiment of a sharp-edged tool. 
           [0010]      FIG. 3  is an elevated view of one embodiment of a pair of diagonal cutters. 
           [0011]      FIG. 4  schematically depicts a cross section of a laminated glass sheet according to one or more embodiments shown and described herein. 
           [0012]      FIG. 5  schematically depicts one embodiment of a fusion draw process for making the laminated glass sheet of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Reference will now be made in detail to embodiments of apparatus and methods for cutting glass sheets, examples of which are illustrated in the accompanying drawings. 
         [0014]    In various embodiments, a method of cutting a glass sheet comprises heating a heating element to a heat temperature; the heat temperature is above the temperature to which the glass sheet must be heated for separation, referred to as the separation temperature. The glass sheet may be positioned immediately adjacent to the heating element. The glass sheet has a cutting line, representing the location on the glass sheet where the cut is desired, and an edge. The cutting line and the edge intersect at a point. The glass sheet may be positioned such that the cutting line and the edge are immediately adjacent to the heating element and at least a portion of the cutting line is in direct contact with the heating element. While the glass sheet is held in position adjacent to the heating element, the glass sheet is held or engaged at the point with a sharp-edged tool. The sharp-edged tool comprises a sharp edge. For example, the sharp edge comprises two opposed sharp edges. The sharp-edged tool lightly holds the glass sheet such that the glass sheet is not nicked or otherwise damaged, and is positioned such that the sharp edge of the sharp-edged tool is aligned with the cutting line. The glass sheet is maintained in position immediately adjacent to the heating element to permit the glass sheet to achieve a separation temperature, whereby the glass sheet separates along the cutting line. Thus, the separation is achieved by engaging the sheet with the sharp-edged tool during heating, and without nicking, scoring, or otherwise forming a defect in the glass sheet. Additionally, or alternatively, the separation is achieved without relative motion between the glass sheet and the sharp-edged tool. For example, the separation is achieved without moving the sharp-edged tool inward toward a center of the glass sheet after initial engagement with the glass sheet (e.g., without bringing opposing sharp edges of the sharp-edged tool together toward one another to cut into the glass sheet) and/or without running the sharp-edged tool across a surface of the glass sheet (e.g., without scribing the glass sheet with the sharp-edged tool). Additionally, or alternatively, the separation is achieved without bending the glass sheet to induce the separation. 
         [0015]      FIG. 1  depicts one embodiment of a glass cutting apparatus for cutting a glass sheet. A glass sheet  10  may include knurled edge portions  12  as a result of the glass manufacturing process. For example, the knurled edge portions  12  comprise beads extending longitudinally along one or more edges of the glass sheet  10  and being thicker than a central region of the glass sheet. Additionally, or alternatively, the knurled edge portions  12  comprise roughened or uneven surfaces, which may result from engagement of the glass sheet  10  by one or more pulling rollers during the forming process. The glass sheet  10  may be designated with a cutting line  13  which represents the location on the glass sheet  10  where a separation is desired. As will be understood, the cutting line  13  may not be physically present on the glass sheet  10 , but merely represents the location where cutting is desired. In some embodiments, the cutting line  13  extends longitudinally along the glass sheet  10  (e.g., substantially parallel to the knurled edge portions  12 ) as shown in  FIG. 1 . Such a configuration can enable removal of the knurled edge portions  12  from the glass sheet. In other embodiments, the cutting line can extend transversely along the glass sheet (e.g., perpendicular to the knurled edge portions  12 ) or in another suitable direction (e.g., at an oblique angle to the knurled edge portions  12 ). The glass sheet also includes an edge  15 . A point  17  represents the location where the edge  15  and the cutting line  13  intersect. 
         [0016]    The glass sheet  10  is positioned adjacent to a heating element  16  such that the cutting line  13  and the heating element  16  are immediately adjacent to each other. Thus, the heating element  16  is aligned with the cutting line  13  as shown in  FIG. 1 . The glass sheet  10  need not be in continuous contact with the heating element  16 . For example, the glass sheet  10  is positioned immediately adjacent to the heating element  16  such that the heating element is spaced from the glass sheet by a distance of at most about 100 mm, at most about 50 mm, at most about 25 mm, at most about 10 mm, at most about 5 mm, or at most about 1 mm along the cutting line. In some embodiments, at least a portion of the glass sheet  10  along the cutting line  13  is in contact with the heating element  16 . For example, the point  17  and a portion of the cutting line  13  immediately adjacent the point  17  are in contact with the heating element  16 . The heating element  16  may heat the glass sheet  10  by conduction, convection, and/or radiation. 
         [0017]    The heating element  16  selectively or preferentially heats the glass sheet  10  along the cutting line  13 . For example, the heating element  16  heats a region of the glass sheet  10  along the cutting line  13  to form a heated region without substantially heating remote regions of the glass sheet spaced away from the cutting line. In some non-limiting embodiments, to achieve such localized heating, the heating element  16  may be very narrow, for example less than or equal to about 3 mm wide. In some embodiments, the heated region of the glass sheet comprises the cutting line  13  and extends a minimal distance to either side of the cutting line  13 . The width of the heated region will depend on the type and thickness of glass sheet that is being cut, which affects the time necessary to achieve the separation temperature. 
         [0018]    In some embodiments, the heating element  16  heats the glass sheet  10  asymmetrically to cause a thermal gradient to develop through the glass sheet  10  in the thickness direction. For example, the heating element  16  heats one surface of the glass sheet  10  (e.g., the surface immediately adjacent to the heating element) without directly heating the opposing surface of the glass sheet. Thus, the heated region of the glass sheet is hotter at the surface adjacent to the heating element  16  than at the opposing surface positioned away from the heating element. 
         [0019]    The heat temperature to which the heating element  16  is heated may depend on the composition of the glass sheet  10  because the heat temperature should be above the separation temperature, which will vary depending on the glass sheet. Alternatively, the heat temperature to which the heating element  16  is heated may be a designated temperature, such as about 320° C., which typically will be above the separation temperature, or higher, and the time for cutting of the glass sheet  10  may vary depending on the composition of the glass sheet  10 . 
         [0020]    The heating element  16  comprises a suitable heating device that generates heat to heat the cutting line  13  of the glass sheet  10 . For example, the heating element  16  comprises a heated wire (e.g., a nichrome wire), a heated rod (e.g., a calrod), a heat tape, a heat plate, a torch or bank of torches, a laser or bank of lasers, or another suitable heating device. In some embodiments, the heating element  16  comprises a heat tape connected by electric wiring  18  to a power supply  14  as shown in  FIG. 1 . A heat tape can provide the required heating and is relatively inexpensive. Using a heat tape eliminates the substantial costs associated with other types of glass cutting equipment, such as lasers or mechanical cutting devices. 
         [0021]    A support  20  may support the glass sheet  10  in a suitable position (e.g., horizontal, vertical, or an intermediate angle, as convenient). In some embodiments, the heating element  16  is embedded in the support  20  such that the heating element  16  is at least partially coterminous with the surface of the support  20  that supports the glass sheet  10 . Thus, the glass sheet  10  may be fastened to the support  20  for ease of handling. 
         [0022]      FIG. 2  is a perspective view of one embodiment of a sharp-edged tool  30 . The sharp edged-tool  30  may include a first leg  32 , a second leg  34 , and a crossbar  36 . The legs  32 ,  34 , each include a blade  38 ,  39 , respectively, which provides a sharp edge to each of the legs  32 ,  34 . The distance, D, between the first leg  32  and the second leg  34  may be slightly less than the thickness of the glass sheet  10  ( FIG. 1 ) to be cut. The first leg  32  and the second leg  34  may be separated slightly so that the glass sheet  10  at the point  17  may be inserted into the sharp-edged tool  30  with the blades  38 ,  39  lightly contacting the glass sheet  10 . The crossbar  36  may provide resistance, biasing the first leg  32  and the second leg  34  to their non-separated position, thereby lightly holding the extreme edge of the glass sheet  10  at the point  17 . The sharp-edged tool  30  holds the glass sheet  30  lightly so that the glass sheet  10  is not damaged or nicked. For example, the blades  38 ,  39  of the sharp-edged tool  30  engage opposing surfaces of the glass sheet  10  to gently squeeze the glass sheet between the blades without damaging the glass sheet (e.g., without scoring, scratching, cutting, nicking, or otherwise forming a defect in the surfaces and/or edges of the glass sheet). In some embodiments, engaging the glass sheet  10  with the sharp-edged tool  30  without forming a defect in the glass sheet comprises engaging the glass sheet such that any crack formed in the surface of the glass sheet by such engagement extends at most about 2 μm, at most about 1 μm, or at most about 0.5 μm from the surface into the glass sheet. Engaging the glass sheet with the sharp edges of the sharp-edged tool can aid in concentrating stresses within the glass sheet along the cutting line so that the glass sheet separates along the cutting line upon reaching the separation temperature. Additionally, or alternatively, avoiding forming a defect in the glass sheet can help to prevent uneven cracking or breaking of the glass sheet. For example, such uneven cracking or breaking can be propagated from a nick or score in the glass sheet before the glass sheet reaches the separation temperature. 
         [0023]      FIG. 3  is an elevated view of one embodiment of a pair of diagonal cutters. In some embodiments, a pair of diagonal cutters  40  may be used as the sharp-edged tool. The pair of diagonal cutters  40  includes sharp-edged jaws  42 . The pair of diagonal cutters  40  can engage the glass sheet  10  as described with reference to the sharp-edged tool  30 , which may provide the proper placement sufficient to generate the initial crack and permit the glass sheet to separate along the area that was preferentially heated by the heating element  16 . 
         [0024]    The apparatus and methods described herein can be used for cutting a suitable glass sheet including, for example, a single layer glass sheet or a laminate glass sheet, which can be difficult to cut due to stresses present in the core and cladding layers. The glass sheet can be substantially planar (e.g., a flat glass sheet) or non-planar (e.g., a curved or shaped glass sheet). As described above, when the glass sheet  10  is heated by the heating element  16  while the point  17  of the glass sheet  10  is lightly held by a sharp-edged tool  30  or a pair of diagonal cutters  40 , the glass sheet  10  will spontaneously separate at the cutting line  13 . The heating element  16  may be heated to an appropriate temperature, such as about 320° C. Within about 5-30 seconds of time the glass sheet  10  will spontaneously separate along the preferentially heated area or cutting line  13 . The time needed for the separation of the glass will be dictated by the characteristics of the glass and will vary with the type of glass, from about 5 to 30 seconds depending on glass ratio and thickness. 
         [0025]    Regarding laminate glass sheets, referring now to  FIG. 4 , one embodiment of a laminated glass sheet  100  is schematically depicted in cross section. The laminated glass sheet  100  generally comprises a glass core layer  102  and a pair of glass cladding layers  104   a,    104   b.  It is noted that, in other embodiments, the laminated glass sheet may include only one glass cladding layer, thereby providing a two-layer sheet. In other embodiments, the laminated glass sheet may include multiple core and/or cladding layers, thereby providing a four-, five-, or more-layer sheet. 
         [0026]    Still referring to  FIG. 4 , the glass core layer  102  generally comprises a first surface portion  103   a  and a second surface portion  103   b,  which is opposed to the first surface portion  103   a.  A first glass cladding layer  104   a  is fused to the first surface portion  103   a  of the glass core layer  102  and a second glass cladding layer  104   b  is fused to the second surface portion  103   b  of the glass core layer  102 . The glass cladding layers  104   a,    104   b  are fused to the glass core layer  102  without any additional materials, such as adhesives, coating layers or any non-glass material added or configured to adhere the respective cladding layers to the core layer, disposed between the glass core layer  102  and the glass cladding layers  104   a,    104   b.  Thus, the first glass cladding layer  104   a  and/or the second glass cladding layer  104   b  are fused directly to the glass core layer  102  or are directly adjacent to the glass core layer  102 . In some embodiments, the laminated glass sheet comprises one or more intermediate layers disposed between the glass core layer and the first glass cladding layer and/or between the glass core layer and the second glass cladding layer. For example, the intermediate layers comprise intermediate glass layers and/or diffusion layers formed at the interface of the glass core layer and the glass cladding layer. The diffusion layer can comprise a blended region comprising components of each layer adjacent to the diffusion layer. In some embodiments, the laminated glass sheet comprises a glass-glass laminate (e.g., an in situ fused multilayer glass-glass laminate) in which the interfaces between directly adjacent glass layers are glass-glass interfaces. 
         [0027]    In some embodiments, the glass core layer  102  is formed from a first glass composition having an average core coefficient of thermal expansion CTE core  and the glass cladding layers  104   a,    104   b  are formed from a second, different glass composition, which has an average cladding coefficient of thermal expansion CTE cladding . The term “CTE,” as used herein, refers to the coefficient of thermal expansion of the glass composition averaged over a temperature range from about 20° C. to about 300° C. The CTE core  may be greater than CTE cladding , which results in the glass cladding layers  104   a,    104   b  being compressively stressed without being ion exchanged or thermally tempered. Thus, the laminated glass sheet comprises a laminated strengthened glass sheet. In other embodiments, the CTE cladding  may be greater than CTE core , which results in the core layer  102  being compressively stressed. 
         [0028]    In some embodiments, the laminated glass sheet  100  may be formed by a laminate fusion draw or fusion lamination process such as the process described in U.S. Pat. No. 4,214,886, which is incorporated herein by reference. 
         [0029]    Referring to  FIG. 5  by way of example, a laminate fusion draw apparatus  200  for forming a laminated glass article comprises an upper isopipe or overflow distributor  202 , which is positioned over a lower isopipe or overflow distributor  204 . The upper overflow distributor  202  comprises a trough  210  into which a molten glass cladding composition  206  is fed from a melter (not shown). Similarly, the lower overflow distributor  204  comprises a trough  212  into which a molten glass core composition  208  is fed from a melter (not shown). In the embodiments, described herein, the molten glass core composition  208  has an average coefficient of thermal expansion CTE core  which is greater than the average coefficient of thermal expansion CTE cladding  of the molten glass cladding composition  206 . 
         [0030]    As the molten glass core composition  208  fills the trough  212 , the molten glass core composition  208  overflows the trough  212  and flows over the outer forming surfaces  216 ,  218  of the lower overflow distributor  204 . The outer forming surfaces  216 ,  218  of the lower overflow distributor  204  converge at a root or draw line  220 . Accordingly, the molten glass core composition  208  flowing over the outer forming surfaces  216 ,  218  rejoins at the draw line  220  of the lower overflow distributor  204 , thereby forming a glass core layer  102  of a laminated glass article. 
         [0031]    Simultaneously, the molten glass cladding composition  206  overflows the trough  210  formed in the upper overflow distributor  202  and flows over outer forming surfaces  222 ,  224  of the upper overflow distributor  202 . The molten glass cladding composition  206  is outwardly deflected by the upper overflow distributor  202 , such that the molten glass cladding composition  206  flows around the lower overflow distributor  204  and contacts the molten glass core composition  208  flowing over the outer forming surfaces  216 ,  218  of the lower overflow distributor, fusing to the molten glass core composition and forming glass cladding layers  104   a,    104   b  around the glass core layer  102 . 
         [0032]    In some embodiments, the molten glass core composition  208  in the viscous state is contacted with the molten glass cladding composition  206  in the viscous state to form the laminated glass sheet. In some of such embodiments, a glass ribbon travels away from the draw line  220  of the lower overflow distributor  204  as shown in  FIG. 5 . The glass ribbon can be drawn away from the lower overflow distributor  204  by a suitable drawing mechanism including, for example, gravity and/or pulling rollers. The glass ribbon cools as it travels away from the lower overflow distributor  204 . The glass ribbon is severed to separate a glass pane from the glass ribbon. Thus, the glass pane is cut from the glass ribbon. In some embodiments, the glass sheet comprises the glass ribbon. In other embodiments, the glass sheet comprises the glass pane cut from the glass ribbon. 
         [0033]    In some embodiments, the glass ribbon is severed as described herein. For example, the heating element  16 , the support  20 , and/or the sharp-edged tool  30  or diagonal cutters  40  are configured to move with the glass ribbon to sever the glass ribbon along the cutting line  13  as described herein. By moving the heating element  16  with the glass ribbon, the heating element can be maintained adjacent to the cutting line  13  to preferentially heat the region of the glass ribbon as described herein. Similarly, by moving the support  20  and/or the sharp-edged tool  30  or diagonal cutters  40  with the glass ribbon, the moving ribbon can be severed along the cutting line  13 . In some embodiments, the cutting line  13  extends transversely across the width of the moving ribbon such that severing the moving ribbon along the cutting line cuts a pane from the ribbon. Additionally, or alternatively, the cutting line  13  extends longitudinally along the length of the moving ribbon (e.g., to enable removal of the beads from the moving ribbon). In various embodiments, the cutting methods described herein can be used to sever a glass ribbon during a forming operation or a glass pane as a post processing step following a forming operation. 
         [0034]    As noted hereinabove, the molten glass core composition  208  may have an average coefficient of thermal expansion CTE core  that is greater than the average cladding coefficient of thermal expansion CTE cladding  of the molten glass cladding composition  206 . Accordingly, as the glass core layer  102  and the glass cladding layers  104   a,    104   b  cool, the difference in the coefficients of thermal expansion of the glass core layer  102  and the glass cladding layers  104   a,    104   b  cause compressive stresses to develop in the glass cladding layers  104   a,    104   b.  The compressive stress increases the strength of the resulting laminated glass article without an ion-exchange treatment or thermal tempering treatment. Glass compositions for the glass core layer  102  and the glass cladding layers  104   a,    104   b  may include, but are not limited to, the glass compositions described in PCT Pat. Publication No. WO 2013/130700 entitled “High CTE Potassium Borosilicate Core Glasses and Glass Articles Comprising the Same”, and PCT Pat. Publication No. WO 2013/130718 entitled “Low CTE Alkali-Free Boroaluminosilicate Glass Compositions and Glass Articles Comprising the Same”, both of which are assigned to Coming Incorporated and incorporated herein by reference in their entireties. 
         [0035]    The methods of the present disclosure are suitable for cutting a laminated glass sheet  100  as described above, even though conventional cutting methods may not be adequate for cutting such a laminate glass sheet  100  due to the stresses present in the core layer  102  and the pair of glass cladding layers  104   a,    104   b.    
         [0036]    It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.