Abstract:
A method for protecting a glass-ceramic surface by applying a layer of silicone to the surface is provided. The method involves utilizing an automated spray nozzle or roller device connected to a robotic arm which applies silicone to the glass-ceramic surface in areas prone to scratching. A cooktop including a glass-ceramic cooking surface with a protective layer of silicone applied thereto is also provided. The layer of silicone is provided on only on an underside portion of the cooktop, opposite a top portion designed to receive cooking implements. Further provided is a method for manufacturing the above described cooktop.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/450,247, filed Feb. 26, 2003, which is incorporated by reference as if fully set forth.  
         BACKGROUND  
         [0002]    The present invention is directed to a protective coating for a glass-ceramic surface, such as a smooth cooktop, and more particularly, to an RTV silicone coating to protect a contact area of the glass-ceramic surface from any articles which contact it.  
           [0003]    A growing percentage of cooktops in the U.S. and in the European markets are glass-ceramic smoothtops. These units are rapidly replacing traditional resistance coil units due to both aesthetic and functional advantages. The heating surfaces of glass-ceramic smoothtop cooktops are generally designed for strength and temperature resistance. However, the underside of glass-ceramic cooktops are susceptible to scratching. While this was not previously believed to have an impact on these cooktops, it has been discovered that even small scratches can weaken a glass-ceramic cooktop making it susceptible to breakage during normal usage at a later point in time.  
           [0004]    Additionally, after the glass-ceramic cooktops are shipped from the factory, the underside surfaces of the cooktops can be scratched during installation by contact with hard surfaces such as metal brackets and/or countertops in which they are installed. This is particularly true in the case of frameless or countertop installation in a home where a contractor or homeowner is generally not as careful as would be desired in handling these units. In such cases, the cooktops are provided without a porcelain, metal or plastic frame to protect the glass-ceramic around its edges. Instead, the edge of the glass-ceramic cooking surface rests directly on the kitchen countertop. The glass-ceramic cooking surface can be unknowingly scratched by the installer.  
           [0005]    A scratch may significantly weaken the surface causing the glass-ceramic cooking surface to later crack under what would be considered routine pressure, for example from a dropped pot or pan, or due to thermal cycling. Such failures are potentially dangerous to the consumer and are costly to repair.  
         SUMMARY  
         [0006]    The present invention provides a method for protecting a glass-ceramic surface by applying a generally uniform layer of silicone to the surface. The method preferably involves utilizing an automated spray nozzle or roller device connected to a robotic arm which applies silicone to the glass-ceramic surface in areas prone to scratching, abrasion, or other damage. The silicone can also be applied manually using a spray gun or other suitable applicators.  
           [0007]    The invention further provides a cooktop including a glass-ceramic cooking surface and a protective layer of silicone applied at least on an underside thereof. In one embodiment the layer of silicone is provided only on an underside portion of the glass-ceramic surface, opposite a top portion designed to receive cooking implements. In another embodiment, the layer of silicone is applied in a gas burner receiving area to prevent the glass-ceramic surface from being damaged by a gas burner and to allow for a seal between the gas burner and the gas burner receiving area. Methods for manufacturing the above described cooktops are also provided.  
           [0008]    The invention further provides a cooktop including cooktop grates with a layer of silicone applied thereto. The cooktop grates contact a glass-ceramic surface of the cooktop, and the layer of silicone protects the glass-ceramic surface from being damaged by the cooktop grates.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a view of a spray nozzle application device shown applying an RTV silicone coating according to a preferred embodiment of the present invention.  
         [0010]    [0010]FIG. 2 is a partial sectional view of a gas burner glass-ceramic cooktop according to a preferred embodiment of the present invention.  
         [0011]    [0011]FIG. 3 is a partial sectional view of a gas burner glass-ceramic cooktop according to a preferred embodiment of the present invention.  
         [0012]    [0012]FIG. 4 is a view of a roller application device shown applying an RTV silicone coating according to a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    Referring to FIG. 1, shown is an application device  10  for coating at least a portion of a glass-ceramic surface  12  of a smooth cooktop  40  with an RTV silicone  20  in accordance with a preferred embodiment of the present invention. The silicone  20  protects the surface  12  from scratching and abrasions.  
         [0014]    The device  10  preferably includes a robotic arm  14  controlled automatically by a programmable controller  30 . Alternatively, the robotic arm  14  may be controlled manually or semi-automatically. A spray nozzle  16  is supported by the robotic arm  14  and is connected via hoses  18  to a source of liquid RTV silicone, which is preferably under pressure, or alternatively gravity fed. A supply of pressurized air may also be provided, via one of hoses  18 , to adequately atomize the silicone  20  dispensed from the nozzle  16 . The nozzle  16  is preferably of a known type for use in connection with spraying atomized high viscosity fluids. Alternatively, the RTV silicone  20  may be applied manually to the glass-ceramic surface  12  using a conventional or HVLP hand-held spray gun, of the type known in the art, employing a hand-trigger or foot peddle controls.  
         [0015]    The RTV silicone  20  is preferably a condensation curing silicone of the type commonly used in cooktop assemblies as a structural adhesive and as a sealant. Alternatively, the silicone  20  may be heat curable, addition curable, UV curable or a type which cures in any suitable manner. Silicone is able to withstand exposure to the high temperatures encountered in cooktop applications. Sustained long-term temperatures up to 250° C. and shorter-term spikes of temperatures between 250° C. and 300° C. will not degrade commercially available silicones for such application.  
         [0016]    The RTV silicone  20  adheres very effectively to the glass-ceramic surface  12  and has a viscosity that allows it to be sprayed with an adequate thickness to prevent scratching and provide cushioning. Alternatively, the silicone  20  may additionally provide a moisture tight seal to prevent water or condensation from contacting electrical components located on an underside portion  22  of the glass-ceramic surface  12 .  
         [0017]    The programmable controller  30  is used to direct the robotic arm  14  to carry the spray nozzle  16  at a desired speed along a desired path with respect to the cooktop  40  to apply an even layer of silicone  20 . The angle of the spray nozzle  16  relative to the cooktop  40  is preferably varied such that the cooktop  40  itself acts as a mask for areas which are not to be coated with the RTV silicone  20 , such as vertical edges  26  of the glass-ceramic surface  12 . Alternatively, a shield, cutout mask or making tape, applied manually or automatically, may be employed in order to shield any areas of the glass-ceramic surface which are not to be coated by the coating process.  
         [0018]    Alternatively, the spray nozzle  16  may be replaced by a roller, brush or pad which applies the silicone  20  by direct contact with the glass-ceramic surface  12 . Referring to FIG. 4, an application device  310 , similar to the application device  10 , is shown. The application device  310  includes a roller applicator  316  supported by a robotic arm  314  and supplied with silicone  20  via hoses  318 . A controller  330 , similar to the controller  30 , controls the motion of the arm  314  and the supply of silicone  20  to the roller applicator  316 . Also, other methods known to those skilled in the art, such as silk screening, may be used to apply silicone to the surface  12 .  
         [0019]    In a preferred embodiment, the RTV silicone  20  is preferably applied in coatings of at least 0.003 inches thick on the glass-ceramic surface  12  on its underside portion  22 . More preferably, the coating is approximately 0.008 to 0.020 inches thick. Thicknesses in this range have been found to be sufficient to prevent scratching during handling, facilitating manufacturing of the cooktop  40  by preventing the occurrence of small scratches often missed during the inspection process. The RTV silicone  20  further provides the benefit of preventing scratches and abrasions during installation of the cooktop  40 , preventing damage which might cause immediate or future failures. Preferably, silicone  20  is not applied to a top portion  24  of the glass-ceramic surface  12  where cooking implements are used and aggressive cleaning or scrubbing may be required. Further, depending on the application, it may be required that only select areas of the underside portion  22  which are susceptible to damage be coated with silicone.  
         [0020]    Referring now to FIG. 2, a partial sectional view of a gas burner glass-ceramic cooktop  140  according to another preferred embodiment of the present invention is shown. In this embodiment, the RTV silicone  20  is preferably sprayed, or otherwise applied in a thin coating on a glass-ceramic surface  112  of the cooktop  140  in an area for receiving a gas burner  150  which is formed for attachment on an underside portion of the gas burner glass-ceramic cooktop  140 . The RTV silicone  20  provides a protective coating for the glass-ceramic surface  112  to protect it from scratches and abrasions. Preferably the gas burner  150  is installed prior to full curing of the silicone  20 . In this manner, after the silicone  20  is cured, it acts as a high temperature seal in the area where the gas burner unit is attached preventing ingress of food, liquid and debris. Alternatively, the silicone  20  may be applied directly to the gas burner  150  in areas that are to contact the glass-ceramic surface.  
         [0021]    [0021]FIG. 3 shows a partial sectional view of a gas burner glass-ceramic cooktop  240  according to another preferred embodiment of the present invention. The cooktop  240  includes cooktop grates  260  which contact a top portion  224  of a glass-ceramic surface  212 . The cooktop grates  260  are preferably formed to support cooking implements and are provided with a coating of RTV silicone  20  on a bottom edge thereof in an area which contacts the glass-ceramic surface  212  of the cooktop  240 . This provides scratch and abrasion protection for the glass-ceramic surface  212 . As described above, the silicone  20  is temperature resistant, and is not easily scrubbed from the grate surface. The glass-ceramic surface  212  remains uncoated on portions accessible to a consumer so that it can be easily cleaned after use in the normal manner, while still being protected from scratching by the coating  20  on the underside of the gas grate.  
         [0022]    While the preferred embodiments of the invention have been described in detail, the invention is not limited to the specific embodiments described above which should be considered as merely exemplary. Further modifications and extensions of the present invention may be developed and all such modifications are deemed to be within the scope of the present invention as defined by the appended claims.