Patent Publication Number: US-5530224-A

Title: System and method for retrofitting cooktops with a ceramic glass cooking surface

Description:
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to ceramic glass cooking surfaces, and more particularly to a system and method of retrofitting existing cooktops and free-standing stoves with a ceramic glass cooking surface. 
     2. Related Art 
     Indoor cooking apparatus have evolved over the years from the open hearth, to wood or coal burning stoves, to more modern natural gas and electric cooktops and free-standing stoves. Microwave ovens, have also become popular for cooking. 
     While virtually all homes are supplied with electricity, there are many that are not supplied with natural gas. Even in homes that are supplied with natural gas, this fuel is often used only for space and water heating, rather than for cooking. Electric kitchen appliances such as free-standing stoves, cooktops and ovens can be installed and used in residential and non-residential settings alike, without the danger of gas leaks. The almost universal availability and convenience of electric power has resulted in the widespread use of electric cooktops. FIG. 1 shows a top view of a typical, well-known, electrical cooking apparatus. 
     Preparation of food at elevated temperatures, such as by frying or simmering, often transfers sufficient kinetic energy to small amounts of the food being prepared that these energetic portions are ejected from the pots or pans and fall onto the cooktop surface. When these food particles land on a burner element they can become &#34;baked-on&#34; and thus difficult to clean. When these food particles land in the well which is formed underneath the burner element, cleaning is again difficult as the burner element itself must be removed to gain access to soiled well region. 0f course, cleaning of the well must wait until the burner element has cooled sufficiently to be safely removed. 
     A conventional approach to this problem is a ceramic glass cooktop that is built-in as a unit in a new stove, or that is installed in a remodeled kitchen after the pre-existing cooktop has been removed. This type of surface is referred to as a &#34;smoothtop&#34; and is formed from a ceramic glass. Typically this ceramic glass is a commercially available material known as CERAN and manufactured by Schott Glaswerke, Hattenbergstrasse 10, Mainz, Germany. Three types of smoothtop, all of the built-in variety, are known today (see FIG. 2). These are the radiant smoothtop, the halogen smoothtop, and the magnetic-induction smoothtop. 
     However, it would be advantageous to have an easy to clean, cooking surface installed without having to remove the pre-existing cooktop. In other words, it would be advantageous to have a retrofit kit for an easy to clean cooking surface installation on an existing stove top. 
     What is needed is a method and apparatus for retrofitting existing cooktops with easy to clean surfaces. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an easy to clean surface, suitable for retrofitting to existing cooktops, as an accessory for existing cooktops and free standing stove units. 
     Briefly, an apparatus having frame members for forming a frame, and at least one smooth-surfaced panel of heat transmissive material, is assembled on-site, to provide an easy to clean surface. In a typical embodiment of the present invention, two symmetrical, rectangular-C shaped frame members form an exterior frame assembly, and four I-beam shaped interior frame members form an interior frame assembly. 
     The rectangular-C shaped members have a longitudinal groove formed on their interior facing surfaces. This groove is typically fitted with a silicone seal which is attached by means of an adhesive. The rectangular-C shaped members also include a portion subjacent the groove that forms the base of the exterior frame, and this portion is referred to as the heat trap. The rectangular-C shaped members further include a portion superjacent the groove that acts as a spill guard. 
     The I-beam shaped interior frame members have one mitered end and one flat end. The flat ends meet the exterior frame members and the mitered ends meet each other in the center of the interior frame assembly. A consequence of the I-beam shape is the presence of two opposite facing, longitudinal, rectangular-C shaped grooves along the length of the interior frame members. The I-beam shaped interior frame members include a conformal silicone seal formed in their opposite facing grooves. 
     To assemble the system of the present invention, a portion of the exterior frame is first established on the cooktop. Ceramic glass panels are installed in that portion of the exterior frame, interior frame members are then installed, further ceramic glass panels may then be inserted into the grooves of the interior and exterior frame members. The final portion of the exterior frame is then established in such a manner that any exposed edges of the ceramic glass panels are fitted into the groove of the final portion of the exterior frame. The exterior frame members are then joined to each other so as to structurally integrate them as a single piece. 
     Other objects and advantages together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a conventional four-burner electric cooktop. 
     FIG. 2 shows a conventional ceramic glass cooktop. 
     FIG. 3 shows the exterior frame members of the frame assembly. 
     FIG. 4 shows the interior frame members as they appear after assembly together with ceramic glass panels inserted into the grooves of the interior frame members, and a temperature-indicating display. 
     FIG. 5 is a cross-sectional view of an exterior frame member. 
     FIG. 6 is a top view of an interior frame member. 
     FIG. 7 is a is a cross-sectional view of an interior frame member. 
     FIG. 8 is an expanded top view showing the relationship of the ceramic glass panels to the interior frame members. 
     FIG. 9 shows the rounded corners of the ceramic glass panels. 
     FIG. 10 shows an alternative embodiment of the present invention wherein a single piece of heat transmissive, easy to clean material is mounted on a stove without the use of a frame assembly. 
     FIG. 11 shows an exemplary thermochroic display pattern. 
     FIG. 12 shows exemplary decorative options possible to assemble with the system and method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Cooktop, range, and stove, are used herein generally interchangeably to refer to apparatus containing thermal energy sources typically used in food preparation. 
     Heating element, burner, burner element and thermal energy source, are used herein generally interchangeably. These terms refer to the heat producing portion of a cooktop, range or stove. Although burner and heating element may be used respectively to describe gas and electric powered thermal energy sources, the term burner or burner element is used throughout this description as a convenient means of referring to a thermal energy source. 
     A stain-resistant, easy to clean member, having a substantially planar surface, is removably attached to a previously installed cooktop or free-standing stove unit by means of a frame assembly. The member has thermal transfer characteristics such that heat is transferred from subjacent heating elements to substantially superjacent portions of the surface, with little lateral transfer of thermal energy. Thermochroic material is incorporated on the visible top surface to provide an indication of the surface heat distribution. The frame assembly includes heat trap and spill guard portions. Although, the preferred embodiment of the present invention is directed to electrically powered cooking apparatus, the invention is not so limited and may be used with combustion powered (e.g., gas burning) cooking apparatus. 
     Referring to FIGS. 3-9, an embodiment of the present invention is described. 
     The present invention utilizes exterior and interior frame members to form a frame assembly that supports, and holds in place, one or more easy to clean panels. In a first embodiment, two symmetrical, rectangular-C shaped frame members 30 form an exterior frame assembly, and four I-beam shaped interior frame members 44 form an interior frame assembly. Frame members 30 and 44 may be made from various materials, such as wood and metal. 
     The outer frame members 30 typically have a groove 52 formed longitudinally on their inner (i.e., interior facing) surfaces. In this way the panels 42 are held in place after insertion therein. The relationship of the groove 52 dimensions to the dimensions of the panels 42 is such that there is adequate space for thermally induced expansion of the panels 42 during cooking. This spacing relationship is true even though the groove 52 is typically fitted with a conformal layer of silicone seal 54 which is attached by means of an adhesive. This adhesive could be a glue or some other means of attachment. The rectangular-C shaped outer frame members 30 also include a portion subjacent the groove that forms the base of the exterior frame, and this portion is referred to as the heat trap 56. The rectangular-C shaped outer frame members further include a portion superjacent the groove that acts as a spill guard 58. 
     The I-beam shaped interior frame members 44 have one mitered end 62 and one flat end 64. The flat ends meet the exterior frame members and the mitered ends meet each other in the center of the interior frame assembly. A consequence of the I-beam shape is the presence of two opposite facing, longitudinal, rectangular-C shaped grooves along the length of the interior frame members. The I-beam shaped interior frame members 44 include a conformal silicone seal 72 formed in their opposite facing grooves. 
     The cooking surface of the panels 42 is not limited to any particular topology, however, it is contemplated that a substantially planar form would be the easiest to fabricate and most convenient for the end user. However, the invention is not limited to planar panels, and crowned, convex, concave, channeled, or other topology surfaces could be used to, for example, direct spilled liquids. 
     FIG. 9 shows panels 42 having rounded corners to enhance handling safety. 
     The frame portion of the frame and panel assembly simply rests upon the cooktop with the panels 42 resting upon the burner elements 48, one of which is shown through the panel 42 in FIG. 4. Alternatively, the panels 42 may be in close proximity to the burner elements without actually being in contact with them. This is possible because the frame is designed to support the entire weight of the panels. 
     Adhesives are not required for attaching the panels 42 to the supporting frame. Further, adhesives are not required to keep the frame assembly attached to the underlying cooktop. Likewise, caulking is not used between the panels 42 and the frame members 30, 44 because the panels 42 are designed to be removed for cleaning. 
     To assemble the system of the present invention, a first exterior frame member 30 is established on a cooktop. Ceramic glass panels 42 are installed in that first exterior frame member 30, a first interior frame member 44 is then installed, between panels 42, such that interior frame member 44 is between panels 42, with panels 42 inserted into the grooves of the I-beam. The interior frame member has its mitered end 62 directed toward the center of the frame assembly, and its flat end 64 directed toward the exterior frame member. Additional interior frame members are installed orthogonal to the first installed interior frame member, with their flat ends toward the exterior frame and their mitered ends toward the center. Further ceramic glass panels 42 may then be inserted into the grooves of the interior and exterior frame members. The final portion of the exterior frame is then established in such a manner that any exposed edges of the ceramic glass panels are fitted into the groove of the final portion of the exterior frame. The exterior frame members are then joined to each other so as to structurally integrate them as a single piece. FIG. 3 shows joining pieces 32 used to secure two rectangular-C shaped outer frame members together via removable wingnuts 33 for quick disassembly. FIG. 5 shows a cross-section of the outer frame member 30, wherein a securing means such as bolt 59, is used in conjunction with joining piece 32 to secure the outer frame members together. 
     FIG. 10 shows the present invention in its simplest form. A single pane of ceramic glass 102 is mounted on top of a cooking apparatus 100. 
     In a second embodiment of the present invention, thermochroic material 46 is applied to the surface of the panels 42, typically in a position toward the peripheral edges of the panels 42 so that the thermochroic material 46 is not directly over a burner element 48. This positioning is chosen because constant placement and removal of pots and pans on the panel 42 in the neighborhood of the underlying burner element 48 would tend to cause excessive wear of the thermochroic material 46. 
     Thermochroic or thermal reactive materials 46 respond to thermal variation by changing their optical characteristics. Some of these material change color, others change from opaque to light transmissive. Thermochroic material 46 is incorporated on the visible top surface to provide an indication of the surface heat distribution. 
     A visible temperature indicator can be built-in to the panels by using a normally opaque thermochroic material 46 that becomes light transmissive within some temperature range that overlaps the temperatures encountered on the cooking surface panels 42, wherein that material covers a temperature display such that portions of the temperature display become visible as the temperature of the glass panel 42 rises above the opaque to transmissive transition temperature. The actual layout of the temperature display/thermochroic material combination can be quite varied. Typically, a substantially straight line emanating from the region of a panel 42 that overlies a burner element 48, heading in the direction of the panel periphery is used. However, FIG. 11 shows another possible configuration wherein a series of rectangles are used. Rather than the thermochroic material becoming clear as shown at 80 and as described above, as shown at 82 the color of each thermochroic panel can change at different temperatures to show a panel temperature. 
     Referring to 
     FIG. 12, a third embodiment of the present invention is shown wherein, panels having different and/or coordinated decorative designs can be used. Decorative panels can be changed to create new designs, or appearances for the cooking surface. This allows cooking surface to help create a number of different ambiances. For example, a Thanksgiving-type pattern, a Christmas-type pattern, or a Fourth of July-type pattern etc., can be used. Additionally, various other design schemes such as landscapes, color combinations, or geometric patterns can be used. 
     While the invention has been described in conjunction with several specific embodiments, it is evident to those skilled in the art that many further alternatives, modifications and variations will be apparent in light of the foregoing description. For example, the smoothtop cooking surface may have some texturing or patterning. Thus the invention described herein is intended to embrace all such alternatives, modifications, applications and variations as may fall within the scope of the subjoined claims.