Patent Publication Number: US-2005116385-A1

Title: Method for producing a holding element

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a holding element in an edge area of a molded body, and a method for producing the holding element, wherein the molded body which is of a brittle material is inserted into a molding tool, a material well in the edge area of the molded body is thus formed by the molding tool, the material well is at least partially filled by a plastic material, and then the molded body with the holding element formed on it is taken out of the molding tool.  
      2. Discussion of Related Art  
      A holding element for a cooking surface is known from German Patent Reference DE 197 03 543, wherein the cooking surface is formed as a molded body made of a brittle material. The holding element is of a duromeric material, which is fiberglass-reinforced for improving its characteristic material values.  
      A holder is described in German Patent Reference DE 196 15 371 A1, which is formed on a molded body by an injection-molding process. The material used is a thermoplastic material. In this method the plastic material shrinks greatly during cooling. So that no impermissibly high tensions are caused in the molded body, a shrinkage-absorbing element is used. This is inserted as a separate part into the mold during the injection-molding process and, when the workpiece is finished, is integrated into the holding element.  
      A method for producing extrusion-coated glass panes is known from European Patent Reference EP 98 112 258 A1.  
     SUMMARY OF THE INVENTION  
      It is one object of this invention to provide a method of the type mentioned above but in which a holding element can be efficiently formed on a brittle molded body.  
      This object is achieved with a molded body maintained in the molding tool by a clamping element, wherein a section of the material well is delimited by the clamping element. A sealing element is placed on the molded body in a transition area between the material well and the clamping element, and the plastic material is placed into the material well and sets during an extrusion process.  
      In accordance with this invention, an extrusion process is used for producing the holding element. During this a clamping element, also called a pressure pad, is used for fixing the molded body in place. The sealing element ensures that the material well is securely sealed. It is thus possible to select the pressure applied to the molded body via the clamping element so that there is no danger of the material breaking.  
      Excess pressures can occur at times during the extrusion process. During this, excess plastic material escapes from the area between the clamping element and the molded body. Excess pressures can be prevented by using the sealing element.  
      In accordance with a preferred embodiment of this invention, an adhesive tape is glued as the sealing element to the molded body. The adhesive tape can be applied in an easy manner. Thus the adhesive surface can be designed so that it simultaneously takes over a sealing function.  
      If the sealing element has an elastically and/or plastically deformable effective layer which is deformed by the clamping element, it is possible to compensate irregularities close to the surface of the molded body by the sealing element, which is of particular interest should the molded body have a structured surface.  
      It is possible, for example, to dependably seal structured surfaces, in particular napped surfaces, as with molded bodies of glass-ceramic material.  
      A sufficiently dependable sealing can be achieved if the effective layer has a Shore hardness in a range between 40 and 80, preferably 50 to 70, Shore A, and/or the thickness of the material of the sealing element is selected to lie in a range of 0.1 to 0.5 mm, preferably in a range of 0.2 to 0.4 mm.  
      Good sealing can be achieved if the sealing element is partially displaced into the area of the material well. Thus it is possible to assure generous tolerances for the exactness of the application of the sealing element.  
      In accordance with this invention, the material well is filled with a fiberglass-reinforced duromeric material. The holding element produced by this material is particularly suited for framing cooking surfaces which are temperature-resistant and dimensionally stable and scratch-proof.  
      Following the removal of the molded body from the molding tool, the sealing element can be removed, depending on the product requirements, or can remain on the molded body. If it remains, it is necessary to select the properties of the material so that they meet the use requirements of the molded body.  
      It is possible to achieve good manufacturing results if the width of the sealing element, extension of the sealing element in the direction of the connecting plane of the sealing element with the molded body, is selected to lie within a range of 10 to 25 mm, preferably in a range of 12 to 18 mm.  
      The sealing element must also be capable of absorbing the manufacturing conditions during the manufacturing process. It is thus possible in accordance with this invention to provide the sealing element with a temperature resistance greater than 160° C. The danger of excess pressure is prevented if the distance of the sealing element from the edge of the molded body is selected to lie in a range between 0 and 10 mm, preferably in a range between 1 and 5 mm.  
      The holding element can be formed in the shape of a frame, for example, and can completely surround the molded body. Then the sealing element is positioned to extend around the molded body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      This invention is explained in view of an exemplary embodiment represented in the drawings, wherein:  
       FIG. 1  shows a fastening arrangement with a holding element and a molded body in a lateral and partial view, and  
       FIG. 2  shows the fastening arrangement represented in  FIG. 1  in a manufacturing tool in a lateral view and in section. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
      A molded body  30 , such as a cooking surface, is represented in  FIG. 1 . The molded body  30  includes a brittle material, such as glass, a glass-ceramic or ceramic material. It is embodied in the form of a plate, which is surrounded by a holding element  10  on its edge. Here, the holding element  10  encloses the edge all around. Thus, a leg  14  of the holding element  10  rests on the top  31  of the molded body. A support element  16  extends parallel with the leg  14 , which supports the molded body from below and is placed on its underside  32 . The leg  14  is connected with the support element  16  by a strip  15 . The strip  15  covers the outer edge area of the molded body  30 . The strip  15  is extended by at least one fastening section  17 . The fastening section  17  projects well beyond the support element  16 .  
      As shown in  FIG. 1 , the support element  16  is supported in a partial area via a sealing element  20  on the underside  32  of the molded body  30 . The sealing element  20  is embodied as an adhesive tape and has an adhesive layer  22 , by which it is glued to the underside  32  of the molded body. An effective layer adjoins the adhesive layer  22  and is made of an elastically yielding material. The function of the sealing element  20  will be explained in greater detail later.  
      The leg  14  of the holding element  20  makes a transition into a protrusion  12  via a support section  11 . The protrusion  12  releases a horizontal section of the support section, which results in a sealing receptacle  13 . In the installed state the protrusions  12  is supported on a work plate. The portion of the arrangement located in the area of the strip  15  and the fastening section  17  is inserted into a recess of the work plate. A seal is inserted into the sealing receptacle  13  for sealing the surface of the work plate against the recess.  
      The process for the manufacture of the molded body  30  with the holding element  10  formed on it will be described with reference to  FIG. 2 .  
      A mold with two partial work molds  40 . 1  and  40 . 2  is shown in  FIG. 2 . The lower partial work mold  40 . 2  has an adjusting body  40 . 3  that can be displaced in the vertical direction by guides. The adjusting body  40 . 3  can be clamped by clamping elements  40 . 4  in the direction of its displacement degree of freedom. For forming the holding element  10 , first the sealing element designed as an adhesive tape is glued to the underside  32  of the molded body  30 . Subsequently the molded body  30  is placed into one of the two partial work molds  40 . 1 ,  40 . 2 . Then, the second partial work mold  40 . 1 ,  40 . 2  is placed on it and the mold is closed. Subsequently, the adjusting body  40 . 3  is linearly displaced until it is seated with its adjusting face against the underside  32  of the molded body  30 . Together with the two partial work molds  40 . 1  and  40 . 2 , the adjusting body  40 . 3  encloses a material well located in the edge area of the molded body  30 . The sealing element  20  extends into the area of the material well. At the same time, the sealing element  20  also projects so far inward that the adjusting body  40 . 3  can be supported flush on it. This results in a seal. The manufacture of the holding element is performed by an extrusion process. Thus, a thermosetting material, for example raw SMC material, is placed into the material well. Following the placement of this material and the closing of the two partial work molds  40 . 1 ,  40 . 2 , a pressure is built up in the mold which causes the shaping of the holding element  10 . The sealing element  20  prevents material from being pushed by excess pressure into the area between the underside  32  of the mold body  30  and the contact surface of the adjusting body  40 . 3 . This effect then causes breakage of the brittle molded body  30  if an impermissible large amount of plastic material is pressed out. The sealing element  20  prevents this excess pressure. A certain amount of unevenness of the molded body  30  in the area of its underside  32  can be compensated by the effective layer used for the sealing element  20 , which is embodied to be elastically yielding. In particular, it is possible to even out structured, for example napped undersides  32  of the molded body. Undersides  32  thus structured are used in cooking surfaces, for example.  
      Following a typical setting time of 2 to 3 minutes, the mold is opened and the finished part can be removed. The adhesive tape is partially pressed in during the manufacturing process. The projecting, still visible portion can either be removed thereafter, or can possibly also be left on the underside  32 . Thus the outlay for finishing is clearly reduced. However, care should be taken that the sealing element  20  has the required characteristic material values in order to prevent waste or a visual interference. Thus the sealing element  20  can possibly have a definite transparency, temperature resistance or dimension.