Glass or glass ceramic plate with a safe edge and method for the manufacture thereof

In a glass or glass ceramic plate for a kitchen appliance the safe edge is to be improved. This safe edge is formed by a rounded rim ( 5 ) having a thickness greater than that of the plate ( 1 ), which merges integrally and seamlessly with the plate ( 1 ).

A glass plate 1 has a planar upper side 2 , as a cook surface for example, and a plane-parallel bottom 3 of a conventional thickness D. It can also be imagined, however, that the upper surface departs in some areas from the planar form in order to accommodate working elements or form functional areas. This applies especially to switch areas or gas burner lead-throughs or the like. At the margin 4 of the glass plate the safe edge is in the form of a cross-sectional profiled portion 5 thicker than the thickness D of the plate 1 , which merges integrally and seamlessly with the top side 2 and bottom side 3 . In the transition zone or zones a hollow curvature 6 , 6 ′, is formed. The profiled portion 5 is rounded at its end face 7 such that no sharp edges are on it. In an upper area 5 ′ the profiled portion 6 , in the embodiment in FIG. 1 , is higher than the top surface 2 by the difference H 1 , and in a lower area 5 ″ it is lower than the bottom side 3 by the difference H 2 . The differences H 1 and H 2 are approximately 1 to 5 mm. They are preferably less than the thickness D of the plate 1 . In zone 5 ′ of the profiled portion there is a convex curve 8 which merges with the curvature 6 . In zone 5 ″ of the profiled portion there is a concave round 9 which merges with the curvature 6 ′. Between round 8 and hollow round 6 and/or round 9 and hollow round 6 ′ flattened areas 10 , 10 ′ (cf. FIG. 4 ) can be formed, which are parallel or approximately parallel with the upper side 2 and bottom side 3 , respectively. The flattened areas 10 , 10 ′ in turn merge via rounds 11 with the hollow rounds 6 , 6 ′. The flattened areas 10 can improve the possibilities for mounding or fastening the plate 1 to or in a baking or roasting oven. In the embodiment shown in FIG. 2 the area 5 ′ of the profiled portion projects by the amount H 1 above the top side 2 of plate 1 . The profiled portion 5 merges level with the bottom side 3 at a rounded edge 12 . Vice versa, in the embodiment in FIG. 3 the profiled portion zone 5 ″ projects below the bottom side 3 ; the profiled portion 5 merges level with the top side 2 . In the embodiments according to FIGS. 2 and 3 the flattened areas 10 and 10 ′ described above can be provided, respectively. The profiled portion 5 in the embodiments according to FIGS. 5 and 6 is provided all around the four margins of the glass or glass ceramic plate 1 . The height (difference H 1 ) of the continuous circumferential profiled portion 5 at its upper level 5 ′ (cf. FIG. 1 , FIG. 2 , FIG. 4 ) creates on the top side 2 , which forms a cooking or baking surface, a recess to contain any liquid issuing from cooking or baking utensils. In common cook surfaces made of glass ceramic plates, the cooking surface, i.e., the top side 2 , has an area of about 50 cm×60 cm, or 3000 cm 2 . In the case of a difference H 1 of about 3 mm, the capacity is about 900 cm 3 , i.e., nearly 1 liter. So any amount of liquid up to about 1 liter leaking onto the cook surface will collect without running over the margin 4 or profiled portion 4 and without penetrating into seams or corners. Any leakage can easily be absorbed with a sponge or a cloth, and a thorough, hygienic cleaning is not difficult. As a result of the difference in level between the lower profiled portion zone 5 ″ (cf. FIG. 1 , FIG. 3 and FIG. 4 ) and the bottom side 3 , the plate 1 can be shelved with its bottom side 3 raised. At the round 6 ′ a circumferential, elastic gasket 14 (shown in broken lines in FIG. 3 ) can be installed which, especially in a kitchen oven with a glass ceramic plate, will prevent the penetration of liquid into the space below the bottom 3 , in which electrical radiant heaters or gas-fueled radiant heaters are usually disposed. At the same time the profiled portion zone 5 ″ covers the gasket 14 so that it is hardly visible if at all from the front end 7 . Mounting the gasket 14 in the area of the round 6 ′ helps to retain it so that it will not slip out when it is necessarily compressed when it is installed. The plate 1 can be affixed, by cementing for example, at its profiled portion zone 5 ″ or at the bottom side 3 , to a substructure of the oven. In the embodiment in FIG. 6 , in contrast to FIG. 5 , the comers 15 of the glass plate 1 are rounded. The profiled portions 5 can here again easily be made continuous all around, which is hardly possible, or possible only at great expense, in the state of the art with a frame made of separate components. In the embodiment in FIG. 7 , in contrast to the embodiments in FIGS. 5 and 6 , thickened profiled portions 5 are provided only at two opposite, parallel margins 4 of the glass plate 1 . The profiled portions 5 can be configured as described in connection with FIGS. 1 to 4 . The glass plate 1 in FIG. 7 can be used as a shelf which can be inserted into a bake oven or a refrigerator, in which case the profiled portions 5 are intended to lie upon guide means. Since its profiled portion 5 ′ serves as framing or safe edgeing function, the glass or glass ceramic plate described has especially the following advantages: a) No frame of separate components needs to be provided and cemented or clipped to the plate 1 . b) There are no seams between the profiled portion 5 and the plate as such, in which hard-to-remove dirt or remnants of liquids can collect. c) The connection between the plate 1 and the profiled portion 5 is permanent and not subject to the aging of adhesives. d) Direct fastening of the plate 1 at the profiled portion 5 to a supporting structure of a cook oven is possible. e) A concealed gasket and fastening of the plate 1 to a supporting structure is possible. f) The profiled portion 5 increases the stability of the plate 1 and improves its impact strength. g) Stresses due to temperature changes do not occur between the glass plate 1 and its margin 4 because the glass plate 1 and the profiled portion 5 consist of the same material. h) A drip-catching capacity is easily arranged for liquid falling on the upper side 2 of the glass plate, combined with ease in cleaning. i) A space can be arranged between a supporting surface and the glass plate 1 . The profiled portion 5 is made on the plate 1 approximately as follows: A glass plate 1 rolled flat and appropriately shaped is heated in the green state and to prevent thermal tensions it is additionally heated in its marginal area and upset or shaped in the marginal area by means of a shaping tool so as to form the profiled portion 5 . Then the glass plate is brought out of its green state in an additional process step, especially by heat treatment and/or ceramization, to its finished state.