A LID MADE OF GLASS FOR A COOKING PAN AND THE LIKE AND A METHOD OF MANUFACTURE THEREOF

Abstract: A lid made of glass for a cooking pot, pan, or the like and a method of manufacture thereof are disclosed, wherein the lid includes a peripheral edge (4) of a particular shape formed from a roundly-cut glass blank (1) by rotating either the glass blank (1) or a thermally-resistant forming roller (2) relative to the other and the method provides such a lid having the features described above. For the purposes of the invention, the forming roller (2) is provided adjacent to the glass blank (1) and includes at least one peripheral recess (5, 6, 11) on the side facing the glass blank (1) so that the peripheral edge (4) in its softened state can be formed to conform to the particular shape of the at least one peripheral recess (5, 6, 11) under the pressure of the forming roller (2) when it is brought closer to the glass blank (1). An additional thermally-resistant nipping roller means includes two rolls (10a, 10b) for engaging the formed peripheral edge (4) therebetween and reforming it to a particular shape. Finally, the formed glass blank (1) is formed by any applied heating so that it can have a curved surface.

Description: The present invention relates to a lid made of glass for use with a cooking pan, pot, or the like, and a method of manufacture thereof. The lid allows the user to check to see how cooking is progressing. Description of the Prior Art When a cooking pan, for example, is used for any cooking purposes, the pan is usually covered with its lid during the cooking process. Whenever it is required to check to see how the contents are being cooked, the lid must be removed from the pan. As this is inconvenient, it is desirable that the contents being cooked inside the pan can be monitored from the outside without removing the lid. In order to meet the above needs, there are already lids made of glass that have been offered in a variety of kinds. For practical uses, those conventional glass lids have a different construction, e.g.: (1) one lid is made of a round glass blank formed to present a curved or bulged surface having its peripheral edge fitted with an annular metal ring; (2) another lid is made of a metal base formed similarly and having a small see-through glass window mounted usually around its central area; and (3) a third lid is totally made of molded glass. The above-listed conventional lids have their own problems including those involved in the process of forming the respective lids and therefore those associated with the products obtained through the respective forming processes. Specifically, the problems may be listed for each of those lids, as follows: (1) The first-mentioned lid, which is formed to provide a bulged surface having a metal ring mounted around the peripheral edge thereof, may have a good visibility and may be obtained through a relatively simplified process. However, the presence of the peripheral metal ring has a problem in several respects. As the contents are being boiled inside the pan, part of the contents, such as soup, may boil over, entering the joint between the peripheral edge of the glass and the metal ring. That portion of the contents which has entered the gap between the two parts cannot be removed by the usual water cleaning, and remains there permanently as dirty solids. This raises a hygienic problem as well an an appearance problem. An example of such a lid is disclosed in European Patent Application EP-A-0173418. (2) The second-mentioned lid, which consists essentially of a formed metal base with a central glass window mounted, provides a narrow field of view into the pan. It is apparent that as this limits the view, it is impossible to see the interior of the entire pan. This construction also has the similar problem as described in the item (1) above, since it allows part of the boiling-over soup to enter the joint where the glass window is mounted, and produces the same hygienic problem. (3) The last-mentioned lid, whose construction is totally made of an appropriately molded glass, may be advantageous over the first two constructions in that it has no problems as described above. Instead, there is a different problem associated with its forming process, which employs a particular metallic mold. The problem is that the glass lid obtained by molding usually presents irregularities on its surface, and an image may be viewed as distorted when the contents are seen through the lid. Furthermore, the glass material must be molded to a shape that can meet the particular requirements for the shape of a pan on which the lid is to be seated. Specifically, a glass blank must be molded to the shape having a peripheral edge that exactly and snugly fits the corresponding peripheral edge of the pan when the lid is seated on the pan. Thus, a metallic mold must meet the particular dimensional and shape requirements. This requires a complex mold, which costs a lot. Usually, the molding process must be followed by a tempering process so that the molded glass can have more strength. For practical purposes, however, it is difficult to pass the molded glass through a tempering process, because the lid is not thick enough to sustain the tempering process. Thus, the molded glass is usually finished as a product without any tempering process. If a tempering process is required so that the molded glass can have the practical strength requirements, it will have to have a greater thickness, which would make the lid heavier and less transparent. A simple method for finishing a peripheral edge is discussed in DE-A-1596486. However, this method does not relate to a method of manufacture of a lid made of glass. SUMMARY OF THE INVENTION The present invention has been developed as a result of careful study of the problems of the above mentioned prior art. It is therefore a principal object of the present invention to provide a lid made of glass for a kitchen pot, pan, and the like and a method of manufacture thereof. According to an embodiment of the invention, a lid made of glass can be produced at less coat, and the lid thus obtained can have a good transparency and can be kept clean at all times. According to the present invention, there is provided a method of manufacture of a lid made of glass for a cooking pan and the like, as described in the appended claims to which reference is hereby directed. (1) In one embodiment of the invention a glass blank is cut to a round shape for forming a lid, after which its peripheral edge is heated to between 820°C and 840°C until it becomes soft. (2) A thermally-resistant forming roller is provided adjacent to the glass blank which is supported on its axis, and includes a peripheral recess of a particular shape in conformity to which the peripheral edge is to be formed when the forming roller is applied with force to the peripheral edge of the glass blank. The forming of the peripheral edge is accomplished by either rotating the glass blank on its supported axis, or causing the forming roller to travel along the stationary glass blank (for example at the rate of 12 turns per minute); (3) A thermally-resistant nipping roller is also provided, which includes two hot-press rolls between which the peripheral edge of the glass blank is sandwiched. Then, one of the two rolls presses the peripheral edge toward the other roller opposite it, thus reforming it to its correct shape from which any warps or other defects have been removed; (4) The glass blank is finally formed to provide a curved or bulged surface like an actual lid under applied heating of 650°C to 700°C; (5) Optionally and preferably, the glass may pass through any suitable tempering process so that it can have more mechanical strength. The glass blank is initially heated to between 820°C and 840°C to allow its peripheral edge to soften evenly. This is prerequisite to the following forming process, which may be done by either rotating the glass on its supported axis with regard to the stationary forming roller, or causing the forming roller to travel along the peripheral edge of the glass blank. The peripheral edge in its softened state may be given the particular shape which conforms to the shape of the peripheral recess in the forming roller, by forcing the forming roller to press the peripheral edge toward the center of the glass blank. The forming roller is provided for free rotation, and can provide a uniform shape to the peripheral edge while rotating with the rotating glass blank or traveling along the stationary glass blank. At this stage, the formed peripheral edge of the glass blank may possibly contain local thick portions that may be caused by the surface tension of the fused glass or the whole glass blank contain warps or undulations. In either case, those problems may be corrected by using the nipping roller. That is, any local thick portions around the peripheral edge or any warps or undulations though the whole glass blank may be removed by rotating the glass blank with its peripheral edge sandwiched by the nipping roller. After those defects have been removed, the glass blank passes through any suitable hot-press shaper where it is shaped by heating to provide a curved surface like a lid. In order to give the glass more strength, the tempering process (such as chemical tempering, water-mist tempering, air-blast tempering, etc.) may optionally be used. Preferably, it should be used. BRIEF DESCRIPTION OF THE DRAWINGS Those and other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments, which are shown by way of example and that will follow with reference to the accompanying drawings, in which: Figs. 1 through 5 illustrate a first preferred embodiment of the present invention, in which Fig. 1 is a general plan view of a glass blank cut to a round shape; Fig. 2 is a partly enlarged section view of a forming roller for use with the method of the invention where the relationship between the glass blank and forming roller is shown to illustrate how the peripheral edge of the glass blank is to be formed by the forming roller; Fig. 3 is a partly enlarged sectional view showing the relationship between the glass blank and a nipping roller; and Fig. 4 is an overall sectional view of the glass blank after it has been formed through the preceding steps of Fig. 2 and 3. Fig. 5 is a partly enlarged sectional view showing how a leg portion of the glass blank which is to be seated on a pan, pot or the like is to be formed. Figs. 6 through 8 illustrate a second preferred embodiment of the present invention, in which Fig. 6 is partly enlarged sectional view showing the relationship between the forming roller and glass blank; and Fig. 7 is a partly enlarged sectional view showing the relationship between the nipping roller and glass blank; and Fig. 8 is an overall sectional view of the glass blank after it has been formed through the preceding steps of Figs. 6 and 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to Figs. 1 through 5, a first preferred embodiment of the present invention is described in detail. The description is provided in the order of those figures shown in which the method of the invention is to be performed. In Fig. 1, a glass blank 1 and a forming roller 2 are shown schematically from which the relative positions of those two may be seen. The glass blank 1 is firstly cut to any suitable shape, usually a round shape, as shown, for forming a lid. It is preferably 1 to 10 mm thick, and has a central aperture 3 into which a knob (not shown) is to be mounted. Then, the glass blank is suppoted on a suitable support (not shown) so that it can rotate about its own axis acting as a fulcrum. The forming roller 2 is located beside the glass blank 1 so that the roller 2 can both turn on its axis and travel along the peripheral edge 4 of the glass blank, and can also travel closer to and away from the glass blank. When the forming roller 2 is brought closer to the glass blank, it can exert a force or pressure on the peripheral edge 4 for forming it to a particular shape. A heater (not shown) is provided for heating the peripheral edge 4 of the glass blank 1 to about 830°C Fig. 2 shows the forming roller 2 in relation to the glass blank 1. As may be appreciated from Fig. 2, the glass blank 1 has its peripheral edge 4 formed to the shape conforming to the particular shape provided by the forming roller 2 when the latter applies force or pressure to the peripheral edge 4. In the one preferred form shown, the forming roller 2 has a first recess 5 and an adjacent second recess 6 on its peripheral side facing the glass blank 1, the first recess 5 extending deeply inwardly and the second recess 6 extending less deeply inwardly. As an initial step, the forming roller 2 is brought closer to the glass blank 1 until it engages the peripheral edge 4 of the glass blank 1. Then, an edge portion 7 formed between the first and second recesses 5 and 6 is brought in alignment with the longitudinal center line of the peripheral edge 4 of the glass blank 1 and is also brought in contact with the peripheral edge 4. When the forming roller 2 gradually travels further toward the glass blank 1, it applies force to the glass blank 1, forming the peripheral edge 4 in its softened state to the shape that conforms to the shape defined by the first and second recesses 5 and 6, that is, a shape including an outer rim 8 that projects upwardly and an inner rim 9 that projects downwardly. As the forming of the inner rim 9 may occur in such a way that it includes an inwardly curled part, a burner 13 may be provided to face the inwardly curled side of the rim 9 (Fig. 5). The rim 9 can be correctly formed on the glass blank by heating its curled part. After the outer rim 8 and inner rim 9 are completely formed by rotating either the glass blank or the forming roller relative to the other, the forming roller 2 is moved back away from the glass blank 1, and then a nipping roller 10 is moved closer to the glass blank. Fig. 3 shows the nipping roller 10 which engages the formed peripheral edge of the glass blank. As shown, the nipping roller 10 includes a first roll 10a and a second roll 10b, between which the outer rim 8 of the peripheral edge of the glass blank 1 is sandwiched. In this condition, the first roll 10a is gradually pushed down toward the second roll 10b opposite it (or the second roll 10b may be operated similarly), and those two rolls cooperate to remove the raised part of the outer rim 8. Thus, the outer rim 8 becomes substantially flat, and any warps and/or undulations over the whole glass blank can be removed. If desired, the nipping roller 10 may be provided with any suitable pattern by engraving or the like. In this way, this pattern may be copied to the peripheral edge of the glass blank. The glass blank 1 whose peripheral edge has been formed and from which any warps, etc. have been removed is then passed through any suitable hot-press shaper (not shown), for example, which provides a curved surface for the glass blank as a whole. An example of a curve surfaced glass lid is shown in Fig. 4. This glass lid may further pass through any suitable tempering process. In this case, the usual tempering process for glass may be employed, whereby the glass is initially heated to a temperature of 700°C, and then is rapidly cooled to 300°C by water or the like. The glass lid thus obtained and shown in Fig. 4 is called the "double type" lid in the relevant industry. When this type of lid is placed on its pan (not show) or the like, its downwardly projecting inner rim 9 is located inside the pan, and its outer rim 8 is seated on the peripheral edge of the pan so that it can cover the whole pan. A second preferred embodiment of the present invention is shown in Figs. 6 through 8. As shown in Fig. 6, a forming roller 2 is varied to include a single recess 11 on its peripheral side facing the glass blank to be formed. The recess 11 has a substantially roundly-shaped end like a letter "U" in cross section. Similarly to the preceding embodiment the forming roller 2 is brought closer to the glass blank 1 until it engages the peripheral edge 4 in a softened state of the glass blank 1. Thus, the peripheral edge 4 is formed to provide a shape like a bead conforming to the shape of the recess 1. After the peripheral edge 4 has been formed. The forming roller 2 is removed and then the nipping roller 10 is brought closer to the glass blank 1 until its first roll 10a and second roll 10b engage the formed peripheral edge 4. Similarly to the preceding embodiment, the first roll 10a is gradually pushed down toward the second roll 10b opposite it, pressing the bead-formed peripheral edge 4 until its upper side becomes slightly flattened, as shown in Fig. 7. The glass blank having its peripheral edge formed in the above manner passes through any suitable hot-press shaper, for example, as for the preceding embodiment, where the glass blank is shaped to provide a curved surface. An example of the thus obtained lid is shown in Fig. 8. The glass lid obtained through the steps described above is called the "single type" lid in the relevant industry. This type of lid is used with a pan or the like that is provided with a peripheral stepped seat inside it, on which the lid is placed. Similarly to the preceding embodiment, the formed glass blank may pass through any suitable tempering process, and may be given more strength under the same conditions as for the preceding case. For both of the preferred embodiments, either the glass blank may be rotated on its axis with the stationary forming roller engaging the peripheral edge of the rotating glass blank as described, or the forming roller may travel around the stationary glass blank with the peripheral edge of the latter engaged by the forming roller. As may be appreciated from the foregoing description, the present invention provides the following advantages and merits: (1) The lid can be completed without using any metal parts. A complete cleaning of the lid is made possible without any dirty solids, such as boiling-over soup, that might otherwise remain on the lid. Thus, this enables the lid to be kept clean without causing any hygienic problem. (2) The lid is made only of transparent glass, which provides a good see-through function. (3) The lid can be obtained simply by forming the glass blank to the shape of the lid, which makes the lid less costly. (4) The tempering process can allow a thin glass blank to be used. Thus, a lighter lid can be obtained. (5) The forming of the peripheral edge to the particular shape makes that part mechanically strong. Although the present invention has been described by reference to the specific preferred embodiments, it should be understood that various changes and modifications may be made without departing from the scope of the invention as defined in the appendant claims.

Claims: 1. A method of manufacturing a lid of glass for a kitchen pan, pot, or the like, comprising the steps of: cutting a glass blank (1) to a suitable round shape for forming a glass lid, said glass blank (1) including a peripheral edge (4), and forming said glass blank (1) to a curved surface by heating the same; characterised in that said peripheral edge (4) is formed to a particular shape by: supporting the glass blank (1) on its axis, and providing thermally-resistant forming roller means (2) adjacent to said glass blank (1), said forming roller means (2) including at least one peripheral recess (5, 6, 11) of said particular shape on the side facing said glass blank (1); heating said peripheral edge (4) of said glass blank (1) to a required softening temperature and thereby allowing the same to soften; engaging said at least one peripheral recess (5, 6, 11) of said forming roller means (2) with said peripheral edge (4) in its softened state and causing relative rotary motion of said glass blank (1) and said forming roller means (2) with regard to each other, thereby forming said peripheral edge (4) of said glass blank (1) to conform to said particular shape of said at least one peripheral recess (5, 6, 11) of said forming roller means (2) by forcing said forming roller means (2) to press said peripheral edge (4) toward said glass blank (1); engaging thermally-resistant dual-roll nipping roll means (10a, 10b) with said formed peripheral edge (4) of said glass blank (1), and forcing one of the two rolls (10a, 10b) of said nipping roller means to press said formed peripheral edge (8, 12) of said glass blank (1) between said two rolls (10a, 10b) in the direction of the width of said peripheral edge (4). 2. A method as defined in Claim 1, wherein the step of forming said peripheral edge (4) of said glass blank (1) includes the step of forming said peripheral edge (4) to conform to a shape including a rim (9) depending downawardly from said peripheral edge (4). 3. A method as defined in Claim 1, wherein the step of forming said peripheral edge (4) of said glass blank (1) includes the step of forming said peripheral edge (4) to conform to a shape including an inner rim (9) depending downwardly from said peripheral edge (4), and also including an outer rim (8). 4. A method as defined in Claim 1, wherein the step of forming said peripheral edge (4) of said glass blank (1) includes the step of forming said peripheral edge (4) to conform a shape like a bead (12) of round cross section. 5. A method as defined in any one of Claims 1 to 4, wherein the step of causing the relative rotary motion of said glass blank (1) and said forming roller means (2) includes the step of causing said glass blank (1) to turn on its supported axis relative to said forming roller means (2). 6. A method as defined in any one of Claims 1 to 4, wherein the step of causing the relative rotary motion of said glass blank (1) and said forming roller means (2) includes the step of causing said forming roller means (2) to travel around said peripheral edge (4) of said glass blank (1). 7. A method as defined in any one of Claims 1 to 6, wherein the step of forming said glass blank (1) to provide a curved surface by heating is performed by using hot-press shaping means. 8. A method as defined in any preceding claim wherein the step of forming said peripheral edge (4) to a particular shape comprises the use of said forming roller means (2), wherein said forming roller means (2) is so configured that it comprises a first recess (5) and an adjacent second recess (6), said first and second recesses (5, 6) being disposed on the peripheral edge of said roller means (2), said second recess (6) being less deep than said first recess (5). 9. A method as defined in any one of claims 1 to 7, wherein the step of forming said peripheral edge (4) to a particular shape comprises the use of said forming roller means (2), wherein said forming roller means (2) is so configured that it comprises a single recess (11) disposed on its peripheral edge, said recess (11) being substantially U-shaped in cross-section.

Inventors: KAWAMURA, MORIO
Applicants: KAWAMURA GLASS MANUFACTURING CO., LTD.
Application year: 1988
Main classification: A47J36
IPC codes: C03B23, A47J36