Description

MOLD APPARATUS FOR FORMING COOKING VESSEL USING FOR INDUCTION RANGE AND THE COOKING

VESSEL

Technical Field

[1] The present invention relates to a cooking vessel for induction ranges, and more particularly to a molding apparatus for die-casting a cooking vessel for induction ranges and a cooking vessel produced thereby. Background Art

[2] Induction ranges are heating means for cooking in which, when an electric current is applied to a coil disposed below the top plate of the induction range, a line of magnetic force is generated in the coil, and only the bottom surface of a cooking vessel placed on the top plate of the induction range is heated using an eddy current which is produced when the line of magnetic force passes through the bottom of the cooking vessel. To be used with the induction range, the bottom surface of a cooking vessel must contain a magnetic material containing an iron (Fe) component. Unlike the bottom surface of the cooking vessel, the body of the vessel is made of a non-magnetic aluminum material, which is inexpensive and widely used for cooking vessels. Heating in the induction range is stopped immediately after the bottom surface of the cooking vessel is removed from the top plate of the induction range, and thus there is no risk of burns resulting from use of the induction range. In addition, the induction range has high thermal efficiency and is harmless to the environment, because the cooking space thereof does not need to be ventilated. Because of such advantages, the induction range is a cooking system that is currently receiving attention.

[3] A cooking vessel which is used for induction ranges is made of two kinds of materials having different properties. Namely, the body of the cooking vessel is made of a non-magnetic material, and the bottom plate of the cooking vessel is made partially of a magnetic material. Efforts to securely attach such different materials to each other have recently been made. For example, the bottom plate includes a magnetic plate (or a heating plate; hereinafter the same) made of stainless steel (SUS 430) having an iron component, and methods for attaching the same are as follows.

[4] First, there is a method of attaching the heating plate by high-frequency thermal melting. However, this method has a problem in that, because the thermal strain of the material of the heating plate differs from that of the body, the heating plate readily separates from the body when it is used for a long period of time.

[5] Second, a die-casting method is also used, when the vessel body is made of

aluminum. However, this method has problems in that it is difficult to securely attach the magnetic plate to the inside of a mold and to accurately maintain the flatness of the magnetic plate. Attempting to solve such problems, Korean Patent Registration No. 10-0534490 discloses a method comprising primarily die-casting a magnetic plate, and then secondarily die-casting the primarily die-cast magnetic plate in a mold. However, this method has a problem in that the die-casting must be carried out twice.

[6] Also, in Korean Patent Registration No. 10-0402929, there is a fatal problem in that a magnetic plate is exposed to the top surface of the bottom plate of a cooking vessel due to an elastic protrusion.

[7] Attempting to solve such problems, Korean Patent Registration No. 10-0611646 discloses a technology in which several metal foils made of the same material as that of the body of a cooking vessel are prepared, placed in a mold and melted at the temperature of a melt so as to be integrated with each other and in which a magnetic plate is supported and fixed in the mold by the metal foils. However, this technology has problems in that the melt pouring rate must be lowered in order to position the metal foils at correct positions, leading to a reduction in working speed, and in that the technology is not suitable for mass production, because it requires manual operation. Disclosure of Invention Technical Problem

[8] The present invention has been made in order to solve the above-described problems occurring in the prior art, and it is an object of the present invention to provide a mold apparatus which can securely attach a non-magnetic vessel body and a magnetic bottom plate (hereinafter referred to as "heating plate") to each other, which are made of two different materials, using a die-casting process. Specifically, it is an object of the present invention to enable the heating plate to be securely fixed at a correct position in a mold during the pouring and solidification of a melt and to allow rapid pouring of the melt and mass production and to enlarge the effective area of the heating plate, thus increasing the thermal efficiency (or heating value) thereof. Technical Solution

[9] The foregoing object of the present invention is accomplished by a molding apparatus for forming a cooking vessel for induction ranges by casting or die casting, the cooling vessel comprising a non-magnetic body and a magnetic heating plate attached to the bottom surface of the body, the molding apparatus comprising an upper mold and a lower mold, which define a cavity when they are closed together, wherein a plurality of magnets are disposed at the bottom surface of the inside of the upper mold, such that the heating plate can be attached to the bottom of the upper mold by magnetic force, the magnets being samarium cobalt (SmCo) or alnico permanent magnets having

a magnetic transition temperature (i.e., Curie point) exceeding the operating temperature of the mold (400-500 ⁰ C).

[10] Specifically, the object of the present invention is accomplished by allowing the magnetic heating plate to be attached to the inside of the mold using the physical properties of the magnetic heating plate, that is, by inserting the magnets into the die- casting mold such that the heating plate is attached to the inside of the mold by the magnets during the pouring and solidification of the melt. Herein, the magnets must be made of a material having a magnetic transition temperature (i.e., Curie point) exceeding at least the operating temperature of the molds (400-500 ⁰ C), and preferably the melting point of aluminum (about 660 ⁰ C).

[11] According to another characteristic of the present invention, the magnets are ejected from the mold at the time point of mold release, such that it is necessary to reduce or remove the magnetic force which is applied to the heating plate before mold release.

[12] Using the above-described molding apparatus, a cooking vessel for induction ranges is provided which comprises a non-magnetic vessel body and a magnetic heating plate which is buried in and attached to the bottom surface of the vessel body.

[13] According to still another characteristic of the present invention, there is provided a molding apparatus for forming a cooking vessel for induction ranges by casting or die casting, the cooling vessel comprising a non-magnetic body and a magnetic heating plate attached to the bottom surface of the body, the molding apparatus comprising upper and lower molds which define a cavity when they are closed together, wherein a plurality of magnets are disposed at the bottom of the inside of the upper mold, the apparatus further comprising a vacuum forming means capable of sucking out air. Brief Description of the Drawings

[14] FIG. 1 is a cross-sectional view of a molding apparatus according to an embodiment of the present invention.

[15] FIG. 2 is a perspective view of a heating plate, FIG. 3 is a top view of FIG. 2, and

FIG. 4 is a cross-sectional view taken along line A-A of FIG. 3.

[16] FIG. 5 is a cross-sectional view sequentially showing the operating state of the molding apparatus.

[17] FIG. 6 is a cross-sectional view of a molding apparatus according to a second embo diment of the present invention.

[18] FIG. 7 is a cross-sectional view sequentially showing the operating state of the molding apparatus of FIG. 6.

[19] FIG. 8 is a top view of a heating plate 22' that is used in the second embodiment.

[20] * Description of important reference numerals used in the figures *

[21] 2: molding apparatus; 4: upper mold;

[22] 6: lower mold; 16: magnets;

[23] 20: magnet fixing bolts; 22 and 22': heating plate;

[24] 24: ascending and descending plates; 28: first long holes;

[25] 32: second long holes; 50: air hole;

[26] 52: nipple; 54: air hose.

Mode for the Invention

[27] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a molding apparatus according to an embodiment of the present invention. FIG. 2 is a perspective view of a heating plate, and FIG. 3 is a top view of FIG. 2. FIG. 4 is a cross-sectional view of the heating plate, taken along line A-A of FIG. 3. FIG. 5 is a cross-sectional view sequentially showing the operating state of the molding apparatus.

[28] Aluminum and alloys thereof have good castability, and thus are processed into precise products having good surface properties by a conventional die-casting process. As shown in FIG 1, a molding apparatus 2 is broadly divided into an upper mold 4 and a lower mold 6. The upper mold 4 may include a cavity core 8 and an upper core 10, and the lower mold 6 may include a stripper 12 and an insert core 14. The name and specific shape of each element are not the subject matter of the present invention.

[29] The subject matter of the present invention is a structure in which magnets 16, particularly permanent magnets, are inserted in the upper mold 4. The cross-sectional views shown in FIGS. 1 and 5 were prepared with respect to the centerline of the molding apparatus for convenient understanding and were taken along line B-B with respect to a heating plate 22.

[30] For this purpose, a plurality of magnet insertion holes 18 are vertically provided in the upper mold 4 (particularly the upper core).

[31] Magnet fixing bolts 20 may be inserted into the magnet insertion holes 18 by screw coupling, and the magnets 16 are screw-coupled to the tops of the magnet fixing bolts 20. The magnets 16 may be in the form of rods having screw threads tapped therein. Accordingly, the magnets 16 can be easily separated from or inserted into the mold, if necessary.

[32] The magnet fixing bolts 20 and the magnets may be coupled to each other by a screw coupling method or other various coupling methods. The magnets 16 may be exposed to the internal bottom 4a of the upper mold or buried in the upper mold 4 to a given depth. Accordingly, the heating plate 22 can be attached to the bottom 4a of the upper mold by magnetic force.

[33] Although the number of magnets 16 inserted has been shown to be six (see FIG. 3), the scope of the present invention is not limited thereto. The diameter of the magnets

16 may also be selected within a broad range.

[34] According to the embodiment of the present invention, some or all of the magnet fixing bolts 20 are fixed to ascending and descending plates 24, such that they can move upward and downward according to the ascent and descent of the plates 24. The magnet fixing bolts 20 can move just like eject pins. Herein, the magnet fixing bolts 20 must be inserted into the magnetic insertion holes 18 in such a manner that they can freely move upward and downward in the upper mold 4.

[35] As shown in FIG. 5, only magnetic fixing bolts 20' provided for positioning are ejected from the upper mold 4 by the ascending and descending plates 24.

[36] According to the present invention, the magnets 16 must be made of a material having a magnetic transition temperature (i.e., Curie point) exceeding the operating temperature (400- 500 ⁰ C) of the mold. Furthermore, the Curie point of the material of the magnets 16 is preferably higher than the melting point of aluminum (about 660 ⁰ C). Thus, the selection of the material of the magnets is critical to the present invention.

[37] According to the present invention, a samarium cobalt(SmCo) magnet or an alnico magnet is recommended. The alnico magnet is an alloy of aluminum (Al) -nickel (Ni)-cobalt (Co)-iron (Fe) which has excellent temperature properties and is frequently used if precision is required. The samarium cobaltmagnet is composed of samarium and cobalt at a given blend ratio and also has excellent temperature properties.

[38] In the central portion of the upper mold 4, a conventional sprue 26 (melt inlet) is provided. A process for producing a cooking vessel using the above-described molding apparatus will now be described with reference to cross-sectional views shown in FIG. 5.

[39] As shown in FIG. 5 (a), in the state in which the upper and lower molds 4 and 6 are separated from each other, the heating plate 22 is interposed between the molds and attached to the magnets 16 inserted in the upper mold. Then, as shown in FIG. 5(b), the molds are closed together, and as shown in FIG. 5(c), an aluminum melt C is poured into the closed molds through the sprue 26. The melt C is poured up to the portion indicated by hatching. After a given time but immediately before separation of the molds, as shown in FIG. 5(d), some of the magnet fixing bolts 20' and magnets 16 are ejected by the ascent of the ascending and descending plates 24. This is performed in order to remove magnetic force from the heating plate 22 or reduce the magnetic force, thus allowing the upper mold to be easily released from the lower mold 6. The reason why the magnetic force is reduced (or removed) as described above is to prevent the adhered portion of the heating plate 22 from being damaged by impact during mold release, because a cooking vessel V is at a high temperature during mold release.

[40] Then, if the cooking vessel is released from the molds after being solidified as shown in FIG. 5(d), the heating plate 22 is buried in and fixed to the bottom surface Vl of the

cooking vessel by insert injection. Then, a portion protruded from the bottom surface Vl is finished by polishing so as to provide a flat surface. In this way, the cooking vessel for induction ranges in which the heating plate 22 of a magnetic material is securely attached integrally to the bottom Vl of the vessel body V2 made of a nonmagnetic material is completed. The vessel body V2 is preferably made of a high- purity aluminum material, such that it is harmless to the human body.

[41] According to the present invention, the heating plate 22 is securely attached to the inside of the mold, and thus the casting process may also be carried out by a pressure casting process in addition to the gravity casting process shown in FIG. 5. Namely, the scope of the present invention is not limited to the casting process shown in FIG. 5.

[42] Hereinafter, the heating plate 22 that is used in the present invention will be described in detail with reference to FIGS. 2 to 4. The heating plate 22 is a thin metal plate material made of a magnetic material and may be an iron plate or aluminum- plated steel plate having excellent heat resistance, high-temperature corrosion resistance and the like. Preferably, the heating plate may be made of stainless steel, for example, SUS430, SUS410S or ASTM TP 409. Namely, among stainless steels, ferromagnetic ferrite stainless steel is used for the heating plate.

[43] As the magnetic material, iron (Fe) is typically used, but in some cases, cobalt, nickel or an alloy thereof may also be used as the material of the heating plate. Namely, any material may be used for the heating plate 22 as long as it is a magnetic material. However, it is more preferable to use a magnetic material having good processability, a thermal strain rate similar to that of the body of a cooking vessel together with corrosion resistance and heat resistance.

[44] The heating plate 22 preferably has a thickness of 0.5-5 mm, and a plurality of first and second arc-shaped long holes 28 and 32 are perforated in the heating plate along the circumferential direction. Aluminum will be filled in the first and second long holes 28 and 32, and thus the adhesion strength of the heating plate to the bottom surface of the vessel will be increased. The number of the long holes 28 and 32 in the cooking vessel that is produced by the inventive molding apparatus does not need to be larger than that in a cooking vessel according to the prior art. Namely, according to the present invention, the area of the heating plate 22 remaining after exclusion of the first and second long holes 28 and 32 can be increased, and thus there is provided a cooking vessel having a structure whose heating value or thermal efficiency can be further increased.

[45] For reference, six small circles S defined by the dotted line in FIG. 3 denote portions at which the magnets 16 are located when attached to the inside of the mold. In the center of the heating plate 22, a melt passage hole 30 is provided.

[46] The second long holes 32 are provided outside the first long holes 28 in the circum-

ferential direction in order to position the magnets 16. The second long holes 32 may be perforated as shown in the figures, but they may also be press-punched such that they are stepped with respect to the reference plane of the heating plate 22 at a slight depth.

[47] The second long holes 32 function to impart magnetic force and to accurately and easily position the center of the heating plate in the mold (see FIG. 1). Accordingly, the width of the second long holes 32 correspond to the diameter of the magnets 16.

[48] The specific shape of the heating plate 22 is not critical to the present invention.

Those skilled in the art can modify the shape of the heating plate 22 into various shapes, if necessary, and all the modified shapes will be within the scope of the present invention.

[49] Hereinafter, a molding apparatus according to another embodiment of the present invention will be described with reference to FIGS. 6 to 8.

[50] FIG. 6 is a cross-sectional view of a molding apparatus according to a second embodiment of the present invention. FIG. 7 is a cross-sectional view sequentially showing the operating state of the molding apparatus. FIG. 8 is a top view of a heating plate 22' that is used in the second embodiment. However, the cross-sectional views of FIGS. 6 and 7 are not accurate cross-sectional views and were prepared with respect to the center line of the molding apparatus for the convenience of description. FIGS. 6 and 7 are cross-sectional views taken along line C-C of FIG. 8 with respect to the heating plate 22'.

[51] The molding apparatus according to this embodiment further comprises a vacuum forming means which applies negative pressure together with the magnets 16 so as to allow the heating plate 22' to be adsorbed and fixed to the top surface of the upper mold. The vacuum forming means may include: an air hole 50 which perforates through the upper mold 40 in a vertical direction; and an air tube or air hose 54 which is connected with a nipple 53 fixed to the upper portion of the upper mold 4, so as to communicate with the air hole 50. To the air hose 54, a conventional vacuum motor (not shown) is connected.

[52] As shown in the figures, the lower end of the air hole 50 that comes into contact with the heating plate 22' is enlarged in the form of a funnel so as to enlarge the adsorption area of the air hole, such that the heating plate is well adsorbed thereto. The diameter of the air hole is sufficiently variable.

[53] The molding apparatus in which such a vacuum forming means is used together with the magnets will now be described with reference to FIG. 7. FIG. 7 (a) shows the state in which the molds were closed together and the heating plate 22' was fixed to the bottom surface of the upper mold 4. The magnetic force of the magnets and the adsorption force caused by negative pressure simultaneously act on the top surface of

the heating plate, and thus the heating plate 22' is securely attached to the bottom surface of the upper mold 4. The portions of the heating plate on which the magnetic force acts are indicated by the circular dotted line S in FIG. 8, and the portions of the heating plate on which the adsorption force acts are indicated by another dotted line S' in FIG. 8. The points S on which the magnetic force acts and the points S' on which the adsorption force acts may be arranged in a pair.

[54] In this state, as shown in FIG. 7(b), an aluminum melt is injected into the mold. After the melt is somewhat injected, the magnet fixing bolts 20 may be moved upward as shown in FIG. 7(c). This upward movement is performed in order to allow the melt to also be injected into the second long holes 32. The movement length of the magnet fixing bolts 20 may also be greater than the thickness of the heating plate 22'. In this case, the melt will be filled to a level higher than the heating plate 22', and thus a portion protruded from the surface of the heating plate can be finished by polishing after solidification (see FIG. 7(d)). The details relating to the ascent and descent of the magnet fixing bolts 20 by the ascending and descending plates 24 are also applied to the above-described embodiment and may be modified in a variety of ways. For example, as shown in FIG. 7(d), only the magnet fixing bolts 22' may be ejected from the upper mold.

[55] In the solidification process or the mold release process, the negative pressure applied through the air hole 50 may be removed. As shown in FIG. 7(d), the mold release process is followed by a surface finishing process.

[56] This embodiment is characterized in that the heating plate 22' is fixed to the inside of the mold using two kinds of forces. The two kinds of forces mutually complement the drawbacks of each other and, at the same time, act in cooperation with each other. This is an embodiment for providing a molding apparatus for forming a cooking vessel for induction ranges, which has reduced shortcomings. Industrial Applicability

[57] As described above, according to the present invention, the heating plate can be easily attached to the inside of the die-casting mold at a correct position. Because the adhesion strength of the heating plate to the inside of the mold can be improved by increasing the number of magnets attached, the heating plate can be securely fixed to the inside of the mold. Accordingly, even when physical impact is applied to the heating plate due to the pouring of a melt, the heating plate can remain fixed at the correct position. Thus, operating speed can be increased, and a pressure casting process may also be used. In addition, the present invention provides a molding apparatus for forming a cooking vessel for induction ranges, which may also be used in a robot- automated process, and thus is suitable for mass production. Also, the present

invention provides a cooking vessel produced by the molding apparatus. [58]