Method for spherodizing molten cast iron and ladle for use in the spherodizing

Abstract: A novel method for spherodizing molten cast iron is disclosed. A cover made of a porous body containing continuous blow holes is mounted at the upper portion of ladle main body containing spherodizing material therein, and spherodizing is effected by pouring molten metal into the ladle main body through the porous body cover. Preferably the cover has a porous body containing continuous blow holes mounted and is partly cut away, and spherodizing is effected by pouring molten metal into the ladle main body through the cut portion of the cover. A ladle preferably used for practicing the novel method for spherodizing molten cast iron is also disclosed.

Description: BACKGROUND OF THE INVENTION: Field of the Invention: The present invention relates to a method for spherodizing molten cast iron available for producing ductile cast iron, and a ladle for use in spherodizing of molten cast iron to be used in the same method for spherodizing. Description of the Prior Art: In the case of spherodizing molten cast iron to produce ductile cast iron, it is a common practice to use the conventional ladle in the prior art or to use a ladle provided with a reaction chamber. Upon production of ductile cast iron, in order to change a state of graphite in a metallurgical structure from a flake state to a nodular state, spherodizing is effected by adding or inserting spherodizing material into molten metal. As the above-mentioned spherodizing method, a set pouring method in which spherodizing material is preliminarily added into a ladle and then molten metal is poured into the ladle, and a candy method in which spherodizing material of block type (candy type) is inserted into molten metal within a ladle and thereby spherodizing is effected, have been known. The spherodizing process according to the set pouring method in the prior art is shown in Fig. 17, and the spherodizing process according to the candy method in the prior art is shown in Fig. 18. In the set pouring method in the prior art illustrated in Fig. 17, a necessary amount of spherodizing material 2 is preliminarily disposed within a ladle main body 1, and cover material 8 for suppressing the reaction is disposed above the spherodizing material 2. Molten metal 4 for producing ductile cast iron within a smelting furnace is poured into the ladle main body 1 and spherodizing of the molten metal 4 is effected. In the candy method in the prior art illustrated in Fig. 18, after the molten metal 4 for producing ductile cast iron has been poured into the ladle main body 1 by about 60%, for example, of the ladle capacity, a cover 8 for preventing splash of molten metal provided with a candy rod 9 having spherodizing material (candy) 2 of block type is set on the ladle main body 1. Thereafter, spherodizing of the molten metal 4 is effected by inserting the spherodizing material 2 of block type into the molten metal 4. In the above-described method for spherodizing molten metal for producing ductile cast iron in the prior art, a violent flash of light and a large amount of white smoke would be generated, and not only it greatly deteriorates the environment within a factory, but also it becomes a social problem as a generating source of a public hazard. In addition, upon abrupt reaction of the spherodizing material, due to violent bubbling phenomena of the molten metal, not only spherodizing of molten metal of the amount of only about 60% of the capacity of the ladle for receiving the molten metal can be effected, but also the risk of generating a hazard due to splash of the molten metal is large, and so, the method involves problems also in view of safety. As a method for resolving these problems, a method of handling the entire ladle almost as a sealingly closed pressure vessel to carry out spherodizing, has been also invented, but it has not yet been brought into practical use, because a workability is very poor and the effect is not sufficient. There is known from "Gießerei-Praxis" (1982), page 260 a tundish-cover-method in which the cover at the upper portion of the ladle main body is in fact a tundish having a through hole for pouring molten metal into the ladle main body. The cover is firmly bolted to the ladle main body. Exact alignment of the cover with the ladle main body and firm sealing are necessary in order to prevent blow-up of the molten metal to the outer side. The entire construction is somewhat complicated as it is also the handling thereof because said cover must be exchanged after a working day or after at least 50 runs. Moreover, there is the risk that molten metal splashes out at the spherodizing because a pressure balancing open port is provided. Furthermore, there is known from "Gießerei-Praxis" (1981), pages 487, 488 a method for spherodizing molten cast iron using a Tea Pot-ladle. The ladle main body is partitioned into a molten metal receiving section and a spherodizing section. The spherodizing section is closed by a cast iron plate which is firmly secured to the upper end of the spherodizing section. Said cast iron cover plate comprises a closable opening for pouring the molten metal into the molten metal receiving section. Also here exact alignment of the cover with the ladle main body and firm sealing are necessary in order to prevent blow-up of the molten metal to the outer side. Finally, there is known from WO-A-8 807 403 a ceramic foam filter for filtering molten metal, in particular iron and iron alloys. The filter is prepared from a ceramic slip containing silicone carbide and a colloidal silicon dioxide binder. Said filter is not provided for a method for spherodizing molten cast iron. It is one object of the present invention to provide a method for spherodizing molten cast iron, which can entirely resolve the problems of public hazards, deterioration of an environment within a factory, dangerous works and a pour workability (complexity and difficulty). The said object is achieved according to one embodiment of a method for spherodizing molten cast iron according to the present invention as defined by claim 1. In an other embodiment of the present invention, the said object is achieved by a method for spherodizing molten cast iron as defined by claim 3. According to the present invention as defined by claim 1, fine particles of white smoke generated upon spherodizing are captured, also the white smoke is suppressed from dispersing to the outside, at the same time produced gas is discharged to the outside to lower the gas pressure within the ladle main body, and also splash of molten metal can be prevented. According to the present invention as defined by claim 3, when pouring molten cast iron into the ladle main body through the cover, said cover prevents slag from entering jointly into the ladle main body and so, only molten cast iron is poured into the ladle. Within the ladle main body, the molten cast iron and the spherodizing material come into contact, resulting in a chemical reaction, and a violent flash of light and a large amount of white smoke (principally composed of MgO) are generated, but fine particles of MgO and the like in the white smoke are captured and adsorbed by the cover, and thereby dispersion of the white smoke into the atmosphere is greatly suppressed. On the other hand, gas produced within the ladle main body as a result of the reaction between the molten cast iron and the spherodizing material, is discharged into the atmosphere through the cover, hence the gas pressure within the ladle main body is lowered and bubbling of molten cast iron is prevented, and in addition, a risk of molten cast iron splashing is almost perfectly eliminated. The present invention will now be described by reference to the following description of preferred embodiments of the invention taken into conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS: In the accompanying drawings: Figure 1 is a longitudinal cross-section view of a first preferred embodiment of the present invention; Figure 2 is a plan view of the same preferred embodiment; Fig. 3 is a longitudinal cross-section view of a second preferred embodiment of the present invention; Fig. 4 is a plan view of the same preferred embodiment; Fig. 5 is a longitudinal cross-section view of a third preferred embodiment of the present invention; Fig. 6 is a plan view of the same preferred embodiment; Fig. 7 is a longitudinal cross-section view of a fourth preferred embodiment of the present invention; Fig. 8 is a plan view of the same preferred embodiment; Fig. 9 is a perspective view of a fifth preferred embodiment of the present invention; Fig. 10 is a longitudinal cross-section view of a ladle in the same preferred embodiment; Fig. 11 is a longitudinal cross-section view of an essential part of the same preferred embodiment; Figs. 12 and 13 are longitudinal cross-section views of essential parts of sixth and seventh preferred embodiments of the present invention; Fig. 14 is a perspective view of an eighth preferred embodiment of the present invention; Fig. 15 is a plan view of the same preferred embodiment; Fig. 16 is a longitudinal cross-section view of the same preferred embodiment; and Figs. 17 and 18 are cross-section views illustrating a method for spherodizing molten cast iron according to a set pouring method and a candy method, respectively, in the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENTS: Now, a first preferred embodiment of the present invention will be described with reference to Figs. 1 and 2. After a necessary amount of spherodizing material 2 has been disposed at a predetermined position within a ladle main body 1 (if necessary, cover material could be disposed over the same spherodizing material 2), a cover 3 made of a porous body containing continuous blow holes (for instance, a gas-permeable heat-resisting filter having a three-dimensional network structure) is mounted over the entire surface of the upper portion of the ladle main body 1. In this preferred embodiment, the ladle main body 1 is disposed in the proximity of a smelting furnace 10, molten metal 4 for producing ductile cast iron within the smelting furnace 10 is poured onto the porous body 3 having continuous blow holes, and the molten metal 4 is poured into the ladle main body 1 as passing through the cover 3 made of a porous body. Within the ladle main body 1, the poured molten ductile cast iron 4 and the spherodizing material 2 come into contact, and as a result of a chemical reaction, violent and a large amount of smoke and flash are generated. The above-mentioned cover 3 of a porous body having continuous blow holes prevents slag from mixing into the molten ductile cast iron 4 when it is poured into the ladle main body 1, and also it captures and adsorbs fine particles of MgO and the like in the white smoke produced at the time of spherodizing, and greatly suppresses dispersion of the white smoke into the atmosphere. In addition, since gas produced within the ladle main body 1 can be easily discharged into the atmosphere owing to the fact that the cover 3 of a porous body having continuous blow holes has gas-permeability, a gas pressure within the ladle main body 1 is extremely lowered, hence in cooperation with screening by the cover 3 made of a porous body, a risk of splashing of molten metal would be almost eliminated, also generation of bubbling of molten metal would be prevented, and so, a large amount of molten metal can be poured into the ladle main body 1. In this preferred embodiment, as the cover 3 of a porous body having continuous blow holes, a ceramic porous body having a three-dimensional network structure (silicon carbide: virtual specific gravity 0.35 - 0.55, percentage of voids 80 - 90%, number of cells 6/25 mm□) is used as a heat-resisting filter, and spherodizing of molten cast iron of FCD400 of 50 kg was tested, and as a result, an amount of generation of white smoke could be suppressed to about 1/10 of that in the heretofore known method, also, splash of molten metal upon reaction could be eliminated. Next, a second preferred embodiment of the present invention will be described with reference to Figs. 3 and 4. A ladle main body 1 is partitioned into a reaction section 1a and a molten metal receiving port 5 by means of an upper partition wall 6 made of refractory, which extends downwards from the upper edge of the same ladle main body 1 and has a bottom end positioned as spaced upwards from the bottom surface of the ladle main body 1. In the above-mentioned reaction section 1a is provided a lower partition wall 7 rising from its bottom surface to form a reaction chamber 1b on one side thereof, and a cover 3 made of a porous body containing continuous blow holes (for instance, a heat-resisting filter having a three-dimensional network structure) is mounted so as to cover the upper portion of the reaction section 1a. The above-mentioned molten metal receiving port 5 expands sideways so that the cross-section shape of its upper portion may form a V-shape as shown in Fig. 4, also it opens upwards, and thus it has a configuration for facilitating to receive molten metal. Within the above-described reaction chamber 1b is disposed spherodizing material 2 (if necessary, cover material could be disposed on the same spherodizing material 2. In this preferred embodiment, molten metal 4 for producing ductile cast iron within a smelting furnace 10 is poured through the opened portion at the top of the above-mentioned molten metal receiving port 5, and this molten metal falls within the molten metal receiving port 5 and is poured into the reaction section 1a. In this case, since the molten metal receiving port 5 has a configuration for facilitating to receive molten metal from the smelting furnace 10 as described above, pouring of molten metal can be effected easily. As a result of that the molten metal 4 for producing ductile cast iron and the spherodizing material 2 come into contact within the reaction chamber 1b, flash and white smoke are generated. The generated white smoke is dispersed into the atmosphere as passing through the cover 3 made of a porous body having gas-permeable continuous blow holes. At that time, fine particles of MgO and the like in the white smoke are almost captured and adsorbed by the cover 3 made of a porous body containing continuous blow holes, hence generation of white smoke can be greatly suppressed, further, produced gas within the reaction section 1b, which is produced by the above-described reaction, also passes through the cover 3 made of a porous body having continuous blow holes, resulting in lowering of a gas pressure within the reaction section 1b, and generation of splash of molten metal as well as bubbling of molten metal can be prevented. In addition, by the above-mentioned upper partition wall 6, out-flow of the reaction gas at the time of spherodizing from the reaction section 1a to the side of the molten metal receiving port 5 can be suppressed. A third preferred embodiment of the present invention will be described with reference to Figs. 5 and 6. A ladle main body 1 of this preferred embodiment has its molten metal receiving section 5 enlarged and also the configuration of the ladle main body 1 is designed in a horizontal drum type as shown in Figs. 5 and 6 for the purpose of facilitating pouring of molten metal 4 for producing ductile cast iron within a smelting furnace 10 as well as pouring of molten metal into a mold not shown, and except for the configuration of the ladle main body 1, this preferred embodiment has a similar construction to that of the above-described second preferred embodiment. In this preferred embodiment also, similarly to the above-described second preferred embodiment, the effects of suppression of white smoke, prevention of splash of molten metal, prevention of bubbling of molten metal, easiness of work, etc. can be pointed out, and also, owing to the large molten metal receiving section 5, the works of pouring of the molten metal 4 for producing ductile cast iron into the ladle main body 1 as well as pouring into a mold can be facilitated. A fourth preferred embodiment of the present invention will be described with reference to Figs. 7 and 8. In this preferred embodiment, the upper partition wall 6 in the above-described second preferred embodiment shown in Figs. 3 and 4 is formed of a porous body having continuous blow holes (for instance, a gas-permeable heat-resisting filter having a three dimensional network structure). This preferred embodiment can achieve the functions and effects possessed by the above-described second preferred embodiment, and also, owing to the upper partition wall 6 made of a porous body having continuous blow holes, it can further lower the gas pressure of the space within the ladle main body 1. In this preferred embodiment, as a result of that a ceramic porous body having a three-dimensional network structure (blend type of cordielite and alumina, virtual specific gravity 0.35 - 0.60, percentage of voids 80 - 90%, number of cells 13/25 mm□) was used as the porous body cover 3 and the upper partition wall 6 and spherodizing of 500 kg of molten metal of FCD400 was carried out, discharge of white smoke to the atmosphere could be almost suppressed, and splash of molten metal could be also prevented. It is to be noted that in the above-described respective preferred embodiments, as the porous body having continuous blow holes, a ceramic porous body having a three-dimensional network structure such as silicon carbide, blend type of cordielite and alumina, or the like can be used. A fifth preferred embodiment of the present invention will be described with reference to Figs. 9 to 11. In this preferred embodiment, a cover 13 made of metal covering the reaction section 1a of the ladle main body of the above-mentioned third preferred embodiment is provided, and the inside of an opening 13a (slag removing port) of the same cover 13 is filled with a porous body 16 having continuous blow holes which consists of fine lumpy coke 12. As a result of that fine lumpy coke shown in Table-1 was used as this porous body 16 and spherodizing of 500 kg of molten metal of FCD400 was carried out, like the above-described respective preferred embodiments, discharge to the atmosphere of white smoke at the time of spherodizing could be almost suppressed, and splash of molten metal could be prevented. It is to be noted that in the case where fine lumps of vermiculite, perlite, shirasu-balloon (pumice stone), etc. was employed as the porous body having continuous blow holes, also nearly similar results were obtained. A sixth preferred embodiment of the present invention will be explained with reference to Fig. 12. In this preferred embodiment, in place of the porous body having continuous blow holes of the above-described fifth preferred embodiment, a porous body 26 having continuous blow holes formed by laminating 8 to 10 sheets of wire nets 23 made of stainless steel (size of meshes of a net: 0.75 m/m and 1.50 m/m) in various combinations and applying refractory (for instance, alumina powder + Georgian kaolin + PVA solution, casting mold wash, or the like) to its surface, was used. In this preferred embodiment also, the effects of suppressing white smoke and preventing splash of molten metal can be obtained. A seventh preferred embodiment of the present invention will be described with reference to Fig. 13. In this preferred embodiment, in place of the porous body having continuous blow holes of the above-described fifth preferred embodiment, a porous body formed by mixing ceramic balls and small pieces of fibrous refractory (for instance, glass wool, silica wool, etc.), adjusting a percentage of voids thereof to 50 - 90%, and sealingly enclosing the prepared binderless refractory in a wire net box 33 made of stainless steel (size of meshes of a net: 0.75 m/m) is used as a porous body 36 having continuous blow holes. In this preferred embodiment also, the effects of suppressing white smoke and preventing splash of molten metal similar to those of the above-described fifth and sixth preferred embodiments can be obtained. Finally, an eighth preferred embodiment of the present invention will be described with reference to Figs. 14 to 16. In this preferred embodiment, the porous body cover and the molten metal receiving section of the ladle main body in the third preferred embodiment are modified in the following manner. That is, a ceramic porous body 46 having continuous blow holes (silicon carbide, virtual specific gravity 0.35 - 0.55, percentage of voids 50 - 90%, number of cells 20/25 mm□) was filled in an opening 13a of a metallic cover 13 similar to that of the above-described fifth to seventh preferred embodiments. In addition, for the purpose of facilitating the ladle main body 1 to receive molten metal, a box-shaped molten metal receiving section 45 is provided, also a strainer 40 is disposed under the same molten metal receiving section 45, and thereby it was tried to prevent mixing of impurities and discharge of white smoke. In this preferred embodiment, as a result of execution of spherodizing of 700 kg of molten metal of FCD500, an effect of suppressing discharge of white smoke to the atmosphere as well as an effect of preventing splash of molten metal were remarkable, and a yield of magnesium was also greatly improved. In addition, lowering of a temperature of molten metal was also small as compared to the method in the prior art, and improvements in quality could be also achieved. As will be obvious from the detailed description of preferred embodiments above, the present invention as claimed can provide the following advantages owing to the fact that a cover made of a porous body containing continuous blow holes is mounted to a ladle main body in which spherodizing of molten cast iron is carried out: (1) A discharged amount into the atmosphere of white smoke produced at the time of reaction between molten cast iron and spherodizing material can be greatly suppressed, and so, the invention is effective for improvement of an environment and counter-measure against public hazard. (2) A gas pressure within a ladle having received molten metal at the time of reaction between molten cast iron and spherodizing material can be decreased, and by reducing splash of molten metal, safety is improved. (3) By reducing an amount of splash of molten metal (bubbling), a ladle main body can be small-sized. (4) As compared to a ladle associated with a top cover in the prior art, according to the present invention, a ladle can be made light in weight, and also a maneuvability is good. In addition to the above-mentioned advantages, according to the present invention as claimed in Claim 3, owing to the fact that molten cast iron is poured into the ladle main body as passing through the cover made of a porous body, slag would not mix with the molten metal, and hence, quality of the produced ductile cast iron can be improved. Also, according to the present invention as claimed in Claim 1, owing to the fact that molten metal is poured into the ladle main body through a cut portion of the cover made of a porous body, pouring of the same molten metal can be carried out in a short period of time and easily. The present invention can achieve the following effects because of the fact that a porous body having continuous blow holes is disposed at the whole or a part of the upper portion of the ladle for performing spherodizing of molten cast iron: (1') A discharged amount into the atmosphere of white smoke produced at the time of reaction between molten cast iron and spherodizing material can be greatly suppressed, and so, the invention is effective for improvement of an environment and counter-measure against public hazard. (2') A gas pressure within a ladle having received molten metal at the time of reaction between molten cast iron and spherodizing material can be decreased, and jointly with a screening effect by a porous body, a safety is improved by reducing splash of molten metal. (3') By reducing an amount of splash of molten metal (bubbling), a ladle main body can be small-sized. (4') As compared to a ladle for receiving molten metal associated with a top cover in the prior art, a ladle can be made light in weight, and also a maneuvability is good. (5') Owing to the fact that molten metal can be poured into the ladle main body as passing through the cover made of a porous body, slag would not mix with the molten metal, and hence, quality of the produced ductile cast iron can be improved. Owing to the fact that the inside of a ladle main body is partitioned into a molten metal receiving section and a spherodizing section and a cover made of a porous body containing continuous blow holes is provided at the upper portion of the spherodizing section, the above-described effects (1') to (4') can be achieved, also pouring of molten metal into the ladle main body can be carried out easily, and so, a workability is improved. Owing to the fact that the partition wall for partitioning the molten metal receiving section from the spherodizing section is formed of a porous body containing continuous blow holes, in addition to the above-mentioned effects of the present invention, the effects of lowering a gas pressure in the space within the molten metal receiving section, preventing white smoke from dispersing to the outside and preventing splash of molten metal can be further enhanced. While a principle of the present invention has been described above in connection to a number of preferred embodiments of the invention, it is intended that all matter contained in the above description and illustrated in the accompanying drawings shall be interpreted to be illustrative and not as a limitation to the scope of the present invention.

Claims: A method for spherodizing molten cast iron, comprising partitioning the interior of a ladle main body (1) by a partition wall (6) into a molten metal receiving section and a spherodizing section containing spherodizing material therein, said both sections being connected through a partition wall opening with each other at a lower portion, a cover (3) made of a porous body containing continuous blow holes with a three-dimensional network structure provided at the whole or a part of the upper portion of said spherodizing section, with spherodizing is effected in the spherodizing section by pouring the molten metal into the molten metal receiving section. A method for spherodizing molten cast iron as claimed in claim 1, characterised in that a porous body containing continuous blow holes is employed as the partition wall (6) for partitioning the molten metal receiving section from the spherodizing section. A method for spherodizing molten cast iron, comprising mounting a cover (3) made of a porous body containing continuous blow holes with a three-dimensional network structure at the upper portion of a ladle main body (1) containing spherodizing material therein, and spherodizing is effected by pouring molten metal into the ladle main body (1) through said porous body cover (3).

Inventors: HIROAKI SANO, HIROO SATO, KIYOTAKA NAGAI, TAKASHI YASUKUNI, HIROAKI, SANO, HIROO, SATO,, KIYOTAKA, NAGAI, TAKASHI, YASUKUNI, Hiroaki, Sano, c/o Mihara Machinery Works, HIROO, SATO, (DECEASED), Kiyotaka, Nagai, c/o Mihara Machinery Works, Takashi, Yasukuni, c/o Mihara Machinery Works
Applicants: MITSUBISHI HEAVY IND LTD, TOYO DENKA KOGYO CO LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA, TOYO DENKA KOGYO CO., LTD.
Application year: 1991
Main classification: C21C1
IPC codes: C21C1