TW202227205A - Filler sand - Google Patents

Abstract

Provided is filler sand with which it is possible to increase a sintering initiation temperature, and to inhibit the penetration of molten steel. The filler sand contains chromite. The filler sand contains secondary particles 10. The secondary particles 10 contain a plurality of primary particles 12. The particle sizes of the plurality of primary particles 12 are greater than 0 micrometers and at most 50 micrometers. At least some of the plurality of primary particles 12 contained in the secondary particles 10 contain chromite. Preferably, the abovementioned primary particles 12 contain at least 20 wt% and less than 50 wt% Cr2O3, and at least 10 wt% and less than 30 wt% FeO.

Description

filled sand

The present invention relates to the invention of packed sand. In particular, the present invention relates to the invention of packing sand suitable for filling in sliding nozzles.

Ladle refers to a container for receiving molten steel. The bottom of the ladle is provided, for example, with a sliding nozzle. The sliding nozzle discharges the molten steel contained in the ladle. Before the molten steel is loaded into the ladle, the interior of the sliding nozzle is filled with refractory filler sand. The packing sand is filled in order to prevent the molten steel from solidifying in the sliding nozzle. After the molten steel is loaded into the ladle, when the sliding nozzle is opened, the filling sand will fall naturally. When the filling sand falls, the molten steel in the ladle will flow out from the sliding nozzle. Hereinafter, the fact that molten steel can flow out from the discharge path by falling of the filling sand filled in the discharge path of the ladle bottom is referred to as "natural opening". If natural openings cannot be generated, it becomes necessary for the operator to manually drop the filling sand. This work is hazardous work. Moreover, in the case where the operator has to manually drop the filling sand, the discharge of the molten steel from the ladle becomes slow. At this time, the molten steel will come into contact with the air. If molten steel comes into contact with air, it may adversely affect its quality. The occurrence of such adverse effects can lead to damage. Therefore, it is desired to realize the filled sand with a natural open porosity of 100%.

Patent Document 1 discloses packed sand. The packed sand will foul at the ladle tap. The filling sand system prevents the molten steel from solidifying in the tap hole. In the packed sand, the weight % of SiO ₂ is 98 weight % or more. In this packed sand, the weight % of the alkali metal oxide is less than 1 weight %. The packing sand system disclosed in Patent Document 1 can suppress the phenomenon that the packing sand does not flow out even if the sliding nozzle is opened.

Patent Document 2 discloses packed sand. The filled sand is formed by blending 10 to 50 wt % of silica sand and 50 to 90 wt % of chromite sand. The silica sand contains 95% by weight or more of particles with a particle size of 0.425 mm or more and less than 1.18 mm. The chromite sand contains 95% by weight or more of particles with a particle size of 0.075 mm or more and less than 0.85 mm. Among them, 0.106 mm or more but less than 0.212 mm is 10 wt % or more, and 0.3 mm or more and less than 0.6 mm is 30 wt % or more. With the packed sand disclosed in Patent Document 2, even with a low chromite sand content, a high natural porosity can be obtained in the high-temperature and long-term treatment accompanied by out-of-furnace refining. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 64-48662 [Patent Document 2] Japanese Patent Laid-Open No. 2006-198671

[The problem to be solved by the invention]

The packed sand disclosed in Patent Document 1 has a problem in that the improvement of the natural porosity is limited. This is due to the limitation on the improvement of the natural porosity, although it can prevent sintering, it will cause the molten steel to penetrate into the voids between the grains. When reducing the concentration of SiO ₂ or adding low-melting substances, the particles of the filling sand will be filled with molten substances. Thereby, penetration of molten steel is prevented. However, when the concentration of SiO ₂ is reduced or low melting point substances are added, the sintering of the packed sand can occur when the packed sand is exposed to high temperature for a long time. Packed sand that has been sintered will become non-porous.

The packed sand disclosed in Patent Document 2 also has a problem in that the improvement of the natural porosity is limited. It is due to the limitation in the improvement of the natural porosity. Although a high natural porosity can be obtained, the initiation of sintering in a high temperature environment cannot be avoided. In order to obtain a higher natural porosity, it is necessary to increase the sintering initiation temperature even higher.

The present invention solves the above-mentioned problems. An object of the present invention is to provide a filling sand which can increase the sintering initiation temperature and suppress the penetration of molten steel. [means to solve the problem]

In order to solve the above-mentioned problems, the packed sand described in claim 1 of the present invention contains chromite. The packed sand contains secondary particles. The secondary particles include plural primary particles. These plural primary particles have a particle diameter of more than 0 micrometers and 50 micrometers or less. At least a part of the plural primary particles contained in the secondary particles contains chromite.

In addition, the packed sand of claim 2 of the present invention is characterized by adding the invention according to claim 1, and wherein the secondary particles contain 20 wt% or more and less than 50 wt% of Cr ₂ O ₃ and 10 wt % The above content is less than 30% by weight of FeO.

In addition, the packed sand of claim 3 of the present invention is characterized by adding the invention described in claim 2, and wherein the weight % of Cr ₂ O ₃ is 37.1 wt % or more and 46.3 wt % or less, and the weight % of FeO is 21.1% by weight or more and 26.4% by weight or less.

In addition, the packed sand of claim 4 of the present invention is characterized by adding the invention according to any one of claim 1 to claim 3, and wherein the secondary particles include particles with a particle size exceeding 106 microns and 1180 microns or less. Particles, the particle size of which exceeds 106 microns and 1180 microns or less accounts for 90 wt % or more and 100 wt % or less in the weight % of the packed sand.

In addition, the packed sand of claim 5 of the present invention is characterized by adding the invention as set forth in claim 4, and wherein particles with a particle size exceeding 106 microns and 1180 microns or less account for 95 weight % or more of the packed sand Among the particles with a particle size of more than 106 microns and below 1180 microns, the particles with a particle size of more than 300 microns and below 850 microns account for 53 wt % or more and 77 wt % or less of the filled sand. [Inventive effect]

The filling sand system of the present invention can increase the sintering initiation temperature and suppress the penetration of molten steel.

Hereinafter, embodiments of the present invention will be described based on the drawings. In the following description, the same code|symbol is attached|subjected to the same component. The names and functions of these are the same. Therefore, detailed descriptions about them are not repeated.

[The composition of filling sand] FIG. 1 is a conceptual diagram showing the configuration of the secondary particles 10 contained in the packed sand of the present embodiment. The packed sand of the present embodiment contains the secondary particles 10 . The secondary particles 10 include a plurality of primary particles 12 . The particle diameters of the plurality of primary particles 12 are more than 0 micrometers and 50 micrometers or less. At least a part of the plurality of primary particles 12 contained in the secondary particles 10 contains chromite.

Preferably, the primary particles 12 contain 20 wt % or more and less than 50 wt % of Cr ₂ O ₃ and 10 wt % or more and less than 30 wt % of FeO.

Preferably, the weight % of the aforementioned Cr ₂ O ₃ is 37.1 wt % or more and 46.3 wt % or less, and the aforementioned FeO weight % is 21.1 wt % or more and 26.4 wt % or less.

It is preferable that the above-mentioned secondary particles 10 include particles with a particle size exceeding 106 microns and below 1180 microns. The particles with a particle size of more than 106 micrometers and less than 1180 micrometers account for 90% by weight or more and 100% by weight or less in the filled sand.

It is preferable that the above-mentioned particles with a particle size exceeding 106 microns and below 1180 microns account for 95 wt % or more and 100 wt % or less in the weight % of the packed sand. Among the particles with a particle size of more than 106 microns and below 1180 microns, the particles with a particle size of more than 300 microns and below 850 microns account for 53 wt % or more and 77 wt % or less of the packed sand.

It is preferable that the above-mentioned secondary particles 10 contain a binder 14 . The type of the binder 14 is not particularly limited. The weight % of the binder 14 in the secondary particles 10 and the packed sand is not particularly limited. Examples of the binder 14 include water, organic solvents, inorganic binders, and organic binders.

Preferably, the above-mentioned adhesive 14 is an organic solvent, or an organic adhesive dissolved in an organic solvent. The reason why an organic solvent or an organic binder dissolved in an organic solvent is preferable as the binder 14 is that the secondary particles 10 do not retain moisture if the binder 14 contains moisture. Examples of organic binders include starch, dextrin, protein, natural rubber, tar, thermoplastic resin, and thermosetting resin. An example of starch is corn starch. Examples of proteins are gum, casein, soy protein. Examples of natural rubber include latex and arabic rubber. Examples of tars include pitch and processing tars. Examples of thermoplastic resins include ethylene, polyvinyl alcohol, polyvinyl butyral, acryl, polyamide, polyethylene, and cellulose. Examples of thermosetting resins include urea, melamine, phenol, furan, epoxy, polyester, and polyurethane.

[Manufacturing method of filled sand] The manufacturing method of the packed sand of this embodiment is not specifically limited. For example, the packed sand system of the present embodiment can be produced by the method described below. This method includes: a raw material mixing and pulverizing step S40, a granulation step S42, and a particle size distribution adjustment step S44.

In the raw material mixing and pulverizing step S40, the operator mixes the silica-based raw material and the chromite-based raw material so as to have a predetermined chemical component. When the silica-based raw material and the chromite-based raw material are mixed, the operator will pulverize the mixture of the silica-based raw material and the chromite-based raw material until the particle size is 50 μm or less. In the present invention, the "silicon dioxide-based raw material" refers to a raw material that becomes a supply source of SiO ₂ . Examples of silica raw materials include silica sand, silica, and fused silica. "Chromite-based raw material" refers to a raw material that becomes a supply source of Cr ₂ O ₃ and FeO. Examples of chromite-based raw materials include chromite sand and chromite powder. The silica-based raw material and the chromite-based raw material are not limited to these examples. In addition, as a silica-based raw material, one kind or a mixture of plural kinds selected from the above-mentioned ones can also be used. As a chromite-based raw material, one kind or a mixture of plural kinds selected from the above can also be used. What kind of raw material should be selected as the silica-based raw material, and which kind of raw material should be selected as the chromite-based raw material, does not significantly affect the properties of the packed sand. The above-mentioned silica-based raw materials and the above-mentioned chromite-based raw materials may also include Fe ₂ O ₃ , TiO ₂ , CaO, MgO, Na ₂ O, K within the scope of not hindering the action of the packed sand of the present invention. At least one of ₂ O. The content ratio of the total content of the filling sand is preferably 5% by weight or less. In addition, in the raw material mixing and pulverizing step S40, the silica-based raw material and the chromite-based raw material may be separately pulverized before mixing.

In the granulation step S42, the operator puts the mixture of the silica-based raw material pulverized to a particle size of 50 μm or less and the chromite-based raw material pulverized to a particle size of 50 μm or less into a known vibrating granulator (oscillating granulator). granulator). Preferably, the operator also throws the binder-based raw material into the vibratory granulator. In the present invention, the "binder-based raw material" refers to a material raw material that becomes the binder 14 of the secondary particles 10 . The amount of the binder-based raw material may be appropriately determined according to a known method. For example, in the case of using polyvinyl butyral as the binder 14, the operator dissolves it in 2-propanol to obtain a solution of 5 to 15% by weight to the difference between the silica-based raw material and the chromite-based raw material. The mixture is added at 10 to 30% by weight. Then, the operator operates the vibration granulator. Thereby, the particle|grains containing these mixtures (even when a binder system raw material is thrown into a vibration granulator) are produced. In addition, in this embodiment, as a vibration granulator used for granulation, a well-known thing can be used without limitation. For example, a pan granulator, a Malmerizer granulator, a high-speed stirring granulator, or the like is used as the vibration granulator used for granulation. Among them, a high-speed stirring granulator is suitable for reasons such as being easy to control the particle size distribution of the granulated material. In this step, the mixture and the binder-based raw material to be supplied to the vibratory granulator can be the same as those used in the known vibratory granulator. For example, in order to supply the above-mentioned mixture to a vibrating granulator, a vibrating feeder or a screw feeder can be used. The vibrating feeder and screw feeder are easy to control the supply amount. In order to supply the above-mentioned binder-based raw material to the vibrating granulator, a vibrating feeder or a screw feeder can be used. In the case of using a high-speed stirring granulator, it is preferable that the binder-based raw material is added by dripping or by spraying into a mist.

In the particle size distribution adjustment step S44 , the operator removes particles larger than 1180 μm and small particles smaller than 106 μm from the aggregate of particles produced in the granulation step S42 . The specific means for removing is not particularly limited. An example of a specific means for removal is screening. In this way, the aggregate of particles larger than 1180 microns and particles smaller than 106 microns removed can be made into a filling with a particle size exceeding 106 microns and a particle size of 1180 microns or less in weight % of 90 wt % or more and 100 wt % or less. sand. In addition, in the present embodiment, the particle size distribution adjustment step S44 may not be performed.

[How to use filling sand] The filling sand of the present invention is used for filling the molten steel discharge path provided at the bottom of the ladle. Preferably, the sand-filled molten steel of the present invention is filled into the sliding nozzle before entering the ladle. If the sliding nozzle is opened after the molten steel is in the ladle, the filling sand will fall naturally. The filling sand creates natural openings by falling. [Example]

Hereinafter, Examples 1 to 5 and Comparative Examples 1 to 2 of one embodiment of the present invention will be described together. [Example 1] In the raw material mixing and pulverizing step S40, the operator puts chromite sand (trade name: Chromite sand Foundry grade AFS44-50 manufactured by Samancor Chrome Limited. The same applies in the following examples and comparative examples) into the raw material storage. A cylindrical ball mill with an inner diameter of 34 cm and a height of 32 cm was used to grind the chromite sand until the particle size of the chromite sand was 50 microns or less. In the granulation step S42, the operator puts the primary chromite particles obtained in the raw material mixing and pulverization step S40 into a vibration granulator (the device is called Ladyge mixer M20 manufactured by Matsuzaka Techken Co., Ltd.) and stirs for 10 minutes. Thereby, an aggregate of chromite secondary particles is obtained. In the particle size distribution adjustment step S44, the operator puts the aggregate of the chromite secondary particles obtained in the granulation step S42 into a circular vibrating screener (the device is called KGO-500 manufactured by Xinghe Industry Co., Ltd.), Particles larger than 1180 microns and small particles below 106 microns were removed from the aggregate of chromite secondary particles. The aggregate of the chromite secondary particles after removing these particles is the packing sand of this embodiment.

[Example 2] In the raw material mixing and pulverizing step S40, the operator mixes 20% by weight of silica sand (No. 6 silica sand manufactured by Tashiro Silica Mining Co., Ltd. under the trade name. It is the same in the following Examples 1 to 7.) with chromium 80% by weight of iron ore sand was put into the above-mentioned ball mill, and pulverized until the particle size of the sand was 50 microns or less. Hereinafter, the packing sand of this example was obtained by the same operation sequence as Example 1.

[Example 3] In the raw material mixing and pulverizing step S40, the operator puts 30% by weight of silica sand and 70% by weight of chromite sand into the above-mentioned ball mill, and pulverizes until the particle size of these sands is 50 microns or less. Hereinafter, the packing sand of this example was obtained by the same operation sequence as Example 1.

[Example 4] In the raw material mixing and pulverizing step S40, the operator puts 40% by weight of silica sand and 60% by weight of chromite sand into the above-mentioned ball mill, and pulverizes until the particle size of these sands is 50 microns or less. Hereinafter, the packing sand of this example was obtained by the same operation sequence as Example 1.

[Example 5] In the raw material mixing and pulverizing step S40, the operator puts 50% by weight of silica sand and 50% by weight of chromite sand into the above-mentioned ball mill, and pulverizes until the particle size of these sands is 50 microns or less. Hereinafter, the packing sand of this example was obtained by the same operation sequence as Example 1.

[Example 6] The operator added small particles with a particle diameter of 106 μm or less among the particles removed once to the packed sand of Example 3 again. The amount of the small particles added was 5% by weight of the filled sand before the addition. The packed sand to which small particles have been added is the packed sand of this embodiment.

[Example 7] The operator added small particles with a particle diameter of 106 μm or less among the particles removed once to the packed sand of Example 3 again. The addition amount of the small particles was 10% by weight of the filling sand before the addition. The packed sand to which small particles have been added is the packed sand of this embodiment.

[Comparative Example 1] The operator mixed 30% by weight of silica sand (trade name No. 4 silica sand manufactured by Sanhe Silica Co., Ltd.) and 70% by weight of chromite sand to obtain packed sand. The packed sand is the packed sand of the comparative example.

[Comparative Example 2] The operator mixed 30% by weight of silica sand (trade name: No. 5 silica sand manufactured by Sanhe Silica Co., Ltd.) and 70% by weight of chromite sand to obtain packed sand. The packed sand is the packed sand of the comparative example.

[The effect of filling sand in the embodiment] [Ingredients for filling sand] The operator analyzed the mixing ratio of the packed sands of Examples 1 to 5 and the packed sands of Comparative Examples 1 to 2 by means of a fluorescent X-ray analyzer (the device name is ZSX100e manufactured by Rigaku Co., Ltd.). FIG. 3 shows the blending ratio of the packed sands of Examples 1 to 5 and the packed sands of Comparative Examples 1 to 2.

[Particle size distribution of filling sand] The operator measured the particle size distribution of the packed sands of Examples 1 to 7 and the packed sands of Comparative Examples 1 to 2 by the particle size test method of foundry sand (JISZ2601). That is, the nominal size of the sieve is selected to be 2360 microns, 1180 microns, 850 microns, 600 microns, 425 microns, 300 microns, 212 microns, 150 microns, 106 microns, 75 microns, 53 microns standard sieves, and these overlaps are put into A sample of 100 grams was sieved using a RO-TAP sieving machine for 15 minutes. And calculate and measure the weight on each sieve to make a distribution ratio. The particle size distributions of the packed sands of Examples 1 to 7 and the packed sands of Comparative Examples 1 to 2 are shown in FIG. 4 .

[Cold strength, surface composition and particle size of filling sand] The operator added 2.7 grams of molding hardener (product name Kao Step (registered trademark) DH-35 manufactured by Kao Quaker Co., Ltd.), molding resin (product name Kao) to 1 kg of filling sand of Example 1. Kao step (registered trademark) SH-8010) made by Quaker Co., Ltd. 14 grams, and these were kneaded. The kneaded mixture of filling sand and molding binder is called "sample for test piece". The operator fills the test piece into a mold of φ30 mm×30 mm. The operator used the same operation procedure to fill a total of four molds with samples for test pieces. After preparing the samples for test pieces in a total of 4 molds, the operator fired the molds filled with the samples for test pieces for 2 hours using an electric furnace (the device name is Kantar super electric furnace manufactured by Kotorii Electric Furnace Manufacturing Co., Ltd.). (7200 seconds). The temperatures at which these molds are fired are different from each other. The molds were fired at temperatures of 1000°C (1273.15 grammes), 1200°C (1473.15 grammes), 1400°C (1673.15 grammes), 1600°C (1873.15 grammes). After completion of the firing, the sample for a test piece was taken out from the mold. The sample for the test piece taken out from the mold is called a "test piece". FIG. 5 is a photograph showing the test piece just after being taken out of the mold at a firing temperature of 1200° C. (1473.15 grams of elvin). It can be clearly seen from FIG. 5 that the test piece will flow out when it is taken out from the mold. The results clearly show that the test piece is not sintered. Allow the test piece to cool to room temperature. After the test piece was cooled, the operator measured the cold strength of the test piece using a pressure resistance tester (the device name is H-3000D manufactured by Takachiho Seiki Co., Ltd.). However, the cold strength was not measured on the test piece whose shape collapsed when it was taken out from the mold. For the packed sands of Examples 2 to 5 and the packed sands of Comparative Examples 1 to 2, the operator also used the same operation sequence to measure the cold strength. FIG. 6 is a photograph showing the test piece of Example 2 immediately after being taken out of the mold at a firing temperature of 1200° C. (1473.15 grams of elvin). FIG. 7 is a photograph showing the test piece of Example 3 immediately after being taken out of the mold at a firing temperature of 1200° C. (1473.15 grams of elvin). FIG. 8 is a photograph showing the test piece of Example 4 immediately after being taken out of the mold at a firing temperature of 1200° C. (1473.15 grams of elvin). FIG. 9 is a photograph showing the test piece of Example 5 immediately after being taken out of the mold at a firing temperature of 1200° C. (1473.15 grams of elvin). It can be clearly seen from FIG. 6 to FIG. 9 that the test pieces all flow out when they are taken out from the mold. The results clearly show that the coupons were not sintered. 10 is a photograph showing the test pieces of Comparative Examples 1 to 2 in a state in which the mold was filled at a firing temperature of 1200° C. (1473.15 gram elvin). In FIG. 10 , the test piece of Comparative Example 1 is the one that is not clamped by the jig. In FIG. 10 , the test piece of Comparative Example 2 is not clamped by the jig. Regarding the packed sands of Examples 6 to 7, the operator made one test piece for each. The firing temperature of these coupons was 1600°C (1873.15 grams of elvin). In addition, an operator used the chromite sand used in the comparative example 1, and produced four test pieces by the same procedure. The temperature for firing the test piece was 1000°C (1273.15 gram alvin), 1200°C (1473.15 gram elvin), 1400°C (1673.15 gram elvin), 1600°C (1873.15 gram elvin). For this test piece, the operator also used the same sequence of operations to measure the cold strength.

The cold strengths of the test pieces of Examples 1 to 7 and the test pieces of Comparative Examples 1 to 2 are shown in FIG. 11 . As shown in FIG. 11 , the cold strength of the test pieces of Examples 1 to 5 was 0 megapascals when the firing temperature was 1400° C. (1673.15 gram elvins) or less. This is due to the collapse of the shape of the test piece after being taken out from the mold. This means that the coupons were not sintered. On the other hand, the test pieces of Comparative Examples 1 and 2 were not 0 megapascals regardless of the firing temperature and the low temperature. This means that the coupons have been sintered. When the firing temperature is below 1600° C. (1873.15 gram elvin), there is no significant difference in cold strength between the test pieces of Examples 1 to 7 and the test pieces of Comparative Examples 1 to 2.

Figure 12 shows particle size ratio versus cold strength. It can be clearly seen from Table 4 that the cold strength of the test pieces of Examples 1 to 3 and Example 6 at a firing temperature of 1600°C (1873.15 grams of elvin) is the same as that of the test piece of Comparative Example 1 at a firing temperature of 1600°C. (1873.15 gram elvins) the value of the same degree of cold strength.

[Influence on the formation of iron beads] The operator measured the surface components of the test pieces of Examples 1 to 5 and the test pieces of the chromite sand used in Comparative Example 1. The measurement of the surface composition is to use a test piece with a firing temperature of 1200°C (1473.15 gram alvin), a test piece with a firing temperature of 1400°C (1673.15 gram elvin), and a test piece with a firing temperature of 1600°C (1873.15 gram elvin). piece. The surface composition was measured using an energy dispersive X-ray analyzer (the device name is INCA (registered trademark) Penta FET x3 manufactured by Oxford Instruments Co., Ltd.). The weight % of _Cr2O3 to _FeO for this measurement is shown in Figure 13. As shown in FIG. 13 , among the test pieces of Examples 1 to 5, the values of those with a firing temperature of 1200° C. (1473.15 gram elvin) were large. This means that among the test pieces of Examples 1 to 5, the % by weight of Cr ₂ O ₃ is large among those whose firing temperature is 1200° C. (1473.15 gram elvin). As mentioned above, the sinterability of the packed sand is mainly attributable to the precipitation of iron beads when the chromite sand is fired. The iron beads contain Fe. From these matters, it is presumed that Cr ₂ O ₃ on the surface of the filled sand has a relationship of sinterability to the wt % of FeO. Since it is presumed that there is such a relationship, it is presumed that the precipitation of iron beads is suppressed at the firing temperature of 1200° C. (1473.15 gram elvin) for the packed sands of Examples 1 to 5. Since it is presumed that the precipitation of iron beads is suppressed, it is presumed that the sinterability of the packed sands of Examples 1 to 5 is low at a firing temperature of 1200° C. (1473.15 gram elvin).

[Effect for molten steel penetration] The operator produced test pieces from the packed sand of Example 1. The sequence of operations for making the test piece is the same as that described above. The maker also produced test pieces in the same manner with the packed sands of Examples 2 to 5 and the packed sands of Comparative Examples 1 to 2. After making the test pieces, the operator uses the above-mentioned electric furnace to burn the test pieces. At this time, iron balls were placed on these test pieces. About 5 grams of iron balls are placed on one test piece. The size of these iron balls is Φ1 mm. The name of these iron balls is steel shot made by W Abrasives. The firing temperature in the electric furnace was 1600°C (1873.15 gram elvin). The firing time was 2 hours (7200 seconds). The fired test piece was placed in the air until normal temperature. When the temperature of these test pieces becomes normal temperature, the operator cuts these test pieces. These test pieces were cut so that the cross section of the place where the iron balls were placed would be exposed. After the test pieces were cut, the operator measured the thickness of the formed layer (penetration depth) by infiltrating molten steel from the test piece surface. The penetration depth is shown in Figure 14. It can be clearly seen from FIG. 14 that the penetration depths of Examples 1 to 5 are thinner than those of Comparative Examples 1 to 2. In particular, the penetration depths of Examples 1 to 2 were significantly thinner than those of Comparative Examples 1 to 2 and Examples 3 to 5.

[Summarize] As is clear from the above description, when the following requirements are satisfied, the filling sand can increase the sintering initiation temperature and suppress the penetration of molten steel. The requirement is that the packed sand contains secondary particles 10 , the secondary particles 10 contain a plurality of primary particles 12 with a particle diameter exceeding 0 μm and a diameter of 50 μm or less, and at least a part of the plurality of primary particles 12 contained in the secondary particles 10 contains Chromite mines.

In addition, when the packed sand satisfies the above-mentioned requirements and also satisfies the following two requirements, the sintering initiation temperature can be made particularly high. The first requirement is that the particle size of the secondary particles 10 exceeds 300 microns and 850 microns or less accounts for 53 wt % or more and 77 wt % or less in the weight % of the packed sand. The second requirement is that among the secondary particles 10, particles with a particle diameter exceeding 106 microns and 1180 microns or less account for 95 weight % or more of the filled sand. Among the secondary particles 10 , when the particle size of the particles exceeding 106 μm and 1180 μm or less accounts for 99.9% by weight or more of the packed sand, the sintering initiation temperature can be further increased. And also in this case, it becomes possible to suppress the usage-amount of chromite sand.

In addition, when the filling sand satisfies the above-mentioned requirements and the following requirements, in particular, the penetration of molten steel can be suppressed. This requirement is that the primary particles 12 contain 37.1 wt % or more and 46.3 wt % or less of Cr ₂ O ₃ and 21.1 wt % or more and 26.4 wt % or less of FeO.

10: Fill Sand 12: Secondary particles 14: Primary particles 16: Adhesive

Fig. 1 is a conceptual diagram showing the configuration of secondary particles contained in packed sand according to an embodiment of the present invention. [ Fig. 2] Fig. 2 is a conceptual diagram showing the steps of a method for producing packed sand according to an embodiment of the present invention. [Fig. 3] Fig. 3 is a diagram showing the blending ratio of the packed sand according to an embodiment of the present invention in the form of a table. [ Fig. 4] Fig. 4 is a diagram showing the particle size distribution of the packed sand according to an embodiment of the present invention in the form of a table. [ FIG. 5 ] A photograph showing the test piece of Example 1 immediately after being taken out from the mold at a firing temperature of 1200° C. (1473.15 g elvin). [ FIG. 6 ] A photograph showing the test piece of Example 2 immediately after being taken out from the mold at a firing temperature of 1200° C. (1473.15 g elvin). [ FIG. 7 ] A photograph showing the test piece of Example 3 immediately after being taken out from the mold at a firing temperature of 1200° C. (1473.15 gram elvin). [ FIG. 8 ] A photograph showing the test piece of Example 4 immediately after being taken out from the mold at a firing temperature of 1200° C. (1473.15 g elvin). [ FIG. 9 ] A photograph showing the test piece of Example 5 immediately after being taken out from the mold at a firing temperature of 1200° C. (1473.15 g elvin). [ Fig. 10] Fig. 10 is a photograph showing the test pieces of Comparative Examples 1 to 2 immediately after being taken out from the mold at a firing temperature of 1200°C (1473.15 gram elvin). [ Fig. 11 ] A diagram showing the cold strength of an embodiment of the present invention in the form of a table. [ Fig. 12 ] A graph showing the relationship between the particle size ratio and the cold strength in a table form according to an embodiment of the present invention. [ Fig. 13 ] A graph showing the results of energy dispersive X-ray analysis according to an embodiment of the present invention in the form of a table. [ Fig. 14 ] A diagram showing the penetration depths in the form of a table in an example and a comparative example according to an embodiment of the present invention.

10: Fill Sand

12: Secondary particles

14: Primary particles

Claims (5)

A packed sand characterized by comprising chromite, The aforementioned packed sand includes secondary particles, and the secondary particles include a plurality of primary particles having a particle diameter of more than 0 micrometers and less than 50 micrometers, At least one part of the plurality of the primary particles included in the secondary particles includes the chromite. The packed sand of claim 1, wherein the secondary particles contain 20 wt% or more but less than 50 wt% of Cr ₂ O ₃ and 10 wt % or more but less than 30 wt % of FeO. The packed sand according to claim 2, wherein the Cr ₂ O ₃ wt % is 37.1 wt % or more and 46.3 wt % or less, and the FeO wt % is 21.1 wt % or more and 26.4 wt % or less. The packed sand according to any one of claim 1 to claim 3, wherein the secondary particles include particles with a particle size exceeding 106 microns and below 1180 microns, The particles with a particle size exceeding 106 microns and below 1180 microns account for 90 wt % or more and 100 wt % or less in the weight % of the filling sand. The packed sand of claim 4, wherein the particles with a particle size exceeding 106 microns and below 1180 microns account for 95 wt % or more of the packed sand, Among the particles with a particle size of more than 106 microns and below 1180 microns, the particles with a particle size of more than 300 microns and below 850 microns account for 53 wt % to 77 wt % of the packed sand.

Images