JP2007000921A - System for producing molten metal for cast product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the productivity and the energy efficiency in a producing process of molten metal for casting. <P>SOLUTION: Total blending ratio to raw material A of pig iron for casting having near the level of the cast product C of C content and Si content and large bulk density, and casting scrap, is made to be ≥80 mass%, desirably ≥90 mass%. In this raw material A, the total of steel scrap and one or two kinds in carburizer and siliconizer is blended with <20 mass%, desirably <10 mass% blending ratio, and the blending of the raw material A into a high frequency induction furnace 1 is performed so as to obtain the molten metal B for casting, having target compositions and thus, the divided charge of the raw material A and component adjustment after melting down are unnecessary, and the productivity and the energy efficiency can be improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a molten metal manufacturing system for casting that is excellent in productivity and energy efficiency.

  Cast products are manufactured by melting raw materials in a melting furnace such as a cupola or induction heating type induction furnace, and casting the molten molten metal for casting with a mold such as a sand mold. Cast iron for castings, pig iron, casting scraps, steel scraps, etc. obtained from a blast furnace are used. Steel scraps for adjusting the carbon content to these raw materials, graphite as a carburizing material The component composition of the molten metal for casting is adjusted by blending ferrosilicon or the like as a silica material.

  In recent years, steel scrap generated from various steel products has been used not only as a raw material for crude steel but also as a raw material for molten metal for castings. The mixing ratio of steel scrap to the raw material for molten metal for casting is about 45% by mass, and steel scrap is the main raw material with the highest mixing ratio. The remainder is about 15% by mass of the cast iron pig iron and about 40% by mass of the casting scrap.

The conventional system for producing a molten metal for casting from a raw material having a high steel scrap content as described above has the following problems.
・ Most steel scraps have a C content of 1% by mass or less, and most steel scraps of the thin steel plates that occur most often have a C content of 0.1% by mass or less. The amount of Si and the amount of Si are also small, so that a large amount of carburized material or silica material is required for adjusting the components of the molten metal, and it takes time and effort to adjust the components.
・ Since steel scrap has a small bulk specific gravity, the packing density when the raw material is charged into the melting furnace is lowered, and it is necessary to divide the raw material into several times to dozens of times.
・ Since many steel scraps in recent years have many additive elements and have been subjected to surface treatment such as plating, inappropriate elements are mixed into the molten metal.

Moreover, when using an induction furnace which is a batch type melting furnace, there are the following problems.
-Due to the above-described component adjustment and divided charging of raw materials, the melting time of one charge becomes as long as 1 hour or more.
・ If a large melting furnace is used to compensate for the decrease in productivity due to the extension of the melting time, it takes time to divide one charge into several times and take out divided hot water. Therefore, it is necessary to increase the molten metal temperature, and energy efficiency is lowered.
-It is necessary to open the furnace lid for operation in the above-described divided charging and divided hot water, so that energy loss increases and energy efficiency further decreases.

  As described above, conventional molten metal production systems for castings contain a large amount of steel scraps that have significantly different levels of C content from the original castings, have a low bulk specific gravity, and a variety of component elements. As a result, productivity and energy efficiency are low, and in the era of pursuing high productivity and energy saving, it is a big problem related to the life and death of the casting industry.

  Then, the subject of this invention is improving productivity and energy efficiency in the manufacturing process of the molten metal for castings.

  In order to solve the above-mentioned problems, the present invention provides a total system for blending casting pig iron and casting scraps into the raw material in a casting molten metal manufacturing system in which the raw material is melted in a melting furnace to produce a molten metal for casting. The rate is set to 80% by mass or more, and one or more of steel scraps, carburized materials, and siliconized materials are added to the raw material at a total mixing rate of less than 20% by mass to adjust the component composition of the molten metal for casting. Adopted the system.

  That is, the total blending ratio of cast iron and foundry scrap with a C content and Si content close to the level of the final product casting and a large bulk specific gravity is 80% by mass or more, preferably 90% by mass or more. In this raw material, one or more of steel scraps, carburized materials, and silica materials are blended at a blending rate of less than 20% by mass, preferably less than 10% by mass, so that a molten metal for casting as a target component can be obtained. In addition, by blending the raw materials charged into the melting furnace, it is possible to eliminate the need for divided charging of raw materials and adjustment of the components after melting, thereby improving productivity and energy efficiency. Moreover, the mixing rate of steel scraps can be remarkably reduced, and mixing of inappropriate elements into the molten metal can be suppressed.

  The total blending ratio of the pig iron for casting and the casting scrap was set to 80% by mass or more because the total blending ratio of the steel scrap for adjusting the components of the molten metal, the carburized material, and the siliconized material should be less than 20% by mass. This is because the total blending ratio of the pig iron for casting and the casting scrap is preferably 90% by mass or more. When adjustment of the components of the molten metal is not necessary, the total blending ratio of the casting pig iron and the casting scrap is 100. It can also be made into the mass%.

  By increasing the blending ratio of the pig iron for casting and casting scrap 5 to 5 or more, preferably 7 to 3 or more and the casting iron for casting, the compounding amount of the casting pig iron with a clear composition is increased. In addition, it is possible to easily adjust the components of the molten metal.

By setting the eutectic saturation of the pig iron for casting to 0.9 to 1.1, the melting temperature of the molten metal can be lowered and the energy efficiency can be further increased. As is well known, the eutectic point in the Fe-C system equilibrium diagram is when the carbon equivalent (CE = C + Si / 3.2) is 4.23 mass%, and the eutectic point at which the melting temperature is the lowest. The eutectic saturation, which is a parameter representing the proximity to the crystal point, is expressed by the following equation.
Eutectic saturation = C / (4.23-Si / 3.2) (1)
Here, C and Si are mass% of each element, and become eutectic points when the eutectic saturation is 1.0.

  By setting the bulk specific gravity of the pig iron for casting to 3.5 or more, the packing density when the raw material is charged into the melting furnace can be sufficiently increased, and the divided charging of the raw material can be made unnecessary.

  By making the melting furnace an induction heating type induction furnace, the melting time of one charge is shortened, and the number and times of opening the furnace lid are reduced, so that the effect of increasing productivity and energy efficiency is exhibited more greatly. can do.

  By setting the power density of the induction furnace to 1.0 kW / kg or more, preferably 1.5 kW / kg or more, the melting time for one charge can be further shortened. In addition, the power density of the conventional induction furnace is less than 1.0 kW / kg, and more than half is about 0.6 kW / kg. This is because the conventional raw material contains a large amount of steel scrap having a low bulk specific gravity, so that a sufficient packing density of the raw material in the furnace cannot be obtained.

The power density α is defined by the following equation, where the dissolution amount is Mkg and the input power is WkW.
α = W / M (2)
When the molten metal temperature is 1450 ° C. and the energy of the molten metal is 312 kcal / kg (= 0.363 kWh / kg), the melting time t (minute) is expressed by the following equation.
t = (0.363 × 60) / (α · η) (3)
Here, η is power efficiency. If the dissolution time t in the equation (3) is represented by a graph, it becomes a hyperbola with the power density α as a parameter as shown in FIG. As can be seen from the graph of FIG. 2, for example, when the power efficiency η is 60%, the dissolution time t when the power density α is 0.6 kW / kg, which is the conventional level, is calculated to be 60.5 minutes, When α is increased to 1.0 kW / kg, the dissolution time t is shortened to 36.3 minutes, and when the power density α is further increased, it is 24.2 minutes at 1.5 kW / kg and 12.1 at 3.0 kW / kg. Minutes and dissolution time t are significantly reduced. In other words, in the past, it took 60 minutes or more to melt one charge and the batch system had a long waiting time for pouring, whereas the melting system for castings according to the present invention significantly shortened the melting time. In addition, the melting of the next lot can be completed while pouring, so the waiting time for pouring can be eliminated, resulting in a one-charge, one-shot, substantially continuous melting and pouring system. You can also.

  By setting the inner height of the induction furnace within twice the effective height of the induction heating coil, while the raw material in the lower part of the furnace is melted by the induction heating coil disposed on the lower outer periphery of the induction furnace In addition, the raw material in the upper part is preheated, and the thermal energy can be efficiently utilized for melting the raw material.

  The production system for molten metal for casting according to the present invention has a C content and Si content close to the level of the casting as the final product, and the total blending ratio of pig iron for casting and casting waste with a high bulk specific gravity is 80% by mass. Or more, preferably 90% by mass or more, and one or more of steel scraps, carburized materials and silica materials are added to this raw material at a total content of less than 20% by mass, preferably less than 10% by mass, Since the component composition of the molten metal for castings is adjusted, it is easy to adjust the component of the molten metal, the number of times of dividing and charging the raw material into the melting furnace can be reduced, and the productivity and energy efficiency can be improved. . In addition, by significantly reducing the mixing ratio of steel scrap with a low C content, the amount of carburized material that dissolves in iron by an endothermic reaction can be suppressed, which is further advantageous in terms of energy efficiency, And Ti, Al, Cr, Cu, Mn, Zn, P, S, etc., which are added to enhance the properties of high-strength steel and surface-treated steel, etc., elements that are generally considered undesirable in cast iron products It is also possible to suppress contamination of the molten metal.

  By increasing the blending ratio of the pig iron for casting and casting scrap 5 to 5 or more, preferably 7 to 3 or more and the casting iron for casting, the compounding amount of the casting pig iron with a clear composition is increased. Therefore, it is possible to adjust the composition of the molten metal more easily, leading to stabilization of the properties and components of the molten metal, improvement of the method yield, and reduction of the defective rate. Furthermore, since the component adjustment can be accurately performed at the initial raw material charging stage by increasing the blending amount of pig iron for casting, no component adjustment during melting is required.

  By setting the eutectic saturation of the pig iron for casting to 0.9 to 1.1, the melting temperature of the molten metal can be lowered and the energy efficiency can be further increased.

  By setting the bulk specific gravity of the pig iron for casting to 3.5 or more, the packing density when the raw material is charged into the melting furnace can be sufficiently increased, and the divided charging of the raw material can be made unnecessary.

  By making the melting furnace an induction heating type induction furnace, the melting time of one charge is shortened, and the number and times of opening the furnace lid are reduced, so that the effect of increasing productivity and energy efficiency is exhibited more greatly. can do. In addition, by shortening the charge cycle time, it is possible to secure a sufficient production volume even if the furnace is downsized, it is possible to cope with the production of various types of small lots, and the equipment cost can be reduced, so that the construction cost of the factory building can be reduced. Reduction and improvement in land use efficiency are also possible. Furthermore, the working environment can be kept good.

  By setting the power density of the induction furnace to 1.0 kW / kg or more, preferably 1.5 kW / kg or more, the melting time for one charge can be further shortened.

  By setting the inner height of the induction furnace within twice the effective height of the induction heating coil, while the raw material in the lower part of the furnace is melted by the induction heating coil disposed on the lower outer periphery of the induction furnace In addition, the raw material in the upper part is preheated, and the thermal energy can be efficiently utilized for melting the raw material.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of a casting product manufacturing facility that employs a molten metal manufacturing system for castings according to the present invention. This casting product manufacturing equipment includes an induction heating type high frequency induction furnace 1 as a melting furnace for melting the raw material A to be charged, and a mold 2 for casting the casting product from the molten casting B. Yes. The high frequency induction furnace 1 is provided with a raw material charging lid 1a at the top and an induction heating coil 1b on the outer periphery of the lower part. The furnace height H is 2 which is the effective height h of the induction heating coil 1b. It is supposed to be within double. The molten metal B melted in the high frequency induction furnace 1 is poured out into the ladle 3 and poured from the ladle 3 into the pouring port 2a of the mold 2, and the cast product C is taken out from the mold 2 after solidification.

  Using a high frequency induction furnace (furnace capacity 500 kg, electric power 375 kW, frequency 500 Hz) as shown in FIG. 1, a ductile cast iron melt was manufactured. As shown in Table 1, as Example 1, a raw material containing 97.5% by mass of pig iron for casting with an average bulk specific gravity of 3.55 and an eutectic saturation adjusted to a range of 0.9 to 1.1 was used. Production of molten metal for castings used, and as a comparative example, the mixing ratio of pig iron for castings obtained as it is from a blast furnace is 15.0 mass%, the mixing ratio of casting scraps is 40.0 mass%, and the mixing ratio of steel scraps is Production of a molten metal for casting using a raw material having an average blending ratio that was conventionally used and 43.0% by mass was performed. The balance of the raw material of Example 1 is 2.4% by mass of steel scrap for component adjustment, 0.1% by mass of graphite and ferrosilicon, and the average bulk specific gravity of the raw material is 3.55. Further, the balance of the raw material of the comparative example is 2.0% by mass of component adjusting graphite and ferrosilicon, and the average bulk specific gravity of the raw material is 0.98.

  Table 2 shows a comparison between the chemical components of the cast iron for castings used as the raw materials of Example 1 and the comparative example and the target chemical components of the molten metal for castings. The pig iron for casting used as the raw material of Example 1 has a C content close to the target value of the molten metal for casting, and the eutectic saturation is 1.027. Further, the pig iron for casting obtained as it is from the blast furnace used as the raw material of the comparative example has a C content much higher than the target value of the molten metal for casting, and the eutectic saturation is 1.186.

  Table 3 shows the results of manufacturing the molten castings of Example 1 and the comparative example for each of 5 charges. The raw material input amounts are all 517 kg / charge, and the actual values of Example 1 and Comparative Example shown in Table 3 are average values of 5 charges. When comparing the actual values of Example 1 and the comparative example, first, in the comparative example where the mixing ratio of steel scrap having a small bulk specific gravity is large, the raw material is divided and charged in five portions, whereas the bulk specific gravity is In Example 1 in which the blending ratio of the cast iron for casting having a high chemical composition and a clear chemical composition was 97.5% by mass, the raw material was charged only once and no intermediate raw material was charged. In addition, the same high frequency induction furnace is used in both Example 1 and the comparative example, and the apparent power density is 0.73 kW / kg, but the actual power density (average power considering fluctuation during operation) The density was 0.70 kW / kg in Example 1, whereas it was 0.51 kW / kg in the comparative example. This is because in the comparative example, the bulk specific gravity of the raw material is low, and the electrical output is cut during component adjustment. As a result, although the time until dissolution was not so different between Example 1 and the comparative example, the time until the start of pouring of the molten metal affecting productivity was 75.8 minutes in the comparative example. In Example 1, it was shortened by nearly 30% to 54.9 minutes, and the power consumption was 712.1 kWh / ton in the comparative example, whereas in Example 1, it was reduced by about 10% to 642.0 kWh / ton. ing. From the comparison of these production results, it can be seen that productivity and energy efficiency can be remarkably improved in the cast metal manufacturing system according to the present invention. The reason for the large difference between the time until the start of pouring and the power consumption was that it took time to adjust the components while maintaining the temperature after the last charged raw material melted in the comparative example.

  Tables 1 to 3 show, as Example 2, a high-frequency induction furnace for actual production having a furnace capacity of 10 tons, a melting amount per charge of about 2 tons and a power density of about 1.times. The average performance data when melting up to 22 kW / kg for one month is also shown. The raw material compounding ratio of Example 2 is 70.0% by mass of cast iron for casting, 25.0% by mass of casting scrap, 4.4% by mass of steel scrap, 0.6% by mass of graphite and ferrosilicon, and the average bulk specific gravity is 3.00. Also in this case, as in the case of Example 1, the intermediate raw material charging is not performed. In this Example 2, the time until the start of one charge of hot water is 29.1 minutes, which is about 60% shorter than the comparative example, about 46% shorter than the first example, and the power consumption is 603.8 kWh. It can be seen that the energy efficiency is also improved. These are the effects of increasing the power density with respect to the comparative example and Example 1.

  Table 4 is based on the actual data of Example 1 and Example 2 shown in Table 3 and the dissolution amount when the power density is increased to 3.0 kW / kg by decreasing the dissolution amount per charge. The result of estimating the time is shown. From this estimation result, it can be seen that by increasing the power density to 3.0 kW / kg, the time until the start of pouring becomes approximately 10 minutes which is substantially equal to the pouring time. Therefore, it is speculated that the above-described one-charge one-shot melting system is possible. Further, by operating in such a short cycle, it is considered that the amount of power used can be leveled in one day, and the demand power (demand) can be reduced. Usually, the monthly maximum value (maximum demand power) of the average value of demand power every 30 minutes (average power) is adopted as the standard for calculating the basic electricity charge. It is expected that the basic electricity charge will be reduced by 20-30% by operating with the melting system.

As a result, the system for producing a molten metal for casting according to the present invention described above is useful for reducing CO ₂ , that is, preventing global warming. It is possible to reduce the amount of decarburized pig iron in steel production, that is, the amount of CO ₂ emission, by reducing the mixing ratio of steel scrap in the production of molten metal for castings, and turning that amount to steel recycling. On the other hand, in the production of cast iron, carbon contained in pig iron can be used without being discharged as CO ₂ . According to a calculation by one of the inventors, it is possible to reduce 1 million tons of CO ₂ annually in the entire iron industry in Japan.

  In the above-described embodiment, a high-frequency induction furnace is used as the melting furnace, and the molten metal for casting of ductile cast iron is manufactured. However, the casting molten metal manufacturing system according to the present invention uses a low-frequency induction furnace or a cupola as the melting furnace. It is also possible to produce other types of castings such as gray cast iron.

  Further, in the embodiment described above, the molten metal for casting is poured into the ladle and poured from the ladle into the mold, but the induction furnace such as a high frequency induction furnace is miniaturized so that it can be moved by a crane or a track. It is also possible to pour the molten metal directly from the induction furnace.

The schematic which shows the manufacturing equipment of the casting product which employ | adopted the manufacturing system of the molten metal for castings concerning this invention Graph showing the relationship between power density, power efficiency and melting time in induction furnaces

Explanation of symbols

A Raw material B Molten metal C Casting product 1 High frequency induction furnace 1a Lid 1b Induction heating coil 2 Mold 2a Pouring port 3 Ladle

Claims (7)

  In a molten metal production system for casting, in which a raw material is melted in a melting furnace, the total blending ratio of cast iron and casting scrap to the raw material is set to 80% by mass or more. One of at least one of a carburized material and a siliconized material is blended at a blending ratio of less than 20% by mass to adjust the component composition of the cast metal melt. Manufacturing system.   The manufacturing system of the molten metal for casting according to claim 1, wherein the compounding ratio of the pig iron for casting and the casting scrap is 5 to 5 or more and the compounding amount of the pig iron for casting is increased.   The molten metal manufacturing system for casting according to claim 1 or 2, wherein the eutectic saturation of the pig iron for casting is 0.9 to 1.1.   The casting molten metal manufacturing system according to any one of claims 1 to 3, wherein a bulk specific gravity of the pig iron for casting is 3.5 or more.   The molten metal manufacturing system for casting according to any one of claims 1 to 4, wherein the melting furnace is an induction heating type induction furnace.   The casting molten metal manufacturing system according to claim 5, wherein the induction furnace has a power density of 1.0 kW / kg or more.   The casting molten metal manufacturing system according to claim 5 or 6, wherein the height of the induction furnace is set to be within twice the effective height of the induction heating coil.

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