JPH01177334A - Manufacture of ferroboron - Google Patents

Abstract

PURPOSE:To increase the yield of boron and to reduce the consumption of unit electric power by specifying the amounts of a carbonaceous material for the reduction of boron source and manufacturing ferroboron by an electric method in the use of a DC girod furnace provided with specific size of basined layer under a tapping spout. CONSTITUTION:At the time of manufacturing ferroboron by an electric furnace method, the DC girod furnace provided with the basin having 100-500mm depth under the tapping spout as an electric furnace. In this way, the floating and discharging of B4C are smoothly executed and its accumulation is simultaneously prevented. The amounts of the carbonaceous material reducing the boron source such as boron oxide and boric acid are furthermore regulated to 91-100% for the theoretical required amounts. By this method, the yield of boron is increased and the generation of the substance difficult to melt is furthermore suppressed to permit the stabilizing operation and to reduce the consumption of electric power per unit weight of a manufacture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing ferroboron using an electric furnace method.

[Prior Art] In recent years, amorphous alloys, particularly Fe-B-3i-based amorphous alloys, have attracted attention as iron cores for transformers, and ferroboron is used as the boron source. An electric furnace carbon reduction method is used as an inexpensive method for producing ferroboron.

Prior art related to the method for producing ferroboron using an electric furnace method is disclosed in Japanese Patent Publication No. 9108-1983 and Japanese Patent Publication No. 1973-1989.
18841, Special Publication No. 51-37613, Special Publication No. 60-1
03151, but all of these methods have problems such as difficulty in stable operation over a long period of time and low boron yield, and are not satisfactory methods.

In other words, the method disclosed in Japanese Patent Publication No. 34-9108 involves powdering iron, boron compounds such as boron oxide and boric acid, and carbonaceous substances such as charcoal and coke into powders of 5 mesh or less, and adjusting the amount of the carbonaceous reducing agent to the oxygen in the raw material. This method is characterized by adding an excessive amount of reducing agent to the amount required to reduce the reducing agent. However, in this method, the excessive addition of reducing agent generates poorly soluble substances such as 84C in the furnace, which accumulates on the hearth. As the hearth rises, long-term stable operation is impossible.

Publication No. 40-18841 uses iron ore as an iron source, and by reducing the amount of carbon to less than the theoretical value required for deoxidizing it, easily soluble slag is produced as a by-product, and furthermore, boron compounds are melted and separated from other raw materials. In order to prevent this, all raw materials were ground to 5 mm or less, mixed with a small amount of water, and mixed for 20 minutes.
It is characterized in that it is heated to 0°C and then put into an electric furnace. However, this method requires pre-treatment of the raw material, which incurs processing costs, and the loss of boron to the slag is unavoidable due to the production of slag in the furnace.
The carbon content is extremely small, less than the theoretically required amount of 50X, so a high yield of boron cannot be expected, and the reduction reaction is solid.
It becomes a liquid reaction, and the reaction rate is lower than that of a solid-solid reaction.
It is also clear that power consumption per unit product weight increases, so it is difficult to say that this technology is suitable for industrial production.

The method of Japanese Patent Publication No. 51-37613 proposes adding lime to the raw materials in order to prevent the accumulation of poorly soluble substances in the hearth, but boric acid easily slags with lime in the furnace. , thus avoiding the loss of boron to the slag,
Furthermore, an increase in power consumption per unit product weight due to the sensible heat of the generated slag is unavoidable.

Special Publication No. 60-103151 was an attempt to make active use of the poorly soluble deposits that form in the hearth. After that, when the bottom of the furnace reaches the appropriate temperature, the highly reactive reducing agent, mainly charcoal, is switched to a weakly reducing operation using less than 90% of the theoretically required amount to prevent the growth of refractory deposits. By suppressing the layer thickness and maintaining an appropriate layer thickness, long-term stable operation is possible, and at the same time, Ti, A1
It is said that high-purity products with low impurities such as

However, as the inventor of this patent has stated, it is difficult to suppress the growth of poorly soluble deposits once they exceed a certain amount of deposits, and it is not easy to control their evolution. If weak reducing operation is performed on the deposited layer, the boron source in the furnace becomes low melting point slag due to the lack of reducing agent in the furnace, which lowers the temperature inside the furnace, resulting in a decrease in boron yield and an increase in power consumption. In addition, there is a possibility that the amount of poorly soluble substances may increase due to poor reaction due to insufficient heat. It is clear that long-term stable operation is difficult with this method. In addition, in weak reduction operation, the carbon content of the electrode is likely to be carburized, and the amount of electrode consumption increases significantly, increasing costs, so it cannot be said to be an advantageous operation method.

[Problems to be solved by the invention] As mentioned above, in the production of ferroboron using conventional electric furnaces, if carbonaceous material is added in excess of the theoretical value, a refractory substance will be generated and deposited on the hearth, making it unstable. operations became impossible,
On the other hand, if the blended amount of carbonaceous material is suppressed more than necessary, the boron yield will decrease due to a decrease in the metallization rate, the power consumption per unit weight of the product will increase, and furthermore, the decomposition reaction of poorly soluble substances will occur due to insufficient heat. However, similar to the case of excessive blending of carbonaceous material, there is a problem that refractory substances are deposited on the hearth, resulting in unstable operation.

The present invention was made in view of the above circumstances, and aims to increase the yield of boron without depositing refractory substances on the hearth.
The present invention aims to provide a method for producing ferroboron that reduces power consumption per unit weight of the product.

[Means for Solving the Problems] The method for producing ferroboron according to the present invention is a method for producing ferroboron using an electric furnace method, in which a direct current type Giraud furnace is provided with a reservoir layer having a depth of 100 mm to 500 mm below the tap. The present invention is characterized in that the blending amount of a carbon material for reducing a boron source such as boron oxide or boric acid is 91% to 100% of the theoretically necessary amount for reducing the boron source.

[Operation] The reason why a DC Ziraud type electric furnace was selected as an electric furnace for melting and reducing high melting point materials such as ferroboron will be described. The following reaction formulas (1) to (3) are known as reduction reactions of boron oxide using a carbonaceous reducing material.

2/3B203+7/3C=1/3B4C+2COΔF
=173900-83.61T...■2/3B20s
+2C=4/3B+2CO.

ΔF=179407-85.017...■2/3
B203 +284C=2/3B+2CO.

ΔF=196168-89.57T...■■,■
It is thought that the reactions in the formula are proceeding almost simultaneously in the furnace, but in the case of insufficient heat, the B4C of the poorly soluble substance produced in the formula 0
is deposited in the furnace without causing the type 0 decomposition reaction. Therefore, in order to prevent the accumulation of hardly soluble substances in the furnace, it is preferable to use a direct current Giro type electric furnace, which is a heat-concentrating electric furnace and is easy to operate.

A pool with a depth of 100 mm to 500 mm installed under the tap tap allows the refractory B4C to float and be discharged smoothly, and its depth remains stable during operation, preventing erosion of the bottom electrode of the Giraud furnace. There is no risk of it happening.

Furthermore, if the blended amount of carbonaceous material becomes excessive, the deposition of 84C on the hearth progresses due to the formation of B4C, which is a poorly soluble substance, or a decrease in B2O3, which decomposes B4C, as shown in equation (1) and 0 above. On the other hand, if this is insufficient, the reduction of 8203 will be insufficient and the yield of boron will decrease. As a result of repeated tests with this balance in mind, the blending amount of carbon material to reduce the boron source was determined to be 91% to 100% of the theoretically required amount to reduce the boron source.
And so.

[Example] First, a description will be given of how it was discovered that it was optimal to use a direct current Ziraud furnace in which a molten metal pool was provided below the tap in a method for producing ferroboron using an electric furnace method.

Table 1 shows the operation results of a 500 KVA test electric furnace with a target of 20 continuous channels, and the amount of reducing agent mixed in the charging raw material was kept constant at 95% of the theoretically required amount of boric acid. In addition, none of the furnaces were built with a sump on the hearth.

In the 3-phase L-furnace shown in Table 1, in the 6th channel of operation, there was a failure in tapping due to the rise of the hearth, and the operation was suspended. As a result of dismantling this hearth zone and investigating the rise of the hearth, it was found that the amount of refractory substances deposited on the hearth was 240+ am.
Met. Therefore, the heat concentration in the three-phase L-furnace is 0 as above.
It was found that the reaction of Eq.

The AC Giraud furnace gave better results than the three-phase L-furnace, and was able to achieve the target of 20 channels. but,
The results of the dismantling of the furnace body showed that the hearth had risen by 90mm.

The AC Giraud furnace is a much more heat-concentrating furnace than the three-phase L-furnace, and although continuous operation is possible as an electric furnace for ferroboron, it is not satisfactory in terms of hearth rise.

Next, a comparative test of hearth rise between AC and DC Ziro furnaces was conducted using a small test furnace as shown below, and it was confirmed that the DC Ziro furnace was suitable.

Table 2 shows the results of a 10-channel operation carried out in a 75KVA test furnace that can be switched between an AC and DC Ziro furnace, and the charged raw materials were the same as in the case of the 500KVA test electric furnace.

The target 10 channels in Table 2 were all operational, but in the AC Ziro furnace, no hearth rise was observed as in the 500KVA test electric furnace, but in the DC Ziro furnace, there was no hearth rise at all, and the reverse was true. The hearth was lowered by 20mm.

In the electric furnace type comparison test mentioned above, it was found that in the case of a DC Giraud furnace, the bottom of the furnace eroded during operation. When the bottom of a Giraud furnace is eroded, operations are interrupted due to the need to replace the bottom electrode, which is not normally necessary, and there is a risk of hot water leaking from the bottom, which may lead to a major accident. As a solution to this problem, a test was conducted in a 500 KVA DC Ziraud furnace in which the bottom electrode was placed lower than the sprue level and a sump was provided. The raw material to be charged in this test is the reaction of formula 0 above, which is necessary to decompose 84C, which is a difficult-to-melt substance, and in order to avoid a shortage of 203,
In order to suppress the reaction of the formula, the amount of carbon material added to boric acid was reduced from 95% of the theoretically required amount to 91%. The water pool depth started at 200 mm, but after 5 days, at the 40th channel, it reached 280 mm, and after 5 days of operation, it remained unchanged. This depth is balanced with the scouring temperature inside the furnace, and it is easy to assume that it will be slightly deeper as the heat capacity increases in larger furnaces, but we do not think that the bottom of the furnace will be further eroded. It will be done.

Next, in the same furnace, a 20-channel test was conducted in which the amount of carbon material mixed with the boric acid used as the charging material was 95% of the theoretically required amount. In this test as well, there was no rise in the hearth, the excess 4C was discharged out of the furnace as the hot water was tapped, and the pool depth remained at 280 cm. On the other hand, by providing this hot water pool, a third
As shown in the table, a reduction in product quality variation and power consumption was observed.

The reason why it is optimal to set the effective depth of the third front pool to 100 mm to 500 mm is as follows.

If there is no puddle under the tap, if B4C is generated due to excess reducing agent in the furnace, the 84C will not dissolve if there is almost no ferroboron molten metal in the hearth after tapping, resulting in hearth deposits. It can be easily inferred that
If molten ferroboron remains on the hearth immediately after tapping,
The B4C is on top of the fluid molten metal due to the difference in specific gravity,
It has also been confirmed in test operations that the ferroboron melt flows out of the furnace during tapping. 900kw with a 300mm hot water pool under the hot water outlet
When the depth of the hearth was measured immediately after tapping in the test operation of the furnace, the depth of the hearth below the tap was as deep as 350+++a, but the depth of the remaining metal was 250t+*. Therefore, it was determined that the effective depth of the hot water pool should be 100 mm+ or more. In addition, the upper limit is determined by heat balance, but according to the results of one month's operation, it is balanced at 370 mm, and furthermore, we are considering creating a layer of 130 mm in which almost no ferroboron is released to protect the bottom electrode. , the upper limit depth was set to 500 mm. The reason why the blending amount of the carbonaceous material was set to 91% to 100% of the theoretically necessary amount for reducing the boron source was based on the results of the study on the boron yield as follows. The poorly soluble B4C produced in the reaction of formula 0 above is
If the amount of carbonaceous material blended is set to a small value for oxidative decomposition by the reaction of the formula, the boron yield will decrease, and conversely, if more carbonaceous material is blended than necessary to increase the boron yield, there will be a shortage of boric acid. B4C is deposited in the furnace in the form of B4C without causing the Equation 0 reaction, or even if it is discharged during tapping, it is removed as an impurity in the purification process, resulting in a lower boron yield.

Therefore, there is naturally an appropriate amount of carbon material to obtain a high boron yield without depositing B4C, which is a poorly soluble substance, in the furnace.The inventors have conducted various experiments based on the above idea. , this amount of carbon material is such that the ratio of the actual amount of blended carbon material to the theoretical amount of carbon material required to reduce the total amount of oxygen in the raw material (hereinafter referred to as FC equivalent ratio) is 91% to 1.
It has been found that it is desirable to be in the range of 00%. FIG. 1 is a graph showing the relationship between boron yield and FC equivalent rate, and shows the results when boric anhydride of 0.5 mm or less was used as the boric acid source and pulverized coal or charcoal was used as the carbon material.

That is, as estimated by the present inventors, the boron yield has a maximum value with respect to the FC equivalent ratio, and the boron yield increases significantly when the FC equivalent ratio is 88% or higher, and increases significantly when the FC equivalent ratio exceeds 100%. Although it shows a decreasing tendency, the FC equivalent rate for obtaining a stable high boron yield is 91% to 100%. On the other hand, improved boron yield has the effect of reducing power consumption per unit weight of the product. Figure 2 shows the power consumption and F per unit weight of the product from the experiment that yielded the results shown in Figure 1 above.
In relation to the C equivalent rate, the power consumption is low at an FC equivalent rate of 91% to 100%.

Next, specific numerical values will be listed as examples of the present invention. Table 4 shows the results of 30 days of continuous operation in a 900kw DC Giro furnace. At this time, the depth of the hot water pool reached 370 mm after 7 days of operation, and remained the same thereafter.

Table 4 [Effects of the Invention] According to the method for producing ferroboron of the present invention, a direct current type Giraud furnace with a pool provided under the tap is used, and the reducing agent of the boron source is reduced to less than the theoretically required amount. It is possible to increase the yield of boron without depositing refractory substances on the hearth, and to reduce power consumption per unit weight of the product.

[Brief explanation of the drawing]

FIG. 1 is a graph showing boron yield versus FC equivalent rate, and FIG. 2 is a graph showing power consumption per unit weight of product versus FC equivalent rate.

Claims (1)

[Claims] In the electric furnace method for producing ferroboron, a direct current type Giraud furnace with a 100 mm to 500 mm deep molten metal layer under the tap is used, and the amount of carbon material used to reduce boron sources such as boron oxide and boric acid is determined. 91% to 100% of the theoretically required amount for reducing the boron source.