JPS5918346B2 - Manufacturing method of carbon furnace material for metal smelting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-performance carbon furnace material for metal smelting by developing the use of graphitized coke powder obtained from a graphitizing furnace.

Conventionally, carbon furnace materials used for aluminum electrolytic furnace lining materials and blast furnace bottom bricks are mainly composed of aggregate mixed with force-calcined anthracite grains and powder, to which a caking agent (for example, coal tar pitch) is added. After mixing and molding, heat is removed in a non-oxidizing atmosphere and fired at around 1000°C.

Power-burning petroleum coke may also be added to improve the strength and density of the resulting product.

In addition, with the aim of improving the thermal conductivity of blast furnace bottom members and the alkali resistance and electrical conductivity of aluminum electrolytic furnace lining materials, processed scraps of artificial graphite material produced from petroleum coke were used as aggregate. Carbon furnace materials are also manufactured.

If processed graphite waste is used as aggregate, considerable effects such as alkali resistance and compressive strength can be expected, but the processed waste is limited in quantity and is always difficult to obtain as a raw material. Moreover, using crushed artificial graphite products has the disadvantage of being expensive.

This invention focuses on the recovered graphitizing powder of coal-based coke that is used as a packing powder for the material to be graphitized in a graphitizing furnace during the production of artificial graphite materials, and uses this material as an aggregate to create a carbon furnace material. The purpose is to manufacture.

In order to facilitate understanding of the graphitized packing powder used in this invention, an outline of the manufacturing process of a normal artificial graphite material will be described.

Pitches are added as a caking agent to aggregate mainly composed of petroleum coke, heated and mixed at 100 to 150°C, and this mixture is pressure-molded by extrusion or die-casting method. It is buried and fired at about 1000°C to obtain a fired body.

The fired bodies are placed in an electric furnace (graphitization furnace) equipped with electrodes at opposing wall ends of the furnace body, and the voids are filled with coal-based metallurgical coke.

This coke powder is called "stuffed powder" in this field.

Since the furnace wall bricks of graphitization furnaces are exposed to high temperatures, a layer of silica sand or the like is provided between the furnace wall and the packing powder to extend the life of the furnace wall bricks (for example, chamotte bricks).

Furthermore, the top surface of the fired body packed in the furnace is covered with a thick layer of coke powder.
This is to prevent oxidation and heat radiation.

Next, the fired body is electrically resistance heated by passing a large current through the electrode at the hearth and heated to 2500°C to 3000°C following a predetermined load curve.
Heat to ℃ to graphitize.

At this time, the powder in the furnace is also graphitized at the same time.

This graphitized packed powder is taken out from the furnace when the graphitized product is discharged from the furnace and is sieved to remove particles with a predetermined particle size or higher.

It is reused as stuffing powder.

In the graphitization furnace, the packed calcined body and packed coke grains are used as resistance heating elements, and the packed coke grains are made of high electrical resistance and ash content whose sieve content has been adjusted (for example, 20 mesh to 7 mvt). Coal-based metallurgical coke with low carbon content is used.

As mentioned above, the silica sand charged between the inner circumferential surface of the furnace wall and the packing powder becomes 5i02+3 during the graphitization process.
C-) Silicon carbide is produced by the reaction of SiC and CO, and SiC and unreacted SiO□ are mixed therein.

The above-mentioned sieved reusable rejected graphitized stuffing powder (approximately 20 mesh or less) is usually about 9 out of 150 per 1 ton of graphitized product, and this graphitized stuffing powder is made of carburized materials such as cast iron. The reality is that the amount of use is limited, and there is no appropriate way to use it in large quantities.

According to the research conducted by the present inventors, coal-based packed coke is powdered as graphitization progresses, so the portion below 20 meshes has a high degree of graphitization and is preferable as aggregate for carbon furnace materials for metal smelting. I understand.

The amount of 5i02 and SiC mixed into the graphitized filler differs depending on the distance to the charged silica sand layer, load conditions, etc.

An example is shown in the table below. In order to develop the use of graphitized powder, the present inventors conducted the following tests to use it as a raw material for producing furnace materials for metal smelting.

Test Example 1 Each blended raw material shown in Table 2 was heated at 100 to 150°C in a kneading machine.
60'X1.15X225 by mold making
A molded body having a diameter of mm was prepared, and this molded body was buried in coke powder and fired at a temperature of 1100° C. for 48 hours in a non-oxidizing atmosphere.

The performance of each fired body was measured and the results are shown in Table 3.

The alkali resistance and erosion rate in Table 3 were determined by the following method.

(1) Determination of alkali resistance According to the method described in ASTM C454-62,
A 50 mm cube is cut out from the sample, a hole of 22 mm φ x 25 mm (deep) is bored in the center, 8 g of anhydrous potassium carbonate is placed in this hole, and the hole is covered with a 6 mm thick carbon plate.

This sample was buried in coke grains, heated at a rate of 200°C or less per hour, and held for 5 hours after reaching 955 ± 8°C.
After cooling, the sample was taken out and the degree of cracking caused by the alkali was observed and judged as follows.

U: No cracks at all LC: Slight cracks C: Cracks with a width of about 0.4 ym or more D:
Near disintegration (2) Erosion rate A sample cut into a 20mmφ x 150mm diameter was immersed to a depth of 100mm in hot metal with a carbon concentration of about 4 heated to 1400℃ in a magnetic crucible, 54 times/min. The sample was held for about 30 minutes while rotating, and the sample was pulled up and the adhering iron content was removed with dilute hydrochloric acid.The amount of erosion of the left rear sample was determined, and the erosion rate (k) was calculated using the following formula.

However, Ca: carbon saturation concentration, C: average carbon concentration at the time of measurement, t: immersion time (seconds), A: surface area of immersion part of sample (d)
, △W: amount of erosion <g>.

As shown in the results in the table above, when graphitized packing powder (A1) and graphite powder (A7) are compared, they show similar properties, and when compared with force-calcined anthracite (A5), graphitized packing powder (A1) has similar properties. Product furnace material properties are good.

The unexpected effects of graphitized packing powder on alkalinity resistance and erosion rate are due to the 5iC contained in graphitized packing powder.
It is impossible to think that this is due only to 1Sin2.

This is because the material according to the present invention is superior to the material of Comparative Example A6 in which these are added in terms of alkalinity resistance and erosion rate.

Possible causes of this effect include impurities contained in silica sand and coke that are exposed to high temperatures along with carbon, and that coke is relatively hard.

As mentioned above, by using graphitized packing powder, it can be used as a substitute for the conventional raw material for producing carbon furnace materials for metal smelting, and the amount of conventional raw materials can be reduced by blending graphitized packing powder. Moreover, it becomes a furnace material with excellent alkalinity resistance and hot metal resistance.

Graphitized packed powder, force-calcined anthracite, artificial graphite in Test Example 1,
A test example of a combination other than the combination with force-baked petroleum coke is shown in the fourth example.
Table 1 is shown.

The manufacturing method was carried out according to Test Example 1.

These products have high levels of strength, alkalinity resistance, and thermal conductivity, and their erosion rate is relatively low.
It can be seen that it is suitable as a furnace material.

Test Example 2 A mixture of 40 parts by weight of graphitized powder (under 100 mesh), 40 parts by weight of 20-40 mesh of force-burned petroleum coke, and 20 parts by weight of 100 mesh was mixed with 29 parts by weight of coal tar pitch, By extrusion molding method, 90mwφ×
A hollow rod with a diameter of 35 mm and a diameter of 3000 mm was made and fired in the same manner as in Test Example 1.

This fired body (SiC+SiO, Section 2, 16) was vacuum impregnated with coal tar, fired in the same manner, and further heated with electricity to 2300'C to obtain a lance.

The bending strength of this product was 320 kg/cyit, and the erosion rate (k) was 1.9.

Instead of graphitized powder, an artificial graphite layer is mixed in the same way, molded,
The bending strength of the lance made under exactly the same firing conditions was 3.
To 25! g/ffl, but the erosion rate (k) was 2.
4, indicating that a lance made of graphitized powder as an aggregate is more effective in reducing erosion loss than a lance made of an artificial graphite layer as an aggregate.

As shown in the above test examples, graphitized packing powder can be used as a raw material for furnace materials for metal smelting, and it is extremely meaningful that it can be used effectively.

Claims (1)

[Claims] 1 In a method for manufacturing carbon furnace materials for metal smelting, silicon carbide and silicon dioxide recovered from a graphitization furnace in which graphitization is performed by providing a layer of silica sand between furnace wall bricks and coal-based coke packing powder. A method for producing a carbon furnace material, characterized in that 10 parts by weight or more of graphitized recovered packing powder containing the above is used as an aggregate.