JP5171919B2 - Method for producing granular mold powder for continuous casting of steel - Google Patents

Description

  The present invention relates to a method for producing granular mold powder added to a mold in continuous casting of steel.

  The form of the mold powder added on the molten steel in the mold during continuous casting of steel is roughly classified into a powder type and a granule type. Since powdered mold powder generates a lot of dust when it is put into the mold and causes problems such as worsening the working environment, granular mold powder is usually used. There are various types of granular mold powders depending on the production method, but the most common is a spray granule obtained by a spray granulation method of granulating and drying with a spray dryer.

  In the spray granulation method, raw material slurry is sprayed in a drying tower in a high temperature atmosphere, and slurry droplets are dried in a short time to form granules. As a method for spraying the raw material slurry, there are a disk type and a pressure nozzle type. The disk type is a system in which raw material slurry is supplied to a disk that rotates at high speed and the raw material slurry is pulverized by centrifugal force. The disc type is usually used to obtain granules having a relatively small particle size. In the disc type, since the raw slurry is sprayed in the radial direction of the disc, it is necessary to increase the diameter of the drying tower as compared with the pressurized nozzle type.

  On the other hand, the pressure nozzle type is a method in which pressure is applied to the raw material slurry to be sprayed and the slurry droplets are sprayed from the pressure nozzle to be atomized. The pressure nozzle type is used when it is desired to obtain granules having a larger particle size than the disk type. In the pressurized nozzle type, a spray is applied after a swirl flow is applied to the raw slurry, and the slurry droplets form a hollow cone type spray pattern, and the slurry droplet particles The diameter is uniform and the contact between the slurry droplet and the hot air is good. The pressurized nozzle type has a simpler structure than the disk type and has lower equipment and maintenance costs. However, in order to respond to changes in the type and throughput of the raw slurry, the nozzle parts called orifices and cores must be replaced. Is required. The diameter of the drying tower is smaller than that of the disk type and tends to be longer in the height direction. The pressure nozzle type is mainly used for low-mix and mass production.

  The contact method of hot air and slurry droplets in the drying tower in the spray granulation method is roughly classified into a cocurrent type and a countercurrent type. The co-current type often used in the disk type is a system in which hot air introduced from the upper part of the drying tower descends with the slurry droplet flow sprayed from the upper part of the drying tower, and the temperature of the dried granules is higher than the hot air outlet temperature. It will not be high. In the countercurrent type employed in the pressure nozzle type, hot air is introduced from the upper part of the drying tower and discharged from the lower part. The raw material slurry is sprayed upward from the lower part of the drying tower using a pressure nozzle to bring the slurry droplets and hot air into countercurrent contact in the initial stage of drying, and then the dropped granules are recovered from the lowermost part of the drying tower. The counter-current type can take a long residence time of slurry droplets, and is therefore suitable for granulating relatively large granules.

  Since the granular mold powder for continuous casting of steel requires large particles with an average particle size of 300 μm or more, all the spray granules produced by the spray granulation method are conventionally used with a countercurrent type using a pressurized nozzle type. Manufactured by. The hot air introduction temperature is 400 to 600 ° C., the slurry solid content concentration is about 50 to 70% by mass, and the pressure nozzle for spraying the raw slurry is 3 to 10 at the bottom of the drying tower in consideration of the spray amount and the like. Generally, it is arranged about this amount. By this method, a granular mold powder having an average particle size of about 300 to 500 μm is obtained.

  For example, in Patent Document 1, when the raw material slurry of mold flux is spray-dried in a hot air drying tower and the hollow mold flux is discharged from the lower part of the drying tower, the hot air for drying at 400 to 550 ° C. is directed downward from the top of the drying tower. And a plurality of lance nozzles for spraying the raw material slurry disposed in the lower part of the drying zone in the drying tower, the solid-liquid ratio is 55 to 75% and the viscosity is 50 to 1000 mPa.s. A method for producing a hollow granule mold flux is disclosed, in which the raw material slurry of S is sprayed upwardly and the initial droplet drying of the generated raw material slurry is performed by countercurrent contact with hot air for drying. .

  Further, Patent Document 2 is an apparatus for vapor-drying a raw material slurry of mold flux, and connects a hot air conveying pipe for conveying hot air from a hot air supply source to the top of a cylindrical drying tower, A plurality of lance nozzles for injecting slurry into the drying tower are detachably arranged through the side wall of the drying tower, point-symmetrically in the straight body of the drying tower, and with the nozzle inclined upward. A hollow granule mold flux comprising a hot air exhaust part for separating and discharging product flux and exhaust of dried hot air, and a mold flux product storage cut-out part below the drying tower straight body part A manufacturing apparatus is disclosed.

  Further, Patent Document 3 includes spherical particles composed of a flux component for metal casting and a carbonaceous powder, and the carbonaceous powder is dispersed and contained throughout the solid portion in the particles. Disclosed is a metal casting flux characterized in that the proportion of the carbonaceous powder on the surface of the particles is larger than the total proportion of the carbonaceous powder in the solid portion of the particles. Further, FIG. 3 discloses a flux production apparatus in which a rotating disk type sprayer and a hot air supply port are provided at the top of the drying tower, and the slurry and hot air flow in parallel downward. This apparatus is provided with a cyclone for recovering the flux, and since the rotating disk and the cyclone are used in combination, the particle size of the obtained flux is presumed to be quite fine. Due to the small particle size obtained, this disk-type and co-current method has not been put to practical use in the production of mold powders.

  Further, in Patent Document 4, when a raw slurry of a mold flux for continuous casting of steel is sprayed into a high-temperature atmosphere through a lance nozzle installed in a cantilever manner in a spray drying tower, the lance nozzle is dried. A method for producing a mold flux for continuous casting of steel is disclosed in which slurry adhesion to the nozzle tip portion is prevented by applying vibration to the nozzle tip portion. Further, paragraphs [0034] and [0035] disclose a monitoring system in which individual lance nozzles are monitored by a video camera or the like and vibration is applied to the lance nozzles based on the results.

  Further, Patent Document 5 discloses a device in which a raw material slurry of mold flux is spray-dried in a hot air drying tower, and the hollow granule mold flux and hot air exhaust are separated and discharged from the lower part of the drying tower. A coating layer was formed on the inner surface of the drying zone constituting the upper part of the drying slurry up to the hot air inlet at the top of the drying tower, from the attachment position of the lance nozzle for injecting the raw material slurry. An apparatus for producing a hollow granule mold flux is disclosed.

Japanese Patent Laid-Open No. 10-146657 Japanese Patent Laid-Open No. 10-193060 Japanese Patent Publication No. 3-79100 JP 10-211153 A JP-A-10-166122

  However, as described in the above-mentioned Patent Documents 1 and 2, there are various problems when a granular mold powder is produced by a counter-current type and a pressure nozzle type. First, when the raw material slurry is sprayed upward from the pressure nozzle, the spread angle of the sprayed slurry droplets increases, so it is necessary to increase the drying tower diameter to prevent the slurry droplets from adhering to the inner wall of the drying tower. is there. Also, when the raw material slurry is sprayed upward, a part of the slurry drips from the tip of the nozzle, and the raw material slurry that has dripped down for a long period of time accumulates and grows, and the slurry droplet contacts the deposit. Abnormal spraying in which the spraying direction changes is generated and adheres to the drying tower, and further, as deposition progresses, the spray amount may decrease and the pressure nozzle may be blocked. When the pressure nozzle is closed, the spray amount as set cannot be secured, and the productivity is deteriorated. In addition, when the closed pressure nozzle receives heat, the slurry in the pressure nozzle coagulates. If left as it is, the solidified slurry cannot be removed even if washed, and the pressure nozzle itself must be reused. Once the pressure nozzle is blocked, the pressure nozzle must be replaced.

  In addition, the pressure nozzle is attached to a nozzle support bar installed on the side wall of the drying tower. Undried slurry droplets falling inside the drying tower adhere to and accumulate on the nozzle support bar. Form deposits. A manufacturing method as disclosed in Patent Document 4 has been proposed in order to prevent liquid dripping deposits at the nozzle tip and adhesion and accumulation on the nozzle support rod. It is impossible to completely prevent the growth of deposits due to dripping or the accumulation of slurry droplets on the nozzle.

  In addition, when the raw material slurry is sprayed upward from a pressure nozzle installed at the lower part of the drying tower by a countercurrent type, slurry droplets adhere to the upper part of the drying tower. Since the upper part of the drying tower is close to the hot air inlet and becomes high temperature, the carbon black in the mold powder adhering to the upper part of the drying tower is oxidized by receiving heat. Usually, about 1 to 2% of carbon black is added to the mold powder, and the color tone of the mold powder is black. However, when the carbon black is oxidized as described above, the mold powder becomes white. If the whitened mold powder deposit falls, a defective product in which carbon black is oxidized is mixed in the granular mold powder, which is not preferable. In order to prevent the white mold powder from being mixed, conventionally, the hot air temperature has been kept low so that the carbon black is not oxidized. However, when the hot air temperature is lowered, it becomes difficult to dry, so that there is a problem that adhesion of slurry droplets into the drying tower is promoted. When there is much adhesion in the drying tower, there is a problem that the recovery rate of the granular mold powder is deteriorated and the production cost is increased. Moreover, since it is a high place when adhering to the upper part in a drying tower, there also exists a problem that the removal operation | work is difficult and dangerous.

  Then, although the manufacturing apparatus currently disclosed by patent document 5 is proposed, the adhesion prevention effect to the upper part in the drying tower of the sprayed slurry is limited, its durability is low, and the cost which forms a coating layer However, it has not been put into practical use.

  Therefore, the object of the present invention is to prevent abnormal spraying due to clogging of the pressure nozzle when producing granular mold powder with the pressure nozzle type, and to reduce the adhesion of slurry droplets sprayed into the drying tower. The recovery rate of the granular mold powder can be improved, and it is not necessary to replace the pressure nozzle during operation, which can save labor, and even if slurry droplets adhere to the drying tower. An object of the present invention is to provide a method for producing a granular mold powder for continuous casting of steel, which is less prone to whitening due to oxidation of carbon black in the granular mold powder.

That is, in the method for producing a granular mold powder of the present invention, hot air of 600 to 750 ° C. is introduced from the hot air inlet provided in the upper part of the drying tower, exhausted at the lower part of the drying tower, and the mold powder raw material slurry is removed from the drying tower. The slurry is sprayed downward from a pressure nozzle provided in the upper part and dried while moving the slurry droplets in parallel with hot air, and the obtained granular mold powder is recovered from the lower part of the drying tower.

  Furthermore, the manufacturing method of the granular mold powder of this invention of this invention is characterized by the solid content concentration of a mold powder raw material slurry being 50-70 mass%.

  Moreover, the manufacturing method of the granular mold powder of this invention provides a 2nd hot air inlet in the drying tower center vicinity vicinity, and provides a swirl flow to the hot air which goes to a lower part from a drying tower upper part.

  Furthermore, the manufacturing method of the granular mold powder of the present invention is characterized in that the length of the straight body portion of the drying tower is 10 to 20 m.

  According to the method for producing a granular mold powder of the present invention, when producing a granular mold powder by a pressure nozzle type, abnormal spraying due to clogging of the pressure nozzle can be prevented, and adhesion of slurry droplets into the drying tower can be prevented. It can be reduced to improve the recovery rate of granular mold powder, and it is not necessary to replace the pressure nozzle during operation, saving labor, and slurry droplets adhere to the drying tower. However, since the adhering site is a relatively low temperature zone away from the hot air inlet, there is an effect that there is less fear of whitening due to oxidation of carbon black in the mold powder.

It is the schematic of the drying tower used in the Example. It is the schematic of the drying tower used in the comparative example.

  The method for producing a granular mold powder according to the present invention, when producing a granular mold powder by a pressure nozzle type, introduces hot air from the upper part of the drying tower and exhausts it at the lower part of the drying tower, and removes the mold powder raw material slurry from the drying tower. The slurry is sprayed downward from a pressure nozzle provided at the upper part and dried while moving the slurry droplets in parallel with hot air, and the obtained granular mold powder is recovered from the lower part of the drying tower.

  In this invention, the average particle diameter of the granular mold powder obtained can be adjusted to the range of 300-500 micrometers, Preferably it is 310-450 micrometers by spraying mold powder raw material slurry using a pressure nozzle. Here, when the mold powder raw material slurry is sprayed downward with a pressure nozzle, the spread angle of the slurry droplets can be reduced to about 45 °. On the other hand, when the mold powder raw material slurry is sprayed upward by the pressure nozzle, the spread angle of the slurry droplets is expanded to about 60 °. That is, by spraying downward from the pressure nozzle, the spread angle of the slurry droplet is reduced, the sprayed slurry droplet is difficult to reach the inner wall of the drying tower, and the drying tower diameter can be reduced. . Although the spray angle is basically directly below the vertical, depending on the direction of hot air introduction, it is also possible to make an angle slightly below the vertical so that undried slurry droplets do not reach the inner wall of the drying tower. Also, by spraying the mold powder raw material slurry downward from the pressure nozzle, it is possible to prevent liquid dripping from the nozzle tip, and there is no accumulation of raw material slurry on the nozzle tip, resulting in abnormal spraying or blockage of the pressure nozzle Can be prevented. Furthermore, a support rod as in the case of installing a pressure nozzle at the bottom of the drying tower is not required, and it is possible to obtain granular mold powder of a certain quality without causing adhesion and accumulation of slurry droplets on the support rod. Can do.

  When the mold powder raw material slurry is sprayed downward from the upper part of the drying tower with a pressure nozzle as in the present invention, the adhesion of slurry droplets mainly occurs at the lower part of the drying tower, and at the upper part of the drying tower where the temperature is high near the hot air inlet. Does not adhere. Since the lower part of the drying tower is away from the hot air inlet, the temperature of the hot air contacting the slurry droplets at the upper part of the drying tower is lowered. Therefore, even if slurry droplets adhere to the lower part of the drying tower, the hot air temperature is lower than about 400 to 500 ° C., which is the oxidation temperature of carbon black in the mold powder, so that the carbon black is oxidized. In other words, the adhered slurry droplets are not whitened. Therefore, even if the deposits fall off and are mixed in the granular mold powder, the product quality is not affected.

  The structure of the pressure nozzle is not particularly limited, and a conventional pressure nozzle can be used. Further, in order to prevent the slurry from solidifying in the pressure nozzle due to heating, a double tube structure in which cooling air is allowed to flow around the outer periphery of the pressure nozzle can be used. Further, the orifice diameter of the mold powder raw material slurry discharge port of the pressure nozzle can be changed according to the particle diameter of the granular mold powder, for example, about 1.5 to 4.0 mm, preferably 1.8 to 3. It can be about 8 mm.

In the present invention, the hot air temperature is 600 to 750 ° C., preferably 600 to 700 ° C., at the inlet to the drying tower. Here, if the temperature of the hot air is less than 600 ° C., the slurry droplets cannot be dried, and more undried slurry droplets adhere to the lower part of the drying tower, and particularly large droplets are dried. This is not preferable because it is difficult to form and adheres in an undried state, so that a granule having a large particle size cannot be obtained. Furthermore, since the granule moisture does not decrease and secondary drying is required, it is not preferable. Further, if the temperature exceeds 750 ° C., it becomes necessary to install a refractory on the surface of the hot air blowing equipment or the inner wall of the drying tower, which increases the cost of manufacturing the drying tower; Repeating decreases durability; thermal efficiency deteriorates and fuel cost increases; when mold powder raw material slurry comes into contact with hot air, it dries too quickly and the hollowness becomes too high, and the resulting mold powder has a high particle strength. This is not preferable because of problems such as lowering.

  Further, the composition of the mold powder raw material slurry is not particularly limited, and those having a conventional composition can be used. Further, the solid content concentration of the mold powder raw material slurry is set to 50 to 75% by mass, preferably 54 to 65% by mass. Here, when the solid content concentration of the mold powder raw material slurry is less than 50% by mass, the water content is excessively increased, the drying efficiency is lowered, the drying takes time, and the adhesion to the lower portion of the drying tower is increased. Therefore, it is not preferable, and when it exceeds 75% by mass, the viscosity of the mold powder raw material slurry becomes too high, and it is necessary to increase the pressure for pumping the mold powder raw material slurry, which imposes a heavy burden on the pressure pump and piping. This is not preferable.

  The average particle size of the granular mold powder obtained by the method of the present invention is 300 to 500 μm, preferably 310 to 450 μm. Here, when the average particle diameter of the granular mold powder is less than 300 μm, the amount of fine powder increases, which is not preferable because the effect of the granules is small, and when it exceeds 500 μm, adhesion to the drying tower increases. This is not preferable because the product recovery rate deteriorates.

  When producing granular mold powder in the range of 300 to 500 μm, it is necessary to spray large slurry droplets from a pressure nozzle, and it takes a long time to dry into granular mold powder. In order to spray slurry droplets downward from the top of the drying tower with a pressure nozzle and ensure a sufficient drying time, it may be necessary to lengthen the length of the straight body of the drying tower. The length of the drying tower straight body is preferably 7 to 20 m, more preferably 10 to 20 m, and still more preferably 15 to 20 m. If the length of the straight section of the drying tower is less than 7 m, the slurry droplets cannot be completely dried, and the large slurry droplets are not dried and adhere to the lower part of the drying tower, so Since it cannot be obtained, it is not preferable, and even if the length of the straight body portion of the drying tower exceeds 20 m, an action / effect corresponding to the length cannot be expected.

  In the method for producing a granular mold powder of the present invention, hot air and slurry droplets are moved in a co-current manner from the upper part of the drying tower to the lower part, but at the lower part of the drying tower, the hot air temperature is too low and the drying efficiency is lowered. Therefore, a new hot air can be introduced into the drying tower by providing an auxiliary hot air supply port in the middle of the drying tower. In addition, this auxiliary hot air supply port is installed in a direction to give a swirl flow to the hot air in the drying tower, and the horizontal temperature distribution in the drying tower is made uniform, or the contact efficiency between the granular mold powder and hot air is increased. be able to. The temperature of the hot air introduced from the auxiliary hot air supply port is about 250 to 500 ° C, preferably about 300 to 400 ° C.

The production method of the granular mold powder of the present invention will be further described below with reference to examples and comparative examples.
First, the drying tower used for the Example and the comparative example is demonstrated with a figure.
FIG. 1 is a schematic view of a drying tower used in the examples. The drying tower (1) is composed of a tower top part (A), a straight body part (B), and a lower cone part (C).
A hot air inlet (2) is provided at the center of the tower top (A), and hot air having a predetermined temperature shown in Table 1 below can be introduced into the drying tower. A predetermined number of pressure nozzles (5) are concentrically arranged downward from the center of the tower top (A), and the raw slurry (4) is dried as slurry droplets by the pump (3). 1) It is the structure sprayed in. As the pressure nozzle (5), a pressure nozzle having a double structure capable of flowing cooling air around the outer periphery of the nozzle was used. Further, the length of the straight body part (B) is as shown in Table 1, and the hot air and the slurry droplets are configured to move down the straight body part (B) in a parallel flow manner.
Furthermore, the lower cone part (C) is configured with a cone angle of 60 °, and has a configuration in which a hot air exhaust port (6) and a granular mold powder outlet (7) are installed.

FIG. 2 is a schematic view of the drying tower used in the comparative example. The drying tower (1) is comprised from the tower top part (A), the straight body part (B), and the lower cone part (C) similarly to FIG.
A hot air inlet (2) is provided at the center of the tower top (A), and hot air having a predetermined temperature shown in Table 1 below can be introduced into the drying tower.
Further, a pressure nozzle (5) is installed upward at the lower part of the straight body part (B), and the raw slurry (4) is sprayed as slurry droplets into the drying tower (1) by the pump (3). It has a configuration.
Furthermore, the lower cone part (C) is configured with a cone angle of 60 °, and has a configuration in which a hot air exhaust port (6) and a granular mold powder outlet (7) are installed.

  Examples and Comparative Examples were performed under the conditions described in Table 1, using the drying tower described in FIG. 1 and FIG. 2 and using a mold powder raw material powder containing 1.2% by mass of carbon black.

In Table 1,
The granular mold powder recovery rate (%) is the recovery rate during continuous 10-hour operation;
The adhering moisture of the granular mold powder is obtained from the mass before and after drying the obtained granular mold powder at 105 ° C .;
The bulk specific gravity of the granular mold powder is determined from the volume when 100 g of a granular mold powder sample is placed in a 200 ml measuring cylinder and loosely filled;
The particle strength of the granular mold powder was determined from the powdering rate after mixing with an alumina boat for 10 minutes with a V-type mixer, ○ indicates that the powdering rate is small and there is no problem in use, and × indicates Indicates the case where the dusting rate is large and the dust generation is conspicuous;
The average particle diameter of the granular mold powder is the median diameter measured with a dry sieve.

In Example 1 of the present invention, a slight amount of deposit was observed in the lower cone after the experiment, but the deposit was black and the carbon black in the granular mold powder was not oxidized.
In Example 2 of the present invention, deposits were observed in the lower cone after the experiment was completed, but the deposits were black and the carbon black in the granular mold powder was not oxidized.
In Example 3 of the present invention, a slight amount of deposit was observed in the lower cone after the experiment, but the deposit was black and the carbon black in the granular mold powder was not oxidized.
In Comparative Example 1, after the experiment was completed, many deposits were observed above the vicinity of the center of the straight body and on the pressure nozzle, and the deposits were white and mixed with granular mold powder in a state where carbon black was oxidized. Observed.

  According to the present invention, a granular mold powder used for continuous casting of steel can be produced.

  DESCRIPTION OF SYMBOLS 1 Drying tower; 2 Hot air introduction port; 3 Pump; 4 Raw material slurry; 5 Pressurization nozzle; 6 Exhaust port; 7 Granular mold powder outlet; 8 Adhesives; A Tower top part; B Straight body part;

Claims (5)

A hot air of 600 to 750 ° C. is introduced from the hot air inlet provided at the upper part of the drying tower and exhausted at the lower part of the drying tower, and the mold powder raw material slurry is sprayed downward from a pressure nozzle provided at the upper part of the drying tower. A method for producing granular mold powder for continuous casting of steel, characterized in that the slurry droplets are dried while being moved in parallel with hot air, and the obtained granular mold powder is recovered from the lower part of the drying tower. The solid content of mold powder slurry is 50 to 75 wt%, The process according to claim 1, wherein the continuous casting granular molding powder steel. The method for producing granular mold powder for continuous casting of steel according to claim 1 or 2 , wherein the average particle diameter of the granular mold powder is in the range of 300 to 500 µm. The granular mold for continuous casting of steel according to any one of claims 1 to 3, wherein a second hot air inlet is provided near the center of the drying tower to impart a swirling flow to the hot air from the upper part of the drying tower to the lower part thereof. Powder manufacturing method. The manufacturing method of the granular mold powder for continuous casting of steel of any one of Claim 1 thru | or 4 whose length of a drying tower straight body part is 10-20m.

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