JP7684563B2 - Extrusion Molding Method - Google Patents

Description

The present invention relates to an extrusion molding method.

As a method for agglomerating fine iron ore or dust generated in steelworks, the sintering method and the fired pellet method are generally used, but the non-fired agglomeration method, which does not require a firing process, is also used from the viewpoint of energy saving. In the non-fired agglomeration method, cement is used as a binder to give the non-fired agglomerated ore, which is the product of the method, strength sufficient to withstand use in a blast furnace. The main forming methods in the non-fired agglomeration method are the rolling granulation method and the extrusion molding method. Of these methods, the extrusion molding method is effective because it can obtain a stronger molded body. In the extrusion molding method, when the raw materials for the non-fired agglomerated ore are fed into an extrusion molding machine (e.g., a screw-type extrusion molding machine), the raw materials are extruded in a specified direction in the extrusion molding machine and consolidated (granulated), and are discharged as a molded body. The obtained molded body is cured for a specified period of time, and strength is developed due to the hardening action caused by the hydration of cement, and it becomes a non-fired agglomerated ore. In order to stably produce molded bodies using the extrusion molding method, it is important to adjust the particle size of the raw materials.

More specifically, in the extrusion molding method, if the particle size of the raw material becomes too large (coarse), the plasticity of the raw material decreases, the shape of the molded body cannot be maintained, and the yield of the molded body decreases. On the other hand, if the particle size of the raw material becomes too small (fine), a problem of the raw material adhering to the raw material inlet and the inner wall surface of the extrusion molding machine may occur. The raw material adhering to the raw material inlet and the inner wall surface of the extrusion molding machine gradually grows due to the hardening action of the cement, and has a negative effect on the supply of raw material. For example, the raw material inlet is blocked by the adhesion of the raw material. For this reason, cleaning work is required to remove the adhesion of the raw material. As a result, productivity decreases. For this reason, in order to stably produce molded bodies using the extrusion molding method, it is necessary to adjust the particle size of the raw material to an appropriate range. If the particle size of the raw material can be adjusted to an appropriate range, the above-mentioned problems can be avoided and molded bodies can be stably produced.

JP 2007-31768 A JP 2006-322058 A

However, because the appropriate range of particle size varies depending on the type of raw material, the blending ratio, etc., when the raw materials change, the particle size must be adjusted by trial and error, which often leads to production problems (i.e., the problems mentioned above). Although Patent Documents 1 and 2 disclose techniques related to the manufacturing method of non-sintered agglomerate ore, they do not state or suggest anything about adjusting the particle size of the raw materials to the appropriate range.

The present invention has been made in consideration of the above problems, and aims to provide a method for determining the appropriate particle size of the raw material during extrusion molding in the process of manufacturing non-calcined agglomerates by extrusion molding.

In order to solve the above problems, according to one aspect of the present invention, there is provided a method for extrusion molding of raw materials including iron-based raw materials, characterized in that the method includes the steps of: preparing an evaluation raw material for identifying a correlation between dynamic adhesion, which is an evaluation index of the fluidity of the raw material, and the manner of extrusion molding; determining the dynamic adhesion of the evaluation raw material when extrusion molding is performed normally as an appropriate range of dynamic adhesion; and determining the particle size of the raw material to be used during extrusion molding so that the dynamic adhesion of the raw material to be used falls within the appropriate range.
The evaluation index for the fluidity of the raw material may be flow energy.

According to the above-mentioned aspect of the present invention, it is possible to determine the appropriate particle size of the raw material during extrusion molding in the process of manufacturing non-sintered agglomerates by extrusion molding.

FIG. 1 is a schematic diagram showing an overview of a screw extruder, which is an example of an extruder. FIG. 1 is a schematic diagram showing an overview of a roller-type extrusion molding machine, which is an example of an extrusion molding machine. 1 is a graph showing an example of an appropriate range of particle sizes of raw materials. 1 is a graph showing the correlation between the median diameter of raw materials and dynamic adhesion.

A preferred embodiment of the present invention will be described in detail below with reference to the attached drawings. Each raw material used in this embodiment is an aggregate of many particles. Unless otherwise specified, the name of each raw material refers to the aggregate of particles that make up that raw material. A numerical range expressed using "~" refers to a range that includes the numerical values written before and after "~" as the lower and upper limits. Numerical values indicated as "greater than" or "less than" are not included in the numerical range.

<1. Extrusion molding process>
In this embodiment, the particle size of the raw material is adjusted so that a molded product is normally formed in the extrusion molding process. Here, the extrusion molding process will be briefly described. The extrusion molding process is a process in which a molded product is extruded using an extruder.

The raw materials to be used in this embodiment (raw materials to be used) may be any materials generally used in the production of non-sintered agglomerates, including iron-based raw materials. The raw materials to be used include, for example, iron ore, coke powder, and iron-making dust, and contain cement as a binder. The raw materials are usually pulverized in a ball mill or the like to a particle size of 1 mm or less before being fed into the extrusion molding machine. The pulverized raw materials are conditioned with moisture suitable for extrusion molding, and are molded in the extrusion molding machine. In this embodiment, the particle size of the raw materials is set within an appropriate range. The obtained molded body is cured for a predetermined period of time, and strength is developed due to the hardening action of the cement hydration reaction, becoming non-sintered agglomerates.

Examples of the extrusion molding machine include a screw-type extrusion molding machine 1A shown in FIG. 1 and a roller-type extrusion molding machine 1B shown in FIG. 2. The screw-type extrusion molding machine 1A includes a main body 10, a raw material inlet 11, a screw 12, and a die 13. The main body 10 has a hollow structure and extends in the left-right direction in FIG. 1. One end of the main body 10 is closed, and a die 13 is provided at the other end. The raw material inlet 11 is provided on the upper side of the closed end of the main body 10, and raw material X is introduced into the main body 10, i.e., into the screw-type extrusion molding machine 1A, from the raw material inlet 11. The screw 12 is installed in the main body 10 and rotates in the direction of the arrow A. As a result, the raw material X in the main body 10 is consolidated (granulated) while being extruded to the right in FIG. 1, and is discharged from the die 13 as a molded body Y. A gap 13a is formed in the die 13, and the molded body Y is discharged from this gap 13a. Here, if the grain size of the raw material X becomes too large (coarse), the plasticity of the raw material X decreases, the shape of the molded body Y cannot be maintained, and the yield of the molded body Y decreases. On the other hand, if the grain size of the raw material X becomes too small (fine), a problem may occur in which the raw material X adheres to the raw material inlet 11 or the inner wall surface of the extrusion molding machine 1A. The raw material X adhered to the raw material inlet 11 or the inner wall surface of the extrusion molding machine 1A gradually grows due to the hardening action of the cement, adversely affecting the supply of raw materials. For example, the raw material inlet 11 is clogged with the adhesion of the raw material X. For this reason, cleaning work is required to remove the adhesion of the raw material X. As a result, productivity decreases.

The roller-type extrusion molding machine 1B shown in FIG. 2 includes a main body 20, a raw material inlet 21, a rotating roller 22a, a rotating shaft 22b, and a die 23. The main body 20 has a cylindrical shape and is open at the top. This opening is the raw material inlet 21. The die 23 is provided on the bottom end surface of the main body 20. Raw material X is introduced into the main body 20, i.e., into the roller-type extrusion molding machine 1B, from the raw material inlet 21. The rotating shaft 22b is inserted into the main body 20 and rotates in the direction of arrow B. The rotating roller 22a is driven in conjunction with the rotation of the rotating shaft 22b and rotates along the inner circumferential surface of the main body 20. As a result, the raw material X in the main body 20 is compacted (granulated) while being extruded downward in FIG. 2, and is discharged from the die 23 as a molded body Y. A gap 23a is formed in the die 23, and the molded body Y is discharged from this gap 23a. Here, if the grain size of the raw material X becomes too large (coarse), the plasticity of the raw material X decreases, the shape of the molded body Y cannot be maintained, and the yield of the molded body Y decreases. On the other hand, if the grain size of the raw material X becomes too small (fine), a problem may occur in which the raw material X adheres to the raw material inlet 21 or the inner wall surface of the extrusion molding machine 1B. The raw material X adhered to the raw material inlet 21 or the inner wall surface of the extrusion molding machine 1B gradually grows due to the hardening action of the cement, and has a negative effect on the supply of raw materials. For example, the raw material inlet 21 is clogged with the adhesion of the raw material X. For this reason, cleaning work is required to remove the adhesion of the raw material X. As a result, productivity decreases. The extrusion molding method according to this embodiment is preferably applied to an extrusion molding machine in which the above-mentioned problem may occur. Therefore, the extrusion molding method according to this embodiment is preferably applied to extrusion molding machines other than the above-mentioned screw type extrusion molding machine 1A and roller type extrusion molding machine 1B as long as the extrusion molding machine is in which the above-mentioned problem may occur.

<2. Dynamic adhesion>
The raw material used in extrusion molding is required to have a fluidity sufficient to be discharged from the extruder. In addition, it is desirable for the raw material to have high fluidity in order to suppress adhesion of the raw material in the extruder. On the other hand, if the raw material has too high a fluidity, a molded body cannot be formed, so the raw material is also required to have a moderate adhesiveness.

The inventors focused on the fact that both the adhesion and molding of raw materials occur when the raw materials are in a flowing state, and devised a method to determine the appropriate range of raw material particle size by evaluating in advance the adhesion of the raw materials in a dynamic state (dynamic adhesion). The outline of this method is as follows.

In this embodiment, first, raw materials (evaluation raw materials) for evaluating dynamic adhesion are prepared. Next, raw materials are sampled when extrusion molding is performed normally and when an abnormality occurs in extrusion molding (i.e., the shape of the molded body cannot be maintained as described above, raw materials adhering to the raw material inlet or the inner wall surface of the extruder gradually grow due to the hardening action of the cement and have a negative effect on raw material supply, etc.). Next, the dynamic adhesion of the raw materials is measured. Then, based on these results, the appropriate range of dynamic adhesion is determined.

Next, the raw materials to be used in the extrusion molding (raw materials to be used) are sampled in advance, and the particle size of the raw materials is changed to measure the dynamic adhesion. Then, the particle size of the raw materials that brings the dynamic adhesion into the appropriate range is determined.

The lower limit of the appropriate range of dynamic adhesion corresponds to the minimum value of dynamic adhesion at which a molded body can be formed. The upper limit of the appropriate range of dynamic adhesion corresponds to the maximum value of dynamic adhesion when the raw material does not adhere in the extruder (the raw material does not grow in the extruder). These values are determined by measuring the dynamic adhesion of the raw material when no molded body is formed and when raw material adhesion occurs in the extruder.

Next, we will explain how to measure dynamic adhesion. Dynamic adhesion is one of the indices for evaluating the fluidity of powder raw materials, and its measurement method is described, for example, in Non-Patent Document 1 (Nagashima et al., "Evaluation of the fluidity of fine powders based on dynamic flow characteristics by aeration and stirring", Journal of the Society of Powder Technology, Vol. 52 (2015), No. 10, pp. 576-584) and Non-Patent Document 2 (Reg Freeman, "Measuring the flow properties of consolidated, conditioned and aerated powders - A comparative study using a powder rheometer and a rotational shear cell", Powder Technology 174 (2007). 25-33).

In this embodiment, the dynamic adhesion of the raw material is measured by the following method. First, the raw material to be measured (evaluation raw material) is filled into a cylindrical container with a diameter (inner diameter) of 25 mm and a height of 50 mm, and the filling layer is created by leveling it to a height of 50 mm. Next, the rotating blade is lowered into the filling layer. Here, the blade is rotated so that the blade tip (here, the outer edge end in the radial direction) draws a spiral trajectory at a speed of 100 mm/s while descending and penetrating into the filling layer. Meanwhile, the torque T and vertical load F acting on the rotation axis of the blade are continuously measured. Next, the flow energy E is calculated by the following formula (1). As is clear from formula (1), the flow energy E is defined as the sum of the work done when the blade moves in the rotational direction and vertical direction.

Since the amount of work done in the vertical direction is smaller than the amount of work done in the rotational direction, the flow energy E may be simply defined as the amount of work done in the rotational direction only. However, by defining the flow energy E as the sum of the amounts of work done in both the rotational and vertical directions, the dynamic adhesion of the raw material can be evaluated more accurately.

In formula (1), T and F are the torque and vertical load acting on the blade's rotation axis measured as described above, respectively. Furthermore, R is the blade radius, α is the angle (helical angle) between the blade tip path and the horizontal plane, and H1 and H2 are the height positions of the packed bed, where R = 11.75 mm, α = 5°, H1 = 5 mm, and H2 = 50 mm, respectively. Of course, the specific values of the parameters are not limited to these.

The measured value of the flow energy E tends to vary greatly if the filling state of the raw material is not uniform. Therefore, the rotating blade is repeatedly moved up and down in the packed bed, and the flow energy E during the ascent and descent is measured based on the formula (1). By repeatedly moving the rotating blade back and forth in the packed bed, the packed bed becomes almost homogeneous. Therefore, the flow energy E during the blade ascent in the sixth and seventh strokes is obtained, and the average value of these is taken as the flow energy E. The reason why the flow energy E during the blade ascent is used is that the flow energy E during the blade descent includes the effect of the force (consolidation force) that the blade pushes the raw material. In other words, almost no consolidation force is applied to the raw material adhering to the inner wall surface of the extruder (for example, the inner wall surface of the raw material inlet). For this reason, it can be said that the flow energy E during the blade ascent is more appropriate as an index for evaluating the adhesion to the inner wall surface of the extruder when almost no consolidation force is applied. In the above example, the flow energy E was always measured, but it is also possible to measure only the flow energy E during the blade ascent in the sixth and seventh strokes. It is also possible to use the flow energy E when the blade rises on the other strokes. Although this will include the influence of compaction force, it is also possible to use the flow energy E when the blade descends. In the following explanation, the flow energy E is obtained by obtaining the flow energy E when the blade rises on the sixth and seventh strokes, and calculating the average value of these as the flow energy E.

Furthermore, the flow energy E also depends on the weight of the raw material at the time of measurement. Therefore, in order to eliminate the influence of weight, the flow energy E per 1 g of raw material is used as the dynamic adhesion. Therefore, dynamic adhesion indicates the difficulty of the wet powder (raw material) to flow in the absence of an external load. The higher the dynamic adhesion value, the more difficult the raw material is to flow.

3. Detailed Description of the Embodiments
Next, the extrusion molding method according to the present embodiment will be described in detail. The extrusion molding method according to the present embodiment includes a step (step 1) of determining an appropriate range of dynamic adhesion when the extrusion molding of the raw material to be evaluated is normally performed, and a step (step 2) of determining the particle size range of the raw material to be used so that the dynamic adhesion of the raw material to be used falls within the appropriate range.

(Step 1) Determination of the appropriate range of dynamic adhesion First, prepare an evaluation raw material for identifying the correlation between dynamic adhesion and the state of extrusion molding. The evaluation raw material may be any raw material that can be used for non-sintered agglomerated ore. The evaluation raw material is actually a blended raw material of multiple raw materials (iron ore powder, sintered dust, coke powder, and high-early-strength cement, etc.). If possible, prepare multiple types of evaluation raw materials. Next, extrusion molding is performed by arbitrarily changing the blending ratio, particle size, moisture content, etc. of each raw material constituting the evaluation raw material. Then, at least once or more, the evaluation raw material is sampled when extrusion molding is performed normally, when a molded body is not formed, and when a deposit grows on the inner wall surface of the extrusion molding machine, and the dynamic adhesion of each raw material is measured. The lower limit of the appropriate range of dynamic adhesion can be obtained as the average value of the minimum value Amin of dynamic adhesion when extrusion molding is normal and the maximum value Bmax of dynamic adhesion when a molded body is not formed. The upper limit of the appropriate range of dynamic adhesion can be determined as the average value of the maximum dynamic adhesion Amax when extrusion molding is normal and the minimum dynamic adhesion Cmin when deposits grow on the inner wall surface of the apparatus.

Here, whether or not deposits have grown on the inner wall surface of the extruder can be confirmed by, for example, visually inspecting the raw material inlet. Furthermore, when deposits grow on the inner wall surface of the extruder, the success or failure of extrusion molding is not in question. Furthermore, "when extrusion molding is performed normally" refers to a case that does not correspond to either a case where a molded body is not formed or a case where deposits grow on the inner wall surface of the extruder. In other words, "when extrusion molding is performed normally" generally refers to a state where a molded body is formed and deposits do not grow on the inner wall surface of the extruder.

An example of the measurement results is shown in Figure 3. The horizontal axis indicates when extrusion is performed normally, when a molded body cannot be formed, and when deposits grow on the inner wall surface of the extruder, while the vertical axis indicates the dynamic adhesion of the raw material (flow energy per 1 g of raw material (mJ/g)). Point P1 indicates the dynamic adhesion when extrusion is performed normally, point P2 indicates the dynamic adhesion when a molded body cannot be formed, and point P3 indicates the dynamic adhesion when deposits grow on the inner wall surface of the extruder. In the example of Figure 3, the flow energy of the raw material was measured five times for each extrusion condition.

Next, the arithmetic mean of the minimum dynamic adhesion Amin when extrusion molding is performed normally and the maximum dynamic adhesion Bmax when a molded body cannot be formed is determined as the lower limit of the appropriate range. Furthermore, the arithmetic mean of the maximum dynamic adhesion Amax when extrusion molding is performed normally and the minimum dynamic adhesion Cmin when adhesion grows on the inner wall surface of the extruder is determined as the upper limit of the appropriate range. Graph L1 in Figure 3 shows the lower limit of the appropriate range, and graph L2 shows the upper limit of the appropriate range. Therefore, the area between graphs L1 and L2 is the appropriate range. In this example, the appropriate range of dynamic adhesion is approximately 13 to 18 mJ/g. Of course, the method of determining the appropriate range is not limited to this method.

(Step 2) Determination of the particle size of the raw material Next, the particle size of the raw material to be newly used in extrusion molding (the raw material to be used. In reality, it is a blended raw material in which a plurality of raw materials are blended) is changed and the dynamic adhesion is measured. Then, the particle size of the raw material to be used is adjusted so that the dynamic adhesion falls within the appropriate range determined in step 1. Here, the particle size of the raw material is measured, for example, by a laser diffraction scattering method or classification by sieving. In either measurement method, it is preferable that the particle size of the raw material is the median diameter D50 (50% cumulative particle diameter). Here, when the particle size of the raw material is determined by the laser diffraction scattering method, the 50% particle diameter is a particle diameter based on volume. When the particle size of the raw material is measured by sieving, the 50% particle diameter is a particle diameter based on weight. An example of the results is shown in FIG. 4. The horizontal axis of FIG. 4 indicates the median diameter D50 (μm) of the raw material, and the vertical axis indicates the dynamic adhesion (mJ/g) of the raw material. Point P4 in FIG. 4 indicates the measurement results of the median diameter and dynamic adhesion of the raw material, and graph L4 connects points P4.

When the optimum range of dynamic adhesion is 13 to 18 mJ/g as shown in Figure 3, the optimum range of the raw material particle size (median diameter D50) can be determined to be approximately 160 to 250 μm. Therefore, by adjusting the raw material particle size (median diameter D50) to 160 to 250 μm and performing extrusion molding, a molded product can be stably formed. Note that dynamic adhesion is a versatile parameter, and as long as the same extruder is used, the same range can be used as the optimum range of dynamic adhesion. Conversely, if the extruder is changed, the optimum range of dynamic adhesion must be re-measured.

Next, extrusion molding is performed using the raw materials to be used that have been adjusted to the determined particle size. This allows the extrusion molding to be performed properly; that is, a molded body is formed and no deposits grow on the inner wall surface of the extruder.

Next, examples of this embodiment will be described. Of course, the present invention is not limited to the following examples.

(Step 1) Determination of the appropriate range of flow energy of raw materials Various raw materials for evaluation were extruded using a roller-type extruder (Fuji Paudal Co., Ltd., Model F-5S/11-175D, die hole diameter 10 mm). At this time, one or more of the blending ratio, particle size, and moisture content of each raw material (iron ore powder, etc.) constituting the raw materials for evaluation were varied in various ways. In parallel with this, the dynamic adhesion of each raw material for evaluation was measured. The results are shown in FIG. 3 for five times each when extrusion molding was performed normally, when a molded body could not be formed, and when deposits grew on the inner wall surface of the roller-type extruder. At this time, Amin = 14 mJ/g, Bmax = 12 mJ/g, Amax = 17 mJ/g, and Cmin = 19 mJ/g. Therefore, the lower and upper limits of the appropriate range of dynamic adhesion were determined to be 13 mJ/g and 18 mJ/g, respectively.

(Step 2) Determination of particle size of raw materials to be used Next, the particle size (median diameter) of the blended raw material 1 (raw material to be used) to be newly used in extrusion molding was changed, and the dynamic adhesion was measured. Blended raw material 1 was composed of 40% iron ore powder, 35% sinter dust, 20% coke powder, and 5% high-early-strength cement, and the moisture content was 12% (excluding figures). The measurement results are shown in Table 1. The particle size was the median diameter based on volume.

When the particle size (median diameter) was 200 μm, the dynamic adhesion was 16 mJ/g, which was within the appropriate range determined in step 1. As a result, the target particle size of this blended raw material was determined to be 200 μm. Therefore, when the particle size (median diameter) of the raw material to be used was set to 200 μm and extrusion molding was performed using the roller extruder described above, a molded product could be formed normally without the raw material adhering inside the roller extruder. On the other hand, when the particle size was set to 310 μm or 118 μm, either a molded product could not be formed or adhesion grew on the inner wall surface of the roller extruder.

Next, a similar test was conducted on another raw material mixture 2 (raw material to be used). Raw material mixture 2 was composed of 20% iron ore powder, 55% sinter dust, 20% coke powder, and 5% high-early-strength cement by mass, with a moisture content of 12% by mass (not included). The measurement results are shown in Table 2. The particle size was the median diameter based on volume.

When the particle size (median diameter) was 160 μm, the dynamic adhesion was 15 mJ/g, which was within the appropriate range determined in step 1. As a result, the target particle size of this blended raw material was determined to be 160 μm. Therefore, when the particle size (median diameter) of the raw material to be used was set to 160 μm and extrusion molding was performed using the roller extruder described above, a molded product could be formed normally without the raw material adhering inside the roller extruder. On the other hand, when the particle size was set to 200 μm or 110 μm, either a molded product could not be formed or adhesion grew on the inner wall surface of the roller extruder.

The results of the above experiments also confirmed that the dynamic adhesion determined above is versatile (applicable to a variety of intended raw materials).

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited to such examples. It is clear that a person with ordinary knowledge in the technical field to which the present invention pertains can conceive of various modified or revised examples within the scope of the technical ideas described in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

1A Screw-type extruder 10 Body 11 Raw material inlet 12 Screw 13 Die 1B Roller-type extruder 20 Body 21 Raw material inlet 22a Rotating roller 22b Rotating shaft 23 Die

Claims (2)

A method for extrusion molding of a raw material including an iron-based raw material, comprising the steps of:
A step of preparing an evaluation raw material for identifying a correlation between dynamic adhesion , which is an evaluation index of the fluidity of the raw material , and the mode of extrusion molding;
A step of measuring the fluidity of the raw material for evaluation when extrusion molding is normally performed, and determining the dynamic adhesion as an appropriate range;
and determining a particle size of the raw material to be used during extrusion molding so that the dynamic adhesion of the raw material to be used falls within the appropriate range. 2. The extrusion molding method according to claim 1, wherein the evaluation index for the fluidity of the raw material is flow energy.

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