Extrusion molding method

Abstract

To provide a novel and improved extrusion molding method capable of suppressing the push clogging of raw material.SOLUTION: An extrusion molding method has: a step of obtaining the proper ranges of the uniaxial decay stress and shear stress of raw material capable of normal extrusion molding in which the push clogging of the raw material is not generated; and a step of determining the raw material conditions of the raw material to be used so that the uniaxial decay stress and shear stress of the raw material to be used reach the proper ranges.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an extrusion method. [Background technology]

[0002] Sintering and sintered pelleting are commonly used methods for agglomerating fine iron ore and dust generated in steelworks. However, non-sintered agglomeration methods, which do not require a sintering process, are also used to save energy. In non-sintered agglomeration methods, cement is used as a binder to give the compacts strength sufficient for use in blast furnaces. The main forming methods known are tumbling granulation and extrusion molding. In order to steadily produce compacts using the extrusion molding method, it is important to prevent the raw materials from clogging the die.

[0003] In the extrusion molding method, as shown in Figure 1, raw materials are fed into the barrel and move toward the die while being pressurized by an extrusion section (not shown) such as a screw provided inside the barrel. The raw materials are then consolidated as they pass through the die, becoming a compact, which is then discharged from the extruder.

[0004] Here, the following empirical formula (1) is known for the pressure required to extrude the raw material in the body portion toward the die portion (Non-Patent Document 1).

[0005]

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[0006] In equation (1), P is the total pressure required to extrude the raw material, P1 is the pressure loss due to the decrease in cross-sectional area (cross-sectional area perpendicular to the length of the body), P2 is the pressure loss due to extrusion in the die, V is the extrusion speed of the raw material in the die, A0 is the cross-sectional area of ​​the hollow part of the body (cross-sectional area perpendicular to the length of the body), A is the cross-sectional area of ​​the hollow part of the die (cross-sectional area perpendicular to the length of the body), L is the length of the hollow part of the die, C is the circumference of the hollow part of the die, τ yis the yield value of the raw material, τ0 is the shear stress on the inner wall surface of the body, and α and β are constants. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Powder Molding: Edited by the Society of Powder Technology, Nikkan Kogyo Shimbun, Tokyo, 2009, p.121 Summary of the Invention [Problem to be solved by the invention]

[0008] In operations where the production rate of molded products is maintained constant using the same extruder, the extrusion load fluctuates when the conditions of the raw material being molded change. The motor output (torque) of the extruder is adjusted according to the fluctuations in the extrusion load, but when the extrusion load reaches the upper limit of the motor output of the extruder, the extruder becomes unable to discharge the raw material (molded product) and enters a "clogging" state. As a result, it becomes difficult to continue producing molded products.

[0009] Therefore, in order to stably produce molded products by extrusion molding, it is important to prevent clogging and to suppress fluctuations in the extrusion load (especially excessive increases). However, no method has been proposed to maintain the proper conditions of the raw materials to avoid clogging and continue stable production.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a new and improved extrusion molding method capable of suppressing clogging of raw materials. In particular, the present invention provides an extrusion molding method that prevents clogging during extrusion molding of wet powder raw materials, assuming a process for producing unsintered agglomerated ores by extrusion molding in the steel industry. [Means for solving the problem]

[0011] In order to solve the above problems, according to one aspect of the present invention, there is provided an extrusion molding method comprising the steps of: determining appropriate ranges of uniaxial collapse stress and shear stress of a raw material that allows normal extrusion molding without clogging of the raw material; and determining raw material conditions for the raw material to be used so that the uniaxial collapse stress and shear stress of the raw material to be used fall within the appropriate ranges.

[0012] Here, the raw material conditions may include at least one of the moisture content of the raw material, the particle size of the raw material, and the blending ratio of the raw material. [Effects of the Invention]

[0013] According to the above-described aspects of the present invention, it is possible to prevent the raw material from being jammed, and therefore it is possible to prevent a decrease in productivity. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a side cross-sectional view showing an outline of an extrusion molding method. [Figure 2] FIG. 1 is an explanatory diagram for explaining the definition of uniaxial collapse stress. [Figure 3] FIG. 1 is a side cross-sectional view showing an example of an extrusion molding machine. [Figure 4] FIG. 1 is an explanatory diagram showing an outline of a powder bed shear test method and a method for measuring uniaxial collapse stress. [Figure 5] 1 is a graph showing an example of measurement results of uniaxial collapse stress and shear stress. DETAILED DESCRIPTION OF THE INVENTION

[0015] <1. Investigation by the Inventor> First, the inventor's investigation will be described. According to the above-mentioned formula (1), the factor that causes fluctuations in the extrusion load during operation is the raw material property, that is, τ y and τ0. It is believed that the phenomenon that generates the pushing load and the jamming phenomenon that is the focus of this embodiment do not occur through the same mechanism. However, the present inventors have determined that the factors that govern the jamming phenomenon are also τ yThe inventors thought that τ y The uniaxial collapse stress and shear stress of the raw material correspond to τ and τ respectively, and are parameters that can be measured independently as raw material properties. y It is difficult to directly measure τ0 and τ1. These parameters can be indirectly determined by varying V and die dimensions and operating the actual machine.

[0016] The inventors of the present invention conceived the idea that clogging could be prevented by measuring the uniaxial collapse stress and shear stress of the raw material in advance (before the raw material to be used is fed into the extruder) by a powder bed shear test and adjusting the physical properties of the raw material in advance using the results. This possibility was confirmed through experiments as described below, and the present invention was completed.

[0017] <2. Extrusion molding method> Next, the extrusion molding method according to this embodiment will be described. The extrusion molding method according to this embodiment is composed of the following three processes (steps). (Step 1) Determine the appropriate ranges of uniaxial collapse stress and shear stress of the raw material that allows normal extrusion molding without clogging of the raw material. (Step 2) Determine the raw material conditions for the raw material to be used so that the uniaxial collapse stress and shear stress of the raw material to be used fall within the appropriate range. (Step 3) Extrusion molding is carried out under the raw material conditions determined in Step 2.

[0018] (2-1. Uniaxial collapse stress) The yield value τ of the raw material in Eq. (1) y Since σ is a parameter corresponding to the stress when the raw material begins to flow, the inventors focused on uniaxial collapse stress as an index thought to be related to it. Uniaxial collapse stress is the stress applied to a powder layer whose sides are not constrained (horizontal stress σ) as shown in Figure 2. h =0) to collapse (flow), the normal stress (σ c) Figure 2(a) shows the state where no normal stress is applied to the compact, and Figure 2(b) shows the state where the compact has collapsed after normal stress is applied to the compact by the pressing part. The uniaxial collapse stress can be determined by a powder bed shear test. Details will be given later.

[0019] (2-2. Shear stress) In actual extrusion molding machines, raw materials adhere to the inner wall surface. Therefore, the shear stress τ0 on the inner wall surface of the barrel can be considered as the shear stress between powder particles. Therefore, the inventors focused on the shear stress measured in a powder bed shear test as an index thought to be related to the shear stress τ0 on the inner wall surface of the barrel.

[0020] (2-3. Extrusion molding process) The extrusion molding process to which this embodiment can be applied is not particularly limited. The raw materials for the extrusion molding process are, for example, those generally used in the production of non-calcined agglomerates, and include iron ore, coke powder, and steelmaking dust, and cement as a binder. The raw materials are usually pulverized using a ball mill or the like to particles of 1 mm or less. The pulverized raw materials are adjusted to a moisture content suitable for extrusion molding and then molded using an extrusion molding machine. The obtained molded body is cured for a predetermined period of time, during which strength is developed by the hardening action of the cement hydration reaction, and the molded body becomes non-calcined agglomerates.

[0021] Here, examples of extrusion molding machines include screw-type extrusion molding machines and roller-type extrusion molding machines (Figure 3). In a screw-type extrusion molding machine, raw material fed into the barrel is extruded from the die section by a screw rotating inside the barrel. In a roller-type extrusion molding machine, raw material fed into the barrel is extruded from the die section by a roller rotating inside the barrel. In either case, clogging can occur depending on the properties of the raw material. The extrusion molding method according to this embodiment is applied to extrusion molding machines where clogging is a problem.

[0022] (2-4. Measurement method of uniaxial collapse stress) Uniaxial collapse stress is one of the indices measured by powder bed shear tests. As shown in Figure 2, it is the value of the horizontal stress σ h= 0) collapses (flows).

[0023] The main types of powder bed shear testers include the Jenike cell type, the rotating cell type, the lower cell direct acting type, and the parallel plate type, and any of these may be used in this embodiment. Details of each tester and the measurement method using the powder bed shear test are shown in JIS Z 8835:2016.

[0024] Figure 4 shows an overview of the powder bed shear test method and the method for measuring uniaxial collapse stress. First, the sample is filled into the measurement cell (Figure 4(b)). Here, the measurement cell can be divided into upper and lower halves, which means that shearing is possible. Next, a predetermined normal stress is applied to the sample to consolidate (pre-consolidate). Next, the sample powder layer is sheared while normal stress σ is applied, and the shear stress τ is measured. The normal stress applied to the sample powder layer is changed, and the shear stress is repeatedly measured. The failure envelope is obtained by plotting this on a σ-τ diagram (Figure 4(a)). Next, a Mohr's circle is drawn that is tangent to the failure envelope and passes through the origin (Figure 4(a)). At this point, the intersection of the Mohr's circle and the σ axis is the uniaxial collapse stress σ. c This becomes: The uniaxial collapse stress may also be measured by a uniaxial compression test in which a normal stress is applied to the side surface of the molded product in a state where the side surface is not restrained, as shown in FIG.

[0025] (2-5.Method of measuring shear stress) As mentioned above, shear stress is measured in the process of determining uniaxial collapse stress. Since shear stress varies depending on the magnitude of normal stress, the shear stress at a specific normal stress is used to determine the appropriate range of uniaxial collapse stress and shear stress. Normally, shear stress varies linearly with normal stress, so there are no particular restrictions on the normal stress used. However, once the normal stress is determined, the shear stress at that normal stress is used.

[0026] (2-6. Step 1: Determining the appropriate range of uniaxial collapse stress and shear stress) In step 1, the appropriate ranges of uniaxial collapse stress and shear stress of the raw material are determined so that normal extrusion molding is possible without clogging of the raw material. In other words, the uniaxial collapse stress and shear stress of the raw material are measured by the powder bed shear test described above when extrusion molding is proceeding normally and when clogging occurs, and the appropriate ranges of uniaxial collapse stress and shear stress without clogging are determined. Here, clogging refers to a state in which the raw material clogs the die and the compact cannot be extruded from the die.

[0027] More specifically, raw materials are sampled at least once when extrusion molding is normal and when clogging occurs, and their uniaxial collapse stress and shear stress are measured. An example of the measurement results is shown in Figure 5 (specific measurement methods will be explained in the Examples). The raw materials when clogging occurs exhibited high values ​​of uniaxial collapse stress and shear stress. Considering this based on the above-mentioned formula (1), τ y This is thought to be due to an increase in τ (related to uniaxial collapse stress) and τ0 (related to shear stress), resulting in an increase in the extrusion load. On the other hand, the uniaxial collapse stress and shear stress when extrusion molding is normal are smaller than those when jamming occurs. In the example of Figure 5, the appropriate range is a uniaxial collapse stress of 15.5 kPa or less and a shear stress of 9.6 kPa or less. Here, the upper limit of the appropriate range is the maximum value of the uniaxial collapse stress and shear stress when extrusion molding is normal. There is no particular restriction on the lower limit of the appropriate range, but it should be a value that allows the molded product to be extruded.

[0028] (2-7. Step 2: Determining raw material conditions) Next, the raw material conditions for the raw material to be used are determined so that the uniaxial collapse stress and shear stress of the raw material to be used fall within appropriate ranges.

[0029] Specifically, the uniaxial collapse stress and shear stress of the raw material to be used are measured by a powder bed shear test. If the measured uniaxial collapse stress and shear stress are within the appropriate range, the raw material can be used for extrusion molding as is. On the other hand, if the measured uniaxial collapse stress and shear stress are outside the appropriate range, the raw material conditions are changed and the uniaxial collapse stress and shear stress are repeatedly measured to determine conditions that bring them within the appropriate range. Specifically, for example, at least one of the moisture content of the raw material, the particle size of the raw material, and the raw material composition is changed. The raw material composition refers to, for example, the types of iron ore, coke powder, and steelmaking dust, as well as the composition ratios of these.

[0030] As the moisture content of the raw material increases, liquid bridges are formed between the raw material particles, improving the bonding strength between them. In other words, the uniaxial collapse stress and shear stress increase. However, when the moisture becomes excessive and exceeds the capillary region (a state in which the voids between the raw material particles are completely filled), the raw material changes to a slurry-like state, and the uniaxial collapse stress and shear stress decrease. Extrusion molding is usually performed at moisture levels lower than the capillary region, so the moisture content is changed within a range lower than the capillary region.

[0031] Reducing the particle size of the raw material (pulverizing the raw material) increases the adhesiveness of the raw material, improving the uniaxial collapse stress and shear stress. On the other hand, if the raw material particle size is excessively large, clogging of the die holes and jamming due to particle bite-in can occur, so the raw material particle size is preferably 1 mm or less. Here, the raw material particle size is measured, for example, by laser diffraction scattering or sieving. Furthermore, the raw material particle size is preferably expressed as the median diameter (50% particle diameter by mass).

[0032] When the raw material blend is changed, the uniaxial collapse stress and shear stress change in a complex manner due to differences in the wettability of the raw materials, particle shape, etc. When changing the raw material blend, the uniaxial collapse stress and shear stress can be adjusted by changing the type and blending ratio of iron ore, coke powder, and steelmaking dust, as well as by adding binders and lubricants.

[0033] (2-8. Process 3: Extrusion molding) In step 3, extrusion molding is performed under the raw material conditions determined in step 2. Under these raw material conditions, the uniaxial collapse stress and shear stress are within appropriate ranges, so extrusion molding can be performed without causing clogging of the raw material.

[0034] As explained above, according to this embodiment, the appropriate ranges of the uniaxial collapse stress and shear stress of the raw material that enable normal extrusion molding without clogging of the raw material are determined, and the raw material conditions of the raw material to be used are determined so that the uniaxial collapse stress and shear stress of the raw material to be used fall within the appropriate ranges. Therefore, extrusion molding can be performed without causing clogging of the raw material. In other words, it is possible to prevent clogging of the raw material, and ultimately to prevent a decrease in productivity. [Example]

[0035] Next, an example of this embodiment will be described. In this example, the effects of this embodiment were confirmed by carrying out the following steps.

[0036] <1. Step 1: Determining the appropriate ranges for uniaxial collapse stress and shear stress> Based on the operational results of extrusion molding using various raw materials in a roller-type extruder (Fuji Paudal Co., Ltd., model F-5S / 11-175D, die hole diameter 10 mm), the uniaxial collapse stress and shear stress of the raw materials were measured four times each when the extrusion molding was normal and when clogging occurred.

[0037] The powder bed shear test was performed using a rotating cell type apparatus (Freeman Technology, Model FT-4, cell inner diameter 50 mm). The pre-compression was 9 kPa, and then the normal stress σ was varied to 7 kPa, 6 kPa, 5 kPa, 4 kPa, and 3 kPa, and the shear stress was measured. The uniaxial collapse stress was determined using the method described above (Fig. 4(a)), and the shear stress was taken as the value at a normal stress of 7 kPa. The measurement results are shown in Fig. 5. The optimum ranges were determined to be 15.5 kPa or less for the uniaxial collapse stress and 9.6 kPa or less for the shear stress. The upper limits of the optimum ranges were determined to be the maximum values ​​of the uniaxial collapse stress and shear stress when the extrusion molding was normal.

[0038] <2. Step 2: Determining raw material conditions> Next, the uniaxial collapse stress and shear stress were measured for blended raw material A, which was to be newly used in extrusion molding. Blended raw material A consisted of 40% by mass of iron ore powder, 35% by mass of sintered dust, 20% by mass of coke powder, and 5% by mass of high-early-strength cement (dry basis proportions). The moisture content was 12% by mass (wet basis proportion), and the raw material particle size was 110 μm (mass cumulative median diameter). Table 1 shows the measurement results.

[0039] [Table 1]

[0040] Both the uniaxial collapse stress and shear stress of blended raw material A were outside the appropriate ranges determined in step 1. Here, blended raw material A' was created by changing the moisture content to 13 mass% and the raw material particle size to 210 μm, and the uniaxial collapse stress and shear stress were measured again. As a result, the uniaxial collapse stress and shear stress were found to be within the appropriate ranges determined in step 1.

[0041] <3. Step 3: Extrusion molding> Therefore, when blended raw material A' was extrusion molded, a molded product could be formed normally without clogging.

[0042] Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to these examples. It is clear that a person skilled in the art to which the present invention pertains can conceive of various modifications and alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

Claims

1. A process for determining, from operational experience, the appropriate ranges of uniaxial collapse stress and shear stress of raw materials for non-sintered agglomerates that enable normal extrusion molding without clogging of said raw materials; determining raw material conditions for the raw material to be used so that the uniaxial collapse stress and shear stress of the raw material to be used fall within the appropriate ranges.

2. 2. The extrusion molding method according to claim 1, wherein the raw material conditions include at least one of the moisture content of the raw material, the particle size of the raw material, and the composition of the raw material.

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