A high proportion concentrate sintering reinforced mixing granulation method

Abstract

The application discloses a kind of high proportion concentrate sintering reinforced uniform mixing granulation methods, it is characterized in that, including: step S1, iron concentrate and flux are placed in strong mixer and are carried out pre-position forced mixing, and mixed material 1 is obtained;Step S2, mixed material 1 is mixed with non-iron concentrate iron ore powder uniformly and then is carried out flat laying directly, and mixed material 2 is obtained;Step S3, mixed material 2 is mixed with sintering auxiliary materials including quicklime, return ore and fuel, and then is carried out uniform mixing granulation, and sintering mixed ore is obtained;Iron concentrate accounts for 40~90% of the total mass of sintering mixed ore.The application is combined by source forced dispersion and multi-section uniform mixing, significantly improves the sintering mixture uniformity under the condition of high proportion concentrate, improves the granulation effect, promotes the uniformity of sintering ore forming process, effectively improves the yield and quality uniformity of sintered ore, and is especially suitable for sintering production with concentrate ratio of 40%~90%.

Description

Technical Field

[0001] This invention relates to a sintering-strengthened mixing and granulation method, specifically a high-proportion concentrate sintering-strengthened mixing and granulation method, belonging to the field of metallurgical sintering technology. Background Technology

[0002] In the iron ore sintering process, with the increasing depletion of high-quality iron ore resources and the ever-increasing requirements for blast furnace feed grade, the use of a high proportion of fine-grained iron concentrate with a large specific surface area has become an industry trend. However, there are many technical challenges in the traditional preparation of sintering raw materials for concentrate powder, which restricts the improvement of sinter quality and production efficiency.

[0003] Traditional sintering processes typically employ a "raw material flat-laying and direct extraction + one- or two-stage cylindrical mixer mixing + cylindrical mixer granulation" flow. This involves first mixing all iron ore powder in the raw material yard using a flat-laying and direct extraction method, then mixing it with flux, fuel, and return ore using a cylindrical mixer. However, iron concentrate has an extremely fine particle size, typically exceeding 40% -200 mesh content, and in some cases even reaching over 80%. Due to the significant particle size difference between the concentrate powder and coarse-grained materials (such as return ore and coarse iron ore), the "throwing and rolling" action of the cylindrical mixer is insufficient to adequately separate the fine concentrate from the coarse materials in a short time, let alone achieve a microscopically uniform coating of the concentrate and flux. The uniform distribution of flux during the sintering process is crucial, directly affecting the amount of calcium ferrite generated and the strength of the sinter. If the flux fails to adequately coat the concentrate particles, it will lead to insufficient solid-phase reaction during sintering, resulting in low sinter yield and large fluctuations in metallurgical properties.

[0004] In the industrial production of high-proportion iron concentrate sintering, the concentrate powder not only suffers from uneven mixing with coarse-grained ore powder, but also easily agglomerates into lumps or self-agglomerates during the storage and transportation of raw materials in modern steel enterprises due to moisture, pressure, and natural agglomeration. When using the "flat-laying direct extraction" process to mix iron-containing raw materials, these iron concentrate agglomerates will cause severe segregation in the stockpile, resulting in large fluctuations in the composition of the extracted mixture, directly affecting the stability of the subsequent sintering process and the uniformity of the sinter quality. It should be particularly noted that even with the additional use of strong mixing technology in subsequent processes, it is impossible to fundamentally change the problem of unstable incoming materials and uneven sinter quality caused by raw material segregation—a long-standing but unresolved structural contradiction in this field.

[0005] To address the aforementioned issues, some patents have proposed improvement solutions. Baoshan Iron & Steel Co., Ltd.'s invention patent application (CN104232883A) employs a combination of vigorous mixing and secondary cylindrical granulation, with different particle sizes of recycled ore and fine ore added in stages. While this method improves the mixing effect, it fails to resolve the instability of the incoming material caused by iron ore component segregation due to the stockpiling at the raw material yard—the vigorous mixing occurs after the raw material is laid flat and directly extracted, at which point the concentrate powder has already segregated in the stockpile, and subsequent vigorous mixing cannot reverse the macroscopic component segregation that has already occurred.

[0006] The invention patent (CN111041195B) from Central South University divides the material into three stages for mixing and granulation, and controls the moisture content at each stage to enhance the uniformity of the dispersion of different materials. Although this technology involves strong mixing, its core lies in the synergistic formulation of fine-grained materials, binders, and moisture to achieve uniform mixing and enhanced granulation of fine-grained materials. It does not offer a solution to the problem of concentrate segregation during the storage and transportation of raw materials.

[0007] In addition, for difficult-to-sinter concentrates such as specular hematite, existing technologies also use high-pressure roller mill pretreatment combined with organic binder pelletizing to improve the pelletizing properties of the concentrate. However, this method is mainly applicable to specific minerals and has limited versatility.

[0008] A recent patent application (CN119061260A) from Beijing Shougang Co., Ltd. proposes to enhance the ore-forming process through a high-alkalinity adhesion layer, which indirectly confirms the importance of the uniformity of the adhesion powder (iron ore <0.5mm) distribution to sintering quality. However, this method focuses on alkalinity control at the sintering cup test level and does not address segregation control at the raw material field scale.

[0009] The closest prior art to this application is Chinese patent application (CN114085992A). This patent discloses a granulation method for addressing problems such as uneven mixing and a high proportion of large particles caused by high moisture content in sintered materials. It adopts a three-stage mixing method of strong mixing + first mixing + second mixing: all sintered raw materials (including concentrate, flux, fuel, return ore, etc.) are strongly mixed at once in a strong mixer, and then the first and second mixing are carried out in a cylindrical granulator. The filling rate of the cylindrical granulator is controlled to be <10.8%, the strong mixing time is 2 minutes, and the first and second mixing times are 5 minutes each. However, this existing technology has significant shortcomings in the following aspects: First, all materials are fed into the high-intensity mixer at once, failing to provide targeted pretreatment for the fine particle size and easy agglomeration of the concentrate powder. Fine concentrate, coarse return ore, and fuel are simultaneously subjected to shearing in the high-intensity mixer, and the presence of coarse materials will interfere with the full contact between the fine concentrate and the flux. Second, the process does not include a flat-laying and direct extraction step, that is, it does not utilize the macroscopic homogenization effect of interlayer mixing in the raw material field, and relies entirely on equipment mixing, making it difficult to achieve macroscopic uniformity of composition on a raw material processing scale of hundreds or even thousands of tons. Third, the filling rate is strictly limited to <10.8%, which greatly restricts the equipment utilization rate.

[0010] In summary, existing technologies still lack effective means to control concentrate segregation from the source in the field of high-proportion concentrate sintering, and the micro-mixing uniformity of concentrate and flux is insufficient. Therefore, developing a high-proportion concentrate enhanced mixing and granulation method that can systematically solve the above problems has important industrial application value. Summary of the Invention

[0011] To address the problems existing in the prior art, the first objective of this invention is to provide a high-proportion concentrate sintering and granulation method. This method involves pre-mixing iron concentrate and flux in a high-power mixer before flat-laying and direct extraction. This pre-mixing breaks down the natural agglomerates of the concentrate powder at the source and ensures the flux is evenly distributed on the surface of the concentrate particles. The resulting mixture is then flat-layed and piled with other iron ore powder, and subjected to end-face extraction to achieve secondary homogenization at the macroscopic scale. Finally, after secondary batching and cylindrical mixing and granulation, granulated pellets with a uniform "core-adhesion layer" structure are formed. This systematically solves the problems in the prior art where the concentrate powder easily segregates and caking in the raw material field, and the uneven mixing with coarse ore leads to poor uniformity of chemical composition in the sintering mixture, poor granulation effect, and poor uniformity of sinter quality. This significantly improves the yield and strength uniformity of the sinter.

[0012] To achieve the above technical objectives, the present invention provides a method for high-proportion concentrate sintering, strengthening, mixing, and granulation, comprising:

[0013] Step S1: Place the iron concentrate and flux together in a high-pressure mixer for pre-mixing to obtain mixture 1;

[0014] Step S2: Mix the mixture 1 with the natural iron ore powder evenly and then spread it out to obtain the mixture 2.

[0015] Step S3: Mix the mixture 2 with sintering auxiliary materials including quicklime, return ore and fuel, and then mix and granulate to obtain sintered homogenized ore.

[0016] The iron concentrate accounts for 40-90% of the total mass of the sintered blended ore.

[0017] The technical solution provided by this invention uses a pre-mixing process of "concentrate + flux" to forcefully separate fine-grained concentrate and flux in advance, forming a relatively stable and surface-activated mixture of concentrate and flux. This fundamentally avoids the problems of caking and segregation caused by fine particle size and easy agglomeration of concentrate powder during storage and transportation in the raw material field. On the other hand, it enables uniform contact between flux and concentrate at the microscale, creating ideal conditions for the formation of calcium ferrite during sintering, thereby significantly improving the strength and reducibility of sintered ore.

[0018] The method provided by this invention is mainly for high-proportion concentrate sinter, especially when the iron concentrate mixture exceeds 40%, and can systematically and effectively solve the segregation and mixing problems caused by high-proportion concentrate.

[0019] As a preferred embodiment, the flux is at least one of limestone, dolomite, and magnesite powder; the natural iron ore powder is hematite powder and / or limonite powder, with a particle size range of ≤8mm.

[0020] As a preferred embodiment, the mass ratio of the iron concentrate, flux, non-iron concentrate iron ore powder, and sintering auxiliary materials is 50~80:6~10:30~50:7~28.

[0021] As a preferred embodiment, the pre-forced mixing conditions are: a time of 30~90s and a rotor linear speed of 5~15m / s.

[0022] Under these conditions, the high-intensity mixer, through the shearing action of the high-speed rotor and the forced convection between materials, generates strong impact, shearing, and diffusion effects, ensuring full contact and dispersion between the iron concentrate particles and flux particles, thus disrupting the "natural agglomeration" state of the concentrate powder. After this step, the flux and iron concentrate achieve a uniform distribution, i.e., mixture 1. The core function of this step is to eliminate the tendency of concentrate powder to segregate during subsequent stockpiling, while creating favorable microscopic contact conditions for subsequent solid-phase reactions, laying a microscopic foundation for the uniformity of the final sinter quality.

[0023] As a preferred embodiment, the process of flat-laying and vertically extracting materials involves: stacking materials in a flat-laying manner to form a material pile, and then vertically extracting materials from the end face of the material pile.

[0024] The material is piled up using a flat-laying method, employing a cantilever stacker to spread the mixture layer by layer to form a stockpile. During the laying process, mixture 1 and natural iron ore powder form an alternating layered structure in the vertical direction. After the stockpile is completed, a reclaimer is used to vertically remove material from the end face of the stockpile. The reclaimer cuts along the entire cross-section of the stockpile's end face, ensuring that each scoop contains material from all layers, thereby achieving macro-scale interlayer homogenization. Through the interlayer mixing effect of "flat-laying and direct removal," secondary homogenization of the concentrate, flux, and other iron ore powders is achieved, resulting in mixture 2. The core function of this step is to homogenize the premixed iron concentrate and flux with the iron ore powder, ensuring the stability of the raw material in the feedstock.

[0025] As a preferred embodiment, the number of layers in the flat-laying stack is ≥400, and the thickness of each layer is ≤15mm. When the number of stack layers is less than 400, the interlayer mixing effect decreases significantly, and the fluctuation of the material composition increases.

[0026] As a preferred embodiment, the mixing and granulation process is performed using a cylindrical mixer under the following conditions: a filling rate of 10-20% and a rotation speed of 6-10 r / min. In this invention, dry slaked lime or activated quicklime can be used, with an addition amount of 3-8% of the total material. Its main function is to provide binding properties during subsequent granulation. Return ore, as a sintering recycling material, acts as a framework and nucleation core; fuel (coke powder or coal powder) provides the heat required for sintering.

[0027] As a preferred embodiment, the mixing and granulation time is 3-5 minutes, and the moisture content of the sintered homogenized ore obtained after granulation is 6.0-7.5%. This invention controls the granulation conditions so that, under the rotation of the mixer, the mixture undergoes rolling and falling motion. Fine-grained materials (mainly "concentrate-flux" composite particles) gradually adhere to the surface of coarse-grained materials (return ore, coarse iron ore powder), forming granulated spheres with a "core-adhesion layer" structure.

[0028] As a preferred embodiment, the proportion of particles with a diameter greater than 3 mm in the sintered homogenized ore is not less than 70%, and its drop strength is not less than 3 times / 0.5m.

[0029] Compared with the prior art, the beneficial technical effects of the technical solution provided by the present invention are as follows:

[0030] 1) The method provided by this invention uses a pre-mixing process of "concentrate + flux" to forcefully separate fine-grained concentrate and flux in advance, forming a relatively stable, surface-activated concentrate + flux mixture. This fundamentally avoids the problems of caking and segregation caused by fine particle size and easy agglomeration of concentrate powder during storage and transportation in the raw material field. On the other hand, it enables uniform contact between flux and concentrate at the microscale, creating ideal conditions for the formation of calcium ferrite during sintering, thereby significantly improving the strength and reducibility of the sinter.

[0031] 2) In the technical solution provided by this invention, the pre-mixing high-intensity mixing solves the problem of sufficient contact and uniform distribution of concentrate and flux at the microscale. The subsequent flat-laying and direct extraction step, utilizing at least 400 layers of thin-layer material, each no more than 15mm thick, and a full-section end-face extraction method, achieves interlayer homogenization of the "concentrate-flux" composite particles with other iron ore powders at the macroscale. This two-stage mixing mode of "micro-agglomeration-macro-homogenization" overcomes the inherent contradiction in traditional processes where neither a single high-intensity mixer nor a single cylindrical mixer can simultaneously achieve micro-dispersion and macro-homogenization. Experimental data shows that after adopting this technical solution, the standard deviation of the sinter drum strength is reduced by 52%–59%, proving that the uniformity of the mechanical properties of the sinter is significantly improved.

[0032] 3) In the technical solution provided by this invention, since the concentrate surface has been uniformly coated with flux in the pre-mixing process and uniformly mixed with coarse iron ore powder after being spread and directly removed, the fine-grained "concentrate-flux" composite particles can orderly adhere to the surface of coarse-grained return ore and coarse iron ore powder during the rolling-throwing motion of the cylindrical mixer in the final cylindrical granulation process, forming a dense and uniformly sized "core-adhesion layer" granulation sphere. This structure not only improves the permeability of the mixed material layer, which is beneficial to the improvement of gas-solid heat and mass transfer efficiency during sintering, but also makes the liquid phase generation more uniform during sintering, and the binder phases such as calcium ferrite are uniformly distributed in the sinter, thereby significantly improving the yield and strength uniformity of the sinter. Experimental data show that the drop strength of the granulated pellets reaches 3-4.5 times / 0.5m, the proportion of particles with a diameter greater than 3mm is not less than 70%, the yield of sintered ore (+5mm) increases by 4.8-6.1 percentage points, and the standard deviation of FeO content decreases by 45%-50%.

[0033] 4) The technical solution provided by this invention is applicable to sintering raw materials with an iron concentrate ratio of 40% to 90%, covering a wide range of operating conditions from medium to high concentrate ratios. Compared to other process routes that require large-scale modifications to existing sintering production lines, this solution only requires the addition of a high-power mixer at the front end of the existing raw material yard equipment for pre-mixing of concentrate and flux. The equipment investment is small, the modification cycle is short, and it is easy to quickly promote and apply in existing sintering plants. Attached Figure Description

[0034] Figure 1 The flowchart of the high-proportion concentrate sintering enhanced mixing and granulation method provided by the present invention is shown. Detailed Implementation

[0035] To make the technical solution, mechanism, and beneficial effects of the present invention clearer, a detailed description is provided below with reference to specific embodiments and comparative examples. It should be understood that these embodiments are for explanation and illustration only and do not constitute a limitation on the scope of protection of the present invention. Simple modifications, parameter adjustments, and equipment replacements based on the technical concept of the present invention, as long as they do not depart from the essential spirit of the technical solution of the present invention, all fall within the scope of protection of the present invention.

[0036] Example 1

[0037] This embodiment provides a method for improving the uniformity of sinter quality through high-proportion concentrate sintering, enhanced mixing, and granulation, wherein the iron concentrate ratio is 50%, and the specific process is as follows:

[0038] First stage: Pre-mixing with high-intensity materials. Weigh 50 parts of iron concentrate and 3 parts of flux (limestone and dolomite), and feed them into a high-intensity mixer. Set the mixing time to 60 seconds and the rotor linear velocity to 12 m / s. After processing, mixture 1 is obtained, which has no visible agglomerates, and the contact area between the concentrate and flux is increased by approximately 35% compared to traditional mixing methods.

[0039] Section 2: Flat Laying and Direct Extraction. Mixture 1 and natural iron ore powder (23 parts hematite powder, 17 parts limonite) are transported to the raw material yard. A cantilever stacker is used for flat laying and stockpiling, with a set stacking layer of 500 layers and a single layer thickness of 12mm. After stockpiling is completed, material is extracted from the end face of the stockpile to obtain Mixture 2.

[0040] The third stage: multi-stage mixing and granulation. Mixture 2 is further batched with quicklime (4 parts), fuel (4 parts coke powder), and return ore (20 parts). After a primary mixing using a cylindrical mixer, the mixture is fed into a cylindrical granulator. The cylinder filling rate is 15%, the rotation speed is 8 r / min, and the granulation time is 4 minutes. The moisture content of the mixture is controlled at 7.0%. After granulation, the proportion of particles larger than 3 mm in the sintered homogenized ore reaches 78%, and the drop strength of the granulated pellets is 4.5 drops / 0.5 m.

[0041] The granulated sintered homogenized ore was subjected to sintering tests to detect the quality uniformity indicators of the sintered ore, including the drum strength, FeO content and basicity of the sintered ore. The standard deviation of each indicator was calculated, and the results are shown in Table 1.

[0042] Example 2

[0043] This embodiment is exactly the same as Embodiment 1, except that:

[0044] First step: Weigh out 80 parts of iron concentrate, 8 parts of limestone, and 2 parts of dolomite, mix them in a high-powered mixer for 45 seconds at a linear velocity of 14 m / s.

[0045] Second section: Mixture 1 and natural iron ore powder (20 parts of returned ore and 10 parts of coarse limonite powder) are spread and piled up in 600 layers with a single layer thickness of 10mm. Mixture 2 is obtained by taking material from the end face.

[0046] The third step involves a secondary batching of mixture 2 with quicklime (2 parts) and coke powder (5 parts). The pelleting time is 5 minutes, the moisture content is 7.3%, the cylinder filling rate is 12%, and the rotation speed is 9 r / min. After a primary mixing process using a cylinder mixer, the mixture is granulated. After granulation, the proportion of particles larger than 3 mm in mixture 3 is 72%, and the drop strength of the granulated pellets is 4.0 drops / 0.5 m.

[0047] The quality uniformity index of the sintered ore was tested using the same method as in Example 1, and the results are shown in Table 1.

[0048] Comparative Example 1

[0049] This comparative example is exactly the same as Example 1, except that the raw materials, including concentrate, flux, hematite powder, return ore, and fuel, are mixed once by a drum and then directly granulated in a cylinder after 90 seconds of mixing, without the use of a pre-mixing process.

[0050] The quality uniformity index of the sintered ore was tested using the same method as in Example 1, and the results are shown in Table 1.

[0051] Comparative Example 2

[0052] This comparative example is exactly the same as Example 2, except that the raw materials, including concentrate, flux, hematite powder, return ore, and fuel, are mixed once by a drum and then directly granulated in a cylinder after 90 seconds of mixing, without the use of a pre-mixing process.

[0053] The quality uniformity index of the sintered ore was tested using the same method as in Example 1, and the results are shown in Table 1.

[0054] Comparative Example 3

[0055] This comparative example is exactly the same as Example 2, except that its process flow is based on Chinese patent application (CN114085992A): the raw materials, including concentrate, flux, hematite powder, return ore and fuel, are first mixed once by a high-power mixer for 2 minutes, and then directly granulated in a cylinder for 5 minutes each.

[0056] The quality uniformity index of the sintered ore was tested using the same method as in Example 1, and the results are shown in Table 1.

[0057] Table 1. Sinter quality uniformity index of each embodiment and comparative example

[0058]

[0059] As shown in Table 1, the standard deviation of the chemical composition (TFe, SiO2, CaO) of the mixture in Example 1 along the width direction of the sintering machine trolley was reduced by 48% compared to Comparative Example 1; the standard deviation of the sinter drum strength was reduced by 52%, the standard deviation of FeO content by 45%, and the standard deviation of basicity by 50% compared to Comparative Example 1; and the sinter yield (+5mm) was increased by 6.1 percentage points compared to Comparative Example 1. These results indicate that the uniformity of sinter quality is significantly improved after adopting the method of the present invention.

[0060] Furthermore, comparing Example 2 with Comparative Example 2, the results show that even under extreme conditions of a high proportion of concentrate (80%), after adopting the method of the present invention, the standard deviation of the chemical composition (TFe, SiO2, CaO) of the sintering mixture in the width direction of the sintering machine trolley in Example 2 was reduced by 55% compared to Comparative Example 2; the drum strength of the sinter was increased by 3.2 percentage points compared to Comparative Example 2, the standard deviation of drum strength was reduced by 58%, the standard deviation of FeO content was reduced by 50%, and the standard deviation of basicity was reduced by 48%; the yield of sintered ore (+5mm) was increased by 4.8 percentage points compared to Comparative Example 2. These results indicate that the method of the present invention has a particularly significant effect on improving the uniformity of sintered ore quality under high concentrate conditions, and the technical advantages of the present invention become more prominent as the concentrate ratio increases.

[0061] As described above, the core of this invention lies in proposing a hierarchical synergistic process route of "pre-mixing (concentrate + flux) - direct extraction - secondary batching and granulation," along with the corresponding range of key process parameters. In this invention's technical solution, the concentrate and flux must first undergo pre-mixing to eliminate segregation at the source, followed by direct extraction to achieve macroscopic homogenization, and finally, cylindrical granulation to form uniform granulated pellets. If this order is changed, for example, by first extracting directly and then mixing, or by performing these processes in parallel, the core technical effect of controlling concentrate segregation at the source, as proposed in this invention, cannot be achieved. This is because once the concentrate powder enters the stockpile in agglomerated form and forms segregation, no subsequent mixing method can completely reverse the macroscopic component segregation that has already occurred.

Claims

1. A method for high-proportion concentrate sintering, strengthening, mixing, and granulation, characterized in that, include: Step S1: Place the iron concentrate and flux together in a high-pressure mixer for pre-mixing to obtain mixture 1; Step S2: Mix the mixture 1 with the natural iron ore powder evenly and then spread it out to obtain the mixture 2. Step S3: Mix the mixture 2 with sintering auxiliary materials including quicklime, return ore and fuel, and then mix and granulate to obtain sintered homogenized ore. The iron concentrate accounts for 40-90% of the total mass of the sintered blended ore.

2. The method for high-proportion concentrate sintering, strengthening, mixing, and granulation according to claim 1, characterized in that: The flux is at least one of limestone, dolomite and magnesite powder; the natural iron ore powder is hematite powder and / or limonite powder, with a particle size range of ≤8mm.

3. The method for high-proportion concentrate sintering, strengthening, mixing, and granulation according to claim 1, characterized in that: The mass ratio of the iron concentrate, flux, non-iron concentrate iron ore powder and sintering auxiliary materials is 50~80:6~10:30~50:7~28.

4. The method for high-proportion concentrate sintering, strengthening, mixing, and granulation according to claim 1, characterized in that: The conditions for the pre-forced mixing are: a time of 30~90s and a rotor linear speed of 5~15m / s.

5. The method for high-proportion concentrate sintering, strengthening, mixing, and granulation according to claim 1, characterized in that: The process of flat-laying and vertically extracting materials is as follows: materials are piled up in a flat-laying manner to form a material pile, and then materials are extracted vertically from the end face of the material pile.

6. The method for high-proportion concentrate sintering, strengthening, mixing, and granulation according to claim 5, characterized in that: The number of layers in the flat-laying stack is ≥400, and the thickness of a single layer is ≤15mm.

7. The method for high-proportion concentrate sintering, strengthening, mixing, and granulation according to claim 1, characterized in that: The mixing and granulation process is performed by a cylindrical mixer under the following conditions: a filling rate of 10-20% and a rotation speed of 6-10 r / min.

8. The method for high-proportion concentrate sintering, strengthening, mixing, and granulation according to claim 1, characterized in that: The mixing and granulation time is 3-5 minutes, and the moisture content in the sintered and homogenized ore obtained after granulation is 6.0-7.5%.

9. The method for high-proportion concentrate sintering, strengthening, mixing, and granulation according to claim 1, characterized in that: The proportion of particles with a diameter greater than 3 mm in the sintered homogenized ore shall not be less than 70%, and its drop strength shall not be less than 3 times / 0.5m.

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