JPH0637678B2 - Sintered body evaluation method and manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is directed to a sintered body produced from powder particles by ventilation type self-combustion sintering, that is, an iron ore sintered body and Cr, Mn,
The present invention relates to an evaluation method and a manufacturing method of a sintered body manufactured in a manufacturing process of a sintered body of an ore for alloy such as Ti.

(Prior Art) In a ventilation type self-combustion type sintering in which a fuel such as coke is mixed in a granular material in advance, the fuel is burned by ventilation, and the generated heat is used for sintering. When the binding reaction progresses too much, the number of open pores, which are the paths for ventilation, is reduced, and a so-called over-melting phenomenon in which a defective sintering portion occurs due to airflow inhibition is likely to occur. In the iron ore sintering process, combustion heat is generated by the combustion of the fuel contained in the raw material, and this heat causes a so-called sintering reaction in which a melt is generated and ore powder is fused. Therefore, in order to continue the sintering reaction, it is necessary to continue the combustion, and it is necessary to stably supply the air to the raw material layer which is the lower layer of the combustion layer and becomes the next combustion layer because the air required for the combustion is in the lower layer. However, in the over-melting phenomenon in which excessive melting occurs, the melt is too much to block the pores of the ventilation, so that the air is not supplied and sintering failure occurs due to obstruction of ventilation. Operational malfunctions based on these overmelting phenomena cannot be directly detected by normal operational management, so it is difficult to determine the cause of the yield decrease, and the operational action has to rely on experience and intuition.

On the other hand, Japanese Patent Laid-Open No. 63-101738 proposes a method of controlling the generation of incompletely sintered parts by obtaining a two-dimensional porosity of a sintered body using a CT scanner. This method takes an image of an arbitrary cross section of a sintered body using a CT scanner, finds the ratio of pores with a circle equivalent diameter of 5 mm or more from the obtained image, and makes sure that the porosity does not exceed 40%. It controls the sintering process. However, this conventional method is merely a means for preventing the occurrence of incompletely sintered parts, and even when this method is applied to the operation control, the operation failure due to the overmelting phenomenon that occurs in the actual sintered body manufacturing process And it is not possible to control the yield reduction. Therefore, it is strongly desired to establish an evaluation method and an optimum operation condition adjusting method that can determine the occurrence of such an over-melting phenomenon.

(Problems to be Solved by the Invention) The present invention quantifies the open porosity of a sintered body after firing in a sintered body manufacturing process by using a radiation CT scanner, so that an unprecedented detection can be performed. It is intended to provide a new evaluation method capable of quantitatively evaluating a melting phenomenon, and at the same time, to provide a rational adjustment method of a sintered body manufacturing process to which this diagnostic method is applied.

(Means for Solving the Problem) In the first aspect of the present invention, an image of a preset horizontal cross section of a sintered body is captured using a radiation CT scanner, and the porosity of the sintered body is evaluated from the captured image. In the method, CT value data is collected by repeating imaging for each cross section continuously translated in the vertical direction by the distance of the radiation beam width from the imaging cross section, and then the X-ray tube voltage 42
The CT value when it is set to 0 kV is substantially equal to less than 0
Pixels at the value level are regarded as pores, the ratio of open pores that are three-dimensionally connected to the outside world (open porosity) is determined by computer processing, and the degree of sintering of the sintered body is determined based on the open porosity. Is characterized by.

A second aspect of the present invention is a method for producing a sintered body by capturing an image of a preset horizontal cross section of the sintered body using a radiation CT scanner, and evaluating the porosity of the sintered body from the captured image. , CT value data was collected by repeating imaging for each cross section continuously translated in the vertical direction by the distance of the radiation beam width from the imaging cross section, and then the CT value when the X-ray tube voltage was 420 kV. Pixels having a CT value level substantially equal to less than 0 are regarded as pores, and the ratio of open pores three-dimensionally connected to the outside world (open porosity) is obtained by computer processing, and the open porosity is 15% to 25%.
When it is less than the reference value preset within the range of%, the raw material blending condition or the operating condition is adjusted so as to be more than the reference value.

The present invention will be described in detail below.

First of all, the sintered body to be measured, as it is in a sinter cake,
Or sample a part of it. At this time, in the case of a sample of a large sintered body, for example, a sinter cake of an iron ore sintered body, it may be directly collected from the sintering bed by a sampler as proposed in Japanese Utility Model Publication No. 56-13639. it can.

Next, the horizontal cross-sectional image can be picked up by the radiation CT scanner, for example, by the tomography method described in JP-A-61-110726. The resulting 2D image is
The X-ray tube voltage 42 depending on the CT value of each pixel forming the image
The CT value when 0 kV is set, and the CT value which is substantially equal to 0 is used as a reference and is divided into more and less than that. Ie positive C
The T value corresponds to the solid portion of the sintered body, and the negative CT value corresponds to the pore portion of the sintered body. The CT value used here is a value obtained by the following equation (1).

CT value = (μs−μw) / μw (1) where μs: absorption coefficient of radiation of sample μw: absorption coefficient of radiation of water Next, in the present invention, the radiation beams should not overlap in the width direction. The CT value data corresponding to the three-dimensional coordinates of the sintered body is obtained by repeating the same two-dimensional image capturing operation for each cross section that is continuously translated in the vertical direction by the distance of the radiation beam width from the horizontal section. Collect. The CT value data thus adopted is assigned to each pixel on the three-dimensional lattice set in the memory of the electronic computer.

At this time, the number of three-dimensional pixels is determined by the size of the sample and the pixel size. For example, when the radiation beam width is 0.25 mm and the resolution is 0.25 mm for a 120 mm cube sample, about 110 million pixels are required. Become.

Also, a computer is used to identify the negative CT value parts corresponding to the pores, determine the three-dimensional connectivity of those pores, and determine the volume ratio of the pores that are three-dimensionally connected to the outside world, so-called open pores. Find the rate. For three-dimensional connectivity determination, for example, three methods are commonly used to determine connectivity for adjacent pixels in 6 directions, 18 directions, or 26 directions with respect to a pixel of interest. However, when the size of the pores to be analyzed is sufficiently larger than the size of the pixel, whichever of the three determination methods is used, the absolute value of the porosity is not significantly affected. In addition, as another determination method, it is possible to visualize by using a graphic display so that a human can visually determine (for example, measurement and control, Vol. 19 , pp923.
-936,1080).

In the method of the present invention, the degree of sintering of the sintered body is determined as follows according to the open porosity obtained by such a method. That is, when the open porosity is significantly lower than that of a normal sintered body, specifically, when the open porosity is smaller than a reference value preset in the range of 15% to 25%, the sintered body is overheated. It is considered to be in a molten state, and at the same time, it is evaluated that the sintering process in which the sintered body is manufactured is also in a malfunction due to the overmelting phenomenon. When such an over-melting phenomenon occurs, the open porosity is adjusted to be equal to or higher than the reference value by, for example, reducing the fuel blending amount or adding quick lime.

Since the present invention is configured as described above, it is possible to accurately evaluate the over-melted state of the sintered body and optimally adjust the sinter production process.

(Operation) The operation of the present invention will be described below.

In the sintering reaction, the disappearance of pores due to the fusion and coalescence promotes the strength and yield of the sintered body.
However, according to the experiments by the present inventors, in the ventilation type self-combustion type sintering in which air is introduced from the outside to burn the fuel in the raw material, the pores disappear excessively and the ventilation path becomes an opening. The porosity is remarkably reduced, and the subsequent sintered portions are hardly sintered due to airflow inhibition, so that the yield of the whole sintered body is reduced.

As an example of the analysis, FIG. 1 shows the relationship between the open porosity obtained by the method of the present invention and the +5 mm yield of the portion corresponding to the 50 mm lower layer from the analyzed location. Open porosity 15 to 25
The yield peak appears in the range of%, and the yield is lowered regardless of whether the open porosity is higher or lower. The decrease in yield when the open porosity is high is considered to be due to the increased contribution of pores as structural defects. Therefore, in this case, the yield can be recovered by an action such as an increase in the fuel blending amount according to the method described in JP-A-63-101738. However, it was found that a large decrease in yield was observed even when the open porosity was low, which seems to correspond to a phenomenon empirically called the overmelting phenomenon in the past. Under such a circumstance, if the action of increasing the fuel blending ratio is taken, the overmelting phenomenon further increases and the yield decreases.
Therefore, in order to detect such an over-melting phenomenon,
It is important to identify areas with low open porosity that cause overmelting. Specifically, for example, an evaluation method in which an open porosity that shows a yield peak in FIG. 1 is set as a reference value and a portion having an open porosity that does not reach the reference value is determined as overmelting can be considered. .

However, in the conventional two-dimensional CT analysis, the connectivity of actual pores having a three-dimensional spread cannot be recognized in principle. In particular, regarding a sintered body having a mesh-like complex pore shape, it is considered impossible to determine open pores and closed pores in a two-dimensional image. As shown in the analysis example in FIG. 2, when the open porosity obtained by the analysis of the two-dimensional image does not match the open porosity obtained by the three-dimensional analysis in absolute value and does not correspond relatively. There is. As described above, the measurement of the open porosity is insufficient only by the two-dimensional image analysis.

Therefore, as a means for quantifying the open pores, it was considered to construct a three-dimensional image, actually confirm the connectivity of the pores, and then measure the existence ratio thereof. CT is a non-destructive device capable of observing a cross section, and by continuously changing the measurement surface in the vertical direction by the amount of the thickness of the radiation beam and repeating imaging, the data of the three-dimensional structure is not leaked. It is also possible to collect easily.

Regarding the occurrence of the over-melting phenomenon in the actual sintered body manufacturing process, for example, a method of adjusting the amount of fuel to be reduced or a method of reducing the amount of melting by reducing the amount of easy-melting ore, addition of quick lime or sintering It is effective to use an adjusting method that improves the air permeability of the entire sintered layer by reducing the layer thickness of the layer.

(Example) a) In a large-scale sintering machine for iron making with a sintering area of 500 m ² , under a suction negative pressure of 1500 mmAq and constant operating conditions, length 150 mm x width 150 mm
Two sinter cakes A and B having an X height of 500 mm were collected. Imaging was performed by a CT scanner according to the method of the present invention as set forth in claim 1, and the open porosity was determined by computer processing. As a result, the sinter cake A had an open porosity of 26.7% and the yield at this time was 74.9%. On the other hand, Sinter Cake B has an open porosity of 14.6% and a yield of 6
It was 6.1%. From the relationship in FIG. 1, A is judged to be in a good sintered state, but B can be regarded as overmelting. When 1.5% of lime was added under the condition B, the open porosity increased to 22.0% and the yield improved to 73.0%. B) In the above sintering machine, a cylindrical sinter cake having a diameter of 120 mm and a height of 500 mm is sampled every 8 hours under the condition of a negative suction pressure of 1000 mmAq, and the open porosity is measured by the method of the present invention according to claim 2. And the determination of the overmelting phenomenon based on the open porosity of 24% were continuously carried out for 30 days. At this time, for the first 15 days, X-R was calculated by obtaining the manufacturing yield every 30 minutes.
As a conventional operation for controlling (method described in JP-A-63-101738), for the last 15 days, in addition to the conventional operation, a controlled operation (method of the present invention) in consideration of determination of overmelting was performed. In the conventional operation, when an abnormal value is determined on the X-R chart, it is considered that heat is insufficient on the low yield side to increase the fuel blending amount, and on the high yield side, it is considered to be excessive heat and the fuel is considered to be excessive. This was dealt with by reducing the composition. On the other hand, according to the method of the present invention, the following three actions were taken during the period when it was determined to be overmelting.

(a) Reduction of fuel blending amount (coke 0.02%) and quick lime 1%
Addition (b) Reduction of fuel blending amount (coke 0.02%) and layer thickness reduction of 100 mm (c) Reduction of easily meltable ore amount 10% and addition of quicklime 1% The transition of product yield during the experiment period Shown in the figure. During the period of the conventional method, it was not possible to determine the cause of the operational malfunction, so appropriate actions could not be taken, and the yield decreased significantly. On the other hand, during the period of the method of the present invention, it is possible to accurately detect the occurrence of the overmelting phenomenon, and therefore it is possible to avoid a decrease in yield by promptly performing an appropriate action. That is, when the yield decreases due to overmelting decrease, the yield does not improve just by increasing the coke as in the normal action, but conversely, the aim was to reduce the amount of melting and improve the air permeability (a) ~ The adjustment method shown in (c) was extremely effective.

(Effect of the Invention) The present invention is a method for accurately determining a three-dimensional open porosity in a sintered body without destroying the sintered body and accurately determining the overmelting phenomenon. In the actual manufacturing process of the sintered body, the diagnosis result of the sintering operation is output promptly and accurately as needed, so that the real-time action against the yield variation becomes possible. Therefore, the effect thereof is extremely large in improving the yield of the sintered body manufacturing process and reducing the manufacturing cost.

[Brief description of drawings]

Fig. 1 shows the open porosity obtained by the method of the present invention and +5 mm of the part corresponding to the lower layer 50 mm from the place where the CT analysis was performed.
Drawing showing the relationship with the yield, Fig. 2 is a drawing showing the relationship between the open porosity obtained by two-dimensional analysis and the three-dimensional open porosity, and Fig. 3 is a conventional example of the iron ore sintered body manufacturing process. 5 is a drawing showing changes in product yield in Examples.

Claims (2)

[Claims] 1. A method of capturing an image of a preset horizontal cross section of a sintered body using a radiation CT scanner, and evaluating the porosity of the sintered body from the captured image, wherein the radiation beam width from the captured cross section is measured. The CT value data is collected by repeating the imaging for each cross section continuously translated in the vertical direction by the distance, and then the X-ray tube voltage 420
The CT value when it is set to kV is substantially equal to less than 0
Pixels at the value level are regarded as pores, the ratio of open pores that are three-dimensionally connected to the outside world (open porosity) is determined by computer processing, and the degree of sintering of the sintered body is determined based on the open porosity. And a method for evaluating a sintered body. 2. A method for producing a sintered body by capturing an image of a preset horizontal cross section of the sintered body using a radiation CT scanner, evaluating the porosity of the sintered body from the captured image, and producing the sintered body. CT value data is collected by repeating imaging for each cross section that has been continuously translated in the vertical direction by the distance of the radiation beam width from the cross section, and the CT value is less than 0 when the X-ray tube voltage is 420 kV. Pixels with a CT value level substantially equivalent to
The ratio of open porosity (open porosity) which is three-dimensionally connected to the outside world is obtained by computer processing, and the open porosity is 15% to 2
A method for producing a sintered body, which comprises adjusting raw material blending conditions or operating conditions so as to be equal to or higher than a reference value preset within a range of 5%.