JP2016215238A - Runner for underfeed ingot-making and underfeed ingot-making method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress surely involution of a material in a mold, without damage of productivity, and without causing erosion and breakage of refractory with a simple structure.SOLUTION: A start part 5c of a runner for underfeed ingot-making is the runner start part 5c which is used for performing underfeed ingot-making. A taper part 11 extending toward an inside side of a casting mold 1 is formed on a lower entry hole 6 formed on a bottom of the casting mold 1, and when inner diameter on an inlet side of the taper part 11 is d, inner diameter on an outlet side is d, length of the taper part 11 along a vertical direction is s, and a casting flow rate of molten steel per unit time which is casted to the casting mold 1 side through the taper part 11 is Q, the taper part 11 is formed into a shape which satisfies a predetermined formula. The taper part 11 is formed so that, in a cross section obtained by cutting the taper part 11 along the vertical direction, an end part on the inlet side and an end part on the outlet side of the taper part 11 are connected with a straight line for satisfying relationship of the predetermined formula.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a runner for a bottom pouring ingot used for producing a steel ingot while pouring molten steel by bottom pouring and a method for pouring ingot casting.

  In general, as an ingot forming method in which molten steel is solidified in a mold to produce a steel ingot (ingot), an upper pouring method and a lower pouring method in which molten steel is injected into the mold are known. These ingot-making methods are applied to the production of products with shapes that cannot be produced with rolled steel or large-sized products, but the down-pour method has the advantage that a good ingot skin can be obtained. Therefore, it is applied to the production of high-grade steel where quality is important. This bottom pouring ingot method has a structure in which a double surface plate is previously disposed on a large surface plate, and a mold is disposed thereon. And the groove | channel for installing the refractory brick for runners is formed in the horizontal direction from this large surface plate, and the through-hole is formed in the vertical direction in the double surface plate. Refractory bricks with runners already formed in these grooves and through holes are installed to form runners that lead from the ladle to the mold. In the bottom pouring ingot method, the molten steel that has passed through the round hole-like runner is discharged into the mold from the end of the runner, so that the molten steel is supplied to the mold and the ingot is cast. .

  In this bottom pouring and ingot-making method, a molten steel coating agent is added to the bath surface (surface) of the molten steel for the purpose of preventing reoxidation of the molten steel poured down into the mold and preventing heat removal. This molten steel coating agent can prevent the atmospheric oxidation of molten steel and suppress heat removal from the surface of the molten metal by covering the surface of the molten metal. However, when the molten steel coating that floats on the bath surface is entangled in the molten steel because the molten steel bath surface is disturbed in the mold, it becomes a defect due to non-metallic inclusions, and the quality of the product is significantly reduced, The yield of the product may be reduced by cutting off the occurrence site. Accordingly, when casting forged steel, it is preferable that the above-described defects due to non-metallic inclusions are completely suppressed.

  It is considered that such inclusion defects often occur mainly due to entrainment of the in-mold material (molten steel coating agent) supplied into the mold. In other words, the mold inner material floats so as to cover the surface of the cast molten steel, and keeps the molten steel warm, but the molten steel discharged from the runner into the mold is too strong and the molten steel Is strongly stirred in the mold, the floating mold material is caught in the molten steel and inclusion defects (coarse inclusion defects) are generated.

Therefore, in order to suppress the occurrence of such inclusion defects, it is necessary to reduce the momentum of the molten steel discharged from the runner end of the runner into the mold to prevent the in-mold material from being caught. Therefore, in Patent Documents 1 to 3, it is possible to prevent the in-mold material from being caught by changing the flow of molten steel in the mold by various means.
For example, in Patent Document 1, the leading end of a runner (runner discharge port) is formed in a tapered shape such that the diameter increases from the base end side toward the tip end side, and the runner enters the mold. A technique capable of reducing the momentum of discharged molten steel and preventing the in-mold material from being caught is disclosed.

  Patent Document 2 discloses an agglomeration facility in which a runner discharge port provided at the bottom of a mold has a cross-sectional shape (curve taper shape) whose diameter decreases in a curved shape downward from a starting point as a discharge port. Is disclosed. Even when a discharge port as shown in Patent Document 2 is provided in the runner, it is possible to reduce the momentum of the molten steel discharged from the runner discharge port into the mold and suppress the entrainment of the mold inner material. It becomes possible.

  Further, Patent Document 3 discloses a technique in which a twisted tape-like member is provided in the runner (inside the pouring pipe), and a swirling flow is generated in the molten steel flowing through the runner. If a swirl flow is generated in the molten steel in this way, the flow of the molten steel along the discharge direction is weakened by the amount of swirl, and bare metal is less likely to be generated on the molten steel surface, preventing the in-mold material from being caught. It becomes possible.

JP-A-9-239494 JP 2012-86233 A JP 2007-216295 A

By the way, as shown in Patent Document 1 described above, if the runner outlet (end on the discharge side) is formed in a tapered shape, the molten steel is ejected from the runner so as to diffuse, and the amount of diffusion has occurred. It is considered that the flow of molten steel discharged from the runner becomes weak, and it is difficult for the in-mold material to be caught.
However, the flow of molten steel discharged from such a runner is closely related to the size of the mold and the supply rate (casting flow rate) of the molten steel to the mold. In this respect, although the cited document 1 has a description of the casting flow rate, it does not describe at all what the taper shape should be made when the casting flow rate is changed. The value of the discharge flow rate discharged from the mold into the mold is also unknown. Therefore, even if the method of Patent Document 1 is adopted, the flow of molten steel discharged from the runner cannot be sufficiently weakened at the manufacturing site where steel ingots of various sizes are cast. There is a possibility that entrainment of the material cannot be suppressed.

Further, the taper shape of Patent Document 1 does not define the length of the runner formed in the taper shape, in other words, the length along the vertical direction of the portion formed in the taper shape. Therefore, the tapered shape of Patent Document 1 includes a shape in which the length of the runner is short and the opening diameter on the taper outlet side is large, that is, a shape having a large taper angle.
However, if the taper angle of the discharge port is too large, the molten steel cannot be diffused along the tapered surface, and the discharged molten steel flow is separated from the side wall of the discharge port. Then, the molten steel does not flow along the tapered surface, and as a result, even if the runner outlet is formed in a tapered shape, the discharge flow rate discharged from the runner cannot be reduced sufficiently, and the inside of the mold is entrained. There is also a possibility that it cannot be reliably suppressed.

  Further, even when the tapered surface is formed in a curved surface as disclosed in Patent Document 2, when the casting flow rate is large, the curved steel taper cannot be aligned due to the inertia of the molten steel, and the flow of the molten steel to be discharged is the discharge port. May peel from the side wall. In addition, even in Patent Document 2, since the relationship between the casting flow rate and the taper shape is not known, it is difficult to actually apply to the manufacturing site.

  When the tapered surface is formed in a curved shape, a portion where the taper angle becomes large always exists in the tapered surface. For example, in the case of the tapered surface shown in Patent Document 2, the diameter of the runner abruptly increases near the tip, and the taper angle increases. Therefore, the above-described peeling tends to occur near the opening, and when peeling occurs, the discharge flow rate is not sufficiently reduced, and it becomes difficult to reliably suppress the entrainment of the in-mold material.

  Furthermore, in the technique of Patent Document 3, a twisted tape-like member capable of generating a swirling flow must be installed in the runner, and if such a member is provided, the refractory in the runner is greatly damaged or damaged. There is a risk. Moreover, since the shape of the twisted tape-like member is complicated, it is difficult to produce such a complicated shape with a refractory material, which may lead to an increase in the production cost of the mold. Furthermore, when the swirl flow is generated, the discharge flow rate of the molten steel discharged from the runner into the mold is reduced by the amount of flow generated in the swirl direction, and the supply speed (casting speed) of the molten steel supplied into the mold is reduced. Get smaller. Therefore, there is a possibility that the casting time becomes long and the productivity of the steel ingot is reduced, or the risk of occurrence of sedimentary inclusion defects is increased.

  The present invention has been made in view of the above circumstances, and does not cause melting or damage of the refractory, and while having a simple structure, reliably entraining the in-mold material without impairing productivity. It is an object of the present invention to provide a runner for bottom pouring and an ingot casting method that can be suppressed.

In order to solve the above-mentioned problems, the runner for the pouring ingot of the present invention takes the following technical means.
That is, the runner for the bottom pouring ingot of the present invention is a runner used when performing the bottom pouring ingot, and is formed in the lower injection port formed at the bottom of the mold and on the inner side of the mold. toward the tapered portion that extends is formed, the inner diameter of d _i of the incoming side of the tapered _portion, the inner diameter of the exit side of d _o, the length along the vertical direction of the tapered portion s, through the tapered portion mold In a cross-sectional shape in which the taper portion is shaped so as to satisfy the formula (1) when the casting flow rate of molten steel per unit time to be cast on the side is Q, and the taper portion is cut in the vertical direction. The tapered portion is formed so as to connect the end portion on the entry side and the end portion on the exit side of the taper portion with a straight line satisfying the relationship of the expressions (2) and (3). Features.

  Moreover, the bottom pouring ingot method of the present invention is characterized by performing the bottom pouring ingot using the above-described runner.

  According to the runner and the pouring ingot method of the present invention, the refractory is not damaged or damaged, and the simple structure does not impair the productivity of the in-mold material. It can be surely suppressed.

It is the schematic diagram which showed the bottom pouring ingot apparatus provided with the runner of this embodiment. It is the schematic diagram which showed the taper part used for the simulation of an Example and a comparative example. It is the figure which showed the relationship between the curve order of the cross-sectional profile of a taper part, and cross-sectional shape. It is the figure which showed how the discharge flow velocity of the molten steel discharged from a runner changes when the curve order of the cross-sectional profile of a taper part is changed. It is the figure which put together how the relationship between the taper angle of a taper part and the discharge flow velocity of the molten steel discharged from a runner will change when the diameter of the entrance runner is changed. It is the figure which put together how the relationship between the taper angle of a taper part and the discharge flow velocity of the molten steel discharged from a runner changes when a casting flow rate is changed. It is a figure which shows distribution of the discharge flow velocity of molten steel in case a taper angle is appropriate. It is a figure which shows distribution of the discharge flow rate of molten steel in case a taper angle is larger than an appropriate value.

Hereinafter, the runner and the bottom pouring method for bottom pouring ingot according to the present embodiment will be described with reference to the drawings.
First, with reference to FIG. 1, the ingot-making apparatus 2 (under-injection ingot-making apparatus) to which the down-pour ingot-making method of this embodiment is applied is demonstrated. In addition, FIG. 1 shows a schematic configuration of an agglomeration apparatus 2 that performs bottom pouring agglomeration.

As shown in FIG. 1, the ingot making apparatus 2 of the present invention casts a steel ingot, and has a large surface plate 3 formed in a flat plate shape, and a tower shape formed in the center of the large surface plate 3. Injection pipe 4. Molten steel injected from the upper end of the injection tube 4 is supplied to the mold 1 placed on the upper surface of the large surface plate 3, and the ingot is cast by the mold 1.
The large surface plate 3 is a flat plate member on which the mold 1 can be placed on the upper surface, and a tower-like injection tube 4 is disposed at the center of the large surface plate 3. Inside the large surface plate 3, a runner 5 for circulating molten steel is formed so as to connect two points of the lower side of the injection pipe 4 and the lower side of the mold 1 along the horizontal direction ( Horizontal part 5b) which will be described later.

The injection pipe 4 is formed with a runner 5 (a vertical portion 5a described later) penetrating along the vertical direction. These runners 5 are formed by installing refractory bricks having circular through holes, and the molten steel in the ladle 7 can be circulated downward (to the mold 1 side) through the runner 5. ing.
The runway 5 is a flow path through which the molten steel of the ladle 7 is circulated in the mold 1 and has three parts: a vertical part 5a, a horizontal part 5b, and a rising part 5c. The vertical portion 5a is a portion formed so as to penetrate the inside of the injection tube 4 and the large surface plate 3 along the vertical direction, and is a portion through which the molten steel is circulated from above to below. Moreover, the horizontal part 5b is a part formed so that the inside of the large surface plate 3 might be penetrated along a horizontal direction, Comprising: Molten steel is distribute | circulated horizontally. Furthermore, the rising portion 5c is a portion formed so as to penetrate the inside of the large surface plate 3 and the double surface plate 13 along the vertical direction, and is a portion in which the molten steel is circulated from below to above. Yes, it communicates with the interior of the mold 1. Like the vertical part 5a and the horizontal part 5b, it is formed of a refractory having a through hole in advance.

  In the ingot making by the ingot forming apparatus 2 as described above, first, the double surface plate 13 is placed on the large surface plate 3, and the mold 1 is further placed on the double surface plate 13. Then, the ladle 7 filled with molten steel is arranged on the upper side of the injection pipe 4 with a crane. Thereafter, by opening the slide valve 8 provided at the bottom of the ladle 7, the molten steel in the ladle 7 is introduced into the runway 5 of the injection pipe 4, and the runway 5 of the surface plate 3. To the mold 1 via. The molten steel that has reached the mold 1 through the runner 5 in this way is supplied into the mold 1 from the upper end (terminal) of the rising portion 5 c and the lower inlet 6. Eventually, when the amount of molten steel supplied into the mold 1 reaches the upper feeder 9 in the mold 1, the inflow of molten steel is stopped. In this way, the molten steel cooled in the mold 1 is cooled and solidified to become an ingot such as an ingot.

By the way, when the ingot making apparatus 2 performs ingot making, when the molten steel supplied into the mold 1 comes into direct contact with the atmosphere, the molten steel is oxidized from the contact surface with the atmosphere, and the cleanliness of the molten steel decreases. End up. Therefore, in the bottom pouring and ingot-making method, the molten steel bath surface is coated at the stage where injection of molten steel into the mold 1 is started so that the molten steel bath surface supplied to the mold 1 does not come into contact with the atmosphere. A coating material called “in-mold material 10” is added into the mold 1. In general, the “in-mold material 10” includes an oxide (for example, SiO ₂ —CaO—Al ₂ O ₃ ) serving as a molten slag component, and a powder so that the “in-mold material 10” uniformly covers the surface of the molten steel. C is contained for the purpose of improving the fluidity of the molten steel, and the “in-mold material 10” having a specific gravity smaller than that of the molten steel covers the surface of the molten steel while floating, so that the temperature of the molten steel can be maintained.

However, when the momentum of the molten steel discharged from the lower inlet 6 is strong as described above, the “in-mold material 10” floating on the surface is caught in the molten steel, and the “in-mold material 10” entrained is Since solidification is performed in a state of being caught inside the molten steel, the “in-mold material 10” captured at the solidification interface in the cooling process may become inclusion defects.
Therefore, in the mold 1 of the present invention, the tapered portion 11 is provided on the outlet side (rising portion 5 c) of the runner 5, and the molten steel in the runner 5 is discharged into the mold 1 through the tapered portion 11. Yes. In other words, in the runner 5 of the present invention, the rising portion 5 c has the tapered portion 11.

The tapered portion 11 is a conical portion having a larger inner diameter on the exit side (upper side) than on the entry side (lower side), and the molten steel is fed along the inner peripheral surface formed in a conical shape. By discharging while being diffused, the flow of the molten steel discharged into the mold 1 can be suppressed (weakened) by the amount that the cross-sectional area of the portion through which the molten steel flows is increased. Further, the tapered portion 11, the upper and lower has a circular opening, the inner diameter of the opening located the inner diameter of the opening located on the lower side (the inlet side) to d _i, the upper (exit side) Where d _o , the length of the taper portion 11 along the vertical direction s, and the casting flow rate of molten steel per unit time cast into the mold 1 through the taper portion 11 as Q, the equation (1) It is formed into a satisfactory shape.

  In addition, the tapered portion 11 has a cross-sectional shape obtained by cutting the tapered portion 11 along the vertical direction, and an opening end on the entry side and an opening end on the exit side of the taper portion 11 are expressed by the following equations (2) and (3). ) Is a shape that is connected by a straight line that satisfies the above relationship.

  If the rising portion 5c is provided with the tapered portion 11 that satisfies the relationship of the above-described formulas (1) to (3), the lower inlet (conventional lower inlet) that is not tapered, for example, a cylindrical bottom Compared to the case where the molten steel is directly discharged from the inlet into the mold, the flow of the molten steel discharged into the mold 1 can be suppressed, and the inclusion defect caused by the “in-mold material 10” being trapped in the molten steel. Occurrence can be suppressed. Although there is a case where the mold 1 is directly placed on the large surface plate 3 without placing the double surface plate 13, even in such a configuration, the inlet and the casting flow rate defined in the present invention are not affected. If the relationship is satisfied, the effect of the present invention is exhibited.

Next, the relationship between the shape of the tapered portion 11 and the above-described formula will be described in detail with respect to the tapered portion 11 provided in the rising portion 5c for the bottom pouring ingot of the present invention.
As shown in FIG. 2, the tapered portion 11 is a portion that discharges the molten steel sent to the mold 1 side through the runner 5 into the mold 1 while diffusing along the tapered surface 12. It is formed in an inverted conical shape (funnel shape) so that the inner diameter gradually increases toward the upper side.

Specifically, the taper part 11 is open by receiving both upward and downward, and the molten steel taken in from the lower opening can be discharged from the upper opening. That is, the diameter of the upper opening provided in the tapered portion 11, the "entry side inner diameter: d _o" of the formula (1) described above is also the diameter of the lower opening of which is provided in the tapered portion 11 has the formula (1) “Outside diameter: d _i ”. Note that the diameter of the lower opening is equal to the inner diameter of the horizontal portion 5b of the runner.

Further, “Q” in the equation (1) indicates a casting flow rate. The casting flow rate indicates the amount of molten steel supplied per unit time to the mold 1. The casting flow rate varies depending on the size of the steel ingot to be cast, etc., but usually the weight indicated by “t / min” is often used as the amount of molten steel supplied per unit time. . However, in a manufacturing site where not only high-purity steel but also a steel type having an alloy composition may be cast, the substantial volume may vary greatly depending on the composition and components of the molten steel. Therefore, in the bottom pouring ingot method of the present invention, the volume (volume) indicated by “m ³ / s” is applied to the casting flow rate.

Incidentally, the inner diameter of the entry side as described above: d _o, exit side of the inner diameter: d _i, casting rate: during Q, the relationship of Equation (1) to (3) is satisfied, the following This is because.
That is, with respect to the discharge flow velocity V _o of the molten steel discharged from the taper portion 11, if the discharge flow velocity V _{o is set} to 0.55 m / s or less, inclusion defects will not be detected even if UT inspection or the like is performed. The inventors have empirically found from the operational results that the entrainment of the material 10 does not occur. In principle, since the density increases and decreases depending on the type of the mold inner material 10, the ease of winding is considered to change, but no difference was found in the types normally used by those skilled in the art.

Here, since both the entrance side and the exit side of the taper portion 11 are opened in a circular shape, the entrance-side opening area S _i can be calculated using the entrance-side inner diameter d _i. it is possible to calculate the output side of the opening area S _o with the inner diameter d _o of the outlet side similarly to the side. On the other hand, the casting flow rate Q of molten steel is equal to the product of the opening area S _i on the inlet side and the discharge flow velocity V _i on the inlet side, and is the product of the opening area S _o on the outlet side and the discharge flow velocity V _o on the outlet side. equal. Since the outlet opening area S _o is larger than the inlet opening area S _i , the outlet discharge flow velocity V _o is smaller than the inlet discharge velocity V _i . Here, when the discharge flow velocity V _o on the outlet side is divided by the discharge flow velocity V _i on the inlet side and the flow velocity of the molten steel is arranged in a dimensionless manner, it is proportional to −1.42 of d _o / d _i . Further, if the inequalities in which the discharge flow velocity V _o is 0.55 m / s or less are arranged, the relationship of the above-described equation (1) is derived. The above is the reason why the relationship of formula (1) is established.

On the other hand, even when the above-described expression (1) is satisfied, the inclination (taper angle θ) of the inner peripheral surface of the tapered portion 11 (hereinafter, this inner peripheral surface may be referred to as the tapered surface 12) is too large. In this case, it becomes impossible to guide the molten steel along the tapered surface 12, and the flow is separated. In this state, the flow of the molten steel does not follow the tapered surface 12, and the molten steel is insufficiently diffused and flows into the mold 1 while maintaining the discharge flow rate on the inlet side. It is more likely to occur. Further, if the distance s to the outlet side from the inlet side of the tapered portion 11 is too short even by the taper angle θ of the tapered portion 11 is too large, the discharge flow rate V _o of the outlet side exceeds 0.55 m / s there is a possibility.

That is, when the distance s from the entry side to the exit side of the taper portion 11 is sufficiently large, or the taper angle θ shown as “the angle formed by the inner peripheral surface of the taper portion 11 with respect to the vertical direction” is a suitable angle. In this case, the molten steel flows along the inner peripheral surface of the tapered portion 11 and spreads along the inner peripheral surface, so that the discharge-side discharge flow velocity V _o can be suppressed to 0.55 m / s or less. Become. However, if the distance s from the entry side to the exit side of the taper portion 11 is too small, or if the taper angle θ is too large, the flow of molten steel peels off from the inner peripheral surface, and the potential core is separated from the inner peripheral surface. Since a region where the flow velocity is not reduced is formed, the molten steel does not diffuse along the inner peripheral surface.

For the reason described above, in the runner rising portion 5c of the present invention, the distance s from the entrance side to the exit side of the taper portion 11 is at least the inner diameter of the entrance opening, as shown in the following formula (2). As a result, the taper angle θ is prevented from becoming excessively large and peeling of the molten steel flow is prevented.
Moreover, as shown in Formula (3), by setting the taper angle θ to 7.3 deg or less, the taper angle θ is prevented from becoming too large and the molten steel flow is prevented from being separated. In addition, since the inner peripheral surface of the taper portion 11 described above is generally formed using a core, it is necessary to provide a certain taper angle in order to allow the core to be pulled out due to manufacturing restrictions. There is. Therefore, in the taper part 11 of the present invention, the lower limit value of the taper angle θ is set to 1 deg or more.

  For the reasons as described above, the relations of the expressions (2) and (3) are derived.

The taper angle θ described above means a taper gradient, and uses an inner diameter: d _o on the input side, an inner diameter: d _{i on} the output side, and a distance s from the input side to the output side of the taper portion 11. Is expressed as shown in Equation (4).

Moreover, the relationship of the above-mentioned formulas (1) to (3) is limited to the case where the cross section of the tapered surface 12 cut along the vertical direction is not a curve but a straight line. The reason why the shape of the tapered portion 11 is limited to the case where the cross section is a straight line is as follows.
First, let us consider a case where the cross section of the tapered surface 12 is a curve having an order larger than the first order or a curve having an order less than the first order.

  For example, as can be seen from FIG. 3, in the example in which the cross section of the tapered surface 12 is formed by a second-order to fifth-order curve, a linear taper that linearly connects the upper opening and the lower opening. With respect to the cross section of the surface 12, the tapered surface 12 has a curved shape so that the cross section swells upward. In this case, the closer to the upper opening, the greater the taper angle, and the greater the taper angle than the straight line.

  Further, in the example in which the cross section of the tapered surface 12 is formed with a 1/2 order curve, the taper angle of the lower opening is large, and the taper angle is larger than the straight line. That is, if the taper surface 12 has a linear cross section, the taper angle can be maintained at a limit angle at which the molten steel flow does not separate from the taper surface 12 at any position within the taper surface 12. In the tapered surface 12 having a curved cross section, a place where the taper angle is partially increased is generated, so that it is impossible to reliably suppress the flow of molten steel from the tapered surface 12. Therefore, in the mold 1 of the present invention, the tapered surface 12 has a straight section.

  In the runner 5 in which the linear taper portion 11 satisfying the above-described formulas (1) to (3) is provided at the end of the runner 5, the molten steel is discharged into the mold 1 even when the casting flow rate Q of the molten steel changes. It becomes possible to suppress the flow of the molten steel to be 0.55 m / s or less. Therefore, the in-mold material 10 floating on the surface of the molten steel is not caught in the molten steel, and it is possible to reliably suppress the occurrence of inclusion defects caused by the entrainment of the in-mold material 10. In addition, if only a simple member such as the tapered portion 11 is provided at the end of the runner 5, the refractory constituting the runner 5 does not cause melting or breakage, and is a simple structure. There is no worry of raising the equipment costs for casting.

Next, the operation and effects provided by the runner and the method for bottom pouring ingots according to the present invention will be described in more detail using Examples and Comparative Examples.
Examples and Comparative Examples, with respect to the tapered portion 11 as shown in FIG. 2, as a parameter, "the inner diameter of the opening of the inlet side: d _i (m)", "the exit side of the aperture inner diameter: d _o (m) ”,“ Distance from entry side to exit side of taper part 11: s (m) ”,“ Taper angle: θ (deg) ”,“ Pouring flow rate: Q (m ³ / s) ” An experiment was conducted using simulation to see how the discharge speed of the molten steel changes on the exit side of the tapered portion 11.

  In addition, the fluid analysis software “ANSYS Fluent 14.5” was used for the simulation, and the simulation experimental conditions shown in Table 1 were adopted. In addition, the “discharging flow rate of molten steel on the outlet side of the taper portion 11” obtained by simulation means that the molten steel generated on the outlet side of the taper portion 11 on a line extending vertically through the center of the taper portion 11 (runner channel 5). The flow rate is measured. Hereinafter, the discharge flow rate of the molten steel protruding from the tapered portion 11 into the molten steel may be simply referred to as “discharge flow rate”.

First, it was calculated | required by the simulation mentioned above how the discharge flow rate changes, when the order of the curve which the cross section of the taper part 11 shows changes by 1/2 order-5th order.
Note that the case where the order of the curve indicated by the cross section of the taper portion 11 is the first order indicates that the cross section of the taper portion 11 cut along the vertical direction is configured by a straight line, and the opening on the entry side. And the exit opening have a cross section connected by a straight line. Further, when the order of the curve indicated by the cross section of the taper portion 11 is from the second order to the fifth order, the straight line connecting the opening on the entry side and the opening on the exit side swells upward from the straight line. It shows that the cross section of the taper portion 11 is formed in a curved curve. Further, when the order of the curve indicated by the cross section of the tapered portion 11 is 1/2, the curve connecting the opening on the entry side and the opening on the exit side is curved so as to swell downward from the straight line. It is shown that the cross section of the taper portion 11 is formed in the curved line.

  When the “order of the curve indicated by the cross section of the taper portion 11” is changed, how the discharge flow rate changes is measured, and the measurement results are shown in Table 2 and FIG.

  As shown in FIG. 4, when the “order of the curve indicated by the cross section of the taper portion 11” is larger than 1, the discharge flow rate of molten steel tends to increase as the order increases. In addition, even when the “order of the curve indicated by the cross section of the taper portion 11” is smaller than 1, the smaller the order, the higher the discharge flow rate of the molten steel. It turns out that it takes a minimum value. From this, the cross-sectional shape of the taper portion 11 that is most effective for reducing the discharge flow rate of molten steel is the linear curve of the variable, that is, the radial distance when the radial distance is a variable. It can be determined that the shape changes linearly.

  Therefore, when the cross-sectional shape of the taper portion 11 is a straight line shape, the change in the discharge flow rate when the above-described parameters are changed was obtained by experiments. The results are shown in Table 3.

As shown in Table 3, FIG. 5, and FIG. 6, when the taper angle θ is increased from 0 deg with the casting flow rate Q maintained at 2.2 t / min, the discharge flow rate decreases as the taper angle θ increases. There is a trend. Furthermore, tendency thus discharge flow rate is reduced relative to the taper angle theta while holding the inner diameter d _i of the inlet side to 80 mm, even when increasing the taper angle theta, similarly seen. From this, it can be seen that the discharge flow rate affects the taper angle θ, the casting flow rate Q, the inner diameter d _i on the entry side, and the like.

Further, when the taper angle θ is increased to 7.3 deg, the discharge flow rate does not decrease any more, and when the taper angle θ is greater than 7.3 deg, the discharge flow rate increases. That is, it is determined that the discharge flow rate can be minimized when the discharge flow rate has a minimum value in the vicinity of 7.3 deg with respect to the taper angle θ and the taper angle of the taper portion 11 is about 7.3 deg.
Specifically, from the past operation results, when the discharge flow rate is 0.55 m / s or less as shown by the solid line in FIG. It is known that can be prevented. From this, the taper angle θ, the casting flow rate Q, and the inner diameter d _i on the entry side are determined so that the discharge flow velocity becomes smaller than the solid line in FIG. 5, in other words, each so as to satisfy the expression (1) in Table 3. It can be seen that by determining the parameters, the inclusion of the in-mold material 10 can be suppressed and the occurrence of inclusion defects can be prevented.

Even when the discharge flow velocity is smaller than the solid line in FIGS. 5 and 6, the actual discharge flow velocity is as shown in FIGS. 5 and 6 when the flow of the molten steel is separated from the inner peripheral surface of the tapered portion 11. May not be sufficiently small, and the entrainment of the mold inner material 10 may not be reliably suppressed.
For example, as shown in FIG. 7A, when the taper angle θ is 7.3 deg or less, the flow of molten steel peels from the inner peripheral surface (taper surface 12) of the taper portion 11 as indicated by “C” in the figure. However, the flow of molten steel diffuses along the tapered surface 12, and the discharge flow rate of the molten steel discharged from the tapered portion 11 is also 0.55 m / s or less.

  However, when the taper angle θ is larger than 7.3 deg as shown in FIG. 7B, the molten steel peels from the inner peripheral surface of the taper portion 11 as shown by “D” in the drawing, and the flow in the vicinity of the inner peripheral surface. However, there is a region that is reverse to the direction of the discharge flow velocity. When such peeling occurs, the flow of the molten steel does not diffuse along the tapered surface 12, and the discharge flow rate of the molten steel discharged from the tapered portion 11 is not decelerated and may exceed 0.55 m / s. Get higher. Moreover, when the disorder of the molten steel produced in the vicinity of the inner peripheral surface occurs, there is a high risk that the refractory is separated or promotes melting damage.

From the above, it is necessary not only to determine each parameter so as to satisfy Equation (1) in Table 3, but also to determine each parameter so as to satisfy the relationship of Equation (2) and Equation (3). It is judged that there is. In Table 3, when all the relations of the formulas (1) to (3) are satisfied, the discharge speed of the molten steel is within the range of 0.263 to 0.538 m ³ / s, It can be seen that the discharge flow rate of the molten steel can be kept sufficiently low, and the occurrence of inclusion defects caused by the entrainment of the in-mold material 10 can be effectively suppressed.

  As mentioned above, it should be thought that embodiment disclosed this time is an illustration and restrictive at no points. In particular, in the embodiment disclosed this time, matters that are not explicitly disclosed, for example, operating conditions and operating conditions, various parameters, dimensions, weights, volumes, and the like of a component deviate from a range that a person skilled in the art normally performs. Instead, values that can be easily assumed by those skilled in the art are employed.

1 Mold for bottom pouring ingot 2 Ingot making device (bottom pouring ingot device)
3 Daijoban 4 injection tube 5 runner 5b horizontal portion 5a vertical portion 5c rising portion 6 under inlet 7 ladle 8 slide valve 9 riser portion 10 inch inside member 11 tapered portion 12 tapered face 13 two Shigesada Release d _i input The inside diameter of the opening located on the side d _o The inside diameter of the opening located on the exit side s The length along the vertical direction of the taper part Q The casting flow rate of molten steel per unit time cast into the mold side θ The taper angle of the taper part

Claims (2)

It is a runway that is used when performing the pouring ingot,
In the lower injection port formed at the bottom of the mold, a taper portion is formed extending toward the inner side of the mold,
Inner diameter d _i of the inlet side the tapered _portion, the inner diameter of d _o of the outlet _side, the length of s along the vertical direction of the tapered portion, per unit time cast into the casting mold side through said tapered portion When the casting flow rate of the molten steel is Q, the tapered portion has a shape that satisfies the formula (1),
In the cross-sectional shape obtained by cutting the taper portion along the vertical direction, the end portion on the entry side and the end portion on the exit side of the taper portion are straight lines that satisfy the relationship of the expressions (2) and (3). The tapered portion is formed so as to be tied.
  A bottom pouring ingot method, wherein the pouring ingot is performed using the runner according to claim 1.