Discharge Nozzle For Molten Metal In Molten Metal Vessel, Method For Operation Of Converter Having The Discharge Nozzle, And Sleeve Replacing Apparatus For Discharge Nozzle Of Molten Metal Vessel

Abstract

An arrangement for reducing an average discharging time in a molten metal vessel, such as a converter, having a molten-metal discharge nozzle particularly a molten-metal discharge nozzle comprises a sleeve-shaped refractory member so as to achieve enhanced operational efficiency of the molten metal vessel. A discharge nozzle comprises an upper sleeve mounted in a refractory lining of a converter and a lower sleeve adapted to be detachably attached to a lower end of the upper sleeve, wherein a hole sectional area of the lower sleeve is set in the range of 60 to 98% of a hole sectional area of the lower sleeve in its used state requiring replacement.

Description

TECHNICAL FIELD

The present invention relates to a discharge nozzle for discharging molten metal from a molten metal vessel, such as a converter, particularly a discharge nozzle comprising a replaceable sleeve-shaped refractory member. The present invention also relates to a method for operation of a converter having the discharge nozzle, and an apparatus for replacing the sleeve-shaped refractory member.

BACKGROUND ART

In a refining process for molten metal, such as molten steel, high-temperature molten metal is carried to a refining furnace by a transport vessel, such as a ladle, and transferred from the transport vessel to the refining furnace to refine the molten metal. Then, refined molten metal is discharged and returned from the refining furnace to the transport vessel, and carried to a subsequent work station.

Fundamentally, an operation cycle of the refining furnace consists of three steps: a step of receiving molten metal; a step of refining the molten metal; and a step of discharging refined molten metal. In a steelmaking converter as a typical example of the refining furnace, it is required to take about 42.5 minutes as a total operation cycle time, specifically, about 5 minutes for a step of receiving molten steel (charging), about 30 minutes for a step of refining the molten steel (blowing) and about 7.5 minutes for a step of discharging refined molten steel (tapping).

That is, with respect to the total operation cycle time in the steelmaking converter, the charging time accounts for about 12%, and the tapping time accounts for about 18%. The charging and tapping, i.e., receiving and discharging, are a process of simply transferring molten metal, and therefore a time to be spent for the molten metal transfer is commonly called wasted time which has no direct relationship with a fundamental function of the converter. Thus, a reduction of a time required for the molten metal transfer during the refining process can contribute to improvement in operational efficiency of a converter to achieve increased annual refining capacity per converter and enhanced productivity, which leads to reduction in production cost.

Practically, when it is tried to reduce a time required for the receiving and discharging during the refining process, there are some points to be considered in each of the receiving and discharging steps, in addition to developing a technique directly connected to the reduction of receiving and discharging times.

Firstly, in the receiving step of transferring molten metal from a transport vessel to a converter, the transport vessel is tilted to pour the molten metal into the converter. This pouring operation (e.g., control of flow volume) has to be accurately managed to prevent damages in a refractory lining of the converter. Secondly, in the discharging step of transferring the molten metal from the converter to the transport vessel, it is required to prevent a large amount of slag generated during the refining step from flowing into the transport vessel. Further, this discharge operation has to be managed to prevent the occurrence of turbulence in a discharged molten metal flow, which causes entrainment of ambient air in the discharged molten metal and oxidation of the discharged molten metal due to oxygen contained in the ambient air to result in significant quality deterioration.

As above, the requirements in managing the receiving and discharging of molten metal during the refining process are different from each other. With a view to facilitating coping with these different management requirements, there is a converter having a receiving portion and a discharge nozzle individually. In this type of converter, the discharge nozzle is designed to have a specific inner diameter or opening area so as to minimize outflow of slag therefrom and allow a discharged molten metal flow to be formed as close to laminar flow as possible.

Generally, in a converter, an intense flow of high-temperature molten steel will cause significant chemical/mechanical wear in a tapping nozzle as a discharge nozzle, and a bore of the tapping nozzle will be gradually increased. Along with gradual increase in an opening area of the tapping nozzle, a discharge flow volume will be increased, and thereby a discharging time, i.e., tapping time, will be reduced.

Then, when the opening area of the tapping nozzle is increased up to a given value, further intensified flow generates whirls around the tapping nozzle, to entrain slag on a surface of the molten steel in the converter, and a large amount of entrained slag will be undesirably discharged to a transport vessel. It is essential to avoid discharging a large amount of molten steel with entrained slag within a short period of time, because the slag has adverse effect on quality of steel.

Specifically, it is necessary to set an allowable upper limit to the opening area of the tapping nozzle to be increased every tapping due to wear of a refractory member of the tapping nozzle, or set an allowable lower limit to the tapping time based on a relationship between the allowable upper limit of the opening area and the tapping time under the condition that the opening area is freely increased to reduce the tapping time, and replace the tapping nozzle with a new one when the opening area reaches the allowable upper limit or the tapping time reaches the allowable lower limit, so as to return an inner diameter (i.e., the opening area) of the tapping nozzle to the initial condition.

As typical measures against outflow of slag during tapping, the timing of tilting or rotating of the converter itself is adjusted without providing a valve for blocking the molten steel and slag flow. That is, an actual technique of preventing outflow of slag during tapping is designed to tilt or rotate the converter itself in response to detecting entrainment of slag in molten steel flow. Thus, a certain amount of slag is inevitably discharged to a transport converter together with molten metal.

An amount of slag to be discharged to the transport vessel is approximately proportional to the opening area of the tapping nozzle, and further dependent on controllable tilting or rotating speed as one performance of the converter. Thus, an amount of slag to be discharged to the transport vessel can be controlled at a given value or less only if the allowable upper limit of the opening area of the tapping nozzle is determined in consideration of the performance of the converter. Further, the allowable upper limit of the opening area of the tapping nozzle for controlling the amount of slag at a given value or less is varied depending on the performance of the converter.

Generally, it takes long hours to replace a tapping nozzle which has an opening area reaching the allowable upper limit due to wear, and an operation of the converter has to be interrupted during the replacement to cause lowering in quantity of refining (production).

For this reason, various measures for reducing a time to replace a tapping-nozzle have been taken. For example, the following Patent Publication 1 discloses a structure of a tapping nozzle formed with a replaceable sleeve-shaped refractory member, wherein the sleeve-shaped refractory member is replaced to facilitate reduction in replacement time of the tapping nozzle. The Patent Publication 1 further discloses a technique of selecting a highly-durable material excellent in wear resistance to molten metal flow to allow for reducing a frequency of replacement of the sleeve-shaped refractory member.

As a technique for speeding up the replacement of such a sleeve, a tundish nozzle replacing apparatus designed to push out an old nozzle by a new nozzle has been studied, as disclosed, for example, in the following Patent Publications 2 and 3.

In the above conventional technique of replacing a sleeve-shaped refractory member, a new sleeve-shaped refractory member is designed to have a relatively small bore (inner diameter) and a relatively large wall thickness, which correspond to an allowable upper limit of tapping time (i.e., allowable longest tapping time), so as to provide further extended usable life to the sleeve-shaped refractory member itself. Typically, in a converter, a new tapping nozzle is designed to have a bore (inner diameter or opening area) which is equal to about one-half of an upper limit thereof, or which provides a tapping time (i.e., discharging time) about two times greater than a lower limit thereof.

For example, in a sleeve-shaped refractory member to be used for 200 heats (the number of batches of molten steel), while a tapping time is relatively long, e.g., 10 minutes, in an initial stage of use, it will be reduced to about 5 minutes in a last stage of use. That is, an average tapping time defined by “a sum of respective tapping times in the entire use period/the number of times of use of the sleeve-shaped refractory member” is 7.5 minutes.

In this case, given that the shortest tapping time free of entrainment of slag in a converter is 5 minutes, a tapping time of 2.5 minutes/heat is uselessly spent.

In typical conventional converters, an average time necessary for replacement of a sleeve-shaped refractory member is about 75 minutes, and a usable life of the sleeve-shaped refractory member is 150 to 250 heats, and 200 heats on an average, at most. In a single converter used in a typical steel plant, a tapping interval (tap-to-tap) is 40 minutes on an average, and about 12,000 heats of molten steel is refined for the year. Given that a usable life of the sleeve-shaped refractory member is 200 heats on an average, a replacement frequency (number of times of replacement) is 60 times/year. When an average time necessary for the replacement is 75 minutes/replacement, an annul operation interruption time to be spent for the replacement runs up to about 4,500 minutes (75 hours).

If the time necessary for the replacement of the sleeve-shaped refractory member can be reduced to half, i.e., 37.5 minutes on an average, the annul operation interruption time to be spent for the replacement will be reduced to half, i.e., about 2,250 minutes (37.5 hours), and an operating time of the converter and a quantity of production can be increased by just that much. Further, if the usable life of the sleeve-shaped refractory member can be doubled, i.e., 400 heats on an average, the replacement frequency will be reduced to half, i.e., 30 times/year. When the average time necessary for the replacement is 75 minutes/replacement, the annul operation interruption time to be spent for the replacement will also be reduced to half, i.e., about 2,250 minutes (37.5 hours), and an operating time of the converter and a quantity of production can also be increased by just that much.

In reality, the sleeve-shaped refractory member is firmly bonded to a refractory lining of a converter using a castable refractory material, such as mortar, and a replacement operation has to be carried out in a high-temperature environment. Thus, there is an actual problem about extreme difficulty in further reducing the replacement time.

While it is contemplated to use the tundish nozzle replacing apparatuses disclosed in the Patent Publications 2 and 3, in replacement of a tapping sleeve of a converter, a heat resistance of these apparatuses will emerge as a serious problem, because the converter is continuously operated while handling molten steel which has a higher temperature than that in a tundish by about 50 to 100° C. Particularly, in the tundish nozzle replacing apparatuses, springs for pressing a tundish nozzle or immersion nozzle (corresponding to the replaceable sleeve-shaped refractory member) against an upper nozzle, and a hydraulic cylinder for slidingly moving the tundish nozzle or immersion nozzle in a horizontal direction will be subjected to high temperatures to cause thermal degradation. While a cooling device may be added to suppress this problem, a tilt or rotational movement of the converter will cause another problem about structural complexity and increase in size of the cooling device.

In a sliding nozzle apparatus, the following Patent Publication 4 discloses a technique of controllably opening and closing an nozzle opening using a plate brick with a hole having an excessively large hole diameter to maintain an optimal flow volume so as to reduce an average tapping time.

A converter has to handle molten steel which has a higher temperature than a ladle or tundish by about 50 to 100° C. and a flow volume 5 to 10 times greater than that in the ladle or tundish. Thus, if the above sliding nozzle apparatus for a ladle or tundish is used in a converter, a refractory component will have severe wear and have to be frequently replaced due to shortened usable life thereof to cause a problem about deterioration in operational efficiency, contrary to the intended purpose. Moreover, the above sliding nozzle apparatus is designed to narrow a nozzle opening using a plurality of plate bricks so as to control a flow volume. Thus, a molten steel flow to be discharged becomes turbulent to cause a problem about entrainment of air in the molten metal.

[Patent Publication 1] Japanese Patent Laid-Open Publication No. 05-195038

[Patent Publication 2] Japanese Patent Laid-Open Publication No. 200-1-150108

[Patent Publication 3] Japanese Patent Laid-Open Publication No. 10-286658

[Patent Publication 4] Japanese Patent Publication No. 55-038007

DISCLOSURE OF THE INVENTION

It is an object of the present invention to find means for reducing an average discharging time in a molten metal vessel, such as a converter, having a molten-metal discharge nozzle particularly a molten-metal discharge nozzle comprising a sleeve-shaped refractory member, so as to achieve enhanced operational efficiency of the molten metal vessel.

It is another object of the present invention to provide a molten-metal discharge nozzle comprising a sleeve-shaped refractory member mounted in a molten metal vessel in a readily replaceable manner, and having excellent heat resistance and compactness.

It is yet another object of the present invention to provide a sleeve replacing apparatus capable of readily replacing the sleeve-shaped refractory member of the discharge nozzle.

The inventors of this application assumed that an average discharging time may be reduced by using a conventional molten-metal discharge nozzle under the condition that an inner hole of a sleeve-shaped refractory member has a relatively large cross-sectional area from an initial stage of use.

While the use of a sleeve an inner hole having an initially large cross-sectional area causes a problem about increase in the frequency of replacement due to shortened usable life, this problem has been solved by dividing the sleeve-shaped refractory member of the discharge nozzle into two upper and lower sleeves, i.e., by frequently replacing only the lower sleeve. That is, the two-split structure allows the lower sleeve to be formed in a relatively small size having enhanced handleability so as to reduce a replacement time. Thus, it has been proven that the advantage of reducing an average tapping time is fairly greater than the disadvantage of increasing the replacement time. Reversely, the upper sleeve can be formed to have a relatively long usable life, and thereby the frequency of replacement for the upper sleeve will be advantageously reduced.

Further, a problem about heat resistance in an elastic member for pressing the lower sleeve is improved by associating the elastic member with the lower sleeve and replacing the elastic member every time the lower sleeve is replaced. Specifically, the lower sleeve is designed to be held by a metal housing incorporating the elastic member to form an integral unit.

Specifically, the present invention provides a discharge nozzle for molten metal in a molten metal vessel which comprises an upper sleeve and a lower sleeve adapted to be detachably attached to a lower end of the upper sleeve. Each of the upper and lower sleeves comprises a refractory member having an inner hole serving as a discharge passage of molten metal. This refractory member may be integrally formed as a single piece, or may be an assembly of a plurality of refractory members. The upper sleeve is mounted to a refractory lining of the molten metal vessel, and made of a refractory material having a longer usable life than that of the lower sleeve. For example, the upper sleeve is made of a refractory material having a usable life approximately equal to or longer than that of the conventional sleeve-shaped refractory member.

A flow volume of molten metal is controlled primarily by designing the inner hole of the lower sleeve to have a cross-sectional area providing an optimal molten-metal discharging time, and managing the cross-sectional area in a narrow range (a cross-sectional area of the inner hole of the upper or lower sleeve will hereinafter be referred to as “hole sectional area”). The frequency of replacement for the lower sleeve is 2 to 50 times greater than that for the upper sleeve. This frequency of replacement is dependent on a time necessary for replacement, and a usable life and/or cost of a refractory material to be used therefor. If the replacement time is relatively short, the cost of the refractory material is relatively low, the frequency of replacement can be increased to allow the average tapping time to be closer to an optimal value. In this case, the upper sleeve can be formed to have a longer useable life than the conventional sleeve-shaped refractory member.

In the present invention, a hole sectional area of the upper sleeve in its newly-installed state, and a hole sectional area of the lower sleeve in its newly-installed state, are determined on the basis of a hole sectional area of the lower sleeve in its used state requiring replacement. As used in this specification, the term “hole sectional area (i.e., cross-sectional area of the inner hole) of the lower sleeve in its used state requiring replacement” means a hole sectional area of the lower sleeve, at a time when the lower sleeve is replaced with a new one after the inner hole of the lower sleeve is enlarged due to wear along with increase in the number of heats, based on a user's or operator's decision that the lower sleeve reaches the end of a usable life thereof.

For example, in a steelmaking converter, if a given lower limit of a tapping time is set up primarily for preventing entrainment of slag, the lower sleeve will be replaced with a new one when the tapping time reaches the given lower limit. The usable life of the lower sleeve may be determined by a state, i.e., level, of entrainment of slag.

As used in this specification, the term “hole sectional area (i.e., cross-sectional area of the inner hole)” means a cross-sectional area in a portion of the inner hole where a flow rate in each of the upper and lower sleeves is substantially regulated, i.e., a cross-sectional area in the narrowest portion of the inner hole in each of the upper and lower sleeves. Even if the inner hole partially has a stepped portion or a convex portion, the term “hole sectional area (i.e., cross-sectional area of the inner hole)” means a portion of the inner hole where a flow rate is substantially regulated, irrespective of such configurations.

In the present invention, the hole sectional area of the lower sleeve in the newly-installed state is set preferably in the range of 60 to 98%, more preferably in the range of 67 to 97%, of the hole sectional area of the lower sleeve in the used state requiring replacement. If the hole sectional area is less than 60%, a time required for discharging molten metal will be excessively increased, and the effect of reducing the average discharging time cannot be adequately obtained. If the hole sectional area exceeds 98%, the frequency of replacement for the lower sleeve will be excessively increased to increase a time to be uselessly spent for replacement and preclude an intended improvement in operational efficiency of the molten metal vessel, such as a converter, from being obtained. The above term “newly-installed state” means a state at a time just after of the lower sleeve is newly installed in the molten metal vessel or replaced with a new one, i.e., an unused state.

As described, the flow volume is controlled primarily by the lower sleeve. Thus, the effects of the present invention can be obtained without particularly restricting the hole sectional area of the upper sleeve. Thus, the number of usable times of the upper sleeve can be drastically extended (increased). The reason is that, for example, even if the hole sectional area of the upper sleeve in its newly-installed state is less than the hole sectional area of the lower sleeve in its newly-installed state, the effect of the flow volume control of the lower sleeve becomes prominent as the number of times of use is increased. In view of obtaining greater effect of the present invention, the hole sectional area of the upper sleeve in its newly-installed state is preferably set in the range of 85 to 200% of the hole sectional area of the lower sleeve in the used state requiring replacement. The hole sectional area being less than 85% causes excessive increase in molten-metal discharging time, and the hole sectional area exceeding 200% causes poor handleability. More preferably, the lower sleeve may be used in such a manner that the hole sectional area of the lower sleeve in the newly-installed state is set at a value less than the hole sectional area of the upper sleeve. In this case, the average tapping time can be further reduced.

In the present invention, the lower sleeve may be detachably attached to the upper sleeve in such a manner that the lower sleeve is brought into press contact with the upper sleeve by a reaction force of the elastic member compressed when the metal housing is supported by a rail of a retention member fixed to the molten metal vessel, and moved along a longitudinal direction of the rail. The rail may have opposite longitudinal ends each formed with an inclined surface adapted to relax the compression of the elastic member. Further, in view of facilitating detachable attachment of the lower sleeve to the lower end of the upper sleeve, the upper sleeve is preferably installed in the molten metal vessel in such a manner that the lower end of the upper sleeve protrudes from an outer surface of the molten metal vessel.

The present invention further provides a sleeve replacing apparatus for replacing the lower sleeve with a new one. This sleeve replacing apparatus comprises a new-sleeve holding portion adapted to hold a new lower sleeve which is the lower sleeve in its unused state and before a replacement operation, a current-sleeve receiving portion adapted to receive therein the lower sleeve which is currently in press contact with the upper sleeve while being supported by the rail, an old-sleeve holding portion adapted to hold an old lower sleeve which is the lower sleeve in its used state and after the replacement operation, and arranged together with the new-sleeve holding portion and the current-sleeve receiving portion in a linear manner, and an actuator adapted to push out the new lower sleeve held by the new-sleeve holding portion toward the current-sleeve receiving portion. The actuator is operable to push out the new lower sleeve toward the current-sleeve receiving portion in such a manner that the new lower sleeve is brought into press contact with the upper sleeve while being supported by the rail, so as to allow the lower sleeve which has been in press contact with the upper sleeve to be pushed out and moved to the old-sleeve holding portion and held by the old-sleeve holding portion as an old lower sleeve.

This sleeve replacing apparatus may be adapted to be moved while being held by a manipulator, and provided with a guide rod adapted to be inserted into a guide horn provided on the molten metal vessel. In this case, during the replacement operation, the guide rod is inserted into the guide horn according to a manipulation of the manipulator, so as to fix a position of the sleeve replacing apparatus.

As above, according to the present invention, the discharging time of molten metal in the molten metal vessel can be minimized while preventing entrainment of contaminants, such as slag, and the discharge nozzle can be efficiently replaced to drastically improve operational efficiency of the molten metal vessel.

Further, a problem about heat resistance in an elastic member for pressing the lower sleeve can be improved by associating the elastic member with the lower sleeve and replacing the elastic member every time the lower sleeve is replaced. This makes it possible to achieve enhanced heat resistance of the discharge nozzle in its entirety.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be specifically described based on an embodiment thereof where the present invention is applied to a tapping nozzle of a steelmaking converter.

FIG. 1 is a sectional view showing a tapping nozzle 31 of a converter in a state after the converter is tilted to allow an axis of the tapping nozzle 31 to extend vertically. The tapping nozzle 31 comprises an upper sleeve 32 mounted to a refractory lining of the converter, and a lower sleeve 33 adapted to be detachably attached to a lower end of the upper sleeve 32. Each of the upper and lower sleeves 32, 33 illustrated in FIG. 1 is a new product in an unused state.

The upper sleeve 32 comprises a cylindrical-shaped refractory member 34, and a plate-shaped refractory member 35 provided at a lower end thereof and formed with a nozzle hole. In the installed state, the lower end of the upper sleeve 32 protrudes from an outer surface 36 of the converter, and the upper sleeve 32 is fixed to a support brick 37 by mortar. The lower sleeve 33 comprises a cylindrical-shaped refractory member 38, and a plate-shaped refractory member 39 provided at an upper end thereof and formed with a nozzle hole. The lower sleeve 33 is held by a lower-sleeve replacing apparatus 40 disposed along the lower end of the upper sleeve, and an upper end surface of the lower sleeve is in press contact with a lower end surface of the upper sleeve. In FIG. 1, the lower-sleeve replacing apparatus 40 is fixed to a shell of the converter to hold the lower sleeve while pressing the lower sleeve against the upper sleeve by an elastic member (not shown). When the tapping nozzle 31 is repeatedly used in this state, an inner diameter of an inner hole of the lower sleeve will be gradually increased, and the lower sleeve will finally reach the end of its usable life. In this embodiment, an inner diameter of an inner hole of the upper sleeve in its newly-installed state is designed to be 88% of an inner diameter of the inner hole of the lower sleeve in its used state requiring replacement.

As shown in FIG. 2, the lower sleeve 33 which has reached the end of the usable life is replaced with a new lower sleeve 41. An immersion-nozzle replacing apparatus disclosed in Japanese Patent Laid-Open Publication No. 2002-346705 is used as the replacing apparatus for this replacement operation. Specifically, the new lower sleeve 41 is pushed in a horizontal direction by a drive device, such as a hydraulic cylinder, so that the old lower sleeve 33 is pushed out and replaced with the new lower sleeve 41. More specifically, the replacing apparatus comprises a retaining metal frame fixed to a side surface of the converter and adapted to receive therein the upper sleeve, a pair of spring members (not shown) disposed in opposed relation to each other on both sides of the upper sleeve having a sliding surface, a plurality of latch plates (not shown) associated with a spring member and biased upwardly, and a guide rail. In this apparatus, a pusher for pushing the new lower sleeve and a drive source thereof are detachably attached to the converter, instead of being fixed to the converter.

Table 1 and FIG. 3 show an operation of the converter using the sleeve-type tapping nozzle illustrated in FIG. 1.

	TABLE 1
	Comparative	Inventive
	Example 1	Example 1
Hole sectional area of lower sleeve after		100
use (%)
Hole sectional area of upper sleeve in newly-		100
installed state (%)
Hole sectional area of lower sleeve in newly-		88
installed state (%)
Hole sectional area of sleeve in used state	100
requiring replacement (%)
Hole sectional area of conventional sleeve in	50
newly-installed state (%)
Tapping time in initial stage of use (min/heat)	10.0	6.3
Tapping time in last stage of use (min/heat)	5.0	5.0
Average tapping time (min/heat)	7.50	5.63
Reduction in tapping time relative to		1.87
Comparative Example 1 (min/heat)
Effect of reduction of average tapping time		374
(min/200 heats)
Usable life of lower sleeve (heat)		50.0
Frequency of replacement for lower sleeve		4
Total lower-sleeve replacement time		80
(min/200 heats)
Improvement of operational efficiency		294
(min/200 heats)

In Comparative Example 1 and Inventive Example 1 shown in Table 1, a hole sectional area of the lower sleeve after use was obtained by measuring respective hole sectional areas of four lower sleeves after use, and calculating an average of the measured hole sectional areas. Specifically, the calculated average was 707 cm² (inner diameter: 300 mm), and this value was used as a reference hole sectional area of the lower sleeve in the used state requiring replacement, or defined as 100%. A hole sectional area of the upper sleeve in the newly-installed state was set at the same value as the hole sectional area of the lower sleeve in the used state requiring replacement. A hole sectional area of the lower sleeve in the newly-installed state was 88% of the hole sectional area of the lower sleeve after use. The number of tappings was set at 200. The average tapping time in Table 1 indicates an average of 200 tapping times. A length of the upper sleeve was set at 700 mm, and a length of the lower sleeve was set at 300 mm. Each of Inventive Example 1 and Comparative Example 1 was made of a magnesia-carbon refractory material.

FIG. 4 shows the structure of Comparative Example 1 as a conventional tapping nozzle. The tapping nozzle of Comparative Example 1 was formed of a single sleeve-shaped refractory member 51 with an inner hole having an approximately constant cross-sectional area, and installed in the same converter as that in Inventive Example 1. This sleeve-shaped refractory member had a hole sectional area of 707 cm² (inner diameter: 300 mm) after being used 200 times, i.e., in the used state requiring replacement, and an initial hole sectional area was 50% of the hole sectional area after use.

As shown in FIG. 5, Comparative Example 1 has a relatively long tapping time of 10 minutes in an initial stage of use because of its initial hole sectional area of 50%, and the tapping time is gradually reduced along with increase in the number of times of use. As the result, Comparative Example 1 had an average tapping time of 7.5 minutes. In contrast, as shown in FIG. 3, Inventive Example 1 has a relatively short tapping time of 6.25 in an initial stage of use because of an initial hole sectional area of 88% which is greater than that of Comparative Example 1. Thus, Inventive Example 1 had an average tapping time of 5.63 minutes which is shorter than that of Comparative Example 1 by 1.87 minutes as shown in Table 1. The lower sleeve has to be replaced every 50 heats, and the average replacement time is 20 minutes. That is, the lower sleeve has to be replaced 4 times during a period of 200 heats, and therefore a total replacement time is 80 minutes. Thus, when the tapping is performed 200 times in this converter, an advantage of 1.87 min/tapping×200 tappings−80 min=294 minutes can be obtained as improvement of operational efficiency.

This converter is operated at 12000 heats a year. Thus, an advantageous time is 294 hours for a year. If this time is used for refining, a quantity of production will be increased by 442.5 heats/year or 132,750 ton/year.

Table 2 shows the result on improvement of operational efficiency calculated by variously changing the hole sectional area of the lower sleeve in the newly-installed state and the lower-sleeve replacement time in the above example.

	TABLE 2
	Comparative	Comparative	Inventive	Inventive	Inventive	Inventive	Inventive
	Example 1	Example 2	Example 2	Example 3	Example 4	Example 5	Example 6
Hole sectional area of lower sleeve after use (%)		100	100	100	100	100	100
Hole sectional area of upper sleeve in newly-installed		100	100	100	100	100	100
state (%)
Hole sectional area of lower sleeve in newly-installed		99	98	97	94	88	67
state (%)
Hole sectional area of sleeve in used state requiring	100
replacement (%)
Hole sectional area of conventional sleeve in newly-	50
installed state (%)
Tapping time in initial stage of use (min/heat)	10.0	5.1	5.2	5.3	5.6	6.3	8.3
Tapping time in last stage of use (min/heat)	5.0	5.0	5.0	5.0	5.0	5.0	5.0
Average tapping time (min/heat)	7.5	5.0	5.1	5.2	5.3	5.6	6.7
Reduction in average tapping time relative to		2.46	2.42	2.34	2.19	1.88	0.83
Comparative Example 1 (min/heat)
Reduced time in average tapping time relative to		492	484	469	438	375	167
Comparative Example 1 (hour/year) (1)
Usable life of lower sleeve (heat)	0	3.1	6.3	12.5	25.0	50.0	133.3
Replacement time of lower sleeve (min/tapping)		5	5	5	5	5	5
Replacement time of lower sleeve (2) (hour/year)		320	160	80	40	20	8
Improved time in operational efficiency (1) −		172	324	389	398	355	159
(2) (hour/year)
Replacement time of lower sleeve (min/tapping)		10	10	10	10	10	10
Replacement time of lower sleeve (3) (hour/year)		640	320	160	80	40	15
Improved time in operational efficiency (1) −		−148	164	309	358	335	152
(3) (hour/year)
Replacement time of lower sleeve (min/tapping)		20	20	20	20	20	20
Replacement time of lower sleeve (4) (hour/year)		1280	640	320	160	80	30
Improved time in operational efficiency (1) −		−788	−156	149	278	295	137
(4) (hour/year)
(Note)
Replacement time of lower sleeve (hour/year) was calculated by the following formula: (12000/usable life of lower sleeve) × replacement time of lower sleeve

The above calculation was performed on the assumption that the converter is operated at 12000 tappings a year. Further, a wear rate was set at the same value as that in Inventive Example 1. As seen in Table 2, the improvement of operational efficiency becomes larger as the lower-sleeve replacement time is shorter. When the replacement time is 5 minutes, all Inventive Examples 2 to 6 and Comparative Example 1 can get good results. When the replacement time is 10 minutes, no advantage is obtained if the hole sectional area is equal to or greater than 98% of the hole sectional area of the lower sleeve after use. This result shows that the hole sectional area of the lower sleeve in the newly-installed state is more preferably in the range of 97 to 67% in consideration of some margin in replacement time. A lower-sleeve replacement time of 20 minutes can be surely achieved by a conventional technique, e.g., a technique for a continuous casting nozzle, of fixing the lower sleeve using a bayonet, bolt or the like.

FIG. 6 is an exploded perspective view showing a molten-metal discharge nozzle and a sleeve replacing apparatus, according to a second embodiment of the present invention, and FIG. 7 is a perspective view showing an upper portion of the molten-metal discharge nozzle in FIG. 6.

The molten-metal discharge nozzle illustrated in FIGS. 6 and 7 comprises an upper sleeve 2 mounted to a refractory lining of a converter 1, and a lower sleeve 3 adapted to be detachably attached to an distal end of the upper sleeve 2. FIGS. 6 and 7 show only a part of the converter, specifically, a vicinity of a tapping port of the converter.

FIG. 8(a) is a top plan view showing the lower sleeve 3. FIG. 8(b) is a sectional view taken along the line A-A in FIG. 8(a), and FIG. 8(c) is a sectional view taken along the line B-B in FIG. 8(a). As shown in FIGS. 8(a) to 8(c), the lower sleeve 3 is mounted to a metal housing 4 comprising an outer metal frame 4a and an inner metal frame 4b. As shown in FIG. 8(c), an elastic member 5 composed of a coil spring is embedded in a space between the outer metal frame 4a and the inner metal frame 4b, so that the outer metal frame 4a holds the inner metal frame 4b through the elastic member 5 in a vertically movable manner. Specifically, the elastic member 5 is fit on a guide protrusion 6 extending downwardly from a lower surface of the inner metal frame 4b, so as to be kept from moving laterally. As shown in FIG. 8(b), a guide pin 7 is provided as a means to guide the vertical movement of the inner metal frame 4b. The guide protrusion 6 has a length set to avoid conflict with the outer metal frame 4a even when the elastic member 5 is maximally compressed. In this embodiment, a total of the ten guide protrusions 6 are arranged in a concentric pattern. Further, the outer metal frame 4a is provided with a cooling horn 8 serving as an ambient air inlet for introducing ambient air to the elastic member 5 to cool the elastic member 5.

The inner metal frame 4b has a lateral surface provided with a sleeve lock device 9 for locking the lower sleeve 3. The sleeve lock device 9 comprises a screw mechanism and a sleeve pressing plate 9a attached at distal end of the screw mechanism. According to the screw mechanism, the sleeve pressing plate 9a is moved inwardly and pressed against a lateral surface of the lower sleeve 3 to lock the lower sleeve 3 to the inner metal frame 4b.

The lower sleeve 3 is made of a refractory material, and an upper surface of the lower sleeve 3 is formed as a contact surface 3a with the upper sleeve 2. The contact surface 3a has a generally circular shape, and an outer periphery of the contact surface 3a includes a pair of parallel edges 3b. Each of the parallel edges 3b is formed to extend in a direction orthogonal to a moving direction of the lower sleeve during an after-mentioned replacement operation. Further, each of the parallel edges 3b is formed to have a length greater than a diameter of the inner hole 3c so as to prevent the lower sleeve 3 from being damaged due to a pushing force during the replacement operation. If the contact surface 3a is formed in a perfect circle without the parallel edges 3b, the contact surface 3a will come into point contact with the inner metal frame 4a during the replacement operation, and resulting stress concentration is likely to damage the contact surface 3a. Further, if the length of each of the parallel edges 3b is less than the inner hole 3c, a crack occurring from the parallel edges 3b is likely to penetrate through the inner hole 3c.

In this embodiment, the lower sleeve 3 is a single-piece product. Alternatively, the lower sleeve 3 may be a multi-part product formed, for example, by preparing an upper portion including the contact surface 3a and a cylindrical-shaped lower portion separately, and joining them together. Further, an outer surface of the lower sleeve 3 may be covered by a metal case to effectively prevent damages.

FIG. 9 is a fragmentary sectional view showing the upper sleeve 2. As shown in FIG. 9, the upper sleeve 2 is mounted to a metal housing 10 comprising an outer metal frame 10a and an inner metal frame 10b. The outer metal frame 10a is fixed to a base plate 11 secured to the converter 1, and the inner metal frame 10b is attached to the outer metal frame 10a by a pin 12 in a vertically movable manner. The inner metal frame 10b has a lateral surface provided with a sleeve lock device 13 for locking the upper sleeve 2. The sleeve lock device 13 has the same structure as that of the aforementioned sleeve lock device 9 for locking the lower sleeve 2, and its description will be omitted.

The upper sleeve 2 is made of a refractory material as with the lower sleeve, and a lower surface of the upper sleeve 2 is formed as a contact surface 2a with the lower sleeve 3. As shown in FIG. 7, the contact surface 2a has a generally circular shape, and an outer periphery of the contact surface 2a includes a pair of parallel edges 2b. Each of the parallel edges 2b is formed to extend in a direction orthogonal to a moving direction of the lower sleeve during the after-mentioned replacement operation. Further, each of the parallel edges 2b is formed to have a length greater than a diameter of an inner hole 2c of the upper sleeve 2.

The upper sleeve 2 is fixed to the refractory lining of the converter 1 through a castable refractory material filled therebetween.

FIG. 10 is a fragmentary sectional view showing the lower sleeve 3 after being brought into press contact with the lower end of the upper sleeve 2. A pair of retention members 14 are fixed to the base plate 11 and provided with a rail 14a, and the lower sleeve 3 is held by the rail 14a. In this retention state, the outer metal frame 4a of the metal housing 4 which holds the lower sleeve 3 is pushed upwardly, i.e., lifted, to compress the elastic member 5. Then, according to a reaction force of the elastic member 5, the inner metal frame 4a is lifted together with the lower sleeve 3, and the contact surface 3a of the lower sleeve 3 is reliably brought into press contact with the contact surface 2a of the upper-sleeve 2.

As above, the metal housing 4 which holds the lower sleeve 3 can be slidingly moved along a longitudinal direction of the rail 14a. Thus, an operation of replacing the lower sleeve 3 with a new one can be performed by slidingly moving the metal housing 4 (lower sleeve 3) along the longitudinal direction of the rail 14a. In this embodiment, a liner 26 is provided on the lower surface of the outer metal frame 4a of the metal housing 4 and each surface of the rail 14a to facilitate the sliding movement and provide enhanced frictional resistance.

Further, as shown in FIG. 7, the rail 14a has opposite lateral ends each formed with an inclined surface 14b. This inclined surface 14b is formed to extend downwardly toward each end edge of the rail 14b. Thus, when the metal housing 4 (lower sleeve 3) is slidingly moved along the longitudinal direction of the rail 14a, a lift amount of the outer metal frame 4a of the metal housing 4 is reduced in these regions having the inclined surface 14b, and thereby the compression of the elastic member 5 is relaxed to reduce a pressing force of the lower sleeve 3 against the upper sleeve 2. This makes it possible to smoothly perform the replacement operation for the lower sleeve 3.

The sleeve replacing apparatus according to the second embodiment of the present invention will be described below.

As shown in FIG. 6, the sleeve replacing apparatus 15 comprises a new-sleeve holding portion 16 adapted to hold a new lower sleeve which is the lower sleeve 3 in the unused state and before the replacement operation, a current-sleeve receiving portion 17 adapted to receive therein the lower sleeve 3 which is currently in press contact with the upper sleeve, an old-sleeve holding portion 18 adapted to hold an old lower sleeve which is the lower sleeve 3 in the used state and after the replacement operation, and a base 19. The new-sleeve holding portion 16, the current-sleeve receiving portion 17 and the old-sleeve holding portion 18 are arranged on the base 19 in a linear manner in this order. Each of the new-sleeve holding portion 16 and the old-sleeve holding portion 18 is formed with a guide rail (16a, 18a) adapted to slidably support the metal housing for each of the new lower sleeve and the old lower sleeve. The sleeve replacing apparatus 15 further includes an actuator 20 composed of a hydraulic cylinder and disposed on the side of the new-sleeve holding portion 16.

As shown in FIGS. 6 and 7, a pair of positioning guide horns 21 are fixed to the base plate of the converter 1 and disposed to allow a center of a diagonal line connecting between the guide horns 21 to be located at a center of the inner hole 2c, and a pair of guide rods 22 are fixed on the base 19 of the sleeve replacing apparatus 15 at respective positions corresponding to the guide horns 21.

A lower-sleeve replacement operation using the sleeve replacing apparatus 15 will be described below.

FIGS. 11(a) and 11(b) are explanatory views of the lower-sleeve replacement operation using the sleeve replacing apparatus, wherein FIGS. 11(a) and 11(b) are a top plan view and a side view of the sleeve replacing apparatus. FIG. 12 is a fragmentary sectional view showing the sleeve replacing apparatus during the lower-sleeve replacement operation.

In advance of the lower-sleeve replacement operation, a new lower sleeve 3′ is slidingly attached to the guide rail 16a and held by the new-sleeve holding portion 16 of the sleeve replacing apparatus 15 (see FIG. 12). Then, as shown in FIGS. 11(a) and 11(b), the sleeve replacing apparatus 15 is held by a manipulator 24 on a movable dolly 23, and the dolly 23 is moved along a track 25 to allow the sleeve replacing apparatus 15 to come close to the converter 1. Then, the manipulator 24 is manipulated to insert the guide rods 22 of the sleeve replacing apparatus 15 into the corresponding guide horns 21 while adjusting vertical and horizontal positions of the sleeve replacing apparatus 15 so as to fix a position of the sleeve replacing apparatus 15.

Referring to FIG. 12 to describe a subsequent process, the actuator 20 of the sleeve replacing apparatus 15 is driven forward (extended) to push out the new lower sleeve 3′ held by the new-sleeve holding portion 16, toward the current-sleeve receiving portion 17. Through this operation, the new lower sleeve 3′ is ridden on the rail 14a and brought into press contact with the upper sleeve 2, as shown in FIG. 10, to allow a lower sleeve 3″ (see FIG. 12) which has been in press contact with the upper sleeve to be pushed out and slidingly moved to the old-sleeve holding portion 18 along the guide rail 18a and held by the old-sleeve holding portion 18 as an old lower sleeve. Through the above process, the lower-sleeve replacement operation is completed.

A discharge nozzle having the structure according to this embodiment was applied to an actual concreter, and a lower-sleeve replacement operation was carried out using the sleeve replacing apparatus. As the result, the replacement operation could be completed within 5 minutes.

INDUSTRIAL APPLICABILITY

The present invention can be applied to not only steelmaking converters but also nonferrous-metal refining converters and other tilt furnaces.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view showing a molten-metal discharge nozzle according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a lower sleeve of the molten-metal discharge nozzle during a replacement operation.

FIG. 3 is a graph showing a replacement operation for a lower sleeve of a molten-metal discharge nozzle as Inventive Example 1.

FIG. 4 is a schematic sectional view showing a molten-metal discharge nozzle as Comparative Example 1.

FIG. 5 is a graph showing an operation of replacing a lower sleeve of Comparative Example 1.

FIG. 6 is a fragmentary exploded perspective view showing a sleeve replacing apparatus and a molten-metal discharge nozzle, according to a second embodiment of the present invention.

FIG. 7 is a fragmentary perspective view showing an upper portion of the molten-metal discharge nozzle in FIG. 6.

FIGS. 8(a) to 8(c) show a lower sleeve of the molten-metal discharge nozzle in FIG. 6, wherein FIGS. 8(a), 8(b) and 8(c) are a top plan view, a sectional view taken along the line A-A in FIG. 8(a) and a sectional view taken along the line B-B in FIG. 8(a), respectively.

FIG. 9 is a fragmentary sectional view showing an upper sleeve of the molten-metal discharge nozzle in FIG. 6.

FIG. 10 is a fragmentary sectional view showing the upper sleeve and the lower sleeve in the molten-metal discharge nozzle in FIG. 6, wherein the lower sleeve is in press contact with the upper sleeve.

FIGS. 11(a) and 11(b) are explanatory views of the lower-sleeve replacement operation using the sleeve replacing apparatus, wherein FIGS. 11(a) and 11(b) are a top plan view and a side view of the sleeve replacing apparatus.

FIG. 12 is a fragmentary sectional view showing the sleeve replacing apparatus during the lower-sleeve replacement operation.

DESCRIPTION OF THE REFERENCE NUMERALS AND SIGNS

• 1 converter
• 2 upper sleeve
• 2a contact surface
• 2b parallel edge
• 2c inner hole
• 3 lower sleeve
• 3′ new lower sleeve
• 3″ old lower sleeve
• 3a contact surface
• 3b parallel edge
• 3c inner hole
• 4 metal housing
• 4a outer metal frame
• 4b inner metal frame
• 5 elastic member
• 6 guide protrusion
• 7 guide pin
• 8 cooling horn (ambient air inlet)
• 9 sleeve lock device
• 9a sleeve pressing plate
• 10 metal housing
• 10a outer metal frame
• 10b inner metal frame
• 11 base plate
• 12 pin
• 13 sleeve lock device
• 14 retention member
• 14a rail
• 14b inclined surface
• 15 sleeve replacing apparatus
• 16 new-sleeve holding portion
• 16a guide rail
• 17 current-sleeve receiving portion
• 18 old-sleeve holding portion
• 18a guide rail
• 19 base
• 20 actuator
• 21 guide horn
• 22 guide rod
• 23 movable dolly
• 24 manipulator
• 25 track
• 26 liner
• 31 tapping nozzle
• 32 upper sleeve
• 33 lower sleeve
• 34, 38 cylindrical-shaped refractory member
• 35, 39 plate-shaped refractory member
• 36 outer surface of converter
• 37 support brick
• 40 lower-sleeve replacing apparatus
• 41 new lower sleeve
• 51 sleeve-shaped refractory member

Claims

1. A discharge nozzle for molten metal in a molten metal vessel, comprising an upper sleeve and a lower sleeve adapted to be detachably attached to a lower end of said upper sleeve, wherein said lower sleeve is formed with an inner hole in such a manner that a cross-sectional area of the inner hole of said lower sleeve in its newly-installed state is in the range of 60 to 98% of a cross-sectional area of the inner hole of said lower sleeve in its used state requiring replacement.

2. The discharge nozzle as defined in claim 1, wherein said upper sleeve is formed with an inner hole in such a manner that a cross-sectional area of the inner hole of said upper sleeve in its newly-installed state is in the range of 85 to 200% of the cross-sectional area of the inner hole of said lower sleeve in said used state requiring replacement.

3. The discharge nozzle as defined in claim 1, wherein said upper sleeve is adapted to be installed in said molten metal vessel in such a manner that the lower end of said upper sleeve protrudes from an outer surface of said molten metal vessel.

4. A discharge nozzle for molten metal in a molten metal vessel, comprising:

an upper sleeve; and

a lower sleeve adapted to be detachably attached to a lower end of said upper sleeve, in such a manner that said lower sleeve is associated with an elastic member for allowing said lower sleeve to be brought into press contact with said upper sleeve, and held by a metal housing incorporating said elastic member to form an integral unit, wherein said lower sleeve is brought into press contact with said upper sleeve by a reaction force of said elastic member compressed when said metal housing is supported by a rail of a retention member fixed to said molten metal vessel, and allowed to be detached from said upper sleeve when moved along a longitudinal direction of said rail.

5. The discharge nozzle as defined in claim 4, wherein said metal housing has an ambient-air inlet for introducing ambient air to said elastic member.

6. The discharge nozzle as defined in claim 4, wherein said rail has opposite longitudinal ends each formed with an inclined surface adapted to relax the compression of said elastic member.

7. The discharge nozzle as defined in claim 4, wherein each of said upper sleeve and said lower sleeve is formed to have a generally circular-shaped contact surface therebetween, and an inner hole having an axis aligned with a center of said contact surface, said contact surface having an outer periphery which includes a pair of parallel edges each extending in a direction orthogonal to said moving direction of said lower sleeve during the detachment and having a length greater than an inner diameter of said nozzle hole.

8. The discharge nozzle as defined in claim 4, wherein a cross-sectional area of the inner hole of said lower sleeve in its newly-installed state is in the range of 60 to 98% of a cross-sectional area of the inner hole of said lower sleeve in its used state requiring replacement.

9. The discharge nozzle as defined in claim 8, wherein a cross-sectional area of the inner hole of said upper sleeve in its newly-installed state is in the range of 85 to 200% of the cross-sectional area of the inner hole of said lower sleeve in said used state requiring replacement.

10. The discharge nozzle as defined in claim 8, wherein said upper sleeve is adapted to be installed in said molten metal vessel in such a manner that the lower end of said upper sleeve protrudes from an outer surface of said molten metal vessel.

11. A sleeve replacing apparatus for the discharge nozzle as defined in claim 4, comprising:

a new-sleeve holding portion adapted to hold a new lower sleeve which is the lower sleeve in its unused state and before a replacement operation;

a current-sleeve receiving portion adapted to receive therein the lower sleeve which is currently in press contact with said upper sleeve while being supported by said rail;

an old-sleeve holding portion adapted to hold an old lower sleeve which is the lower sleeve in its used state and after said replacement operation, and arranged together with said new-sleeve holding portion and said current-sleeve receiving portion in a linear manner; and

an actuator adapted to push out said new lower sleeve held by said new-sleeve holding portion toward said current-sleeve receiving portion, said actuator being operable to push out said new lower sleeve toward said current-sleeve receiving portion in such a manner that said new lower sleeve is brought into press contact with said upper sleeve while being supported by said rail, so as to allow said lower sleeve which has been in press contact with said upper sleeve to be pushed out and moved to said old-sleeve holding portion and held by said old-sleeve holding portion as an old lower sleeve.

12. The sleeve replacing apparatus as defined in claim 11, which is adapted to be moved while being held by a manipulator, and provided with a guide rod adapted to be inserted into a guide horn provided on the molten metal vessel, wherein, during said replacement operation, said guide rod is inserted into the guide horn according to a manipulation of said manipulator, so as to fix a position of the sleeve replacing apparatus.

13. A method for operation of a converter having a molten-metal discharge nozzle which includes an upper sleeve and a lower sleeve detachably attached to a lower end of said upper sleeve, comprising:

allowing said lower sleeve to have an inner hole formed such that a cross-sectional area of the inner hole of said lower sleeve in its newly-installed state is in the range of 60 to 98% of a cross-sectional area of the inner hole of said lower sleeve in its used state requiring replacement; and

operating said converter under the condition that the cross-sectional area of the inner hole of said lower sleeve is maintained at a value equal to or less than a cross-sectional area of an inner hole formed in said lower sleeve.

14. The method as defined in claim 13, which includes operating said converter under the condition that a cross-sectional area of the inner hole of said upper sleeve at a time when said lower sleeve is replaced and newly installed is maintained in the range of 85 to 200% of the cross-sectional area of the inner hole of said lower sleeve in said used state requiring replacement.