NOZZLE FOR BLOWING GAS INTO MOLTEN METAL AND USAGE THEREOF

Abstract: There is provided a gas blast nozzle for molten metal that has a prolonged service life and which is free from gas leakage. There is also provided a method of repairing it. It comprises a refractory block having a narrow straight bore and a small metal pipe slidably arranged in the straight bore. As gas is blown by a small metal pipe. When the gas blast nozzle is partly worn away, the small metal pipe is moved upward to project into the furnace and the worn away portion is filled with a refractory material.

Description: Technical Field This invention relates to a gas blast nozzle for molten metal in a smelting furnace such as an electric furnace or another refining furnace. In particular, it relates to a gas blast nozzle for molten metal that can be repaired easily, and a method of using the same. Background Art Fig. 5 of the accompanying drawings illustrates examples of conventional gas blast nozzles. Fig. 5(a), Fig. 5(b) and Fig.5(c), respectively, show a single pipe nozzle, a double pipe nozzle and a multi-pipe nozzle, and Fig. 5(d) shows a porous plug. In Fig. 5, reference numerals 10 and 11, respectively, denote a gas feed hose and a refractory block in a furnace bottom, whereas 17 and 18, respectively, denote a cooling gas feed pipe and a porous brick. A multi-pipe nozzle of Fig. 5(c) may be realized by burying a plurality of small metal pipes in a refractory block and such a multi-pipe nozzle has been popularly used for electric furnaces because fine and evenly sized gas bubbles can be produced in molten metal by means of the multi-pipe nozzle. As gas is blown into molten metal through a gas blast nozzle in a refining furnace, the inner side of refractory of the furnace becomes remarkably worn away in an area surrounding the gas blast nozzle as shown at 8 in Fig. 2(a) as the molten metal in the furnace is vigorously moved by the gas in an area near the gas blast nozzle. When the worn away portion 8 has grown too big, the gas blast nozzle has to be replaced, which results in suspending the operation of the furnace. Furthermore, such a nozzle replacing operation has to be conducted in an adverse environment and, according to this aspect, it is not recommendable to replace the gas blast nozzle frequently. Japanese patent application laid-open publication No. 58-81937 discloses a gas blast plug comprising a refractory nozzle block having a bore therethrough and a small metal pipe placed in the bore with an annular gap to an inner surface of the bore. Fig. 6 of the accompanying drawings illustrates the gas blast plug according to the above prior art. Referring to Fig. 6(a), an annular gap is formed between the inner surface of the bore and the outer surface of the small metal pipe 2, such that the thickness of the annular gap is sufficiently thin so as to avoid any leaking of molten metal. In Fig. 6(a), a gas feed hose (not shown) is connected to the small metal pipe 2. The arrangement shown in Fig. 6 seems to be effective for prolonging the service life of a gas blast nozzle, since the gas blast nozzle can be repaired when it has been partly worn away during its usage, and can be served for long term without replacing it. However, the inventors of the present invention have found that, when the gas blast plug according to the above is used in an electric refining furnace, the gas tends to move into the annular gap rather than entering into the molten metal as shown in Fig. 6(b). When the gas from the small metal pipe 2 is supplied at a low rate and the gas is blown in from the bottom of the furnace, a high static pressure of the molten metal at the bottom of the furnace may resist the gas entering into the molten metal, and the gas may move more easily into the annular gap than into the molten metal. However, the above construction does not provide a solution to this problem. Disclosure of the Invention The present invention provides a gas blast nozzle that minimizes the breakdown time of a furnace for replacing the gas blast nozzle because it seldom requires the replacement, reduces the work load of the replacing operation under adverse working conditions and is free from the problem of gas leaking through the gas blast nozzle. Fig. 1 of the accompanying drawings shows a gas blast nozzle according to the invention. Fig. 1(a) is a longitudinal sectional view of the gas blast nozzle itself, and Fig. 1(b) is also a longitudinal sectional view of the gas blast nozzle showing how it is arranged in the bottom of a furnace, whereas Fig. 1(c) is also a longitudinal section view illustrating it with a coupler for connecting it with a gas feed hose. According to the invention, there is provided a gas blast nozzle for molten metal comprising a refractory block 4 having a narrow straight bore 3 being bored from the inside to the outside of a furnace, a tubular metal fitting 22 formed in one body with the refractory block 4, a small metal pipe 2 arranged slidably through the straight bore 3 of the refractory block 4 and a metal coupler 23 for connecting a gas hose 15 to an end of the tubular metal fitting 22, and is characterized in that an outer end portion of the small metal pipe 2 is made to penetrate through a rubber block 14 in the metal coupler 23, and the gas 12 fed to the metal coupler 23 is blown into the molten metal in the furnace from the inner end of the small metal pipe 2. The tubular metal fitting 22 is tubular at an end and has a saucer-like profile at the other end to snugly receive the bottom of the refractory block 4 so that the refractory block 4 is fitted and bonded to the tubular metal fitting 22 at its bottom to combine them in one body with each other. Since the refractory block 4 and the tubular metal fitting 22 are integrated in one body with each other and the small metal pipe is made to penetrate through the rubber block, gas is securely prevented from leaking through the annular gap between the small metal pipe 2 and the refractory block 4 unlike the case of Fig. 6(b). As can be seen from Fig. 1(c), the tubular end of the metal fitting 22 is connected to an end of the metal coupler 23, and the other end of the metal coupler 23 is connected to a gas hose 15. The outer end of the small metal pipe 2 is made to penetrate the rubber block 14 and open for the gas hose 15. The gap between the outer periphery of the small metal pipe 2 and the inner surface of the metal coupler 23 is sealed by the rubber block 14 so that all the gas 12 fed in from the gas hose 15 is blown into the small metal pipe 2. While Fig. 1 shows a gas blast nozzle 1 having a single small metal pipe 2, a gas blast nozzle according to the invention may alternatively comprise a plurality of small metal pipes 2 in such a way that the gap between each of the small metal pipes 2 and the corresponding metal coupler 23 is filled with a rubber block 14 so that all the gas fed in may be blown into the small metal pipes 2 regardless of the number of small metal pipes 2. As shown in Fig. 1(b), the gas blast nozzle 1 is fitted to the tuyere-forming bricks 6 at the refractory bottom 11 of the furnace and secured to an outer shell 19 of the furnace by means of a securing ring 21 and a lock member 20. At the same time, the gap between the nozzle and the tuyere-forming bricks is filled with some castable refractory substance 5. The small metal pipe 2 may be a stainless steel pipe having an inner diameter of 1 to 2 mm, although the inner diameter and the number of pipes may be selected depending on the gas flow rate. Additionally, the small metal pipe may be a single pipe or a double pipe. It should be noted that the inner diameter of the straight bore 3 is made greater than the outer diameter of the small metal pipe 2 by 0 to 4 mm in order to allow the small metal pipe 2 to move smoothly vertically. Fig. 2 illustrates a method of using the gas blast nozzle 1 according to the invention. A gas blast nozzle 1 according to the invention is worn away, in particular the inner refractory is worn away during its usage which produces a worn away portion 8 as shown in Fig. 2(a). According to the invention, the worn away portion 8 is repaired by moving upward the small metal pipe 2 in the straight bore 3 until the inner end of the small metal pipe 2 projects over the inner surface of the furnace as shown in Fig. 2(b). Then, the worn away portion 8 is filled with a refractory material 16 without closing the inner end of the small metal pipe 2 as shown in Fig. 2(c). In this Fig. 2(c), the inner end of the small metal pipe 2 is projecting over the inner surface of the furnace after the worn away portion has been filled with the refractory material 16. Also, the inner end of the small metal pipe 2 would neither be buried nor clogged by this projection even if in a usual repairing apparatus of the furnace a lining such as a sand slinger is used to fill the worn away portion 8 with an ordinary refractory material for repairing the lining of the furnace. Thus, with a gas blast nozzle 1 according to the invention, the gas blast nozzle and its peripheral area can be repaired easily, if necessary, in the routine operation for maintaining the furnace bottom and the furnace wall, which consequently prolongs the service life of the gas blast nozzle so that the frequency of replacing the gas blast nozzle will be remarkably reduced. When gas is blown into the molten metal in the furnace after filling the worn away portion as shown in Fig. 2(c), the projecting portion of the small metal pipe 2 is immediately molten away and the inner end of the gas blast nozzle will show a profile as shown in Fig. 1(b). Also, the gas blast nozzle operates to blow gas into the molten metal as stably as before. Fig. 3 illustrates another embodiment of a gas blast nozzle according to the invention. Fig. 3(a) is a longitudinal sectional view of the gas blast nozzle and Fig. 3(b) is also a longitudinal sectional view showing how the gas blast nozzle is arranged in the bottom of a furnace. The gas blast nozzle of Fig. 3(a) differs from that of Fig. 1(a) in that the refractory block 4 is divided into upper and lower pieces. Otherwise, it is the same as its counterpart of Fig. 1(a). As described earlier in connection with Fig. 1(c), the tubular metal fitting 22 is coupled at its outer end to a gas hose 15 by means of a metal coupler 23 and the annular gap around the small metal pipe 2 is sealed by a rubber block 14. As shown in Fig. 3(b), the gas blast nozzle is also fitted to the tuyere-forming bricks 6 at the refractory bottom 11 of the furnace and secured to the outer shell 19 of the furnace by means of a securing ring 21 and a lock member 20. Also, the gap between the nozzle and the tuyere-forming bricks is filled with some castable refractory substance. Fig. 4 illustrates a method of using the gas blast nozzle illustrated in Fig. 3. The worn away portion 8 in Fig. 4(a) is repaired by moving upward the small metal pipe 2 in the straight bore until the inner end of the small metal pipe 2 projects over the inner surface of the furnace, replacing the damaged upper piece 4a of the refractory block with a new upper piece 4a (hereinafter referred to as a repairing brick) as shown in Fig. 4(b) and filling the remaining portion with a refractory material 16. Thereafter, the small metal pipe 2 is moved downward until the inner end arrives at the same level as that of the upper surface of the repairing brick 4a. With the method of Fig. 4, the service life of the gas blast nozzle will be further prolonged compared with its repairing where the worn away portion is filled only by a castable refractory material. Additionally, since the small metal pipe 2 is not projecting into the furnace after repairing, it will be consumed at a reduced rate. Brief Description of the Drawings Fig. 1 illustrates an embodiment of a gas blast nozzle according to the invention. Fig. 2 illustrates a method of using the gas blast nozzle of Fig. 1. Fig. 3 illustrates another embodiment of a gas blast nozzle according to the invention. Fig. 4 illustrates the method of using the gas blast nozzle of Fig. 3. Fig. 5 illustrates a conventional gas blast nozzle. Fig. 6 illustrates a conventional gas blast plug. Best Mode for Carrying out the Invention A straight bore having an inner diameter of 5 mm was formed through a refractory block 4 as shown in Fig. 1(a) in order to provide a gas blast nozzle for feeding gas from the bottom of an electric furnace. The small metal pipe 2 had an inner diameter of 2 mm, an outer diameter of 4 mm and a length of 2 m and was used with a metal coupler 23 as shown in Fig. 1(c). Gas was blown into the molten metal in the furnace at a rate of 30 to 100 liter/min. When the gas blast nozzle 1 had been worn away by about 200 mm at the inner end, the gas feeding hose 15 as shown in Fig. 1(c) was removed, the small metal pipe 2 was moved upward until the upper end arrived at the same level as that of the surface of a repaired refractory bottom 11 of the furnace and the worn away portion was filled with refractory material. After this repairing, it was coupled with the gas hose 15 again by means of the metal coupler 23. An ordinary refractory material for repairing furnace bottom was used to fill the worn away portion of the furnace. In order to prevent the inner end of the small metal pipe 2 from being clogged, gas was continuously blown during the operation of filling the refractory material. After four times to five times of repairing, the small metal pipe 2 was replaced by a new one, and the cycle of usual furnace operation and repairing was further repeated. When moving and/or replacing the small metal pipe 2, it was found in some cases that molten metal had entered into the annular gap between the straight bore 3 and the metal pipe 2 and been solidified there. However, the small metal pipe 2 could be easily moved by striking it from the underside. The gas blast nozzle 1 was replaced when the worn away portion 8 of the nozzle became as deep as 300 mm, and it was found that the gas blast nozzle 1 according to the invention can withstand more than 300 charges, showing a remarkable improvement in the service life when compared with conventional gas blast nozzles that were replaced at every 50 charges. Furthermore, a gas blast nozzle having a split refractory block as shown in Fig. 3 was also tested to see the improvement in the service life. Table 1 shows some of the results of their service lives obtained thereby. Case 1 2 Type of nozzle Two piece type (FIG. 3) One piece type (FIG. 1) Repairing method Using repairing brick (4a) and filling refractory Using only filling refractory Service life from replacement to the 1st repair 170 - 200 (h) 170 - 200 (h) Service life from repairing to the next repairing 170 - 200 (h) 80 - 100 (h) Number of repairing from replacement to the next replacement 5 times 4 times Service life from replacement to the next replacement 1150 (h) 550 (h) Case 1 in Table 1 represents the use of a split type gas blast nozzle as shown in Fig. 3 which was repaired by using a repairing brick 4a and filling refractory material. After 170 to 200 hours of gas blast operation, the upper piece of refractory block 4a was removed and the small metal pipe 2 was moved upwards. Thereafter, a new upper piece of refractory block 4a was connected to the lower piece of refractory block 4b with power applied therebetween. At the same time, the annular gap between the small metal pipe 2 and the straight bore 3 of the refractory block was also filled with a nonporous refractory material. Thereafter, the worn away portion was filled with a filling material to complete the first repair. Thus, the gas blast nozzle was repaired after every 170 to 200 operating hours for the second through fifth repairs. The (upper) tuyere-forming brick 6 was also replaced at the even-numbered repairs. The upper piece of refractory block 4a had an orginal length of 200 mm, although the remaining length was between 50 and 100 mm at the time of each repair. The nozzle was replaced 170 to 200 hours after the fifth repair, then the lower piece of refractory block 4b was undamaged and could be used further. Case 2 in Table 1 represents the use of a one piece nozzle as shown in Fig. 1, which was repaired only by means of a filling refractory material. After 170 to 200 hours of gas blast operation, the small metal pipe 2 was moved upwards by a length greater than the height of the worn away portion of the nozzle, and the worn away portion was filled with a filling refractory material. Then, the gas blast nozzle was repaired after every 80 to 100 operating hours for the second and fourth repairs. At this time, the nozzle had been worn away by 250 to 300 mm, and along with the upper tuyere-forming bricks they were replaced by the new ones, because they were so damaged that the time required for further repairing seemed to exceed the specified repairing time. As seen from Table 1, the service life of the repaired nozzle, the number of repairs and the service life from replacement to the next replacement had been increased in Case 1. Advantages of the Invention The gas blast nozzle according to the invention can reduce the frequency of replacement of the gas blast nozzle, and can reduce the breakdown time of the furnace operation. Additionally, it reduces the work load of the replacing operation under adverse working conditions and is free from the problem of gas leaking through the gas blast nozzle. Finally, it can be applied at reduced cost because it is structurally simple. List of Reference Numerals, Symbols, and Items 1: Gas blast nozzle for molten metal 2: Small metal pipe 3: Straight bore 4: Refractory block 5: Castable refractory substance 6: Tuyere-forming brick 8: Worn away portion 10: Gas feed hose 11: Refractory bottom of a furnace 12: Gas 14: Rubber block 15: Gas feed hose 16: Repairing refractory material 17: Cooling gas feed pipe 18: Porous brick 19: Outer shell of a furnace 20: Lock member 21: Securing ring 22: Tubular metal fitting 23: Metal coupler

Claims: A gas blast nozzle for molten metal comprising a refractory block (4) having a narrow straight bore (3) being bored from the inside to the outside of a furnace, a tubular metal fitting (22) formed in one body with the refractory block (4), a small metal pipe (2) arranged slidably through the straight bore (3), and a metal coupler (23) for connecting a gas hose (15) to an end of the tubular metal fitting (22), characterized in that an outer end portion of the small metal pipe (2) is made to penetrate through a rubber block (14) in the metal coupler (23), so that the gas (12) can be fed to the outer end of the small metal pipe (2) and can be blown into the molten metal from the inner end of the small metal pipe (2). A method of using a gas blast nozzle for molten metal as defined in claim 1, characterized in that , in repairing a worn away inner portion (8) of the gas blast nozzle and a surrounding area, a refractory material is filled into the worn away portion (8) after having moved the small metal pipe (2) upwards through the straight bore (3) so that its inner end projects over the inner surface of the furnace in order to prevent its inner end from being clogged by a refractory material. A gas blast nozzle for molten metal according to claim 1, characterized in that the refractory block (4) is composed by two or more refractory pieces being piled vertically. A method of using a gas blast nozzle for molten metal as defined in claim 3, characterized in that , in repairing a worn away inner portion (8) of the gas blast nozzle and a surrounding area, the used upper refractory piece (4a) is changed to a new upper refractory piece (4a), and a refractory material is filled into the worn away portion (8) after moving the small metal pipe (2) upwards through the straight bore (3) so that its inner end projects over the inner surface of the furnace in order to prevent its upper end from being clogged by a refractory material.

Inventors: YAMADA HIROSHI, YAMADA, HIROSHI
Applicants: JAPAN CASTING FORGING CORP, JAPAN CASTING & FORGING CORPORATION
Application year: 1996
Main classification: C21C7
IPC codes: F27D1, C21C7, B22D1, C21C5