JP5302836B2 - Stopper control type immersion nozzle - Google Patents

Description

  The present invention relates to an immersion nozzle used for continuous casting of steel, particularly aluminum killed steel, and more specifically, a stopper-controlled immersion nozzle that closes an inner hole by fitting a stopper to the inner hole of the nozzle body from above. About.

  In a submerged nozzle used for continuous casting of aluminum killed steel or the like, alumina inclusions in the steel adhere to the inner hole of the nozzle body, and this tends to cause nozzle clogging. As a method for preventing this nozzle clogging, it is known that a refractory containing CaO is used on the inner hole side of the nozzle body (Patent Document 1).

  The inventors of the present invention manufactured a stopper-controlled immersion nozzle using a dolomite graphite refractory containing CaO, MgO and carbon and used it for melting aluminum killed steel. As a result, the nozzle clogging has been eliminated, but a new problem has occurred in which the melting damage of the fitting portion that comes into contact with the stopper is increased.

  Therefore, in order to prevent melting of the fitting portion, the inventors of the present invention include an immersion nozzle body immersed in a mold and a fitting portion connected to the upper end of the immersion nozzle body in Patent Document 2, The immersion nozzle body is composed of a refractory consisting of [C] 25-40% by mass, [CaO] 20-50% by mass, [MgO] 10-40% by mass, and the fitting part is [C] 1-10% by mass. %, [CaO] 40-60% by mass, and [MgO] 30-50% by mass, a stopper-controlled immersion nozzle composed of a refractory material is disclosed.

  On the other hand, in the stopper-controlled immersion nozzle, a structure is known in which a fitting ring such as zirconia having excellent durability is mounted on the inner hole side of the upper end portion of the nozzle body. However, since zirconia has a large thermal expansion, there is a problem that the nozzle body is likely to be cracked or broken during use. Therefore, Patent Document 3 discloses a structure in which the fitting ring is not disposed on the inner hole side, but the immersion nozzle is separated vertically and the entire upper part is made of a fitting ring material and the periphery is covered with a metal case.

Japanese Examined Patent Publication No. 61-44836 Japanese Patent Laid-Open No. 2008-809 JP-A-10-5942

  In the structure of Patent Document 2 or Patent Document 3, there is a joint portion that leads to the outer peripheral surface of the nozzle between the nozzle body and the fitting portion on the upper portion thereof. When the present inventors used the stopper control type immersion nozzle of patent document 2, although the effect was confirmed in prevention of nozzle clogging, although the frequency is small, this joint part is locally melted and molten steel leaks. I found out that As the cause, it is presumed that the air has entered between the immersion nozzle 52 and the metal case 51 from the lower end portion of the metal case 51 and entered the joint portion 53 of the mortar as indicated by an arrow in FIG.

  On the other hand, if the fitting ring is simply disposed on the inner hole side as shown in FIG. 8 of Patent Document 3, there is a problem that the nozzle body cracks due to the difference in thermal expansion as described above.

Accordingly, the problem to be solved by the present invention is to prevent the intrusion of air from the fitting portion fitted to the stopper in the stopper-controlled immersion nozzle, and to generate cracks in the nozzle body due to the thermal expansion of the fitting portion. It is to suppress.

  In the present invention, a fitting ring having a larger thermal expansion than the nozzle body is disposed on the inner hole side of the upper end portion of the nozzle body having an inner hole, and a stopper is fitted to the fitting ring to close the inner hole. A stopper-controlled immersion nozzle, wherein a stepped portion having an enlarged diameter portion is formed on the inner hole side of the upper end portion of the nozzle body, and a fitting ring is disposed on the stepped portion, and the fitting ring A groove is formed on the outer peripheral surface side of the fitting ring and the bottom surface of the enlarged diameter portion, and a holding block straddles the fitting ring and the bottom surface of the enlarged diameter portion in the groove. And a retractable mortar inserted between the holding block and the fitting ring and between the outer peripheral surface of the fitting ring and the stepped portion. Stopper control type immersion nozzle filled It is.

  In the present invention, the groove is formed in an annular shape, and the pressing block has a cylindrical shape, and the pressing block can be screwed into the nozzle body as a floating prevention means.

  In the present invention, the contractible mortar preferably has a contractible ratio of 10% to 80% in a non-oxidizing atmosphere at 1000 ° C. under a pressure of 2.5 MPa.

  If the contractibility is less than 10%, it is necessary to make a large mortar joint cost, which is not preferable because the nozzle body becomes thin. Further, if the shrinkage ratio is greater than 80%, the mortar joint cost can be reduced. However, since the joint margin is close to the open joint, the possibility of molten steel penetration into the joint becomes high, and the refractory is easily melted.

  Further, in the present invention, the refractory raw material constituting the nozzle body is 25 to 40% by mass of graphite, the remainder is composed of dolomite clinker, or dolomite clinker and magnesia clinker, and the refractory raw material constituting the fitting ring is graphite 1 It is preferable that -10 mass% and the remainder consist of dolomite clinker or dolomite clinker and magnesia clinker.

  If the graphite in the refractory raw material constituting the nozzle body is less than 25% by mass, the thermal shock resistance may be insufficient, and if it exceeds 40% by mass, the corrosion resistance may be insufficient. Further, with respect to the fitting ring, it is preferable to reduce the amount of graphite from the nozzle body from the viewpoint of further improving the corrosion resistance in order to prevent an impact at the time of fitting with the stopper and wear due to the molten steel flow. Specifically, if the graphite in the refractory raw material constituting the fitting ring exceeds 10% by mass, the required corrosion resistance may not be obtained. On the other hand, if the graphite content is less than 1% by mass, the thermal shock resistance may be insufficient. In addition to graphite, it is preferable to use dolomite clinker, or dolomite clinker and magnesia clinker, in addition to graphite, for the nozzle body and the fitting ring.

  According to the present invention, the end face of the joint between the fitting ring and the nozzle body is located on the bottom surface of the tundish container instead of the outer peripheral surface of the nozzle and is in contact with the molten steel. Can be prevented from entering.

  In addition, since a sufficient expansion allowance is secured between the fitting ring and the nozzle body and the holding block by a contractible mortar, the occurrence of cracks in the nozzle body due to thermal expansion of the fitting ring should be prevented. Can do. For this reason, the durability of the stopper-type immersion nozzle is improved and the risk of steel leakage is eliminated.

  Furthermore, since the fitting ring is securely fixed to the nozzle body by the pressing block, even if it is stuck at the time of fitting with the stopper and then lifted, the lifting can be prevented.

It is a longitudinal cross-sectional view in the state which attached the stopper control type immersion nozzle of this invention to the tundish. (A) is an enlarged view of the fitting part in FIG. 1, (b) is a figure which shows only a nozzle main body in (a). It is a longitudinal cross-sectional view of the conventional stopper control type immersion nozzle.

  An embodiment of the present invention will be described with reference to FIGS.

  In FIG. 1, a stopper-controlled immersion nozzle (hereinafter simply referred to as “immersion nozzle”) 1 is attached to a tundish tuyere 2 via a mortar. The immersion nozzle 1 includes a nozzle body 11, a fitting ring 13 connected to the inner hole 12 side of the upper end portion thereof by a mortar, and a pressing block 15 disposed in a groove 14 on the outer peripheral side of the fitting ring 13. The fitting ring 13 becomes a fitting portion with the stopper 20. In addition, a head 16 having a large diameter is formed at the upper end of the nozzle body 11, and a step at the lower end of the head 16 is engaged with the periphery of the tuyere of the iron skin 3 through a mortar. Slip-off is prevented.

  As shown in FIG. 2B, a stepped portion 17 having an enlarged diameter portion 17 a at the upper portion is formed on the inner hole 12 side of the upper end portion of the nozzle body 11. Then, as shown in FIG. 2A, the fitting ring 13 is disposed in the stepped portion 17. Further, on the outer peripheral surface side of the fitting ring 13, a groove 14 whose bottom surface is formed by the fitting ring 13 and the bottom surface of the enlarged diameter portion 17 a of the stepped portion 17 is formed. The groove 14 is formed in an annular shape over the entire outer peripheral surface side of the fitting ring 13, the inner peripheral side surface of the groove 14 is the outer peripheral surface of the fitting ring 13, and the outer peripheral side surface of the groove 14 is the nozzle body 1. The inner surface of the stepped portion 17 (the enlarged diameter portion 17a) and the bottom surface of the groove are constituted by the fitting ring 13 and the bottom surface of the enlarged diameter portion 17 (nozzle body 11) through a gap 19 in the central portion. Further, a female screw groove is formed on the outer peripheral side surface of the groove 14, and is screwed into a male screw groove formed on the outer peripheral surface of the holding block 15.

  The holding block 15 has a cylindrical shape, and is screwed to the side surface on the outer peripheral side of the groove 14 via the contractible mortar 18. Accordingly, the holding block 15 is inserted into the groove 14 so as to straddle the fitting ring 13 and the bottom surface of the enlarged diameter portion 17a. Further, a 2 mm gap is secured as a mortar joint margin between the holding block 15 and the fitting ring 13, and the gap is also filled with a contractible mortar. Further, a gap of 2 mm is similarly secured between the outer peripheral surface of the holding block 15 and the stepped portion 17 (nozzle body 11), and this gap is also filled with the contractible mortar 18. In addition, the clearance gap between the bottom face of the fitting block 13 and the nozzle main body 11 is 0.5 mm or less, and normal mortar is filled.

  The holding block 15 is mounted for the purpose of preventing the fitting block 13 from floating. Therefore, the holding block 15 needs to be fixed to the nozzle body 11 by the floating prevention means so as not to float. As the floating prevention means, a bayonet type may be used in addition to the screwed structure as in the present embodiment. Or it is good also as a structure which prevents a float by pinning by providing the through-hole which penetrates a fitting ring and a control block from an inner-hole side, and leads to a nozzle main body, and inserting the pin made from a refractory into this through-hole. . This holding block can be used without any problem as long as it is a basic refractory, but it is preferable to use the same material system as the fitting ring or the nozzle body.

  In the immersion nozzle 1 having the above configuration, even when the temperature of the fitting portion (fitting ring 13) rises rapidly during use and expands thermally, the expansion allowance is absorbed by the contraction of the contractible mortar 18, Since the stress due to the thermal expansion to the nozzle body 11 can be relaxed, the nozzle body 11 can be prevented from cracking. Further, the joint ring 13 and the nozzle body 11 side joint portion, specifically, the end surface of the joint portion of the joint ring 13 and the holding block 15 and the joint portion between the holding block 15 and the nozzle body 11 is the bottom surface of the tundish. Because it is located and in contact with molten steel, air does not enter. And even if the fitting ring 13 sticks and is lifted at the time of fitting with the stopper 20, the pressing block in which the bottom surface of the groove 14 formed on the outer periphery of the fitting ring 13 is fixed to the nozzle body 11 by the anti-lifting means. Since it is in contact with 15, lifting can be prevented.

  The contractible mortar 18 used in the present invention is preferably a contractible ratio of 10% to 80% in a non-oxidizing atmosphere at 1000 ° C. under a pressure of 2.5 MPa. If the contractibility is less than 10%, the mortar joint cost needs to be increased, and the nozzle body 11 becomes thin. On the other hand, when the shrinkage ratio is greater than 80%, the mortar joint cost can be reduced. However, since the joint margin is close to the open joint, the possibility of penetration of molten steel into the joint becomes high, and the refractory is likely to be damaged. The joint thickness by the contractible mortar 18 is preferably 1 to 3 mm, and it is possible to select a contractible mortar having an appropriate contraction ratio so that the thermal expansion of the fitting ring can be absorbed by the joint thickness. preferable.

The shrinkage ratio K of mortar is measured as follows. A mortar is sandwiched between the end faces of two refractory samples having a shape of φ20 × 40 mmL, and bonded to a thickness of about 2 mm. A refractory sample bonded with mortar is heat treated to solidify the mortar. Place this refractory sample in the furnace of a material testing machine that can control the temperature, atmosphere, and pressurization speed, raise the temperature to 1000 ° C in a non-oxidizing atmosphere, hold it until the temperature becomes uniform, and then add Press. First, the initial thickness t ₀ (mm) of the mortar layer in a non-pressurized state after the heat treatment is measured. Next, after holding the measurement sample at 1000 ° C. in a non-oxidizing atmosphere and compressing the sample from the top and bottom and pressurizing to 2.5 MPa, the displacement h ₁ (mm) is measured. In advance, the two refractory samples to be used are pressed under the same conditions in a state where there is no mortar layer, and the displacement h ₂ (blank value) is measured. By calculating these measured values according to the following equation, the contractible ratio K (%) in a non-oxidizing atmosphere at 1000 ° C. can be obtained.
K = (h ₁ −h ₂ ) / t ₀ × 100 (%)

The reason why the pressurizing condition is 2.5 MPa here is that, in the case of a tubular refractory material mainly composed of Al ₂ O ₃ —C, which is a material of a general nozzle body of an immersion nozzle, When a pressure of several MPa is applied to the inner wall surface of the nozzle body, it breaks. For example, Al is a refractory material having an almost minimum radial structure in practice (inner diameter φ80 mm, outer diameter φ135 mm) and a maximum tensile strength of 6 MPa. _In the case of a refractory material made of ₂ O ₃ -graphite, if pressure is applied from the inner wall surface of the pipe, it will break when a pressure of about 2.5 MPa is applied to the inner wall surface by calculation.

  Table 1 shows the results of testing in an actual tundish with the stopper-controlled immersion nozzle shown in FIG. Example 1 has the shape shown in FIG. 1, and the nozzle body is made of 30% by mass of graphite and the balance is made of dolomite clinker. The fitting ring and the holding block are made of 8% by mass of graphite and the balance is made of dolomite clinker. As the material to be used, magnesia mortar (magnesia: 70% by mass) having a contractibility of 50% in a non-oxidizing atmosphere at 1000 ° C. under a pressure of 2.5 MPa was used. Comparative Example 1 has the shape of FIG. 3 and uses the same material as FIG. 1, and Comparative Example 2 has the shape of FIG. 3 and uses the alumina graphite material for both the fitting portion and the main body portion.

  In Example 1, intrusion of air from the fitting portion is prevented, cracking of the nozzle body due to thermal expansion of the fitting portion can be suppressed, and deposits are confirmed on the nozzle body and the fitting ring. In addition, it was good without melting of the fitting ring. In Comparative Example 1, no adhering matter was confirmed on the nozzle body and the fitting ring, and there was no melting damage of the fitting ring, but intrusion of air from the fitting portion occurred. In Comparative Example 2, adhesion to the nozzle main body and the fitting ring was recognized, and intrusion of air from the fitting portion also occurred.

DESCRIPTION OF SYMBOLS 1 Stopper type immersion nozzle 2 Tuyere 3 Iron skin 11 Nozzle body 12 Inner hole 13 Fitting ring 14 Groove 15 Holding block 16 Head 17 Stepped part 17a Expanded part 18 Retractable mortar 19 Center part gap 20 Stopper 51 Metal Case 52 Immersion nozzle 53 Joint

Claims (4)

A stopper control type in which a fitting ring having a thermal expansion larger than that of the nozzle body is disposed on the inner hole side of the upper end portion of the nozzle body having an inner hole, and a stopper is fitted to the fitting ring to close the inner hole. An immersion nozzle,
On the inner hole side of the upper end portion of the nozzle body, a stepped portion having an enlarged diameter portion is formed at the top,
A fitting ring is disposed on the stepped portion,
On the outer peripheral surface side of the fitting ring, a groove whose bottom surface is formed by the fitting ring and the bottom surface of the enlarged diameter portion is formed,
A pressing block is inserted into the groove so as to straddle the bottom surface of the fitting ring and the enlarged diameter portion, and is fixed to the nozzle body by the floating prevention means,
A stopper-controlled immersion nozzle in which a contractible mortar is filled between the pressing block and the fitting ring and between the outer peripheral surface of the fitting ring and the stepped portion.   2. The stopper-controlled immersion nozzle according to claim 1, wherein the groove is formed in an annular shape, the pressing block has a cylindrical shape, and the pressing block is screwed into the nozzle body as a floating prevention means.   The stopper-control-type immersion nozzle according to claim 1 or 2, wherein the contractible mortar has a compressible ratio of 10% to 80% in a non-oxidizing atmosphere at 1000 ° C under a pressure of 2.5 MPa.   The refractory raw material constituting the nozzle body is 25 to 40% by mass of graphite, the remainder is composed of dolomite clinker, or dolomite clinker and magnesia clinker, and the refractory raw material constituting the fitting ring is 1 to 10% by mass of graphite. The stopper-controlled immersion nozzle according to claim 1, 2 or 3, wherein the remaining portion comprises dolomite clinker, or dolomite clinker and magnesia clinker.

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