JP2011041959A - Guide roll for continuous casting for steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently exhibit a slab heat extraction effect by water for cooling the surface layer of a roll. <P>SOLUTION: The guide roll is used for continuous casting for a steel, and its inside is water-cooled. The guide roll includes: one cooling hole 2 provided at the central part of a cross-sectional face so as to perform water passing along a shaft direction; and a plurality of cooling holes 3 uniformly provided so as to perform water passing along the shaft direction on almost the same circumference in the surface layer part of the cross-sectional surface. The plurality of the cooling holes 3 provided at the surface layer part are provided in a range to a depth of 50 mm from the surface of the roll. Into the cooling holes 3, cooling water is introduced from the edge part of the roll shaft on either side through the cooling hole 2 provided at the central part in the cross-sectional surface to the vicinity of the edge part of the roll shaft in the other cooling side. The ratio( Hw2/Hw1) of the heat transfer coefficient Hw2 of the plurality of cooling holes 3 in the surface layer part to the heat transfer coefficient Hw1 by the cooling hole in the central part, is controlled to 1.0 to 3.0. The improvement of cooling capacity and the elongation of the service life of the roll upon high speed casting can be achieved. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is a guide roll used for transporting a continuous cast slab, and a roll cooling water system is arranged in the vicinity of the surface layer to increase the heat removal efficiency of the slab, thereby preventing slab unsolidification at the end of the continuous caster. This prevents high-speed casting.

  In continuous casting, the slab drawn from the mold is solidified in the solidified shell by forced cooling in the secondary cooling zone. However, when the drawing speed of the slab increases, the solidification of the molten steel is not completed on the outlet side of the continuous casting machine, and the solidified shell is deformed (hereinafter referred to as end-of-machine bulging) due to the static iron pressure. You will be forced to have operational troubles due to lower surface levels.

  Accordingly, it has been desired to improve the cooling efficiency in the secondary cooling zone as the slab drawing speed increases. The slab cooling method in the secondary cooling zone includes spray cooling or water-cooled roll cooling, and it is known that the cooling effect by water-cooled roll cooling is particularly large.

  By the way, since the cast hot slab is in direct contact with the guide roll used for continuous casting, the conventional roll structure in which the cooling hole is provided only in the shaft core portion lacks the cooling function of the roll and slab. Was.

  In view of this, various rolls have been proposed as countermeasures, and are effective in preventing the roll surface from being cracked or bent due to the thermal influence of the slab.

  For example, in Patent Document 1, U-shaped grooves having a predetermined depth in the circumferential direction of the roll surface layer portion covering the overlay layer and the width of the convex portion of the groove are engraved at an equal interval pitch, while the roll body portion A sleeve-type roll having a spiral cooling hole on the surface has been proposed.

  In the sleeve type roll proposed in Patent Document 1, the entire roll surface layer is cooled by cooling water flowing through the cooling holes, and thermal stress in the width direction is absorbed and dispersed in the uneven portions of the groove, thereby generating cracks in the roll surface layer. And to reduce wear.

  Moreover, in patent document 2, the lid | cover for 4 to 64 cooling water passage which has a predetermined cross-sectional area in the range of 1/3 to 4/5 length with respect to the trunk | drum length of a trunk | drum length direction center outer peripheral part. There has been proposed a revolver type roll in which a groove is provided and both ends of the groove are communicated with a water passage hole of a roll axis through a water passage hole.

  In the revolver type roll proposed in Patent Document 2, the water cooling groove is arranged only in the vicinity of the center part in the roll body length direction, thereby suppressing the temperature drop of the slab corner part contacting both ends of the roll body part. .

  Although these rolls proposed in Patent Documents 1 and 2 are effective in preventing the above problems, they are not inventions aimed at improving slab cooling by improving heat removal from the roll, but proposals regarding roll life and slab end cooling. Thus, the effect on the slab cooling improvement (acceleration of solidification by improving the slab heat removal) is unknown.

JP-A-9-192808 JP-A-9-277004

  The problem to be solved by the present invention is that the rolls proposed in Patent Documents 1 and 2 do not show an effective method of heat removal from the slab by roll surface cooling water. Is still inadequate.

The guide roll for continuous casting of the steel of the present invention,
In order to be able to fully demonstrate the effect of heat removal from the slab by roll surface cooling water,
A water-cooled guide roll used for continuous casting of steel,
The guide roll is
One cooling hole provided in the center of the cross section to allow water to pass along the axial direction;
A plurality of cooling holes provided uniformly to allow water to pass along the axial direction on substantially the same circumference in the surface layer portion of the cross section;
The plurality of cooling holes provided in the surface layer portion are provided in a range from the roll surface to a depth of 50 mm, and in these cooling holes, cooling provided in the central portion of the transverse section from one roll shaft end portion. The cooling water is led from the vicinity of the other end of the roll shaft through the hole,
The ratio of the heat transfer coefficient Hw2 of the plurality of cooling holes in the surface layer part to the heat transfer coefficient Hw1 due to the cooling hole in the central part, and Hw2 / Hw1 is set to be 1.0 or more and 3.0 or less. It is a feature.

  The present invention improves the cooling performance during high speed casting by defining the ratio (Hw2 / Hw1) of the heat transfer coefficient Hw2 of the plurality of cooling holes in the surface layer portion to the heat transfer coefficient Hw1 due to the cooling hole in the central portion within the optimum range. It is possible to extend the roll life.

(A)-(c) is the figure which showed the cross section of the roll used for the evaluation test of the cooling ability by a heat-transfer analysis model. It is the figure which showed the result of the heat transfer analysis about the reference roll shown to Fig.1 (a). It is the figure which showed the result of the heat transfer analysis about the test roll A shown in FIG.1 (b). It is the figure which showed the result of the heat-transfer analysis about the test roll B shown in FIG.1 (c). It is a figure explaining the heat-transfer analysis result of FIG. It is a figure which shows the result of having compared the cooling capability of the heat-transfer analysis result shown in FIGS. It is the figure which showed the relationship of the heat influence range in case heat transfer coefficient ratio Hw2 / Hw1 is 3.45 and 0.95 with the object roll diameter. It is the figure which showed transition of the cooling water temperature in a roll in the cooling water exit side of each roll shown in FIG. It is the figure which showed the result of having calculated the slab extraction heat amount by the temperature difference of the cooling water in and out of the roll water calculated based on the result of FIG.

  In the present invention, the heat transfer coefficient Hw2 of the plurality of cooling holes in the surface layer portion with respect to the heat transfer coefficient Hw1 due to the cooling holes in the central portion is intended to allow the slab heat removal effect by the roll surface cooling water to be sufficiently exerted. This was realized by defining the ratio (Hw2 / Hw1) within the optimum range.

The present invention will be described below with reference to the accompanying drawings.
In the sleeve type roll proposed in Patent Document 1 and the revolver type roll proposed in Patent Document 2, the slab cooling effect is not sufficient, and operational troubles such as end-of-machine bulging remain a problem.

  On the other hand, when the slab cooling by the roll becomes excessive, it leads to a quality defect in the slab corner portion. Therefore, it is desirable to perform appropriate roll cooling from the viewpoint of operation and quality.

  Therefore, in the present invention, a surface layer cooling type roll capable of highly efficient slab cooling is designed and the problem is solved. The continuous casting guide roll of the present invention has a diameter of 200 mm to 350 mm and an inner diameter of the cooling hole provided in the axial direction at the center of the cross section is 40 mm to 60 mm.

  That is, according to the present invention, in addition to a single cooling hole provided in the central portion of the cross section that allows water to pass along the axial direction, a plurality of cooling holes having a circular cross section or a kamaboko type cross section are provided along the axial direction. And a guide roll provided on the surface layer of the transverse section.

  And the supply of the cooling water to the plurality of cooling holes provided in the surface layer part includes the water holes provided on the opposite side through the cooling holes provided in the central part of the transverse section from the cooling water inlet side. Do through. The supplied cooling water flows along the roll surface layer from the side facing the surface, and is discharged from a drain hole provided at substantially the same position as the cooling water inlet side.

  In the guide roll configured as described above, an increase in the flow rate of the cooling water supplied into the roll has the effect of improving the amount of heat removed from the slab in contact with the roll surface layer, and by adjusting the flow rate of the cooling water, It is possible to avoid both quality defects and improve the cooling capacity of the slab.

  The inventors have provided a cooling roll 2 having an inner diameter of 55 mm only at the center of the cross section, the reference roll 1 conventionally used (FIG. 1 (a)), and the same circumference in the surface layer of the cross section. The test roll 4 (FIGS. 1B and 1C) provided with a plurality of cooling holes 3 in the upper equal position was evaluated.

  The reference roll and test roll are both made of medium carbon steel with a carbon content of 0.4% by mass. The outer diameter of both the reference roll and test roll is 250 mm, and the cooling holes of the test roll are crossed. It provided in the position of 32 mm from the surface layer of the surface.

  FIG. 1B shows a revolver type roll (test roll A) in which twelve circular cooling holes 3 having an inner diameter of 15 mm are provided on the surface layer of the cross section. FIG. 1 (c) shows a sleeve-type roll (test roll) in which a roll body 4a having a groove having a width of 20 mm and a depth of 5 mm on the outer periphery is shrink-fitted with an outer cylinder 4b and 20 kamaboko-shaped cooling holes 3 are provided. B). Each of these test rolls 4 is provided with a cooling hole 2 having the same size as that shown in FIG.

  In addition, 5 in FIG. 1 is led to the cooling hole 3 provided in the surface layer part of the cross section through the cooling hole 2 provided in the center part of the cross section and drains the cooling water after cooling the surface layer part. It is a drainage hole with an inner diameter of 55 mm.

  About each roll shown to Fig.1 (a)-(c), the heat transfer analysis by the two-dimensional nonlinear model was performed on the heat transfer analysis conditions shown in the following Table 1, and the slab cooling ability was evaluated in advance. The results are shown in FIGS.

The other analysis conditions for the cooling performance evaluation by the heat transfer analysis model shown in FIGS. 2 to 4 are as follows.
・ Cooling water: Original flow rate Q = 15.0 liters / min
Water volume: Test roll A 1.25 liters / min / piece
Test roll B 0.75 liter / min / piece
Flow velocity: Test roll A 0.12m / sec
Test roll B 0.13 m / sec
-Roll base temperature: 40 ° C

  Corresponding to the contact time in the heat transfer analysis where the rotation of the roll is unsteady, the positions shown in FIGS. 1 (a) to 1 (c) are the positions 23mm and 28mm from the roll surface. FIG. 1 (c) shows positions of 11 mm and 16 mm from the roll surface.) A thermocouple 6 was attached to verify the temperature analysis. Moreover, the temperature analysis estimated the time when the cooling hole 3 left | separated from the contact position with a slab, and implemented the analysis under the situation where heat removal was unfavorable.

  2 is an analysis result of the reference roll shown in FIG. 1A, FIG. 3 is an analysis result of the test roll A shown in FIG. 1B, and FIG. 4 is a test roll shown in FIG. The analysis result about B is shown.

  2 to 4 are diagrams showing a quarter of the cross section of the roll. For example, as shown in FIG. 5 showing the analysis result of FIG. 2, the result of the heat transfer analysis is shown by the temperature distribution. is there. From FIG. 2 to FIG. 4, when the cooling effect is judged using the heat removal influence range of the cooling water in the roll as an index, either the revolver type shown in FIG. 1B or the sleeve type test roll shown in FIG. Also, it can be seen that the cooling ability is superior to that of the reference roll shown in FIG. In this example, the cooling effect of the sleeve type test roll B was greater than that of the revolver type test roll A.

  FIG. 6 shows the result of comparing the cooling ability of the heat transfer analysis results shown in FIGS. As an index for comparing the cooling ability, a roll internal cooling range, which is a range in which the influence of the temperature rise from the roll surface is excluded, was used.

  This roll internal cooling range was read from the temperature rise range in FIGS. 2 to 4, and the read values (reference roll 26.96 mm, test roll A 7.23 mm, test roll B 8.55 mm) The value is subtracted from the radius of 125 mm. The larger this value, the narrower the range of heat influence on the inside of the roll, and the greater the cooling capacity.

  Table 2 below shows a comparison of the heat transfer coefficients of the surface side cooling water when the inner diameter and the number of holes in the surface layer portion of the roll (diameter: 250 mm) used in obtaining the heat transfer analysis result are changed.

  In Table 2, the ratio of the heat transfer coefficient Hw2 of the revolver type and sleeve type test rolls to the heat transfer coefficient Hw1 of the roll shaft center (hereinafter referred to as the ratio of heat transfer coefficient) Hw2 / Hw1 is 3.45. FIG. 7 shows the relationship of the heat affected range (temperature rise influence depth from the roll surface to the inside) in the case of 95 together with the target roll diameter.

  By the way, there is an optimum value in the heat affected range, and when the heat affected range (depth) is shallow, the cooling capacity is sufficient, but the thermal cycle (fatigue) applied to the roll surface is large, and the roll surface is cracked. And the like are increased, resulting in a decrease in the service life.

  On the other hand, when the heat-affected range is deep, high-efficiency slab cooling cannot be achieved because the cooling capacity of the roll is reduced.

  From various tests and analysis results by the inventors, it was found that the heat-affected range is the most effective range from 5 mm to 10 mm.

  In addition, from FIG. 7, when the heat transfer coefficient ratio Hw2 / Hw1 is 3.43, the flow rate of the cooling water increases, but in the case of a large-diameter roll having a diameter of 350 mm, the pitch of the cooling holes provided in the surface layer portion increases. It can be seen that the heat-affected range is 20 mm and the cooling capacity is lowered. In addition, although the size of the pitch of the cooling holes is slightly improved in the small-diameter roll having a diameter of 200 mm, there is still a problem in terms of cooling ability because the heat affected range becomes 13 mm.

  On the other hand, when the heat transfer coefficient ratio Hw2 / Hw1 is 0.95, the heat-affected range is 5 to 6 mm and the cooling capacity is small diameter rolls with a diameter of 200 mm and large diameter rolls with a diameter of 350 mm. There is no problem in terms of. However, when the heat transfer coefficient ratio Hw2 / Hw1 is 0.95, the number of cooling holes is too large compared to the inner diameter of the cooling holes, which is problematic in terms of roll strength.

  As a result, it was confirmed that the range of Hw2 / Hw1 in the range of 1.0 to 3.0 was effective in order to obtain a surface-layer cooled roll capable of highly efficient slab cooling.

  The heat transfer coefficient of the cooling holes 2 and 3 is calculated using the following formula 1.

The present invention has been made based on the above analysis results,
A water-cooled guide roll used for continuous casting of steel,
The guide roll is
One cooling hole provided in the center of the cross section to allow water to pass along the axial direction;
A plurality of cooling holes provided uniformly to allow water to pass along the axial direction on substantially the same circumference in the surface layer portion of the cross section;
The plurality of cooling holes provided in the surface layer portion are provided in a range from the roll surface to a depth of 50 mm, and in these cooling holes, cooling provided in the central portion of the transverse section from one roll shaft end portion. The cooling water is led from the vicinity of the other end of the roll shaft through the hole,
The ratio of the heat transfer coefficient Hw2 of the plurality of cooling holes in the surface layer portion to the heat transfer coefficient Hw1 due to the cooling hole in the central portion is such that Hw2 / Hw1 is 1.0 or more and 3.0 or less. Yes.

  In the present invention, the plurality of cooling holes provided in the surface layer portion are provided in a range from the roll surface to a depth of 50 mm because the heat removal effect from the cooling holes is reduced when it exceeds 50 mm.

  According to the study by the inventors, the preferable lower limit when approaching the surface layer portion is about 20 mm. This is because when the depth from the roll surface is shallow, cracks due to thermal fatigue on the roll surface propagate and water leakage easily occurs.

  In the guide roll of the present invention having the above-described configuration, the casting speed can be improved by improving the cooling ability of the cast slab, and the effect of improving the roll life can be obtained as a derivative effect.

  In the present invention, if the ratio of the heat transfer coefficient Hw2 of the plurality of cooling holes in the surface layer portion to the heat transfer coefficient Hw1 due to the cooling hole in the central portion, Hw2 / Hw1 is 1.0 or more and 3.0 or less, the surface layer portion The number and inner diameter of the cooling holes provided in are not particularly limited.

  However, considering the cooling in the circumferential direction of the roll surface layer, when there are few cooling holes provided in the surface layer portion, it is preferable to provide five or more because the heat removal effect between the cooling holes is reduced. On the other hand, from the viewpoint of supplying cooling water to each cooling hole, the number is preferably 60 or less.

  Further, in a roll having a diameter of 200 mm to 350 mm and a cooling hole having an inner diameter of 40 mm to 60 mm provided in the axial direction at the center of the cross section, the cooling hole provided in the surface layer portion has a cross section. Is a circular shape, the inner diameter is preferably 10 mm or more and 25 mm or less. Even when the shape of the cooling hole is a kamaboko type, it is necessary to have a size that provides an equivalent cross-sectional area.

  If the inner diameter of the cooling hole provided in the surface layer is small, the cooling water contact length (circumference) is long with respect to the cross-sectional area of the cooling hole, so that the cooling efficiency is good and advantageous. This is because it is difficult and the cooling hole may be blocked. On the other hand, when the inner diameter of the cooling hole is large, the cooling water contact length (circumference) is short with respect to the cooling hole cross-sectional area, so that the cooling efficiency is poor, and further, the section modulus of the roll is reduced.

  Based on the above analysis results, a guide roll was manufactured, and the results of cooling performance evaluation during actual operation will be described below.

  The amount of cooling water in the rolls of each roll shown in FIGS. 1 (a) to 1 (c) and the water temperature at entry / exit were measured. In the roll mounting segment, the cooling water in the roll supplied from a common system was divided and supplied to the test rolls A and B and the reference roll. The test conditions are shown in Table 3 below.

  FIG. 8 shows the transition of the cooling water temperature in the roll on the outlet side of the cooling water in the roll during continuous casting when the reference roll and the test rolls A and B are supplied with 15 N liter / min of cooling water. Moreover, the result of having calculated the slab extraction heat amount by the temperature difference of the in-roll cooling water calculated from the result shown in FIG. 8 using the following formula 2 is shown in FIG. In addition, the heat removal part effective area A used for calculation of the heat removal amount Q shown in FIG. 9 was calculated by setting the slab contact arc length Lr to 0.065 m.

  As a result, as is clear from FIG. 9, it was confirmed that the heat removal amounts of the test roll A and the test roll B were both improved by about 80 to 100% compared to the conventional roll.

  Needless to say, the present invention is not limited to the above-described examples, and the embodiments may be appropriately changed within the scope of the technical idea described in the claims.

  For example, the cooling hole provided in the surface layer portion may be a round shape of the test roll A, a round shape of the test roll B, or a curved shape of a rectangular shape.

Claims (2)

A water-cooled guide roll used for continuous casting of steel,
The guide roll is
One cooling hole provided in the center of the cross section to allow water to pass along the axial direction;
A plurality of cooling holes provided uniformly to allow water to pass along the axial direction on substantially the same circumference in the surface layer portion of the cross section;
The plurality of cooling holes provided in the surface layer portion are provided in a range from the roll surface to a depth of 50 mm, and in these cooling holes, cooling provided in the central portion of the transverse section from one roll shaft end portion. The cooling water is led from the vicinity of the other end of the roll shaft through the hole,
The ratio of the heat transfer coefficient Hw2 of the plurality of cooling holes in the surface layer portion to the heat transfer coefficient Hw1 due to the cooling hole in the central portion, Hw2 / Hw1 is set to 1.0 or more and 3.0 or less. Guide roll for continuous casting of steel.   The guide roll for continuous casting of steel according to claim 1, wherein the cross-sectional shape of the plurality of cooling holes provided in the roll surface layer portion is a circular shape or a kamaboko shape.