Cooling system for hot-rolled steel strip

FIG. 1 is a sectional side view of a cooling system for a hot-rolled steel strip showing Example 1 of the present invention, FIG. 2 is a plan view of an upper guide, FIG. 3A is a plan view of the upper guide during rolling, and FIG. 3B is a plan view of the upper guide at the time of roll changing.

As shown in FIG. 1 , in a last stand Sn in a finishing mill line of hot rolling mill equipment, an upper work roll 12 A is supported in a housing 10 via a pair of right and left upper work roll chocks 11 A so as to be rotatable by an unillustrated motor, and a lower work roll 12 B is similarly supported in the housing 10 via a pair of right and left lower work roll chocks 11 B so as to be rotatable by an unillustrated motor. An upper cooling apparatus 13 A and a lower cooling apparatus 13 B are arranged above and below a rolled material W on the delivery side of the upper work roll 12 A and the lower work roll 12 B.

Further, the upper and lower work rolls 12 A and 12 B, as shown in FIG. 3B described later, are replaceable together with the upper and lower work roll chocks 11 A and 11 B from the housing 10 in a state where the upper and lower work rolls 12 A and 12 B are supported by the upper and lower work roll chocks 11 A and 11 B, respectively.

In the upper cooling apparatus 13 A, a nozzle block 14 A, which is long in a strip-widthwise direction of the rolled material W, is supported on both its right and left sides by the housing 10 so as to be slidable in a conveyance direction of the rolled material W. The nozzle block 14 A is capable of advancing and retracting relative to the work roll 12 A according to extending and retracting actions of a pair of right and left hydraulic cylinders 15 A which have piston rods coupled, at the distal ends thereof, to a back face of the nozzle block 14 A via pins (advancing and retreating mechanism).

A plate-like guide 16 A is provided below the nozzle block 14 A so as to be capable of following a variation in the diameter of the upper work roll 12 A. The guide 16 A is made of a hard material and has a guide face 16 a for guiding the rolled material W, leaving from the upper and lower work rolls 12 A and 12 B, in the conveyance direction.

Specifically, the guide 16 A is swingably coupled by pins 18 A to a lower portion of the nozzle block 14 A via brackets 17 A at middle portions of both right and left sides of the guide 16 A. The guide 16 A is urged by a weight 19 placed on a proximal end of the guide 16 A, such that a soft plate 20 attached to a distal end of the guide 16 A is always brought in contact with a surface of the upper work roll 12 A.

A large number of jet holes 21 A are opened in the guide 16 A, as shown in FIG. 2 . In the example shown in FIG. 2 , a large number of slit-like jet holes 21 A, which are arranged in the strip-widthwise direction of the rolled material W and inclined at predetermined angles, are formed in three rows in the conveyance direction of the rolled material W with alternately changed directions of inclination. The present invention, however, is not limited to this. The number, the number of rows, the shape, the arrangement, and the like, of the jet holes 21 A may be selected in each case depending on a cooling water jet nozzle to be used.

Then, a cooling water header 22 A is incorporated in the nozzle block 14 A. Rolled material cooling nozzles 23 A, the number of which corresponds to the jet holes 21 A, are attached to the cooling water header 22 A to face downward so as to jet a large amount of cooling water directly to an upper face of the rolled material W through the jet holes 21 A. The rolled material cooling nozzles 23 A communicate with a header portion for rolled material cooling water 24 A. The header portion for rolled material cooling water 24 A is supplied with high-pressure cooling water from an unillustrated source of cooling water.

Further, a header portion for work roll cooling water 25 A is integrally formed in the cooling water header 22 A, such that cooling water in the header portion for work roll cooling water 25 A is jetted to the surface of the upper work roll 12 A from roll cooling nozzles 26 A attached to the cooling water header 22 A. A large number of the roll cooling nozzles 26 A are provided in the strip-widthwise direction of the rolled material W. Further, the header portion for work roll cooling water 25 A is supplied with high-pressure cooling water from an unillustrated source of cooling water.

Further, a separating plate (separating member) 27 is extended between a front face of the nozzle block 14 A and the distal end of the guide 16 A. The separating plate 27 is for preventing the cooling water, jetted from the roll cooling nozzles 26 A, from dropping on the upper face of the rolled material W through the jet holes 21 A of the guide 16 A. The separating plate 27 is made of a flexible member, such as a rubber plate, capable of allowing the following action (swinging) of the guide 16 A.

On the other hand, in the lower cooling apparatus 13 B, a nozzle block 14 B, which is long in the strip-widthwise direction of the rolled material W, is supported on both its right and left sides by the housing 10 so as to be slidable in a conveyance direction of the rolled material W. The nozzle block 14 B is thus capable of advancing and retracting relative to the work roll 12 B according to extending and retracting actions of a pair of right and left hydraulic cylinders 15 B which have piston rods coupled, at the distal ends thereof, to a back face of the nozzle block 14 B by pins (advancing and retreating mechanism).

A plate-like guide 16 B is provided above the nozzle block 14 B so as to be capable of following a variation in the diameter of the lower work roll 12 B. The guide 16 B is made of a soft material and has a guide face 16 b for guiding the rolled material W, leaving from the upper and lower work rolls 12 A and 12 B, in the conveyance direction.

Specifically, the guide 16 B is swingably coupled by pins 18 B to an upper portion of the nozzle block 14 B via brackets 17 B at proximal ends of both right and left sides of the guide 16 B. The guide 16 B is configured such that a distal end of the guide 16 B is always brought in contact with a surface of the lower work roll 12 B by its own weight. It should be noted that the soft plate 20 is not attached to the distal end of the guide 16 B, unlike the distal end of the guide 16 A; the soft plate 20 is attached to the distal end of the guide 16 B, like the guide 16 A, when the guide 16 B is made of hard material.

A large number of jet holes 21 B are opened in the guide 16 B, like the guide 16 A described above. For example, a large number of slit-like jet holes 21 B, which are arranged in the strip-widthwise direction of the rolled material W and inclined at predetermined angles, are formed in two rows in the conveyance direction of the rolled material W with different directions of inclination. The present invention, however, is not limited to this. The number, the number of rows, the shape, the arrangement, and the like, of jet holes 21 B may be selected in each case depending on a cooling water jet nozzle to be used.

Then, a cooling water header 22 B is incorporated in the nozzle block 14 B. Rolled material cooling nozzles 23 B, the number of which corresponds to the jet holes 21 B, are attached to the cooling water header 22 B to face upward so as to jet a large amount of cooling water directly to a lower face of the rolled material W through the jet holes 21 B. The rolled material cooling nozzles 23 B communicate with a header portion for rolled material cooling water 24 B. The header portion for rolled material cooling water 24 B is supplied with high-pressure cooling water from an unillustrated source of cooling water.

Further, a header portion for work roll cooling water 25 B is integrally formed in the cooling water header 22 B, such that cooling water in the header portion for work roll cooling water 25 B is jetted to the surface of the lower work roll 12 B from roll cooling nozzles 26 B attached to the cooling water header 22 B. A large number of the roll cooling nozzles 26 B are provided in the strip-widthwise direction of the rolled material W. Further, the header portion for work roll cooling water 25 B is supplied with high-pressure cooling water from an unillustrated source of cooling water.

It should be noted that since a large amount of cooling water is jetted in rapid cooling, drainage of the cooling water might be difficult. On the other hand, since part of the cooling water jetted from a rapid cooling apparatus penetrates the vicinity of a delivery side of a roll bite during rapid cooling, the rolls are also cooled in the vicinity of the delivery side of the bite, in addition to roll cooling. In such a case, the amount of water to be drained from the mill can be reduced by reducing excessive cooling water for roll cooling. On the upper face side, the amount of cooling water flowing out from widthwise ends of the cooling apparatus can be reduced. On the lower face side, a jet of roll cooling water blocks drainage water flowing down through the openings of the guide 16 B, a space between the guide 16 B and the lower work roll 12 B, or the like, but the influence of the jet of roll cooling water can be reduced.

Further, the reference sign 28 in FIG. 1 denotes a fixed guide. The cooling water in the header portion for rolled material cooling water 24 B is directly jetted to the lower face of the rolled material W from a rolled material cooling nozzle 23 C through notches 28 a in a distal end of the fixed guide 28 . A large number of the notches 28 a are formed in the strip-widthwise direction of the rolled material W.

With this configuration, during rolling (including threading), the extending actions of the hydraulic cylinders 15 A and 15 B move the nozzle blocks 14 A and 14 B of the upper and lower cooling apparatuses 13 A and 13 B to an advanced position shown in FIGS. 1 and 3A , thereby bringing the distal ends of the guides 16 A and 16 B, supported on the nozzle blocks 14 A and 14 B by the pins 18 A and 18 B, into contact with the surfaces of the upper and lower work rolls 12 A and 12 B, respectively.

This prevents the rolled material W from winding around the upper work roll 12 A or the lower work roll 12 B during threading, and prevents a leading end of a following rolled material W from winding around the upper work roll 12 A or the lower work roll 12 B in the case of strip breakage.

Further, since the guides 16 A and 16 B are supported on the nozzle blocks 14 A and 14 B by the pins 18 A and 18 B and are swingable, even when roll changing (that is frequently performed) shown in FIG. 3B or the like causes a change in the diameters of the upper and lower work rolls 12 A and 12 B, the guides 16 A and 16 B can follow this change such that the distal ends of the guides 16 A and 16 B are always brought in contact with the surfaces of the upper and lower work rolls 12 A and 12 B, respectively. As another method of the following action, it is also possible to change retraction amounts of the hydraulic cylinders 15 A and 15 B according to the change in the diameters of the upper and lower work rolls 12 A and 12 B. In this case, the swinging function is unnecessary, and therefore the structure can be simplified.

It should be noted that, at the time of roll changing, as shown in FIG. 3B , the retracting actions of the hydraulic cylinders 15 A and 15 B move the nozzle blocks 14 A and 14 B of the upper and lower cooling apparatuses 13 A and 13 B to a retreated position, thereby separating the distal ends of the guides 16 A and 16 B, supported on the nozzle blocks 14 A and 14 B by the pins 18 A and 18 B, from the surfaces of the upper and lower work rolls 12 A and 12 B (see a travel distance (advance/retreat amount) S at the time of roll changing in FIGS. 1 and 3A ), so that interference in a removal directions of the upper and lower work roll chocks 11 A and 11 B (the strip-widthwise direction of the rolled material W) is avoided.

Then, in Example 1, a large amount of cooling water is jetted directly to the upper and lower faces of the rolled material W, from the large number of rolled material cooling nozzles 23 A, 23 B, and 23 C, through the jet holes 21 A and 21 B of the guides 16 A, 16 B and the notches 28 a of the fixed guide 28 , during rolling. Accordingly, the cooling rate of the rolled material W immediately after the rolling is raised to, for example, a cooling rate of about 1000° C./s, so that the rolled material W can be rapidly cooled.

Therefore, the rapid cooling after high reduction by the finishing mill line makes it possible to industrially obtain a hot-rolled steel strip made of a fine-grained structure, so that a high-tensile steel of high quality or the like can be easily manufactured at a very low cost without adding an alloy element or the like.

Further, in Example 1, the header portions for work roll cooling water 25 A and 25 B are integrally formed in the cooling water headers 22 A and 22 B, and the cooling water in the header portions for work roll cooling water 25 A and 25 B are jetted to the surfaces of the upper and lower work rolls 12 A and 12 B by the roll cooling nozzles 26 A and 26 B. Accordingly, the upper and lower work rolls 12 A and 12 B are also cooled, and thermal deformation of the rolls or the like is avoided.

In addition, since the header portions for rolled material cooling water 24 A and 24 B and the header portions for work roll cooling water 25 A and 25 B are integrated into the single cooling water headers 22 A and 22 B, the nozzle blocks 14 A and 14 B can be made compact.

Further, the separating plate. (separating member) 27 is extended between the front face (a face opposite the work roll) of the nozzle block 14 A and the distal end of the guide 16 A in the upper cooling apparatus 13 A. Accordingly, when jetting of the cooling water from the header portions for rolled material cooling water 24 A and 24 B is stopped so that rolled material is not cooled, that is, in normal (ordinary) rolling which does not manufacture a hot-rolled steel strip made of a fine-grained structure, the cooling water jetted from the roll cooling nozzles 26 A can be prevented from dropping on the upper face of the rolled material W through the jet holes 21 A of the guide 16 A, so that reduction in quality of the rolled material W is avoided. In addition, since the separating plate 27 is made of a flexible member such as a rubber plate, the separating plate 27 can allow the following action (swinging) of the guide 16 A.

Further, when the cooling water jetted from the roll cooling nozzles 26 B should be prevented from hitting the rolled material W through the jet holes 21 B of the guide 16 B, or when the cooling water jetted from the roll cooling nozzles 26 B should be prevented from influencing jetting of rolled material cooling water, a separating member, such as a separating member 101 in FIG. 6 or a separating member 103 in FIG. 7 , is provided. The separating member 101 is caused to abut on the nozzle block 14 B by a spring 102 . This makes it possible to prevent the work roll cooling water, jetted from the roll cooling nozzles 26 B, from hitting the rolled material W through the jet holes 21 B. This also makes it possible to prevent the rolled material cooling water, jetted from the rolled material cooling nozzles 23 B, from being disturbed by the work roll cooling water.

Here, it is also possible to use the separating member 101 in FIG. 6 instead of the separating plate 27 above. Further, the separating member 103 in FIG. 7 is a flexible member similar to the separating plate 27 used above in FIG. 1 so as to exert its separating function following the vertical movement of the guide 16 B.

FIG. 4 is a sectional side view of a cooling system for a hot-rolled steel strip showing Example 2 of the present invention. FIG. 5A is a plan view during non-cross rolling. FIG. 5B is a plan view during cross rolling.

Example 2 is an example of application of the upper and lower cooling apparatuses 13 A and 13 B to a cross mill crossing the upper and lower work rolls 12 A and 12 B in the conveyance direction of the rolled material W.

Specifically, the pairs of right and left hydraulic cylinders 15 A and 15 B located above and below the rolled material W are coupled to the nozzle blocks 14 A and 14 B, and to the housings 10 by pins so as to be capable of horizontally pivoting, at distal ends of piston rods and at head proximal ends, respectively, and spacers 30 A and 30 B abutting on the upper work roll chocks 11 A and 11 B are attached to front sides of both the right and left portions of the nozzle blocks 14 A and 14 B via brackets 29 . The spacers 30 A and 30 B are shaped and positioned so as not to block drainage. The rest of the configuration in Example 2 is the same as in Example 1, and therefore the same members as in FIGS. 1 , 3 A, and 3 B are denoted by the same reference signs in FIGS. 4 , 5 A, and 5 B, and overlapping descriptions are omitted.

Therefore, as shown in FIG. 5A , extending and retracting the pairs of right and left hydraulic cylinders 15 A and 15 B with the same stroke causes the nozzle blocks 14 A and 14 B and the guides 16 A and 16 B to be advanced and retreated relative to the upper and lower work rolls 12 A and 12 B, as in the case of FIG. 3A and 3B (advancing and retreating mechanism). As shown in FIG. 5B , extending and retracting the pairs of right and left hydraulic cylinders 15 A and 15 B with different strokes causes the upper and lower work rolls 12 A and 12 B to be crossed at a predetermined cross angle θ via the spacers 30 A and 30 B and the upper and lower work roll chocks 11 A and 11 B on which the spacers 30 A and 30 B abut (crossing mechanism).

According to Example 2, in terms of the cooling functions for the rolled material W and the upper and lower work rolls 12 A and 12 B, the same operation/effect as in Example 1 can be obtained, but, in terms of high reduction, since the upper and lower cooling apparatuses 13 A and 13 B are applied to a cross mill crossing the upper and lower work rolls 12 A and 12 B, higher reduction than that in Example 1 becomes possible, so that operation and effect due to high reduction and rapid cooling can be expected.

In addition, the hydraulic cylinders 15 A and 15 B, which are used for only the advancing and retreating mechanism in Example 1, can be used as both the advancing and retreating mechanism and the crossing mechanism of the nozzle blocks 14 A and 14 B and the guides 16 A and 16 B This makes it possible to simplify the structure and to reduce the cost.

Further, FIG. 8 is a graph showing a relation between a flow density and a cooling rate. It is a test result of the cooling rate for a 3-mm-thick steel plate when a water-feeding pressure, namely, the pressure of the header portions for rolled material cooling water 24 A and 24 B is 1.5 MPa. From this test result, if the flow density (=nozzle flow rate÷widthwise nozzle pitch÷nozzle pitch in the conveyance direction) is set to 6 m 3 /(m 2 ·min) or more, a cooling rate of 500° C./s or more can be obtained for the 3 mm thick steel plate even with a water-feeding pressure of 1.5 MPa, which is used in ordinary cooling equipment, making it possible to manufacture a steel plate having a fine structure.

Further, the present invention is not limited to the above Examples, and it is obvious that without departing from the scope of the present invention, various changes are possible, such as a structural change and material change of the guides 16 A and 16 B, a structural change of the mechanism capable of following a crossing state, including the hydraulic cylinders 15 A and 15 B, a structural change of the cooling water headers 22 A and 22 B, and various structural combinations of the cooling water headers 22 A and 22 B and the header portions for work roll cooling water 25 A and 25 B.