JPH05310A - Wiper device for hot rolling mill and method for controlling the same - Google Patents

Abstract

PURPOSE:To provide a wiper device and method for controlling the same by which surface roughening of rolling roll of stand at the previous stage of finishing mill is prevented and scale biting flow due to the surface roughening of roll can be reduced. CONSTITUTION:In the wiper device, which is arranged on the inlet side of a continuous hot finishing mill, having a structure that the flow of roll cooling water along the outer peripheral surface of roll can be interrupted by pressing a dewatering plate 11 against the outer peripheral surface of a roll 4, an adjusting means with which a clearance between the tip part of the dewatering plate the outer peripheral surface of the roll is adjusted is provided and the surface of a material to be rolled when the material is bitten between rolls is cooled by roll cooling water which is made to flow out of the clearance. The above-mentioned wiper device arranged on the inlet side of at least one or more stands at the previous stage and the clearance between the tip part of the dewatering plate and the outer peripheral surface of the roll is adjusted according to the load that is applied to the roll surface at the stand. Then, by making the clearance between the tip part of the dewatering plate and the outer peripheral surface of the roll at the time of rolling at least either the front end part or rear end part of the material 3 to be rolled smaller than that at the time of rolling the normal part of the material to be rolled, the front and rear end parts of the material to be rolled is prevented from undercooling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hot rolling of a steel strip, and more particularly to a wiper device capable of preventing roughening of a rolling roll of a front stand for finishing and reducing bite scale flaws caused by the roughening of the roll and its control. It is about the method.

[0002]

2. Description of the Related Art In a front stand of a continuous hot rolling mill, high chrome rolls or adamite rolls are used as rolling rolls. These rolls are characterized in that an oxide film mainly called magnetite, which is mainly composed of magnetite, is formed on the surface by contact with a high-temperature rolled material during rolling. This black skin has the effects of preventing metal-to-metal contact between the material to be rolled and the roll base material, preventing roll wear, and smoothing the surface of the material to be rolled on the roll roll exit side.

[0003]

However, with the progress of rolling, the black skin may be partially peeled off, and so-called roll surface roughness may occur. When the black skin peels off,
Since the surface of the rolled roll in the separated portion has a concave shape, the surface of the material to be rolled rolled by such a rolling roll has a partially convex shape. This convex portion is smoothed again by the rolling roll of the next stand.At that time, the secondary scale generated in the convex portion of the surface of the material to be rolled is caught in the inside of the material to be rolled, and The product may have surface quality defects called bite scale flaws.

FIG. 4 shows the ratio of occurrence of bite scale flaws by type in hot finish rolling. Meteor-shaped scale flaws occur when the black skin peels off in a band shape, and sand-sand scale scale defects occur when the black skin peels off in a dot shape. The spindle-shaped scale flaws are generated independently of the peeling of the black scale, and it is presumed that the secondary scale on the surface of the material to be rolled is simply pushed into the rolling roll. Therefore, it is understood that most of the occurrence of the bite scale flaw is caused by the rough surface of the roll of the front stand.

Many studies have been made so far on the peeling phenomenon of the black skin, and the causes thereof are the thermal stress fatigue of the roll surface layer due to heating during rolling and cooling, and the surface temperature rise on the roll bite. It is considered that the black skin is softened by the rolling, the rolling fatigue of the roll surface due to the rolling load, the shearing force at the interface between the roll and the rolled material, and the like. In fact, it seems that some of these factors combine to lead to exfoliation of the black skin.

With respect to the technique for preventing the peeling of the black scale, there have hitherto been attempted a method of increasing roll cooling to lower the roll surface temperature and a method of performing rolling lubrication to reduce the shearing force at the roll interface. Although these methods have been found to have some effect on the prevention of exfoliation of the black skin, they are still insufficient. Fig. 5 shows the effect of reducing the roll surface temperature by increasing the roll cooling introduced in "Technical information meeting of the plastic processing spring lecture in 1988," Surface damage of hot-rolled work rolls and rolling conditions ", p.22. . The reduction amount of the roll surface temperature due to the enhancement of the roll cooling is as large as 30 ° C. to 60 ° C. in the part other than the roll bite, but is about 20 ° C. in the part of the roll bite where the roll surface temperature rises most. Hot rolling lubrication has been adopted in many mills in recent years.However, since the front stand of the hot finish rolling mill has a large biting angle, improving lubricity may cause biting failure due to slip. There is a limit to the reduction of the friction coefficient.

The present invention has been made in view of the above circumstances, and a wiper device and its control which can prevent the roughening of the rolling roll of the front stand of the finishing rolling mill and reduce the bite scale flaw caused by the roughening of the roll. The purpose is to provide a method.

[0008]

In order to achieve the above-mentioned object, the present invention is arranged on the inlet side of a continuous hot finishing mill, and along the outer peripheral surface of the roll by pressing a draining plate against the outer peripheral surface of the roll. In a wiper device having a structure capable of blocking the flow of the roll cooling water, adjusting means for adjusting the gap between the tip of the draining plate and the outer peripheral surface of the roll is provided, and the roll cooling water flowing out from the gap is used when the roll is caught. The surface of the material to be rolled is cooled.

Further, in carrying out the above-mentioned invention, the wiper device is disposed on the entrance side of at least one stand in the preceding stage, and the tip end portion of the draining plate is arranged according to the load acting on the roll surface of the stand. The gap between the roll and the outer peripheral surface of the roll is adjusted. Further, the gap between the draining plate tip portion and the roll outer peripheral surface, at least one of the front end rolling and the rear end rolling of the material to be rolled, by making smaller than the steady portion rolling of the material to be rolled, This is intended to prevent supercooling of the front and rear ends of the rolled material.

[0010]

According to the present invention, the wiper device 5 having the adjusting means for adjusting the gap between the tip of the draining plate 11 and the outer peripheral surface of the roll 12 is provided on the inlet side of the front stand 1 of the continuous hot finishing mill. The gap is adjusted according to the load acting on the roll surface of the stand, and the surface of the material to be rolled at the time of biting the rolling roll is cooled by the roll cooling water flowing out from the gap, and the roll surface temperature in the roll bite. By reducing the heat stress fatigue of the surface layer of the roll and the softening of the black skin due to the surface temperature rise on the roll bite, preventing the roughening of the roll and preventing the occurrence of bite scale flaws due to the roughening of the roll. In addition, during rolling of the front and rear ends of the rolled material where the temperature of the rolled material is likely to decrease, the roll cooling water that flows out from the gap is reduced by making the gap smaller than that during steady rolling. With less to prevent excessive cooling of the rolled material, thereby preventing the occurrence of rolling troubles strip passing failure or Rorukizu like due to excessive cooling of the rolled material.

The object of the present invention is to cool the surface of the material to be rolled when the rolling roll is bitten, and to lower the surface temperature of the roll on the roll bite. In general, the surface temperature of a material to be rolled immediately after rolling and water cooling is rapidly lowered, and then recovered and raised in a short time due to heat recovery from the inside of the plate. Usually, the passage time of the rolled material from the outlet side of the descaling device on the inlet side of the continuous hot rolling mill to the inlet side of the finishing first stand and the passage time of the rolled material between the front stands of the finishing rolling mill are 2 to
It takes about 4 seconds. Therefore, the surface of the material to be cooled that has been cooled by contact with the descaling water or the rolling rolls reheats to a value close to the plate center temperature when the rolling rolls of the next stand bite.

According to the present invention, a wiper device, which is usually installed for the purpose of preventing roll cooling water from directly contacting a material to be rolled, has a structure capable of adjusting a gap between a tip end portion of a draining plate and a roll outer peripheral surface. Since the gap is adjusted and the surface of the material to be rolled is cooled immediately before the roll is caught by the roll cooling water flowing out from the gap, the time for recuperation is eliminated, and the material of the material to be rolled is most effectively cooled. The surface temperature at the time of roll biting can be lowered.

FIG. 3 shows an example in which the temperature distribution in the plate thickness direction of the rolled material when the present invention is carried out on the entrance side of the finishing second stand and when the conventional second stand rolling roll is engaged is calculated by the difference method. Show. The heat transfer coefficient of water cooling by the cooling water flowing out from the gap between the draining plate and the roll is 1300 kcal / m ² hr ℃
Was calculated as The plate thickness of the material to be rolled was 15 mm. When the present invention is carried out, the surface temperature of the material to be rolled at the time of biting the rolling roll is about 70 ° C. lower than in the prior art. Also,
When the material to be rolled having the temperature distribution in the plate thickness direction shown in FIG. 3 is rolled by the second stand, the roll surface temperature of the roll bite is about 40 ° C. lower in the present invention than in the conventional case.

In the present invention, the gap between the draining plate and the roll is adjusted according to the load acting on the roll surface of the stand, because the biting is performed when the temperature of the material to be rolled is high and the rolling pressure is high. This is due to the fact that scale defects are likely to occur. FIG. 6 shows an example of the relationship between the occurrence of bite scale flaws in the rolling cycle and the magnitude of the load acting on the roll surface of the second stand when the present invention is not carried out. The ratio of the average rolling pressure to the roll surface strength of the roll bite (hereinafter referred to as the roll load ratio) is considered as a parameter that represents the magnitude of the applied load. The roll surface strength was determined as the roll strength corresponding to the calculated roll surface temperature in the roll bite from the softening characteristic curve at high temperature of the high chromium cast iron roll used in the front stand. In the example shown in FIG. 6, when the roll load ratio is 0.33 or more, the occurrence rate of bite scale flaws is high. Therefore, in this example, in order to prevent the occurrence of bite scale scratches, at least the roll load ratio 0.33 or more, it is necessary to provide a gap between the draining plate and the roll to cool the surface of the material to be rolled with roll cooling water. Yes, but roll load ratio 0.33
If it is less than the above, it is not always necessary to provide a gap. On the other hand, the temperature of the front and rear edges of the material to be rolled tends to drop, so if cooling with roll cooling water is performed as in the steady part, it may become overcooled and rolling trouble such as defective rolling and roll scratches may occur. . Therefore, even when the gap is adjusted according to the roll load ratio and cooling is performed by the roll cooling water, it is desirable that the gap between the front and rear ends be smaller than that in the steady part, or zero.

[0015]

EXAMPLE FIG. 1 shows an outline of equipment of a continuous hot finish rolling mill according to the present invention. As the rolling roll 4, high chromium rolls were used for the first to third stands in the front stage, and nickel grain rolls were used for the fourth to seventh stands in the rear stage. Regarding the third stand in the previous stage, the wiper device 5 on the stand 1 entry side
The gap between the tip of the draining plate 11 and the outer peripheral surface of the roll 4 is adjustable. FIG. 2 shows an example of a top surface wiper device according to the present invention. When the hydraulic cylinder 8 is actuated, the main body 9 of the wiper device 5 rotates about the fulcrum 10 as an imaginary line, and the gap between the tip of the draining plate 11 and the outer peripheral surface of the roll 5 changes. The cooling water discharged from 13 is made to flow out from the gap. The gap is adjusted by, for example, inputting the roll diameter, the rolling position, and the target gap between the draining plate 11 and the roll 4 to the control device 14 connected to the hydraulic cylinder 8, and the cylinder for achieving the target gap. It is performed by calculating the set value of the ram position and controlling the ram position to the set value using the ram position detecting device. Alternatively, the cylinder 8 is pressed in the direction of pressing the draining plate 11 against the roll 4.
When the ram position detection value has not changed for a certain period of time, the clearance is determined to be zero, and the ram position may be changed by an amount corresponding to the target clearance with reference to the position.
Further, as another adjusting means, a device for directly measuring the gap between the draining plate 11 and the roll 4, for example, an air cylinder device with a position detecting device is attached to the wiper device main body 9, and the detected value of the gap becomes the target value. The hydraulic cylinder 8 may be controlled as follows. Further, the surface temperature of the material to be rolled is detected between the first and second stands and between the second and third stands in order to calculate the magnitude of the load acting on the roll surface (roll load ratio in this embodiment). There is a thermometer 6 installed for this purpose. The surface temperature of the material to be rolled on the entry side of the first stand was estimated using a thermometer on the entry side of the finishing rolling mill installed in front of the descaling device 7. Then, the roll load ratio is obtained from the measured or estimated surface temperature of the material to be rolled and the average rolling pressure obtained from the rolling load, and the roll load ratio is 0.3.
In the above case, the gap between the water draining plate tip portion 11 and the outer peripheral surface of the roll 4 was set to 5 mm, and the gap was set to zero when the roll load ratio was less than 0.3. However, at the time of the front end rolling and the rear end rolling of the material to be rolled, the gap was always zero regardless of the roll load ratio. As a result, as shown in Fig. 7, the surface quality defect rate of hot rolled products due to bite scale flaws caused by roll roughening is reduced from the conventional 0.31% (3 months average) to 0.08% (2 months average). I was able to. Further, during the practice of the present invention, rolling trouble caused by supercooling of the front and rear end portions of the material to be rolled did not occur.

[0016]

As described in detail above, according to the present invention,
It is possible to prevent the occurrence of roll roughening in the front stand of the finishing rolling mill, and to significantly reduce the surface quality defect rate of hot rolled products due to bite scale flaws caused by roll roughening,
The contribution to the improvement of yield and the surface quality of hot rolled products is great.

[Brief description of drawings]

FIG. 1 is a schematic view of equipment of a continuous hot finish rolling mill according to the present invention.

FIG. 2 is a schematic view of an example of a wiper device according to the present invention.

FIG. 3 is a diagram showing a comparison of the temperature distribution in the plate thickness direction of the material to be rolled when the rolling roll is engaged with the conventional case and the present invention case.

FIG. 4 is a diagram showing an occurrence ratio of bite scale defects by type.

FIG. 5 is a diagram showing the relationship between the roll cooling enhancement and the roll surface temperature reduction effect in the prior art.

FIG. 6 is a diagram showing a relationship between a conventional state of occurrence of bite scale flaws and a load acting on a roll surface.

FIG. 7 is a diagram showing monthly changes in surface quality defect rate of hot rolled products due to bite scale flaws.

[Explanation of symbols]

1 Finishing mill front stand 2 Finishing mill rear stand 3 Rolled material 4 rolling rolls 5 Rolling mill entry side wiper device 6 thermometer 7 Descaling device 8 hydraulic cylinders 9 Wiper device body 10 fulcrums 11 Drainer 13 Cooling water header 14 Control device

Claims (3)

[Claims] 1. A wiper device, which is arranged on the inlet side of a continuous hot finishing mill and has a structure capable of blocking the flow of roll cooling water along the outer peripheral surface of the roll by pressing a draining plate against the outer peripheral surface of the roll. 2. A wiper device for a hot rolling mill, comprising adjusting means for adjusting a gap between the tip end portion of the draining plate and the outer peripheral surface of the roll. 2. When rolling a material to be rolled in a continuous hot finish rolling mill, a draining plate is pressed against the outer peripheral surface of the roll at the entrance side of at least one stand in the preceding stage so as to follow the outer peripheral surface of the roll. A heat, characterized in that a wiper device for blocking the flow of roll cooling water is provided, and the gap between the tip end portion of the draining plate and the outer peripheral surface of the roll is adjusted according to the load acting on the roll surface of the stand. Method for controlling wiper device of hot rolling mill. 3. The gap between the leading end of the draining plate and the outer peripheral surface of the roll should be smaller than that during rolling of the steady part of the material to be rolled during at least one of the leading end rolling and the trailing end rolling of the rolled material. The method for controlling the wiper device of the hot rolling mill according to claim 2.