JPH0722766B2 - Online grinding method for rolling rolls - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an on-line grinding method for a work roll in a hot rolling mill, and more particularly to an on-line grinding method capable of significantly extending the life of the work roll.

[Prior art]

Work rolls for hot strip mills such as steel strips are generally formed from materials such as high Cr cast iron, adamite cast steel, and high alloy cast iron. An oxide film of magnetite (generally referred to as a black scale) is produced and adhered to the surface of these work rolls as the rolling progresses, that is, as the number of rolled materials increases. Since this black scale is super hard, it is known that it has excellent wear resistance and rough skin resistance and contributes to the extension of roll life. On the other hand, the black scale that has grown with the progress of rolling is repeatedly exposed to heat absorption from the material to be rolled and cooling by cooling water, so that heat cracking occurs in the surface layer. When this heat crack grows, due to the shearing stress generated between the roll during rolling and the material to be rolled, the so-called rough skin is generated, in which the black scale is separated from the roll starting from the heat crack. It is well known that this roll roughening adversely affects the rolled product surface. In order to suppress such a rough surface of the roll, various measures have been conventionally considered. For example, in order to reduce the roll load, the rolling ratio, the method of rolling by keeping the surface pressure below a certain value, the method of increasing the roll cooling water amount to suppress the rise of the roll temperature, the rolling material with a large roll load is rolled. In that case, instead of rolling the material continuously, by rolling it alternately with a material with a small roll load, a black scale is further generated on the roll surface where roughening of the surface has started, and the recovery of the roll surface skin There is a method of rolling while trying. However, none of these methods can suppress the roughening of the surface of the roll, and the roll must be taken out after rolling a certain amount and the surface must be polished offline. On the other hand, as a method of grinding a roll online, for example, as disclosed in JP-A-61-49713, the roll wear profile is estimated from the wear coefficient and rolling tonnage of the roll in use, By performing a predetermined grinding on the roll surface, a method of restoring the roll profile to the state before the roll is incorporated, as disclosed in JP-A-61-56713, information on the steel plate surface inspection before the coiler. Roll grinding online to remove the rough surface of the roll surface, return the roll profile to the state before it was installed in the rolling mill, and roll the roll while continuing rolling without pulling out the roll. be able to. However, even in such an online grinding method, it is necessary to scrape off all the black scales when grinding the rough skin portion, and the characteristics of the wear resistance and the rough skin resistance of the black scales should be fully utilized. There is a problem that you cannot do it. Further, as described above, the grinding to scrape off all the black scales is to reduce the roll diameter, and due to this grinding and roll wear, the roll becomes a small diameter over time during use, and it has a short duration. There was a problem that I had to replace it with a new roll.

[Object of the Invention]

This invention has been made in view of the above conventional problems, prevents the occurrence of roll roughening without impairing the wear resistance of the black scale in the roll, thereby,
An object of the present invention is to provide an on-line grinding method for rolling rolls, which is capable of dramatically improving roll life.

[Means for Solving the Problems]

This invention, the roll surface in the steel strip hot rolling mill,
The oxide scale film adhered and formed on the roll surface is subjected to on-line grinding to a thickness of at least 5 μm when the thickness reaches 20 μm, thereby achieving the above object.

[Action]

In this invention, the thickness of the black scale that grows on the roll surface is kept in a range where heat cracking is unlikely to occur,
Increases wear resistance and rough surface resistance without sharpening the black scale, greatly improves roll life, and because the black scale is ground when it is about to reach 20 μm, the grinding frequency is minimal. Become.

[Detailed Description of the Invention]

The black scale grows on the roll surface as the rolling progresses. The thickness of the black scale depends on the material of the material to be rolled, the temperature, the rolling load, the roll cooling conditions, the rolling speed, the roll contact arc length, and the rolling oil. Therefore, the present inventor, in several types of roll schedules, when the work roll was extracted several times in the same schedule and the thickness of the black scale was measured using an electromagnetic thick film meter, the thickness t was t = f (material of rolled material, temperature,
By using the evaluation function f expressed by rolling load, rolling speed, rolling arc length, rolling oil), it was found that it is possible to predict with an accuracy of ± 5 μm up to t = 25 μm, as shown in FIG. Here, since the evaluation function f differs depending on the stand or rolling mill, the parameters of the evaluation function are obtained from experimental values for each stand or rolling mill. In this case, when the rough skin of the roll occurs, the black scale is removed, and the accuracy of the prediction formula of the black scale thickness t is found to be deteriorated. Therefore, the prediction formula is set only for the roll in which the rough skin is not generated. Created. The evaluation function f is specifically expressed by the multiple regression equation shown in the following equation (1). t: Black skin thickness, k: Roll material coefficient (0.1 to 1.0) Ti: i-th rolling temperature, Pi; i-th rolling load, Wi; i-th plate width, Vi; i
Rolling speed of the Xth, X: contact arc length of the i-th rolling, Q: rolling oil amount of the i-th rolling, Li: rolling length of the i-th rolling, D; roll diameter, a, b, c, d, e; constant t = Multiple regression equations (predicted) falling within ± 5 μm up to 25 μm were created. Here, t = 5 to 25 μm, K is a roll material coefficient of high speed steel roll, high Cr cast iron roll, high Cr cast steel roll, Ti = 800 ° C. to 1
100 ℃, Pi = 500ton-4000ton, Wi = 600mm-2000mm, Vi
= 30mpm to 300mpm, X = 20mm to 100mm, Q = O to 250cc / mi
n, Li = 40m to 500m (total rolling length 10km to 500km), D
= 600 mm to 800 mm, the target stands were the four stands in the front stage of the hot finishing tandem rolling mill. On the other hand, each time the roll is replaced, the thickness of the black skin scale is measured with an electromagnetic film thickness meter, and at the same time, the roll skin is also observed, and the relationship between the roughness of the roll skin and the thickness of the black skin scale, which is considered to have an adverse effect on the product. As a result of the investigation, as shown in FIG. 2, it was revealed that the occurrence rate of roll roughening significantly increases when the thickness t of the black scale exceeds t = 25 μm. Here, the roll roughening occurrence coefficient in Fig. 2 is a coefficient expressing the occurrence frequency of roll roughening, and rolls having a black skin thickness of 30 µm generate rough skin at a frequency of 11 rolls / 1000 rolls = 1.1%. Then, with a roll with a black skin thickness of 20 μm
It is shown that rough skin occurs only at a frequency of 0.1% = 1/1000. From the above results, it can be seen that if the thickness of the black scale can be set to 20 μm or less, the roughening of the roll surface can be almost completely prevented. However, if the black scale on the roll surface is completely removed, as described above, the abrasion resistance of the black scale cannot be fully utilized, and the roll wear progresses. As a result of an offline investigation of the relationship between the thickness of the black scale and the wear resistance, it was found that the roll has sufficient wear resistance if the thickness t = 5 μm or more. (See Figure 3). It is generally considered to be the amount of wear ∝ rolling length. The wear coefficient in FIG. 3 is the proportional coefficient when the black skin thickness is 0 μm, and is normalized to 1.0.
What percentage of wear is reduced (eg black skin 0
μm ... 1.0 km wear after 1 km rolling, black skin 5 μm ... 0.2 μm wear after 1 km rolling). From the above, the thickness of the black scale on the roll surface should be 5
When the thickness is in the range of μm to 20 μm, it is possible to prevent the roughening of the roll surface while sufficiently maintaining the wear resistance of the roll surface, and thus to significantly extend the roll life. In order to maintain the thickness of the black scale of the roll surface in the range of 5 μm to 20 μm, it is possible to predict up to t = 25 μm by the above-mentioned prediction formula. Carry out skin scale grinding. Grinding of this predetermined amount of black scale is described, for example, in JP-A-61-161.
As disclosed in Japanese Patent No. 49712, it can be extremely easily performed by determining the pressing force in the roll width direction and the grinding time or the grinding length. When the above prediction formula is not used, an electromagnetic film thickness meter is placed in the line and the black scale thickness is directly measured in-line. Next, the experimental results of the present invention will be shown. In a hot strip mill with a 7-stand finish rolling mill, low carbon materials with a plate thickness of 2.0 to 3.0 mm and a plate width of 700 to 1250 mm were sequentially applied to the finish rolling mill with a coffin cage as shown in FIG. I went through the board. A belt type online roll grinder was installed on the upper part of the F2 stand (the second stand of the hot finishing tandem rolling mill), and in this F2 stand, rolls were installed as disclosed in the above-mentioned JP-A-61-49713. Ground. Rolls were replaced every 100 rolls to prevent defective products other than the F2 stand. Here, the material of the F2 roll was high Cr cast iron, the diameter of the F2 roll was 700 mm, the width of the grinding belt was 360 mm, the pressing force of the grinding belt was 200 kgf, and the grain size of the grinding belt was # 150. According to the prediction formula of the black scale thickness t described above, the first 80
Since t = 20 μm after rolling the book, in order to grind until t = 5 μm, the grinding belt is traversed to the width corresponding to the thickness of the black scale (1000 mm), and grinding is performed for a time corresponding to a grinding length of 1 km. Ivy (for example, 7 minutes at 60 rpm).
Here, the relationship between the grinding length and the grinding amount when grinding the black scale is experimentally obtained in advance as shown in FIG. It is estimated that the thickness t of the black scale will be 20 μm again when 60 more pieces are rolled after the first grinding. Therefore, t
= 900 μm to traverse to a corresponding width of 900 mm
Grinding was performed for a time equivalent to a grinding length of 0.9 km. Thereafter, every 60 minutes, the same rolling and grinding as described above are repeated corresponding to the plate width of the coffin cage shown in FIG. After the rolling was completed, the F2 work roll was taken out, and the surface of the roll was observed. As a result, no rough surface of the roll was observed, and the roll was hardly worn. It is empirically known that when the rolls are continuously rolled without grinding under the above conditions, the roll surface may be roughened on the F2 stand if 100 or more rolls are rolled.

【The invention's effect】

Since the present invention is configured as described above, the thickness of the black scale produced on the surface of the work roll in the hot rolling mill is 5
By maintaining the thickness within the range of 20 μm to 20 μm, it is possible to suppress the occurrence of roughening of the roll and to significantly improve the life of the roll without lowering the wear resistance of the roll. . Further, since the black scale is ground when it is about 20 μm, the grinding frequency is minimum.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the calculated value and the measured value of the black skin scale thickness based on the prediction formula by the present inventor, and FIG. 2 is a line showing the relationship between the black skin scale thickness and the roll skin roughening incidence. Fig. 3 is a diagram showing the relationship between the thickness of the black scale and the wear coefficient of the roll, Fig. 4 is a diagram showing the coffin scale during the experiment conducted by the inventor, and Fig. 5 is the black scale. It is a diagram showing the relationship between the grinding length and the grinding amount when grinding the.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 63-160709 (JP, A) JP 62-64411 (JP, A) JP 60-24206 (JP, A) JP 50- 158516 (JP, A) JP-A-52-37535 (JP, A) JP-A-64-40105 (JP, A)

Claims (1)

[Claims] 1. A roll surface of a steel strip hot rolling mill,
An online grinding method for a rolling roll, which grinds an oxide scale film adhered and formed on the roll surface to a thickness of at least 5 μm when the thickness becomes 20 μm.