JP5525321B2 - Strip rolling method - Google Patents

Description

  The present invention relates to a method for hot rolling steel bars including wire rods, rods, and square bars, and particularly to a steel bar rolling method capable of producing steel bars while reducing surface defects.

  A method of rolling a wire is generally a method of reducing the cross-sectional area while sequentially changing the cross-sectional shape using a hole shape called a caliber (see, for example, Non-Patent Document 1). There are innumerable deformation processes, each with advantages and disadvantages.

  In general, a material (billet) to be rolled is a quadrangular shape, and a square diamond method is adopted in a coarse rolling mill in a rolling line in consideration of descaling property and strain uniformity. A product manufactured by rolling has many round shapes, and a hole shape such as a square-oval method is usually used at least once in a rolling line.

  As described above, the rough diamond rolling mill employs the above square-diamond method. In this case, since the cross-sectional shape of the material is a square (diamond), the roll comes into contact with the material from the corner portion. The temperature drop at the material corner increases due to the heat transfer to. Furthermore, since the rolling speed is slow in the continuous rolling mill that is continuously rolled, the temperature drop amount becomes more remarkable.

  In the square-oval method, unlike the other hole type methods, the material and the hole type come into contact with each other from the outside, and therefore the hole type has uneven wear that differs greatly from the design value. If it becomes remarkable, a fine surface flaw will generate | occur | produce in a wear inflection point part during rolling by the round hole type (or square hole type) following a next process.

  Furthermore, for example, in the round-oval method, the wear of the roll proceeds, but the material and the hole mold contact in order from the center toward the outside, so that the amount of uneven wear that is directly connected to the surface flaw is small.

  FIGS. 10A to 10C are schematic views showing a surface flaw generation mechanism in the square-oval method.

  In FIG. 5A, F is a material, Fa is a material shape before rolling, Fb is a material shape after rolling, Ma and Mb are two perforated rolls arranged facing each other, Mc is a perforated profile before wear, Mc 'represents the hole profile after wear.

  The material F ′ rolled by the hole profile Mc ′ is continuously rolled by the two hole rolls Md and Me shown in FIG. 4B while changing the angle of 90 °, and the upper and lower ends of the material F ′ are rolled down. When (see arrow P), a surface defect D occurs at the wear inflection point as shown in FIG.

  The occurrence of surface flaws D becomes more prominent as the temperature of the corner portion of the material progresses. Therefore, the generation of surface flaws appears remarkably particularly in low-temperature rolling that has become popular recently.

  As a method for improving the generation of such surface defects D, it is conceivable to replace the roll at an early stage or to improve the perforation method. However, the former has a drawback that the roll reassignment frequency is increased and the productivity is lowered.

3rd Edition Iron and Steel Handbook III (2), Steel and Steel Pipe and Rolling Common Equipment Mourning Japan Iron and Steel Association, Maruzen, issued November 20, 1980, P862-863

  Therefore, we investigated a hole mold method that can reduce surface defects without sacrificing productivity.

  The square-oval method is conventionally said to be prone to wrinkles due to its deformation. Regarding surface flaws generated in such a hole type series, we presented one improvement measure in the “hot rolling method of strip material” of Japanese Patent Application Laid-Open No. 2007-90429.

  The above improvement measure is to control the circumferential compressive strain generated during rolling, and by appropriately controlling this compressive strain (hole shape, roll gap, entry side shape, etc.), for example, square ( Square) -Oval rolling is also possible without causing surface flaws due to deformation.

  However, the above improvement measures do not improve the change in rolling shape due to caliber wear, so even if it is known that surface flaws occur as wear progresses and the hole shape changes, such as There was no direct improvement for surface defects.

  The present invention has been made in consideration of the problems in the conventional method for rolling a steel bar as described above, and in particular, a pass schedule for manufacturing a steel bar having a round cross-section from a material having a square cross-section through two rolling operations. The present invention provides a method for rolling steel bars that can reduce surface wrinkles without reducing productivity by reducing uneven wear of calibers that roll square-shaped materials.

The present invention, in a rolling method for rolling the bar steel while sequentially reducing the cross-sectional area in a plurality of rolling mills,
The rolled material is molded into a square shape with each corner having a curved surface,
The next hole mold in which the formed rolled material is rolled has a flat groove bottom, and has an indented portion formed of a curved surface that squeezes each corner of the rolled material between the groove bottom and the flange. Then, when the radius of curvature of the corner curved surface of the rolled material is r, and the radius of curvature of the indented curved surface is R, the next hole shape is formed so that R> r,
Introducing the rolled material on the entry side of the next hole mold,
The corner of the rolled material is reduced from the opposite direction by the indented portion,
It is a rolling method of the bar steel, in which the rolled material reduced by the indented portion is further rolled into a round cross section or a square cross section with the following hole shape.

In the present invention, the distance between the intersection and the center of the hole shape when the virtual line is orthogonal to the hole center axis from the starting point of the radius of curvature r in the cross section of the rolled material is represented by r _x ,
In the case where R _x is the distance between the intersection point and the hole center when the imaginary line is orthogonal to the hole center axis from the starting point of the radius of curvature R in the cross section of the indentation,
r _x / R _x is preferably 1.3 or less.

In the present invention, r _x / R _x is most preferably 1.0 or less. Thereby, generation | occurrence | production of a wear inflection point can be prevented reliably.

  In the present invention, it is preferable to reduce the cross-sectional area of the rolled material so that the circumferential compressive strain of the rolled material in the next hole shape becomes −0.5 or more.

  According to the method for rolling strip according to the present invention, it is possible to reduce uneven wear of a caliber that rolls a square-shaped material, thereby reducing the surface flaw of a product without impairing productivity.

It is explanatory drawing which showed the relationship of the raw material shape in a square shape-> oval rolling, a caliber shape, and the raw material shape after rolling. It is explanatory drawing which showed the surface pressure distribution in square shape-> oval rolling. It is explanatory drawing which showed the relative sliding speed in square shape-> oval rolling. It is the graph which measured the amount of caliber wear in square shape-> oval rolling. (a)-(c) is explanatory drawing which showed geometrically the shape which reduces the amount of rolling reduction in the rolling method of the bar steel of this invention. It is explanatory drawing for demonstrating the circumferential direction compressive strain. It is the principal part enlarged view which showed the hole-type profile which concerns on this invention. It is a graph showing the r x _/ R _x and circumferential compressive strain relationship. It is the graph which showed the amount of wear by the rolling method of the steel bar concerning the present invention. (a)-(c) is the schematic diagram which showed the surface flaw generation | occurrence | production mechanism in the conventional square (corner) -oval method.

  Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.

  Wear in a rolling mill is generally represented by the product of the surface pressure acting on the caliber by rolling and the sliding distance between the roll and the material. Therefore, in order to reduce the amount of wear, it is necessary to prevent the reduction amount in the surface pressure distribution from having an inflection point.

  FIG. 1 is an explanatory view showing the relationship among a rolled material shape, a caliber shape, and a rolled material shape after rolling, which have been examined in connection with the present invention.

  In the figure, 1 is a rolled material (raw material) having a square cross section, and 2 and 2 are a pair of opposed hole shapes (next hole shapes) into which the rolled material 1 is introduced. is there.

  The profile of the hole mold 2 is formed as a symmetrical curve with a straight line L connecting the center of the groove bottom 2a and the hole center O as a target axis, and the hole mold is formed by a curved surface 2b having a radius of curvature R. Yes. In the figure, C represents the center axis of the hole mold, and 1 ′ represents the shape of the rolled material 1 after rolling. In the figure, r represents the radius of curvature of the curved surface of the rolled material corner A.

  In the square shape → oval rolling, since the largest reduction occurs at the corner of the rolled material 1, it is estimated that a wear inflection point occurs at this portion.

  The colored portion in FIG. 2 shows the surface pressure distribution in the square shape → oval rolling, and the colored portion in FIG. 3 shows the result obtained by the numerical analysis of the square shape → relative sliding speed in the oval rolling.

  As shown in FIG. 2, it can be confirmed that the surface pressure becomes higher at the corner and flange side of the rolled material 1 with which the roll first comes into contact. In particular, it is expected that the temperature of the corner portion of the rolled material 1 with which the roll first comes into contact is significantly reduced during low temperature rolling.

  Further, as shown in FIG. 3, the relative sliding speed is highest at the corner portion of the rolled material 1.

  From these results, it can be seen that when the surface pressure × slip distance from the roll bite entry side to the exit side is integrated, the amount of wear near the corner of the rolled material with which the roll is initially contacted is maximized.

  FIG. 4 is a graph in which the amount of caliber wear in the square shape → oval rolling was measured, and it was confirmed that the wear had a maximum value at the first contact portion as expected.

  In the figure, E represents the caliber shape before rolling, E ′ represents the caliber shape after rolling, and F represents the roll wear profile after rolling.

  In the wear profile, S1 and S2 indicate wear inflection points at which the wear amount rises (reverses) upward once without being attenuated downward.

  As is apparent from the figure, the wear amount takes the minimum value on the flange side. Therefore, in order not to have the wear inflection point, the amount of reduction in the next caliber shape into which the rolled material 1 is introduced is reduced along the roll width direction (from the caliber center toward the flange side). It can be seen that such a shape is sufficient.

  5 (a) to 5 (c) are explanatory views showing geometrically the caliber shapes that can reduce the amount of reduction in the rolling method of the bar steel of the present invention.

  The reduction amount reduction shape shown in FIG. 2A includes a hole shape of a box, a flat oval, and a bastard oval. In the following description, a box, a flat oval, and a bastard oval are collectively referred to as a square hole mold 3.

  A flat roll 4 having no caliber is shown as the reduction amount reduction shape shown in FIG. However, in this case, since there is no caliber, a roller guide is necessary in order to eliminate the shift in the thrust direction on the rolling entry side.

  As a reduction amount reduction shape shown in FIG. 5C, a concave bastard oval mold 5 is shown.

  The dent formed in the groove bottom of the bar steel by concave busted oval rolling becomes a free surface during the next round hole rolling. For this reason, in order to ensure the dimensional accuracy of the round shape, it is necessary to increase the breadth in rolling by increasing the amount of reduction during round hole rolling, and to expand the recess.

  In consideration of the radius of curvature r of the corner A of the rolled material 1 and each shape of the hole shape, it is desirable to adopt a square hole shape 3 (described later) shown in FIG.

  Even if the next hole mold for introducing the rolled material 1 having a square cross section is changed from the conventional oval to the square hole mold 3 as described above, When the circumferential compressive strain exceeds − (minus) 0.5, surface wrinkles due to deformation occur.

  Therefore, in order not to always generate surface flaws, in addition to controlling the reduction amount by changing the hole shape to a square shape, the raw material is set so that the circumferential compressive strain is -0.5 or more. It is desirable to design a 1 entrance shape and a hole shape.

Note that the circumferential compressive strain ε is a length S ₀ of a curved side of the rolled material surface side of the element e before and after the rolling deformation by the hole 11 of the entry-side rolled material 10 as shown in FIG. , S ₁ is a conventional strain calculated by the following equation.
ε = (S ₁ −S ₀ ) / S ₀

Further, the circumferential compressive strain ε is generally indicated by a negative numerical value because the length S ₁ after rolling deformation is smaller than the length S ₀ before rolling deformation. Therefore, the larger the amount of change from S ₀ to S ₁ , the larger the negative value.

  The above-mentioned “so that the circumferential compressive strain is −0.5 or more” means “so that the compressive strain is a positive value including −0.5, for example, −0.4”. .

  FIG. 7 is an enlarged view of the profile of the next hole shape that reduces the corner of the rolled material 1 having a square cross section. In the figure, the upper right quarter of the hole type is shown enlarged.

  In the figure, a rolled material 1 introduced into the entrance side of the square hole mold 3 has a cross section formed into a square shape, and a curved surface 1a having a radius of curvature r is formed at each corner.

  The square hole mold 3 has a flat groove bottom 3a, and an indentation B comprising a curved surface 3c for reducing the corner A of the rolled material 1 is provided between the groove bottom 3a and the flange 3b. It has been.

  When the radius of curvature of the curved surface 1a in the rolled material 1 is r and the radius of curvature of the curved surface 3c in the indented portion B is R, the profile of the square hole mold 3 is formed so that R> r.

Further, the distance between the intersection b with Anagata center O when was perpendicular to an imaginary line L ₁ with respect to the grooved central axis C from the start point a of the radius of curvature r in the cross section of the rolled material 1 r _x,
If the distance between the intersection d and Anagata center O when the starting point c of the radius of curvature R in the cross section of the pressure part B that are perpendicular to an imaginary line L ₂ with respect to the grooved central axis C and the R _x,
It is preferable that r _x / R _x is 1.3 or less because a significant wear inflection point does not occur.

Moreover, if r _x / R _x is 1.0 or less, the occurrence of wear inflection points can be reliably prevented.

As shown in FIG. 8, when r _x / R _x is in the range of 1.14 to 1.36, it gradually decreases from the center of the hole mold toward the flange side, but when r _x / R _x increases, circumferential compression strain is increased. ε decreases (compressive strain increases) because the larger the value, the closer the rolled material becomes to the oval shape, that is, the roll comes in contact from the corner of the rolled material. A wear inflection point as shown in FIG. 4 appears in the wear profile.

Conversely, if r x _/ R _x is smaller, closer to a variant the rolled material and the roll to continue to contact with the surface, will not occur a difference in variations from r x _/ R _x is more than about 1.2, As a result, the circumferential compressive strain is not changed (see range G in the figure), and the wear inflection point does not appear in the hole-type wear profile.

As described above, in order not to generate surface flaws due to deformation, it is important to prevent wear inflection points from appearing in the hole-type wear profile, and for that purpose, R> r. If the profile of the square hole mold 3 is formed, r _x / R _{x is set} to 1.3 or less, and the circumferential compressive strain is set to a predetermined value, specifically −0.5 or less. I know it ’s good.

Further, as described above, when r _x / R _x is about 1.2 or less, there is no difference in deformation form, and as a result, circumferential compression strain ε does not change, so r _x / R _x is within that range. More desirable.

When r _x / R _x is 1.0 or less, the occurrence of wear inflection points can be reliably prevented.

Since the absolute value of the circumferential compressive strain ε varies depending on the gap of the roll, the area reduction ratio, and the hole shape, the circumferential direction can be set by setting r _x / R _x to 1.3 or less in the hole mold according to the above embodiment. Even if the compressive strain becomes -0.5, the absolute value also changes when the hole type is changed.

  In order to avoid this, it is preferable to be 1.2 or less in which the change in the circumferential compressive strain ε is eliminated. Therefore, even if the hole type (dimension) changes, the wear inflection point does not appear in the wear profile.

Regarding the lower limit of the value of r _x / R _{x, when} the value of r _x / R _x is sufficiently smaller than 1, the relationship between the rolled material 1 and the rolled material 1 ′ after rolling as shown in FIG. Thus, the material is not filled in the curved surface portion of the hole mold after rolling. In order to avoid such a shift in the thrust direction, it is desirable that the lower limit value of r _x / R _{x be} set to about 0.85.

In addition, _if the value of r _x / R _x becomes too small, a large amount of reduction is required in the hole mold in order to properly fill the square hole mold, and the circumferential compressive strain ε increases on the contrary, resulting in surface flaws. It tends to occur.

  Returning to FIG.

  The rolled material 1 is introduced into the entrance side of the square hole mold 3 having the above-described configuration, and the corner of the rolled material 1 is rolled down from the opposite direction by the indented portion B.

  The rolled material 1 squeezed by the indented portion B is further rolled into a round cross section or a square cross section with the next hole mold (not shown).

  In the figure, 1 'shows a cross section of the rolled material after being rolled by the square hole mold 3.

  Next, the influence of the square hole mold 3 having the flat groove bottom 3a on the wear profile and the circumferential strain was investigated.

The hole shape was changed only for R _x (r _x / R _x was 1.14 to 1.36), and the R dimension and the width W of the flange portion were the same.

  FIG. 9 is a graph showing a wear profile obtained based on the strip rolling method of the present invention.

  On the right side from the center of the hole shape, a small inflection point (not a single decreasing trend) is recognized in the wear profile, but on the left side, there is a single decreasing trend in which the amount of wear decreases as it approaches the flange side. It was confirmed that the hole profile of the present invention has a shape suitable for suppressing the amount of wear.

  In the rolling line, the rolled material was rolled by changing the square shape → oval → round pass line to the square shape → box → round pass line.

a. Experimental conditions Rolling temperature: Normal rolling Pore shape: Square shape → Oval, Square shape → Box two levels Circumferential compression strain: All −0.5 or less

b. Judgment Criteria Comparison of surface flaws By adopting a square shape to a box, good rolling without surface flaws became possible until the end of rolling (even when wear progressed).

DESCRIPTION OF SYMBOLS 1 Rolled material 1 'Rolled material after rolling 1a Curved surface 2 Hole type 2a Groove bottom part 2b Curved surface 3 Square hole type 3a Groove bottom part 3b Flange part 3c Curved surface 4 Flat roll 5 Hole type of concave bastard oval A Corner part B Inferior part

Claims (4)

In the rolling method of rolling the bar steel while sequentially reducing the cross-sectional area with a plurality of rolling mills,
The rolled material is molded into a square shape with each corner having a curved surface,
The next hole mold in which the formed rolled material is rolled has a flat groove bottom, and has an indented portion formed of a curved surface that squeezes each corner of the rolled material between the groove bottom and the flange. Then, when the radius of curvature of the corner curved surface of the rolled material is r, and the radius of curvature of the indented curved surface is R, the next hole shape is formed so that R> r,
Introducing the rolled material on the entry side of the next hole mold,
The corner of the rolled material is reduced from the opposite direction by the indented portion,
A method for rolling steel bars, comprising rolling the rolled material reduced by the indented portion into a round cross-section or a square cross-section with the following hole shape. R _x , the distance between the intersection point and the center of the hole shape when the virtual line is orthogonal to the hole center axis from the starting point of the radius of curvature r in the cross section of the rolled material
In the case where R _x is the distance between the intersection point and the hole center when the imaginary line is orthogonal to the hole center axis from the starting point of the radius of curvature R in the cross section of the indentation,
The method for rolling strip according to claim 1, wherein r _x / R _x is 1.3 or less. The method for rolling bar steel according to claim 2, wherein the r _x / R _x is 1.0 or less.   The rolling method of the bar steel according to any one of claims 1 to 3, wherein the cross-sectional area of the rolled material is reduced so that a circumferential compressive strain of the rolled material in the next hole shape becomes -0.5 or more.