JP4871250B2 - Strip rolling method - Google Patents

Description

  The present invention is a rolling roll which is a pair of rolling stands arranged in a plurality of rows at a predetermined interval, and the rolled material is rolled while being divided into a plurality of passes and sequentially changing the rolling direction. The present invention relates to a method for rolling a bar steel, which sequentially reduces the cross-sectional area to finish a bar steel such as a wire rod, a bar steel, a square bar having a predetermined product size.

  It is necessary to ensure that the surface flaws are within an allowable range in the steel bars such as wire rods, bar steels, and square bars manufactured by hot rolling or the like. This is because, if surface flaws exceeding the allowable range remain in the bar steel, for example, processing defects such as cracks starting from the surface flaws may occur in the subsequent forging process in the so-called secondary processing step. It is. The surface flaws that cause problems often occur at the tail end and tip end of the rolled material, and the incidence at the tail end is particularly high. In the case of wire rods shipped as a coil, it is difficult to inspect the full length of the product, so investigate the tail end and the end sample of the tip, and if there is a problem surface flaw, Until the surface flaws disappeared, the edges were cut and removed, which involved very laborious inspection and removal work.

  As a method of reducing the surface flaws of the strip steel, there is an invention described in Patent Document 1 that the inventors previously invented. The present invention finds that the cause of surface flaws occurring in the bar steel is local circumferential compressive strain in each pass at the time of manufacturing, and controls the value of this compressive strain by optimizing the rolling conditions. Invention. By implementing this invention, it has become possible to significantly reduce the occurrence of surface flaws that are a problem, particularly in the middle part of the bar steel, but it is possible to reduce the surface flaws generated at the tail end and the tip part of the bar steel. I couldn't say that I was able to do it.

  The inventors investigated the cause of the occurrence of surface flaws particularly at the tail end and tip end of the strip. At the time of rolling with the rolling roll 1, unlike the intermediate portion (also referred to as a steady region) of the rolled material 2 as shown in FIG. 11, the tail end portion and the tip portion of the rolled material 2 are shown in FIGS. 9 and 10. As described above, since the material (rolled material 2) does not exist on the upstream side or downstream side in the roll bite during rolling with the rolling roll 1, the width of the rolled material 2 by rolling with the rolling roll 1 is expanded from other parts. (For this reason, the tail end and the tip end are referred to as unsteady regions). Rolling the expanded part in the next pass while changing the rolling direction (in steel rolling, the rolling direction is often changed by 90 degrees for each pass) may cause surface flaws. This investigation revealed it.

  Since the length of the widened part (unsteady region) is about the length of the projected contact length, it seems to be short when only one pass is considered. For example, a 155 mm square rolled material When 2 is a wire of φ5.5 mm in 30 passes, as shown in Table 1, the length of the unsteady region in the first pass is 800 when the rolling of the 30th pass, which is the final pass, is completed. The length becomes more than double, and a surface flaw that becomes a problem over the length is generated.

  Below, the generation | occurrence | production mechanism of the surface flaw in the tail end part and front-end | tip part of a bar steel is demonstrated. In the case of strip rolling, when only the first pass is considered, the width dimension of the rolled material 2 after rolling increases for both the tail end portion and the tip end portion. On the other hand, the thickness dimension (dimension in the rolling direction) decreases at the tip. The reason why the thickness dimension of the tip portion decreases is that, as shown in FIGS. 12 and 13, the material center portion when viewed in the cross section is extended forward from the other portions. On the other hand, the tail end portion is in a state opposite to the tip portion, and the material center portion is recessed, so that there is almost no increase or decrease in the thickness dimension.

  Next, considering the second pass, since the 90-degree reduction direction is generally shifted in the second pass, the width direction in the first pass is the reduction direction in the second pass. Therefore, the free surface of the tail end portion and the tip end portion projecting on both sides in the first pass is pressed down by the rolling of the rolling roll 1 in the second pass, and is in a folded state. This folding is the cause of surface flaws. The width dimension after rolling of the rolled material 2 in the second pass increases in the tail end portion in the same manner as in the first pass, but the size in the reduction direction in the first pass decreases at the tip end portion. By offsetting the amount, the increase in the width dimension is almost eliminated, or even if it is increased, the increase is smaller than the tail end. Even after the third pass, the width dimension further increases at the tail end as in the description of the second pass. Since the width dimension increases in each pass by the mechanism as described above, it can be estimated that the generation of surface defects at the tail end is greater than the generation of surface defects at the tip.

  As a means for solving this problem, a cutting device for cutting the tail end or tip end of the rolled material 2 is installed at a plurality of locations on the rolling line of the bar steel, but the dimensions actually cut are The current situation is that the number of surface defects has not been solved. Although it is considered that this problem can be solved by increasing the cutting length, the yield is naturally reduced, and a new problem occurs.

  Further, Patent Document 2 discloses that when a driven horizontal roll, a roll with a caliber for rolling in the driven width direction is arranged on the entry and exit sides, and the width rolling of the rivet roll with a caliber is performed, the width In a hot reversible rolling process in which a local plate thickness increasing portion generated by directional rolling is horizontally reduced, and width direction rolling is repeated again, a local plate thickness increasing portion is generated by width rolling of a metal slab with a roll. Is further increased by rolling in the reverse direction width of the heel roll, hot rolling oil is applied to the inlet caliber side wall of the heel roll in contact with the increased local plate thickness increasing portion, and the outlet caliber side wall portion is A method for hot width rolling of a metal slab characterized by grinding with a roll grinding wheel is disclosed.

  However, the rolling method described in Patent Document 2 is intended to reduce linear wrinkles due to the transfer of the rough surface of the roll to the material. By combining a grinding means with oil rolling, an excellent rough surface of the roll is obtained. The prevention effect is obtained. Therefore, from this rolling method, it is impossible to achieve the operational effect peculiar to the present invention to reduce surface flaws generated by pressing down the tail end and the tip with increased width dimensions in the next pass. It is believed that there is. Moreover, in the rolling method described in Patent Document 2, hot rolling oil (lubricating oil) is applied to the inlet caliber side wall, but since the purpose is to prevent roughening of the roll, the lubricating oil is used in the rolling process. Among them, it is considered that the oil is always supplied continuously, and there is a problem that it is necessary to supply a very large amount of lubricating oil.

  When the technique of constantly supplying the lubricating oil described in Patent Document 2 is applied to the conventional technique of the present invention, it is possible to reduce the increase in the width dimension of the unsteady region such as the tail end and the tip. At the same time, the width of the steady region is reduced (see ○ in FIG. 6), and as a result, the rolled material after rolling cannot be made substantially the same width over the entire length. To do.

JP 2007-90429 A JP-A 63-2502

  The present invention was made as a solution to the above-described conventional problems, and the surface generated by pressing the tail end and the tip increased in width by pressing the rolling roll with the rolling roll of the next pass. It is an object of the present invention to provide a method for rolling steel bars that can reduce wrinkles and does not reduce yield.

  The method of rolling a steel bar according to claim 1 is a rolling roll which is a pair of rolling stands arranged in a plurality of rows at a predetermined interval, and the rolled material is rolled while being divided into a plurality of passes and sequentially changing the rolling direction. By this, it is a rolling method of the strip steel to finish the predetermined product dimensions by sequentially reducing the cross-sectional area of the rolled material, only when rolling the tail end portion and / or the tip portion of the rolled material in each pass, A lubricant is supplied between the surface of the rolling roll and the surface of the rolled material, and the tail end portion and / or the front end portion of the rolled material is rolled.

  According to a second aspect of the present invention, the region for supplying the lubricant is a region corresponding to the projected contact length in each pass.

Furthermore, the rolling method of the strip according to claim 3 is the rolling in which a plurality of rows are arranged when the length from the tail edge and / or the edge of the tip of the final product where surface flaws occur is α ′. Among the stands, the rolling stand that supplies the lubricant is each rolling stand that satisfies the following formula.
α ′ ≧ A0 / A ′ × Ld
In the above equation, A0 is the cross-sectional area of the rolled material on the entry side of the rolling stand, A ′ is the cross-sectional area of the final product (steel bar), and Ld is the projected contact length of the rolling stand.

  According to the rolling method of the bar steel according to claim 1 of the present invention, the surface flaw generated by pressing the tail end portion and the tip end portion whose width dimension is increased by rolling the rolling roll with the rolling roll of the next pass. Can be reduced. Further, since it is not necessary to cut a very long tail end or tip end where surface flaws have occurred, it is possible to prevent a decrease in yield.

  According to the method for rolling steel bars according to claim 2 of the present invention, the supply amount of the lubricant can be set within a range in which an error due to the adjustment of the roll gap can be absorbed, and the necessary amount of the lubricant is reliably used without waste. be able to.

  According to the method for rolling strip according to claim 3 of the present invention, even if surface flaws occur, the surface flaw occurrence region can be set to the minimum necessary length that does not cause yield reduction. The number of rolling stands for supplying the lubricant can be limited to the minimum necessary rolling stands.

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

  As a method that can reduce the occurrence of surface flaws at the tail end and the tip of the steel bar without causing a reduction in yield and rolling stability, and without incurring a large cost, the inventors, A method of supplying the lubricant 3 between the surface of the rolling roll 1 and the surface of the rolled material 2 during rolling was invented. 1 shows a state in which the tail end portion of the rolled material 2 is rolled by the rolling roll 1, and FIG. 2 shows a state in which the tip portion of the rolled material 2 is rolled by the rolling roll 1. As described above, the tail end and the tip end are referred to as unsteady regions. FIG. 3 shows a state where the intermediate part of the rolled material 2 is rolled by the rolling roll 1. The intermediate portion of the rolled material 2 is referred to as a steady region. In addition, although each drawing has shown only the upper half of the rolling material 2 rolled with the rolling roll 1 for convenience, the lower half of the rolling material 2 is also axisymmetric and the same shape, Rolled with a pair of rolling rolls 1.

  In order to confirm the effect of this rolling method, rolling by the rolling roll 1 was performed in one pass of an angle-oval (ellipse), and the amount of variation in the width dimension of the rolled material 2 was confirmed. In addition, a corner | angular and an oval are the hole types formed in the surface of each rolling roll 1, and show a cross-sectional shape.

  First, a preliminary experiment was performed, and the fluctuation of the width dimension in the steady region and the unsteady region of the rolled material 2 was confirmed. The experimental conditions of this preliminary experiment are shown in FIG. 4, and the experimental results are shown in FIG. The right vertical sectional view shown in FIG. 4 is an enlarged vertical sectional view of a main part of the rolling roll 1 and shows an oval hole type. The vertical axis shown in FIG. 5 indicates the width dimension of the rolled material 2, and the horizontal axis indicates the concentration of the lubricant 3 to be supplied. ○ is the measured value of the middle part of the rolled material 2, that is, the steady region, and ● is the measured value of the tail end of the rolled material 2, ie, the unsteady region. In this experiment, a general hot-rolling jet type liquid lubricant was used as the lubricant 3, but a solid lubricant applied to the rolling roll 1 such as grease can also be used. In any case, since it is used at a high temperature, it will volatilize or burn out after rolling in one pass. In this experiment, rolling was performed only for one pass. However, when rolling is performed in the next pass and the lubricant is used, the lubricant 3 is supplied again in the next pass.

  From FIG. 5, it was confirmed that as the concentration (mass%) of the lubricant 3 increases, the width dimension of the rolled material 2 does not increase but decreases. It was also confirmed that the width dimension of the unsteady region was larger than the width dimension of the steady region under the same concentration (mass%) of the lubricant 3. When the lubricant 3 is not supplied to the steady region (no lubrication), the width of the steady region after rolling is 26.0 mm, but the width of the unsteady region is 26.0 mm which is the same as the width of the steady region. In order to achieve this, it can be seen from FIG. 5 that the concentration of the lubricant 3 should be 0.05 mass%.

  Therefore, in this experiment, when the concentration of the lubricant 3 to be supplied is fixed to 0.05% by mass and the lubricant 3 is not supplied over the entire length of the rolled material 2 (indicated by Δ), When the lubricant 3 was supplied over the entire length (indicated by a circle), and the lubricant 3 was supplied only to the tail end of the rolled material 2 (indicated by a circle), the experiment was performed, The change in width dimension was measured. The measurement results are shown in FIG. The horizontal axis of this FIG. 6 shows the length (unit: mm) from the edge of the tail end part of the rolled material 2, and the vertical axis shows the width dimension (unit: mm) of the rolled material 2, respectively. In addition, when supplying the lubricant 3 only to the tail end portion, the projected contact length was obtained from a sample during rolling in the experiment, and the lubricant 3 was supplied for the projected contact length (30 mm). The projected contact length is also called a projected contact length, and is a length obtained by projecting a range (contact arc) where the rolling roll 1 is in contact with the rolled material 2 during rolling onto the X axis (axis in the rolling direction). Show.

  When the lubricant 3 is not supplied over the entire length of the rolled material 2 (indicated by Δ) and the case where the lubricant 3 is supplied over the entire length of the rolled material 2 (indicated by ○), the lubricant When 3 is supplied, it can be seen that the width dimension of the rolled material 2 decreases in both the steady region (intermediate portion) and the unsteady region (tail end portion). In contrast, when the lubricant 3 is supplied only to the tail end portion of the rolled material 2 (indicated by ●), and when the lubricant 3 is not supplied over the entire length of the rolled material 2 (indicated by Δ). In comparison, when the lubricant 3 is supplied only to the tail end portion, the width dimension of only the unsteady region (tail end portion) as a problem is reduced, and the width dimension of the steady region (intermediate portion) is not changed. It can be seen that the width is substantially the same over the entire length.

  From the above experimental results, it is possible to reduce the width of the rolled material 2 by supplying the lubricant 3, but by supplying the lubricant 3 only to the unsteady region, the rolled material 2 after rolling can be reduced. It turned out that it can be made into the substantially same width over the full length. Further, compared to the case where the lubricant 3 is supplied over the entire length of the rolled material 2, the supply region of the lubricant 3 is a little as long as the length of the unsteady region. Can be reduced.

  In an actual machine, the projection contact length in each rolling stand is calculated | required beforehand, and it can respond by making the area | region corresponded to the projection contact length into the area | region (length) which supplies the lubricant 3. FIG. In addition, it is thought that the appropriate area | region which supplies the lubricant 3 changes a little by adjustment of a roll gap. The region corresponding to the projection contact length described in the present invention does not necessarily indicate the length of the projection contact length itself, but is in a range of 1.0 to 1.3 times the projection contact length depending on the roll gap. fluctuate. In an actual machine, it is desirable to set the area as 1.1 to 1.3 times the projection contact length in consideration of the margin.

Example 1
In Example 1, the increase in the width dimension of the unsteady region was confirmed to cause surface flaws, and the minimum number of rolling stands required to supply the lubricant was verified by actual machine experiments. . In Example 1, a 155 mm square material (rolled material) of SCM435 was used and rolled with a rolling roll provided on a rolling stand until it became a φ5.5 mm wire. The number of rolling stands is 32 in total, and the wire speed is 100 m / s.

Assuming that the cross-sectional area of the rolling material on the entry side at each rolling stand is A0, the cross-sectional area of the final product (wire) is A ', and the projected contact length of each rolling stand is Ld, The relationship between the cross-sectional area of the rolled material on the side and the converted length α of the tail end in the final product when the lubricant is supplied to the target stand can be expressed.
A0 × Ld = A ′ × α
α = A0 / A ′ × Ld

  Figure shows the relationship between the cross-sectional area of the rolled material on each roll stand entry side in the pass schedule used in this actual machine experiment and the converted length (calculated value) α of the tail end of the final product in each cross-sectional area 7 shows. In order to avoid the influence due to the increase in the width of the tail end, if the converted length α of the tail end in the final product is 8 m or less (less than 2 windings of the wound coil), It can be seen that the lubricant may be supplied from 1 stand to 8 stands. ([Alpha] at 8 stands is about 10 m, and if lubricant is supplied up to 8 stands, [alpha] at 9 stands is calculated to be 6.85 m.)

  Next, in order to confirm that this hypothesis was actually correct, an actual machine experiment was conducted under each condition shown in Table 2. From the converted length (calculated value) α of the tail end calculated from each cross-sectional area, and from the edge of the tail end where surface flaws of 0.01 mm or more occurred in the final product manufactured by rolling in an actual machine experiment FIG. 8 shows the relationship with the length of. The calculated value α is almost equal to the confirmation result in the actual machine experiment. By supplying the lubricant up to 8 stands, it is the final product when no lubricant is applied, and the length from the edge of the tail end part. It was possible to reduce the generation area of surface flaws having a depth of 0.01 mm or more generated up to about 60 m to a target value of 8 m or less.

  Therefore, the rolling stand that supplies the lubricant among the rolling stands arranged in a plurality of rows, when the length from the tail end portion or the end edge of the end portion of the final product in which surface flaws occur is α ′, It can be said that this is a rolling stand that satisfies the mathematical formula ≧ A0 / A ′ × Ld.

  According to FIG. 8, the confirmation result in the actual machine experiment tends to be slightly shorter than the calculated value α in the upstream stands (A to D), but this is because the number of downstream stands increases as the number of upstream stands increases. Therefore, it is considered that the material is stretched by rolling at a subsequent rolling stand, the depth of the surface defects is reduced, and there is an influence of scale-off.

(Example 2)
Next, in Example 2, an actual machine experiment was performed in order to confirm the effect when the lubricant was supplied not only to the tail end portion but also to the tip end portion of the rolled material. In Example 2, similarly to Example 1, a 155 mm square material (rolled material) of SCM435 was used and rolled with a rolling roll provided on a rolling stand until it became a φ5.5 mm wire. The number of rolling stands is 32 in total, and the wire speed is 100 m / s.

  Further, in this actual machine experiment, when the lubricant was not lubricated over the entire length of the rolled material (comparative example), when the lubricant was supplied only to the tail end portion of the rolled material (Invention example 1), the tail end portion and the tip end of the rolled material The experiment was conducted under three conditions when the lubricant was supplied to the part (Invention Example 2). Based on the experimental results of Example 1, the number of rolling stands to which the lubricant was supplied in all three conditions was from 1 to 8 stands.

  The surface flaws are evaluated by removing samples at the tail end and the tip excluding the length that is usually discarded for reasons such as the material (in this experiment, two turns of the coil = target value in Example 1). = 10 samples were taken and evaluated by checking the cross section with an optical microscope. If no surface defects with a depth of 0.01 mm or more are recognized, pass with ◎, if no surface defects with a depth of 0.02 mm or more are accepted, pass with ○, and surface defects with a depth of 0.02 mm or more are 1 Those that could be confirmed at some locations were evaluated as failing with ×. Table 3 shows the evaluation results of the experiment. In addition, if there was no surface flaw of 0.02 mm or more in depth, it was accepted as “good” if the surface flaw of such a depth was used as the starting point in the subsequent secondary processing step. This is because processing defects such as cracks do not occur.

  From Table 3, in the comparative example, the evaluation of the unsteady region is ○ at the tip portion and × at the tail end portion, whereas in Invention Example 1 in which the lubricant is supplied to the tail end portion, the tail end portion is evaluated. The evaluation is ◎ which is equivalent to the middle part which is a steady region. Further, in Invention Example 2 in which the lubricant is supplied to the tip portion in addition to the tail end portion, the evaluation of the tip portion is ◎ equivalent to that of the intermediate portion. As described above, by supplying the lubricant during rolling to the unsteady regions such as the tip and tail, it is possible to eliminate the occurrence of surface defects having a depth of 0.01 mm or more, as in the steady region. It could be confirmed.

It is a side view which shows one Embodiment of this invention and shows the state which rolls the tail end part of a rolling material with a rolling roll. It is a side view which shows the same embodiment and shows the state which rolls the front-end | tip part of a rolling material with a rolling roll. It is a side view which shows the same embodiment and shows the state which rolls the intermediate part of a rolling material with a rolling roll. (A) is explanatory drawing which shows the experimental condition for confirming the fluctuation | variation of the width dimension in the stationary region of a rolling material, and a non-stationary region, (b) is a principal part expanded longitudinal sectional view which shows the rolling roll used for the experiment. It is. It is explanatory drawing which shows the relationship between the density | concentration of the lubricant to supply, and the width dimension of the rolling material which supplied the lubricant and rolled. It is explanatory drawing which shows the change of the width dimension of a rolling material at the time of rolling by changing the supply conditions of a lubricant. It is explanatory drawing which shows the relationship between the cross-sectional area of the rolling material in each rolling stand entering side, and the conversion length (alpha) of the tail end part in the final product in each cross-sectional area. Converted length α of the tail end calculated from the cross-sectional area of the rolled material on the rolling stand entry side, and the tail end where surface flaws of 0.01 mm depth or more occurred in the final product manufactured by rolling in an actual machine experiment It is explanatory drawing which shows the relationship with the length from the edge of a part. It is a side view which shows a state which shows background art and rolls the tail end part of a rolling material with a rolling roll. It is a side view which shows background art and shows the state which rolls the front-end | tip part of a rolling material with a rolling roll. It is a side view which shows a state which shows background art and rolls the intermediate part of a rolling material with a rolling roll. It is an analysis result figure of the 1/4 model which shows the deformation behavior of the tip part of the rolling material at the time of rolling with a rolling roll. The deformation | transformation state of the front-end | tip part of the rolling material at the time of rolling with a rolling roll is shown, (a) is a top view, (b) is a side view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Roll roll 2 ... Rolled material 3 ... Lubricant

Claims (3)

By rolling the rolled material into a plurality of passes and sequentially rolling the rolling material while changing the rolling direction with a rolling roll that is a pair of rolling stands arranged in a plurality of rows at predetermined intervals, the cross-sectional area of the rolled material is sequentially changed. A method of rolling a strip that reduces to finish to a predetermined product dimension,
Only when rolling the tail end and / or tip of the rolled material in each pass, a lubricant is supplied between the surface of the rolling roll and the surface of the rolled material, and the tail end of the rolled material. And / or the rolling method of the bar steel characterized by rolling a front-end | tip part.   2. The method for rolling steel bars according to claim 1, wherein the region to which the lubricant is supplied is a region corresponding to a projected contact length in each pass. When the length from the tail edge and / or the edge of the tip of the final product where surface flaws occur is α ′,
The rolling method according to claim 1 or 2, wherein among the rolling stands arranged in a plurality of rows, the rolling stand that supplies the lubricant is each rolling stand that satisfies the following formula.
α ′ ≧ A0 / A ′ × Ld
In the above equation, A0 is the cross-sectional area of the rolled material on the entry side of the rolling stand, A ′ is the cross-sectional area of the final product (steel bar), and Ld is the projected contact length of the rolling stand.

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