JPH0361521B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to rolling of long steel, and more particularly to a finish rolling method for finish rolling a long steel having a substantially circular cross-sectional shape into a circular cross-section. [Conventional technology and its problems] In the case of long steel rolling, for example, in the case of automotive long steel, the product dimensional accuracy is stipulated by the AISI standard to be within ±1% of the standard product diameter. Strict dimensional accuracy is increasingly required. By the way, conventionally, finishing rolling of long steel generally takes 2 steps.
This is done in pass finishing rolling equipment. For example, when finishing rolling a long steel bar having a substantially circular cross-sectional shape into a circular cross-section, the long steel bar is rolled into an oval cross-sectional shape in the first pass, and then the long steel bar with the oval cross-sectional shape is rolled into the oval cross-sectional shape in the second pass. The final product is rolled in a direction perpendicular to the direction of rolling to obtain a final product with a circular cross section. By the way, since rolling of long steel is a three-dimensional deformation, as mentioned above, the width of the long steel rolled in each pass expands (increase in dimension in the direction perpendicular to the rolling direction). There is a problem in that the width of the product fluctuates as the rolling reduction changes, thereby making the width of the product unstable. In other words, the long steel bar before finish rolling (on the first pass entry side) has dimensional errors (usually standard 3% of the dimensions), this dimensional error causes the reduction amount in the first pass to vary in the longitudinal direction of the bar, resulting in an increase in the width of the bar in the first pass, that is, the width of the bar on the exit side of the first pass. The dimensions become unstable, and as a result, the rolling reduction amount in the second pass also fluctuates, making the product width dimension unstable. At that time, in conventional two-pass finish rolling, the reduction amount in each pass is large as shown below, so the width expansion amount is also large (about 15 to 40% of the normal reduction amount). The variation in the amount of width spread also increases, making it impossible to cope with the severe dimensional constraints described above. That is, in conventional two-pass rolling, the strip is usually separated from the rolls of the first pass by a stripper, and then held under pressure by a roller guide and guided to the second pass. In order to prevent the bar from rotating within the guide, the aspect ratio (major diameter/
(breadth axis) must be made quite large (1.5 to 1.6
degree), thereby necessarily making the first and second passes
The amount of reduction in the pass increases, which is a factor that adversely affects the product width dimension. In addition, in caliber (groove) rolling, as shown in Fig. 5, roll G is provided between rolls R and R, so that the rolling of the bar from caliber K to roll G due to widening is prevented. Due to the need to prevent
Final finishing stand roll R, R caliber K,
A bulge S that bulges outward from the standard profile P with a circular cross section is formed near the roll G of K. However, since the amount of width expansion is large in conventional two-pass rolling, the bulge S is formed in the vicinity of G. Increase part S (Roll G center line L, caliber K, K center O and bulge part S
As a result, the contact area between the calibers K and K and the bar steel is reduced (the bulging part S is caused by a bulge on the side of the bar bar). There is a problem that the shape of the product (which is formed to a size that does not touch the part S) deteriorates. Under such adverse conditions, in order to improve the dimensional accuracy and shape of products as much as possible, conventional controls such as keeping the temperature constant in the longitudinal direction of the long steel and keeping the tension between the stands constant have been carried out. However, such control () requires highly skilled workers and ()
There were many problems such as the work was dangerous, () productivity decreased due to frequent sample checks, and () sufficient dimensional accuracy of the product could not always be obtained. Conventionally, a finish rolling train is composed of three passes, in which the long steel bar is rolled in the same direction with light reduction in the first pass and the second pass, and then in the third pass, the steel bar is rolled in the same direction by the first and second passes. A method has been proposed in which final rolling is carried out in a direction perpendicular to the
85760), in such a method, even if the amount of reduction in each of the first and second passes is small, by repeatedly rolling in the same direction, the amount of reduction in the entire first and second passes becomes considerably large. As a result, variations in the amount of width expansion of the bar steel also increase, making it impossible to obtain sufficient product width dimensional accuracy as with two-pass rolling. By the way, in Japanese Patent Publication No. 58-46363, when the material axis ratio is small (<1.02) (nearly circular),
A failure example has been described in which repeated hard and horizontal rolling was impossible due to twisting at the time of introducing the groove, regardless of the groove axis ratio. This is considered to be because when the cross section of the bar steel is close to circular, the holding force of the bar steel is weak, and the bar steel is suddenly twisted due to biting. [Means for Solving the Problems] In order to solve the above-mentioned problems, in the present invention, a long steel bar with a circular cross-section to be finish rolled is rolled into a circular cross-section by three passes of hard-transverse-hard rolling. In the first pass, the incoming bar is lightly rolled into an oval cross-sectional shape with a diameter in a direction perpendicular to the rolling direction of the first pass, using rolls with a caliber groove dimension slightly smaller than the minimum dimension in the cross section. The cross-sectional dimensions of the bar steel are kept constant over the entire length. The next stage, the second pass, is arranged close to the first pass so that the distance between the rolls is within the range of 1 to 2 times the roll diameter, and the long steel bar rolled in the first pass is rolled in the rolling direction of the first pass. While rolling in the orthogonal direction, the bar on the exit side of the second pass is rolled under light rolling into an oval cross-sectional shape having an aspect ratio of 1.05 to 1.2 and a long axis in the direction orthogonal to the rolling direction of the second pass. , the cross-section of the bar has constant dimensions in one direction over its entire length. In the third pass, which is the next step after the second pass, the roll spacing between the rolls and the second pass is set close to each other within a range of 1 to 2 times the roll diameter, and the long steel bar rolled in the second pass is placed between the input side and the output side. The final finish rolling is carried out under light rolling in the same direction as the rolling direction of the first pass so that the ratio of the diameter dimensions of the long steel is 1.015 to 1.05. Note that the caliber groove dimension is explained by referring to FIG. , K is the distance L between the two points B and C that intersect with the profile P. [Operation] The first pass described above is a pass to remove dimensional fluctuations in one direction (for example, the height direction) of the entrance bar bar cross section. By applying a reduction that is slightly larger than the empirically known maximum dimensional error of the inlet bar, this will make the dimensions of the bar on the exit side of the first pass uniform in the rolling direction, and the Minimize fluctuations in the amount of width expansion of the bar.The second pass is placed close to the first pass to suppress twisting of the bar, and the first pass strictly defines the dimension of the cross section in one direction. This is a pass for aligning the dimensions of the bar in the cross-sectional direction (for example, the width direction) perpendicular to the above-mentioned one direction over the entire length.As mentioned above, the dimension in the width direction (for example, the width direction) of the bar on the exit side of the first pass is Since the dimensional variation in the rolling direction (in the rolling direction) is small, the variation in the rolling reduction amount in the second pass is small, and
Since the amount of reduction in the pass itself is small (the aspect ratio of the bar at the output of the second pass is 1.05 to 1.2), the width of the bar at the output side of the second pass takes a stable value. The third pass suppresses twisting of the bar by placing it close to the second pass, and transforms the bar into a circular cross-section with defined dimensions in two mutually orthogonal directions in the first and second passes. This is the final finish rolling pass. At this time, as mentioned above, since the dimensional variation in the width direction of the bar on the exit side of the second pass (the rolling direction of the third pass) is small, the variation in the rolling reduction amount in the third pass is small, and the rolling reduction amount itself in the third pass is small. is the diameter ratio of the inlet and outlet steel bars, which is small at 1.015 to 1.05.
The width dimension of the final product takes a very stable value. [Effects of the Invention] As explained above, in the present invention, the steel bar is rolled in three passes in which the bar is placed close to each other, each under light rolling in a direction orthogonal to the previous pass, thereby minimizing twisting of the bar. It is possible to stabilize the width dimension of the bar at the exit side of each pass while suppressing the Dimensional accuracy becomes extremely high. In addition, since rolling is performed with light rolling and the rolling force is small and the roll diameter can be reduced, width dimension fluctuations are reduced. Angle α in Figure 5
), so the final pass rolls R, R
The contact area between the rolled steel and the rolled steel bar increases, thereby improving the product shape. [Example] Examples will be described below. 2 and 3 show a finishing rolling equipment 1 for long steel products employing the method of the present invention. This finishing rolling equipment 1 is placed on a bed 9 and has a circular cross section to be finished rolled. Three sets of rolls 2a, 3a,
4a is housed in a relatively compact roll stand unit 5, the first roll 2a and the third roll 4a are housed horizontally, and the second roll 3a is housed vertically and rotatably, respectively. The first roll 2a and the third roll 4a are fixed on a pair of horizontal spindles 2, 4 each supported by pinion stands 6, 7 in a roll stand unit 5, and the spindles 2, 4 are It is connected to a drive motor 10 via a speed reducer 8, and the drive motor 10 drives the first and third rolls 2.
a, 4a are adapted to be rotationally driven. Further, the second roll 3a is fixed on a vertical spindle 3 whose base is accommodated in the vertical roll reducer 11, and the spindle 3 is connected to the vertical roll reducer 1.
1 and a drive motor 10 via a distribution reducer 8, the drive motor 10 drives the second roll 3
a is rotationally driven. In this embodiment, each roll 2a, 3a, 4
a in an integrated roll stand unit 5, and by setting the distance between the first and second rolls 2a, 3a and the distance between the second and third rolls 3a, 4a to be extremely small (respectively, the roll diameter (approximately 1 to 2 times as much), it is possible to prevent twisting of the long steel between the rolls only by the holding force of the long steel of each roll 2a, 3a, 4a. As a result, as described below, the first
By setting the aspect ratio of the bar on the exit side of the second pass to be sufficiently small, it is possible to reduce the dimensional variation of the product by lightly rolling down the bar. Note that it is impossible to make the roll spacing smaller than 1, and if it exceeds 2, the holding force of the rolls will be exceeded and the long steel will be twisted, making effective finish rolling of the long steel impossible. Between the first and second rolls 2a and 3a and between the second and third rolls
Width guides 12 and 13 are provided between the rolls 3a and 4a, respectively, in the traveling direction of the bar steel.
2 and 13 restrict the movement of the bar in a direction perpendicular to the direction of movement of the bar. As illustrated in FIG. 4, the width guides 12 between the first and second rolls 2a, 3a have stripper portions 12a, . . . for separating the bar from the upstream roll. An inlet guide 14 is provided at the upstream end 5a of the roll stand unit 5 in the traveling direction of the bar to guide the long bar to be finish rolled to the first roll 2a, and an inlet guide 14 is provided at the downstream end 5b of the roll stand unit 5 to guide the finished product to the roll stand unit 5. An exit guide 15 is provided for unloading. In FIGS. 1a to d, the first roll 2a is a roll for absorbing fluctuations in the vertical dimension of the entrance bar bar 17a (cross-sectional area: A ₀ ) having a circular cross section; A caliber 18 with an oval cross-sectional shape having a caliber groove dimension slightly smaller than the minimum value is provided, and the first roll 2a is used to roll the long steel 1
By rolling 7a under light reduction, the vertical dimension H ₁ of the bar 17b (cross-sectional area: A ₁ ) on the exit side of the first roll 2a is defined. The second roll 3a has a caliber 19 with an oval cross-sectional shape whose short axis direction coincides with the long axis direction of the caliber 18 of the first roll 2a, and by rolling the bar bar 17b under light pressure with this second roll 3a, , the bar 17c on the exit side of the second roll 3a (cross-sectional area:
A ₂ ) dimension H ₂ in the rolling direction is specified. This second
Aspect ratio of the bar 17c on the exit side of the roll 3a
B ₂ /H ₂ is set in the range of 1.05 to 1.2. The third roll 4a is provided with a generally circular caliber 20 having a bulge as shown in FIG. 5 (not shown in FIG. 1d) near the roll.
By rolling the bar 17c under light pressure, the dimensions and shape of the final product 17d (cross-sectional area: A ₃ ) having a circular cross section are defined. The rolling reduction ratio in this case is set so that the ratio of the diameter of the bar on the inlet side of the first pass to the diameter of the bar on the outlet side of the third pass is 1.015 to 1.05. By using the finishing rolling equipment 1 as described above and rolling according to the method of the present invention, the dimensional error of the final product 17d could be stably kept within ±0.5%. In addition, the amount of area reduction in the second pass (A1−A2)
The ratio of the area reduction amount (A2-A3) in the third pass is preferably set to about 6:4 from the viewpoint of minimizing the reduction amount in the final pass. Here, the results of comparing various features of conventional two-pass rolling and three-pass rolling according to the present invention are shown in the table on the next page.

[Table] In the above embodiment, the first and third rolls 2
a, 4a are oriented horizontally, and the second roll 3a is oriented vertically, but the orientation of each roll 2a to 4a is not limited thereto, and the roll of each pass is oriented in a direction perpendicular to the roll of the previous pass. It is sufficient.

[Brief explanation of drawings]

Figures 1 a to d are cross-sectional views showing the bar before finishing rolling and after being rolled by the first to third rolls, respectively;
The figure is a partially cutaway plan view of the finishing rolling equipment according to the present invention, FIG. 3 is a front view taken in the direction of the arrow in FIG. 2, FIG. 4 is a partially enlarged sectional view taken along the - line in FIG. FIG. 3 is an enlarged cross-sectional view of the final finishing roll. 17a to 17d: Bar steel.

Claims (1)

[Scope of Claims] 1. A precision rolling method for a long steel bar, in which a long steel bar having a substantially circular cross-sectional shape to be finish rolled is rolled into a circular cross-sectional shape with good dimensional accuracy through three passes of rolling, the method comprising: Using rolls with a caliber groove dimension slightly smaller than the minimum dimension in the cross section, rolling is performed under light rolling to an oval cross-sectional shape with a major axis in a direction perpendicular to the rolling direction of the first pass, and the roll spacing from the first pass is reduced. In the second pass, which is set within a range of 1 to 2 times the roll diameter, the bar rolled in the first pass is rolled in a direction perpendicular to the rolling direction of the first pass, and the bar on the exit side of the second pass is rolled. It is rolled under light rolling into an oval cross-sectional shape with an aspect ratio of 1.05 to 1.2 and a long axis in the direction perpendicular to the rolling direction of the second pass, and the roll interval between the second pass and the second pass is 1 to 2 times the roll diameter. In the third pass, which was set in the range of A precision rolling method for long steel, characterized in that final finish rolling is performed under light reduction.