JP2658792B2 - Rolling control method for tube elongation mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the rolling of a drawing and rolling mill, particularly a mandrel mill, in the process of manufacturing a seamless steel pipe.

[0002]

2. Description of the Related Art Normally, a seamless steel pipe is pierced at the center of a heated round steel slab using a piercing and rolling mill such as a Mannesmann piercer, and a mandrel mill or the like is inserted by inserting a cored bar into the obtained hollow shell. It is a general manufacturing method to stretch-roll with an elongating rolling machine of No. 1 and finish it into a product having a predetermined outer diameter and thickness with a reducing rolling machine such as a stretch reducer. Stretch reducers, which are most widely used as reduction rolling mills, are usually composed of 8 to 24 stands, and the outer diameter of a raw tube stretched and rolled by a stretching rolling machine such as a mandrel mill is reduced by rolling. The main purpose is to make the diameter constant.

In a stretch reducer, the outer diameter of a pipe is sequentially reduced, and at the same time, the number of roll rotations of adjacent stands is appropriately set, and a slight thickness adjustment is performed by applying a tensile force in the pipe axis direction. However, in the stretch reducer, compared to the steady state in which the pipe is bitten by the entire stand, the pipe is connected to all stands, such as when the pipe tip bites into the mill and when the pipe rear end comes off the mill. In the transient state in which the tube is not bitten, the magnitude of the tensile force acting on the tube in the axial direction of the tube is reduced, so that sufficient tension cannot be applied to the front and rear ends of the tube. Therefore,
The thickness of the drawn and rolled steel pipe in the pipe axis direction is such that the center part is stretched by applying sufficient tension, so that the target wall thickness can be obtained, but the tip and rear ends where the inter-stand tension does not act sufficiently. In such a case, the tension is insufficient, and a pipe end thickening phenomenon that becomes extremely thick as compared with the central portion occurs. Since such a thick portion largely deviates from the target thickness, it is cut off as a crop loss, which is a major obstacle in improving the product yield.

[0004] As a method of reducing the thick portion at the ends of both pipes generated by the stretch reducer, an upper roll and a lower roll are simultaneously symmetrically moved by the same amount with respect to a pass line on a specific stand of a draw rolling mill, and the roll opening degree is reduced. Hydraulic pressure reduction mechanism is provided to control the pressure reduction by the hydraulic pressure reduction mechanism so as to cancel the thickening of the pipe end part that occurs in the next step of the rolling mill at both the time of biting of the pipe and the time of removing the tail. A method of reducing the thickness of this portion (Japanese Patent Publication No. 51-43825), providing a roll having a hole shape that changes in the circumferential direction, and a roll-down amount that changes with the hole shape with rotation is provided. There has been proposed a method (Japanese Patent Laid-Open No. 57-134204) of reducing the thickness of the portion to offset the phenomenon of thickening of the pipe end in the drawing rolling step.

[0005]

SUMMARY OF THE INVENTION The above Japanese Patent Publication No. 51-43.
In the method disclosed in Japanese Patent Application Laid-Open No. 825, it is extremely important that two successive stands control the same position in the axial direction in order to obtain a uniform wall thickness in the circumferential direction of the tube material. By performing the timing management, it is considered that the thickening of the pipe end caused by the stretch reducer is canceled out and the thickness distribution in the pipe axis direction is considered to be uniform, but the rolling reduction of the two stands, that is, the rolling reduction is controlled by the latter-stage rolling stand. In the case, it does not describe in detail how to cope with a variation in the thickness of the flange portion of the second-stage rolling stand roll. Also, the method disclosed in JP-A-57-134204 is
A special hole type roll with a hole shape that changes in the circumferential direction, and the amount of reduction by the hole shape changes with rotation is 90 °.
It is necessary to install the two changed stands at the subsequent stage of the elongation mill, which requires a large capital investment.

An object of the present invention is to provide the above-mentioned JP-B-51-43.
It is an object of the present invention to provide a rolling control method for a draft rolling mill that can suppress unevenness in wall thickness in a pipe end circumferential direction in the method disclosed in Japanese Patent Application Laid-Open No. 825-825.

[0007]

Means for Solving the Problems The present inventors have intensively studied and studied to achieve the above object. As a result, the reduction control pattern in the method disclosed in Japanese Patent Publication No. 51-43825 is different in outer diameter, wall thickness, and material depending on the outer diameter, wall thickness, and material of the stretch reducer. Although a reduction control pattern for reducing the thickness in the elongation rolling mill is set according to the thickness and the material, unlike plate rolling, uniform reduction in the circumferential direction (that is, reduction in thickness) requires at least Two consecutive stands are required. Therefore, for example No. 6 Stand with water at the bottom of the roll groove
A horizontal stand was used to reduce the thickness in the horizontal direction. 7 Star
Vertical at the bottom of the roll groove
As a stand, 6, no. 7 stands around the circumference
If row vomiting uniform wall thickness rolling reduction control countercurrent, No. 6
The thickness was reduced to a predetermined value in the horizontal direction using a stand . 7 Stand to reduce the wall thickness to a predetermined vertical dimension and make the pipe end circumferential
When thinning in a uniform pipe end direction tapered countercurrent, No. 7
The bottom of the roll groove (vertical direction) of the hole-shaped roll in the stand is reduced to a predetermined thickness, but the thickness of the roll flange (horizontal direction) that forms 90 ° with the bottom of the roll groove is reduced due to the tension between stands. I do. For this reason, No. 6
The thinner part at the bottom of the roll groove of the hole-shaped roll of the stand is No. The wall thickness is further reduced at the roll flange portion of the seven stands, and the wall thickness in the circumferential direction of the pipe end becomes uneven. Therefore, by setting the amount of reduction of the stand to be controlled in the preceding stage to be reduced by adding the amount of reduction in thickness of the hole-shaped roll flange generated by the reduction control of the stand to be controlled in the subsequent stage, the wall in the circumferential direction of the pipe end is set. The inventors have sought to suppress the thickness nonuniformity, and have reached the present invention.

That is, according to the present invention, the roll opening is controlled by simultaneously symmetrically moving the upper roll and the lower roll by the same amount with respect to the pass line on a specific stand of a draw rolling mill comprising a plurality of stands provided with a perforated roll. To provide a hydraulic pressure reduction mechanism
The hole shape is tapered to reduce the thickness from the center to the end of the pipe, so as to offset the increase in the thickness of the end of the pipe that occurs in the next step of the rolling mill when the pipe is entrapped and loosened. In a method of controlling roll reduction by the hydraulic reduction mechanism,
The reduction amount of the first-stage reduction control target stand is set to be small by adding the thickness reduction amount of the hole-shaped roll flange portion generated by the reduction control of the second-stage reduction control target stand.

[0009]

According to the present invention, the amount of reduction of the stand to be controlled in the former stage is set to be small by adding the amount of reduction in the thickness of the hole-shaped roll flange generated by the reduction in the stand to be controlled in the latter stage. The reduction in the pipe end wall thickness due to the roll-shaped roll flange part generated by the rolling control of the target stand is compensated for by the reduction amount of the target roll control stand at the preceding stage, and both pipe end crop losses due to uneven wall thickness in the circumferential direction of the pipe end. Can be reduced, and the product yield can be improved.

In the present invention, the roll-down control of the hole-shaped roll of the roll-down control target stand is performed, for example, as described in No. No. 6 stand and No. Assuming that 7 stands are the reduction control target stands, N
o. No. 6 stand and No. The roll spacing of the 7 stands is closed in advance by a predetermined amount of reduction, and the tip of the pipe is no. 5
At the time of being caught in the stand, that is, No. No. 5 set with reference to the load cell ON of 5 stands. No. 6 stand and No. On the basis of the rolling start timing of the 7 stands, No. 6 stand and No. The roll intervals of the seven stands are opened to a predetermined roll interval with a predetermined acceleration. Also, the rear end of the tube is No. No. 4 stand, that is, No. No. 4 set with reference to the load cell OFF of the four stands. No. 6 stand and No. On the basis of the rolling start timing of the 7 stands, No. 6 stand and No. The roll interval of the seven stands is closed with a predetermined acceleration to a predetermined roll interval, and the thickness control of the pipe end tapered thinning is performed.

[0011]

Embodiment 1 Embodiment 1 No. 6 stand and No. No. 7 in which a hydraulic pressure reduction mechanism was provided in the stand No. 7 and the pressure reduction control was performed. 1 to No.
In a mandrel mill consisting of eight stands, a diameter of 158.0 mm with a mandrel bar inserted and a thickness of 6.5 mm
No. tube Tube end 8 with 6-stand hole roll
A thickness reduction control of 2.0 mm was performed for 00 mm, the distance from the pipe end to the rear end of the pipe , the wall thickness of the part rolled down at the bottom of the roll groove of the hole-shaped roll, and the reduction of the roll flange part .
The thickness of the portion not to be measured was measured. The result is shown in FIG.
As shown in Fig. 1, the bottom of the roll groove of a perforated roll is the reduction value.
The thickness is reduced to a predetermined value of 2.0 mm in accordance with
The thickness of the flange portion that was not present was reduced by 0.5 mm.

[0012] The thinning pressure of the hole-shaped roll is set at each of the leading end and the trailing end of the pipe in which the thinning control is performed.
The relationship between the lowered roll groove bottom and the thickness reduction of the flange portion of the hole-shaped roll which was not reduced in thickness was investigated. The result is shown in FIG. FIG. 2 shows a hole-shaped roll having a reduced thickness on the horizontal axis.
Groove bottom thickness reduction (mm) of the portion corresponding to the groove bottom, and vertical axis
Equivalent to the flange of a hole-type roll that does not undergo pressure reduction
The relationship with the flange thickness reduction (mm)
I have. As shown in FIG. 2, hula according to thinning of the groove bottom
And occur thinning of Nji portion, not the tube rear end only, for the tube tip, although small compared to the tube rear end, in accordance with the reduction thinning of the groove bottom portion of the hole-type roll pressure The flange portion which is not used is also reduced in thickness due to the tension between the stands . Therefore, when the pipe end thinning control is performed by two stands from FIGS. 1 and 2, a reduction amount and a reduction pattern according to the thickness reduction pattern of the stretch reducer are set in the mandrel mill subsequent-stage reduction control target stand, In the stand to be controlled in the former stage, if the reduction amount and the reduction pattern are set in consideration of the reduction in the thickness of the hole-shaped roll flange when the reduction in thickness is controlled by the stand in the subsequent stage, the reduction by the stretch reducer is possible. Non-uniform thickness in the peripheral direction can be suppressed.

Example 2 No. 5 stand and No. No. 6 in which a hydraulic pressure reduction mechanism was provided in the 6th stand and the pressure reduction control was performed. 1 to No.
In a mandrel mill consisting of 7 stands, the raw tube in which the mandrel bar was inserted was stretched and rolled to a diameter of 151.0 m.
m, a base tube having a wall thickness of 6.5 mm was drawn and rolled with a stretch reducer to produce a seamless steel tube having an outer diameter of 73.0 mm and a wall thickness of 5.51 mm. In this case, the mandrel mill No. No. 5 stand and No. FIG. 3 and Table 1 show the operation of the hole-shaped rolls during the elongation rolling of the six stands, the reduction control area and the reduction amount of the thinning at the leading and trailing ends of the pipe.

[0014]

[Table 1] When the thickness distribution in the circumferential direction of the end of the obtained seamless steel pipe was measured, the thickness deviation was ± 0.02 mm. For comparison, No. No. 5 stand and No. Table 1 shows the reduction control of thinning at the front and rear ends of the pipes of the six stands.
o. When the test was carried out in the same manner as in the six stands, the wall thickness deviation in the circumferential direction of the pipe end was ± 0.1 mm.

[0016]

As described above, according to the method of the present invention, the thickness control in the circumferential direction of the pipe end in the elongating rolling mill is performed in order to cancel the fluctuation in the thickness in the circumferential direction of the pipe end in the reducing mill. Can be carried out with high precision, and the crop loss due to poor circumferential wall thickness at both ends of the seamless steel pipe is reduced,
Product yield can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a distance from a pipe end and a wall thickness of a rear end of the pipe after reduction control in Example 1.

FIG. 2 is a graph showing a relationship between a roll groove bottom thinning amount and a flange thinning amount after reduction control in Example 1.

FIG. 3 is an operation explanatory view of a hole-shaped roll of a stand to be subjected to a reduction control during elongation rolling in Example 2.

Claims (1)

(57) [Claims] An upper roll and a lower roll are simultaneously symmetrically operated by the same amount with respect to a pass line to control a roll opening degree on a specific stand of a draw rolling mill comprising a plurality of stands provided with a hole-shaped roll. A mechanism is provided to reduce the wall thickness of the pipe end part that occurs in the next step of the rolling mill at the time of biting and trailing of the pipe at the time of biting of the pipe. In the method of controlling the reduction of the hole-shaped roll by the hydraulic reduction mechanism, the reduction amount of the first-stage reduction control target stand is added to the thickness reduction amount of the hole-type roll flange portion generated by the reduction control of the second-stage reduction control target stand. A rolling control method for a tube elongation rolling mill, characterized in that it is set small .