JP2697144B2 - Rolling method of seamless pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a rolling mill using a piercing machine widely used in a Mannesmann pipe manufacturing method which is a typical manufacturing method of a seamless metal pipe. It relates to a rolling method.

[Conventional technology]

In general, a seamless metal pipe manufactured by the Mannesmann pipe method is to first pass a round steel slab, which is a material to be rolled, through a piercer, press a plug into the center of the pierce to make a hole, and pierce to obtain a hollow shell. If necessary, the hollow shell is passed through an elongator, expanded and rolled, then further rolled, for example, with a plug mill, and then refined, shaped, and sized with a reeler and sizer, and manufactured through a refinement process Have been.

By the way, in the above-mentioned piercer and elongator, a so-called inclined rolling machine in which a plug is combined with, for example, a barrel-shaped rolling roll (hereinafter referred to as an inclined roll) in which an axis is inclined with respect to a round steel piece or a hollow shell path sensor is used. Can be For example, as for the piercer, as shown in FIG.
A pair of gorge portions 11 having a maximum diameter in the middle of the axial direction, and a frustoconical entrance surface 12 and an exit surface 13 on both sides of the gorge portion 11, each having a truncated cone whose diameter is gradually reduced toward the terminal. The inclined rolls 1l, 1r, and a rolling section 21, which has a warhead shape as a whole and has a substantially conical shape from the front end side, is subsequently reduced in diameter toward a reeling section 22 having a substantially frustoconical shape, and a base end. The two inclined rolls 11 and 1r are provided on both sides of the path center of the round steel piece B with their axis lines parallel to the path center in plan view, respectively. In side view, one of the inclined rolls 11 is disposed so as to be inclined with respect to the path center such that the tip of the entrance surface 12 faces upward, and the other inclined roll 1r is disposed to be inclined with respect to the path center. Is installed with its axis centered on the path center. .

When the heated round bar B is transported in the axial direction as shown by the white arrow, the entrance surfaces 12, 12 of the two inclined rolls 11 and 1r are moved.
The round piece B is rotated around the axis by the two inclined rolls 11 and 1r, and the plug 2 is inserted into the center of the round steel piece B. The round piece B is pierced and rolled by the inclined rolls 11 and 1r and the plug 2. It has become so.

Using commonly piercer using inclined rolls, the case of producing a hollow shell from round steel piece, the tip draft ratio (the billet radius r shortest distance r ₁ from Pasusenta in the plug tip to the roll peripheral surface with respect to ₀ diameter reduction ( When the percentage of r ₀ −r ₁ ) is increased, a hole (fissure) is generated at the center of the round steel piece B being drilled as shown in FIG. The inner surface of the perforated hollow shell may have flaws. FIG. 3 is a graph showing the relationship between cracks generated by Mannesmann fracture and the roll inclination angle. The abscissa indicates the tip draft rate, and the ordinate indicates the perforation temperature. Black circles indicate the occurrence, and white circles indicate no Mannesmann destruction.

However, free-cutting steel (AISI standard 12L14) was used as the test material, and other conditions included a piercing ratio of 2.8, an inclination angle of 12 °, a piercing temperature of 1100 ° C to 1200 ° C, a pipe expansion ratio of 3%, and a piercing material diameter of 60 mm.
The gorge diameter of the roll was 350 mm.

As is clear from FIG. 3, the Mannesmann destruction can be suppressed by reducing the tip draft rate. However, in order to reduce the tip draft rate, it is necessary to increase the roll opening and the plug advance amount, which is the length of the plug tip projecting from the gorge portion toward the inlet surface. When the roll opening and the plug advance amount are increased as described above, the contact area between the roll and the billet is reduced, so that the propulsive force given by the roll required for rotation and advancement of the billet is reduced.

In particular, at the time of unsteady rolling, the thrust for advancing the material is insufficient due to the reduction of the contact area between the roll and the material at the time of unrolling, and the bottom part is poorly engaged with the round bar. In some cases, a defect in the butt end (peeling-off) may occur, leading to a stoppage of rolling.

In such piercers, the rollable condition and the condition that does not cause flaws in the tube are considered in consideration of the biting property of the perforated material when biting into the roll and the trailing edge when separating from the roll. There is a method in which the amount and the guide shoe interval are determined based on an arithmetic expression and piercing rolling is performed (Japanese Patent Publication No. 59-44927). In addition, there is a method of improving both the biting property and the quality by changing the roll opening or the roll inclination angle during rolling (Japanese Patent Laid-Open No. 62-282713).

[Problems to be solved by the invention]

The propulsive force applied from the roll to the material to be rolled is larger at the intermediate portion in the axial direction of the perforated material in the axial length direction than at the front end portion, and at the intermediate portion, the draft ratio at the front end is lower than that at the top and bottom portions in order to suppress Mannesmann destruction. It is possible to make it smaller.

However, in the method for determining the rolling conditions based on the above-described arithmetic expression, the rolling conditions are determined in consideration of the biting property and the trailing edge, and the same rolling condition is applied to the intermediate portion of the material as the both end portions. Therefore, there is a problem that the tip draft ratio in the intermediate portion cannot be reduced. In the method of changing the roll opening or the roll inclination angle during rolling described above, when the roll opening is changed alone, the thickness of the tube after rolling changes before and after the change, and extends in the longitudinal direction of the tube. There is a possibility that dimensional accuracy may be poor.

Therefore, the present inventor repeated various experiments to find a method of changing the tip draft rate without changing the thickness of the material to be rolled. It has been found that the tip draft rate can be changed without changing. That is, the present invention simultaneously changes the inclined roll opening and the plug advanced amount, and suppresses the inner surface flaws of the material to be rolled by making the draft rate of the middle portion of the material to be rolled smaller than that of the top and bottom portions. It is an object of the present invention to provide a seamless pipe rolling method in which the wall thickness is kept constant.

[Means for solving the problem]

In the seamless pipe rolling method according to the present invention, a plug is penetrated along the axial direction while the material to be rolled is moved in the axial direction using an inclined roll, and the material to be rolled is pierced and rolled. In the process, the tip roll draft and the plug advance amount are set such that the tip draft rate of the plug at the time of the intermediate portion rolling of the material to be rolled is smaller than the tip draft rate at the time of rolling at the top portion and the bottom portion of the material to be rolled. And rolling at the same time without changing the thickness of the material to be rolled.

[Action]

In the present invention, the plug advance amount and the inclined roll are changed so as to cancel the thickness variation phenomenon of the material to be rolled due to the change in the plug advance amount and the thickness variation phenomenon of the rolled material due to the change in the inclined roll opening. The tip draft ratio of the plug is changed without changing the wall thickness by changing the opening.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments. FIG. 1 is a schematic block diagram showing a configuration of a piercing mill used for carrying out a seamless pipe rolling method according to the present invention.

In the figure, reference numerals 11 and 1r denote inclined rolls whose axes are inclined in different directions with respect to the path center XX. The inclined rolls 11 and 1r are provided with a gorge portion 11 at the center in the axial length direction and an angle θ ₁ with the path center XX of the round piece B on both sides of the gorge portion 11.
And an exit surface 13 which forms an angle θ ₂ with the path center XX, and has a barrel shape as a whole. Inclined roll 1
The roll opening degree, which is the roll interval of l, 1r, can be adjusted by the first automatic positioning devices 61, 61.

In addition, a mandrel bar M having a plug 2 at the tip is disposed between the two inclined rolls 11 and 1r. The plug 2 has a warp-shaped rolling section 21 at the tip thereof and the rolling section 21.
A reeling part 22 having a substantially frustoconical shape that is enlarged as it reaches the large diameter part of 21, and a relief part whose one end is in contact with the large diameter end of the reeling part 22 and whose diameter is reduced toward the terminal. twenty three
And At the rear end of the mandrel bar M, there is provided a thrust block 4 for moving the mandrel bar M to move the plug 2 in the axial direction. The thrust block 4 is actuated by the second automatic positioning device 62, whereby the plug advance amount Ld, which is the length of the plug 2 projecting from the gorge portions 11, 11 in the direction of the inlet surface 12, is appropriately adjusted. .

Load cells 3, 3, 3, 3 for detecting the load applied to the inclined rolls 1 l, 1 r on the entrance side and the exit side of the inclined rolls 1 l, 1 r.
Are provided, and the outputs of the load cells 3, 3, 3, 3 are given to the arithmetic and control unit 5. The arithmetic and control unit 5 includes a load cell 3,
In addition to the outputs 3, 3, and 3, the output of the timer setting device 8 for setting the timing at which the roll opening of the inclined rolls 11 and 1r and the plug advanced amount Ld of the plug 2 should be changed is given. The output of the tip draft rate setting device 7 for setting the tip draft rates of both end portions of the perforated material to be changed and the intermediate portion therebetween is provided. Then, the output of the arithmetic and control unit 5 is supplied to the first automatic positioning devices 61, 61 and the second automatic positioning device 62.

Next, a method of performing piercing and rolling by the apparatus configured as described above will be described.

First, before the round slab B is bitten into the inclined rolls 1l and 1r, the initial value of the tip draft rate that does not cause the bite of the round slab B to fail, and the central portion of the round slab B in the axial direction after the start of drilling. Then, the set value of the leading draft rate changed at the bottom portion is set in the leading draft rate setting device 7.

Next, in the roll state setting device 9, the inclined rolls 1l, 1r
In the roll state setting device 9 so that the initial value of the tip draft ratio is realized and the thickness of the round portion B after drilling the top portion becomes a desired value. Initial values of the opening degree Rg and the plug advanced amount Ld are set. This initial value is read into the arithmetic and control unit 5, and the inclination angles of the inclined rolls 11 and 1r are calculated by the operations of the first automatic positioning devices 61 and 61 and the second automatic positioning device 62.
Roll opening Rg and plug advanced amount Ld are actually inclined rolls 1 l, 1
r and plug 2.

In addition, the timing for changing the setting of the tip draft rate set by the tip draft rate setting device 7 after the start of drilling is set in the timer setting device 8.

The arithmetic and control unit 5 reads the data set by the leading draft rate setting unit 7, the timer setting unit 8 and the roll state setting unit 9 as described above, and controls the leading draft rate according to the data.

Next, a method of controlling the tip draft rate will be described. First
In the figure, when the radius of the round billet B is r ₀ , and the shortest distance from the path center XX at the tip of the plug 2 to the inclined roll 11 is r ₁ , the tip draft rate D _f is shown as the following equation (1). It is. However, the tip draft ratio D _f in this case is to be expressed as the ratio.

D _f = (r ₀ −r ₁ ) / r ₀ (1) After the round slab B is bitten into the inclined roll, the tip draft ratio D is changed by changing the plug advanced amount Ld and the roll opening Rg, for example. _{When f} is reduced, if the plug advanced amount Ld is increased, the distance between the maximum diameter portion of the plug 2 and the inclined roll 11 decreases, so that the wall thickness t of the round steel piece B after perforation in this case is reduced. The thickness change Δt ₁ becomes small. Similarly, _{if the} roll opening Rg is increased to reduce the tip draft rate Df, the distance between the maximum diameter portion of the plug 2 and the inclined roll 1l becomes large. The thickness change amount Δt ₂ of the thickness t after drilling B becomes large.

Assuming that the change amount of the plug advanced amount Ld is ΔLd and the change amount of the roll opening Rg is ΔRg, the wall thickness change amounts Δt ₁ and Δt ₂ are:
It is shown geometrically as the following equations (2) and (3). However, the polarity of the plug advanced amount is the inlet surface 12, 12 of the inclined roll 1l.
The direction toward the side is the positive side.

Δt ₁ = −ΔLd tan θ ₂ (2) Δt ₂ = ΔRg / 2 (3) where θ ₁ is the angle between the path center XX and the roll entrance surface 12 θ ₂ : the path center XX and the roll exit surface 13 and the angle this reason, the thick variation Delta] t ₁ in order to change the tip draft ratio D _f by changing the plug advanced amount Ld and roll angle Rg, the thickness t is constant, Delta] t ₂ Can be offset as in the following equation (4).

A conditional expression if _{Δt 1 + Δt 2 = 0 ...} (4) i.e. the following equation (5) changes the tip draft ratio D _f without changing the wall thickness t.

_{ΔRg = 2 · ΔLd · tanθ 2} ... (5) The change amount [Delta] r ₁ of r ₁ with respect to the change amount DerutaLd and roll opening change amount [Delta] rg the plug advanced amount geometrically below (6)
It is shown like an equation.

Δr ₁ = ΔLd tanθ ₁ + ΔRg / 2 (6) Then, the amount of change Δr ₁ of r ₁ when the tip draft rate D _f is changed by ΔD _f is geometrically represented by the following equation (7).

Δr ₁ = −r ₀ ΔD _f (7) From the formulas (5), (6) and (7), the plug advanced amount when the tip draft rate D _f is changed without changing the thickness t.
The amount of change ΔLd of Ld is determined as shown in the following equation (8).

Using the change amount ΔLd of the plug advanced amount Ld obtained by the equation (8), the roll opening change amount ΔRg is obtained by the above equation (5).

In the arithmetic and control unit 5, the time when the load cells 3, 3, 3, 3 detect the biting of the round billet B by the change in the detected amount of the load is defined as the drilling start time. From this time, the change amount ΔLd of the plug advanced amount Ld and the roll opening degree change from the tip draft rate set value read from the tip draft rate setter 7 by the above-described calculation method in accordance with the setting change timing set by the timer setter 8. The amount ΔRg is calculated, and a setting change signal of the plug advanced amount Ld and the roll opening Rg is given to the first automatic positioning devices 61, 61 and the second automatic positioning device 62, whereby the roll opening Rg and the plug advanced amount Ld are calculated. change. The tip draft ratio _Df is set so that the middle portion is smaller than the top and bottom portions of the round slab B.

In addition, since the accuracy of the above-described arithmetic expression changes depending on the drilling temperature and the type of the drilling material, in such a case, the arithmetic result is modified based on an empirical rule before use.

If you want to change the thickness t to a desired value during drilling,
The wall thickness can be changed by appropriately modifying the plug advanced amount Ld and the roll opening Rg.

In this embodiment, the case of the two-roll type inclined punch is described. However, the present invention is not limited to this, and is applicable to an inclined punch having three or more rolls. The inclined punch guide may be any of a plate type, a roller type, and a disk roll, and the roll shape may be any of a roll type and a cone type.

Next, a description will be given of a concrete execution result when piercing and rolling are actually performed using the method of the present invention.

The control according to the present invention was performed under the conditions shown in Table 1 using a piercing mill having the above-described configuration. However, the tip draft ratio changing pattern was such that the tip draft ratio was 6% at the time of rolling at the top portion of the billet, 4% at the time of rolling at the middle portion, and 5% at the time of rolling at the bottom portion. As a comparative example, piercing rolling was also performed when the tip draft ratio was fixed at 6%.

Table 2 shows the internal flaw occurrence rates in the method of the present invention and the comparative example when piercing rolling was performed under the conditions described above.

Further, when the tip draft rate is changed only by the roll opening as a comparative example in order to realize the tip draft rate changing pattern, the roll opening and the plug advanced amount are simultaneously changed using the method of the present invention, Table 3 shows the thickness of the top, middle, and bottom portions after perforation when the tip draft ratio was changed.

As is clear from Tables 2 and 3, the method of the present invention had a lower incidence of inner surface flaws and a constant wall thickness after perforation as compared with the conventional method as a comparative example.

〔effect〕

As described in detail above, in the seamless tube rolling method according to the present invention, the inclined roll opening and the plug advanced amount are simultaneously changed, and the tip draft rate of the intermediate portion of the material to be rolled is made larger than that of the top portion and the bottom portion. The present invention has excellent effects such as suppression of the inner surface flaw of the material to be rolled and the constant thickness after piercing and rolling, because the size is reduced.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS The drawings show an embodiment of the present invention. FIG. 1 is a schematic block diagram showing a configuration of a piercing mill used for carrying out a seamless pipe rolling method according to the present invention, and FIG. FIG. 3 is a schematic diagram showing a rolling state in a rolling mill, and FIG. 3 is a graph showing a relationship between a crack generated by Mannesmann fracture and a roll inclination angle. 1l, 1r: inclined roll, 2: plug, 5: arithmetic control unit, 7: tip draft rate setting device, 8: timer setting device, 9: roll state setting device

Claims (1)

(57) [Claims] In the process of piercing and rolling a material to be rolled, the material to be rolled is screwed in the axial direction by using an inclined roll, and a plug is penetrated along the axial direction. The tip roll draft and the amount of plug advance are determined so that the tip draft rate of the plug at the time of rolling at the intermediate portion is smaller than the tip draft rate at the time of rolling at the top portion and the bottom portion of the material to be rolled. A seamless pipe rolling method, wherein piercing and rolling are simultaneously performed without changing the thickness.