JPS61108409A - Rolling method by mandrel mill - Google Patents

Abstract

PURPOSE:To equalize the wall thickness of pipe in its longitudinal direction by performing rolling while continuously reducing the speed of a mandrel bar, from the time the rolling is started until the time it is finished, within a range shown by a prescribed equation. CONSTITUTION:A mandrel mill is constituted by arranging the roll axes of adjoining stands in state of mutually shifting the roll axes by 90 deg. in the plane perpendicular to a rolling axis. The speed of a mandrel bar at the time of starting rolling, that is when the front end of a hollow pipe stock is bitten by the 1st stand, is represented by vB0, and the speed of mandrel at the time of finishing the rolling, that is when the rear end of said pipe is passed any one of the stands after the 2nd stand, is represented by vB1. In rolling, the speed of mandrel bar is continuously decreased from the time the rolling is started until the time it is finished while maintaining the speed ratio vB1/vB0 within a range shown by the inequality (I). In this way, the wall-thickness change, due to the temperature change in the longitudinal direction of a pipe stock, is made uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of mandrel mill rolling a seamless metal tube.

[Prior Art] Generally, a pipe manufactured through a piercing rolling process, an elongation rolling process, and a reduction rolling process, for example, a seamless steel pipe, is manufactured through a first process.
As shown in the figure, a round steel l is heated in a heating furnace 2 of a rotary hearth type, for example, and then perforated with a piercing rolling mill such as a Mannesmann Piaser 3 to form a hollow tube 4, and then a mandrel mill 5 After the mandrel bar 6 is charged in a drawing mill such as the one shown in FIG. The outer diameter is determined by a reducing mill such as the stretch reducer 10, or the outer diameter is reduced to a small diameter.

The mandrel mill 5 used as an elongation rolling mill in the above-mentioned pipe manufacturing process is a rolling mill that elongates and rolls a hollow tube 4 punched by a Mannesmann piercer 3 with a mandrel bar 6 inserted therein. It consists of eight roll stands, each roll stand tilts its roll axis at 45 degrees to the horizontal in a plane perpendicular to the rolling axis, and the roll axes of adjacent roll stands are tilted alternately at 80 degrees. It is common that the x mils are arranged in a staggered manner. Also,
The rolls 7 of each roll stand are independently driven by a DC motor, and the raw tube that has been stretched with reduced thickness in the two upstream stands is transferred to the third stand. At the 4th stand, the thickness was reduced and extended,
The 5th and 6th stands finish the wall thickness with high accuracy. It is possible to apply pressure on the 7th stand, but normally the 7th stand. The 8th stand is used as a sizing stand to make it perfectly round.

By the way, in conventional mandrel mill rolling, the hollow tube 4
Since the mandrel bar 6 inserted into the roll is held unrestricted in the rolling longitudinal direction, the bar speed depends on the rolling load and roll peripheral speed at each roll stand that is actually rolling down. Therefore, during the process in which the tip of the hollow tube 4 is bitten by each roll stand and the rear end of the tube passes through each roll stand, the mandrel bar speed rapidly increases as shown in FIG. Change. As a result, the speed of the raw tube at each roll stand fluctuates as the bar speed changes, causing inter-stand tension fluctuations and the rolling load also fluctuating significantly. This results in a so-called non-uniform distribution of outer diameter and wall thickness.

In order to solve the above problem, a retained mandrel mill rolling method in which a device for controlling the moving speed of the mandrel bar 6 is provided is employed. According to this rolling method, by keeping the mandrel bar speed constant during rolling, it is possible to prevent the deterioration in dimensional accuracy caused by the above-mentioned bar speed fluctuation.

[Problems to be Solved by the Invention] However, when each part of the hollow tube 4 is rolled at the same roll stand, the rolling temperature differs in the longitudinal direction of the tube, and generally from the tip to the rear end. Since a temperature drop of 10 to several tens of degrees is observed, the load that the roll receives from the material increases accordingly.Therefore, simply keeping the mandrel bar speed constant will cause the rolling load to increase due to the temperature drop. It is impossible to suppress non-uniform wall thickness distribution in the longitudinal direction of the reducer tube 8. In other words, as shown in FIG. 3, for example, the target wall thickness [i, Omm
In contrast, the wall thickness distribution shows a tendency for the thickness to increase by about 0.2■■ from the tip to the rear end of the tube. Possible solutions to this problem include introducing a hydraulic reduction device into the thick-wall finishing stand, and changing the speed of the mandrel bar during rolling relative to the rolling speed of the material instead of controlling it constant.

As the latter method, for example, JP-A-57-14270
No. 3 discloses a method of accelerating or decelerating the mandrel bar speed depending on the rolling location of the hollow shell tube. However, since the upper limit of the mandrel bar speed is set to be lower than the speed of the hollow tube at the slowest rolling stand, it may not be possible to sufficiently compensate for the increase in rolling load due to a temperature drop, or, for example, the mandrel bar If the speed is set to the average value of the material speed at the exit side of the first stand and the material speed at the exit side of the second stand, there are many unreasonable aspects such as acceleration or deceleration control of the bar speed itself becoming impossible. However, it is difficult to say that a satisfactory effect can be obtained.

Furthermore, Japanese Patent Application Laid-Open No. 58-53320 also discloses a method of controlling the wall thickness of the tube material by controlling the relative speed between the mandrel bar during rolling and the material of the hollow tube. Since the effect of the ratio of speed and roll circumferential speed on rolling load is not specified, the rolling load can be kept constant by controlling the mandrel bar speed within which range for each stand's roll circumferential speed. Also, mandrel mill rolling is usually tandem rolling with 7 to 8 stands, and even if the mandrel bar speed is controlled so that the rolling load on one stand is constant, the rolling force on other stands is not clear. .

Fluctuations in the tension between the stands and changes in the relative speed between the mandrel bar and the material of the hollow tube can cause the rolling load to fluctuate, and if rolling is not performed within the optimal control Q range, it may have the opposite effect in some cases. I can think about it for 1 minute. −
- As an example, consider a case where the mandrel bar speeds V and o at the start of rolling are set to be approximately equal to the first stand roll groove bottom circumferential speed. In the latter half of rolling, when the rolling load on the thick-wall finishing stand increases and the wall thickness increases mainly due to a decrease in the temperature of the material, the mandrel bar speed is controlled to the accelerating side,
If you try to keep the wall thickness constant, the load on the upstream stand will decrease, but around the 5th and 6th stands, the load will increase, and the final wall thickness will become more at the rear end. This results in increased meat. In other words, in order to control the mandrel bar speed and make the thickness distribution of the material on the exit side of the mandrel mill uniform, the speed control range must be quite limited. 53320 does not make this point clear.

In view of the above-mentioned circumstances, the present invention aims to reduce the I' 7 "t J
It is an object of the present invention to provide a rolling method for w'& + J @ m n "*t #".

[R stage for solving the problem] The present invention arranges a plurality of roll stands in succession, and arranges the roll axes of adjacent roll stands shifted by 80 degrees from each other in a plane perpendicular to the rolling axis. In a mandrel mill rolling method in which the speed of the mandrel bar is controlled when a hollow shell into which a mandrel bar is inserted is rolled by a mandrel mill, the bar speed at the rolling start stage when the tip of the hollow shell is caught in the first stand. Let be V2O,
When the bar speed at the end of rolling when the rear end of the hollow shell passes through any stand after the second stand is VB+, the bar speed from the start of rolling to the end of rolling is 0.7≦V151. /VBo<1.0 during rolling.

[Function] According to the present invention, the bar speed is controlled to be decelerated within the range where changes in bar speed affect the rolling load and advancement rate, and as a result, the bar speed is controlled to be decelerated within the range where changes in bar speed affect the rolling load and advancement rate. It becomes possible to make the longitudinal wall thickness distribution uniform.

[Example] The present invention utilizes the findings obtained as a result of detailed investigation by the inventors of the effects of mandrel bar speed on rolling load, advancement rate, flange wall thickness, and outer diameter in mandrel mill rolling. This is a control method invented in The present invention will be explained in detail below.

Figures 4 to 7 show the rolling load °, material advance rate, flange wall thickness, and flange outer diameter during single-stand mandrel mill rolling, and the mandrel bar speed ratio (with the roll rotation speed constant and the roll Regarding the rolling load and the advance rate of the material, which shows the relationship between the groove bottom circumferential speed (7 shaku) and the bar speed Vy (expressed as the ratio VB/Vz), Fig. 4 and Fig. 5 show TE0, ?
Bar speed ratio v(?/
It changes depending on Vg, but outside the above range, it does not depend on the bar speed ratio and remains almost constant. The area affected by the movable bar speed ratio VS/V varies depending on the thickness reduction rate in the stand, the outside diameter reduction rate, the dimensions of the raw pipe, etc. on the other hand,
As shown in FIGS. 6 and 7, the wall thickness of the flange and the outer diameter of the flange are constant values almost independent of the mandrel bar speed ratio.

The above are the properties during single-stand mandrel mill rolling, but considering the deformation and load characteristics of the pipe material during normal tandem mill rolling, the advancement ratio of the material fluctuates due to changes in bar speed, and as a result, The fluctuations in tension between the stands that occur are important. In other words, in a rolling state where the bar speed ratio at the 1st and (j+/)th stands is within the material's advanced rate fluctuation range indicated by diagonal lines in Fig. 5, the bar speed is reduced by a certain amount. Considering the case, the tension acting between the first stand and the a<, i+t) stand varies by an amount expressed by the following equation. , f = (VMI
VfL) / VPL-(2)b = (
VFL-Vso) / vPL
-(3) However, vH6: Material velocity on the inlet side of the stand (am/5ec) V: Defined as the material velocity on the outlet side of the stand (■intestine/5ec).

That is, the flange wall thickness and outer diameter of the i1-th, fIYJ(j+/) stand do not change due to the effect of the bar speed reduction alone, but change significantly due to the change in the tension between the stands due to the advance rate change. Therefore, in retained mandrel mill rolling, in order to make the wall thickness uniform, it is necessary to change the mandrel bar speed and the rolling load of the wall finishing stand and the flange wall thickness.
It is important to keep the outer diameter almost constant, and the mandrel bar speed change must be suppressed so that there is almost no variation in the advance rate in the thick-walled finishing stand.Therefore, in the present invention, the tip of the hollow tube is When the bar speed at the rolling start stage where it bites into the first stand is Vg0, and the bar speed at the rolling end stage where the rear end of the hollow shell passes through any of the stands after the second stand is vBI, then at the rolling start stage The bar speed from 0.7≦V to rolling path r stage
Rolling is performed while continuously decreasing s+/vBo in the range of <1.0. There is a relationship between the mandrel bar speed ratio V5/vfL, the pumping load, and the tip a ratio as shown in Fig. 4.5 (the same applies to Figs. 8 and 9).

The same relationship varies depending on the thinning rate, outer diameter reduction rate, and raw pipe size, but in general, Vg / V7 is 1.
．． It becomes constant at 3 or more and 0.7 or less.

To control the flange wall thickness and outer diameter caused by rolling load and rolling rate fluctuations by reducing the bar speed during rolling,
Area where rolling load and advancement rate are affected by changes in bar speed〒,
It is necessary to change the bar speed. Normally, the bar speed is set to a value between the material speed at the entrance of the first stand and the material speed at the exit of the third stand. The speed ratio (v5/v9) is 1 or more. For example, if the initial speed v116 is set so that (v, /v town), = 1.0, the bar speed change amount a V that can control (decrease direction) the rolling load of the first stand
g is the maximum ((Vg6-ΔvB)/vfL), z
Q: Up to about 7, and even if you change it more than that, the first stand rolling load will fall into the constant load area and will have no effect. When it is made faster, the same thing as above can be said about the bar speed ratio (VB' / v, !L) at the second stand, v151 / Veo < 0.7
In this case, the effect of wall thickness control by reducing the load cannot be expected at all.

From the above, the control range of the mandrel bar speed is 0.7≦ver/vBe)<where VBO is the bar speed at the rolling start stage and ver is the bar speed at the end of rolling stage.
It becomes 1.0.

Here, the reason why the rolling end stage is a stage in which the rear end of the hollow shell passes through any of the stands after the second stand is that the control according to the present invention is applied to the entire length including the rear end of the hollow shell. In order to do this, the rear end of the hollow shell tube is passed through the roll of the first stand, and then also passed through the roll of the second stand, which is arranged at least 90 degrees offset from the roll of the first stand. This is because it is necessary to roll the entire region of the rear end of the hollow shell in the circumferential direction with a reduction in bar speed.

Next, a specific method for controlling the speed of the mandrel bar will be described.

The temperature of the hollow tube 4 is approximately 1,200°C immediately after being perforated by the Mannesmann piercer 3, and approximately 1,100°C immediately before being rolled by the mandrel mill 5. , at the tip and rear end of the hollow tube 4,
There will be a temperature difference of several tens of degrees. Therefore, although the deformation resistance of the material varies depending on the steel type, there is a difference of 4 to 5%, and as a result, the rolling load increases on the rear end side, and the wall thickness increases through mill rigidity. This effect occurs in the second to sixth
This also occurs in stands, and the difference in wall thickness from the tip to the rear of the tube increases.

In normal retained mandrel mill rolling, the bundle barrel speed is generally set to a value between the material speed at the entrance of the first stand and the material speed at the exit of the third stand. for example.

Considering the case where the 8-speed is equal to the material speed on the exit side of the first stand, the <-speed ratio V at the 1st to 6th stands.
g3/v Eh, the relationship between rolling load and advance rate is shown in Section 8.
The result is as shown in Figure 9. In this case, the rolling load and tip a ratio are influenced by the bar speed ratio VB/'VR.
Only the second stand. In this state, the mandrel-speed ratio reduction amount Δ(v, / v E), Δ(VB/Hiki) can be determined based on a linear equation.

(a) Relational expression between rolling load and bar speed ratio in rolling load fluctuation range % formula %) (b) Relational formula between advance rate and bar speed ratio in advance rate fluctuation range % formula % (c) For advance rate fluctuation Assuming that the difference in wall thickness due to the difference in tension between the stands, that is, the rolling load difference between the leading end and trailing end of each stand caused by the low temperature, is Δ and λ = 1 to 6), the number of stand grooves is Wall thickness difference ΔtaL, Δt between the tip side and the rear end side of the reducer tube 8 at the bottom of the even-numbered stand groove
AV is given by the following formula. In general, Δtoj Δt
The amount of reduction in rolling load ΔP2. required when compensating for the wall thickness increase Δt, which is assumed to be Lv = MUL, at the 1.2nd stand. Δ
Since the mill rigidity of each mill stand is considered to be approximately equal, P is ΔP,zΔPL=ΔP. ΔP and (
From equations 1), (4), and (5), it is clear that the 1. Mandrel bar speed ratio reduction amount Δ(Vθ/v, L)l lΔ(V
σ/V9)L is calculated. At this time, the mandrel bar speed reduction amount ΔV9 is Δ(V,/V,).

Eight-speed reduction amount ΔV found from Δ(VB/vIL)z
,,.

It is sufficient to set it to the average value of ΔVII2.

From the above, the mandrel bar speed is changed from the initial setting value VaO to (v8.-ΔVg) from the time when the hollow tube 4 is bit into the first stand until it passes through the second stand.
By rolling the thickness while continuously reducing the thickness to 1, a reducer blank tube 8 having a uniform wall thickness distribution in the longitudinal direction can be obtained. FIG. 10 shows an example of setting the par speed.

It should be noted that the set value VB6 of the mandrel bar speed in the negative period is higher than the material speed on the exit side of the first stand, for example, when the mandrel bar speed ratio (VB/Ve) at the first stand is 1.0.
Therefore, if the relationship between the rolling load and the speed ratio shown in Fig. 8 is a monotonically decreasing relationship, as the bar speed is decreased during rolling, P and (VB/V,) In the relationship between , the front element tends to increase, and in the relationship between f and (V, /V good), the load tends to decrease, so the effect of thinning in the first stand is:
It is smaller than the case where V*J is made equal to the material speed on the first stand exit side described above. However, in that case, the effect of thinning due to the reduction in the rolling load of the third stud will occur, so when considering compensation for the amount of increase in wall thickness as a whole, the same degree of effect can be obtained.

In other words, 1. In normal retained mandrel mill rolling, for at least two rolling stands, the bar speed ratio vB/v~ exists in the shaded area in Fig. 8, so the optimum mandrel - speed reduction scene ΔV6 is set. By doing so, a reducer blank tube 8 that is uniform in the longitudinal direction can be obtained.

Mandrel according to the present invention, <- Specific implementation results of the speed control method are shown below, outer diameter 148 mm, wall thickness 8.0 a
This is a case of manufacturing a reducer blank pipe 8 of m, and the standard roll rotation speed NFL+ of each stand of the 1st to 8th stands is
-Nzy are respectively NFL+=92°NLL=I
H, NK3 = 188, NFLq = 195
, Nttr=207, N4. =225, N
, 7=228, N illusion=22 [1 rpm. The initial setting value vgo of one speed to the mandrel 7 is almost equal to the first stand roll groove bottom circumferential speed, which is 1.800++ a/s.
In addition, there is a temperature difference of approximately 20"C between the tip and rear end of the hollow tube 4 when it is bitten into the first stand, and the rolling tube is increased due to increased deformation resistance at the rear end. Mandrel par speed reduction amount ΔVBo required to compensate for
The calculated result is 300m5/sec.

Closed, that is, the speed to the mandrel is VB6 = 1.800a at the time when the hollow tube 4 is caught in the first stand.
m/sec, , and at the time of passing through the second stand, va, = 1,500 mm/sac, during which time the par speed was linearly decreased. The results of measuring the longitudinal distribution of the average wall thickness of the reducer blank tube 8 after mandrel mill rolling are shown in the 11th section. As shown in the figure, as is clear from the figure, the wall thickness in the longitudinal direction shows a uniform distribution.

Compared to the conventional method shown in FIG. 3, a reducer tube 8 was obtained that was stable and had significantly superior dimensional accuracy.

[Effects of the Invention] As described below, the present invention arranges a plurality of roll stands in succession, and arranges the roll axes of adjacent roll stands so as to be offset by 90 degrees from each other in a plane perpendicular to the rolling axis. In the mandrel mill rolling method in which the speed of the mandrel bar is controlled when rolling a hollow shell tube into which a mandrel bar is inserted, a parer at the rolling start stage where the tip of the hollow shell tube is caught in the first stand is used. When the speed is VB6 and the bar speed at the end of rolling when the rear end of the hollow shell passes through any stand after the second stand is VB+, the par speed from the start of rolling to the end of rolling is: 0.7≦VbI/Ve.

Rolling is performed while continuously decreasing the amount within the range of <1.0. Therefore, it is possible to optimally control the speed of the mandrel bar during rolling and to equalize longitudinal wall thickness fluctuations of the reducer blank caused by temperature changes in the longitudinal direction of the blank tube.

[Brief explanation of the drawing]

:51 Figure is a process diagram showing the manufacturing process of seamless pipes by the Mannesmann-mandrel mill rolling method, Figure 2 is a line section representing the speed +5iI ratio of the hollow shell and mandrel bar during full-float mandrel mill rolling, and Figure 3 The figure is a diagram showing the longitudinal distribution of the wall thickness of the rolled tube when rolled at a constant mandrel bar speed, and Figures 4 to 7 respectively show the rolling load, advance ratio, and flange thickness during single-stand mandrel mill rolling. Figure 8.9 is a diagram showing the relationship between the thickness, outer diameter of the flange, and mandrel bar speed ratio, and the relationship between the rolling load, advance ratio, and mandrel bar speed ratio at each stand during retained mantrell mill rolling, respectively. 10 is a diagram showing the speed relationship between the hollow shell tube and the mandrel/<- when the present invention is implemented, and FIG. 11 is a diagram showing the longitudinal thickness of the tube after rolling when the present invention is implemented. It is a line diagram showing thickness distribution. 4...Hollow tube, 5...Mandrel mill, 6...
Mandrel bar-17...roll. Agent Patent Attorney Osamu Shiokawa Figure 1 Figure 2 fil Sufu〉L”1 incl.
c,) Figure 3 Figure 4

Claims (1)

[Claims] (1) In addition to arranging multiple roll stands in succession,
A mandrel mill in which the roll axes of adjacent roll stands are shifted 90 degrees from each other in a plane perpendicular to the rolling axis controls the speed of the mandrel bar when rolling a hollow blank tube into which the mandrel bar is inserted. In the mandrel mill rolling method, the bar speed at the rolling start stage where the tip of the hollow tube is bitten into the first stand is v_B_P,
When the bar speed at the end of rolling when the rear end of the hollow shell passes through any stand after the second stand is v_B_I, the bar speed from the start of rolling to the end of rolling is 0.7≦v_B_I. A mandrel mill rolling method characterized in that rolling is carried out while continuously decreasing the value of /v_B_C<1.0.