JPH0221325B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a rolling control method for a mandrel mill, which is a tube rolling mill.

[Technical background of the invention]

Seamless steel pipes are made by passing a mandrel bar through a pipe material (raw pipe) that has been pierced with a piercer, etc., and then continuously rolling it to a predetermined wall thickness using multiple rolling mills (generally 8 stand configurations) equipped with a pair of grooved rolls. , rolled to length and roundness. The mandrel mill, which consists of a rolling mill group equipped with a mandrel bar and grooved rolls, is a continuous rolling mill using grooved rolls, but the mandrel bar has become an important machine element for rolling pipe materials. This is different from rolling of long steel such as wire rods and bars. The behavior and operation of the mandrel bar during rolling have a great influence on the productivity of the mandrel mill and the quality of the tube material after rolling. Currently, there are two rolling methods for mandrel mills, which can be broadly classified depending on the method of operating the mandrel bar.

That is, one method is a so-called full-float mandrel mill, in which a mandrel bar is inserted into the pipe material on the entrance table, and rolling is completed without any operation being applied to the mandrel bar during rolling. The other one is, for example, an MPM type mandrel mill, in which the mandrel bar is restrained from the entrance side of the rolling mill to keep the advancing speed of the mandrel bar constant during rolling.

FIG. 1 shows a conceptual diagram showing the relationship between the tube material speed during rolling and the mandrel bar speed in the case of a full-float mandrel mill. In Figure 1,
The horizontal axis t is the time after the start of rolling, and the vertical axis is the speed, where VH is the speed of the tip of the tube, VB is the speed of the mandrel bar, and VT is the speed of the rear end of the tube. Note that #1, #2, #3... are stand numbers.
After the #1 stand is engaged, the tube is passed until time _t1 , and the mandrel bar speed VB changes from VB ₁ to VB ₂ every time the stand engages. This VB ₂ is the mandrel bar speed after the final stand bite, and is constant until time t ₂ when it starts to break through. After the start of blanking, the mandrel bar speed VB is VB ₃ by the time only the final stand is rolled.
changes up to.

That is, in a full-float type mandrel mill, the rolling speed of each stand and the relative speed of the mandrel bar change during passing and through-cutting.

This change in the relative speed of the tube material during rolling and the mandrel bar means that the neutral position within the roll bite also changes, and the rolling pressure distribution within the roll bite also changes. Therefore,
The rolling load, rolling torque, torque arm, advance rate, etc. also change.

As described above, the above-mentioned rolling characteristic values change only due to changes in the mandrel bar speed during tube passing and through-through, making it impossible to maintain constant rolling conditions. Also,
In the case of rolling a tube material using a mandrel mill, changes in various rolling characteristic values during tube passing and punch-through account for a large proportion of the total length of the tube material after rolling. Therefore, after rolling,
It is difficult to obtain a uniform wall thickness over the entire length.

In addition, the MPM type mandrel mill restrains the mandrel bar and maintains the speed of the mandrel bar constant during rolling, which has the effect of eliminating mandrel bar speed changes that inevitably occur in the above-mentioned full float type mandrel mill. However, the lubrication problem due to mandrel bar restraint, the method of determining the optimum mandrel bar speed, the control method, etc., remain unresolved, and it is not a rolling technology that has been established in terms of operational stability. Therefore, at present, at least in Japan, mandrel mills are operated using the full float system.

[Purpose of the invention]

The present invention was developed in view of the above circumstances, and is based on the knowledge obtained through logical considerations and specific experiments. The present invention provides a method for controlling the wall thickness of a mandrel mill, which makes it possible to obtain a uniform wall thickness over the entire length of a tube material after rolling by controlling the speed.

Furthermore, specifically, based on the characteristics of rolling by a mandrel mill, the rolling load is controlled by mandrel bar speed control in order to control the wall thickness of the pipe material.

[Summary of the invention]

That is, in order to achieve the above object, the present invention has a plurality of rolling mills each equipped with a pair of grooved rolls, and feeds the tube material between the grooved rolls of these rolling mills while feeding the mandrel bar within the tube material. In a mandrel mill that rolls pipe material using the mandrel bar and the grooved roll, a speed control means for the mandrel bar is provided, and the rolling load of each rolling mill is detected, and the pipe material is transferred from the previous stage to the next rolling mill. When rolling, the feed speed of the mandrel bar is controlled according to the variation in order to suppress the variation in the rolling load of the previous stage to zero, or the feeding speed of the mandrel bar is controlled according to the variation in the rolling load of the preceding stage, or The system detects the rolling loads of several units, and adjusts the amount of change in the rolling load of the previous stage to zero when pipe material is bitten from the previous rolling mill to the next rolling mill. The feed speed of the mandrel bar is controlled, and the other rolling mills use both tension control and reduction control to achieve constant wall thickness control.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. First, specific examples obtained through experiments will be described. Figure 2 shows an example in which the wall thickness from the tip to the rear end (in the final stand rolling direction) of a rolled tube material obtained in a continuous rolling experiment on a mandrel mill was measured continuously using a thickness gauge. This is a mandrel mill, and the number of roll rotations on each stand is set so that tension is applied to the tube material during rolling. In the figure, ←T→ is the region after the start of shearing (Tail), →C→ is the region (Center) where the pipe material was continuously rolled across all stands, and ←H→ This is the area (Head) when pipes are passed to all stands. The vertical axis is the wall thickness h, and hc1 and hc2 indicate the wall thickness of the center portion. There is a clear difference in wall thickness between the center, tail, and head parts.

Figure 3 shows an example in which the mandrel bar is restrained and the speed of the mandrel bar is kept constant from the start of rolling to the end of rolling. It is similar to In this case, there will still be differences in wall thickness between the center, tail, and head portions.

The reason for this is when the mandrel mill inserts into each stand, during continuous rolling across all stands, during continuous rolling across all stands, and when the #1 stand gradually passes through the final stand. This is because the rolling conditions at different times are different.
In addition, in the case of the full-float mandrel mill shown in Fig. 2, the mandrel bar shown in Fig. 3 is restrained, and
When held at a constant speed, the roll gap of each stand of both stands, the diameter of the mandrel bar, the dimensions, shape, and lubrication method of the tube material before rolling, and the wall thickness of both stands after rolling even if the roll rotation speed of each stand is exactly the same. There is also a difference in wall thickness deviation (difference in wall thickness between the head section, tail section and center section after rolling). In other words, the thickness of the center part of the former is hc
1, and the difference between the maximum thickness part and hc1 is △h
1. If the thickness of the latter center portion is hc2, and the difference between the maximum thickness portion and hc2 is △h2, then hc1≠hc2, △h1≠△h2 (1).

In the case of a full float mandrel mill, the first
As shown in the figure, the speed of the mandrel bar changes during pipe passage and when the pipe passes through, and the speed relative to the roll rotation speed also changes. When the mandrel bar is restrained and held at a constant speed, the relative speed between the mandrel bar speed and the roll rotation speed of each stand is constant, but as shown in FIG.
There is a difference in wall thickness between the center portion and the tail portion, and the relationship between the two is as shown in equation (1) above. As mentioned above, this is mainly due to the following reasons.

(1) Change in the relative value of mandrel bar speed and roll rotation speed (or tube material speed during rolling). Changes in various rolling characteristic values such as rolling load, rolling torque, and advance rate due to this relative value change.

(2) By keeping the mandrel bar speed constant, the relative value to the roll rotation speed changes, which causes forward tension or compression force to be generated in the pipe material during passing, and Changes in posterior tension, or compression.

FIG. 4 shows the results of actively controlling the wall thickness of the tube after rolling and the speed of the mandrel bar during rolling using the mandrel mill described above.

In FIG. 4, the horizontal axis VB is the speed of the mandrel bar, and at the position JB=0, the mandrel bar is completely restrained, and the mandrel bar is completely fixed without moving during rolling of the tube material. When VB>0, the speed of the mandrel bar is controlled in the direction in which the tube moves, and when VB<0, the speed of the mandrel bar is controlled in the opposite direction to the direction in which the tube moves. The vertical axis hm is the average wall thickness of the tube material after rolling, and the figure shows measurement examples of the center portion (A in FIG. 4) and the tail portion (B in FIG. 4). The example results shown in Figure 4 are the results of continuous rolling, where the roll hole type, lubrication, roll rotation speed of each stand, and roll gap mandle bar dimensions of each stand are all kept constant, and only the mandrel bar speed during rolling is controlled. This is the result when controlled. Although there is a difference in wall thickness between the center portion and the tail portion as in the cases shown in FIGS. 2 and 3, it is clear that the wall thickness of the tube material after rolling changes depending on the mandrel bar speed.

The example results in FIG. 5 and the example results in FIG. 6 show the relationship between the mandrel bar speed VB and the rolling load P. The case in Figure 5 is an example of single rolling, in which there is no longitudinal tension or compressive force of the pipe material during rolling, and the case in Figure 6 is an example of continuous rolling, in which there is no longitudinal tension or compression force of the pipe material during rolling. There is some tension or compression in the front and back of the tubing. Note that the results shown in FIGS. 5 and 6 are similar to the example shown in FIG. 4 in terms of rolling conditions (roll hole type, lubrication, roll gap, etc.).

That is, in a mandrel mill, the rolling load can be changed only by controlling the speed of the mandrel bar.

As described above, in a mandrel mill, it is possible to change the wall thickness of the tube material after rolling and the rolling load during rolling by controlling the speed of the mandrel bar.

Generally, it is a well-known fact that the following relational expression holds between the thickness of a rolled material and the rolling load.

h=ho+P/M (2) In the second equation, h is the thickness after rolling, ho is the roll setting gap, P is the rolling load, and M is the mill constant. From the above, it was shown that the mandrel mill has the characteristic that the wall thickness and rolling load can be controlled only by controlling the speed of the mandrel bar.

FIG. 7 shows a schematic diagram of a mandrel mill for carrying out the present invention. In FIG. 7, 1 and 1' are a pair of opposing grooved rolls, and the grooved rolls 1 and 1' are drawn as shown in the figure for convenience.
In reality, the roll axes of each stand are arranged at an intersecting angle of 90° to each other in adjacent stands. Reference numeral 2 denotes a tube material to be rolled, and 3 a mandrel bar. The thickness of the tube material 2 is reduced between the grooved rolls 1, 1' and the mandrel bar 3. 4 is an electric motor for driving the grooved roll, and the rotational speed of this electric motor is detected by a speed detector 5. Reference numeral 6 denotes a speed control device for controlling the rotational speed of the electric motor 4, and an amount to be controlled is given by an arithmetic device 7. The rolling load of each stand is detected by a load detector 8, this detected value is stored in a storage device 9, and a predetermined calculation is performed by a calculation device 7. 10 is a drive mechanism for the mandrel bar 3, and the speed of the mandrel bar 3 is controlled by controlling the speed of a mandrel bar drive motor 11 for driving the mandrel bar drive mechanism 10 using a mandrel bar speed control device. 13
is a rotational speed detector of the mandrel bar drive motor 11. In addition, in FIG. 7, an eight-stand configuration is shown, such as rolling stands #1, #2, . . . #8.

Hereinafter, a specific example of controlling the wall thickness of a mandrel mill will be described based on the facts shown in FIGS. 2 to 6.

8a and 8b show side and front sectional views of the roll bite, in which the tube material 2 is reduced in wall thickness in the gap between the grooved rolls 1, 1' and the mandrel bar 3. In the diagram
h ₁ is the wall thickness at the exit side of the roll bite, S ₁ is the roll gap during rolling, D _B is the diameter of the mandrel bar 3,
P is the rolling load. Following the second equation, in the case of a mandrel mill, the following equation is obtained.

S ₁ =So+P/M...(3) In equation (3), So is the roll setting gap before rolling, and M is the mill constant. The relationship among S ₁ , h ₁ , and D _B is as follows.

S ₁ = 2h ₁ + D _B ... (4) From equations (3) and (4), the relationship between roll bite exit side wall thickness h ₁ , roll setting gap S ₀ , and mandrel bar diameter D _B in a mandrel mill. The formula is as follows.

h ₁ = 1/2 (S ₀ −D _B +P/M) ...(5) Here, the mill constant M is a value specific to the rolling mill, and when the roll setting gap S ₀ is kept constant, the exit wall thickness h In order to control ₁ , rolling load P and mandrel bar speed are
All you have to do is control VB.

FIG. 9 shows a state in which the tube material 2 is caught in the #1 stand and has not yet reached the #2 stand. The rolling load _P10 of the #1 stand at this time is detected by the load detector 8 of the #1 stand and stored in the storage device 9 of the #1 stand. At this time, the speed VB ₀ of the mandrel bar 3 is maintained by controlling the rotational speed of the mandrel bar driving electric motor 11 by the speed control device 12. Figure 10 shows
After the pipe material 2 is caught in the #2 stand, it has not yet reached the #3 stand. At this time, #1
The rolling load of each stand #2 is P ₁ ,
Assuming that P ₂ , the rolling load on stand #1 will change from the state shown in Fig. 9 to the state shown in Fig. 10.
This means that the value has changed from P ₁₀ to P ₁ . The difference ΔP ₁ in the rolling load of the #1 stand between the state shown in FIG. 9 and the state shown in FIG. 10 is as follows.

△P ₁ = P ₁₀ − P ₁ ...(6) The difference △P ₁ in equation (6) occurs in the #1 stand because of the tension between the stands due to the uneven roll rotation speed of the #1 stand and #2 stand. Or, this is due to the generation of compressive force, irregularities in the dimensions of the tube material 2, which is the material to be rolled, and temperature changes in the tube material 2.
The difference ΔP ₁ in the rolling load of the #1 stand in the sixth equation is calculated by the arithmetic unit 7, and the speed of the mandrel bar 3 is controlled by the mandrel bar speed control device 12 so that this difference becomes zero. By this speed control, as shown in FIG. 11, the speed of the mandrel bar 3 becomes VB ₁ , and the rolling load of the #1 stand becomes P ₁₀ . The rolling load _P20 of the #2 stand at this time is stored in the storage device 9.

Next, as shown in Fig. 12, the pipe material 2 gets caught in the #3 stand, but assuming that the rolling load of the #3 stand at this time is P ₃ , the rolling load of the #2 stand becomes P ₂ '. Then, the difference ΔP 2 between the rolling load P ₂₀ of the pipe material 2 on the # 2 stand before it is bitten by the # 3 stand and the current rolling load P _{2 '} is as follows.

△P ₂ = P ₂₀ −P ₂ ′ ...(7) Therefore, the mandrel bar speed control device 12 controls the mandrel bar speed so that the difference △P ₂ in the rolling load of the #2 stand expressed by this equation (7) becomes zero. Controls the speed VB ₁ of bar 3. Thereafter, the speed of the mandrel bar 3 is controlled in the same manner until the final stand biting is completed.

In this way, the mandrel bar 3 is adjusted so that there is no rolling load fluctuation for the rolling stand one place upstream from the most downstream rolling stand that bites the pipe material 2.
Implement speed control. This is because the rolling stand has the largest variation in rolling load compared to other rolling stands.

FIG. 13 shows a state in which the speed control of the mandrel bar 3 is completed after the #8 stand is engaged. The speed of the mandrel bar 3 at this point is VB ₇ ,
The rolling loads P ₇₀ and P ₈₀ of #7 and #8 are stored in the storage device 9 of each stand.

What has been said above regarding Figures 9 to 13 is as follows:
This is a method of controlling the speed of a mandrel bar during the process until the end of biting of tube material into each stand in a mandrel mill.

Next, a description will be given of the period just before the tube material 2 starts to pass through, and the period from when the tube material 2 starts to pass through the #1 stand, passes through the #2 stand and #3 stand sequentially, and ends rolling. During this period, the speed of the mandrel bar 3 is controlled to zero the difference between the rolling load P ₈₀ of the #8 stand, which is the final stand, or the rolling load P ₇₀ of the #7 stand shown in FIG. 13. ₈₀ or P ₇₀ is always controlled to a constant value.

By controlling the rolling load by controlling the speed of the mandrel bar 3 in this manner, the wall thickness of the tube material 2 after rolling can be controlled using equation (5). In the above, after the pipe material 2 starts passing through stand #1, constant control of the rolling load is performed until the end of rolling with respect to the rolling load P ₈₀ or P ₇₀ of stand #8 or #7. This is because in mandrel mills, the final stand generally functions more as a forming stand to achieve roundness than to reduce wall thickness, and in this case,
Controlling the rolling load on the final stand by controlling the speed of the mandrel bar 3 is not very effective. In such a case, P ₇₀ of stand #7 in Figure 13
The speed of the mandrel bar 3 is controlled to keep it constant.

In the above explanation, the speed of the mandrel bar 3 is exemplified in which state and for which rolling stand the speed of the mandrel bar 3 should be controlled so that the rolling load does not fluctuate, depending on the relationship of the pipe material 2 to the rolling stand. In this case, rolling stand B is the preceding stage of rolling stand A to be prevented from rolling load fluctuation by controlling the speed of mandrel bar 3 (for example, if rolling stand A is #3 stand, rolling stand B is #2 stand) (stand), the rolling load naturally fluctuates due to this control.

This variation in rolling load is small, but since this variation leads to variation in wall thickness, tension control and rolling reduction control are performed in rolling stand B.

In other words, the rolling stand to which rolling load fluctuation is to be avoided is the one with the largest rolling load fluctuation. The stand with the largest variation in rolling load is the stand in front of the stand where biting has started, and this is rolling stand A.

Therefore, in this embodiment, when the main control is constant wall thickness control by controlling the speed of the mandrel bar, the rolling stand A is used to prevent rolling load fluctuations.

Since the rolling load variation in rolling stand B is smaller than that in rolling stand A, the wall thickness variation is suppressed by tension control and rolling reduction control, which are conventional rolling control techniques.

In other words, for the rolling stand upstream of the rolling stand whose rolling load is to be prevented from changing by controlling the speed of the mandrel bar 3, the thickness of the pipe material at that rolling stand can be reduced by controlling tension and rolling. Suppress pressure fluctuations.

The embodiment of the present invention described above controls the rolling load of all stands from the start of rolling of the pipe material 2 to the end of rolling.
Although an example has been shown in which control is mainly performed by controlling the speed of the mandrel bar 3, the present invention also applies to a part of a rolling mill group constituting a mandrel mill, for example,
Only for one or more front stands of a rolling mill group.
Alternatively, the wall thickness can be kept constant even if the speed of the mandrel bar 3 is controlled to control the rolling load only in one or more rear stands.

For example, Figure 14 shows the front 3 stands (#13
This is an example in which the rolling loads P ₁ , P ₂ , and P ₃ of the #2 and #3 stands are controlled by controlling the speed of the mandrel bar 3, and the control method is the same as that described above.

By controlling these three front stands, irregularities in dimensions, temperature distribution, etc. of the base material (material before rolling) of the tube material 2,
When the influence of other disturbances is reduced and the conventional tension control method and rolling reduction control method are used together after the #4 stand, it is possible to obtain a mandrel mill rolled product with better quality.

Furthermore, the example shown in FIG. 15 is an example in which a wall thickness measuring device 14 is installed to measure the wall thickness of the pipe material on the outlet side of the mandrel mill, and the measured values of the wall thickness measuring device 14 are stored in the wall thickness storage device 15. Make me remember. Then, as time passes, if a difference occurs from the wall thickness stored in the wall thickness storage device 15 or from the predetermined wall thickness set in the wall thickness storage device 15, the speed of the mandrel bar 3 is adjusted so as to make this difference zero. This is to ensure that control is implemented.

In addition, Figure 16 shows the results of measuring the wall thickness after rolling over the entire length when the mandrel bar speed was controlled and when the mandrel bar speed was not controlled in a conventional full-float mandrel mill. An example was given. In the figure, 16 is the result without mandrel bar speed control, and 17 is the result with control, but as is clear from the figure, comparing the two shows the effect of mandrel bar speed control on wall thickness control. It can be seen that this is obvious.

As described above, according to the present invention, although a mandrel bar exists as an important mechanical element in a conventional mandrel mill, it has been difficult to control the rolling of a mandrel mill due to the presence of this mandrel bar. However, by actively controlling the speed of this mandrel bar during rolling, it is possible to accurately control the wall thickness from the tip to the rear end of the tube material to be rolled.

〔Effect of the invention〕

As described in detail above, the present invention focuses on the fact that the pressurized load can be controlled by controlling the speed of the mandrel bar. In a mandrel mill that rolls a tube material by sending a mandrel bar inside the tube material while feeding it between grooved rolls of the machine, a speed control means for the mandrel bar is provided, and the rolling load of each rolling mill is detected, so that the tube material is The feeding speed of each of the mandrel bars is controlled in accordance with the variation in order to suppress the variation in the rolling load of the previous stage to zero when it is bitten from the previous stage to the next rolling mill, or the plurality of rolling mills In order to detect the rolling load of several adjacent units on the previous stage side, and to suppress the change in the rolling load of the previous stage to zero when pipe material is bitten from the previous stage rolling mill to the next stage rolling mill. The feeding speed of the mandrel bar is controlled according to the change, and the other rolling mills use both tension control and reduction control so that the wall thickness can be controlled to be constant.
Rolling control for mandrel mills with features such as actively controlling the speed of the mandrel bar during rolling as described above, making it possible to precisely control the wall thickness from the tip to the rear end of the pipe material being rolled. method can be provided.

[Brief explanation of drawings]

Figure 1 is a diagram showing the speed relationship between the tube material and the mandrel bar in a conventional full-float mandrel mill, and Figure 2 is a diagram showing the longitudinal wall thickness distribution of the tube material after rolling by the full-float mandrel mill.
Figure 3 is a diagram showing the longitudinal wall thickness distribution of the tube material after rolling when the mandrel bar speed is kept constant during rolling, Figure 4 is a diagram showing the relationship between mandrel bar speed and wall thickness, and Figure 5 is a diagram showing the relationship between mandrel bar speed and wall thickness. FIG. 6 is a diagram showing the relationship between mandrel bar speed and rolling load, and FIG. 7 is a simplified block diagram of a mandrel mill for carrying out the present invention.
Figure 8 is a cross-sectional view of the roll bite of the mandrel mill, a conceptual diagram of the roll gap and wall thickness, and Figures 9 to 13.
The figure is an explanatory diagram for controlling rolling load and controlling wall thickness by mandrel bar speed according to the present invention,
Fig. 14 is a diagram showing a modification in which the speed control of the mandrel bar is applied to the front stage stand, and Fig. 15 is a diagram illustrating a modification in which the mandrel bar speed is controlled using a wall thickness measuring device. , FIG. 16 is a diagram for comparing and explaining the effects of wall thickness control according to the present invention. 1, 1'...grooved roll, 3...mandrel bar,
4...Grooved roll drive motor, 6...Speed control device,
7... Arithmetic device, 8... Rolling load storage device, 9... Rolling load storage device, 10... Mandrel bar drive mechanism,
11... Mandrel bar drive motor, 12... Mandrel bar speed control device, 14... Wall thickness measuring device, 15
...Thick memory device.

Claims (1)

[Claims] 1. A plurality of rolling mills equipped with a pair of grooved rolls are provided, and a mandrel bar is passed through the tube material, and while the mandrel bar is being fed, the tube material is fed between the grooved rolls of these rolling mills. Accordingly, in a mandrel mill that rolls a tube material using the mandrel bar and the grooved roll, a speed control means for the mandrel bar is provided, and the rolling load of each rolling mill is detected, so that the tube material is transferred from the previous stage to the next stage rolling mill. A rolling control method for a mandrel mill, characterized in that the feeding speed of the mandrel bar is controlled in accordance with the variation in the rolling load of the preceding stage so as to suppress the variation to zero when the mandrel bar is bitten. 2 A plurality of rolling mills equipped with a pair of grooved rolls are provided, and the mandrel bar is passed through the pipe material, and the mandrel bar is fed while the pipe material is fed between the grooved rolls of these rolling mills. In the mandrel mill that rolls the tube material using the grooved roll, a speed control means for the mandrel bar is provided, and the rolling loads of several adjacent rolling mills on the front stage side or the rear stage side among the plurality of rolling mills are detected, The feeding speed of the mandrel bar is controlled according to the variation in order to suppress the variation in the rolling load in the previous stage to zero when the pipe material is bitten from the previous stage rolling mill to the next stage rolling mill, and A rolling control method for a mandrel mill characterized by using both tension control and reduction control in the rolling mill. 3. After the rear end of the pipe material passes through the rolling mill at the foremost stage, the feeding speed of the mandrel bar is controlled so that the pressing load of the rolling mill at the last stage or the preceding stage remains constant until the end of rolling. A rolling control method for a mandrel mill according to claim 1.