JPH0566202B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a seamless metal tube using an inclined stretching rolling mill, and more specifically, the present invention relates to a method for manufacturing a seamless metal tube using an inclined stretching mill, and more specifically, for straightening uneven thickness by rolling without inner surface regulation. This paper proposes an improvement in the manufacturing method of seamless metal tubes having elongated and rolled sections.

[Prior art]

Generally, in the manufacturing process of seamless metal tubes, elongation rolling is performed using a barrel type inclined roll rolling mill.

In such inclined roll rolling, a core metal such as a plug or a mandrel is used as an inner surface regulating tool to regulate the inner surface of the hollow shell. If the hollow shell is eccentric with respect to the hollow shell, a phenomenon in which the thickness distribution in the cross section of the hollow shell becomes non-uniform, that is, uneven thickness may occur.

The occurrence of uneven thickness can be prevented to some extent by reducing the eccentricity of the core metal with respect to the pass center, but there is a limit to this.

For this reason, several proposals have been made based on the knowledge that uneven thickness can be corrected by reducing the diameter of the inner surface of the hollow shell without restricting it, that is, by so-called empty rolling.

A method of rolling a seamless metal tube based on the principle of correcting thickness unevenness is a method in which after perforating with a perforator, uneven thickness is corrected using an inclined rolling mill that does not have an inner surface regulating process (Japanese Patent Application Laid-Open No. 57-25209 No. and JP-A-57-
68207), or a method of correcting uneven thickness using an inclined rolling mill equipped with a specially shaped roll consisting of an elongated rolling section and an empty kneading section (Japanese Patent Application Laid-Open No. 57-81908 and JP-A No. 51-67511). is proposed.

[Problem that the invention seeks to solve]

The conventional methods described above all use an inclined rolling mill without an inner surface regulating tool or an inclined rolling mill equipped with specially shaped rolls, so it is difficult to install these rolling mills in the rolling process. Accordingly, there is a problem that equipment costs increase.

In particular, in the method of using an inclined rolling mill without an inner surface regulating tool, the rolling process becomes longer due to the addition of the empty rolling process, the material temperature decreases, and it is necessary to install a reheating furnace etc. in the middle of the process. In some cases, there is a problem in that additional equipment costs are required.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing a seamless metal pipe that does not require the installation of a special rolling mill or heater, and is highly effective in correcting uneven thickness. purpose.

[Means for solving problems]

A method for manufacturing a seamless metal tube according to the present invention is a method for manufacturing a seamless metal tube using an inclined stretching rolling mill equipped with a plug, which includes a positioning device for arranging the plug at a predetermined position in the rolling direction. The positioning device positions the plug at a position where the plug contacts the inner surface of the hollow shell at a position where the outer surface of the hollow shell contacts the inclined roll and the gorge portion of the inclined roll when elongation rolling is started. After rolling and the inner surface of the tip of the hollow shell contacts the plug, the flag starts moving in the direction of exit in the rolling direction, and the plug moves when the position where the plug contacts the inner surface of the hollow shell is on the exit side from the gorge part of the inclined roll. The method is characterized in that the plug is positioned at the stop position and the rolling is carried out during the time period from when the rolling process is stopped until the end of the rolling process.

[Effect]

At the start of elongation rolling, the positioning device positions the plug at a position where the position where the plug contacts the inner surface of the hollow shell is between the position where the outer surface of the hollow shell contacts the inclined roll and the gorge part of the inclined roll, and rolling is performed. Therefore, the raw pipe is smoothly bitten by the inclined rolls without causing any trouble due to buckling.

In addition, after the inner surface of the tip of the hollow shell contacts the plug, the plug starts moving toward the exit side in the rolling direction, and stops when the position where the plug contacts the inner surface of the hollow shell is on the exit side from the gorge part of the inclined roll. However, during the subsequent period of time until the end of rolling, rolling is performed with the plug positioned at the stop position, so that a seamless metal tube in which uneven thickness is effectively corrected is manufactured.

〔Example〕

The present invention will be specifically described below based on drawings showing its implementation state.

FIG. 1 is a schematic diagram of an inclined rolling mill used in carrying out the present invention, and FIG. 2 is an enlarged view of the vicinity of the plug when the hollow shell is stably bitten. A hollow shell 6 manufactured by a punching machine (not shown) is formed by inclined rolls 1a and 1 facing each other across a pass line.
b and a plug 2 disposed between them, and after being formed into a thin and long blank tube, it is sent to, for example, a mandrel mill (not shown).

The inclined rolls 1a, 1b are set at a predetermined inclination angle and intersection angle, and the plug 2 is moved a predetermined distance K (this distance is called a flag lead) from the gorge part of the inclined rolls 1a, 1b to the rolling entry side. It is arranged so that its tip is located at the ivy position.

A mandrel bar 3 connected to the plug 2 is rotatably connected to the ram via a shaft joint 4. The ram is coaxially fitted into the cylinder 5, and the ram moves in and out of the cylinder 5 by supplying or discharging pressure oil into the cylinder 5, thereby moving the plug 2.

Therefore, the hollow shell 6 has a distance between the outer circumferential surface thereof in contact with the surfaces of the inclined rolls 1a and 1b and the inner circumferential surface thereof in contact with the plug 2, that is, the distance in the tube axis direction between both contact points, i.e. In a rolled portion having an empty rolling length l, uneven thickness is corrected by diameter reduction rolling without inner surface regulation by a plug, so-called empty rolling.

After that, the hollow shell 6 moves the inclined rolls 1a, 1
A thin-walled long blank tube is formed by elongation-rolling with inner surface regulation until the contact with b is broken, that is, in a rolled portion at a distance L in the tube axis direction.

In the method for manufacturing a seamless metal tube according to the present invention, the position of the plug 2 in the rolling direction is changed by hydraulic operation of a piston, and the tube is stretched and rolled.

That is, the plug 2 is placed on the outer circumferential surface of the hollow shell 6 at a predetermined position before and for a certain period of time after the tip edge contacts the roll surface to prevent poor biting due to head clogging due to buckling. Roll.

The above-mentioned certain period of time refers to the time until the end of the biting of the hollow shell 6 by the inclined rolls 1a, 1b.Actually, after the outer circumferential surface of the tip of the hollow shell 6 contacts the inclined rolls 1a, 1b, the inner circumferential surface of the tip ends. The momentary time it takes for the hollow shell to reach a stable state after contacting plug 2 (usually 0.1 to 0.2
(about seconds).

Note that the above-mentioned certain period of time is the time that has passed since the start of rolling, and the outer surface of the tip of the hollow shell 6 and the inclined roll 1
In order to make the biting more stable, it is preferable to set the time to the point where the contact ends with a and 1b (the exit end point of the rolled portion L in FIG. 2).

This time is determined in advance based on experience, the point at which the hollow shell 6 is bitten is detected by a load meter provided on the inclined roll holding device, and the movement of the plug 2 is started after the set time has elapsed. As a result, the tip of the hollow shell 6 is easily caught between the inclined rolls 1a, 1b and the plug 2.

The predetermined position is, as is clear from FIG.
It is a position between the position where it contacts b and the gorge part (maximum diameter part) of the inclined rolls 1a and 1b,
It is appropriately set within the range of both the above positions according to the pipe manufacturing setup such as the dimensions of the hollow shell 6.

After the biting state of the hollow shell is stabilized, that is, after the inner peripheral surface of the tip of the hollow shell 6 contacts the plug, the time until the end of elongation rolling is at a position closer to the rolling exit side than the above-mentioned position, that is, as shown in Fig. 3. The plug 2 is placed at a position where the position where the plug 2 contacts the inner surface of the hollow shell is on the exit side from the gorge portion of the inclined rolls 1a, 1b, and rolling is performed.

As a result, the diameter reduction rolling without inner surface regulation by the plug 2, that is, the empty kneading length (l in FIG. 2) becomes longer than that at the initial stage of rolling, and the amount of improvement in thickness unevenness of the hollow shell 6 increases.

In this case, it is better to make the amount of movement of the plug 2 as large as possible in order to enhance the effect of correcting uneven thickness, but there is a limit from the viewpoint of preventing buckling.

In carrying out the present invention, the roll opening degree is adjusted in order to keep the rolling ratio of the wall thickness and outer diameter constant at each plug position. That is, when the plug is near the entrance side of the rolling mill, the roll opening degree is increased, and after the plug is moved, the roll opening degree is decreased. Of course, rolling may be performed while allowing the rolling ratio to fluctuate without adjusting the roll opening degree.

Moreover, if rolling is performed with the plug 2 moved a certain amount toward the entrance side of the rolling machine immediately before the end of elongation rolling, so-called bottom clogging can be effectively prevented.

Figure 4 shows the amount of plug movement (mm) when the present invention was carried out using an experimental piercer and changing the amount of plug movement under the following conditions without changing the roll opening degree.
In other words, the relationship between the amount of increase in empty kneading length due to plug movement and the amount of uneven thickness improvement (points) is shown, the horizontal axis shows the amount of plug movement (increase in empty kneading length), and the vertical axis shows the amount of uneven thickness improvement. This is a graph showing the following.

Note that the actual amount of increase in empty kneading due to plug retraction is that the inner diameter is also reduced as the outer diameter is reduced, so the amount of increase will not be increased by the amount of plug retraction as it is, but the amount of increase will be a smaller value than the amount of plug retraction. The value varies depending on the shape of the plug used. In the case of this experiment, the measurement results using the rolling stopping material showed that the empty kneading length l was 6 mm before the plug was moved, but was 27 mm when the plug was moved back 25 mm. The measurement of the empty kneading length l at other plug retraction amounts was omitted due to the complexity of the work to stop the rolling.

Here, the amount of improvement in thickness unevenness is the difference between the thickness unevenness rate before thickness unevenness correction and the thickness unevenness rate after thickness unevenness correction,
Thickness unevenness is a value defined as t _nax − t _nio / t _n × 100 (%), where t _n is the average wall thickness of the pipe, and t _nax and t _nio are the maximum and minimum thicknesses, respectively. .

〔conditions〕

(1) Tool (see Figure 2) Roll entrance face angle θ ₁ : 3.75° Roll exit face angle θ ₂ : 3.5° Plug reeling face angle θ ₃ : 4.0° Plug outer diameter: 48.0mm (2) Tool setting inclination Angle: 6.0° Intersection angle: 3.0° Plug lead K: 46.0mm (before movement) Kaidoshyu opening: 62.0mm (before movement) Gorge roll opening: 45.6mm (after movement) (3) Rolling dimensions Porous shell (uneven thickness) rate 6% and 12.5%): outer diameter
60.3 mm, t _n 8 mm Base pipe: outer diameter 59.0 mm, t _n 3 mm As is clear from Figure 4, the amount of plug movement is large for both hollow shells with a thickness unevenness of 12.5% and 6.0%. In other words, as the empty kneading length increases, the amount of improvement in thickness unevenness increases in a linear function. Further, the amount of improvement in the thickness unevenness ratio is greater when the thickness unevenness ratio of the hollow shell is larger.

According to the present invention, when a hollow shell with a thickness unevenness of 12.5% is stretched and rolled with a plug movement amount of 30 mm,
As a result of the uneven thickness rate being improved by approximately 7 points, the uneven thickness rate
5.5% raw tube is formed.

On the other hand, when rolling is performed with the plug 2 fixed, that is, when the amount of plug movement is zero, the thickness unevenness rate is improved by about 4 points, and a blank pipe with a thickness unevenness rate of 8.5% is formed.

Compared to the case where the plug 2 is fixed and rolled as described above, according to the present invention, it is possible to increase the amount of improvement in thickness unevenness by about 3 points.

Figure 5 shows the plug lead K under the same conditions as above.
An example of the wall thickness distribution in the axial direction of the raw tube after rolling when the plug is moved from 46 mm to 21 mm, that is, the amount of plug movement is 25 mm (the empty kneading length l at this time is 27 mm as described above) is shown on the horizontal axis. The axial distance from the top (cm) to
Also, the vertical axis shows the average wall thickness (mm) at the axial distance.
This is a graph showing the following. The solid line shows the results when the method of the present invention was used, and the broken line shows the results when the conventional method was used. However, if the axial distance from the top indicated by the arrow in the figure is 20
The tube part up to cm is removed by the moving plug.
In other words, this is a portion where uneven thickness has been corrected with the empty kneading length l gradually increasing.

In addition, in the conventional method, the results are obtained when the plug position is fixed at a position where the empty kneading length is 6 mm, which is the same as described above.

Figure 6 is about the same rolling as Figure 5, and the horizontal axis is the axial distance from the top (cm), and the vertical axis is the thickness unevenness rate (%), which shows the average thickness unevenness rate of the steady rolling part. This is a graph shown together with The ● mark indicates the result when the method of the present invention was used, and the ○ mark indicates the result when the conventional method was used. The plug position when using the conventional method is the same as when obtaining the results shown in FIG. The arrow mark in the figure indicates the part where uneven thickness was corrected by the moving plug.

The reason why there is a blank space between the left end of the graph and the vertical axis in Figures 5 and 6 is that flare occurred at the top of the hollow shell, making it unworthy to measure both the wall thickness and thickness unevenness. by.

As is clear from FIG. 6, it can be seen that the thickness unevenness ratio is improved when the method of the present invention is used compared to when the conventional method is used. As is clear from Fig. 5, the average wall thickness increases toward the bottom of rolling when the method of the present invention is used because the roll opening degree was not adjusted. In the conventional method, the thickness decreases toward the bottom of rolling due to the influence of thermal expansion of the mandrel bar, plug, and roll.

〔effect〕

The present invention uses a positioning device that moves the plug in the elongation rolling direction, so that at the start of elongation rolling, the position where the plug contacts the inner surface of the hollow shell is between the position where the outer surface of the hollow shell contacts the inclined roll and the gorge part of the inclined roll. Because the plug is positioned at a position where , the plug starts moving in the exit direction in the rolling direction, stops moving when the position where the plug contacts the inner surface of the hollow shell is on the exit side from the gorge part of the inclined roll, and then the time until the end of rolling is , since rolling is performed with the plug positioned at the stop position, a large uneven thickness correction effect on the hollow shell can be obtained due to the long empty rolling state,
Moreover, unlike the conventional method, it does not require the installation of a new special rolling mill, which is an excellent effect.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an inclined rolling mill used to carry out the present invention, Fig. 2 is an enlarged view showing the vicinity of the plug immediately after the biting state of the hollow shell has stabilized, and Fig. 3 is a diagram showing the plug near the exit side in the rolling direction. FIGS. 4 to 6 are enlarged views showing the vicinity of the plug when it is moved to the desired position, and are illustrations of the effects of the present invention. 1a, 1b... Inclined roll, 2... Plug, 3
...Mandrel bar, 4...Shaft coupling, 5...Cylinder, 6...Hollow shell.

Claims (1)

[Claims] 1. A method for manufacturing a seamless metal tube using an inclined drawing mill equipped with a plug, comprising: a positioning device for arranging the plug at a predetermined position in the rolling direction; At the start of rolling,
The position where the plug contacts the inner surface of the hollow shell is the position where the outer surface of the hollow shell contacts the inclined roll,
The plug is positioned between the gorge part of the inclined roll and rolled, and after the inner surface of the tip of the hollow shell contacts the plug, the plug starts moving in the exit direction in the rolling direction, and the plug contacts the inner surface of the hollow shell. The seamless metal is characterized in that the movement of the plug is stopped at a position where the contact position is on the outlet side from the gorge part of the inclined roll, and the plug is positioned at the stop position for the subsequent time until the end of rolling. Method of manufacturing tubes.