JPS6037209A - Method and device for manufacturing cold drawn steel pipe - Google Patents

Abstract

PURPOSE:To manufacture a cold drawn steel pipe having smooth inner and outer surfaces by cold drawing a straight-seam electric welded pipe after removing the weld beads of its outer and inner surfaces by using a die having an approaching angle capable of minimizing the change of wall thickness. CONSTITUTION:A steel strip 110 is formed into a tubular steel pipe 1111 by a forming mill 12 and the pipe 1111 is welded into a blank pipe 112. Next, the pipe 112 after cutting the beads of its inner and outer surfaces by a bite 14, is cooled through a coolant zone 15 and is drawn, after aligning its center by a push pointer 17, by a continuous drawing machine 18 while supplying a lubricant from a pump 16. The drawing machine 18 consists of two dies 191, 192 arranged in tandem and a drawing mechanism 21; the dies 191, 192, having each an approaching angle capable of making the changing quantity of wall thickness to be zero in accordance with a target reduction rate of outer diam., are used for this purpose. A cold drawn blank pipe 113 is straightened by a straightener 22, and is cut into a steel pipe 114 having a prescribed dimension by a flying press cutter 23.

Description

[Detailed description of the invention] The present invention relates to a method and apparatus for manufacturing cold drawn steel pipes.

More particularly, the present invention relates to a method and apparatus for manufacturing cold drawn steel pipe with smooth inner and outer surfaces from straight seam electric resistance welded pipe.

Cold-drawn steel pipes have good surface properties and dimensional accuracy, and the deformation mechanism itself, in which the pipe changes while abutting against the inner surface of the die, makes it suitable for high-mix, low-volume production of thin-walled, small-diameter pipes, and irregularly shaped pipes. Furthermore, the added value of the product can be increased by controlling the mechanical properties by combining cold drawing conditions and heat treatment conditions.

However, cold drawing of steel pipes, especially inexpensive ERW steel pipes, is a complicated process, so it is often performed on a line separate from the ERW welding line at an ERW pipe factory, or by a secondary processing manufacturer. It's here. Cold drawing of ERW pipes consists of the following steps.

(1) Heat treatment process Necessary to reduce the hardness of the ERW pipe joint weld,
For example, grilling or tempering is performed.

(2) Pickling process The scale deposited on the surface by heat treatment is removed with 5-20% sulfuric acid or the like.

(31i'll lubricating process: Forms a lubricating film of phosphate or metal soap for drawing process.

(4) Mouth drawing process In order to attach a chuck to the steel pipe during drawing, the tip is pre-squeezed with a rotary swager.

(5) Cold drawing process Pull out the ERW tubes one by one using a die.

(6) Process of cutting off and refining the opening part This conventional cold drawing process involves many processes, including (1) a long processing time (usually 2 to 3 days); (21) Processing cost becomes high (pickling cost including degreasing cost, lubrication treatment cost, etc.), f3) Yield is poor (usually deteriorates by 2 to 3% because it is necessary to cut off the opening part, etc.), etc. has the disadvantages of

On the other hand, as a method for manufacturing small diameter steel pipes from electric resistance welded pipes, a hot trench reducer or a cold reducer may be used. However, these facilities are large-scale and expensive, and the deformation mechanism is complex, making it difficult to obtain products with fixed dimensions and shapes.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a simpler method for cold drawing an ERW tube.

A further object of the present invention is to provide a method and apparatus for manufacturing cold-drawn steel pipes with smooth inner and outer surfaces from straight seam electric resistance welded pipes.

Principle of the Invention The inventors of the present invention believe that the main reason why the conventional cold drawing process of electric resistance welded pipes is complicated and takes a long time is the heat treatment process to reduce the hardness of the welded part, so this process was omitted. The present invention was completed by examining the possibility of doing so. If it is possible to omit heat treatment, the pickling process for scale removal can also be omitted, and the other processes include weld bead removal means and lubricating oil at the rear of the electric welding machine on the ERW pipe manufacturing line. By arranging the applying means, the drawing die, etc. in tandem, it becomes possible to carry out the process continuously with the electric resistance stitching process.

In other words, the present inventors have discovered that by omitting the heat treatment process, cold drawing, which was conventionally performed on a separate line or factory, can be continuously performed on the same line as the ERW tube manufacturing line. This is what I focused on.

Figure 1 shows the hardness distribution in and around the welded part of an ERW steel pipe. The hardness test piece was a 0.4%C-1.5%Mn steel strip of 45Φm at a welding speed of 30m/min and a heat coefficient of 13.2.
mX4. The weld beads on the inner and outer surfaces were removed after thermage tool welding was performed on Ova. In the figure, the horizontal axis W indicates the circumferential distance from the center of the weld, and the vertical axis indicates the Vickers hardness HvlO measured under a load of lok+r. In this way, the welded part undergoes thermal cycles of heating, pressurizing, melting, and cooling, so its hardness increases significantly, making it difficult to deform plastically.

Figure 2 shows the welded part and other parts when cold drawing is performed on an ERW pipe that has not undergone heat treatment to reduce the hardness of the welded part, i.e. with the inner and outer weld beads removed after 1st electric welding. It shows the difference in the amount of change in wall thickness. The test piece is 0.12
%C-0,4%Mn steel strip at a speed of 50 m/min.
It is an electric resistance welded steel pipe manufactured by high frequency induction welding of , KHz.
Dry drawing was performed using dies with different approach angles. The diameter Do of the test piece before drawing is 34Φn1
The wall thickness TO was 4.511. As shown in FIG. 2(A), the thickness of the welded part after drawing is T1, the thickness of the other parts is T2, and the amount of decrease in the outer diameter is ΔD. Outer diameter reduction rate ΔD/D. Figure 2 (B) shows the results of tests with different (%) values.

As shown by the letter a in Fig. 2 (B), when the undercut i is relatively large (approximately 0.1 m), as shown by the broken line A, the outer diameter reduction rate increases and the thickness increases in areas other than the welded part. As a result, the amount of undercut has also increased. On the other hand, as shown in the text above, when the undercut amount is small (approximately Owm), the verticality of the undercut increases as the outer diameter reduction ratio increases, but when comparing broken line B with broken line A, It can be seen that this tendency is not as pronounced as in case A. On the other hand, in the case of a high cut (approximately -0.1 mm) as shown by the letter C, as shown by the broken line C, as the outer diameter reduction rate increases, the thickness increases in areas other than the welded part, resulting in T1 and T2.
The difference is shrinking. However, some of the corners (both edges) of the high cut remain and become notched.

As described above, when the outer diameter is continuously reduced by dry drawing, the amount of undercut near the bead generally tends to increase as the outer diameter reduction rate increases. This increase in strength becomes more pronounced as the amount of undercut before drawing increases. If the shape near the weld is undercut, it will not only significantly reduce the commercial value of the steel pipe (it will remain as a notch-shaped groove on the inner surface of the weld,
Practical mechanical properties are adversely affected and problems such as corrosion occur. Such problems of deterioration of mechanical properties and corrosion are not unrelated even when the vicinity of the bead is high cut. In this case as well, two notch-shaped grooves remain in a part of the high cut corner.

Therefore, in the prior art, heat treatment is an essential step in order to remove the influence of the hardness of the welded portion.

The inventors of the present invention conducted various experiments with the aim of streamlining the process of cold drawing of the above-mentioned electric resistance welded pipe and furthermore, making it continuous with the current line, and discovered the following. In other words, it was discovered that even if the ERW pipe is ERW-welded, it is possible to reduce the amount of change in the wall thickness to zero by appropriately combining the approach angle and outer diameter reduction rate. .

The present invention is based on this discovery, and when cold-drawing an ERW raw pipe (ERW steel pipe cut to size may of course be used) with the welded bead removed from the inner and outer surfaces, it is possible to Select a die with an approach angle that makes the amount of change in wall thickness zero according to the diameter reduction rate (predetermined from the outer diameter of the ERW tube and the outer diameter of the cold-drawn steel tube to be processed), and draw with this die. Through processing, we succeeded in providing a steel pipe with a smooth inner surface.

Furthermore, if the approach angle to achieve zero change in wall thickness in one drawing process is too large and cold drawing is mechanically impossible or extremely difficult, cold drawing may be performed using dies with different approach angles. The cold drawing process is performed in two or more times, and the increase in wall thickness from the first time is absorbed by reducing the wall thickness in the second and subsequent drawing processes, resulting in zero or no change in wall thickness as a whole. It is possible to make it a small value.

Therefore, two dies with different approach angles are installed in tandem behind the ERW welding machine on the existing ERW pipe manufacturing line, and the line is modified to change the approach angle and outer diameter reduction ratio of these dies as appropriate. Then, it is possible to continuously manufacture cold-drawn steel pipes with a clean inner surface in a wide range of product dimensions and in various shapes from an electric resistance welded raw pipe of a predetermined size.

Data on wall thickness changes depending on the approach angle of the die and the outer diameter reduction rate, which are the basis of the present invention, will be explained with reference to FIG.

In Figure 3, (A), (B), (C) and (D)
are the wall thickness/outer diameter ratio of the raw pipe To/Do-5%, respectively.
Graphs of experimental data corresponding to representative cases of 10%, 15% and 20% °, showing thickness increase rates Δ when drawing with different approach angles α as parameters.
T / To (%) is the outer diameter reduction rate ΔD /
It is plotted against Do (%). here,
To represents the wall thickness before the drawing process, and ΔT represents the thickness increase due to the process. Note that cold drawing was performed at a constant speed.

As seen in Figure 3, the wall thickness/outer diameter ratio To/
When the approach angle α of the die is selected for Do, the thickness increase rate ΔT / T o (%) becomes the outer diameter reduction rate ΔD /
It can be seen that it can be plotted as a function of Do (%). In other words, the thickness increase rate is determined by selecting the approach angle at a predetermined outer diameter reduction rate. Therefore, first select a graph of the wall thickness/outside diameter ratio of the raw pipe, and then use that graph to determine the wall thickness increase rate within a mechanically reasonable outside diameter reduction rate range (usually 2% to 35%). Determine the schedule for selecting a die with an approach angle that makes the value zero. Perform the drawing process using the selected die. If the intended outer diameter reduction rate in this drawing is within the above range, the machining is completed with this one pass. However, if the outer diameter reduction ratio required to produce the product exceeds the range, measure the wall thickness/outer diameter ratio anew after the first pass, and graph the corresponding ratio. , and from that graph, determine a schedule to reduce the thickness to absorb the previous thickness increase and select an approach angle that will make the total thickness increase zero, and then perform the drawing process using a die with the selected approach angle. conduct. In this second pass, the diameter is reduced to the desired outer diameter and the drawing process is completed. however,
If the desired outer diameter has not yet been achieved, repeat the third and subsequent passes using the same schedule.

In the above description, the thickness increase rate ΔT/To (%) is set to zero by measuring the wall thickness/outer diameter ratio when moving from the first pass to the second pass, or from the graph corresponding to the first pass. Read the outer diameter reduction rate ΔD / Do (%), calculate the diameter after diameter reduction from this value, read and calculate the wall thickness from the graph, and calculate a new wall thickness / outer diameter ratio. You can also select the graph corresponding to the calculated ratio. If you repeat this process, you can simply read ΔD/Do (%) etc. from the graph and calculate the wall thickness/outer diameter ratio, and it will take several passes (in the case of an ERW steel pipe mill line, multiple passes with different approach angles). It is easy to see that the desired outer diameter reduction ratio can be obtained without increasing the thickness by using the die), and the drawing process can be performed continuously in the line according to the entire schedule.

In other words, when drawing is performed multiple times, the thickness increase in the base material can be made zero or minimal in the end, so it is not necessary to select a schedule in which the thickness increase rate is zero in each pass.

For example, even if there is an increase (or decrease) in the approach angle to be selected for each pass due to operational restrictions, a schedule for decreasing (or increasing) the thickness to cancel out the increase may be used to make the final decision. It is also possible to reduce the thickness increase to zero or to a minimum.

In this way, even if there are constraints on the processing conditions themselves, the number and content of schedules can be freely selected within the constraints.

DETAILED DESCRIPTION OF THE INVENTION The layout of a mill line 10 to which the method of manufacturing cold-drawn steel pipes from electric resistance welded pipes according to the present invention is applied will be described below with reference to FIG. 4. First, a steel strip 11°, which is a material, is processed through a forming mill 12 consisting of a plurality of pairs of ■ (vertical) rolls 12a and H (horizontal) rolls 12b.
to form a tubular steel strip 111. This tubular steel strip 11
1 seam, for example, using welder 1 of high frequency induction heating welding.
Join in step 3 and make a pipe. The welder 13 includes a work (induction) coil 13a and a pair of squeeze rolls 13.
It consists of b. After welding, the raw tube 112 is bead-cut on its inner and outer surfaces with a piezo 4 for the outer surface (the cutting tool for the inner surface is not shown), and then cooled by passing it through the coolant zone 15. The cutting tool 14 may be located downstream of the coolant zone 15. Before performing continuous drawing, the cooled raw pipe 112 is supplied with lubricating oil from an oil supply pump 16 and aligned by a bushing pointer 17, and then drawn by a continuous drawing machine 18 used in the method of the present invention. be done.

The lubricating oil contains 3 to 15 wt% sulfur and is heated at 40°C.
It is preferred to use a sulfurized oil or fat having a viscosity of 200 to 5000 cst. In addition, the above sulfurized oil has a particle size of 20
5 to 30 thermoplastic polymer powders of 0 μm or less
It is possible to use a mixture containing wt%.

This continuous drawing machine 18 includes, for example, two tandemly arranged dies 191 and 192;
and a drawing mechanism 21 that continuously cold-draws the raw pipe 112 in combination. As mentioned above, the approach angle α of the die is appropriately selected according to the drawing conditions. Further, the number of dice may be two or more. The extraction mechanism 21 includes a carriage 21 mounted with a pair of catching devices arranged in tandem on the mill line.
A is a mechanism that continuously generates a pulling force in the line direction by complementarily repeating the process of catching, pulling out, and returning to the origin of the raw pipe 112.

The raw tube feeding speed of the carriage 21a is the same as that of the squeeze roll 13.
It is synchronized with the feeding speed of the raw pipe according to b. This speed can be easily calculated by detecting the speed of the roll 13b and from the outer diameter and wall thickness of the raw pipe at each location according to the law of constant volume.

The cold-drawn blank tube 113 is straightened by a straightener 22 and then cut into desired dimensions by a flying press cutter 23. The cut steel pipe 115 is subjected to pipe end processing, anti-corrosion processing, etc. as usual, and then shipped as a product.

The method of the present invention will be explained below using examples.

Example ERW welded pipe (D = 34++un, T = 3.5mm) with weld beads on the inner and outer surfaces removed using a cutting tool
was drawn into a size of 23.1φn x 3.52m. In this case, we used the following two buses (1) and (2).

(11To/D o = 10.3 (%), α=
Add an outer diameter reduction of ΔD/D=15(%) at 30°.

Ru. In this case, as shown by the letter d in Fig. 4(B), approximately 28 mm of raw pipe is obtained by cold drawing using this bath.
．． Processed to 9φvna x 3.5 ta (no thickening).

(2) After processing, “T”o/Do=12.1%, and this time, 20% outer diameter reduction is applied at an approach angle of 20°.

In this second bus, the raw pipe is 23.1Φ, X 3.5
2mm! (The thickness increase is 0.6%).

As a result, the base metal thickness increase was suppressed to 0.02 mm.

On the other hand, if the same 34φ dragon
/D. = 10.3 (%), the aperture condition is approximated by the letter e in FIG. 4(B).

In this case, ΔD/Do = 32%, and the resulting thickening graph shows 3.5 Xo, 02B = 0.1 (mm)
becomes.

The actual values in this case were that the base metal wall thickness of the cold-drawn steel pipe was 3.63 (mm) and the undercut was 0.120.

In this way, compared to the increase in thickness of 0.1 (mm) when an α-20' die is used in one pass, the drawing process is performed in two passes by selecting a schedule that minimizes the increase in thickness according to the present invention. For example, the increase in thickness of the base material can be suppressed to 0.02 (mm).

As described in detail above, according to the present invention, a cold-drawn steel pipe can be manufactured with a small increase in the thickness of the base material, and therefore no thickness deviation in the pipe circumferential direction and smooth inner and outer surfaces.

Furthermore, since the drawing process is performed continuously with the manufacture of the electric resistance welded raw pipe, the processing time is significantly shortened. Furthermore, since the pickling process is replaced by the usual coil pickling of the raw pipe, processing costs are also significantly reduced. Furthermore, it is sufficient to carry out the mouth drawing process once at the start of the continuous drawing process, so that the yield decreases by 0.1% or less.

The effects of the present invention other than greatly shortening the fabrication process are as follows.

■ Continuous production of thin-walled and small-diameter steel pipes becomes easy.

■ Steel pipes with good internal and external properties can be replaced.

■ Steel pipes with good dimensional accuracy can be manufactured.

■ It is now possible to manufacture steel pipes with versatile specifications using the same forming mill, reducing the number of man-hours involved in changing rolls.

■ It becomes possible to manufacture steel pipes with special cross-sectional shapes.

[Brief explanation of drawings]

FIG. 1 is a graph showing the hardness distribution of the welded portion of the raw pipe and its vicinity. Figure 2 is an explanatory diagram showing the principle of the present invention, (A) is an enlarged view of a welded part of an electric F11 steel pipe, and (B) is an enlarged view of the welded part of an electric F11 steel pipe. It is a graph plotting meat against outer diameter reduction rate. FIG. 3 shows a schedule for implementing the method of the present invention, and (A), (B), (C), and (D) are respectively shown when the wall thickness/outer diameter ratio of the raw pipe is 5. %, 10%, 15
% and 20%. An example of an ERW steel pipe manufacturing line including drawing equipment is shown. (Main reference numbers) 11o: steel strip, 111: tubular steel strip, 112: electric welded raw pipe, 113: cold drawn raw pipe, 114: cold drawn steel pipe, 1
2: Forming mill, 13: Welder, 14: Tool for cutting internal and external beads, 15: Coolant zone, 18: Continuous drawing machine, 191.1
92: Dice, 21: Pulling mechanism, 23: Flying press force vine, Applicant: Sumitomo Metal Industries Co., Ltd. Agent Patent attorney: Yasune Arai Figure 1 -y5-yo -5θ 51σ 15 Wc object 4a) Figure 2 j5@ Chojuku Tt -T+ (s sacrifice) Fig. 3 4"/To'%) To/D. = wo outside 41; 'To'%) To/Da = 70 ax Fig. 3

Claims (3)

[Claims] (1) A method for manufacturing a cold-drawn steel pipe, which comprises cold-drawing a straight seam electric resistance welded pipe from which internal and external weld beads have been removed using a die with an approach angle that minimizes changes in wall thickness. (2) The above cold drawing process is performed using two or more dies with different approach angles, and the respective approach angles and outer diameter reduction rates in these cold drawing processes are calculated as follows: Claim 1, characterized in that the change in wall thickness is determined to be minimized based on the ratio of the wall thickness to the outer diameter of the electric resistance welded pipe and the outer diameter of the cold drawn steel pipe to be manufactured. A method for manufacturing cold drawn steel pipes. (3) a forming mill that forms the copper strip into a tubular shape; an electric resistance welding machine that welds the joints of the copper strip; a means for removing weld beads on the inner and outer surfaces of the welded raw pipe; a first die; a second die having a different approach angle from the first die; a means for continuously pulling out the raw pipe from the outlet of the second die; a means for cutting the cold drawn raw pipe; , a cold drawn steel pipe manufacturing apparatus characterized in that these are continuously arranged on the same manufacturing line.