JP4893858B2 - Manufacturing method of seamless metal pipe by cold rolling - Google Patents

Description

  The present invention relates to a method for cold rolling a seamless metal tube, and in particular, manufacturing a high-quality seamless metal tube by cold rolling to guarantee the inner surface quality of a high-grade special tube from the viewpoint of suppressing wrinkle wrinkles on the inner surface of the tube. It is about the method.

  The seamless metal pipe is sent to the cold working process when it cannot satisfy the requirements of quality, strength or dimensional accuracy in the hot finished state. As the cold working process, a cold drawing method using a die and a plug or a mandrel and a cold rolling method using a cold pilga mill are generally used.

  Cold rolling with cold pilga mill has a very high degree of processing of the tube material, can be stretched approximately 10 times by rolling, has a great effect of correcting the uneven thickness of the tube, and further does not require a drawing process. There is an advantage that no yield loss occurs.

  On the other hand, cold rolling with cold pilga mill has the disadvantage that the production efficiency is extremely low compared with the cold drawing method, so that the stainless steel pipe, which is mainly high in material cost and requires intermediate processing costs, Suitable for cold processing of high-grade special pipes such as alloy steel pipes.

  FIG. 1 is a diagram for explaining a cold rolling mechanism by a cold pilga mill. In the cold rolling method using a cold pilga mill, a pair of rolls 2 having a tapered hole mold 3 whose diameter gradually decreases in the circumferential direction, and a tapered mandrel 4 whose diameter gradually decreases in the length direction, The raw tube 1 is reduced in diameter to obtain a rolled tube 5.

  That is, a hole mold 3 is cut on the circumference of a pair of rolls 2 of the cold pill ga mill, and the shape of the roll 2 becomes narrow as the roll 2 rotates. The roll 2 repeats advancing and retreating along the taper of the mandrel while rotating by driving the roll shaft 2s, and the diameter of the raw tube 1 is reduced between the roll 2 and the mandrel 4 (Non-patent Document 1, etc.).

  FIG. 2 is an explanatory diagram showing the cold rolling process principle using a cold pilga mill, wherein FIG. 2A shows the processing status at the starting point of the forward stroke, and FIG. 2B shows the processing status at the starting point of the backward stroke. Yes. As shown in FIG. 2, in the cold Pilgar mill, depending on the outer diameter and thickness dimension (do, to in the figure) and the outer diameter and thickness dimension of the product (d, t in the figure). The roll 2 having the tapered hole mold 3 whose diameter gradually decreases from the biting inlet side to the finishing outlet side of the pair of rolls, and the diameter gradually increasing from the biting inlet side toward the finishing outlet side. The taper-shaped mandrel 4 that is reduced is employed, and the reciprocating rolling process in which the thickness is reduced while the diameter of the base tube 1 is reduced is repeated.

  At the starting point of the reciprocating movement of the cold pilgamill, the tube 1 is intermittently given a rotation angle of about 60 ° and a feed of about 5 to 15 mm, and rolling of a new part of the tube is repeated. .

  Cold Pilgamil consists of a rolling mill developed by “MANNESMANN-DEMAG” that reduces the thickness in both the forward and backward strokes, and a rolling mill developed by “BLAWKNOX” that reduces the thickness only by the forward stroke. There are two methods. Usually, the former is used for rolling stainless steel pipes, high alloy pipes or zirconium pipes, and the latter type of rolling mill is used for rolling aluminum and its alloy pipes and copper and its alloy pipes.

3rd Edition Steel Handbook Volume 3 (2) Common Steel, Steel Pipe and Rolling Equipment 1183 to 1189

  High-grade special pipes that are cold-rolled by cold pilga mill are strongly required to have high-quality characteristics, and in the product pipe after cold rolling, the occurrence of internal flaws due to internal wrinkles must be suppressed. Don't be. However, conventionally, no proposal has been made for a method for producing a high-quality seamless steel pipe free from internal flaws by cold rolling with a cold pilga mill.

  The present invention has been made in view of the above problems, and its object is to propose a method for producing a high-quality seamless steel pipe in cold rolling using a cold pilga mill.

  In the present invention, a cold pilgamill (MANNESMANN-DEMAG) that rolls in both reciprocating strokes will be described. BLAWKNOX) is also applicable.

Means to solve the problem

  In order to solve the above problems, the present inventor has made various studies, and as a result, in cold rolling of seamless metal pipes by cold pilgamil, the outer diameter reduction rate is excessive compared to the wall thickness reduction rate. As a result, it has been found that the circumferential compressive stress applied to the raw tube becomes excessive and wrinkles are likely to occur on the inner surface of the tube.

  Furthermore, apart from the case where the pipe is manufactured by the Eugene extrusion process, when it is manufactured by the Mannesmann mandrel mill process, internal wrinkles are generated at the stage of the pipe by constant diameter rolling (stretch reducer or sizer). There is a risk. Internal wrinkles generated at the raw tube stage have a great influence on the quality of high-grade special tubes to which cold rolling by cold pilga mill is applied.

  The present invention has been completed on the basis of the above findings, and has the gist of the following (1) and (2) a method for producing a seamless metal tube by cold rolling.

(1) A method for producing a seamless metal pipe by a cold pilga mill, which proceeds from the biting inlet side to the finishing outlet side of a pair of rolls according to the outer diameter and the wall thickness of the raw pipe and the product rolled pipe. Using a roll having a tapered hole shape whose diameter gradually decreases and a tapered mandrel whose diameter gradually decreases from the biting inlet side to the finishing outlet side, the thickness is reduced while reducing the diameter. When drawing and rolling, a raw tube finished by hot drawing under a condition of an outer diameter reduction rate of 77% or less by a stretch reducer is used, and the outer diameter reduction rate Rd is set to 1 / th of the wall thickness reduction rate Rt. It is a manufacturing method of the seamless metal pipe by cold rolling characterized by being 2 or less.

However, when do: raw pipe outer diameter, d: finished outer diameter, to: raw pipe wall thickness, and t: finished wall thickness, the outer diameter reduction rate Rd and the wall thickness reduction rate Rt are the following (a ) Calculated by equation (b).
Rd = {1- (d / do)} × 100 (%) (a)
Rt = {1- (t / to)} × 100 (%) (b)

(2) A method of manufacturing a seamless metal pipe using a cold pilga mill from the biting inlet side to the finishing outlet side of a pair of rolls according to the outer diameter and the wall thickness of the raw pipe and the rolled product pipe. Using a roll having a tapered hole shape whose diameter gradually decreases and a tapered mandrel whose diameter gradually decreases from the biting inlet side to the finishing outlet side, the thickness is reduced while reducing the diameter. When drawing and rolling, a raw tube finished by hot drawing with a sizer under a condition that the outer diameter reduction rate is 33% or less is used, and the outer diameter reduction rate Rd is ½ of the wall thickness reduction rate Rt. It is the manufacturing method of the seamless metal pipe by the cold rolling characterized by the following.

  According to the method for producing a seamless metal pipe by cold rolling according to the present invention, when the rolling reduction is performed while reducing the wall thickness while reducing the diameter, the processing balance between the outer diameter reduction rate Rd and the wall thickness reduction rate Rt is achieved. Thereby, generation | occurrence | production of the inner surface wrinkle resulting from an inner surface wrinkle wrinkle can be suppressed, and the product pipe after cold rolling can be made high quality.

  In addition, when the tube is manufactured by the Mannesmann mandrel mill process, the product quality after cold rolling is further improved by limiting the outer diameter reduction rate of constant diameter rolling (stretch reducer or sizer). Can do.

It is a figure explaining the mechanism of the cold rolling by a cold pilga mill. It is explanatory drawing which shows the processing principle of the cold rolling by a cold pilga mill, The figure (a) shows the processing condition in the forward stroke start point, and the figure (b) show the backward stroke start point. It is a figure which shows the division | segmentation model of the pipe cross section rolled with a cold pilga mill. It is a figure which shows the deformation | transformation behavior of the pipe cross section rolled with a cold pilga mill. It is a figure explaining an example of the manufacturing process of the Mannesmann mandrel mill process which manufactures a seamless steel pipe hot.

  FIG. 3 is a diagram showing a divided model of a pipe cross section rolled by a cold pilga mill. Depending on whether or not the inner surface of the tube 1 is in contact with the mandrel 4, the tube cross section can be divided into regions of the groove bottom side 11, 14 and the flange side 12, 13. The groove bottom sides 11 and 14 are subjected to wall thickness processing by a roll and a mandrel 4 and stretch-rolled, and the flange sides 12 and 13 are pulled and deformed by stretching on the groove bottom side. That is, the material on the groove bottom sides 11 and 14 is deformed under external pressure, internal pressure and axial compression force, and the material on the flange sides 12 and 13 is deformed under external pressure and axial tension.

  4A and 4B are diagrams showing deformation behavior of a pipe cross section rolled by a cold pilga mill. FIG. 4A is a deformation behavior in forward rolling (forward rolling), and FIG. 4B is a backward stroke. The deformation behavior in rolling (re-rolling) is shown. The deformation behavior shown in FIG. 4 is based on a processing pattern in which the turn of the tube 1 is given only in the forward rolling and not in the reverse rolling. From the viewpoint of the pipe material, the roll is rotated relative to the pipe material only in the forward stroke. However, there is no relative rotation in the return stroke.

  As shown in Figs. 4 (a) and 4 (b), the cold pilga mill (MANNESMANN-DEMAG), which rolls in both reciprocating strokes, basically has a 60 ° turn. It is not symmetric with respect to the vertical axis, but is asymmetrical deformation. In the deformation behavior shown in FIG. 4, in the i-th forward rolling, sections 11 and 14 indicate the groove bottom side, and sections 12 and 13 indicate the flange side.

In the deformation behavior shown in FIG. 4, if the outer diameter reduction rate Rd is too large with respect to the wall thickness reduction rate Rt, the circumferential compressive strain _φθ on the flange side increases, resulting in a circumferential compressive stress. σ _θ (not shown) becomes excessive, generating inner surface wrinkles, convolved on the groove bottom side, and this is repeated to develop into inner surface wrinkles, deteriorating the inner surface quality.

  In the manufacture of special pipes that require high quality characteristics, the ratio of the outer diameter reduction rate Rd to the wall thickness reduction rate Rt determines the quality of the product. Moreover, apart from the case where the pipe used for the cold pilga mill is manufactured by the hot extrusion (Eugene extrusion) process, the pipe manufactured by the Mannesmann mandrel mill process is generated in the hot drawing rolling process. There are internal wrinkles that appear and are further encouraged in the cold rolling process.

  Drawing 5 is a figure explaining an example of the manufacturing process of the Mannesmann mandrel mill process which manufactures a seamless steel pipe hot. In this process, a solid round billet 21 heated to a predetermined temperature is used as a material to be rolled, the round billet 21 is fed to a piercing and rolling machine 23, and the axial center portion is pierced to form a hollow piece (or a hollow element). Tube) 22 is manufactured. Next, the produced hollow piece 22 is fed as it is to a drawing and rolling device of the subsequent mandrel mill 24 and drawn and rolled to obtain a hollow shell (or a raw tube) 22.

  When the hollow shell 22 is drawn and rolled by the mandrel mill 24, the material temperature of the hollow shell 22 is lowered during drawing by the mandrel bar 24b inserted on the inner surface of the hollow shell 22 and the rolling roll 24r that regulates the outer surface of the hollow shell. For this reason, the hollow shell 22 rolled by the mandrel mill 24 is then charged into the reheating furnace 25 and reheated. Then, it becomes the seamless steel pipe hot-rolled through constant diameter rolling of the stretch reducer 26 or a sizer (not shown). If the temperature drop in the mandrel mill is small, a reheating furnace is unnecessary.

  However, in the above-described Mannesmann mandrel mill process, in the stretch reducer or sizer that performs constant diameter rolling, the hollow shell 22 is passed through the rolling roll 26r without using the inner surface regulating tool such as a mandrel. Since it is finished by drawing, wrinkles are likely to occur on the inner surface of the hot-finished steel pipe.

  Therefore, in addition to the hot extruded element pipe, the present inventor used as a test material an element pipe that has been drawn and rolled with a stretch reducer and a sizer, Rolling experiments were carried out with varying thickness reduction rate, and macro-structural observations were repeated to investigate the conditions for suppressing wrinkles.

  As described above, in the cold rolling of seamless metal pipes by cold pilga mill, if the outer diameter reduction rate is excessive compared to the wall thickness reduction rate, the circumferential strain on the flange side becomes excessive, resulting in The circumferential compressive stress becomes excessive and wrinkles are generated on the inner surface of the pipe, and it is folded on the groove bottom side to form a folded wrinkle, which is repeated to develop into an inner surface wrinkle.

  As a result of the above investigation, apart from the case where the pipe is manufactured by the hot extrusion process, when the pipe is manufactured by the Mannesmann mandrel process, the inner wrinkle is formed at the stage of the pipe by constant diameter rolling (stretch reducer or sizer). In the case where wrinkles may occur and there are wrinkles on the inner surface, it is further promoted by cold rolling, so care must be taken.

  In the method of manufacturing a seamless metal pipe by cold rolling according to the present invention, in addition to the hot extruded element pipe to be adopted, a cold pilga mill is taken into consideration that the element pipe subjected to hot constant diameter rolling is an object. The outer diameter reduction rate at should be ½ or less of the thickness reduction rate.

  In the method for producing a seamless metal pipe by cold rolling according to the present invention, when a constant diameter rolling is performed by a stretch reducer, a raw pipe finished by hot drawing and rolling under a condition that the outer diameter reduction rate is 77% or less is used. In addition, it is desirable to use a raw tube finished by hot drawing and rolling under a condition that the outer diameter reduction rate is 33% or less when constant diameter rolling is performed by a sizer.

  Take as an example the case where a raw material manufactured by the hot extrusion (Eugene extrusion) process and the Mannesmann mandrel mill process (stretch reducer and sizer finish) is used as a test material, and the diameter is reduced by cold working in a cold pilga mill. , Evaluated the internal quality of the product.

Example 1
A 25Cr-30Ni-3Mo high alloy steel pipe having an outer diameter of 50.8 mm and an inner thickness of 5.5 mm manufactured by a hot extrusion process was used as a test element pipe, and an outer diameter of 38.1 mm and a wall thickness of 2. The diameter was reduced to 4 mm. Feed and turn angles are given at the start of the journey. The experimental conditions are summarized below.

Tapered mandrel diameter: dm = 39.6-33.1 mm (with taper)
Outward travel feed (f): f = 8.0mm
Outward turn angle (rotation angle): θ = 60 °
Base tube dimensions: do × to = 50.8 mm × 5.5 mm
Finishing dimensions: d × t = 38.1 mm × 2.4 mm
Reduction ratio: d / do = 0.75
Stretch ratio: to (do-to) / t (dt) = 2.91
Thickness / outer diameter ratio: t / d = 0.063
Outer diameter reduction rate / thickness reduction rate ratio: Rd / Rt = 0.46 <1/2
However, the outer diameter reduction rate: Rd = {1- (do / d)} × 100 (%)
Thickness reduction rate: Rt = {1- (to / t)} × 100 (%)

  Since the extruded tube has no wrinkle generation, the product after cold rolling has very little internal wrinkle due to wrinkle generation, and satisfactory internal quality was obtained. .

(Example 2)
Using a Mannesmann mandrel mill process, a 25Cr-30Ni-3Mo high alloy steel pipe with an outer diameter of 48.6 mm and a wall thickness of 6.0 mm manufactured by a cross-drilling machine, mandrel mill and stretch reducer was used as a cold pill. The steel was reduced in diameter to 41.0 mm in outer diameter and 2.2 mm in thickness with a gamil. The outer diameter reduction rate in the stretch reducer is 77% or less. The experimental conditions are summarized below.

Tapered mandrel diameter: dm = 36.4 mm (no taper)
Outward feed: f = 8.0mm
Outward turn angle: θ = 60 °
Tube size: do x to = 48.6mm x 6.0mm
Finishing dimension: d × t = 41.0mm × 2.2mm
Reduction ratio: d / do = 0.84
Drawing ratio: to (do-to) / t (dt) = 3.0
Thickness / outer diameter ratio: t / d = 0.054
Outer diameter reduction rate / thickness reduction rate ratio: Rd / Rt = 0.25 <1/2
However, the outer diameter reduction rate: Rd = {1- (do / d)} × 100 (%)
Thickness reduction rate: Rt = {1- (to / t)} × 100 (%)

  The outer diameter reduction rate of the stretch reducer is 77% or less, but because it is drawn and rolled while applying the maximum tension between the stands by full stretch setup, the occurrence of wrinkles on the inner surface is suppressed as much as possible. In the product after rolling, the occurrence of inner surface wrinkles due to wrinkle wrinkles was slight, and satisfactory inner surface quality was obtained.

(Example 3)
By using Mannesmann Mandre mill process, 25Cr-30Ni-3Mo high alloy steel pipe with outer diameter of 101.6mm and wall thickness of 7.0mm manufactured by cross drilling machine, mandrel mill and sizer was used as a cold test tube. The diameter was reduced by a mill to an outer diameter of 88.9 mm and a wall thickness of 2.8 mm. The outer diameter reduction rate in the sizer is 33% or less. The experimental conditions are summarized below.

Tapered mandrel diameter: dm = 83.8 mm (no taper)
Outward feed: f = 10.0mm
Outward turn angle: θ = 60 °
Base tube dimensions: do × to = 101.6 mm × 7.0 mm
Finishing dimensions: d × t = 88.9 mm × 2.8 mm
Reduction ratio: d / do = 0.88
Drawing ratio: to (do-to) / t (dt) = 2.8
Thickness / outer diameter ratio: t / d = 0.032
Outer diameter reduction rate / thickness reduction rate ratio: Rd / Rt = 0.21 <1/2
However, the outer diameter reduction rate: Rd = {1- (do / d)} × 100 (%)
Thickness reduction rate: Rt = {1- (to / t)} × 100 (%)

  The outer diameter reduction rate of the sizer is 33% or less, which is considerably smaller than the outer diameter reduction rate of the stretch reducer, so the occurrence of wrinkles on the inner surface is suppressed as much as possible. The generation of internal wrinkles due to wrinkle wrinkles was slight, and satisfactory internal surface quality was obtained.

  According to the method for producing a seamless metal pipe by cold rolling according to the present invention, when the rolling reduction is performed while reducing the wall thickness while reducing the diameter, the processing balance between the outer diameter reduction rate Rd and the wall thickness reduction rate Rt is achieved. Thereby, generation | occurrence | production of the inner surface wrinkle resulting from an inner surface wrinkle wrinkle can be suppressed, and the product pipe after cold rolling can be made high quality.

  In addition, when the tube is manufactured by the Mannesmann mandrel mill process, the product quality after cold rolling is further improved by limiting the outer diameter reduction rate of constant diameter rolling (stretch reducer or sizer). Can do. By these, it can apply widely as a manufacturing method of the high quality seamless metal pipe by cold rolling.

1: Raw pipe, 2: Hole type roll, 3: Tapered hole type 4: Tapered mandrel, 5: Rolled pipe 11, 14: Groove bottom side section, 12, 13: Flange side section 21: Round billet, 22: Hollow piece, hollow shell 24: mandrel mill, 25: reheating furnace 26: constant diameter rolling mill, stretch reducer

Claims (2)

A method of manufacturing a seamless metal pipe by cold pilgamil,
According to the outer diameter and the wall thickness of the raw tube and the product rolling tube, a roll having a tapered hole shape whose diameter gradually decreases from the biting inlet side to the finishing outlet side of the pair of rolls;
Similarly, using a tapered mandrel whose diameter gradually decreases from the biting inlet side toward the finishing outlet side,
When drawing and rolling while reducing the wall thickness while reducing the diameter, use a tube that has been hot-rolled and finished with a stretch reducer with an outer diameter reduction rate of 77% or less. A method for producing a seamless metal pipe by cold rolling, characterized in that the thickness reduction rate R is 1/2 or less.
However, Rd = {1- (d / do)} × 100 (%)
Rt = {1- (t / to)} × 100 (%)
do: outer diameter of raw pipe, d: outer diameter of finish, to: thickness of raw pipe, t: thickness of finished pipe A method of manufacturing a seamless metal pipe by cold pilgamil,
According to the outer diameter and the wall thickness of the raw tube and the product rolling tube, a roll having a tapered hole shape whose diameter gradually decreases from the biting inlet side to the finishing outlet side of the pair of rolls;
Similarly, using a tapered mandrel whose diameter gradually decreases from the biting inlet side toward the finishing outlet side,
When drawing and rolling while reducing the wall thickness while reducing the diameter , a blank tube finished by hot rolling with a sizer under conditions with an outer diameter reduction rate of 33% or less is used, and the outer diameter reduction rate Rd is increased. A method for producing a seamless metal tube by cold rolling, characterized in that the thickness reduction rate Rt is 1/2 or less.
However, Rd = {1- (d / do)} × 100 (%)
Rt = {1- (t / to)} × 100 (%)
do: outer diameter of raw pipe, d: outer diameter of finish, to: thickness of raw pipe, t: thickness of finished pipe

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