JP2022055384A - Manufacturing method and manufacturing facility of seamless steel pipe, and billet processing tool - Google Patents

Abstract

To manufacture a seamless steel pipe having high accuracy thickness dimension by suppressing occurrence of thickness deviation in a pipe circumferential direction on an original pipe in billet drilling and rolling.SOLUTION: Prior to billet drilling and rolling, a convex punch is pushed into a midship part on an apical surface of a hot billet to thereby form a hollow x, and in the billet drilling and rolling, drilling and rolling is started in the state where the tip of a piercing plug is positioned in the hollow x. Hereby, since the center of the piercing plug agrees with the center of the billet, thickness deviation in a pipe circumferential direction on an original pipe is suppressed, to thereby manufacture a seamless steel pipe having high accuracy thickness dimension.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for manufacturing a seamless steel pipe, which is characterized by having a preliminary step performed prior to drilling and rolling the billet, as well as manufacturing equipment and a billet processing tool provided for the manufacture thereof.

Seamless steel pipes used for oil country tubular goods and the like are manufactured from steel slabs called billets (steel slabs with a round or square cross section). In the manufacturing process of seamless steel pipes, billets heated in a heating furnace (for example, round billets) are drilled and rolled in a piercer mill (drilling mill) using an inclined rolling roll and a drilling plug to make a raw pipe, and then this raw material is continued. The pipe is stretched and rolled to the shape of a pipe by a rolling mill group consisting of an elongator, a plug mill and a reeler, or a mandrel mill. The pipe body thus obtained is heated in a reheating furnace and then processed by a sizing mill or a stretch reducer to narrow down the outer diameter and the wall thickness to predetermined dimensions to obtain a product steel pipe (for example, Patent Document 1). ..
In the drilling and rolling of billets by a piercer mill, a special rolling tool called a drilling plug is placed in the direction of travel of the billet while giving advanced force to the hot billet by the tilted rolling roll, and the billet is placed in the gap between the tilted rolling roll and the drilling plug. Introduces strain that leads to plastic deformation, and processes it into the shape of a raw tube by penetrating the billet.

Japanese Unexamined Patent Publication No. 2016-185553

In the drilling rolling of billets by a piercer mill (punching rolling mill), when the drilling plug and the billet start to come into contact immediately before the drilling rolling, if the center of the drilling plug and the center of the billet do not match, the product wall thickness will be increased to the raw pipe. There is a problem that uneven thickness (unbalanced thickness in the circumferential direction of the pipe) that affects the thickness occurs, which becomes a factor that hinders the production of product steel pipes having a highly accurate wall thickness dimension.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art, reduce the uneven thickness of the raw pipe in the drilling and rolling of the billet, and produce a seamless steel pipe having a highly accurate wall thickness dimension. The purpose is to provide a method for manufacturing a steel pipe.
Another object of the present invention is to provide a manufacturing facility and a billet processing tool (punch) suitable for carrying out such a method for manufacturing a seamless steel pipe.

As a result of repeated studies to solve the above problems, the present inventors have formed a dent by pushing a punch into the central portion of the billet tip surface prior to drilling and rolling the billet, and the tip of the piercing plug is formed in this dent. It was found that by starting the drilling rolling with the portion positioned, the center of the drilling plug and the center of the billet can be aligned, which can effectively reduce the uneven thickness of the raw pipe in the pipe circumferential direction. rice field. Furthermore, it was found that by optimizing the shape of the punch for forming the dent, the processing of the dent by the punch can be particularly optimized and efficient, and the life of the punch is also improved.

The present invention has been made based on the above findings, and has the following gist.
[1] As a preliminary step before the drilling and rolling process of the billet, there is a processing step of pushing a convex punch (1) into the central portion of the tip surface of the hot billet to form a depression (x).
In the billet drilling and rolling step, a method for manufacturing a seamless steel pipe, characterized in that drilling and rolling is started with the tip of the drilling plug positioned in the recess (x).
[2] In the manufacturing method of the above [1], a method for manufacturing a seamless steel pipe, characterized in that the depth of the recess (x) is more than 50 mm.
[3] In the manufacturing method of the above [1] or [2], the ratio d / D of the diameter d of the recess (x) and the billet diameter D on the billet tip surface satisfies 0.3 to 0.8. A method for manufacturing a seamless steel pipe.

[4] In any of the above-mentioned manufacturing methods [1] to [3], in the drilling rolling step, the distance L between the tip of the drilling plug and the bottom of the recess (x) at the start of drilling rolling shall be 50 mm or more. A method for manufacturing a seamless steel pipe.
[5] In any of the above-mentioned manufacturing methods [1] to [4], the main body portion (10) of the punch (1) has a substantially conical shape or a substantially conical trapezoidal shape, and the tip has a convex curved surface shape. A characteristic method for manufacturing seamless steel pipes.
[6] In the manufacturing method of the above [5], the main body portion (10) of the punch (1) has a punch head (10a) having a convex curved tip and a tapered substrate connected to the punch head (10a). Consists of part (10b)
The boundary between the punch head (10a) and the tapered substrate portion (10b) constitutes a valley-shaped bent portion (10c).
A method for manufacturing a seamless steel pipe, characterized in that the slope inclination angle θ of the tapered substrate portion (10b) is 50 to 60 °.
[7] In the manufacturing method of the above [6], a method for manufacturing a seamless steel pipe, wherein the convex curved surface at the tip of the punch head (10a) has a radius of curvature R of 30 mm or more.

[8] A processing device (A) for forming a recess (x) in the central portion of the tip surface of the hot billet in the preliminary step before the drilling and rolling process of the billet is provided.
The processing apparatus (A) holds a convex punch (1) for forming a recess (x) by being pushed into the tip surface of the billet, and the punch (1) so as to be able to move forward and backward, and the punch (1). ) Is provided with a punch holding means (2) for pushing the billet tip surface into the center portion, and a clamping means (3) for clamping and restraining the billet when the billet tip surface is processed by the punch (1). Steel pipe manufacturing equipment.
[9] In the manufacturing equipment of the above [8], the main body portion (10) of the punch (1) is a seamless steel pipe having a substantially conical shape or a substantially conical trapezoidal shape and a convex curved tip. production equipment.

[10] In the manufacturing equipment of the above [9], the main body portion (10) of the punch (1) has a punch head (10a) having a convex curved tip and a tapered substrate connected to the punch head (10a). Consists of part (10b)
The boundary between the punch head (10a) and the tapered substrate portion (10b) constitutes a valley-shaped bent portion (10c).
A seamless steel pipe manufacturing facility characterized in that the slope inclination angle θ of the tapered substrate portion (10b) is 50 to 60 °.
[11] In the manufacturing equipment of the above [10], a seamless steel pipe manufacturing equipment characterized in that the convex curved surface at the tip of the punch head (10a) has a radius of curvature R of 30 mm or more.

[12] In any of the above-mentioned manufacturing facilities [8] to [11], the billet holding means (4) for holding the billet carried into the facility and the billet holding means (4) are further held. A seamless steel pipe manufacturing facility comprising a billet moving means (5) for pushing the rear end of the billet and sliding the billet to a machining position by the machining apparatus (A).
[13] In the manufacturing equipment of the above [12], the processing apparatus (A) further stops the billet at the processing position by abutting the tip of the billet that has been pushed and moved by the billet moving means (5). Equipped with a billet stopper (6)
Manufacture of a seamless steel pipe characterized in that the tip of the punch (1) is pushed into the billet tip surface through the hole of the ring of the billet stopper (6) when the billet tip surface is machined by the processing device (A). Facility.

[14] In any of the manufacturing facilities [8] to [13] above, the punch holding means (2) is composed of a cylinder device (20), and is attached to the tip of an operating rod (22) of the cylinder device (20). , The punch (1) is detachably held via the punch holder (23),
The clamping means (3) is rotatably supported by the support frame (9) via an intermediate portion in the longitudinal direction, and clamp fittings (32a) and (32b) for clamping the billet from both sides at the tip thereof are provided. A pair of clamp arms (30a) and (30b) provided and a pair of clamp arms (30a) and (30b) are connected to each other at the rear ends, and the clamp arms (30a) and (30b) are connected by expansion and contraction thereof. A seamless steel pipe manufacturing facility including a hydraulic cylinder (33) that opens and closes.

[15] A punch for pushing into the end face of a hot billet to form a dent.
The main body portion (10) is a billet processing tool characterized by having a substantially conical shape or a substantially conical trapezoidal shape and having a convex curved tip.
[16] In the billet processing tool of the above [15], the main body portion (10) has a punch head portion (10a) having a convex curved tip and a tapered substrate portion (10b) connected to the punch head portion (10a). ) Consists of
The boundary between the punch head (10a) and the tapered substrate portion (10b) constitutes a valley-shaped bent portion (10c).
A billet processing tool characterized in that the slope inclination angle θ of the tapered substrate portion (10b) is 50 to 60 °.
[17] In the billet processing tool of the above [16], the convex curved surface at the tip of the punch head (10a) has a radius of curvature R of 30 mm or more.

According to the present invention, a punch is pushed into the central portion of the billet tip surface to form a dent x prior to drilling and rolling of the billet, and piercing and rolling is performed with the tip of the piercing plug positioned in the dent x. By starting the above, it is possible to reduce the uneven thickness of the raw pipe obtained by drilling rolling in the pipe circumferential direction, and thereby it is possible to manufacture a seamless steel pipe having a highly accurate wall thickness dimension with less uneven thickness. can.
In addition, by optimizing the shape of the punch for forming a dent on the tip surface of the billet, it is possible to process the dent by the punch particularly appropriately and efficiently without causing any trouble, and the life of the punch is also improved. Can be made to. Therefore, the present invention can be carried out at a particularly high productivity and low cost.

Flow chart of the manufacturing method of the present invention Explanatory drawing which schematically shows the implementation state of the preliminary process (the processing process which forms a dent x in the billet tip surface) before the drilling rolling process in the manufacturing method of this invention. Explanatory drawing schematically showing the position of the drilling plug with respect to the billet at the start of drilling rolling in the manufacturing method of the present invention. The billet tip portion in which the recess x is formed in the manufacturing method of the present invention is shown, FIG. 4 (A) is a vertical cross section, and FIG. 4 (B) is a front view. A graph showing the relationship (example) between the ratio d / D of the diameter d of the recess x and the billet diameter D and the uneven thickness ratio of the product steel pipe in the manufacturing method of the present invention. An embodiment of a manufacturing facility used for carrying out the manufacturing method of the present invention and an implementation status of the manufacturing method of the present invention in the manufacturing facility are schematically shown, and a side view showing the entire manufacturing facility. In the embodiment of FIG. 6, a side view partially showing a part of the billet moving means (such as a dolly). In the embodiment of FIG. 6, a plan view partially showing a part of the billet moving means (such as a dolly). A side view showing a part of the processing apparatus A (processing apparatus for forming a dent x on the billet tip surface) in the embodiment of FIG. 6 and showing the entire apparatus. Side view showing a part (punch, punch stopper, etc.) of the processing apparatus A in the embodiment of FIG. A perspective view showing a part of the processing apparatus A (punch, clamping means, punch stopper, etc.) according to the embodiment of FIG. Cross-sectional view taken along line X-X in FIG. Thermography of the punch after processing the first billet and after processing the second billet when the manufacturing method of the present invention is carried out. Explanatory drawing schematically showing wrinkles and cracks generated on the punch surface when the manufacturing method of the present invention is carried out. Explanatory drawing which shows one Embodiment of the punch of the optimum shape used in the manufacturing method of this invention. Explanatory drawing which shows the embodiment of the punch of another shape used in the manufacturing method of this invention. Explanatory drawing which shows the billet processing procedure in the processing apparatus A in one Embodiment of the manufacturing method of this invention. Graph showing uneven thickness ratio of steel pipe manufactured in Example

In the method for manufacturing a seamless steel pipe of the present invention, as shown in the flow chart of FIG. 1, as a preliminary step before the drilling and rolling process of the billet, the tip surface of the hot billet (on the drilling start side in the drilling and rolling step of the billet). It has a processing step of pushing a convex punch (tool) into the center of the end face) to form a dent x, and in the billet drilling and rolling process, the tip of the piercing plug is positioned in the dent x. It is intended to start drilling and rolling.
FIG. 2 schematically shows the implementation status of the preliminary step (processing step of forming a dent x on the tip surface of the billet), and in this preliminary step, as shown in FIGS. , With the hot billet 100 constrained at a predetermined machining position, a convex punch 1 (mainly the punch tip) is located at the center of the tip surface f (the end surface on the drilling start side in the drilling rolling process of the billet 100). ) Is pushed in to form a dent x. After that, as shown in FIG. 3C, the punch 1 is retracted and pulled out from the recess x to complete the preliminary step.

The hot billet that has undergone this preliminary step (machining step) is sent to the drilling and rolling process as it is and is drilled and rolled by a piercer mill (perforation rolling machine). In this drilling and rolling, it is formed on the tip surface f of the billet 100. Rolling is started with the tip of the drilling plug positioned in the recess x. As a result, the center of the perforated plug and the center of the billet can be aligned, and the perforated rolling is performed with the center of the tip of the perforated plug located at the center of the billet. It is possible to suppress the generation of meat and finally produce a seamless steel pipe having a highly accurate wall thickness dimension.

FIG. 3 schematically shows the position of the drilling plug 200 with respect to the billet 100 at the start of rolling in the drilling and rolling process.
As an embodiment in which the tip portion of the drilling plug 200 is positioned in the recess x of the tip surface f of the billet 100 at the start of drilling rolling, a part of the drilling plug 200 is engaged (contacted) with a part of the inner surface of the recess x. Alternatively, the drilling plug 200 may not be engaged (contacted) with the inner surface of the recess x as shown in FIG.
Here, in the drilling and rolling step, it is preferable that the distance L (FIG. 3) between the tip of the drilling plug 200 and the bottom of the recess x at the start of drilling and rolling is 50 mm or more. In drilling rolling, cracking progresses due to the formation of cracks in the central portion of the billet 100, but by setting the distance L to 50 mm or more, such cracks in the central portion of the billet 100 are appropriately generated and the drilling is smooth. Proceed to.

4A and 4B show a billet tip portion in which a recess x is formed, FIG. 4A is a vertical cross section, and FIG. 4B is a front view. In the figure, t is the depth of the recess x (the maximum distance that the tip of the punch reaches from the tip surface f of the billet 100), d is the diameter of the recess x in the tip surface f of the billet 100, and D is the billet diameter.
Here, if the depth t of the dent x is too small, the effect of suppressing uneven thickness in drilling and rolling is lowered, and the biting property in drilling and rolling is likely to deteriorate, and the tip of the drilled plug and the material to be rolled come into contact with each other during drilling and rolling. Since it is easy to do, there is a risk that it will be difficult to pierce. Therefore, the depth t of the dent x needs to have a certain size, and it is particularly preferable to secure a distance L of 50 mm or more between the tip of the piercing plug and the bottom of the dent x at the start of drilling and rolling as described above. Therefore, the depth t of the recess x is preferably more than 50 mm. Here, when the biting property deteriorates in drilling and rolling, it means that the billet is driven by the upper and lower rolling rolls and starts to move forward, and when it comes into contact with the plug, the load becomes excessive and the drilling does not proceed. If the depth t of the dent x is too small, the Mannesmann crack at the tip of the billet does not sufficiently develop, and the load for drilling becomes excessive. On the other hand, if the depth t of the dent x is too large, an inner surface defect (fog defect) may occur at the pipe end portion during drilling and rolling, and the pipe end portion where such an inner surface defect has occurred must be cut and removed. However, the product yield is lowered, so that the depth t of the recess x is preferably 120 mm or less.

The shape of the recess x is determined by the shape of the punch portion pushed into the tip surface of the billet, but as will be described later, the tip of the main body portion 10 of the punch 1 (the portion on the tip side of the attachment portion 11 to the punch holding means 2) is Since it is preferable to have a substantially conical shape or a substantially truncated cone shape having a convex curved surface, the recess x usually has a mortar shape having a concave curved bottom at the bottom.
Further, if the diameter d of the recess x on the billet tip surface is too small or too large with respect to the billet diameter D, the effect of preventing uneven thickness in drilling and rolling is reduced, so the diameter is set according to the billet diameter D. Is preferable. FIG. 5 shows the relationship (one example) between the ratio d / D of the diameter d of the recess x and the billet diameter D and the uneven thickness ratio of the product steel pipe, and the uneven thickness ratio is as described in Examples described later. belongs to. The test (manufacturing) conditions of FIG. 5 are billet material: carbon steel, billet diameter: 300 to 350 mm, billet heating temperature: 1230 to 1290 ° C., and product diameter: 316 to 432 mm.
From the results of FIG. 5, the ratio d / D preferably satisfies about 0.3 to 0.8, and more preferably about 0.4 to 0.6.
The movement of the meat by processing the dent x with the punch 1 may cause deformation such as a slight swelling of the billet tip surface, but the depth t and diameter d of the dent x described above are the values after the processing. It is based on the tip surface of the billet.

6 to 12 schematically show an embodiment of the manufacturing equipment used for carrying out the manufacturing method of the present invention and the implementation status of the manufacturing method of the present invention in the manufacturing equipment. FIG. Is a side view showing the entire manufacturing equipment, FIG. 7 is a side view partially showing a part of the billet moving means 5 (such as a trolley 50), and FIG. 8 is a plan view as well. Further, FIGS. 9 to 12 partially show a processing device A (a processing device for forming a dent x on the tip surface f of the billet) which constitutes a part of the manufacturing equipment, and FIG. 9 shows processing. A side view showing the entire device, FIG. 10 is a side view showing a part of the processing device (punch 1, punch stopper 6, etc.), and FIG. 11 is a side view showing a part of the processing device (punch 1, clamping means 3, punch). A perspective view partially showing the stopper 6 and the like, and FIG. 12 is a cross-sectional view taken along the line XX in FIG. Note that FIG. 6 omits a part of the configuration of the processing apparatus A (punch 1, punch holding means 2, arms 13a, 13b, hydraulic cylinder 53, arm holding body 55, etc.), and FIG. 11 shows a billet stopper. The support member 12 of No. 6 is omitted.

This manufacturing equipment includes a processing device A for forming a dent x in the central portion of the tip surface f of the hot billet 100 in a preliminary process before the drilling and rolling process of the billet 100, and the billet 100 carried into the equipment. It is provided with a billet holding means 4 for holding, and a billet moving means 5 for pushing the rear end of the billet 100 held by the billet holding means 4 and sliding the billet 100 to a machining position by the machining device A.
The processing apparatus A holds a convex punch 1 for forming a recess x by being pushed into the tip surface f of the billet 100 and the punch 1 so as to be able to move forward and backward, and the punch 1 is placed at the center of the billet tip surface. It is composed of a punch holding means 2 for pushing in, a clamping means 3 for clamping and restraining the billet 100 when the billet is processed by the punch 1, and the like, and the entire device is supported by a support frame 9 which is a support structure portion. The specific structure of this processing apparatus A will be described in detail later.

The billet holding means 4 is composed of an elevating trough 40 in the present embodiment, and the elevating trough 40 can be raised and lowered while holding the billet 100, and is a transport means (for example, a V-shaped conveyor) from a heating furnace. , Chain dog, kicker, etc.), receives and holds the billet 100 carried (charged) into the equipment, and lifts the billet 100 to a height that can be processed by the processing device A.
The billet moving means 5 moves a trolley 50 that can move (run) along a guide rail 8 (a guide rail erected in the direction of the processing device A) erected above the billet holding means 4, and the trolley 50. It is composed of a drive mechanism 52, a pusher arm 51 for pressing a billet hanging from the trolley 50, and a hydraulic cylinder 53 that moves the pusher arm 51 in the billet direction by sliding the pusher arm 51 with respect to the trolley 50. By moving the 50, the pusher arm 51 is brought into contact with the rear end of the billet 100 held by the billet holding means 4 (elevating trough 40), and the hydraulic cylinder 53 is operated from this state to cause the pusher arm 51 to move. The billet 100 is pushed so that the billet 100 can be slid and moved in the processing device A direction on the elevating trough 40.

To explain the configuration of the billet moving means 5 in more detail, a gantry frame 7 is erected above the billet holding means 4, and a guide rail 8 is installed on the gantry frame 7 in the direction of the processing device A. The dolly 50 (57 is a wheel of the dolly 50) can move along the 8. The drive mechanism 52 of the carriage 50 is composed of a ball screw (slide screw) mechanism in this embodiment. That is, the drive mechanism 52 is arranged on the gantry frame 7 in parallel with the guide rail 8, and is fixed to the screw shaft 520 rotatably supported by the support member 524 and the trolley 50, and the screw of the screw shaft 520. A nut member 521 that is externally attached to the portion, a motor 522 that rotates the screw shaft 520, a speed reducer 523, and the like, and a nut that is fixed to the carriage 50 by rotating the screw shaft 520 with the motor 522 and the speed reducer 523. By moving the member 521 in the longitudinal direction of the screw shaft 520, the carriage 50 can move along the guide rail 8.

The trolley 50 holds a slide guide 54 (for example, a groove-shaped guide rail on which the guided body can slide and move) and a pusher arm 51, and the arm holder 55 that can slide and move in the trolley moving direction along the slide guide 54. And a hydraulic cylinder 53 that slides and moves the arm holder 55 and the like.
The hydraulic cylinder 53 has an operating rod 56 connected to the arm holding body 5 and slides the arm holding body 55 in the carriage moving direction (processing device A direction).
The upper end of the pusher arm 51 is fixed to the arm holder 55, and the slide movement of the arm holder 55 allows the pusher arm 51 to push the billet 100 and slide the billet 100 toward the processing device A.

Next, the processing apparatus A will be described.
The configuration of the convex punch 1 included in the processing apparatus A will be described in detail later.
The punch holding means 2 is composed of a cylinder device 20 such as a hydraulic cylinder, and the cylinder body 21 is horizontally supported by a support frame 9. The punch 1 is detachably held at the tip of the actuating rod 22 of the cylinder device 20 via the punch holder 23. Then, as shown in FIGS. 10 and 11, the punch 1 held by the cylinder device 20 (punch holding means 2) is attached to the tip surface f of the billet 100 held by the elevating trough 40 (billet holding means 4). It will be opposite.

The clamping means 3 may have any configuration as long as it can firmly clamp the billet 100 and restrain it so as not to move during processing to form a recess x on the tip surface of the billet, but in the present embodiment, the billet from above and below can be used. It is provided with a pair of upper and lower clamp arms 30a and 30b for clamping the tip of 100. The clamp arms 30a and 30b are pivotally supported by the support frame 9 via an intermediate portion thereof so as to be vertically rotatable. Each of the clamp arms 30a and 30b is provided with clamp metal fittings 32a and 32b at the tips thereof. Each of the clamp fittings 32a and 32b has a half-split cylindrical clamp surface 320. On the other hand, the rear ends of both clamp arms 30a and 30b are connected by a hydraulic cylinder 33 for opening and closing the clamp arms 30a and 30b. That is, the end of the cylinder body 34 of the hydraulic cylinder 33 is connected to the rear end of the clamp arm 30b, and the tip of the operating rod 35 of the hydraulic cylinder 33 is connected to the rear end of the clamp arm 30a. When the cylinder 33 expands and contracts, the clamp arms 30a and 30b open and close up and down, and the tip portions of the billet 100 can be clamped from above and below by the clamp metal fittings 32a and 32b.

The processing apparatus A further includes a ring-shaped billet stopper 6 that stops the billet 100 at the processing position when the tip end portion of the billet 100 pushed and moved by the billet moving means 5 abuts. The ring-shaped billet stopper 6 is arranged so as to face the tip end portion of the punch 1, and is supported by the support member 12 on the side portion of the support frame 9. When the tip surface of the billet is processed by the punch 1, the tip of the punch 1 is pushed into the tip surface f of the billet 100 through the hole 60 of the ring of the billet stopper 6.

The processing apparatus A further regulates the open / close (rotation) range of the clamp arms 30a and 30b, and in order to reduce the load on the hydraulic cylinder 33, the clamp arms 30a and 30b are in a closed state (the billet 100 is clamped). It is equipped with a mechanism that is mechanically held in the state).
That is, in the pivot portions 31 of the upper and lower clamp arms 30a and 30b, the plate-shaped arms 13a and 13b having a substantially L-shaped plane having the arm portions 130 and 131 extending in two directions are attached to the arm portions 130 and 131. It is pivotally supported at the base (base). These arms 13a and 13b are locked (fixed) to the clamp arms 30a and 30b, respectively, and are configured to rotate integrally with the clamp arms 30a and 30b. The plate-shaped arms 13a and 13b are provided on both sides of the clamp arms 30a and 30b.

The support frame 9 is provided with a short guide hole 14 (a short arc-shaped guide hole) for guiding each arm portion 130 of the arms 13a and 13b that rotate integrally with the clamp arms 30a and 30b. There is. A pin 15 is supported at the tip of each arm portion 130 of the arms 13a and 13b, and the pin 15 is inserted into the guide hole 14 so that the pin 15 can move in the guide hole 14 as the arm portion 130 rotates. be. Both ends of the guide hole 14 serve as stoppers for the pins 15, and the opening / closing range of the clamp arms 30a and 30b that rotate integrally with the arms 13a and 13b is restricted. That is, when the pin 15 engages with one end of the guide hole 14 (state in FIG. 9), the clamp arms 30a and 30b stop at a predetermined rotation position in the closed state (clamp state of the billet 100), while the clamp arms 30a and 30b stop at a predetermined rotation position. When the pin 15 engages with the other end of the guide hole 14, the clamp arms 30a and 30b are stopped at a predetermined rotation position in the open state (non-clamping state of the billet). Further, as described above, the pin 15 engages with one end of the guide hole 14 (state in FIG. 9), so that the clamp arms 30a and 30b are stopped at a predetermined rotation position in the closed state (billet clamp state). At that time, the position of one end side of the guide hole 14 is determined so that both the arm portions 131 of the arms 13a and 13b are vertically aligned vertically. By forming both arm portions 131 of the arms 13a and 13b in a vertical straight line in the vertical direction in this way, the action of mechanically holding the clamp arms 30a and 30b in the closed state by the driving force of the hydraulic cylinder 33 in that state is exerted. Therefore, the load on the hydraulic cylinder 33 can be reduced.

On the other hand, the tips of the arm portions 131 of both arms 13a and 13b are connected to each other by pins 16, but the arms 13a and 13b rotate integrally with the clamp arms 30a and 30b (within the short length range of the guide hole 14). To enable rotation), as shown in FIG. 12, the end of the arm 131 of the arm 13b is inserted into the end of the arm 131 of the arm 13a, and the end of the arm 131 is pivotally supported by the pin 16. A bracket portion 17 composed of a pair of plate-shaped portions 170 is provided, and a pin 16 is fixed to the bracket portion 17. An elongated pin insertion hole 18 (a long pin insertion hole in the vertical direction) is provided at the end of the arm portion 131 of the arm 13b, and the end portion of the arm portion 131 of the arm 13b is inserted into the bracket portion 17. In this state, the pin 16 is inserted into the pin insertion hole 18, so that both arm portions 131 of the arms 13a and 13b are connected to each other. Then, the pins 16 of the arm portion 131 of the arm 13a can move in the pin insertion holes 18 of the arm portion 131 of the arm 13b, so that the arms 13a and 13b rotate integrally with the clamp arms 30a and 30b (the guide holes 14). It can rotate in a short length range).
The billet holding means 4, the billet moving means 5, the punch holding means 2 and the clamping means 3 constituting the processing device A are not limited to those of the present embodiment, and can fulfill their respective functions. It can be configured by an appropriate specific means.

Next, the configuration of the punch 1 which is a billet processing tool will be described.
The punch 1 is composed of a main body portion 10 responsible for billet processing and a mounting portion 11 coupled to an end portion of the main body portion 10 for connecting to the punch holding means 2 (punch holder 23).
The punch 1 may basically have a convex shape, and it is particularly preferable that the main body 10 of the punch 1 has a substantially conical shape or a substantially conical trapezoidal shape, and the tip thereof has a convex curved surface shape. Here, the substantially conical shape or the substantially conical trapezoid is that the main body portion 10 of the punch 1 used in the present invention has a valley-shaped bent portion in the middle of the inclined surface (tapered surface) of the conical shape or the conical trapezoid in the axial direction. Since there are cases where there are (valley-shaped recesses) and where part or all of the inclined surface is curved in the axial direction, such shapes are included in addition to the usual conical and conical trapezoids. Means to be.
Furthermore, as a result of the study by the present inventors, by optimizing the main body 10 of the punch to a more limited shape, it is possible to particularly optimize and improve the efficiency of the processing of the dent x by the punch, and the life of the punch is also improved. I found that I could do it.

When the present invention is carried out, the processing of the billet tip surface (processing to form the dent x) by the punch 1 of the processing apparatus A is continuously performed on a number of billets at short time intervals. During the continuous processing, the tip temperature of the punch 1 rises to around 500 ° C. FIG. 13 is a thermography of the punch 1 after processing the first (first) billet and after processing the second (second) billet, and the tip temperature of the punch 1 after processing the second billet is It can be seen that the temperature has risen to around 500 ° C due to the heat input from the billet side. On the other hand, the temperature of the base end portion (root portion) of the punch is about 200 ° C., and it can be seen that a large temperature difference is generated from the tip end portion. In FIG. 13, the pair of upper and lower members shown above and below the punch 1 in the upper image and on the right side of the punch 1 in the lower image are clamp arms 30a and 30b, respectively.

When the billet is continuously processed in such a high temperature state, wrinkles and cracks as shown in FIG. 14 occur on the surface of the punch depending on the punch, and it is necessary to replace the billet relatively early (the life is relatively short). In addition, the wrinkles and cracks cause unevenness on the punch surface, and the unevenness on the punch surface prevents the punch tip pushed into the billet tip surface from being pulled out (as a result, the punch 1 processes the billet 100). Since it is pulled into the device A side, it has been found that this phenomenon is hereinafter referred to as "billet pulling"). When such billet pulling occurs, it is necessary to switch the operation to manual and manually move the punch forward and backward by the operator to perform an operation to eliminate the pulling, and if the time is prolonged, the billet or waits. The temperature of the next hot billet will inevitably drop, and the planned rolling will not be possible, resulting in a significant decrease in productivity.

The reason why the above-mentioned wrinkles and cracks occur on the punch surface is not always clear, but when the tip of the punch 1 is pushed into the billet tip surface, heat is input from the billet side as shown in FIG. As a result, only the vicinity of the tip of the punch 1 rises, and that part expands, a large temperature difference occurs between the billet and the punch part that is not in contact, and the punch part pushed into the billet also has a dent x. A temperature gradient occurs in the depth direction of the punch, and while continuous use causes a high temperature during operation, if a tool change occurs, the operation stops during that time and the tip of the punch cools, resulting in such thermal expansion and contraction. May be related to repeated actions.
As a result of repeated studies to solve such problems, by making the punch 1 into a specific shape, wrinkles and cracks on the surface are less likely to occur even during continuous processing, and high durability (long life) can be obtained. It was found that the occurrence of billet pulling was also suppressed.

FIG. 15 shows an embodiment of a punch having such a shape. The main body 10 of the punch 1 having the optimum shape is a two-stage type including a punch head 10a having a convex curved surface (preferably spherical) at the tip and a tapered base portion 10b connected to the punch head 10a. The boundary between the punch head portion 10a and the tapered substrate portion 10b constitutes a valley-shaped bent portion 10c (valley-shaped recess). Further, the tapered substrate portion 10b has a structure in which the slope inclination angle θ is 50 to 60 ° (the embodiment of FIG. 15 is about 56 °).
According to the results of the tests by the present inventors, billet retracting is particularly likely to occur when a billet having a billet diameter of 300 to 350 mm is machined, and therefore, the punch 1 having the optimum shape as described above processes a billet of such a size. It is especially useful when doing so.

The tip of the punch head 10a may have a convex curved surface, but it is generally preferable to form a spherical surface. The punch head 10a of the present embodiment includes a curved surface portion a1 on the tip side and a tapered portion a2 connected to the curved surface portion a1, but the tapered portion a2 may not be provided.
Further, the punch head 10a preferably has a certain volume in order to suppress melting and wear, and from this viewpoint, the convex curved surface (preferably spherical surface) at the tip of the punch head 10a has a radius of curvature R of 30 mm or more. It is preferable to have.
The hardness and material (ingredient composition) of the punch are not particularly limited, but the hardness and material suitable for the processing tool used hot are used. Specifically, the hardness (HS) is preferably 65 or more, and as the material, for example, SCM435, SKD61, or the like is used.

Table 1 shows the results of carrying out the present invention method using the punch 1 shown in FIG. 15 and the punch 1 having another shape, and examining the average life of the punch 1 and the presence or absence of billet pull-in. In Table 1, the punch (iv) is the punch having the optimum shape shown in FIG. 15, and the punches (i) to (iii) are the punches having the shape shown in FIG.
In the punch (iv), the slope inclination angle θ of the tapered substrate portion 10b is about 56 °.
The punches (i) to (iii) are indistinguishable from the punch head 10a and the tapered base portion 10b like the punch (iv) (hence, there is no valley-shaped bent portion 10c), and the slope of the tapered portion is inclined. The angles are about 70 ° for the punch (i) and about 65 ° for the punch (ii) and punch (iii). Further, the shape of the lower portion of the tapered portion differs depending on the punches (i) to (iii).
In this manufacturing test, a billet (carbon steel) having a billet diameter of 260 to 350 mm was targeted, and the driving time of the punch 1 was set to 5 seconds. Further, the depth t of the recess x was set to 67 mm.

According to Table 1, in the punches (i) to (iii), billets are drawn in due to wrinkles and cracks on the surface, and the average life (the average number of billets that can be processed by one punch before replacement) per year. The value) is a little over 8,000 at the maximum. On the other hand, the punch (iv) has an average life of 8300 or more, and billet pulling does not occur.
As a result, the punches (i) to (iii) had an average usage limit of about 15 days due to damage (wrinkles, cracks, etc.), whereas the punch (iv) improved the usage limit to an average of 70 days. I was able to. In addition, since the punch (iv) is less likely to cause wrinkles and cracks at the tip of the punch, the frequency of billet pulling was 20 times / year for the punches (i) to (iii). It was possible to improve up to 0 times / year. By reducing the number of troubles occurring in this way, productivity could be improved by 1 Hr / month. In addition, the tool life can be improved, and the tool cost can be reduced.

Next, a method of using the manufacturing equipment of FIGS. 6 to 12 (one embodiment of the method of the present invention) will be described. 17 (a) to 17 (f) are explanatory views showing the processing procedure of the billet 100 by the processing apparatus A.
The hot (usually about 1200 to 1300 ° C.) billet 100 is carried into the equipment from the side of the manufacturing equipment and placed on the elevating trough 40 (billet holding means 4). The elevating trough 40 is raised to lift (raise) the billet 100 to the height of the machining position by the machining device A (punch 1), and then push the rear end of the billet with the pusher arm 51 to move the billet 100 toward the machining device A. Move it (FIG. 17 (a)). When the tip of the moved billet 100 abuts on the billet stopper 6, the billet 100 is stopped (FIG. 17 (b)), and the billet 100 is processed at this position.

The clamp arms 30a and 30b in the open state are closed by the hydraulic cylinder 33, and the tip end side portion of the billet 100 is clamped by the clamp metal fittings 32a and 32b (FIG. 17 (c)). In this state, the cylinder device 20 (punch holding means 2) is driven to advance the punch 1, and the tip portion of the punch 1 is passed through the inside of the billet stopper 6 (ring hole 60) to reach the tip surface f of the billet 100. A dent x is formed (processed) by pushing it in (FIG. 17 (d)). The punch 1 is pushed (drived) into the tip surface f of the billet 100 at a speed of, for example, about 0.4 to 0.7 m / sec. After that, the punch 1 is retracted, the tip end portion of the punch 1 is pulled out from the tip surface f (formed recess x) of the billet 100 (FIG. 17 (e)), and the billet 100 is clamped by the clamp metal fittings 32a and 32b. Is released (FIG. 17 (f)) to complete the machining. After lowering the elevating trough 40 holding the processed billet 100, the billet 100 is carried out of the equipment. The billet 100 is sent to a drilling and rolling process for drilling and rolling. At that time, as shown in FIG. 3, the tip of the drilling plug 200 is positioned in the recess x formed on the tip surface f of the billet 100. Start rolling at. The billet 100 is processed into a raw pipe by drilling and rolling, and then the raw pipe becomes a product steel pipe through a series of steps such as a stretch rolling step.

Billets were processed by the method of the present invention in the equipment shown in FIGS. 6 to 12, and then drilled and rolled, and then a seamless steel pipe was manufactured through a series of steps. The uneven thickness ratio of the steel pipe manufactured in this manner and the steel pipe manufactured by the conventional method (a method of performing drilling and rolling without a preliminary step of forming a dent x on the tip end face of the billet) was measured. The result is shown in FIG. The uneven thickness ratio is calculated by the following formula based on the maximum wall thickness, the minimum wall thickness, and the average wall thickness in the circumferential direction of the product steel pipe.
Unbalanced wall ratio = [(maximum wall thickness-minimum wall thickness) / average wall thickness] x 100
FIG. 18 shows the position of the tip of the product steel pipe and the uneven thickness ratio at each position of 15 mm, 30 mm, and 45 mm from the tip of the pipe in the longitudinal direction of the pipe.

In the method of the present invention (example of the present invention), the punch 1 of the processing apparatus A has the shape shown in FIG. 15 (slope inclination angle θ: 56 ° of the tapered base portion 10b), and the depth is increased by the punch 1. A 67 mm recess x was formed, and during drilling rolling, rolling was started with the tip of the drilling plug 200 positioned in the recess x in the manner shown in FIG. 18 (a). On the other hand, in the conventional method (conventional example), rolling was started with the tip of the drilling plug 200 positioned in the manner shown in FIG. 18 (b).
The billet material was carbon steel, the billet diameter was 300 to 350 mm, the billet heating temperature was 1230 to 1290 ° C., and the product diameter was 316 to 432 mm.
As shown in FIG. 18, it can be seen that in the example of the present invention, the uneven thickness of the product steel pipe is effectively reduced as compared with the conventional example.
In the method of the present invention (example of the present invention), the test was performed at d / D = 0.24, but as shown in FIG. 5, the d / D was 0.3 to 0.8, preferably 0.4 to 0.6. If so, it is considered that the uneven thickness ratio is further reduced.

1 Punch 2 Punch holding means 3 Clamping means 4 Billet holding means 5 Billet moving means 6 Billet stopper 7 Mount frame 8 Guide rail 9 Support frame 10 Main body part 10a Punch head 10b Tapered base part 10c Bent part 11 Mounting part 12 Support Members 13a, 13b Arm 14 Guide hole 15 pin 16 pin 17 Bracket part 18 pin Insertion hole 20 Cylinder device 21 Cylinder body 22 Actuating rod 23 Punch holder 30a, 30b Clamp arm 31 Pivot support 32a, 32b Cylinder metal fittings 33 Hydraulic cylinder 34 Cylinder body 35 Acting rod 36 Connecting part 40 Lifting trough 50 Truck 51 Pusher arm 52 Drive mechanism 53 Hydraulic cylinder 54 Slide guide 55 Arm holder 56 Operating rod 57 Wheel 58 Connecting part 60 hole 100 Billet 130, 131 Arm part 170 Plate-shaped part 200 Drilling plug 320 Cylinder surface 520 Screw shaft 521 Nut member 522 Motor 523 Reducer 524 Support member x dent f Tip surface A Processing device a1 Curved part a2 Tapered part

Claims (17)

As a preliminary step before the billet drilling and rolling step, there is a processing step of pushing a convex punch (1) into the central portion of the tip surface of the hot billet to form a depression (x).
In the billet drilling and rolling step, a method for manufacturing a seamless steel pipe, characterized in that drilling and rolling is started with the tip of the drilling plug positioned in the recess (x). The method for manufacturing a seamless steel pipe according to claim 1, wherein the depth of the recess (x) is more than 50 mm. The method for manufacturing a seamless steel pipe according to claim 1 or 2, wherein the ratio d / D of the diameter d of the recess (x) on the billet tip surface and the billet diameter D satisfies 0.3 to 0.8. .. The seamless steel pipe according to any one of claims 1 to 3, wherein in the drilling and rolling step, the distance L between the tip of the drilling plug and the bottom of the recess (x) at the start of drilling and rolling is 50 mm or more. Production method. The manufacture of a seamless steel pipe according to any one of claims 1 to 4, wherein the main body portion (10) of the punch (1) has a substantially conical shape or a substantially conical trapezoidal shape, and the tip has a convex curved surface shape. Method. The main body portion (10) of the punch (1) is composed of a punch head portion (10a) having a convex curved tip and a tapered base portion (10b) connected to the punch head portion (10a).
The boundary between the punch head (10a) and the tapered substrate portion (10b) constitutes a valley-shaped bent portion (10c).
The method for manufacturing a seamless steel pipe according to claim 5, wherein the slope inclination angle θ of the tapered substrate portion (10b) is 50 to 60 °. The method for manufacturing a seamless steel pipe according to claim 6, wherein the convex curved surface at the tip of the punch head (10a) has a radius of curvature R of 30 mm or more. A processing device (A) for forming a recess (x) in the central portion of the tip surface of the hot billet in the preliminary step before the billet drilling and rolling step is provided.
The processing apparatus (A) holds a convex punch (1) for forming a recess (x) by being pushed into the tip surface of the billet, and the punch (1) so as to be able to move forward and backward, and the punch (1). ) Is provided with a punch holding means (2) for pushing the billet tip surface into the center portion, and a clamping means (3) for clamping and restraining the billet when the billet tip surface is processed by the punch (1). Steel pipe manufacturing equipment. The seamless steel pipe manufacturing equipment according to claim 8, wherein the main body portion (10) of the punch (1) has a substantially conical shape or a substantially conical trapezoidal shape, and the tip has a convex curved surface shape. The main body portion (10) of the punch (1) is composed of a punch head portion (10a) having a convex curved tip and a tapered base portion (10b) connected to the punch head portion (10a).
The boundary between the punch head (10a) and the tapered substrate portion (10b) constitutes a valley-shaped bent portion (10c).
The facility for manufacturing a seamless steel pipe according to claim 9, wherein the slope inclination angle θ of the tapered substrate portion (10b) is 50 to 60 °. The seamless steel pipe manufacturing equipment according to claim 10, wherein the convex curved surface at the tip of the punch head (10a) has a radius of curvature R of 30 mm or more. Further, by pushing the billet holding means (4) for holding the billet carried into the equipment and the rear end of the billet held by the billet holding means (4), the billet is slid to the processing position by the processing device (A). The seamless steel pipe manufacturing equipment according to any one of claims 8 to 11, further comprising a billet moving means (5) to be moved. The processing apparatus (A) further includes a ring-shaped billet stopper (6) that stops the billet at the processing position when the tip of the billet that has been pushed and moved by the billet moving means (5) abuts.
The twelfth aspect of claim 12, wherein when the billet tip surface is machined by the processing device (A), the tip of the punch (1) is pushed into the billet tip surface through the hole of the ring of the billet stopper (6). Seamless steel pipe manufacturing equipment. The punch holding means (2) is composed of a cylinder device (20), and the punch (1) is detachably held at the tip of an operating rod (22) of the cylinder device (20) via a punch holder (23).
The clamping means (3) is rotatably supported by the support frame (9) via an intermediate portion in the longitudinal direction, and clamp fittings (32a) and (32b) for clamping the billet from both sides at the tip thereof are provided. A pair of clamp arms (30a) and (30b) provided and a pair of clamp arms (30a) and (30b) are connected to each other at the rear ends, and the clamp arms (30a) and (30b) are connected by expansion and contraction thereof. The facility for manufacturing a seamless steel pipe according to any one of claims 8 to 13, further comprising a hydraulic cylinder (33) for opening and closing. A punch for pushing into the end face of a hot billet to form a dent.
The main body portion (10) is a billet processing tool characterized by having a substantially conical shape or a substantially conical trapezoidal shape and having a convex curved tip. The main body portion (10) is composed of a punch head portion (10a) having a convex curved tip and a tapered base portion (10b) connected to the punch head portion (10a).
The boundary between the punch head (10a) and the tapered substrate portion (10b) constitutes a valley-shaped bent portion (10c).
The billet processing tool according to claim 15, wherein the slope inclination angle θ of the tapered substrate portion (10b) is 50 to 60 °. The billet processing tool according to claim 16, wherein the convex curved surface at the tip of the punch head (10a) has a radius of curvature R of 30 mm or more.

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