JP7319598B2 - Seamless steel pipe manufacturing method, manufacturing equipment, and billet processing tool - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a seamless steel pipe characterized by having a preliminary process performed prior to piercing-rolling of a billet, and to a manufacturing facility and a tool for processing a billet used for its implementation.

Seamless steel pipes used for oil well pipes and the like are manufactured from steel slabs (steel slabs with round or square cross sections) called billets. In the process of manufacturing seamless steel pipes, a billet (for example, a round billet) heated in a heating furnace is pierced-rolled in a piercer mill (piercing-rolling mill) using inclined rolling rolls and piercing plugs to obtain a base pipe. The tube is stretch-rolled into a tubular shape by a rolling mill group consisting of an elongator, a plug mill and a reeler, a mandrel mill, or the like. After the tubular body thus obtained is heated in a reheating furnace, it is processed by a sizing mill or a stretch reducer to reduce the outer diameter and wall thickness to predetermined dimensions, thereby producing a product steel pipe (for example, Patent Document 1). .
In the piercing-rolling of a billet by a piercer mill, a special rolling tool called a piercing plug is arranged in the direction of travel of the billet while applying forward force to the hot billet by the inclined rolling rolls. Introduce a strain that leads to plastic deformation to the billet, and process it into the shape of a blank pipe by penetrating the billet.

JP 2016-185553 A

In billet piercing rolling with a piercer mill (piercing rolling mill), if the center of the piercing plug and the billet do not match when the piercing plug and the billet start to come into contact immediately before piercing and rolling, the product wall thickness will be affected by the material tube. There is a problem that thickness unevenness (thickness unevenness in the circumferential direction of the pipe) is generated, which is a factor that hinders the production of product steel pipes having highly accurate thickness dimensions.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the problems of the prior art as described above, to reduce uneven wall thickness of the mother pipe in billet piercing-rolling, and to manufacture a steel pipe having a highly accurate thickness dimension. An object of the present invention 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 seamless steel pipe manufacturing method.

As a result of repeated studies to solve the above problems, the present inventors have found that prior to piercing-rolling of the billet, a punch is pressed into the central portion of the billet tip surface to form a depression, and the tip of the piercing plug is formed in this depression. By starting the piercing-rolling with the part positioned, it is possible to align the center of the piercing plug with the center of the billet. 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 can be improved.

The present invention has been made based on the above findings, and has the following gist.
[1] As a preparatory step before the billet piercing-rolling step, a working step of pressing a convex punch (1) into the central portion of the front end face of the hot billet to form a depression (x),
A method for producing a seamless steel pipe, characterized in that, in the piercing-rolling step of a billet, piercing-rolling is started in a state in which the tip of a piercing plug is positioned in a recess (x).
[2] The method for producing a seamless steel pipe according to the above [1], characterized in that the depth of the depression (x) is more than 50 mm.
[3] The manufacturing method of [1] or [2] above, characterized in that the ratio d/D between the diameter d of the depression (x) on the tip end surface of the billet and the billet diameter D satisfies 0.3 to 0.8. A method for manufacturing a seamless steel pipe.

[4] In the manufacturing method of any one of [1] to [3] above, in the piercing-rolling step, the distance L between the tip of the piercing plug and the bottom of the depression (x) at the start of piercing-rolling is set to 50 mm or more. A method for producing a seamless steel pipe, characterized by:
[5] In the manufacturing method according to any one of [1] to [4] above, the main body (10) of the punch (1) is substantially conical or substantially truncated conical and has a convex curved tip. A method for manufacturing a seamless steel pipe.
[6] In the manufacturing method of [5] above, the main body (10) of the punch (1) includes a punch head (10a) having a convex curved tip and a tapered base continuous with the punch head (10a). consisting of part (10b),
The boundary between the punch head portion (10a) and the tapered base portion (10b) constitutes a valley-like bent portion (10c),
A method for producing a seamless steel pipe, characterized in that the tapered base portion (10b) has an inclination angle θ of 50 to 60°.
[7] The method of manufacturing a seamless steel pipe according to [6] above, 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] Equipped with a processing device (A) for forming a depression (x) in the central portion of the front end surface of the hot billet in a preliminary process before the billet piercing-rolling process,
The processing device (A) includes a convex punch (1) for forming a recess (x) by being pushed into the tip surface of a billet, and holding the punch (1) so as to be able to move back and forth. ) into the center of the billet tip surface, and a clamping means (3) for clamping and restraining the billet when the billet tip surface is processed by the punch (1). Manufacturing equipment for steel pipes.
[9] In the manufacturing facility of [8] above, the body (10) of the punch (1) has a substantially conical or substantially frustoconical shape, and the tip of the seamless steel pipe has a convex curved surface. production equipment.

[10] In the manufacturing facility of [9] above, the main body (10) of the punch (1) includes a punch head (10a) having a convex curved tip and a tapered base continuous with the punch head (10a). consisting of part (10b),
The boundary between the punch head portion (10a) and the tapered base portion (10b) constitutes a valley-like bent portion (10c),
Equipment for manufacturing a seamless steel pipe, characterized in that the inclination angle θ of the tapered base portion (10b) is 50-60°.
[11] In the production facility of [10] above, the seamless steel pipe production facility is characterized in that the radius of curvature R of the convex curved surface at the tip of the punch head (10a) is 30 mm or more.

[12] The manufacturing facility of any one of [8] to [11] above, further comprising billet holding means (4) for holding the billet carried into the facility, and billet holding means (4) for holding the billet A manufacturing facility for seamless steel pipes, comprising billet moving means (5) for pushing the rear end of the billet and sliding the billet to a processing position by the processing device (A).
[13] In the manufacturing facility of [12] above, the processing device (A) further includes a ring that stops the billet at the processing position when the tip of the billet pushed by the billet moving means (5) abuts against it. with a shaped billet stopper (6),
Manufacture of seamless steel pipe characterized in that the tip of a punch (1) is pushed into the tip of the billet through the hole of the ring of the billet stopper (6) when the tip of the billet is processed by the processing device (A). Facility.

[14] In the manufacturing equipment according to any one of [8] to [13] above, the punch holding means (2) is composed of a cylinder device (20), and the tip of the 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 the longitudinal middle portion, and has clamping metal fittings (32a) and (32b) at its tip for sandwiching and clamping the billet from both sides. A pair of clamp arms (30a), (30b) provided and connected between the rear ends of the pair of clamp arms (30a), (30b). A seamless steel pipe manufacturing facility comprising a hydraulic cylinder (33) for opening and closing operations.

[15] A punch for pressing into the end face of a hot billet to form a depression,
A tool for working billets, characterized in that the main body (10) has a substantially conical shape or a substantially truncated conical shape and has a convexly curved tip.
[16] In the billet processing tool of [15] above, the main body (10) includes a punch head (10a) having a convex curved tip and a tapered base (10b) connected to the punch head (10a). ),
The boundary between the punch head portion (10a) and the tapered base portion (10b) constitutes a valley-like bent portion (10c),
A billet processing tool characterized in that a tapered base portion (10b) has an inclination angle θ of 50 to 60°.
[17] The billet working tool according to [16] above, wherein 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, prior to piercing-rolling of the billet, a punch is pushed into the central portion of the billet tip surface to form a depression x, and piercing-rolling is performed with the tip of the piercing plug positioned in this depression x. By starting the process, it is possible to reduce the unevenness in the circumferential direction of the tube obtained by piercing and rolling, thereby manufacturing a seamless steel pipe having a highly accurate thickness dimension with less unevenness. can.
In addition, by optimizing the shape of the punch that forms the dent on the tip of the billet, the dent can be processed properly and efficiently without causing trouble, and the life of the punch is also improved. can be made Therefore, the present invention can be implemented with particularly high productivity and at low cost.

Flow chart of the manufacturing method of the present invention Explanatory drawing schematically showing the state of implementation of a preliminary step (processing step of forming a recess x on the front end face of a billet) before the piercing-rolling step in the manufacturing method of the present invention. FIG. 4 is an explanatory view schematically showing the position of the piercing plug with respect to the billet at the start of piercing-rolling in the manufacturing method of the present invention; FIG. 4(A) is a longitudinal section and FIG. 4(B) is a front view showing a billet tip portion in which a depression x is formed in the manufacturing method of the present invention. Graph showing the relationship (one example) between the ratio d/D between the diameter d of the recess x and the billet diameter D and the thickness deviation ratio of the product steel pipe in the manufacturing method of the present invention. A side view showing the entire manufacturing facility, which schematically shows an embodiment of the manufacturing facility used for carrying out the manufacturing method of the present invention and the state of implementation of the manufacturing method of the present invention in this manufacturing facility. FIG. 7 is a side view partially showing part of the billet moving means (such as a carriage) in the embodiment of FIG. 6 ; FIG. 7 is a plan view partially showing part of the billet moving means (such as a carriage) in the embodiment of FIG. 6 ; FIG. 7 is a side view of the entire apparatus, partially showing the processing apparatus A (processing apparatus for forming a recess x on the tip surface of the billet) in the embodiment of FIG. 6; A side view showing a part (punch, punch stopper, etc.) of the processing apparatus A in the embodiment of FIG. FIG. 7 is a perspective view showing a part of the processing apparatus A (punch, clamp means, punch stopper, etc.) in the embodiment of FIG. 6; Cross-sectional view along line XX in Fig. 9 Thermography of punches 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 surface of a punch when the manufacturing method of the present invention is carried out. Explanatory drawing showing one embodiment of an optimally shaped punch used in the manufacturing method of the present invention. Explanatory drawing showing an embodiment of another shaped punch used in the manufacturing method of the present invention. Explanatory drawing showing a processing procedure of a billet in the processing apparatus A in one embodiment of the manufacturing method of the present invention. Graph showing uneven wall thickness ratios of steel pipes manufactured in Examples

As shown in the flow chart of FIG. 1, the method for producing a seamless steel pipe of the present invention includes, as a preliminary step before the billet piercing-rolling step, the front end surface of the hot billet (on the piercing start side in the billet piercing-rolling step). In the billet piercing-rolling process, the tip of the piercing plug is positioned in the recess x. This is to start piercing and rolling.
FIG. 2 schematically shows the implementation status of the preliminary process (processing process for forming a recess x on the billet tip surface). In this preliminary process, as shown in FIGS. , with the hot billet 100 restrained at a predetermined processing position, a convex punch 1 (mainly the tip of the punch ) to form a recess x. Thereafter, as shown in FIG. 1(c), the punch 1 is retracted and pulled out from the recess x, completing the preliminary process.

The hot billet that has undergone this preliminary process (working process) is sent to the piercing-rolling process as it is, and is pierced-rolled by a piercer mill (piercing-rolling mill). Rolling is started with the tip of the piercing plug positioned in the recess x. As a result, the center of the piercing plug can be aligned with the center of the billet, and piercing-rolling is performed with the tip center of the piercing plug positioned at the center of the billet. The occurrence of thickening is suppressed, and a seamless steel pipe having highly accurate thickness dimensions can be finally manufactured.

FIG. 3 schematically shows the position of the piercing plug 200 with respect to the billet 100 at the start of rolling in the piercing-rolling process.
As a mode for positioning the tip of the piercing plug 200 in the depression x of the tip face f of the billet 100 at the start of piercing-rolling, part of the piercing plug 200 engages (contacts) with a part of the inner surface of the depression x. Alternatively, the perforated plug 200 may not engage (contact) the inner surface of the recess x as shown in FIG.
Here, in the piercing-rolling step, it is preferable that the distance L (FIG. 3) between the tip of the piercing plug 200 and the bottom of the depression x at the start of piercing-rolling is 50 mm or more. In piercing-rolling, piercing progresses by generating a crack in the central portion of the billet 100, but by setting the distance L to 50 mm or more, such a central portion of the billet 100 cracks appropriately and piercing proceeds smoothly. proceed to

4A and 4B show a front end portion of a billet in which a recess x is formed. FIG. 4A is a longitudinal section, and FIG. 4B is a front view. In the figure, t is the depth of the dent x (maximum distance reached by the tip of the punch starting from the tip end face f of the billet 100), d is the diameter of the dent x on the tip end face f of the billet 100, and D is the billet diameter.
Here, if the depth t of the depression x is too small, the effect of suppressing thickness unevenness in piercing-rolling is reduced, and the biting property in piercing-rolling tends to deteriorate. Since it becomes easier to drill, there is a risk that it will become difficult to drill. For this reason, the depth t of the depression x needs to be a certain size, and it is particularly preferable to secure the distance L between the tip of the piercing plug and the bottom of the depression x at 50 mm or more at the start of piercing-rolling as described above. Therefore, it is preferable that the depth t of the depression x is greater than 50 mm. Here, the deterioration of biting property in piercing-rolling means that when the billet is driven by the upper and lower rolling rolls and begins to advance and contacts the plug, the load becomes excessive and piercing does not progress. If the depth t of the depression x is too small, the Mannesmann crack at the tip of the billet will not develop sufficiently, resulting in an excessive load for drilling. On the other hand, if the depth t of the depression x is too large, there is a risk that an inner surface flaw (fog flaw) will occur at the pipe end during piercing and rolling, and the pipe end with such an inner surface flaw must be cut and removed. The depth t of the depression x is preferably 120 mm or less because the product yield is lowered.

The shape of the recess x is determined by the shape of the punch portion that is pushed into the billet tip surface. Since it is preferable to have a substantially conical shape with a convex curved surface or a substantially truncated conical shape, the depression x usually has a mortar shape with a concavely curved bottom.
In addition, 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 piercing-rolling is reduced, so the size is set according to the billet diameter D. is preferred. FIG. 5 shows the relationship (one example) between the ratio d/D between the diameter d of the recess x and the billet diameter D and the thickness deviation ratio of the product steel pipe. belongs to. The test (manufacturing) conditions in FIG. 5 are billet material: carbon steel, billet diameter: 300-350 mm, billet heating temperature: 1230-1290° C., product diameter: 316-432 mm.
From the results of FIG. 5, the ratio d/D preferably satisfies about 0.3 to 0.8, more preferably about 0.4 to 0.6.
It should be noted that, due to the movement of the meat due to processing the recess x with the punch 1, deformation such as a slight swelling of the billet tip surface may occur. It is based on the billet tip surface.

FIGS. 6 to 12 schematically show an embodiment of manufacturing equipment used for carrying out the manufacturing method of the present invention and the state of implementation of the manufacturing method of the present invention in this manufacturing equipment. 7 is a side view showing the entire manufacturing facility, FIG. 7 is a side view partially showing part of the billet moving means 5 (cart 50, etc.), and FIG. 8 is a plan view of the same. 9 to 12 partially show a processing device A (a processing device for forming a recess x on the tip end face f of a billet) that constitutes a part of the manufacturing equipment, and FIG. FIG. 10 is a side view partially showing a part of the processing device (punch 1, punch stopper 6, etc.), FIG. 12 is a cross-sectional view taken along line XX in FIG. 9. FIG. 6 omits part of the configuration of the processing apparatus A (the punch 1, the punch holding means 2, the arms 13a and 13b, the hydraulic cylinder 53, the arm holder 55, etc.), and FIG. 6, the supporting member 12 is omitted.

This manufacturing facility includes a processing device A for forming a recess x in the central portion of the front end face f of the hot billet 100 in a preliminary process before the piercing-rolling process of the billet 100, and a billet 100 carried into the facility. Billet holding means 4 for holding billet 100 and billet moving means 5 for pushing the rear end of billet 100 held by this billet holding means 4 and slidingly moving billet 100 to the processing position by processing apparatus A are provided.
The processing apparatus A includes a convex punch 1 for forming a recess x by being pushed into the front end surface f of a billet 100, and holding the punch 1 so as to be able to move back and forth, and inserting the punch 1 at the center of the front end surface of the billet. It is composed of a punch holding means 2 for pushing and a clamping means 3 for clamping and restraining the billet 100 when the billet is processed by the punch 1, etc. The entire apparatus is supported by a support frame 9 which is a support structure. A specific structure of this processing apparatus A will be described in detail later.

In this embodiment, the billet holding means 4 is composed of an elevating trough 40. The elevating trough 40 can move up and down while holding the billet 100. , a chain dog, a kicker, etc.) and carried (charged) into the facility, receives and holds the billet 100, and lifts the billet 100 to a height at which the processing apparatus A can process it.
The billet moving means 5 includes a carriage 50 that can move (run) along a guide rail 8 (a guide rail laid in the direction of the processing apparatus A) installed above the billet holding means 4, and the carriage 50 is moved. It is composed of a drive mechanism 52, a billet pressing pusher arm 51 suspended from the truck 50, and a hydraulic cylinder 53 that slides the pusher arm 51 relative to the truck 50 to move it in the billet direction. By moving the pusher arm 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). By pushing the billet 100, the billet 100 can be slid in the processing apparatus A direction on the elevating trough 40. - 特許庁

To explain the structure of the billet moving means 5 in more detail, a gantry frame 7 is installed above the billet holding means 4, and a guide rail 8 is installed on the gantry frame 7 in the direction of the processing apparatus A. A carriage 50 (57 is a wheel of the carriage 50) can move along 8. The drive mechanism 52 of the carriage 50 is configured by 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 rails 8 and fixed to the screw shaft 520 rotatably supported by the support member 524 and the carriage 50 . A nut member 521 externally mounted on the carriage 50, a motor 522 that rotates the screw shaft 520, a reduction gear 523, and the like. 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 carriage 50 holds a slide guide 54 (for example, a groove-shaped guide rail on which the object to be guided can slide) and an arm holder 55 that holds a pusher arm 51 and can slide along the slide guide 54 in the movement direction of the carriage. , and a hydraulic cylinder 53 for sliding the arm holder 55 .
The operating rod 56 of the hydraulic cylinder 53 is connected 58 to the arm holder 5, and the arm holder 55 is slid in the carriage moving direction (processing apparatus 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 pushes the billet 100 so that the billet 100 can be slid in the processing apparatus A direction.

Next, the processing apparatus A will be explained.
The configuration of the convex punch 1 provided in the processing apparatus A will be detailed 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 the support frame 9 . A punch 1 is detachably held at the tip of the operating rod 22 of the cylinder device 20 via a 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 placed on the tip surface f of the billet 100 held by the lifting trough 40 (billet holding means 4). will be opposed.

The clamping means 3 may have any configuration as long as it can firmly clamp the billet 100 during the processing for forming the recess x on the tip end surface of the billet and constrain it so that it does not move. A pair of upper and lower clamp arms 30a and 30b are provided for clamping the distal end of 100. As shown in FIG. The clamp arms 30a and 30b are pivotally supported 31 on the support frame 9 through their intermediate portions so as to be vertically rotatable. Each clamp arm 30a, 30b has a clamp fitting 32a, 32b at its tip. Each clamp fitting 32a, 32b has a half-cylindrical clamping surface 320. As shown in FIG. 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 (pivoted) 36 to the rear end of the clamp arm 30b, and the distal end of the operating rod 35 of the hydraulic cylinder 33 is connected (pivoted) to the rear end of the clamp arm 30a. As the cylinder 33 expands and contracts, the clamp arms 30a and 30b are vertically opened and closed so that the tip of the billet 100 can be clamped from above and below by the clamp 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 by abutting the tip of the billet 100 moved by the billet moving means 5 . The ring-shaped billet stopper 6 is arranged so as to face the tip of the punch 1 and is supported on the side of the support frame 9 by a support member 12 . When the punch 1 is used to process the billet tip surface, 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 .

Further, the processing apparatus A regulates the opening/closing (rotating) range of the clamp arms 30a and 30b, and reduces the load on the hydraulic cylinder 33, so that the clamp arms 30a and 30b are closed (when the billet 100 is clamped). state).
That is, plate-like arms 13a and 13b having substantially L-shaped planar surfaces and having arm portions 130 and 131 extending in two directions are attached to the pivot portions 31 of the upper and lower clamp arms 30a and 30b. It is pivotally supported at the proximal end (root). These arms 13a and 13b are locked (fixed) to the clamp arms 30a and 30b, respectively, and are configured to rotate together 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 circular guide hole) for guiding each arm portion 130 of the arms 13a and 13b rotating 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. The pin 15 is inserted into the guide hole 14 so that it 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 pin 15, thereby restricting the opening and closing ranges of the clamp arms 30a and 30b rotating together with the arms 13a and 13b. That is, when the pin 15 is engaged with one end of the guide hole 14 (the state shown in FIG. 9), the clamp arms 30a and 30b stop at a predetermined rotational position in the closed state (clamping state of the billet 100). , the pin 15 is engaged with the other end of the guide hole 14, so that the clamp arms 30a and 30b are stopped at a predetermined rotational position in the open state (the billet is not clamped). Further, by engaging the pin 15 with one end of the guide hole 14 as described above (the state shown in FIG. 9), the clamp arms 30a and 30b are stopped at the predetermined rotational position in the closed state (clamping state of the billet). The position of one end side of the guide hole 14 is determined so that both arm portions 131 of the arms 13a and 13b are vertically aligned when the two arms 13a and 13b are moved. Since the arm portions 131 of the arms 13a and 13b are vertically aligned in this way, the driving force of the hydraulic cylinder 33 mechanically holds the clamp arms 30a and 30b in the closed state. Therefore, the load on the hydraulic cylinder 33 can be reduced.

On the other hand, the ends of the arms 131 of the arms 13a and 13b are connected by a pin 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). 12, the end portion of the arm portion 131 of the arm 13b is inserted into the end portion of the arm portion 131 of the arm 13a and pivoted by the pin 16. A bracket portion 17 consisting of a pair of plate-like portions 170 is provided, and the pin 16 is fixed to this bracket portion 17 . An end of the arm portion 131 of the arm 13b is provided with an elongated pin insertion hole 18 (a vertically long pin insertion hole), and the end of the arm portion 131 of the arm 13b is inserted into the bracket portion 17. By inserting the pin 16 into the pin insertion hole 18 in this state, both the arm portions 131 of the arms 13a and 13b are connected. Since the pin 16 of the arm portion 131 of the arm 13a can move in the pin insertion hole 18 of the arm portion 131 of the arm 13b, the arms 13a and 13b rotate integrally with the clamp arms 30a and 30b (the guide holes 14 can be rotated over a short length range).
Note that the billet holding means 4, the billet moving means 5, the punch holding means 2, the clamping means 3, and the like, which constitute the processing apparatus A, are not limited to those of the present embodiment, and can perform their respective functions. It can be configured by appropriate specific means.

Next, the configuration of the punch 1, which is a billet working tool, will be described.
The punch 1 is composed of a main body 10 for billet processing and a mounting portion 11 continuously connected to the end of the main body 10 to be connected 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 or substantially truncated conical shape and the tip has a convex curved shape. Here, the substantially conical shape or substantially truncated conical shape means that the body portion 10 of the punch 1 used in the present invention is a conical or truncated conical inclined surface (tapered surface) with a valley-like bent portion in the middle of the axial direction. (Valley-shaped concave portion), or part or all of the inclined surface is curved in the axial direction. It means that
Furthermore, as a result of studies by the present inventors, by optimizing the body portion 10 of the punch to a more limited shape, the machining of the recess x by the punch can be particularly optimized and efficient, and the life of the punch can be improved. It turned out to be possible.

When carrying out the present invention, the machining of the tip end surface of the billet by the punch 1 of the machining apparatus A (machining to form the recess x) is continuously performed on a number of billets at short time intervals. The tip temperature of the punch 1 rises up to around 500° C. during continuous working. 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 rises to around 500° C. due to 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 is found that a large temperature difference is generated from the tip portion. In FIG. 13, clamp arms 30a and 30b are a 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.

When the billet is continuously machined at such a high temperature, wrinkles and cracks may occur on the surface of some punches as shown in FIG. In addition, the wrinkles and cracks cause irregularities on the punch surface, and due to the irregularities on the punch surface, the punch tip pushed into the billet tip surface cannot be pulled out (as a result, the punch 1 processes the billet 100). Since the billet is drawn into the apparatus A side, this phenomenon is hereinafter referred to as "billet drawing". When such billet pull-in occurs, it is necessary for the operator to manually move the punch forward or backward and perform an operation to eliminate the billet pull-in. A drop in the temperature of the next hot billet cannot be avoided, and the planned rolling becomes impossible, resulting in a drastic drop in productivity.

Although the reason why such wrinkles and cracks occur on the punch surface is not necessarily clear, when the tip of the punch 1 is pushed into the billet tip surface, heat input from the billet side as shown in FIG. , the temperature rises only in the vicinity of the tip of the punch 1, and that portion expands; a large temperature difference occurs between the punch portion that is not in contact with the billet; The temperature gradient occurs in the depth direction of the punch, and while it is in a high temperature state due to continuous use during operation, when a tool change occurs, the operation stops during that time and the tip of the punch cools down, resulting in such thermal expansion and contraction. may be related to the repeated action of
As a result of repeated studies to solve these problems, it was found that by making the punch 1 into a specific shape, surface wrinkles and cracks 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 entrainment was also suppressed.

Figure 15 shows one embodiment of a punch having such a shape. The body portion 10 of this optimally shaped punch 1 is a two-stage type consisting of a punch head portion 10a having a convex (preferably spherical) tip end and a tapered base portion 10b connected to the punch head portion 10a, The boundary between the punch head portion 10a and the tapered base portion 10b constitutes a valley-shaped bent portion 10c (valley-shaped concave portion). Also, the tapered base portion 10b has a slope inclination angle θ of 50 to 60° (approximately 56° in the embodiment of FIG. 15).
According to the results of tests conducted by the present inventors, billet pull-in is particularly likely to occur when processing a billet with a billet diameter of 300 to 350 mm. It is particularly useful when

The tip of the punch head 10a may have a convex curved shape, but it is generally preferable to have a spherical shape. The punch head 10a of this embodiment comprises a curved surface portion a1 on the tip side and a tapered portion a2 connected thereto, but the tapered portion a2 may be omitted.
In addition, the punch head 10a preferably has a certain amount of volume in order to suppress erosion and wear. From this point of view, the convex curved surface (preferably spherical surface) at the tip of the punch head 10a should have a radius of curvature R of 30 mm or more. Preferably.
The hardness and material (component composition) of the punch are not particularly limited, but the hardness and material suitable for working tools used in hot conditions are used. Specifically, the hardness (HS) is preferably 65 or more, and SCM435, SKD61, or the like is used as the material.

The method of the present invention was carried out using the punch 1 shown in FIG. In Table 1, punch (iv) is the punch having the optimum shape shown in FIG. 15, and punches (i) to (iii) are punches having the shape shown in FIG.
The punch (iv) has a tapered base portion 10b with an inclination angle θ of about 56°.
Punches (i) to (iii) have no distinction between the punch head portion 10a and the tapered base portion 10b (therefore, there is no valley-shaped bent portion 10c) as in the punch (iv), and the slope inclination of the tapered portion is The angles are about 70° for punch (i) and about 65° for punches (ii) and (iii). Moreover, the shape of the lower part of the tapered portion differs depending on the punches (i) to (iii).
In this manufacturing test, a billet (carbon steel) with a billet diameter of 260 to 350 mm was used, and the driving time of the punch 1 was 5 seconds. Also, the depth t of the depression x was set to 67 mm.

According to Table 1, punches (i) to (iii) cause billet retraction due to wrinkles and cracks on the surface. value) is a little over 8000 at maximum. On the other hand, the punch (iv) has an average life of 8,300 or more, and no billet pull-in occurs.
As a result, while punches (i) to (iii) had an average usage limit of about 15 days due to damage (wrinkles, cracks, etc.), punch (iv) has an average usage limit of 70 days. I was able to In addition, with punch (iv), wrinkles and cracks at the tip of the punch are less likely to occur. It was able to improve to 0 times/year. By reducing the number of occurrences of trouble in this way, the productivity was able to be improved by 1Hr/month. In addition, the tool cost was reduced due to the improvement of the tool life.

Next, a method of using the manufacturing equipment shown in FIGS. 6 to 12 (an embodiment of the method of the present invention) will be described. 17A to 17F are explanatory diagrams showing the processing procedure of the billet 100 by the processing apparatus A. FIG.
A hot billet 100 (usually about 1200 to 1300° C.) is carried into the manufacturing facility from the side and placed on the lifting trough 40 (billet holding means 4). After the elevating trough 40 is raised to lift (raise) the billet 100 to the height of the processing position by the processing device A (punch 1), the pusher arm 51 pushes the rear end of the billet to move the billet 100 in the direction of the processing device A. Move (FIG. 17(a)). The tip of the moved billet 100 abuts against the billet stopper 6 to stop the billet 100 (FIG. 17(b)), and the billet 100 is machined at this position.

The open clamp arms 30a and 30b are closed by the hydraulic cylinder 33, and the tip 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 of the punch 1 is passed through the inside of the billet stopper 6 (the ring hole 60) to reach the tip face f of the billet 100. A depression x is formed (processed) by pressing (FIG. 17(d)). The pushing (driving) of the punch 1 into the tip surface f of the billet 100 is performed, for example, at a speed of about 0.4 to 0.7 m/sec. After that, the punch 1 is retracted, the tip of the punch 1 is pulled out from the tip face f (formed recess x) of the billet 100 (FIG. 17(e)), and the billet 100 is clamped by the clamp fittings 32a and 32b. is released (FIG. 17(f)) to complete the machining. After the elevating trough 40 holding the processed billet 100 is lowered, the billet 100 is carried out of the facility. This billet 100 is sent to the piercing-rolling process and is pierced-rolled. At this time, as shown in FIG. Start rolling at . The billet 100 is processed into a steel pipe by piercing-rolling, and then the steel pipe is made into a product steel pipe through a series of processes such as an elongation-rolling process.

A billet was processed by the method of the present invention in the equipment shown in FIGS. 6 to 12, followed by piercing-rolling, and then through a series of steps to produce a seamless steel pipe. The steel pipe thus manufactured and the steel pipe manufactured by a conventional method (a method of performing piercing-rolling without a preliminary step of forming a depression x on the end face of the billet) were measured for uneven wall thickness ratios. The results are shown in FIG. The wall thickness deviation ratio is obtained by the following formula based on the maximum wall thickness, minimum wall thickness and average wall thickness of the product steel pipe in the circumferential direction.
Thickness deviation ratio = [(maximum thickness - minimum thickness) / average thickness] x 100
FIG. 18 shows the tip position of the product steel pipe and the wall thickness deviation ratio at each position of 15 mm, 30 mm, and 45 mm from the pipe tip 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 having a shape shown in FIG. A recess x of 67 mm was formed, and during piercing-rolling, the tip of the drilling plug 200 was positioned in the recess x as shown in FIG. 18(a), and rolling was started. On the other hand, in the conventional method (conventional example), rolling was started with the tip of the drilled plug 200 positioned as shown in FIG. 18(b).
The billet material was carbon steel, the billet diameter was 300-350 mm, the billet heating temperature was 1230-1290° C., and the product diameter was 316-432 mm.
As shown in FIG. 18, it can be seen that the uneven wall thickness of the product steel pipe is effectively reduced in the example of the present invention as compared with the conventional example.
In addition, in the method of the present invention (example of the present invention), d/D was tested at 0.24, but as shown in FIG. Then, it is considered that the uneven thickness ratio is further reduced.

Reference Signs List 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 body portion 10a punch head portion 10b tapered base portion 10c bent portion 11 mounting portion 12 support Member 13a, 13b Arm 14 Guide hole 15 Pin 16 Pin 17 Bracket portion 18 Pin insertion hole 20 Cylinder device 21 Cylinder body 22 Operating rod 23 Punch holder 30a, 30b Clamp arm 31 Pivot portion 32a, 32b Clamp fitting 33 Hydraulic cylinder 34 Cylinder body 35 Operating rod 36 Connecting part 40 Lifting trough 50 Carriage 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 Perforated plug 320 clamp surface 520 screw shaft 521 nut member 522 motor 523 speed reducer 524 support member x recess f tip surface A processing device a1 curved surface portion a2 tapered portion

Claims (12)

As a preparatory step before the billet piercing-rolling step, a processing step of pressing a convex punch (1) into the central portion of the front end surface of the hot billet to form a depression (x),
In the billet piercing-rolling step, piercing-rolling is started with the tip of the piercing plug positioned in the recess (x) ,
The main body (10) of the punch (1) has a substantially conical or substantially frusto-conical shape, and includes a punch head (10a) having a convex surface at the tip and a tapered base body connected to the punch head (10a). (10b) consisting of
The boundary between the punch head portion (10a) and the tapered base portion (10b) constitutes a valley-like bent portion (10c),
A method for producing a seamless steel pipe, characterized in that the tapered base portion (10b) has an inclination angle θ of 50 to 60° . The method for manufacturing a seamless steel pipe according to claim 1, characterized in that the depth of the depression (x) is greater than 50 mm. 3. The method for manufacturing a seamless steel pipe according to claim 1 or 2, wherein the ratio d/D between the diameter d of the recess (x) on the tip end face of the billet and the billet diameter D satisfies 0.3 to 0.8. . 4. The seamless steel pipe according to any one of claims 1 to 3, characterized in that in the piercing-rolling step, the distance L between the tip of the piercing plug and the bottom of the recess (x) at the start of piercing-rolling is 50 mm or more. Production method. The method for manufacturing a seamless steel pipe according to any one of claims 1 to 4, wherein the convex curved surface at the tip of the punch head (10a) has a radius of curvature R of 30 mm or more. Equipped with a processing device (A) for forming a depression (x) in the central portion of the tip surface of the hot billet in a preliminary step before the billet piercing-rolling step,
The processing device (A) includes a convex punch (1) for forming a recess (x) by being pushed into the tip surface of a billet, and holding the punch (1) so as to be able to move back and forth. ) into the center of the billet tip surface, and a clamping means (3) for clamping and restraining the billet when the billet tip surface is processed by the punch (1) ,
The main body (10) of the punch (1) has a substantially conical or substantially frusto-conical shape, and includes a punch head (10a) having a convex surface at the tip and a tapered base body connected to the punch head (10a). (10b) consisting of
The boundary between the punch head portion (10a) and the tapered base portion (10b) constitutes a valley-like bent portion (10c),
Equipment for manufacturing a seamless steel pipe, characterized in that the inclination angle θ of the tapered base portion (10b) is 50-60° . 7. The facility for manufacturing seamless steel pipes 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. Further, billet holding means (4) for holding the billet carried into the facility, and pushing the rear end of the billet held by the billet holding means (4) to slide the billet to the processing position by the processing device (A). 8. Equipment for manufacturing seamless steel pipes according to claim 6 or 7, characterized by comprising billet moving means (5) for moving. The processing apparatus (A) further comprises a ring-shaped billet stopper (6) that stops the billet at the processing position by abutting the front end of the billet pushed by the billet moving means (5),
Claim 8 , characterized in that the tip of the punch (1) is pushed into the tip of the billet through the hole of the ring of the billet stopper (6) when processing the tip of the billet by the processing device (A). production facilities for seamless steel pipes. The punch holding means (2) comprises 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 the longitudinal middle portion, and has clamping metal fittings (32a) and (32b) at its tip for sandwiching and clamping the billet from both sides. A pair of clamp arms (30a), (30b) provided and connected between the rear ends of the pair of clamp arms (30a), (30b). The seamless steel pipe manufacturing facility according to any one of claims 6 to 9, further comprising a hydraulic cylinder (33) for opening and closing. A punch for pressing into the end face of a hot billet to form a depression,
The main body (10) has a substantially conical or substantially truncated conical shape, and consists of a punch head (10a) with a convex curved tip and a tapered base (10b) connected to the punch head (10a). become,
The boundary between the punch head portion (10a) and the tapered base portion (10b) constitutes a valley-like bent portion (10c),
A billet processing tool characterized in that a tapered base portion (10b) has an inclination angle θ of 50 to 60° . 12. The billet working tool according to claim 11 , 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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