JPH07314014A - Seamless steel pipe rolling equipment and rolling method - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a rolling facility and a rolling method for a seamless steel pipe which greatly improves the inner diameter accuracy. [Structure] In a seamless steel pipe rolling facility for piercing and rolling a steel slab heated to a predetermined temperature in a heating furnace 1 to obtain a predetermined outer diameter and wall thickness, next to the piercing machine 2 or piercing machines 2 and 1 Or a plurality of inclined rolling mills 3 and then a forming rolling mill 4 are arranged,
Then, a mandrel rolling mill 5 having a retainer device 6 for moving a bar during rolling is arranged as a final rolling mill in the hot rolling stage, and a seamless steel pipe rolling facility is characterized. A method for rolling a seamless steel pipe, which finishes a pipe having an outer diameter and a wall pressure that are final target values in hot rolling in a mandrel rolling machine 5 arranged in a rolling facility for seamless steel pipe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling facility and a method for significantly improving the product size of a pipe, particularly the precision of the inner diameter of the pipe, when hot rolling a seamless steel pipe.

[0002]

2. Description of the Related Art Conventionally, when ordering a seamless steel pipe, a customer specifies an outer diameter and a wall thickness as product specifications. Incidentally, the dimensional tolerance of the product in the JIS standard is specified for the outer diameter and the wall thickness, but not for the inner diameter. For example, carbon steel pipe for pressure piping,
When the outer diameter is 40 A (48.3 mm) or less and the wall thickness is 4 mm or more, the dimensional tolerance is the outer diameter ± 0.5 mm, the wall thickness + 15% -1.
It is specified as 2.5%. However, recently, when ordering a seamless steel pipe, an inner diameter may be specified, and a product having a high inner diameter accuracy may be required. The request is, for example, an inner diameter tolerance of ± 1% ID. The reason is that when used for a line pipe, if there is a step at the joint portion of the seamless steel pipe, the joint portion is corroded due to a turbulent flow phenomenon, which causes trouble as a line pipe. Here, from the viewpoint of manufacturing a seamless steel pipe with high inner diameter precision, the conventional seamless steel pipe rolling method,
Let us consider rolling equipment.

Conventionally, a typical rolling equipment for producing a seamless steel pipe is, for example, as shown in FIG. 8 of JP-A-57-103714, a heating furnace 10, a punching machine (two-roll Mannesmann punching machine). ) 11, finish rolling mill (mandrel bar constrained multi-stand continuous tube rolling mill) 12,
The forming and rolling mill (sizer) 13 is basically used. If necessary, before the finish rolling mill, an inclined stretching mill (in the example of FIG. 8, 3
A reheating furnace is placed in front of the roll mandrel elongator 14) and the forming and rolling mill. Looking at finishing rolling mills and forming rolling mills in seamless steel pipe manufacturing equipment, when producing small diameter pipes, a mandrel mill (mandrel rolling mill) is used as the finishing rolling mill, a stretch reducer is used as the forming rolling mill, and When manufacturing pipes, it is common to use a plug mill and reeler as the finishing rolling mill and a sizer as the forming and rolling mill. Further, even when an assel mill, a disher mill, or the like is used as the finish rolling mill, a forming / rolling machine such as a sizer or a stretch reducer is arranged next to it. That is, no matter what type of finish rolling mill, by arranging the forming rolling mill next, the inner and outer surfaces are restrained in the finishing rolling mill and the required thickness is determined by rolling. After that, the outer surface of the tube is constrained in the forming rolling machine arranged as the final hot rolling machine, and the rolling is applied to obtain the tube having the final target outer diameter and wall thickness.

[0004]

However, this forming and rolling machine is composed of a stand row having a plurality of rolls, and since the outer surface of the pipe is constrained by the rolls, the accuracy of the outer diameter can be excellently formed, but the inner surface Is deformable, and the pressure applied to the pipe from the roll on the outer surface is different depending on the position along the circumference of the cross section of the pipe, so that the inner diameter cannot be manufactured with good accuracy. As an example, for example, the Iron and Steel Handbook P. 1046, 104
7 describes hexagonal inner surface tensioning in a 3-roll molding. Experience shows that in the case of 2 rolls,
The inner corner is square. From this situation,
Depending on the conventional rolling system and rolling mill train, the inner diameter accuracy is about ± 3% ID even if the JIS standard is satisfied for the outer diameter and wall thickness, and as described above, the inner diameter tolerance of the product is ± 1% ID.
It is difficult to satisfy the dimensional tolerance of the product when it is designated as "very advantageous". It is not possible to manufacture a seamless steel pipe having a high inner diameter accuracy by the conventional rolling method of seamless steel pipe and rolling equipment, and there are the above-mentioned problems.

Therefore, since the deterioration of the inner diameter accuracy of the conventional products is caused by the unconstrained rolling of the inner surface of the pipe in the forming and rolling machine, the forming and rolling machine arranged next to the finishing rolling machine is removed from the rolling mill train. It is conceivable that the final rolling mill is to be eliminated and the finishing mill is not arranged next to the finishing mill, that is, the finishing mill is the final rolling mill. In this case, however, there are two problems described below.

[0006] The first point relates to the size integration of the billet, and it is impossible to advantageously manufacture various outer diameter sizes. In a seamless steel pipe manufacturing facility, the biggest reason for requiring a finish rolling mill followed by a forming roll consisting of a plurality of stands is to advantageously deal with various product sizes. In general, the outer diameter size produced by hot rolling of a seamless steel pipe is in a wide range, for example, from 190 mm to 420 mm, and the number of sizes in that range is often 20 or more. Of course, it is possible to carry out piercing and rolling with a billet size according to the outer diameter size to manufacture various rolling sizes, but with this, the number of tools to be used becomes enormous and frequent tool replacement is required, so work is possible. The time that can be used for actual work is shortened and it cannot be an efficient method. In reality, a forming and rolling machine is installed, and by the method of manufacturing pipes with a limited billet size of at most four types, up to the finishing rolling machine, there are about four types of outer diameter sizes corresponding to the billet size. By changing the number of stands used in the forming and rolling mill installed at, the manufacturing outer diameter can be changed with a short work stoppage. In the example of the outer diameter change according to the conventional method shown in FIG. 3, for example, the outer diameter from 370 mm to 420 mm is 320
mm × 320 mm (square billet with side length 320) 1
The number of stands used in the forming and rolling mill is changed to 12 stands, which can be arranged in the maximum in the equipment when manufacturing 370 mm with a size billet, and 4 stands when 420 mm. That is, in the forming and rolling mill,
Various sizes are formed by using the number of stands that is equal to or less than the maximum number of stands that can be arranged on the equipment.
Since the time required to change the number of stands is at most about 5 minutes, it is possible to advantageously manufacture a large number of tube outer diameters from a limited billet size with a short work stoppage. If the forming and rolling mill were not located next to the finishing mill, such advantages would be lost.

The second point is a problem in the case where the finishing rolling mill is not arranged next to the forming rolling mill and the finishing rolling mill completes the product dimension. First, there is a case where the finish rolling mill is a typical plug mill method. In the plug mill method, a reeler that is an inclined rolling mill is required after the plug mill. In the case of an inclined rolling mill, although the wall thickness accuracy is a desired value on the principle of rolling, the outer diameter accuracy is far from ± 1.0% OD which is a general user's requirement ± 3 to 5% OD. Will be. The same applies to the Assel mill method and the Disher mill method, which are finish rolling methods using an inclined rolling mill, and it is difficult to manufacture the outer diameter accuracy within the range required by the user. Therefore, it follows that the forming and rolling mill is required after the finish rolling mill.

Next, it is a case where the finish rolling mill is a mandrel rolling mill. It is well known in the art that there are three methods of operating the bar in the mandrel mill method. That is, (1) a full float system that does not control the speed of the bar at all, (2) a semi-float system that controls the bar until the end of rolling and finally opens the bar, and (3) a retract system that controls until the end of rolling. is there. In any of these cases, the bar progresses in the rolling direction, and it is necessary to pull out the bar from the pipe after the rolling is completed.
In order to pull out the bar from the pipe, in the full float method of (1) and the semi-float method of (2), as shown in FIG. 9, the flange portion 16 of the roll 15 of the final stand that determines the wall thickness is The bar 17 is formed into an overhanging shape without coming into contact with the bar 17, and the part is pressed down by the next stand and rounded up to provide a gap between the bar and the pipe over the entire cross section. At that time, it is known that the vicinity of the boundary between the thickness determining portion and the flange portion (mark c in FIG. 9) in the final stand that determines the thickness shows a clear increase in thickness when rounded up at the next stand. ing. This occurs at four points in the cross section as shown in FIG. 10, and at the opposite positions, and the amount of increase in thickness is about 0.5 mm (reference numeral 18).
Therefore, the inner diameter accuracy is significantly deteriorated. Therefore, even if the accuracy of the outer diameter can be improved by the round-up, it is clearly different from the goal of obtaining a tube with high accuracy of the inner diameter. Further, in the retract method of (3), the rolling speed of the pipe is controlled to be higher than the feeding speed of the bar after the rolling in the mandrel rolling mill is completed by applying the rolling from the outer surface to the pipe. However, in order to pull out the bar from the pipe, a forming and rolling mill (extractor) is required on the rolling exit side of the rolling pass line. This extractor has about 3 stands, and the deterioration of the inner diameter accuracy is smaller than that of the normal forming and rolling mill, but especially when the ratio of the wall thickness to the outer diameter (wall thickness / outer diameter) exceeds 15%. Etc., even if the number of stands is about 3, the squareness of the inner surface becomes remarkable, and the inner diameter accuracy cannot be said to be good.

As described above, there is no method or equipment for producing a seamless steel pipe having a good inner diameter accuracy in hot rolling, and after hot rolling, after cold rolling in which the outer surface is held by a die and the inner surface is held by a plug. There is no choice but to rely on methods such as pulling out, and manufacturing costs will rise significantly. The present invention, based on such a current situation, can provide a seamless steel pipe rolling facility and a rolling method, which can advantageously manufacture a seamless steel pipe having a good inner diameter accuracy without adding a process such as cold drawing. The purpose is.

[0010]

In order to achieve the above object, the seamless steel pipe rolling equipment according to the present invention has a predetermined outer diameter by punching and rolling a steel slab heated to a predetermined temperature in a heating furnace. In a seamless steel pipe rolling facility for obtaining a wall thickness, a forming mill is arranged next to a perforator or after the perforator and one or more inclined rolling mills, and then a final rolling mill in a hot rolling stage. As a mandrel rolling machine having a retainer device for moving the bar during rolling. Here, the forming and rolling mill in the present invention,
A sizer or stretch reducer. By arranging such a forming rolling mill in front of the mandrel rolling mill which is a finishing rolling mill, it is possible to advantageously roll various outer diameter sizes without arranging a forming rolling mill like the conventional one next to the finishing rolling mill. it can. Since the number of stands of the forming mill placed in front of the finish rolling mill must be sufficient to manufacture many outer diameter sizes, the number of stands of the forming mill that can be arranged in the equipment of the prior art. It is preferably equal to or more than. By the way, as described above, the forming and rolling mill is a rolling mill that forms various sizes by using the number of stands that is equal to or less than the maximum number of stands that can be arranged on the equipment. Therefore, in terms of equipment, the number of stands of the forming and rolling mill refers to the maximum number of stands that can be arranged. For reference, the Iron and Steel Handbook P. 1038-Table 1
The fact that the number of stands of the sizer is 7 in 1.105 means that a maximum of 7 stands can be arranged, and in actual use, the number of stands of 7 or less can be arranged. Now, the above-mentioned Steel Handbook P. 1038-Table 11.1
According to 05, the number of stands of the sizer is typically seven, and even in recent years, as the number of stands to be arranged in the sizer used as a forming and rolling mill to obtain the final outer diameter in hot rolling. Considering that 7 or less is not adopted, rolling type, size,
From the viewpoint of billet integration and the like, it is preferable that the forming and rolling mill arranged in front of the finishing rolling mill has seven or more stands.
However, as described above, the number of actually used stands may be less than seven. The maximum number of stands may be set to 24 in consideration of a stretch reducer having a larger number of stands than the sizer. The number of stands of the inclined rolling mill is usually 1 to 2.

Next, a method for rolling a seamless steel pipe according to the present invention is a method for rolling a seamless steel pipe using the above-mentioned seamless steel pipe rolling equipment, which comprises forming and rolling a perforated or perforated and rolled pipe. After forming and rolling with a mill and inserting a bar on the inner surface of the pipe, a pipe having an outer diameter and a wall thickness that are final target values in the hot rolling stage is obtained by finish rolling with a mandrel rolling mill. In the present invention, the mandrel rolling mill is arranged next to the forming rolling mill, so that the target outer diameter and wall thickness in the final stage of hot rolling can be determined by the mandrel rolling mill at the same time, and at the same time, Since the rolling mill whose inner surface is not freely deformed by the existence of the bar becomes the final rolling mill, the accuracy of the inner diameter is greatly improved. In other words, the mandrel rolling machine, which is the final rolling machine in the hot rolling stage, can finish the product dimension when the inner diameter tolerance is small in ordering the seamless steel pipe. The mandrel rolling mill is composed of 2 to 8 stands, and each stand incorporates a plurality of rolls. And
The rolled stock tube has a reduced wall thickness between a bar inserted on the inner surface and a roll incorporated in a stand. The bar inserted into this rolled material is previously coated with a lubricant containing graphite as a main component to form a strong film, and the quality of the inner surface of the pipe after rolling is improved.

Further, the method for rolling a seamless steel pipe of the present invention is the above-mentioned method for rolling a seamless steel pipe, wherein the tip of the bar inserted into the rolling material of the mandrel rolling machine at the start of pipe rolling in the mandrel rolling machine. End of the pipe with the bar inserted in the mandrel rolling machine by moving the bar in the direction opposite to the rolling direction during rolling in the mandrel rolling machine. Also, it is constructed by slipping the tube from the roll and the bar. As a result of searching for a mandrel mill method in which the bar does not have to be pulled out from the tube after rolling, the inventor has come to the finding that it is possible by moving the bar during rolling in the direction opposite to the rolling direction. It was. Conventionally, in a mandrel rolling mill, by advancing the bar during rolling in the same direction as the rolling direction, it is possible to roll at the bar portion where fresh lubricant is applied, over the entire length of the rolled material, The quality of the inner surface of the pipe after rolling is maintained. The inventor decided not to move the bar forward, but to move it backward in the direction opposite to the tip direction of the bar in order to supply fresh lubricant.
By selecting the retreat speed of the bar according to the roll speed during rolling, the tip of the bar is located at the center line of the roll of the final stand at the end of rolling and is involved in rolling, but after the rolling is completed, The pipe is slipped out by the rolling force of the mandrel rolling machine and the action of the bar without remaining in the rear end. Conventionally, pulling out a bar from a tube after rolling has been a cause of deterioration in accuracy of the inner diameter, but the cause has been fundamentally eliminated. The finish rolling machine arranged next to the forming rolling machine requires a retainer device for controlling the backward moving speed of the bar during rolling in accordance with the rolling speed of the tube rear end and the tailing speed.

[0013]

According to the present invention, in a seamless steel pipe rolling facility for punching and rolling a steel slab heated to a predetermined temperature in a heating furnace to obtain a predetermined outer diameter and wall thickness, next to the piercing machine or the piercing machine. And one or a plurality of inclined rolling mills, followed by a forming rolling mill, and then a mandrel rolling mill having a retainer device capable of moving a bar during rolling as a final rolling mill in a hot rolling stage. Thereby, the piercing, or the pierced and rolled pipe is molded and rolled by the forming and rolling machine, and the pipe into which the bar is inserted after the forming and rolling is the inner / outer diameter which is the final target value in the hot rolling stage, The thick tube is finished and rolled by a mandrel rolling mill. Further, at the time of starting the tube rolling in the mandrel rolling mill, the tip of the bar inserted in the rolling material of the mandrel rolling mill is made to face the exit side from the final stand of the mandrel rolling mill, and the bar is rolled during rolling in the mandrel rolling mill. By moving the tube in the mandrel rolling machine in the direction opposite to the rolling direction, the tube with the bar inserted is withdrawn from the roll and the bar at the end of rolling at the final stand.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the arrangement of a seamless steel pipe rolling facility according to the present invention. The rolled material is heated in a walking beam type heating furnace 1, and a puncher 2 of a press roll piercer is used.
In the machine, rolled by a Mannesmann-type inclined stretching mill (elongator) 3, formed by a three-roll sizer 4 having 10 stands, and then two stands equipped with a retainer facility 6 (stand spacing is 1
In m), the pipe is finally hot-rolled by the three-roll mandrel rolling machine 5, and the finished pipe having a specified inner / outer diameter and wall thickness is sent to the cooling floor 7. FIG. 2 shows a situation of the outer diameter change on the delivery side of each rolling mill of FIG. For comparison, FIG. 3 shows changes in the outer diameter on the delivery side of each rolling mill when the rolling is performed by the conventional method. Also in the present invention, the same billet size as that of the conventional method can be used, and the outer diameter change is exactly the same up to the elongator. When the product outer diameter changes, it is necessary to replace the stand of the mandrel rolling mill together with the sizer, but the mandrel rolling mill is composed of 3 rolls, and the stand in a short time is the same as the time to replace the stand of the sizer. Can be exchanged.

Next, the movement of the bar at the final stand of the mandrel rolling mill will be schematically shown. FIG. 4 shows a case where the bar, which is the technique of the present invention, is retracted (the direction opposite to the rolling direction). Here, the mandrel rolling mill has two stands.
In FIG. 4 (a), at the start of rolling, the bar 9 is projected and positioned on the outlet side of the second stand.
When the rolling in the second stand is completed, the tip of the bar 9 is positioned at the roll center of the second stand at the end of rolling in the second stand. The operation of the bar 9 and the driving of the roll of the rolling mill cause the pipe 8 to slip. FIG. 5 shows the case of the prior art corresponding to FIG. 4, but the bar 9 is advanced during rolling, and at the end of rolling on the second stand, the bar 9 is inserted into the pipe 8.

Here, the rolling of the pipe will be further described by showing specific rolling conditions. Table 1 exemplifies the outer diameter, wall thickness, and length dimensions on the outlet side of each rolling facility, and the inner and outer diameters, and wall thickness on the outlet side of the mandrel rolling mill exemplify the designated dimensions of a seamless steel pipe product. Table 2 shows rolling conditions in the mandrel rolling mill.

[0017]

[Table 1] (Note) The target inner diameter of the mandrel rolling mill is 195.4 mmφ, which is the specified dimension of the product.

[0018]

[Table 2] Note) The bar protrusion length is the length from the rolled material tip to the bar tip at the start of rolling. Now, when the tube sizes illustrated in Table 1 were rolled under the rolling conditions shown in Table 2, according to the method of the present invention, the tip of the bar at the start of rolling was at the exit side of the second stand of about 6.0 m. When the bar was stopped at the end of rolling, the pipe was conveyed by the inertia during rolling and the exit side roller table and was completely pulled out from the pipe. Of course, during rolling, the rolled material is in a state of being rolled by a bar and a roll over the entire length of the rolled material. Therefore, even if the bar is not pulled out during rolling, the mandrel rolling which does not need to be pulled out can be realized. On the other hand, in the conventional method, the bar remains about 5.8 m in the rolled pipe, and it is necessary to pull out the bar from the pipe separately. As an effect of applying the present invention, the inner diameter accuracy according to the present invention is shown in FIG. 6, and the inner diameter accuracy of the tube according to the conventional technique is shown in FIG. According to the present invention, an ID of ± 0.5% is achieved and a dramatic improvement can be realized, and it is possible to cope with a strict specified dimensional tolerance of a seamless steel pipe. (± 3.0% ID in conventional technology
Out. ) In addition, the outer diameter accuracy is well within ± 1.0% OD, and the inner diameter accuracy has improved, achieving a wall thickness accuracy of ± 3.5%. Together with the inner diameter accuracy, the wall thickness accuracy is also dramatically improved. Improved.

[0019]

EFFECTS OF THE INVENTION According to the present invention, it is possible to advantageously manufacture a seamless steel pipe having dramatically improved inner diameter accuracy in hot rolling without requiring additional steps such as cold drawing. Became.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of arrangement of rolling equipment for a seamless steel pipe of the present invention.

FIG. 2 shows an example of changes in outer diameter on the delivery side of each rolling facility according to the present invention.

FIG. 3 shows an example of a change in outer diameter on the outlet side of each rolling facility according to the conventional method.

FIG. 4 is a diagram showing movement of a bar of the mandrel rolling mill in the present invention.

FIG. 5 is a diagram showing the movement of a bar of a mandrel rolling mill in the conventional method.

FIG. 6 is a diagram showing the inner diameter accuracy of a tube according to the present invention.

FIG. 7 is a diagram showing the inner diameter accuracy of a tube according to a conventional method.

FIG. 8 is a diagram showing a conventional technique.

FIG. 9 is an explanatory diagram showing a deformed state of the cross section of the rolled material in the stand for determining the final thickness of the mandrel rolling mill.

FIG. 10 is an explanatory diagram showing a cross-sectional shape of a cross section of a rolled material on the delivery side of a mandrel rolling mill having a round-up function.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Punching machine 3 Inclination stretching rolling machine 4 Forming rolling machine 5 Mandrel rolling machine 6 Retainer equipment 7 Cooling floor 8 Tube 9 Bar 10 Heating furnace 11 Punching machine 12 Finishing rolling machine 13 Forming rolling machine 14 3 Roll mandrel elongator 15 Roll 16 Flange 17 Bar 18 Thickness increase

Claims (4)

[Claims] 1. A seamless steel pipe rolling facility for piercing and rolling a steel slab heated to a predetermined temperature in a heating furnace to obtain a predetermined outer diameter and wall thickness, next to the piercing machine, or the piercing machine and 1 to 1. Forming rolling mill is arranged next to a plurality of inclined rolling mills, and then a mandrel rolling mill having a retainer device that makes it possible to move the bar during rolling is arranged as the final rolling mill in the hot rolling stage. Characteristic seamless steel pipe rolling equipment. 2. The seamless steel pipe rolling facility according to claim 1, wherein the number of stands of the forming and rolling mill is 7 to 24. 3. A method for rolling a seamless steel pipe using the seamless steel pipe rolling equipment according to claim 1 or 2, wherein the piercing or piercing and rolling the pipe is formed and rolled by a forming rolling machine. A method for rolling a seamless steel pipe, characterized in that, after inserting a bar on the inner surface of the pipe, a pipe having an outer diameter and a wall thickness that are final target values in the hot rolling stage is obtained by finish rolling with a mandrel rolling machine. . 4. The mandrel rolling machine is arranged such that at the start of pipe rolling, the tip of the bar inserted into the rolling material of the mandrel rolling machine faces the exit side from the final stand of the mandrel rolling machine. The seamless steel pipe according to claim 3, wherein by moving the bar in the direction opposite to the rolling direction during rolling, the pipe with the bar inserted in the mandrel rolling machine is unrolled from the roll and the bar at the end of rolling at the final stand. Rolling method.