JP2765390B2 - Rolling method of seamless steel pipe by mandrel mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling method for producing a seamless steel pipe by a mandrel mill, and more particularly to a rolling method capable of preventing the removal of a mandrel and the occurrence of seizure flaws.

[0002]

2. Description of the Related Art When manufacturing a seamless steel pipe, a round or square billet is heated and then drilled to produce a hollow shell. This hollow shell is stretched and rolled by a mandrel mill and then further rolled. A finish rolling method using a sizer or a stretch reducer is widely used. The mandrel mill is usually composed of about 5 to 8 roll stands, and each roll stand is composed of a pair of opposed hole type rolls. Then, the hollow shell in which the mandrel is inserted is continuously rolled by these rolls to reduce the thickness of the hollow shell between the roll and the mandrel.

[0003] Mandrel mills are roughly classified into the following three types according to mandrel operation methods. (1) Full float mandrel mill (2) Rest-retained mandrel mill or retained mandrel mill (3) Semi-float mandrel mill

[0004] Fig. 10 is an explanatory view illustrating the equipment and rolling method of a full float mandrel mill that does not restrain the mandrel during rolling, and the contents are described in the Iron and Steel Handbook Third Edition III.
(2), P972 (edited by the Iron and Steel Institute of Japan, Maruzen 1980). Hollow shell 3 sent to insert line 31
2, the mandrel 33a is inserted by the pusher 30 until the predetermined protruding length is reached, and the hollow shell 32 is set together with the mandrel on the mill line 35 on the entry side of the mandrel mill 34. Feed rolling is performed. The seamless steel pipe 38a manufactured by rolling is splashed out to the return line 39 while holding the mandrel 33b, and the mandrel 33c is pulled out of the seamless steel pipe 38b by the stripper table 40.
Thereafter, the mandrel 33 d retreats on the return line 39, is water-cooled in the cooling zone 41, and returns to the insert line 31 again. The mandrel is then used again in the state described above.

[0005] The mandrel 33 used in the above rolling
Is coated with a lubricant. As a place where the lubricant is applied, either a position immediately before the mandrel 33a is inserted into the hollow shell 32 on the insert line 31 or a position after the removal of the mandrel 33c on the return line 39, Or both are usually chosen.

FIG. 11 is an explanatory diagram for explaining the equipment and rolling method of a wrist-retained mandrel mill or a retained mandrel mill for restraining a mandrel during rolling. The mandrel 53a is inserted into the hollow shell 52 through the insert line 51. Next, the mandrel 53a
The hollow shell 52 is sent to the mill line 54, and the rear end of the mandrel 53b is set in the restraining device 55. The mandrel 53b is advanced by the restraining device 55, and the hollow shell 52 is moved.
To the mandrel mill 56 to start rolling. This rolling reduces the forward speed of the mandrel 53b by the restraining device 55.
It is performed while controlling with. When the rolling is completed, the mandrel 53b is further advanced to feed the semi-finished seamless steel pipe 57 to the sizer 58 or the extractor (the figure is a sizer). When rolling is started in the sizer 58, the mandrel 53b is retracted and pulled out from the semi-finished seamless steel pipe 57.

[0007] Next, the mandrel 53c is jumped out to the return line 59 and sent to the rear. The mandrel 53c is cooled by the water in the cooling zone 60 and is moved to the insert line 51 again, and waits for the next rolling. Also in this case, a lubricant is applied to the mandrel 53 as in the case of the full float mandrel mill.
The place where the lubricant is applied is insert line 5
1 before the mandrel 53a is inserted into the hollow shell 52, or at a position where the mandrel is retracted on the return line 59, or both, or on the mill line 54 as disclosed in JP-A-3-90205. At the position on the entry side of the first stand 61 of the mandrel mill 56, when the mandrel retreats after the rolling is completed, the lubricant is applied.

A semi-float mandrel mill is a compromise between the two methods described above in terms of mandrel operation. That is, after the mandrel is inserted into the hollow shell at the insert line, the mandrel is set in the same restraining device as the rest-reinforced mandrel mill. The mandrel is controlled in advance by a restraining device in the same manner as a wrist ladle mandrel mill during rolling, but the mandrel is released from the restraining device on the way, and in the latter half of rolling, rolling is performed in the same state as a full float mandrel mill . Withdrawal of the mandrel after rolling is completed, and subsequent water cooling in the transport and cooling zones and lubrication of the mandrel are performed in the same manner as in the case of the full float mandrel mill.

Water-soluble or oil-soluble graphite is widely used as a lubricant in any of the mandrel mill types, and is used in a coating apparatus having a plurality of spray nozzles.
Applied on the mandrel. The mandrel having the lubricating film formed on the surface in this manner is inserted into a hollow shell and rolled.

[0010]

As described above, in any of the mandrel mill types, as a conventional lubrication method, a method of forming a lubricating film on the surface of the mandrel before rolling is widely used. Problems.

That is, in the conventional lubrication method, even if the lubricant can be uniformly applied on the mandrel prior to the rolling, it is not possible to stably maintain a constant frictional state over the entire length of the hollow shell to be rolled. difficult. In other words, when rolling the pipe tip at the beginning of rolling, the lubricating coating on the mandrel reduces the contact frictional resistance between the mandrel and the inner surface of the pipe in a thick state as applied, but as the rolling progresses The lubricating film on the mandrel is gradually carried away by the hollow shell contacting with the mandrel. When the rear end of the tube is rolled, the lubricating film becomes very small. Therefore, when rolling one tube, the coefficient of friction gradually increases from the start to the end of rolling. Such a change in the coefficient of friction causes a change in the rolling conditions in the longitudinal direction, which causes a problem in that the dimensional accuracy in the longitudinal direction of the pipe as a product is deteriorated.

In addition, rolling under the condition of a thin-walled tube, a long tube, or a condition with a large amount of reduction, and a rolling of a material having high deformation resistance and easily seizing such as stainless steel, high Cr, high Ni alloy steel, etc., which have been increasing in demand in recent years. In this case, the friction condition between the mandrel and the inner surface of the hollow shell becomes severe, and the friction coefficient at the time of rolling one tube is remarkably increased. This not only causes a reduction in the rolling efficiency, but also causes chattering and makes it difficult to remove the mandrel from the seamless steel pipe after the rolling is completed. Further, there is a problem that the quality of the product is deteriorated due to seizure flaws on the inner surface of the tube.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is necessary to maintain a constant lubrication state between the mandrel and the inner surface of the tube over the entire length of the tube from the start to the end of rolling. It is an object of the present invention to provide a rolling method capable of maintaining a good condition.

[0014]

A method of rolling a seamless steel pipe by a mandrel mill according to the present invention is directed to a method of rolling a seamless steel pipe by a mandrel mill in which a hollow shell is continuously rolled with a hole roll and a mandrel. When the mandrel is inserted into the hollow shell, a lubricant is supplied through the hollow mandrel, and the lubricant is sprayed onto the inner surface of the hollow shell before rolling from an injection hole provided at the tip of the mandrel, thereby forming the hollow shell. All inside
After depositing the lubricant over the length, and performs rolling.

[0015]

In the method for rolling a seamless steel pipe by a mandrel mill according to the present invention, the entire length of the inner surface of the hollow shell before rolling is reduced.
Over and have injected a lubricant. And, by this, the lubrication state between the inner surface of the hollow shell and the outer surface of the mandrel,
From the start of rolling to the end of rolling, it is possible to maintain a certain favorable state. Therefore, since the rolling can be performed stably, the mandrel does not seize to the rolled seamless steel pipe and cannot be pulled out, and the seamless steel pipe does not have seizure flaws, and the quality of the product does not deteriorate.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to rolling of a type in which a mandrel is restrained will be described with reference to FIGS. FIG. 1 is an explanatory view showing a configuration of a facility for injecting a lubricant into the inner surface of a hollow shell, FIG. 2A is a longitudinal sectional view showing a state in which the lubricant is being injected into the hollow shell via a mandrel, FIG. 2 (b)
2A is a view taken along the line AA in FIG. 2A, and FIG. 2C is a view in FIG.
FIG.

Prior to rolling, the hollow shell 1 is placed on the mill line 4 on the entry side of the first stand 3 of the mandrel mill 2. Then, the mandrel 5 is inserted into the hollow shell 1 at this position. The mandrel 5 advances toward the hollow shell 1 with its rear end held by the restraining device 6. The mandrel 5 moves forward, and the lubricant supply pipe 7 connected to the rear end of the mandrel 5 supplies the lubricant 9 from the lubricant tank 8 to the pump 9.
Activate and feed lubricant. Note that reference numeral 10 in FIG.
Is a sizer, 11 is a cooling water pipe for cooling the mandrel, 12
Is a cooling water supply pump.

The lubricant is supplied from the lubricant supply pipe 7 as shown in FIG.
As shown in (1), the lubricant 15 is guided to the supply pipe 13 provided inside the hollow mandrel 5, and the lubricant 15 is injected toward the inner surface of the hollow shell 1 from the injection hole 14 provided at the tip of the mandrel 5. . The injection of the lubricant 15 is continued until the tip of the mandrel 5 is inserted into the rear end of the hollow shell 1 until it reaches the tip, and the lubricant 15 is applied over the entire inner surface of the hollow shell 1. When the tip of the mandrel 5 comes out of the tip of the hollow shell 1, the supply of the lubricant 15 is stopped. The mandrel 5 is further advanced by the restraining device 6 until a predetermined protrusion length is reached.

If necessary, the hollow shell 1 is rotated around its axis so that the applied lubricant 15 spreads on the inner surface. This rotation may be performed during insertion of the mandrel 5. As shown in FIG. 2B, the hollow shell 1 is rotated by placing the hollow shell 1 on two rollers 16 and driving one or more of the rollers 16 to rotate the hollow shell 1. . FIG. 2B illustrates a case where one set of rollers is arranged in the longitudinal direction. However, a plurality of sets of two rollers may be arranged in the longitudinal direction to support the hollow shell 1. In addition, FIG.
2B, reference numeral 17 denotes a cooling water supply channel in the mandrel, and reference numeral 18 denotes a cooling water drainage channel.

FIGS. 3A and 3B are explanatory views of an apparatus for rotating the hollow shell 1, wherein FIG. 3A is a plan view and FIG. 3B is a side view.
As shown in FIG. 3, at the start of rolling, these two rollers 16 are lowered, and instead, the feed roller 19 is raised to support the hollow shell 1, and at the same time, the pinch roller 20 is moved.
Comes down from above, sandwiches the hollow shell 1, and drives it to feed the hollow shell 1 into the first stand 3. The mandrel 5 advances at a speed controlled by the restraining device 6 during rolling. In the continuous stand, the wall thickness of the hollow shell 1 is sequentially reduced between the roll and the mandrel 5, but since the inner surface of the tube is coated with a lubricant, the friction condition between the mandrel and the inner surface of the shell is constant and good. And rolling is performed stably.

FIG. 4 is a longitudinal sectional view showing a state in which the hollow shell 1 is rolled by a mandrel mill. Inside of the hollow mandrel 5 is cooling water supplied from a pipe connected to the rear end of the mandrel 5. However, the cooling water is guided to a cooling water supply channel 17 provided inside the mandrel 5 and cooled down to the tip of the mandrel 5, and the cooling water reaching the tip passes through a cooling water drainage channel 18 outside the mandrel 5, and is cooled after the mandrel 5. It returns to the end and is discharged from another pipe. Cooling may be freely performed according to the degree of rise in the temperature of the mandrel 5.

When a lubricant which is easily solidified by a rise in temperature, such as an aqueous solution of water-soluble graphite or boric acid or a salt thereof, is used as the lubricant, it is necessary to maintain a low temperature when guiding the inside of the mandrel 5. In that case, as shown in FIG. 4, it is preferable that the cooling water supply passage 17 through which the cooling water passes is provided outside the pipe 13 that guides the lubricant. In other cases, it is possible to reverse the lubricant supply pipe 13 and the cooling water supply channel 17 for guiding the cooling water, and there is a case where water cooling is not required.

FIG. 5 is a longitudinal sectional view showing a state where the mandrel 5 is set on the restraining device 6. A neck portion 21 provided at the rear end of the mandrel 5 is dropped into a recess (chuck portion) 22 formed at the tip of the restraining device 6. A pipe 13 for guiding the lubricant into the mandrel 5 to the rear end of the neck 21 of the mandrel 5, and a cooling water supply channel 17 for guiding the cooling water.
The cooling water drainage passage 18 is in communication with the cooling water drainage passage 18, and the end is tapered as shown in the figure. When the neck portion 21 of the mandrel is set in the restraining device 6, the portion 23 having the pipe end waiting at the rear advances to the neck portion 21 of the mandrel, and the pipe end processed into a tapered shape. The portions 24 are pressed and fitted to the inner tube ends of the neck portion 21 at corresponding positions. The advance of the pipe end 24 and the pressing of the pipe end 24 against the neck 21 may be performed by pneumatic or hydraulic cylinders 25 (in the case of pneumatic pressure in the figure).

In this state, when the pumps 9 and 12 shown in FIG. 1 are started, the lubricant or cooling water passes through the pipes from the lubricant tank 8 or the cooling supply pipe 11, respectively, and the respective inner pipes 13 of the mandrel 5 are formed. The cooling water is supplied to the cooling water supply channel 17, and the wastewater is discharged through the cooling water drainage channel 18. When removing the mandrel 5, the supply of the lubricant and the cooling water is stopped, and after the pipe end 24 retreats and the connection with the neck 21 is released, the mandrel 5 is sprung out of the restraining device 6 by an appropriate device. In order to prevent leakage of lubricant or cooling water at the fitting portion between the pipe end portion 24 and the inner pipe end portion of the neck portion 21, each tapered portion, which is a fitting portion, is made of a copper alloy metal seal. In order to obtain a good bonding state, it may be made of a material such as resin or rubber.

When the lubricant is a powder of graphite, borax, glass or the like, the shape of the nozzle need not be particularly limited, but for example, the shape shown in FIG. 2B is generally used. The lubricant can be jetted from the jet holes 14 formed in the mandrel 5. Similarly, when the lubricant is a liquid such as water-soluble graphite, grease, oil or fat, or an aqueous solution of boric acid or a salt thereof, 1 g / kg of the injection hole 14 formed in the mandrel 5 can be obtained. The lubricant can be discharged at a relatively low pressure of not less than cm ^{2 and not} more than 10 kg / cm ² .

Further, as shown in FIG.
Is installed, the pressure of the liquid lubricant 15 is increased to 10 to 80 kg / cm ² by the pump 9, and sprayed from the nozzle 26, whereby the lubricant 15 can be uniformly applied to the inner surface of the hollow shell 1. As shown in FIGS. 2 and 6, the injection hole 14 for injecting the lubricant 15 is formed by tapering the tip of the mandrel 5 and providing one or more through holes on the tapered surface (FIG. 2 shows a concentric circle). When four small holes are provided in the shape). The angle between the axis of the injection hole and the axis of the mandrel 5 is desirably in the range of 10 to 90 degrees, and the angle of the taper at the tip of the mandrel 5 is in the range of 10 to 60 degrees with the axis of the mandrel 5. Is preferred. The diameter of the injection hole 14 may be appropriately selected depending on the viscosity and particle size of the lubricant, but is preferably in the range of 1 to 10 mm. Instead of processing the tip of the mandrel 5 into a tapered shape, as shown in FIG. 7, a plug 28 in which the injection hole 14 has been previously processed may be attached to the tip of the mandrel 5.

As shown in FIG. 8, one or more lubricant jets are provided on a mandrel portion not used in rolling, that is, a parallel portion at the tip of the mandrel 5 which does not make rolling contact with the inner surface of the hollow shell during rolling. 29 may be provided. Further, the lubricant may be ejected from both the tapered portion and the parallel portion at the tip of the mandrel 5. Also, full circumferential nozzles can of course be used.

As shown in FIG. 1, the mandrel 5 is controlled in its forward speed by the restraining device 6 until the rolling of the hollow shell 1 is completed at the final stand of the mandrel mill. When the rolling is completed, the mandrel 5 is further advanced, and the semi-finished seamless steel pipe is fed into the sizer 10 or the extractor (the figure is a sizer). When rolling is started by the sizer 10 or the extractor, the mandrel 5 is retracted, and the mandrel 5 is pulled out of the hollow shell 1. The mandrel 5 further retreats on the mill line 4 and waits for the next rolling.

Then, the hollow shell 1 to be rolled is transported to a position on the mill line 4 where the mandrel 5 is inserted, and the mandrel 5 is inserted into the hollow shell 1 again, and at the same time, the hollow shell 1 is inserted. A series of rolling operations are repeatedly performed such that the lubricant is applied to the inner surface as shown in FIG. As for the mandrel 5, one mandrel can be repeatedly used continuously for rolling a tube of the same size. When changing the size of the tube to be rolled or replacing the mandrel with another mandrel for any reason, refer to FIG.
As shown by 1, the mandrel after rolling is sent laterally to the return line and transported to a storage yard (not shown).

On the other hand, a new mandrel is fed from the insert line to the mill line and set in the restraining device. Although the case where the inside of the mandrel is cooled with the cooling water has been illustrated above, this may be omitted. In this case, after the removal of the mandrel after the completion of the rolling is completed, the mandrel is retracted on the mill line, sent to the return line in the lateral direction as in the conventional method, and sent backward to be cooled by the water in the cooling zone. After that, it is transferred to the insert line and waits until the next rolling, set again on the restraining device on the mill line, and at the same time as inserting the mandrel into the hollow shell, lubricant is injected from the mandrel tip and the hollow shell The lubricant is applied to the inner surface, and a series of rolling operations are repeatedly performed. In this case, only the inner pipe for guiding the lubricant is provided inside the hollow mandrel. The mechanism for ejecting the lubricant toward the inner surface of the pipe is the same as the above-described method.

When the mandrel is inserted into the hollow shell according to the present invention described above, the method of applying a lubricant to the inner surface of the hollow shell and the method of forming a lubricating film on the mandrel are used in combination. Is also possible.

That is, after the lubricant is applied to the inner surface of the hollow shell according to the present invention and rolling is performed, as in the case described with reference to FIG. 11, when the mandrel starts retreating, the first stand of the mandrel mill is moved. A lubricant application device provided immediately before the entrance side applies a lubricant on the mandrel to form a lubricating film on the mandrel. The lubricated mandrel retreats from the return line to the cooling zone, is cooled by water, is moved to the insert line, and waits for the next rolling. Of course, in addition to the lubrication coating device in the mill line, a coating device may be provided in the return line or the insert line, which is a conventional method, and the lubricant may be further coated on the mandrel. The combination of the present invention and the conventional lubricant application on a mandrel is used when the amount of reduction in a mandrel mill is large, when rolling a thin-walled tube or a long tube, or when rolling a stainless steel or a high alloy steel. This is effective when the friction conditions of the mandrel are severe.

In order to increase the amount of the lubricant to be applied, the supply amount of the lubricant is changed by changing the pressure and flow rate of the pump, or by changing the diameter of the small hole from which the lubricant is jetted or the nozzle diameter, and by changing the insertion speed. However, after inserting the mandrel into the hollow shell, the operation of retracting the mandrel and inserting the mandrel again is repeated one or more times, during which the lubricant is spouted repeatedly and the lubricant is applied to the inner surface of the tube. Can also.

The present invention was also applied to a rolling facility (full float mandrel mill) that does not restrain the mandrel.
Referring to FIG. 10, the embodiment will be described. In the insert line 31 for inserting the mandrel 33a into the hollow shell 32, the tip of the pusher 30 for advancing the mandrel 33a has the same mechanism as that described in FIG. in this case,
The mandrel 33a is an inner tube 1 for guiding the lubricant shown in FIG.
3 penetrates to the rear end of the mandrel and passes through the lubrication pipe end 24 of the chuck and the inner pipe 13 at the rear end of the mandrel.
Are fitted and connected. The connection mechanism is performed in the same manner as shown in FIG.

When the mandrel starts to be inserted into the hollow shell, the pump is started and the lubricant is supplied from the lubricant tank to the pipe 7.
The lubricant is fed into the inside of the mandrel 33a through the injection hole 14 drilled at the tip of the mandrel 5 or the nozzle 26 connected to the tip thereof, as shown in FIG. 2 or FIG. It is squirted toward the inner surface. The mandrel 33a is further advanced until it reaches a predetermined protrusion length. Next, the pusher 30 starts retreating from the neck at the rear end of the mandrel 33a, and the pipe end comes off. On the other hand, the hollow shell 32 is fed laterally while holding the mandrel 33a, and is placed on the mill line 35 at the entrance side of the first stand 37. The hollow shell 32 is rotated around the axial direction as necessary, so that the lubricant is evenly distributed around the circumference.

Further, while waiting for the start of rolling on the mill line 35, as shown in FIG. 2B, the hollow shell 32 or the hollow shell 32 and the mandrel 33a are simultaneously rotated around the axial direction by rollers. By rotating the lubricant, the lubricant is uniformly distributed on the inner circumference of the hollow shell 32. At the start of rolling, the feed roller supports the hollow shell 32 and the mandrel 33a at the same time as the roller descends in the same manner as shown in FIG. 3, and the hollow shell 32 is rotated by rotating the feed roller.
And the mandrel 33a are simultaneously sent to the first stand 37. In the continuous stand, the wall thickness of the raw tube is sequentially reduced between the roll and the mandrel.However, according to the present invention, the friction condition between the mandrel and the inner surface of the hollow raw tube in a state where the lubricant is applied to the entire inner surface of the tube or a necessary portion is applied. Is carried out in a state where is maintained in a certain good condition.

After rolling, as in the conventional method shown in FIG. 10, the mandrel is removed from the hollow shell, the mandrel is jumped out to the return line, the mandrel is cooled in the cooling zone, and the mandrel is carried into the insert line. The rolling is repeated. Also in this case, the lubrication of the mandrel on the return line or the insert line, which is the conventional method, can be used in combination with the conventional method.

As a rolling operation when the present invention is applied to a semi-float mandrel mill, the application of a lubricant to the inner surface of a hollow shell performed prior to the rolling of the present invention is performed by the above-described wrist-rein mandrel mill (mandrel). Is performed in the same manner as described above for the full float mandrel mill after rolling.

That is, the insertion of the mandrel into the tube is shown in FIG.
In the same manner as in the wrist-rained mandrel mill shown in Fig. 2, the lubrication is performed by the mandrel restraining device on the mill line. At this time, the lubricant is ejected from the end of the mandrel toward the inner surface of the hollow shell, as shown in Fig. Control of the mandrel advancing speed during rolling, in which the lubricant is applied, is performed by a mandrel restraining device as in the wrist-retrained mandrel mill, but in the latter half of rolling, the mandrel is released from the restraining device, and FIG. To the same rolling state as the full float mandrel mill shown in FIG. Subsequent removal of the mandrel, transfer work, and the like are performed in the same manner as in the full float mandrel mill.

Next, examples in which the present invention is applied to an actual mandrel mill will be described. (1) Example with Rest-Resin Mandrel Mill 1) A 300-dia. X 1630-L billet made of carbon steel heated to 1250 ° C was pierced, and a hollow base tube with a size of 295 dia. With a mandrel mill,
Rolled to size 250φ × 6.0t × 25000L. The mandrel used was 231φ × 1500L in size, and the inner pipes for lubricant, cooling water and drainage were 30 and 4 in inner diameter, respectively.
It was provided with dimensions of 0 and 50φ. Table 1 shows the conditions of the examples of the method of forming a lubricant film on a mandrel beforehand and the method of applying a lubricant to the inner surface of a hollow shell beforehand of the method of the present invention, which were measured by the conventional method, and measured at that time. 4 shows the change in the coefficient of friction between the mandrel and the inner surface of the hollow shell during rolling.

[0041]

[Table 1]

The coefficient of friction is obtained by calculating the mandrel restraint force (tensile force in the axial direction) detected by the load cell attached to the mandrel restraining device by the sum of the roll reaction force detected by the load cell attached to each rolling stand. The divided value was regarded as the average coefficient of friction. While the change in the coefficient of friction is large in the conventional method, the change in the coefficient of friction is suppressed to be small in any of the methods of the present invention.

FIG. 9 shows the thickness deviation distributions of the conventional method and the method of the present invention when each of the 60 hollow shells is rolled. FIG. 9 (a)
9 shows the case of the conventional method, and FIG. 9B shows the case of the method of the present invention.
It can be seen that the thickness accuracy was greatly improved by the method of the present invention. This is because, according to the method of the present invention, the change in the coefficient of friction during rolling as shown in Table 1 is suppressed small, and the rolling conditions in the longitudinal direction are kept constant during rolling of one hollow shell. It is.

2) 230φ × 13 of 13% Cr steel heated to 1250 ° C.
Perforated 60L billet, size 240φ × 21.0t × 9100
The hollow shell set to L was rolled to a size of 195φ × 9.0t × 25000L using a 6-stand wrist-relay mandrel mill. Table 2 shows the conditions of the conventional method and the example of the method of the present invention and the results of rolling.

[0045]

[Table 2]

The mandrel used was 125 φ × 15000 L, and inner pipes for lubricant, cooling water and drainage were provided inside with dimensions of 20, 28 and 36 φ, respectively. In the conventional method, the coefficient of friction was high and the coefficient of friction increased during rolling was large, causing chatter and seizure of the mandrel, and flaws were observed on the inner surface of the tube. On the other hand, in the method of the present invention, the coefficient of friction was low and stable, and in each case a good tube could be obtained without causing chattering.

(2) Example of Full Float Mandrel Mill A hollow shell having a size of 176φ × 20.3t × 5200L formed by perforating a 170φ × 2200L billet of 22% Cr steel heated to 1270 ° C. was used for 7 stands. It was rolled to a size of 148φ × 8.3t × 14000L with a full float mandrel mill. Table 3 shows the conditions of the conventional method and the examples of the method of the present invention and the results of rolling.

[0048]

[Table 3]

The mandrel used was 128 φ × 18000 L, and inner pipes for lubricant, cooling water and drainage were provided inside with dimensions of 16, 25 and 34 φ, respectively. In the conventional method, frictional lubrication during rolling is severe, and defective (strip) of the mandrel from the hollow shell after rolling and seizure of the mandrel frequently occur. On the other hand, in the method of the present invention, the friction lubrication state during rolling was good and stable, and in each case, a good tube could be obtained without causing stripping failure or seizure.

[0050]

As is apparent from the above description, the present invention can apply a lubricant to the inner surface of a raw tube prior to rolling, so that the following remarkable effects can be obtained. (1) A stable lubrication state is realized over the entire length during rolling of one pipe, and a constant coefficient of friction is obtained. Therefore, constant rolling conditions can be obtained, and a high-precision pipe having no dimensional variation over the entire length of the pipe can be obtained.

(2) When the friction condition of the mandrel is severe, the application amount can be easily increased by increasing the discharge amount of the lubricant to the inner surface of the tube, and it can be realized over the entire length of the tube. As a result, a good lubrication state can be obtained over the entire length of the pipe even when rolling with a large amount of reduction, rolling of thin-walled pipes or long pipes, and rolling of stainless steel or high-alloy steel, preventing the occurrence of seizure and chattering and defects. Can produce high-quality product pipes without waste. Further, since the mandrel can be stably and easily extracted from the tube after the end of the rolling, no defective products are generated, and the frequency of interrupting the operation is reduced, which is extremely effective in improving the yield and the productivity.

(3) Since the friction and lubrication state between the mandrel and the inner surface of the hollow shell is stably maintained during rolling, the mandrel is free from seizure and the wear is reduced. , The mandrel life is improved.

(4) When the present invention is applied to a rolling method in which a mandrel is constrained, there is no need to circulate and use a plurality of mandrels as in the prior art, and one mandrel is repeatedly and continuously used. Can be used. This is extremely effective not only for improving productivity by shortening the mandrel replacement time and the like, but also for reducing tool costs. In addition, since the number of mandrels held is extremely small, the storage space for mandrels can be reduced.

If the inside of the mandrel is cooled as shown in the embodiment, the mandrel does not need to be water-cooled off-line. In addition to the omission of the conventional mandrel circulation equipment, the water-cooling zone can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of equipment for injecting a lubricant into an inner surface of a hollow shell.

2A is a longitudinal sectional view showing a state in which a lubricant is injected into a hollow shell via a mandrel, FIG. 2B is a view taken along the line AA in FIG. 2A, and FIG. It is a BB arrow line view of a).

FIG. 3 is an explanatory view of a device for rotating a hollow shell,
(A) is a plan view and (b) is a side view.

FIG. 4 is a longitudinal sectional view showing a state where the hollow shell is being rolled by a mandrel mill.

FIG. 5 is a longitudinal sectional view showing a state in which a mandrel is set in a restraining device.

FIG. 6 is an explanatory view of a mandrel in which an ejection nozzle is attached to an ejection port.

FIG. 7 is an explanatory view of a mandrel in which a plug provided with an injection hole is connected to a tip.

FIG. 8 is an explanatory view of a mandrel having an injection hole provided in a parallel portion.

FIG. 9 is a bar graph showing the thickness deviation distribution of the conventional method and the method of the present invention.

FIG. 10 is an equipment layout of a full float mandrel mill.

FIG. 11 is a layout diagram of a wrist-retained mandrel mill or a retained mandrel mill.

[Explanation of symbols]

 Reference Signs List 1 hollow shell 2 mandrel mill 3 first stand 4 mill line 5 mandrel 6 restraining device 7 pipe 8 lubricant tank 9 pump 10 sizer 11 cooling water pipe for cooling mandrel 12 cooling water supply pump 13 lubricant supply pipe 14 injection hole 15 Lubricant 16 Hollow tube rotating roller 17 Cooling water supply channel in mandrel 18 Cooling water drainage channel in mandrel 19 Feeding roller 20 Pinch roller 21 Mandrel neck portion 22 Chuck portion of restraining device 23 Portion provided with pipe end 24 Pipe End 25 Pneumatic or hydraulic cylinder 26 Spray nozzle 27 Spray hole 28 Plug 29 Spout

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-49-112852 (JP, A) JP-A-58-116910 (JP, A) JP-A-63-154207 (JP, A) JP-A-63-154207 188407 (JP, A) JP-A-4-309403 (JP, A) JP-A-5-293513 (JP, A) JP-A-56-100202 (JP, U) JP-A-57-189601 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) B21B 17/02 B21B 25/04

Claims (1)

(57) [Claims] 1. A method for rolling a seamless steel pipe by a mandrel mill in which a hollow shell is continuously rolled with a hole-shaped roll and a mandrel, wherein a lubricant is supplied through the hollow mandrel when the mandrel is inserted into the hollow shell. Then, the lubricant is injected from the injection hole provided at the tip of the mandrel to the inner surface of the hollow shell before rolling, and after the lubricant is applied over the entire inner surface of the hollow shell, rolling is performed. A method for rolling seamless steel pipes using a mandrel mill.