JP3344325B2 - Mandrel mill rolling method - 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 using a mandrel mill, which is an elongation rolling step in manufacturing a seamless pipe.

[0002]

2. Description of the Related Art A caliber roll conventionally used in a mandrel mill has a shore hardness of 60 on the roll surface.
Therefore, when the roll is stretched, the surface of the roll is damaged, and the abrasion and rough surface of the roll itself are increased. Since wear and roughening of the roll itself deteriorates the quality of the product, it is desirable to use a caliber roll having a shore hardness of 60 or more and having little wear and rough surface.

[0003] By the way, in the groove rolling using a caliber roll, such as a mandrel mill, since the roll bottom has a small roll diameter, the roll rotation speed is slower than the rolling speed of the material to be rolled. Since the roll diameter is large at the flange portion of the roll, the roll rotation speed is higher than the rolling speed of the material to be rolled. Therefore, slip occurs at the groove bottom and the flange portion of the roll where the relative speed difference between the material to be rolled and the roll is large, and the roll tends to seize.

[0004] In addition, in the mandrel mill, the material to be rolled during or after rolling at each stand tends to have a shape in which the portion from the flange portion to the gap portion of the roll swells and protrudes. Then, during rolling, the material to be rolled comes into strong contact with the flange portion, and it becomes easier to seize. Further, the portion protruding from the flange portion after rolling in the previous stand is locally strongly bitten into the groove bottom of the next stand, and seizure easily occurs in the groove bottom.

[0005] Such a seizure peculiar to a caliber roll is more likely to occur in the case of a high-hardness roll having a hard surface because the surface hardly wears. Therefore, conventionally, as a caliber roll, a high-hardness roll having a shore hardness of 60 or more on the roll surface has not been used.

On the other hand, as a measure against wear and seizure of the caliber roll, use of a lubricant is disclosed in Japanese Patent Laid-Open No. 2-30 / 1990.
No. 312 and the like. However, JP
According to the method proposed in -30312 or the like, it is possible to reduce the seizure of the roll, but it is not possible to improve the wear and the like caused by the surface hardness of the roll.

[0007] Therefore, as a caliber roll in a mandrel mill, a high hardness roll of a specific steel type and a Shore hardness of 60 or more on the roll surface is used.
By continuously spraying roll lubricant with cooling water,
One that prevents wear and seizure of the caliber roll has been proposed in Japanese Patent Publication No. 7-73727. Japanese Patent Publication No. 7-73722 proposes an optimum lubricant supply region.

[0008]

SUMMARY OF THE INVENTION The above-mentioned Tokuho 7-7
In the method proposed in No. 3727, the use of a high-hardness roll having a Shore hardness of 60 or more prevents wear and roughening of the caliber roll, and for seizure, a lubricant is sprayed on a roll of a specific steel type. However, spraying the lubricant requires a lubricant supply facility, as well as a lubricant cost and a repair cost for the facility, thereby increasing the manufacturing cost.

In a conventional mandrel mill rolling in which the rolling reduction at the groove bottom of the caliber roll exceeds 50%,
When a high-hardness roll having a Shore hardness of 60 or more is used as a measure against abrasion and roughness, slippage between the roll and the material to be rolled hardly occurs, so that slippage at the tip of the material to be rolled tends to cause biting failure. Also, in many cases, slippage during rolling causes abnormal tension between stands. If the tension between the stands becomes abnormal, it cannot be rolled into a predetermined shape or size. The poor biting and slip during rolling are likely to occur not only when the material to be rolled is an alloy steel or stainless steel, but also when a thin material is used even with ordinary steel.

Similarly, the seizure phenomenon is likely to occur when the material to be rolled is not only an alloy steel or stainless steel, but also a thin material of ordinary steel. This seizure is likely to occur in the unsteady rolling portion at the leading end or the trailing end where the material to be rolled bites. The tip first contacts the roll or plug with a piercer in the previous process,
Further, even during mandrel mill rolling, since the roll first comes into contact with the roll at each stand, the temperature is low and the deformation resistance is high. In addition, since the unsteady rolling portion at the rear end does not generate a tension on the material to be rolled during the rolling in addition to the low temperature, the bulging shape of the flange portion tends to be larger, and the roll comes into strong contact with the roll. . At these sites, even if a lubricant is sprayed, seizure cannot be completely prevented.

The present invention has been made in view of the above-mentioned conventional problems, and has a roll surface having a Shore hardness of 60.
An object of the present invention is to provide a rolling method capable of preventing as much as possible the occurrence of slip and seizure during rolling at the tip end when rolling with a mandrel mill equipped with the above caliber roll.

[0012]

In order to achieve the above object, a mandrel mill rolling method according to the present invention is directed to a stand incorporating a cast iron or cast steel or forged caliber roll having a shore hardness of 60 or more on the roll surface. The rolling is performed without using a lubricant such that the rolling reduction at the groove bottom of the caliber roll is 50% or less. And by doing in this way, when rolling with a mandrel mill provided with a caliber roll having a shore hardness of 60 or more on the roll surface, it is possible to prevent occurrence of poor biting and seizure as much as possible. become.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor used a mandrel mill equipped with a caliber roll having a shore hardness of 60 or more on the roll surface to prevent slipping during the leading end of the material to be rolled and during rolling and to prevent seizure. As a countermeasure, various experiments were repeated.
In the case of rolling in the following manner, it was found that, without using a lubricant in principle, it is possible to prevent as much as possible the prevention of slippage and seizure during the tip and rolling, The present invention has been made as follows.

That is, in the mandrel mill rolling method of the present invention, a cast iron roll, a cast steel roll or a forged roll having a shore hardness of 60 or more is used as a caliber roll. 50% reduction in caliber roll groove bottom
As described below, rolling without using a lubricant, or, when using a lubricant unavoidably , at least one of the unsteady rolling portion at the leading end or the trailing end of the material to be rolled or to unused, if necessary, for all of the stand except for the molding stand, 1.0 ultra-
A caliber roll having a hole shape having an ellipticity of 1.4 is used. As shown in FIG. 1, the ellipticity in the method of the present invention refers to the length between the intersections 4 and 4 of the extension line of the arc 2 closest to the flange side and the path center 3 excluding the reverse R portion 1 for escape. A is the length (major axis), and the length between the groove bottoms 5 is B
(Shorter diameter) means A / B. The rolling reduction at the groove bottom of each stand is (inlet thickness-outlet thickness) /
(Inlet thickness) x 100%
It means a range of 2 m (0.5 seconds in rolling time) at the end.

The method for rolling a mandrel mill according to the present invention is characterized in that the roll surface has a Shore hardness of 60 or more at room temperature, for example, a cast iron or cast steel such as a high chromium steel or a high speed steel having a chromium content of 8 to 20% by weight. This applies when using forged caliber rolls. This is to prevent roll wear and rough skin.

In addition, in the mandrel mill rolling method of the present invention, in principle, even if a lubricant is not used and a lubricant is unavoidably used, only when the material to be rolled is a material that is liable to cause seizure, the seizure is performed. Is limited to only the portion where the occurrence of cracks easily occurs, that is, the unsteady rolling portion at the front end or the rear end of the material to be rolled. This is because a large amount of carbide is dispersed on the surface of the high-hardness roll having a shore hardness of 60 or more on the roll surface, so that metal-to-metal contact hardly occurs and seizure itself does not easily occur. In addition, when a lubricant is used, running costs are increased and manufacturing costs are increased.
This is because seizure cannot be completely prevented at these sites even if a lubricant is used.

In the mandrel mill rolling method of the present invention, the caliber roll is rolled so that the rolling reduction at the groove bottom is 50% or less. The reason is that when the rolling reduction at the groove bottom of a caliber roll having a shore hardness of 60 or more on the roll surface exceeds 50%, the indentation force of the material to be rolled increases between the roll and the material to be rolled, but the material to be rolled is increased. This is because slippage at the tip tends to cause poor biting, and slippage during rolling often causes abnormal tension between stands. In addition, the amount of protrusion in the portion from the flange portion to the gap portion of the roll increases, and the roll is easily seized.

Further, in the mandrel mill rolling method of the present invention, the stand other than the forming stand may
It is desirable to use a caliber roll in the form of a hole having an ellipticity of 1.4, because when the ellipticity exceeds 1.4,
This is because seizure easily occurs at the flange portion during rolling with the caliber roll, and seizure easily occurs at the groove bottom portion during rolling with the caliber roll of the next stand. If the ellipticity is 1.0 or less, stable rolling cannot be performed.

In the mandrel mill rolling method of the present invention, the use of the caliber roll having a hole shape having an ellipticity of more than 1.0 to 1.4 is excluded from the forming stand only because the caliber roll in the forming stand is elliptical. This is because, in the case of the sizer-reducer rolling in the next step, a biting failure in the caliber roll is likely to occur.

The lubricant used in the mandrel mill rolling method of the present invention is inevitably used, but is not particularly limited, and mineral oils or synthetic ester-based rolling oils used in general hot rolling, or any of these. Rolling oil containing an extreme pressure additive or solid lubricant to enhance seizure resistance, or a water-soluble lubricant containing graphite or mica, or an oxidizing agent proposed in JP-A-10-30097. An oxide-based water-soluble lubricant such as an iron-boric acid-based lubricant may be used.

It is desirable that the lubricant used inevitably be concentrated and supplied to the flange portion and the groove bottom portion of the caliber roll where seizure easily occurs. As a method for supplying the lubricant, a so-called neat method, which is directly supplied from a nozzle, or a so-called water injection method, which is mixed with water to form an emulsion and then supplied through a nozzle with a pressure of air or the like, is employed.

Generally, the cooling water is used continuously at least during rolling. However, in the mandrel mill rolling method of the present invention, when a lubricant is used, the lubricant is diluted with the cooling water. In order to prevent the coolant from being blown or blown off, the use of the cooling water may be stopped only while the lubricant is being supplied, or the cooling water may be made hard to flow to the lubricant supply site by the draining device.

[0023]

EXAMPLES The results of experiments conducted to confirm the effects of the mandrel mill rolling method of the present invention will be described below.
(Example 1) A steel pipe for machine structure of STKM13A of JIS standard and a steel pipe for 13% chromium oil well of API standard are prepared in a Mannesmann-mandrel mill pipe line of small diameter having the specifications shown in Table 1 below. Manufactured under conditions.

A high-speed steel caliber roll having a Shore hardness of 70 to 85 on the roll surface is used for all the # 1 to # 6 stands except for the 7-stand type mandrel mill forming stand (# 7 stand). used.

[Tube production conditions] Rolled material Billet diameter: Outer diameter φ187 mm Dimension after piercing: Outer diameter φ191 mm × wall thickness 17.0 m
mx length 10.5m dimensions after mandrel mill: outer diameter φ 151mm x wall thickness 6.
0mm x length 35.7m Dimensions after stretch reducer: Outer diameter 63.5mm
× wall thickness 5.51 mm × length 97.2 m Billet heating temperature: 1230 ° C Reheating temperature after mandrel mill: 1000 ° C

2. Lubricant 13% chromium Only iron oxide (Fe ₂
O ₃ ) 20%, borate amine 15%, dispersant 2%
Then, an iron oxide-boric acid-based aqueous solution consisting of water is supplied from the nozzle to the flange portion on the roll entry side and the groove bottom portion. 3. Lubricant supply pattern Pattern A: No lubrication for all stands (corresponding to claims 1 and 3). Pattern B: Only the # 2 stand is continuously supplied to the entire length of the material to be rolled during rolling (comparative example). Pattern C: In the # 5 and # 6 stands, only in the unsteady rolling portions at the leading end and the trailing end of the material to be rolled (rolling just before and after the end of the rolling operation.
5 seconds) supply (corresponding to claims 2 and 3).

4. Cooling water The stand using lubricant was not used during rolling, and the stand not using lubricant was used during rolling. After rolling, cooling water was used at all stands. 5. Number of rolls Pattern A: 200 STKM13A, 50 13 chrome steel. Pattern B: 20 STKM13A. Pattern C: 50 STKM13A and 10 13 chrome steel.

[0028]

[Table 1]

In the pattern A corresponding to the first and third aspects, when the obtained product is inspected, the STKM13A,
No external flaws were found in any of the 13 chrome steels. In addition,
The specifications such as the rolling state and the load were the same as when rolling was performed without lubrication using an adamite roll having a shore hardness of 50 on the roll surface.

Pattern B as a comparative example of claims 2 and 3
Then, since the lubricant was continuously supplied to the entire length of the material to be rolled at the # 2 stand, the slip was generated at the # 2 stand, in conjunction with the reduction rate at the groove bottom of 50% or less. #
Biting into the three stands became unstable. In addition, a portion where the wall thickness was locally small occurred, and five products were determined to be defective in product inspection.

In pattern C corresponding to claims 2 and 3, the lubricant is supplied only to the unsteady rolling portions at the leading and trailing ends of the material to be rolled at the # 5 and # 6 stands, but the rolling state is stable. Was. When the obtained product was inspected, S
No external flaws occurred in both TKM13A and 13 chrome steel.

(Example 2) An experiment of pattern A was performed under the same conditions as in Example 1 except that the rolling reduction at the groove bottom in the # 2 stand was 55%. Roll seizure occurred in the # 2 stand. did. Then, when the obtained product was inspected, STKM13A found that 10 out of 200
With 13 chromium steel, seizure flaws occurred in 45 (all after 6).

Example 3 A small-sized Mannesmann-mandrel mill pipe line having the specifications shown in Table 2 below was used.
JIS standard steel pipes for machine structural use, for example, low carbon steel such as STKM13A, Cr-Mo steel pipes, and DIN 1
7175-10-3 2% chromium steel pipe was manufactured under the following conditions.

A high-speed steel caliber roll having a shore hardness of 65 to 85 on the roll surface was used for all of the # 1 to # 6 stands except for the 7-stand type mandrel mill forming stand (# 7 stand). used.

[Tube production conditions] Rolled material Billet diameter: Outer diameter φ187 mm Dimension after piercing: Outer diameter φ181 mm x wall thickness 15-21
Dimensions after mandrel mill: outer diameter φ 151 mm x wall thickness 4.
0-10.0mm x length 16-47m Dimensions after stretch reducer: outer diameter φ60-85m
mx thickness 3.5-11.00 mm Billet heating temperature: 1230 ° C Reheating temperature after mandrel mill: 1000 ° C

2. Lubricant The same lubricant as in Example 1 was supplied from the nozzle to the flange portion on the roll entry side and the groove bottom only during the production of a 2% chrome steel pipe. 3. Lubricant supply pattern and cooling water Same as Example 1. 4. Rolling number 1500 for each steel pipe.

[0037]

[Table 2]

Experiment No. 3 corresponding to claim 3 is also described. Nos. 1 to 3 and No. In No. 5, since the hole ellipticity was set to 1.4 or less, even when rolling was performed without lubrication, there was no occurrence of poor biting or seizure. However, when the ellipticity exceeded 1.4 and no lubricant was supplied, the experiment No. 1 corresponding only to claim 1. In No. 4, although biting failure did not occur, burn-in flaws were generated to such an extent that they could be shipped by care.

On the other hand, although the ellipticity exceeded 1.4, the experiment No. 2 corresponding to claim 2 only supplied the lubricant. In Experiment No. 6, The results were the same as in the case of Experiment No. 4, but the burn-in flaws generated were the same as those in Experiment No. 4. It was smaller than the case of 4.

[0040]

As described above, according to the present invention, the use of a cast iron or cast steel or forged caliber roll having a shore hardness of 60 or more on the roll surface prevents wear and roughening of the roll while reducing the caliber roll. 50% reduction at groove bottom
%, So that, in principle,
It is possible to prevent the occurrence of slip and seizure during rolling at the tip end and without rolling as much as possible. Then, at this time, for all stands except the molding stand, if a caliber roll having a hole shape having an ellipticity of 1.0 to 1.4 is used, seizure can be more effectively suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an ellipticity according to the present invention.

Continuation of front page (56) References JP-A-4-22502 (JP, A) JP-A-8-243603 (JP, A) JP-A-6-320206 (JP, A) JP-A-8-276208 (JP JP-A-9-155414 (JP, A) JP-A-8-47714 (JP, A) JP-A-5-154514 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) B21B 27/10 B21B 17/02 B21B 27/02

Claims (3)

(57) [Claims] 1. A calender roll using a cast iron roll, a cast steel roll, or a forged roll having a shore hardness of 60 or more on a roll surface, and a reduction ratio at a groove bottom portion of the caliber roll in a stand in which the caliber roll is incorporated.
((Inlet thickness-Outlet thickness) / (Inlet thickness) x 100%)
Milling method, wherein the rolling is carried out without using a lubricant so that the value is 50% or less. 2. A caliber roll, comprising :
Cast iron roll or cast steel roll with shear hardness of 60 or more
Using the forging roll, the caliber roll was incorporated
Reduction rate of caliber roll at the bottom of groove at stand
((Inlet thickness-Outlet thickness) / (Inlet thickness) x 100%)
Milling method, wherein a lubricant is used only in at least one of the front end portion and the unsteady rolling portion at the rear end of the material to be rolled when the rolling is performed so as to be 50% or less . 3. The mandrel mill according to claim 1, wherein a caliber roll having a hole shape having an ellipticity of more than 1.0 to 1.4 is used for all stands except the forming stand. Rolling method.