JPH0773722B2 - Hot rolling method for seamless steel pipe - Google Patents

Description

TECHNICAL FIELD The present invention relates to a hot rolling method for a seamless steel pipe by a Mannesmann mandrel mill system, a Mannesmann plug mill system, or the like.

[Prior Art] Generally, in a hot rolling method for a seamless steel pipe, a mandrel mill as shown in FIGS. 4 (A) and 4 (B) and a stretch reducer as shown in FIGS. 5 (A) and 5 (B) are generally used. As in the sizer mill as shown in FIG. 6, the hollow shell is thin-walled and stretch-rolled hot by using a hole-type roll.

Hereinafter, a rolling mode by each of the above mills will be described.

The mandrel mill 1 (see FIGS. 4 (A) and 4 (B)) has 7 to 9 roll stands equipped with a pair of hole type rolls 2 which are arranged in 90 degree arrangement with respect to each other. The mandrel bar 4 is inserted therein, and the element pipe 3A is continuously passed by passing through the continuous roll stand described above.
Is thinned and stretched to obtain the outlet pipe 3B.

In addition, the stretch reducer mill 5 (Fig. 5 (A),
(Refer to (B)) is a large number of roll stand rows equipped with oval hole type rolls 6, and without drawing a mandrel bar, the hollow shell 3B is squeezed and rolled to obtain a finish tube 3C having a predetermined outer diameter and thickness. Mold. Here, Stretch Reducer Mill 5
The hole type inner diameter of each hole type roll 6 in the continuous roll stand row of is set so that the diameter becomes smaller toward the subsequent stage,
The hole type inner diameter of the final roll stand has a size corresponding to the outer diameter of a predetermined finishing tube 3C, and thereby the outer surface of the finishing tube 3C can be finish-molded.

Further, in the sizer mill 8 (see FIG. 6), 5 to 8 roll stands each consisting of a pair of hole type rolls 9 are arranged 90 ° apart from each other in a continuous arrangement and the mandrel bar is not inserted into the raw pipe. The finished pipe 10 having a predetermined outer diameter is obtained by subjecting the finished pipe 10 to reduction rolling.

[Problems to be Solved by the Invention] By the way, when rolling a seamless steel pipe by each mill using a hole type roll as described above, the hole type central groove bottom of the hole type roll and the shallow parts of the hole type on both sides of the hole type roll are provided. That is, in the vicinity of the flange portion, as a result of a large relative speed difference between the roll peripheral speed and the advancing speed of the surface of the hollow shell, seizure occurs between the hollow shell and the hole-shaped roll, and the final product Impair surface quality,
Further, roll wear is promoted and the roll life is shortened.

In particular, in recent years, the demand for high alloy steel pipes represented by 9% Cr steel, 13% Cr steel, 22% Cr steel, etc. has increased, but the above-mentioned seizure is likely to occur during rolling of these high alloy steel pipes and It's a problem.

In order to solve the problem as described above, for example, Japanese Patent Laid-Open No. 58-
In 119409 publication, by continuously stretching and rolling the raw pipe with a set of three rolls in a mandrel mill, the roll peripheral speed of the hole-shaped portion is made smaller than that of the conventional two rolls. Although a method of reducing the seizure flaw has been proposed, this method has a drawback that a large amount of capital investment is required.

Further, JP-A-63-260606 proposes a method for preventing seizure by rolling while supplying a lubricant, but this method supplies the lubricant only to the hole type flange portion. Since it is intended, it is effective against the seizure flaw generated in the hole type flange portion, but is ineffective against the seizure flaw at the bottom of the hole type groove. Therefore, in a stand with a large amount of wall thinning such as a stand in the front stage of the mandrel mill, seizure is likely to occur at the bottom of the groove, which cannot be prevented by this method.

Further, in order to solve these drawbacks, various materials and cooling methods for the hole-type roll have been studied, but so far, no sufficient effect has been obtained.

The present invention effectively supplies a lubricant to the entire contact area between the hollow shell and the hole-type roll to prevent seizure, prevent the occurrence of surface flaws on the pipe material, and reduce roll wear to reduce roll life. The purpose is to prevent the decrease of.

[Means for Solving the Problem] In the present invention according to claim 1, when the thin wall material is stretch-rolled by hot rolling using a hole roll, the hollow on the surface of the hole roll. The lubricant is supplied on the surface of the hole-shaped roll in a range having a certain width in the counter-rotational direction of the hole-shaped roll on the surface of the hole-shaped roll with reference to the contact start line at which the respective outer peripheral portions of the raw tube start to contact The area is defined as the area for rolling while supplying the lubricant to the area for supplying the lubricant.

According to a second aspect of the present invention, the lubricant supply region is set within a range having a width of 30 mm from the contact start line in the counter-rotational direction of the hole type roll.

[Operation] In FIGS. 1 to 3 (A) and (B), 1 is a hole type roll, 2 is a rotating shaft of the hole type roll 1, 3 is a hollow shell (material to be rolled), 4 is a spray nozzle 5 is a lubricant, 6 is a lubricant 5
Injection area, 7 is the injection direction of the lubricant 5, 8 is the hole-type roll 1
Is a contact start line at which the outer peripheral portions of the hollow shell 3 start contacting on the surface of the.

The contact start line 8 of the space tube 3 to the hole type roll 1 is shown in FIG.
As shown in FIG. 2, the height differs depending on the axial position of the hole-type roll 1, and the hole-type roll 1 comes into contact with the hollow shell 3 at the groove bottom earlier than the flange portion. Therefore,
When the lubricant is supplied to the surface of the hole-type roll 1 by using the spray nozzle 4 such as a flat spray nozzle, if the spray is simply sprayed in the direction orthogonal to the roll rotation axis 2, it is uniform per unit length in the roll axis direction. As a result of supplying a sufficient amount of lubricant, the flange portion has a smaller supply amount of lubricant per unit arc length as compared with the groove bottom portion, and the seizure prevention effect is reduced at the flange portion.

Therefore, according to the present invention as set forth in claim 1, a contact start line for starting contact of each outer peripheral portion of the hollow shell 3 with the surface of the hole roll 1 on the entire surface of the flange portion and the groove bottom portion of the hole roll 1. A uniform quantity of lubricant is supplied per unit length along 8, resulting in a uniform supply of lubricant per unit arc length on both the flange and the groove bottom.
Therefore, the lubricant can be effectively supplied to the entire area between the hollow shell and the hole type roll, seizure can be prevented to prevent the surface defects of the pipe material, and the wear of the roll can be reduced to reduce the roll life. The decrease can be prevented.

However, if a lubricant is supplied to the surface of the hole-type roll 1 at a position away from the contact start line 8 between the hole-type roll 1 and the hollow shell 3, the lubricant may be washed away by the roll cooling water, or the lubricant itself may be removed. Due to its own weight, the upper roll tends to flow toward the flange side, and the lower roll tends to flow toward the groove bottom side, which tends to cause a non-uniform lubrication state in the outer peripheral direction of the intermediate shell 3.

However, according to the present invention as set forth in claim 2, a lubricant is supplied to the surface of the hole-type roll 1 within a range of 30 mm width from the contact start line 8 between the hole-type roll 1 and the hollow shell 3. Therefore, the hollow shell 3 is not in the non-uniform lubrication state in the outer peripheral direction as described above, and the flange portion and the groove bottom portion of the hole-shaped roll 1 are supplied with the lubricant amount per unit arc length thereof. Can be reliably equalized to each other.

[Embodiment] FIG. 1 is a plan view schematically showing an embodiment of the present invention.
The figure is a side view of the main part of FIG. 1, FIG. 3 (A) is a schematic view showing a lubricant supply state using two spray nozzles per roll, and FIG. 3 (B) is three per roll. FIG. 6 is a schematic diagram showing a lubricant supply state using the spray nozzle of FIG.

As shown in FIG. 1, the lubricant 5 mixed with water in the mixer spreads from the two spray nozzles 4 toward the contact start line 8 between the surface of the hole type roll 1 and the hollow shell 3. To
It is jetted from a direction inclined with respect to the rotating shaft 2 of the hole-type roll 1. Further, as shown in FIG. 2, since the lubricant 5 is supplied in the vicinity of the contact start line 8 between the surface of the hole type roll 1 and the hollow shell 3, it is flowed by the roll cooling water or the flow due to its own weight. Is almost eliminated, and a uniform lubrication state is obtained in the outer peripheral direction of the hollow shell 3.

In the practice of the present invention, the number of spray nozzles 4 is not limited to two per nozzle. FIG. 3 (B) shows an example in which three spray nozzles 4 are used per roll, as compared with the case of using two spray nozzles 4 in FIG. 3 (A). Further, if the tip shape of the spray nozzle 4 is adjusted and the spray injection area 6 is set to expand in an arc shape, the present invention can be implemented even when one spray nozzle 4 is used per roll. .

Hereinafter, the results of specific implementation of the present invention will be described.

(Example 1) As the second pass of the Mannesmann mandrel mill system,
The present invention was applied to the No. 2 stand to No. 5 stand of 4 stands for thinning and drawing the hollow shell after piercing rolling. All roll stands have inner diameters of roll stands
It is 500 mmφ. Then, two sprue nozzles were installed on each of the stands at the upper and lower sides of the rolling mill. Each spray nozzle is installed at a position 400 mm away from the roll rotation axis, and the hollow shell and the roll surface are inclined from the direction inclined with respect to the roll rotation axis so that the injection angle θ shown in FIG. 1 is 58 degrees. To the contact start line, an aqueous lubricant containing 8% of a phosphoric acid salt was spray-supplied at a spray rate of 2 / min. Under this lubricant supply condition, the outer diameter is 110mmφ including 40% of high alloy steel.
2500 hollow core tubes were rolled.

Table 1 shows the effect of the first embodiment. By practicing the invention,
Hole type roll surface after rolling (Ductile roll surface)
The rolling surface roughness, which causes scratches on the scale, was improved from 143 μm to 46 μm at the maximum roughness. In addition, the amount of wear at the bottom of the groove is also 292μm to 161μ
Approximately halved to m. Therefore, the outer surface of the rolled pipe material was not roughened, and the hole-type roll could be extended and used as it was.

(Example 2) In a stretch reducer mill as a finish rolling mill as a Mannesmann mandrel mill system, a lubricant is supplied to all stands at an injection rate of 3 / min / stand by the same method as in Example 1 above. 2500 hollow hollow tubes were continuously rolled.

As a result, the edge mark flaw caused by the difference in wind speed between the hole-type roll and the hollow shell was eliminated by the practice of the present invention. Also, the amount of roll wear was reduced by about 35%.

(Example 3) When 100 rolls of only 22% Cr steel are finish-rolled by the sizer mill which is the final mill of the Mannesmann plug mill system, the lubricant injection amount of 3 / stand is 3 / stand for 3 stands in the same manner. Supplied with min. stand.

As a result, the occurrence of rough skin, mainly due to edge mark flaws, disappeared, and maintenance of the pipe material after rolling became unnecessary.

[Effects of the Invention] As described above, according to the present invention, by effectively supplying the lubricant to the entire contact portion between the hollow shell and the hole-type roll, seizure is prevented to prevent the occurrence of surface flaws on the pipe material. In addition, the roll wear can be reduced to prevent the roll life from being shortened.

[Brief description of drawings]

FIG. 1 is a plan view schematically showing an embodiment of the present invention, FIG.
The figure is a side view of the main part of FIG. 1, FIG. 3 (A) is a schematic view showing a lubricant supply state using two spray nozzles per roll, and FIG. 3 (B) is three per roll. Schematic diagram showing a lubricant supply state using the spray nozzle of FIG. 4, FIGS. 4 (A) and 4 (B) are schematic diagrams showing a mandrel mill, and FIGS. 5 (A) and 5 (B) are schematic diagrams showing a stretch reducer mill. FIG. 6 is a schematic view showing a sizer mill. 1 ... Hole type roll, 3 ... Hollow shell, 4 ... Spray nozzle, 5 ... Lubricant, 8 ... Contact start line.

Claims (2)

[Claims] 1. When the hollow shell is thin-walled and stretch-rolled by using a hole roll, the contact start of each outer peripheral portion of the hollow shell is started on the surface of the hole roll. A line is used as a reference, and a range having a certain width in the counter-rotational direction of the hole roll from the contact start line on the surface of the hole roll is set as a lubricant supply region, and the lubricant is supplied to the lubricant supply region. A method for hot rolling a seamless steel pipe, which comprises rolling while rolling. 2. The hot rolling method for a seamless steel pipe according to claim 1, wherein the lubricant supply region is set in a range having a width of 30 mm from the contact start line in a counter-rotational direction of the hole-shaped roll.