JP2937044B2 - Mandrel bar for hot seamless tube rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot seamless tube rolling tool, and more particularly to a mandrel bar of a mandrel mill used as a hot seamless tube rolling mill.

[0002]

2. Description of the Related Art As a method of manufacturing a hot seamless tube, a drawing method using a mandrel mill is frequently used. In this pipe manufacturing method, after inserting a mandrel bar which is a rolling tool for inner surface regulation into the inner surface of a hollow shell obtained by piercing and rolling a heated billet, a stand formed of opposed hole type rolls is prepared. The hollow shell is rolled into a seamless pipe of a predetermined size through a plurality of mandrel mills. Then, the inserted mandrel bar is pulled out from the seamless pipe after the rolling, and is reused by circulation.

[0003] In the mandrel mill rolling, a lubricating agent containing a solid lubricant as a main component is applied to the surface of the mandrel bar before the mandrel bar is inserted into the hollow shell to prevent tool damage such as abrasion of the mandrel bar and rough skin. A coating is formed in advance.
Thereby, the frictional force between the inner surface of the pipe and the surface of the mandrel bar generated at the time of rolling and at the time of pulling out the mandrel bar is reduced to prevent tool flaws from being generated.

[0004] As a mandrel bar used for mandrel mill rolling, a mandrel bar (hereinafter, referred to as a straight bar) whose outer diameter is processed so that the outer diameter becomes uniform in the longitudinal direction has been conventionally used.

[0005] In the mandrel mill rolling, as described above, the mandrel bar is pulled out of the seamless pipe after the end of the rolling. Usually, however, the mandrel bar is inserted into the seamless pipe after the end of the rolling for this drawing. In this state, it is transported to the mandrel bar drawing equipment. For this reason, during the transport, the temperature of the seamless tube decreases due to heat radiation to the atmosphere and heat transfer to the mandrel bar, while the temperature of the mandrel bar increases due to heat transfer from the seamless tube. As a result, the diameter of the seamless pipe becomes smaller, the diameter of the mandrel bar becomes larger, and the clearance between the seamless pipe and the mandrel bar becomes smaller than immediately after rolling.

[0006] The mandrel bar is pulled out of the seamless pipe in this state (hereinafter referred to as stripping). At this time, the conventional straight bar and the inner surface of the seamless pipe are subjected to severe friction over the entire length of the contacting portion. Occurs. In addition, in mandrel mill rolling, usually, due to its rolling principle,
QPs are placed at approximately four equally spaced locations in the circumferential direction of the rolled seamless pipe
In the QP part, the clearance is particularly small, so the seamless pipe and the mandrel bar are in a state close to "tight fit", which reduces the frictional force during stripping. It is one of the major causes of growth.

[0007] As the severe friction is repeated, the surface of the mandrel bar is damaged such as abrasion, rough skin, seizure, cracks, etc., which causes a reduction in the life of the mandrel bar. In addition, seizure flaws and the like may occur on the inner surface of the seamless pipe, and there is a problem in product quality.

[0008] Such a phenomenon is caused by a high deformation resistance and a high coefficient of thermal expansion.
US410TK, SUS304TK, SUS316TK
This is particularly noticeable when stripping stainless steel such as stainless steel and high alloy steel tubes such as Ni-based alloys.

Japanese Patent Application Laid-Open No. Hei 4-182009 discloses a small-diameter portion near the distal end of the seamless pipe, which focuses on a phenomenon that the distal end of the seamless pipe has a smaller diameter than the steady portion in order to reduce the friction during stripping. There has been proposed a method for manufacturing a seamless steel pipe using a mandrel bar provided with. However, even with such a method, the friction caused by the contact between the inner surface of the seamless tube and the mandrel bar cannot be sufficiently reduced, and the bar surface wears, becomes rough when stripping,
It was a fact that sufficient effects could not be obtained for various problems such as damage due to seizure and cracks, and occurrence of seizure flaws on the inner surface of the tube.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and can reduce the frictional force at the time of stripping and can cause seizure flaws on the inner surface of the seamless pipe. It is to provide a mandrel bar which has no long life.

[0011]

The gist of the present invention resides in the following mandrel bar.

At least the outer diameter of the portion which comes into contact with the seamless steel pipe when used for rolling is gradually increased from the leading end to the trailing end, and the gradually increasing average gradient of the outer diameter is 1/100.
000-10 / 100,000 der Rukoto hot seamless pipe rolling mandrel bar according to claim.

The above mandrel bar of the present invention has a
The entire length of the part that contacts the seamless steel pipe is tapered.
As described later, the seamless pipe and mand
The clearance with the rel bar increases. As a result,
Low pull-out force required when starting tripping
And the subsequent stripping can be performed very smoothly
Therefore, abrasion damage on the surface is greatly suppressed.
Also, since the taper is extremely loose, the dimensional accuracy of the product
Has no adverse effect.

[0014]

FIG. 1 is a schematic view showing an example of the mandrel bar 1 of the present invention. The outer diameter of a region L to be subjected to actual rolling is small at the leading end side, DT, and large at the rear end side, DB. Are formed into a single taper so that the outer diameter D of the intermediate portion of the region L has a predetermined reference outer diameter.

FIG. 2 shows a mandrel bar 1 of the present invention.
0 is a schematic diagram showing another example of the outer diameter D M of the middle part of the area L actually subjected to rolling is set to a predetermined reference outer diameter, and the outer diameter D T on the tip side is smaller than the outer diameter D M of the middle part. Small, the outer diameter DB on the rear end side is larger than the outer diameter DM on the middle part,
It is formed so that the taper on the rear end side is larger than the taper on the front end side.

As shown in FIGS. 1 and 2, a mandrel bar (hereinafter, referred to as a tapered bar) of the present invention in which the outer diameter of a region L to be actually subjected to rolling gradually increases from a front end to a rear end. If, for example, the seamless tube thermally contracts while being transported to the stripping facility while holding the mandrel bar after mandrel mill rolling, while the mandrel bar thermally expands and mutual clearance decreases,
A larger clearance can be obtained as compared with a conventional straight bar having an outer diameter uniform in the axial direction, and the clearance on the top side of the rolling becomes large.

That is, in the mandrel mill rolling, the advancing speed of the seamless pipe at least downstream of the final stand is faster than the advancing speed of the mandrel bar due to the rolling principle.

For this reason, focusing on an arbitrary point in the axial direction of the seamless pipe, when this arbitrary point passes through the final stand and further advances, the pipe inside the pipe at the time when the thickness reduction is completed immediately below the final stand is completed. Since the position of the mandrel bar that has been in contact with the surface is located upstream (at the final stand side) of any one point of the seamless pipe, when the tapered bar of the present invention is used, the seamless pipe and the mandrel bar are connected. This is because the clearance between the two becomes larger by the difference between the outer diameters of the bars in the shift length portion in the axial length direction, whereas when the straight bar is used, there is no difference between the outer diameters of the bars.

Therefore, in the taper bar of the present invention, the frictional resistance in the initial stage of the stripping is reduced, and thereafter the clearance between the two gradually increases, so that the frictional resistance in the stripping process over the entire length of the use area becomes smaller. As a result, the pulling force required for stripping is reduced, and wear and damage on the surface of the mandrel bar are suppressed, so that the bar life is extended. In addition, as the frictional resistance is reduced, the occurrence of flaws on the inner surface of the pipe is also suppressed.

The taper is preferably a single taper as shown in FIG. 1 in consideration of the quality of the inner surface of the pipe and the workability of the outer diameter of the mandrel bar.

The larger the taper is, the more remarkable the above-mentioned effect becomes, but the average gradient is 20/1.
If it exceeds 00000, the effect gradually saturates. However, the mandrel bar is a tool that determines the inner diameter of the seamless pipe after rolling.If the outer diameter changes greatly, it causes the inner diameter fluctuation and wall thickness fluctuation of the seamless pipe after rolling, and the gauge turns off. The average gradient ｛For example, in the case of the tapered bar shown in FIG. 1, (DB-DT) /
When 2L｝ is in the range of 1/100000 to 10 / 100,000, there is no problem, and the initial pulling force at the time of stripping can be reduced, and the mutual frictional force in the stripping process can be reduced. . Therefore, the taper has an average gradient of 1 / 100000-1.
It is desirable to set it in the range of 0/100000.

[0022]

[Example] Outer diameter: 181 mm, inner diameter: 146 mm, length: 70
A hollow shell made of 00 mm carbon steel and having a temperature of 1000 ° C. is used. A mandrel bar having a reference outer diameter of 134 mm and a length of 15000 mm for actual rolling is used.
In drawing and rolling a seamless pipe having a diameter of 7 mm, an inner diameter of 134 mm and a length of 21000 mm with a mandrel mill consisting of eight stands, a conventional straight bar and a single-taper taper bar of the present invention having a single taper having variously changed average gradients are drawn and rolled. Thereafter, the mandrel bar was stripped while the temperature of the seamless tube was 900 ° C., and the pulling force and the bar life required during the stripping were determined. The results are shown in Table 1 together with the average gradient value of the mandrel bar of the present invention.

Both the pull-out force and the bar life are shown as multiples of the conventional straight bar when it is set to 1.

[0024]

[Table 1]

As is clear from the results shown in Table 1, when the mandrel bar of the present invention was used, the frictional resistance between the inner surface of the seamless pipe and the surface of the mandrel bar was reduced.
While the pull-out force during stripping is greatly reduced, damage to the mandrel bar surface such as abrasion, rough skin, seizure and cracks is suppressed, and the bar life is greatly improved. Although the display of the data is omitted, the inner surface quality of the seamless pipe has been remarkably improved.

[0026]

According to the mandrel bar of the present invention, the pull-out force at the time of burst ripping is reduced, and the mutual frictional resistance between the pipe and the bar is also reduced. Is extended and the quality of the inner surface of the pipe is improved, so that a great effect is exhibited, such as an improvement in tool unit consumption and product yield.

[Brief description of the drawings]

FIG. 1 is a view schematically showing one example of a mandrel bar of the present invention.

FIG. 2 is a view schematically showing another example of the mandrel bar of the present invention.

[Explanation of symbols]

 1: Mandrel bar 2: Mandrel bar

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B21B 25/00 B21B 17/02

Claims (1)

(57) [Claims] An outer diameter of at least a portion which comes into contact with a seamless steel pipe when used for rolling is gradually increased from a front end side to a rear end side, and a gradually increasing average gradient of the outer diameter is 1/100.
000-10 / 100,000 der Rukoto hot seamless pipe rolling mandrel bar according to claim.