JP4352634B2 - Method for improving life of mandrel bar for rolling mandrel mill of Cr-containing steel and mandrel bar circulation equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for improving the life of a mandrel bar used in the production of seamless steel pipes by the Mannesman mandrel mill method, and a mandrel bar circulation facility suitable for carrying out this method.
[0002]
[Prior art]
In the manufacture of Mannesmann mandrel mill type seamless steel pipe, the mandrel bar cost accounts for a large proportion of the manufacturing cost. Particularly in the rolling of 13% Cr-containing steel, the rolling load increases due to the large deformation resistance, which further shortens the life of the mandrel bar. Therefore, improving the life of the mandrel bar greatly contributes to a reduction in the manufacturing cost of the seamless steel pipe.
[0003]
Therefore, in Japanese Patent No. 2822918, the outer surface of the mandrel bar with poor surface properties is polished to about 0.04 mm using a belter or the like, and then heated to room temperature to 100 ° C. to the surface of the mandrel bar. A technique for performing rusting and using it again as a mandrel bar of the same size is disclosed (bar regeneration method).
[0004]
Japanese Patent Application Laid-Open No. 11-226614 discloses a mandrel bar whose surface condition has deteriorated and heat treated at a temperature lower than the original tempering temperature to make the surface hardness uniform, and then is ground to 0.06 mm or more using a belter or the like. , After cutting, soaking in seawater and attaching rust, heat treatment below the original tempering temperature again to produce a scale film for seizure resistance and use it again as a mandrel bar of the same size or downsized (Bar playback method) is disclosed.
[0005]
[Problems to be solved by the invention]
Any of the techniques disclosed in the above publications is an effective method, but (1) both methods require the surface of the mandrel bar to be cut off-line, so that continuous rolling is impossible. (2) This is a method for regenerating a mandrel bar whose bar surface condition has already deteriorated to some extent, and does not improve the deterioration of the bar surface condition, that is, does not improve the continuous rolling life.
[0006]
The present invention has been made in view of the above-described conventional problems, and reproduces a mandrel bar without cutting the surface of the bar, thereby preventing deterioration of the surface state of the bar and improving the continuous rolling life. It is an object of the present invention to provide a mandrel bar circulation facility suitable for carrying out this method and a method for improving the mandrel bar life.
[0007]
[Means for Solving the Problems]
In order to achieve the above-described object, the method of improving the life of a mandrel bar for mandrel mill rolling of Cr-containing steel according to the present invention eliminates seizure generated on the outer surface of the mandrel bar used for mandrel mill rolling. after mill rolling, in until lubricant application, each pass of the mandrel mill rolling, or are performed by the online every predetermined number of passes, the seizure of the removal, mechanical friction and sliding outer surface of the mandrel bar The scale layer applied to the outer surface of the mandrel bar is not removed by removing only the seizure by moving. And by doing in this way, deterioration of the surface state of a bar can be prevented and a continuous rolling lifetime comes to improve.
[0008]
In addition, the mandrel bar circulation facility according to the present invention includes a mandrel bar outer surface seizure removal facility for mechanically rubbing and sliding the mandrel bar outer surface between the mandrel mill and the lubricant application facility. I am going to do that. By doing so, it is possible to remove seizure generated on the outer surface of the mandrel bar online.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The main factor that deteriorates the surface property of the mandrel bar is seizure of the outer surface of the mandrel bar by repeated rolling, and the present inventor removes this seizure, thereby deteriorating the surface property of the mandrel bar. We thought that we can prevent.
[0010]
And when the present inventors used the rolling after removing the seizure by rubbing and sliding the outer surface of the mandrel bar, which is not suitable for rolling due to deterioration of the surface properties, using a wire brush, the rolling was sufficiently performed. It was found that this is possible. Based on this result, when the surface of the mandrel bar subjected to rolling for a certain period of time was rubbed and slid with a wire brush to remove seizure and then subjected to rolling again, Patent No. 2822918 and JP-A-11-226614 It has been found that the lifespan is improved without scraping the surface of the mandrel bar as in the method disclosed in the above-mentioned issue.
[0011]
The life improvement method of the mandrel bar for mandrel mill rolling of the Cr-containing steel according to the present invention is made based on the above-mentioned knowledge, and removes seizure generated on the outer surface of the mandrel bar used for mandrel mill rolling. the, after mandrel mill rolling, in until lubricant application, are performed by the online for each path of the mandrel mill rolling, the seizure of the removal, be mechanically friction and sliding outer surface of the mandrel bar Thus, only the seizure is removed, and the scale layer applied to the outer surface of the mandrel bar is not removed. The seizure removal of the mandrel bar outer surface is performed by mechanically rubbing and sliding the outer surface of the mandrel bar using, for example, a seizure removal facility equipped with a wire brush, steel wool, a flap wheel, etc. At this time, the scale layer applied to the outer surface by removing only seizure should not be removed. According to the method for improving the life of a mandrel bar for mandrel mill rolling of Cr-containing steel according to the present invention, only the seizure generated on the surface of the mandrel bar by mandrel mill rolling is removed, so that deterioration of surface properties is prevented. become.
[0012]
In the above-described method for improving the life of a mandrel bar for rolling a mandrel mill of a Cr-containing steel according to the present invention, the seizure removal work on the outer surface of the mandrel bar is performed online for each pass , and the outer surface of the mandrel bar is mechanically rubbed. since the scale layer which is applied to the outer surface of the mandrel bar by removing only seizure by sliding is carried out so as not to remove, I do good work efficiency, and significantly improved continuous rolling life of the mandrel bar you.
[0013]
As a result of rolling the steel containing 13% Cr in order to confirm the effect of the method for improving the life of the mandrel bar according to the present invention described above, the bar life after removing the seizure on the outer surface of the mandrel bar is It was found that each time the number of seizure removals was repeated, the length gradually decreased. This can be presumed to be caused by the gradual dropping of the scale layer applied to the outer surface of the mandrel bar by heat treatment during rolling of the 13% Cr-containing steel.
[0014]
Therefore, particularly when rolling 13% Cr-containing steel, in the above-described method for improving the life of a mandrel bar for rolling a mandrel mill of Cr-containing steel according to the present invention, after the seizure on the outer surface of the mandrel bar is removed, the mandrel is removed. By performing a heat treatment below the original tempering temperature of the bar to produce a scale film, it is possible to effectively suppress the shortening of the mandrel bar life .
[0016]
Instead of performing seizure removal on the outer surface of the mandrel bar in the method for improving the life of the mandrel bar for rolling the mandrel mill of the Cr-containing steel according to the present invention described above, it is performed every predetermined number of passes. Also, it has a sufficient effect of improving the continuous rolling life .
[0017]
In carrying out the above-described method for improving the life of a mandrel bar for rolling a mandrel mill of Cr-containing steel according to the present invention, a mandrel provided with a wire brush, steel wool, a flap wheel, etc. between a mandrel mill and a lubricant application facility What is necessary is just to install the seizing removal equipment of the bar outer surface. This is the mandrel bar circulation facility according to the present invention.
[0018]
【Example】
Hereinafter, the implementation result performed in order to confirm the effect of the lifetime improvement method of the mandrel bar for mandrel mill rolling of Cr containing steel which concerns on this invention is demonstrated.
A 10% mandrel bar made of a Cr-Mo-V-based material having an outer diameter of 134.0 mm and a length of 22 m is used as a set. As an accelerated test, the surface properties of the 13% Cr-containing steel are likely to deteriorate. Rolling was repeated. The life of the mandrel bar is determined by setting a threshold value for the measured coefficient of friction between the mandrel bar and the material to be rolled, and when the use limit (life) is reached, the outer surface of the mandrel bar is offline. Friction / sliding was performed in a seizure removal facility equipped with a wire brush, and then subjected to mandrel mill rolling of the next 13% Cr-containing steel.
[0019]
Conventionally, after continuous rolling, it has been necessary to perform conventional regeneration processing such as polishing, grinding, cutting, and scaling of the mandrel bar, but it could not be used for the next mandrel mill rolling, as shown in FIG. By continuously rubbing and sliding the outer surface of the mandrel bar with a seizure removal facility equipped with a wire brush after continuous rolling, it can be used for mandrel mill rolling without grinding, grinding, cutting, scaling, etc. Became.
[0020]
However, when the outer surface of the mandrel bar is rubbed and slid with a seizure removal facility equipped with a wire brush, the life of the mandrel bar becomes shorter as the number of times increases, as shown in FIG. This can be presumed to be caused by the gradual dropping of the scale layer applied to the outer surface of the mandrel bar by heat treatment during the mandrel mill rolling of the 13% Cr-containing steel.
[0021]
Therefore, after rubbing and sliding the outer surface of the mandrel bar with a seizure removal facility equipped with a wire brush, the mandrel bar is heat-treated at the original tempering temperature or lower to give a scale for seizure resistance to the outer surface. As a result, as shown in FIG. 1, the life of the mandrel bar returned to the initial life in which the number of friction and sliding of the outer surface was repeated.
[0022]
Furthermore, when rolling 13% Cr-containing steel under the same conditions as the set of mandrel bars described above, seizure removal provided with a wire brush for each pass after burst ripping and before applying the lubricant. the outer surface of the mandrel bar and frictionally-sliding at facilities, was repeated mandrel mill rolling. The results at that time are shown in FIG. The deterioration of the surface properties of the mandrel bar in this case was determined by the same determination method as in FIG.
[0023]
When the outer surface of the mandrel bar is rubbed and slid with a seizure removal equipment equipped with a wire brush for each pass and mandrel mill rolling is repeated, as shown by the ● mark in FIG. Compared with this, the continuous rolling life was greatly improved. In addition, it is possible to use this mandrel bar as a mandrel bar of the same size by subjecting the mandrel bar to a regeneration process by the method disclosed in Japanese Patent No. 2822918 and JP-A-11-226614.
[0024]
The results shown in FIG. 1 are the results of off-line friction and sliding on the outer surface of the mandrel bar, but when the outer surface of the mandrel bar is friction and sliding on-line, the life of the mandrel bar is improved. Needless to say, the rolling efficiency can be improved as it is.
[0025]
In addition, the result shown in FIG. 2 is that the outer surface of the mandrel bar is rubbed and slid using a wire brush for each pass, but the outer surface of the mandrel bar is removed using a wire brush every predetermined number of times. Even if it rubs and slides, it has a sufficient effect of improving the continuous rolling life.
[0026]
【The invention's effect】
As described above, according to the present invention, the mandrel bar can be regenerated without scraping the surface of the bar, the deterioration of the surface state of the bar can be prevented, and the continuous rolling life can be improved. Further, by using the mandrel bar circulation facility according to the present invention, it is possible to remove seizure generated on the outer surface of the mandrel bar online.
[Brief description of the drawings]
FIG. 1 is an implementation result illustrating an effect of a comparative example of a mandrel bar life improvement method according to the present invention .
FIG. 2 is an implementation result illustrating the effect of the mandrel bar life enhancement method according to the present invention .

Claims (4)

A method for improving the life of a mandrel bar for rolling a mandrel mill of Cr-containing steel,
The removal of the seizure that occurred on the outer surface of the mandrel bar used in mandrel mill rolling, after mandrel mill rolling, in until lubricant application, are performed by the online for each path of the mandrel mill rolling,
The removal of seizure is characterized in that only the seizure is removed by mechanically rubbing and sliding the outer surface of the mandrel bar and the scale layer applied to the outer surface of the mandrel bar is not removed. A method for improving the life of a mandrel bar for rolling a mandrel mill of Cr-containing steel. A method for improving the life of a mandrel bar for rolling a mandrel mill of Cr-containing steel,
The removal of the seizure that occurred on the outer surface of the mandrel bar used in mandrel mill rolling, after mandrel mill rolling, in until lubricant application, are performed by the online every predetermined number of passes of the mandrel mill rolling,
The removal of seizure is characterized in that only the seizure is removed by mechanically rubbing and sliding the outer surface of the mandrel bar and the scale layer applied to the outer surface of the mandrel bar is not removed. A method for improving the life of a mandrel bar for rolling a mandrel mill of Cr-containing steel. In the method for improving the life of a mandrel bar for rolling a mandrel mill of the Cr-containing steel according to claim 1 or 2 ,
A method for improving the life of a mandrel bar for rolling a mandrel mill of Cr-containing steel, wherein after removing the seizure on the outer surface of the mandrel bar, heat treatment is performed at a temperature lower than the original tempering temperature of the mandrel bar to generate a scale film. . A mandrel bar circulation facility characterized in that a mandrel bar outer surface seizure removal facility for mechanically rubbing and sliding the mandrel bar outer surface is interposed between the mandrel mill and the lubricant application facility.

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