JPH05237514A - Method and device for rolling by mandrel mill - Google Patents

Abstract

PURPOSE:To drastically reduce the possessing number of mandrel bars by arranging respective shafts of at least a pair of rolling rolls obliquely in the direction opposite to each other to the advancing direction of a rolled stock, and thereby drawing a steel tube into which a mandrel bar is inserted. CONSTITUTION:When the steel tube 2 in which the mandrel bar 3 is inserted is reduced in thickness and drawn, the roll shafts of at least a pair of rolls 1, 1' are arranged obliquely by an angle theta in the direction opposite to each other to the advancing direction of the steel tube 2, thereby the thickness distribution in the peripheral direction is uniformized to obtain the steel tube 2 uniform in thickness. Further, the inclined angle theta is decided by a roll caliber, and the angle that an interval in the circumferential direction between the roll and the mandrel is uniformized and rotation in the circumferential direction is canceled to each other is found in advance by an experiment, thereby the angle is adjusted and set whenever the roll gap is changed. Therefore, since the major diameter pitch of the mandrel bar can be roughened, the possessing number of the mandrel bars can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling method by a mandrel mill and a device for thinning and stretching a steel tube having a mandrel bar inserted therein in a manufacturing process of a seamless steel tube by a mandrel mill.

[0002]

2. Description of the Related Art In a rolling line for producing a seamless steel pipe using a mandrel mill, a billet is pierced with a piercer, then a mandrel mill is used to reduce the wall thickness to a predetermined wall thickness, and then a stretch reducer. The outer diameter is reduced and finished to a predetermined outer diameter to obtain a seamless steel pipe.

In this case, in the mandrel mill, the gap between the hole-type roll and the mandrel bar is pressed to finish to a predetermined wall thickness. At that time, in order to reduce variations in wall thickness as much as possible, the roll die diameter and the mandrel bar diameter are uniquely determined. Therefore, if the finished wall thickness is different, it is necessary to use a mandrel bar having a different diameter each time, such as changing to a different mandrel bar. It is better than replacing the perforated roll
This is because it is easier to replace the mandrel bar.

When the roll gap is changed, uneven thickness may occur in the circumferential direction. Since the wall thickness is determined geometrically by the pore diameter of the roll and the outer diameter of the mandrel bar used, the pore diameter (shape) defined by a pair of rolls except for a certain roll gap. Is changed, and accordingly, the interval also changes in the circumferential direction.

This is schematically shown in FIG. 7 using a perfect circular hole type as an example. In FIG. 7 (a), the interval defined by the roll pairs 1, 1'and the mandrel bar 3 is the circumference. If the wall thickness is uniform in the direction, that is, the wall thickness is uniform in the circumferential direction, the same figure (b)
Shows the case where the wall thickness becomes non-uniform in the circumferential direction by changing the roll gap. Therefore, the mandrel bar must have a large number of dimensions depending on the pitch of the finished wall thickness. Therefore, a large number of mandrel bars are required, which increases the manufacturing cost.

In order to solve such a problem
There is an attempt to prevent uneven thickness by performing a pair of rolls asymmetrically as shown in JP-A 61-86020 and adjusting the set position of the rolls. However, this method requires at least three finishing stands. This is because, in the example shown in Table 1 of JP-A-61-86020, the # 3 stand and the # 5 stand are set asymmetrically to adjust the roll reduction asymmetrically, and the # 4 stand is placed between those stands. While intervening, it is necessary to adjust the roll reduction in the # 5 stand in the opposite direction to the # 3 stand.
Therefore, at least three finishing stands # 3, # 4 and # 5 are required. Usually, there are two finishing stands. In that case, it is necessary to install one extra stand or reduce the amount of reduction in the mandrel mill by one stand, which increases equipment costs or increases the degree of processing. There are problems such as not being able to take it.

[0007]

Among the methods for producing seamless steel pipe, the drawing and rolling method using a mandrel mill is often used because of its high productivity and good inner surface quality. However, the mandrel mill has a larger number of stands than the plug mill, and the mandrel bar is much longer than the short plug, so the material cost of the mandrel bar and the investment cost for its handling equipment, etc. Will be too large.

Therefore, it is important for factory operation to reduce the number of mandrel bars. In order to reduce the number of mandrel bars owned, it is necessary to share mandrel bars. That is, it is necessary to establish a technique for using the same mandrel when rolling seamless steel pipes having different wall thicknesses.

In the case of rolling seamless steel pipes having different wall thicknesses with the same mandrel bar, if the roll gap is simply adjusted, uneven thickness in the circumferential direction will occur due to the reasons described above. It is necessary to prevent the uneven thickness from occurring. Here, a general object of the present invention is to provide an inexpensive and simple method and apparatus for preventing the variation of the wall thickness in the circumferential direction at the time of thinning and drawing rolling by a mandrel mill. Further, a specific object of the present invention is to make it possible to stretch and roll a seamless steel pipe having a greater number of different wall thicknesses with a mandrel bar having the smallest possible number and different circumferential thickness deviations. A mandrel mill rolling method and a rolling apparatus therefor.

[0010]

Here, the present inventor has
The present invention has been completed based on the knowledge that the arrangement of the roll pair itself can be devised to obtain the same or more effective effects as compared with the above-mentioned conventional technique in which the roll rolling of the pair is asymmetrical. Therefore, the gist of the present invention is that, in the process of manufacturing a seamless steel pipe, at the time of thinning stretch rolling of a steel pipe into which a mandrel bar is inserted, at least one roll axis of a pair of rolling rolls arranged in parallel to each other is used. A rolling method for a mandrel mill, which is characterized in that rolling is performed by arranging the materials in a direction opposite to each other with respect to the traveling direction of the rolled material.

From another aspect, the present invention comprises a plurality of roll stands provided with a pair of rolling rolls arranged in parallel with each other for thinning and stretching and rolling a steel pipe having a mandrel bar inserted therein. Mandrel mill rolling equipment,
This is a mandrel mill rolling apparatus having at least one roll stand in which the roll axes of a pair of rolling rolls are tilted in mutually opposite directions with respect to the traveling direction of a rolled material, and the tilt can be adjusted.

[0012]

Next, the present invention will be described more specifically with reference to the accompanying drawings. FIG. 1 is an explanatory view of a rolling line for carrying out the rolling method according to the present invention, in which a steel pipe 2 having a mandrel bar 3 inserted therein has roll pairs 1a, 1b, 1c, 1d, 1e.
Thinning stretch rolling is performed through a series of rolling stands consisting of.

According to the present invention, the rolling roll pairs in the last two stands which are at least finishing roll stands in the rolling roll pairs 1a to 1e arranged in parallel with each other.
The rolls of 1d and 1e are inclined in the directions opposite to each other with respect to the traveling direction of the rolled material. The situation is as shown in FIG. 2, where FIG. 2 (a) is a plan view and FIG. 2 (b). Is a side view, the same figure (c)
Is a front view.

In FIG. 2, the roll pairs 1, 1'are arranged so that their roll axes are tilted at an angle θ in directions opposite to each other with respect to the traveling direction of the rolled material (indicated by a white arrow).

That is, the hole types of the roll pairs of the final two stands constituting this finishing stand are usually set as follows.

FIG. 3 is a schematic explanatory view of a perfect circular hole type as an example. The figure (a) shows the i-th stand and the figure (b) shows i.
Shows + 1st (final stand). As is clear from this figure, both stands are connected in phase around the rolling pass line by 90 °, and the outer diameter M in the axial direction for rolling is M.
For the mandrels 3 having the same D, the roll hole diameters R _i and R _{i + 1} of both stands are set so that the distance between the mandrel peripheral surface and the hole peripheral surface during the standard dimension rolling becomes the same in the circumferential direction.
Are set to be the same, and more desirably, by setting so that the relationship of α ₂ + α ₂ > 90 ° is established between the thickness reduction regions α ₁ and α ₂ at each stand, Tube finish rolling with a uniform thickness is performed.

The mandrel mill rolling apparatus according to the present invention may be a continuous mill in which a roll stand composed of each roll pair 1, 1'shown in FIG. 2 is applied to all roll stands. Note that the stands adjacent to each other are arranged such that their roll axes are alternately phased by 90 degrees, as can be seen from FIG. When a plurality of roll stands composed of roll pairs 1, 1'shown in FIG. 2 in which the roll axes are inclined in the opposite directions to the rolling direction by an angle θ are provided in series, each of the adjacent stand stands. It is arranged so that the angle θ given to the pair of rolls becomes sequentially opposite in order to cancel the rotational force acting on the steel pipe being rolled in the circumferential direction.

The inclination angle θ is, for example, as shown in FIG. 4 only for one roll shaft end side, the roll chocks 11 and 1 of the one roll 1 and the other roll 1 '.
Jacks 13, 13 and 13 ', 13' which are installed on support bases 12 and 12 'in which 1'is directly or indirectly attached to the roll housing 10 and which are operated by an electric motor or the like not shown.
Therefore, it is possible to make adjustments by displacing them in opposite directions. The adjusting mechanism for the inclination angle θ is not limited to the illustrated example, and a hydraulic mechanism is used instead of the jack mechanism, for example. Still further, for example, the sliding groove portion of the roll chock in the rolling-down direction (roll gap adjusting direction) is divided into one roll and the other roll, and the divided sliding groove portion is formed with respect to the roll housing. It goes without saying that it may be configured to be slidably mounted in a direction orthogonal to the sliding direction and to be moved by an appropriate conventional means such as the jack mechanism or the hydraulic mechanism.

According to the rolling method using the mandrel mill having such a structure, the following effects can be obtained. That is,
Normally, the finished wall thickness is determined by the geometric relationship between roll die and mandrel outer diameter in the finishing stands (usually the last two stands).

However, in the finishing stand of such a mandrel mill, when it is attempted to finish with different wall thicknesses by changing only the roll gap with the same mandrel outer diameter, circumferential uneven thickness occurs. That is, as described above, when rolling a thinner wall than the standard wall thickness with the same mandrel outer diameter, the roll gap is narrowed so that the wall thickness at the groove bottom of the roll hole die is set to a predetermined thin wall thickness. Therefore, the distance between the roll hole die and the mandrel in the direction orthogonal to the groove bottom is larger than the distance between the groove bottoms. In that case, the wall thickness distribution in the circumferential direction is the thinnest at the groove bottom, and becomes thicker as it goes away from the groove bottom.

According to the present invention, even in such a case, the wall thickness can be made uniform in the circumferential direction by arranging the roll shaft so as to be inclined with respect to the rolling direction. .. The inclination angles of the pair of roll stands are arranged in opposite directions as shown in FIG. In this way, depending on the inclination angle θ, the hole shape in the plane orthogonal to the hole axis line defines a shape close to a perfect circle, as shown by the broken line in FIG. A substantially uniform gap between the rolls 1 and 1'and the mandrel 3 is defined in the circumferential direction, and a uniform thickness steel pipe is obtained in the circumferential direction. In this case, the twisting force (rotational force described above) acts on the steel pipe, so in order to cancel it, the other pair of stands should have their roll pairs tilted in the opposite direction. Is preferable as described above.

The inclination angle θ is determined by the specifications of the roll hole type used, and the distance between the roll and the mandrel in the circumferential direction is made uniform as much as possible by experiments or calculations in advance, and the circumferential rotational forces are mutually equal. It is only necessary to obtain an angle that cancels out the above and adjust and set each time the roll gap is changed.

Thus, according to the present invention, it was possible to reduce the thickness to about 1/3, whereas it was necessary to have about 50 kinds of mandrel bars in the past. The variation could be suppressed to almost 2%. Moreover, since the last two stands may be used as the finish rolling stands, it is not necessary to use three stands as a set as in the conventional case, and the number of rolling stands can be reduced accordingly.

[0024]

EXAMPLES Examples and effects of the mandrel mill according to the present invention will be described below. The experimental conditions in this example are shown in Table 1. The inclination angle θ of the roll pair was adjusted using the stand shown in FIG. The mandrel mill rolling of this example was performed by changing the inclination angle θ of the roll pair into two types, 5 degrees and 10 degrees. In this example, the number of stands is one, and after one pass of the material, the material was rotated by 90 degrees around the rolling axis to perform the second pass rolling. In this way, a total of 5 passes were made.
The tilt angle was set during the last two passes.

The thickness distribution of the result of this experiment is shown in FIG.
In the conventional stand-free test without a roll inclination, uneven thickness occurred in the material thinner than the specified thickness, but by tilting the roll, it is possible to roll without uneven thickness even with the same mandrel or other than the specified thickness. I know there is.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

As described above, according to the present invention, the outer diameter pitch of the mandrel bars to be held can be made coarse, so that the number of mandrel bars held can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a rolling line according to the present invention using a mandrel mill.

2A and 2B are schematic explanatory views of roll arrangement of a roll pair used in the present invention, in which FIG. 2A is a plan view and FIG.
Is a side view and (c) is a front view.

FIG. 3 is a schematic explanatory view at the time of rolling in the standard size on the final stand, where FIG. 3 (a) is the i-th stand and FIG. 3 (b).
FIG. 6 is an explanatory diagram showing the (i + 1) th stand.

FIG. 4 is an explanatory diagram of an inclined rolling stand used in an example of the present invention.

FIG. 5 is a schematic explanatory diagram showing that the circumferential distance between the roll and the mandrel becomes uniform when the roll pair is inclined.

FIG. 6 is a graph showing a wall thickness distribution of a steel pipe after rolling in an example.

FIG. 7 is an explanatory diagram of the reason why the circumferential thickness deviation occurs, and
(a) is explanatory drawing at the time of standard dimension rolling, and the same figure (b) is explanatory drawing at the time of non-standard dimension rolling.

[Explanation of symbols]

 1: Roll 2: Steel pipe 3: Mandrel

Claims (2)

[Claims] 1. In the process of manufacturing a seamless steel pipe by a mandrel mill, at the time of thinning stretch rolling of a steel pipe into which a mandrel bar is inserted, at least one roll axis of a pair of rolling rolls arranged in parallel with each other is made of a rolled material. A rolling method by means of a mandrel mill, wherein rolling is carried out by arranging in a direction opposite to each other with respect to the traveling direction. 2. A mandrel mill rolling apparatus comprising a plurality of roll stands, each of which is provided with a pair of rolling rolls arranged in parallel with each other, for thinning and rolling a steel pipe having a mandrel bar inserted therein. A mandrel mill rolling apparatus comprising at least one roll stand in which each roll axis of a pair of rolling rolls is arranged in an opposite direction to the traveling direction of a rolled material, and the tilt can be adjusted.