JPH06106233A - Method for hot-extruding tube - Google Patents

Abstract

PURPOSE:To almost maintain the outer diameter of a part passing through a die and that of a part after passing through the die at specified values to equalize the diameter of the middle part by making the outer diameter of a mandrel smaller toward the rear end side since the thermal expansion of the mandrel at the part passing through the die becomes remarkable with the advance of extrusion. CONSTITUTION:A heated hollow billet 3 is inserted into a container 1 and this billet is extruded to the front from a gap between the die 2 positioned before this container 1 and the mandrel 4 inserted by penetrating the billet 3 into this die 2 to make a tube. A tapered mandrel in which a part on the rear end side of a part in contact with the billet 3 upset at least at an upset time is reduced in diameter gradually toward the rear end side is used as this mandrel 4 so that a tube extruded in front of the mandrel is equalized in diameter in the axial direction at a completion time of extrusion. This method can restrain a diameter expanding phenomenon in the middle part of an extruded tube contributes to improvement of the dimensional accuracy of the extruded tube and prevents reduction of yield by seizure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot extrusion pipe forming method used for producing a seamless pipe.

[0002]

2. Description of the Related Art In a typical Eugene extrusion method as a hot extrusion tube forming method, as shown in FIG. 1, first, a heated hollow cylindrical billet 3 is loaded into a container 1. The front end of the container 1 is brought into contact with the die holder 7 to which the die 2 is attached.

Next, the hollow billet 3 and the mandrel 4 are attached.
And the hollow billet 3 is pushed forward by the stem 6 via the dummy block 5. Since the tip of the mandrel 4 is inserted through the die 2 with a gap, the hollow billet 3 is pushed forward from the annular gap between the die 2 and the mandrel 4 by pushing the hollow billet 3 forward. To become the extruded pipe P.

At this time, the mandrel 4 also moves forward as the stem advances. Therefore, at the end of the extrusion, the mandrel 4 remains in the bottom portion of the extrusion pipe P. Therefore,
After the extrusion, the mandrel 4 is pulled out rearward from the inside of the bottom portion of the extrusion pipe P. Then, the extruded pipe P is cut at the base to separate it from the residual dust remaining in the container 1.

By the way, in the production of a seamless pipe by such a Eugene method, the outer diameter of the extruded pipe P gradually increases at the so-called middle portion from the portion excluding the top end portion to the bottom end portion, It is known that the outer diameter of the bottom end portion rapidly increases toward the end surface. The cause of this large-diameter phenomenon is mainly the thermal expansion of the mandrel 4 in the middle part, the bottom part prevents the mandrel 4 from contracting the bottom part, and the mandrel 4 withdraws the shaft from the bottom part. It is considered to be a radial bulge to receive a compressive force in the direction.

On the basis of such a cause, as a countermeasure for increasing the diameter of the mandrel 4 provided with a large-diameter diameter-aligned portion at the tip thereof, Japanese Patent Application Laid-Open No. 63-235020 and Japanese Patent Application Laid-Open No. 3-235020 are available.
No. 226308.

[0007]

As a countermeasure for increasing the diameter, the diameter of the middle portion, which gradually increases with the progress of extrusion, is increased by a large diameter aligning portion provided at the tip of the mandrel. Although the diameter is made even larger than the maximum diameter due to the above, the diameter is made equal in the axial direction, but a considerably large diameter alignment portion is required to obtain a predetermined effect.

Generally, the lubrication of the inner surface of the billet during hot extrusion is carried out by charging glass powder into the heated billet using a spoon or the like, and therefore the lubricating film on the inner surface of the extruded tube is extremely thin. . Under such circumstances, when the extruded pipe is expanded at the large-diameter diameter-aligned portion away from the extruding position, lubrication is cut off due to the expansion, and internal seizure occurs depending on the pipe-making conditions. Therefore, the application range is narrow.

An object of the present invention is to provide a hot-extrusion pipe manufacturing method capable of suppressing enlargement of the diameter of the middle portion of the extruded pipe without causing internal sticking.

[0010]

According to the hot-extrusion tube-making method of the present invention, a heated hollow billet is charged into a container and a die positioned in front of the container and the billet penetrates the die. In the hot-extrusion tube manufacturing method in which the billet is extruded forward from the annular gap formed between the mandrel and the mandrel, the mandrel contacts at least the billet upset during upsetting. The part on the more rear end side is characterized by using a tapered mandrel with gradually decreasing diameter toward the rear end side so that the pipe extruded forward of the mandrel at the end of the extrusion is coordinated in the axial direction. And

[0011]

The function of increasing the diameter of the middle portion of the extruded tube during hot extrusion occurs as follows.

As shown in FIG. 2 (A), when the billet 3 in the container 1 is upset by the stem through the dummy block 5, the billet 3 has the inner surface at the front end and the inner surface at the rear end on the outer surface of the mandrel 4. The inner surface of the tip portion is in close contact with the outer surface of the mandrel 4 more widely. This tendency is shown in FIG.
It does not change during the extrusion shown in (B), and as a result, the region X from the tip of the container 1 to the inside of the die 2 becomes the main mandrel heating region. Since the mandrel 4 heated by the billet 3 in the container 1 is sent to the heating region X, the die passing portion of the mandrel 4 gradually becomes hot. Therefore, when the mandrel 4 has an equal diameter in the axial direction, the diameter of the die passing portion gradually increases, and when looking at the part that has advanced to the front of the die 2, as shown in FIG. 2 (C), it goes toward the rear end side. It becomes a so-called tapered shape in which the diameter is gradually increased. Therefore, at the end of extrusion, the outer diameter of the middle portion gradually increases toward the rear end side.

The hot-extrusion pipe manufacturing method of the present invention is shown in FIG.
As shown in (A) to (C), in order to offset the increase in diameter of the mandrel 4 due to the progress of extrusion, a so-called tapered taper mandrel whose diameter is gradually reduced toward the rear end side is used. The diameter of the middle part can be prevented from increasing. That is, the thermal expansion of the die passing portion of the mandrel 4 becomes remarkable as the extrusion progresses, but since the outer diameter of the mandrel 4 becomes smaller toward the rear end side, the die passing portion and the portion after passing through the die are The outer diameter is maintained at a predetermined value, and the middle part is made uniform in diameter.

Since the outer diameter variation of the extruded pipe P is affected by the dimension variation due to the thermal expansion of the die 2, it is desirable to consider the dimension variation of the die 2 when setting the taper of the mandrel 4.

The taper angle applied to the mandrel 4 is
Although it depends on the extrusion speed, that is, the contact time between the mandrel 4 and the billet 3, the inner surface temperature of the billet 3 and the linear expansion coefficient of the mandrel 4, it is usually about 0.011 degree.

Further, since the tip of the mandrel 4 is already positioned in front of the heating region X at the time of upsetting, the front portion, that is, the portion on the tip side of the portion where the material upset at the time of upsetting contacts. The taper may be excluded.

In the hot extrusion pipe making method of the present invention,
The mechanism as described above prevents the diameter of the middle portion of the extruded pipe from increasing, and the diameter of the middle portion is made uniform in the axial direction. Further, the extruded pipes are aligned in diameter when extruded from between the die and the mandrel, and thereafter, the extruded pipes are advanced along a mandrel having a substantially equal diameter, and are not subjected to diameter expansion processing, so that there is no risk of seizure. Also, the mandrel which became almost equal in diameter at the end of extrusion,
The mandrel can be pulled out more easily than a mandrel having a large-diameter aligning portion at the tip, which contributes to suppressing the increase in diameter of the bottom portion.

[0018]

EXAMPLES Examples of the present invention will be described below.

When performing hot extrusion under the conditions shown in Table 1, Table 2
3 types of mandrels and dies shown in A to C were used.

[0020]

[Table 1]

[0021]

[Table 2]

The mandrel A has an equal diameter over the entire length in the axial direction, and the mandrel B has a large diameter uniformed portion provided at the tip of the equal diameter mandrel. The mandrel C is a tapered mandrel whose diameter is gradually reduced toward the rear end side. The results of measuring the outer diameter of the extruded tube manufactured using each mandrel in the axial direction of the tube are shown in FIG.

In the pipe manufacturing using the equal diameter mandrel A,
A remarkable increase in diameter occurred in the middle part, which gradually increased toward the bottom, and 1.3% (2 out of 152) seizure occurred. In the case of the mandrel B provided with the diameter-aligned portion, the phenomenon of increasing the diameter of the middle portion was prevented, but the inner surface of the extruded tube was 2.4%.
Image sticking (3 out of 123) occurred. On the other hand, in the pipe manufacturing method of the present invention using the taper mandrel C, enlargement of the diameter of the middle portion was prevented, and seizure of the inner surface of the extruded pipe did not occur. Also, the diameter of the bottom portion was prevented from increasing.

[0022]

As is apparent from the above description, the hot extrusion pipe manufacturing method of the present invention can suppress the diameter enlargement phenomenon in the middle portion of the extruded pipe and only contribute to the improvement of the dimensional accuracy of the extruded pipe. In addition, there is no concern that seizure will occur on the inner surface of the pipe, and it is effective in preventing the yield from decreasing due to seizure.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an outline of a hot-extruded pipe.

FIG. 2 is a schematic diagram showing a mechanism in which a diameter increase occurs in a conventional method.

FIG. 3 is a schematic view showing a mechanism of preventing enlargement by the method of the present invention.

FIG. 4 is an outer diameter distribution diagram of an extruded tube showing an effect of carrying out the method of the present invention.

[Explanation of symbols]

 1 Container 2 Dice 3 Billet 4 Mandrel 5 Dummy Block 6 Stem

Claims (1)

[Claims] 1. A heated hollow billet is charged into a container, and an annular shape is formed between a die located in front of the container and a mandrel inserted through the billet into the die. In the hot extrusion pipe manufacturing method of extruding the billet forward from the gap to form a pipe, as the mandrel, at least a portion on the rear end side of the portion where the billet that is upset during upsetting comes into contact with the mandrel forward at the end of extrusion. A hot-extrusion tube-making method, characterized in that a tapered mandrel whose diameter is gradually reduced toward the rear end side is used so that the extruded tube has an equal diameter in the axial direction.