JP2597923B2 - Hot extrusion pipe making method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot extrusion method for producing a seamless tube by extruding a hollow billet while hot.

[Conventional technology]

A typical Eugene extrusion pipe making method as a hot extrusion pipe making method is performed as shown in FIG. That is, the heated hollow hollow billet 3 is loaded into the container 1 in which the die 2 is disposed using the die holder 6 and the die backer 6a at one end.

Next, the mandrel 4 is inserted through the hollow billet 3 from the other end side of the container 1, the leading end thereof is concentrically passed through the die 2, and is positioned so as to protrude a predetermined length forward of the die 2.
Further, the stem 5 is brought into contact with the other end surface side of the hollow billet 3 via the dummy block 9, and the mandrel 4 and the stem 5 are advanced as it is. Since an annular gap is formed between the mandrel 4 and the die 2, when the hollow billet 3 is pushed forward by the stem 5, the hollow billet 3 is extruded forward from the annular gap, and the extruded pipe P is formed. Manufactured.

Since the mandrel 4 also moves forward as the stem 5 advances, the mandrel 4 is left in the bottom of the extruded tube P at the end of the extrusion. Therefore, after extrusion, the extruded pipe P
The mandrel 4 is pulled out from the bottom portion of the above. However, the outer diameter locally increases in the portion where the mandrel 4 is left, and the dimensional tolerance is likely to be deviated in this portion, the yield is reduced due to the increase in crop, or the extrusion process is performed. However, there are problems such as an increase in manufacturing costs due to an increase in maintenance work following the increase in the number of maintenance operations and a decrease in production efficiency.

As a countermeasure, such a local increase in the outer diameter at the rear end of the extruded pipe P (hereinafter, referred to as a local diameter increase) is described as follows.
During the time from the time when the stem 5 reaches the forward limit position to the time when the mandrel 4 starts retreating, the distal end portion and the intermediate portion of the extruded tube P shrink with cooling, whereas the rear end portion of the extruded tube P has a mandrel. 4 is cooled in a state where the inner diameter is constrained, that is, the rear end of the extruded pipe P is inhibited from thermal contraction by the mandrel 4. The following method has been proposed.

That is, before the stem reaches the forward limit position, stop the advance of the mandrel, and before the stem reaches the forward limit position,
Alternatively, the mandrel is retracted simultaneously with the arrival (Japanese Patent Laid-Open No. 63-286216).

[Problems to be solved by the invention]

By the way, according to the above-described method, the local large diameter phenomenon at the rear end of the extruded pipe is suppressed. However, according to the results of extruding pipes in large quantities in actual operation using this method, the normal mandrel retreating method, that is, stopping the mandrel advance almost at the same time as the stem reaches the forward limit position, and then 2 to 2 Compared to the method of retracting the mandrel after 3 seconds and pulling it out from the rear end of the extruded tube, the surface of the mandrel is more liable to burn and roughen the surface of the mandrel, resulting in a drastic reduction in mandrel life. There was a problem that the damage generated on the surface frequently caused streak-like flaws on the inner surface of the extruded pipe, which had a large effect on the quality of the pipe.

The present inventors have conducted experimental studies to eliminate such a local large diameter phenomenon and a reduction in the mandrel life, and have found the following facts as follows.

The local large diameter phenomenon occurs after the stem reaches the forward limit position.
Mandrel embedment due to heat shrinkage of extruded tube and temperature decrease of glass lubricant existing on inner surface of extruded tube (= decrease in viscosity)
, The rear end of the extruded pipe receives an axial compressive force due to an increase in frictional force when the mandrel retreats, causing so-called bulge deformation.

In addition, the position where the large diameter phenomenon occurs at the rear end of the extruded tube always coincides with the position where the mandrel was inserted into the inner surface of the extruded tube when the mandrel reached the advance limit,
Bulge deformation should occur very shortly at the beginning of the retreat of the mandrel.

In order to suppress the increase of the frictional force within the range where the bulge deformation does not occur or does not cause a problem in the dimensional accuracy, it is required at most about 1 second until the mandrel starts retreating after the stem reaches the forward limit position. That there is only room.

If the mandrel starts retreating while the stem is moving forward, the pressing force of the stem causes the material in the container (referred to as the rest portion) to pull out the mandrel while holding the mandrel at a high surface pressure. When the mandrel is retracted, the mandrel located on the inner surface of the extrusion pipe on the die exit side and the mandrel located immediately below the push-back portion are retracted without sufficient glass lubricant on the outer surface. Receiving a large amount of frictional force from the unstressed portion, causing seizure and rough skin, which is a factor of shortening the mandrel life.

The present invention has been made based on such knowledge,
Its purpose is to suppress the local diameter phenomena occurring at the rear end of the extruded tube, at the same time reduce the mandrel life,
It is still another object of the present invention to provide a hot extrusion pipe manufacturing method capable of preventing deterioration of the inner surface properties of the extrusion pipe and the quality of the pipe.

[Means for solving the problem]

The hot extrusion pipe manufacturing method according to the present invention is characterized in that a heated hollow billet is charged into a container provided with a die at an opening on one end side, and a mandrel having a predetermined diameter passed through the hollow billet and the die from the other end side. And a method in which a stem abutted on the hollow billet is moved toward the one end side, and the hollow billet is extruded from between a die and a mandrel to produce a tube. Stop the mandrel advancement before reaching, and after reaching the advance limit position of the stem 1.
The mandrel starts retreating within 0 seconds (except at the same time).

[Action]

In the hot extrusion pipe manufacturing method according to the present invention, since the mandrel starts retreating within 1.0 second after the stem reaches the advance limit position, the increase in the frictional force between the mandrel and the inner surface of the pipe causes the local diameter to increase. It is not so large as to induce a large phenomenon, and the mandrel can be retracted in a state in which the pressing force of the stem acting on the mandrel via the rest portion is released.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments.

FIG. 1 is a side sectional view showing a configuration of an extruder used for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a container, 2 denotes a die, 3 denotes a hollow billet, 4 denotes a mandrel, and 5 denotes a stem.

The container 1 is provided at its center with a housing 1c surrounded by a liner 1a fixed by a liner holder 1b, and the die 2 uses a die holder 6 and a die backer 6a so as to face an opening on one end side thereof. The mandrel 4 and the stem 5 held by the mandrel holder 7 facing the opening on the other end side of the housing portion 1c are arranged concentrically, and each is independently formed by a hydraulic or hydraulic cylinder (not shown). It is supported so that it can move back and forth.

Next, a case where a pipe is formed using such an extruder will be specifically described.

The hollow billet 3 has a core hole 3a formed by machining or press drilling in advance. After being heated to a predetermined temperature, a glass lubricant is applied to the inner and outer surfaces, and the glass disk 8, the hollow billet 3, and the dummy block are formed. 9 and individually inserted directly into the container 1c of the container 1 and then the mandrel 4 was inserted into them, or the dummy block 9, the hollow billet 3 and the glass disk 8 were first inserted into the mandrel 4 in this order. Later, in this state, the container 1
Charged in 1c.

Then, the mandrel 4 and the stem 5 for pressing the dummy block 9 from the rear end face are integrally moved to move forward (to the left in the drawing), and the hollow billet 3 is extruded through the annular space between the die 2 and the mandrel 4. To form an extruded tube P.

The stem 5 stops when it reaches the forward limit position by a position detector (not shown). At the same time when the stem 5 reaches the forward limit position, the mandrel 4 also stops moving forward. The timer starts counting at the same time when the stem 5 reaches the forward limit position, and starts retreating the mandrel 4 at the same time as a predetermined time within 1.0 second (but not zero) which has been set in advance. The mandrel 4 is extracted from the hollow billet 3 remaining in the container 1 and the container 1c of the container 1.

Note that, after issuing a signal for instructing retreat of the mandrel 4, a time until the power system (hydraulic or hydraulic) for applying a forward force to the mandrel 4 is switched to a circuit for retreating the mandrel 4 and the retreat is started. If the mandrel 4 cannot start retreating within a predetermined time, the stem 5
Before reaching the forward limit position, the mandrel 4 may be stopped from moving forward and the mandrel 4 may be retracted within 1.0 second (but not simultaneously) after the stem 5 reaches the forward limit position.

As a result, the stem 5 reaches its forward limit position and stops, and the stem 5 pressurizes the hollow billet 3 via the dummy block 9 and the hollow billet 3 associated therewith.
After the release (pressing) of the mandrel 4 by the
The mandrel 4 is retracted to avoid damage to the surface of the mandrel 4, and after the stem 5 reaches its forward limit position, the holding force of the mandrel 4 due to the thermal contraction of the rear end of the extruded tube P increases. At the beginning, immediately after the viscosity of the glass lubricant present between the rear end of the extruded tube P and the mandrel 4 starts to decrease due to its own temperature drop, 1.0
By retracting the mandrel 4 within seconds (but not zero), an increase in the frictional force generated between the mandrel 4 and the inner surface of the extruded pipe P is suppressed, and the occurrence of bulge deformation at the rear end of the extruded pipe is avoided. I can do it.

Within 1.0 seconds after the stem 5 has reached the forward limit position, the bulge deformation cannot be suppressed due to an increase in the frictional force between the pipe inner surface and the mandrel beyond this, and a local diameter phenomenon occurs. This is because

In order to avoid retreating the mandrel 4 at the same time when the stem 5 reaches the forward limit position, the pressure applied to the rest portion 3a by the stem 5 is not released, so that the rest portion in the container 1 removes the mandrel 4. This is because the mandrel 4 is in a state of being pressurized and tied, and it is impossible to suppress a decrease in the life of the mandrel 4.

The frictional force between the inner surface of the extruded pipe and the mandrel 4 that induces bulge deformation starts to increase at the same time when the stem 5 reaches the forward limit position. When the wall thickness / outer diameter ratio (hereinafter referred to as t / d) of the pipe is smaller, bulge deformation is more likely to occur. Therefore, when trying to obtain an extruded pipe having a smaller t / d,
It is desirable to set the mandrel retreat timing earlier (set the timer to a smaller value or advance the mandrel advance / stop timing).

However, it is needless to say that the mandrel 4 must not be retracted before the stem 5 reaches the forward limit position.

[Test Example 1] FIG. 2 shows the result of investigating the occurrence of the local diameter phenomena with respect to the time elapsed from when the stem reached the forward limit position to when the mandrel was retracted. In addition, the diameter enlargement rate shown in the following equation was adopted as an index expressing the local diameter increase phenomenon.

The position 800 mm from the rear end of the extruded tube is a position about 100 mm forward of the mandrel tip in the extrusion direction when the stem reaches the forward limit position, and is a place where the local diameter increase phenomenon does not occur.

 Extrusion conditions are as follows.

Hollow billet: Outer diameter 173mm Inner diameter 44mm Length 680mm Material SUS304 Heating temperature 1220 ℃ Extruded tube dimensions: Outer diameter 46.7mm Wall thickness 3.5mm Length 30m Extrusion ratio: Hollow billet cross section / extruded tube cross section = 46.3 Mandrel: 40mm diameter 750mm length Material SKD61 Chrome plating after heat treatment The time from reaching the stem advance limit position to the start of mandrel retreat (hereinafter referred to as the mandrel retreat start time) is -0.2s
ec to 2.0 sec (set by changing the mandrel forward / stop position and the timer set value).

In FIG. 2, the horizontal axis indicates the mandrel retreat start time (second), and the vertical axis indicates the diameter increase rate (%). Note that the negative time indicates a time before the time when the stem reaches the forward limit position (set to 0).

As is clear from this graph, it can be understood that the diameter enlargement rate rapidly deteriorates near the time when the mandrel retreat start time exceeds 1.0 second, and the occurrence of the local diameter increase phenomenon becomes remarkable.

For example, the minimum requirements are to satisfy the outer diameter tolerance of the hot-finish seamless steel pipe specified in JIS G3459 (stainless steel pipe for piping) and JIS G3446 (stainless steel pipe for machine structure). If this is the case, the mandrel retreat start time needs to be 1.0 second or less in order to make the diameter increasing ratio representing the above-described local diameter increasing phenomenon 1% or less.

[Test Example 2] Next, the mandrel retreat start time was set to −0.2, 0.1, 0.5, 1.0, 2.0 seconds under the same extrusion conditions as shown in Example 1, and 2
The mandrel life was investigated using a book mandrel. Table 1 shows the results.

The life is the total number of extrusions at the time when the surface of the mandrel becomes rough and seizure cannot be used again.

As is apparent from Table 1, if the mandrel is retracted 0.2 seconds (-0.2) before the forward movement of the stem during reaching the forward limit position, the life is greatly reduced. This means that the load applied to the mandrel at -0.2 seconds is extremely large. Conversely, after the stem reaches the forward limit,
If the mandrel is retracted after a second, no change in life is observed.

The reason that the life of the mandrel does not decrease even when a frictional force that causes bulge deformation to act on the extruded tube is that the bulge deformation occurs in a very short time immediately after the start of the retreat of the mandrel. This is due to the fact that the pressing area between the shaft and the mandrel is greatly reduced and the frictional force is reduced.

As described above, according to the embodiment, it is possible to suppress the local diameter increase phenomenon occurring at the rear end portion of the extruded tube, and at the same time, to prevent the life of the mandrel from being shortened and the deterioration of the inner surface quality of the extruded tube.

〔effect〕

As described above, according to the present invention, the local diameter phenomena at the rear end of the extruded tube are suppressed while the mandrel life is reduced,
Further, the present invention has excellent effects, for example, it is possible to prevent deterioration of the inner surface quality of the extruded tube.

[Brief description of the drawings]

FIG. 1 is a side sectional view of an extruder used in Example 1 of the present invention, FIG. 2 is a graph showing a relationship between a mandrel retreat start time (second) and a diameter increasing rate (%), and FIG. 3 is a conventional method. It is a side view of the extrusion apparatus used in. DESCRIPTION OF SYMBOLS 1 ... container, 2 ... dice, 3 ... hollow billet, 4 ... mandrel, 5 ... stem, 6 ... die holder, 7 ... mandrel holder, 8 ... glass disc,
9 ... Dummy block, 14 ... Mandrel, 14d ... Diameter

Claims (1)

(57) [Claims] 1. A heated hollow billet is charged into a container having a die disposed at an opening at one end, and a hollow mandrel having a predetermined diameter is passed through the hollow billet and the die from the other end, and is contacted with the hollow billet. In a method of moving the stem toward the one end side and extruding the hollow billet from between the die and the mandrel to produce a tube,
Simultaneously with or before the stem reaches the forward limit position, stop the mandrel from advancing, and start retreating the mandrel within 1.0 second (except at the same time) after reaching the forward limit position of the stem. A hot extrusion pipe making method.