JP5497559B2 - Extrusion dies - Google Patents

Description

  The present invention relates to an extrusion die used for extrusion of a hollow material.

  In the description of the present specification and claims, the direction in which the extruded material and the extruded material travel is referred to as downstream or downstream side, and the reverse direction is referred to as upstream or upstream side.

  In an extrusion die, a cemented carbide material such as cemented carbide or ceramic is used for a part of the die including the bearing unit in order to give wear resistance to the bearing unit (see Patent Documents 1 to 3).

  Patent Document 1 describes a die in which a ring-shaped die made of a super hard material is shrink-fitted in a recess of a die case made of tool steel. In Patent Document 2, a mandrel mandrel is formed of tool steel, a mandrel ring made of a super hard material is fitted on the mandrel, and a retaining nut is attached to the tip of the mandrel to fix the mandrel ring to the mandrel. The male type of the porthole die configured as described above is described. In addition, the die described in Patent Document 3 is obtained by shrink-fitting a mandrel ring with a sleeve softer than the mandrel interposed between the mandrel and the mandrel ring.

JP-A-6-15348 JP 2003-181525 A Japanese Examined Patent Publication No. 4-69009

  However, the type of die for shrink-fitting a super hard material has a problem that it takes time and effort for the preparation process and maintenance of extrusion.

  In addition, cemented carbide has a characteristic that its thermal expansion coefficient is smaller than that of tool steel, and it is weaker in tensile force than tool steel. For this reason, when a mandrel ring made of a super hard material is externally fitted to a mandrel made of tool steel, the mandrel expands during hot extrusion and may be damaged if the clamping force against the mandrel ring is too strong. On the other hand, if the tightening force is too weak, the mandrel ring is not firmly fixed, and there is a possibility that the piecing portion of the extruded material may be wavy or uneven. Further, the mandrel ring may come off the mandrel due to the flow of the extruded material.

  In order to solve such problems of the prior art, the present inventors, in Japanese Patent Application No. 2009-739, utilize the difference in thermal expansion coefficients of the mandrel and mandrel ring materials, Therefore, a mandrel was proposed in which the mandrel ring is detachable and the mandrel ring is fixed to the mandrel without gaps due to thermal expansion at the die temperature during extrusion.

  In general, the extrusion die is washed as maintenance after use. In the mandrel, when the die temperature is lowered after extrusion, the mandrel ring loosens and a gap is formed between the mandrel and the mating surfaces of the mandrel, that is, the outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring must be cleaned.

  However, it is necessary to disassemble the mandrel and remove the mandrel ring from the mandrel in order to clean the mating surfaces of both, and this is a laborious operation including assembly after cleaning.

  In view of the above-described technical background, the present invention aims to provide an extrusion die that can clean the outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring without disassembling the mandrel in the mandrel that can be attached to and detached from the mandrel. And

  That is, the present invention has the configurations described in [1] to [9] below.

[1] A mandrel for molding the inner surface of the extruded material has a mandrel and a mandrel ring fitted on the mandrel.
The mandrel ring is made of a material having a smaller coefficient of thermal expansion than the mandrel,
The outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring are in a state where the mandrel ring is externally fitted to the mandrel, there is a gap between them at room temperature, and at the die temperature during extrusion, at least in the axial direction of the mandrel It is set so that the gap disappears and both come into contact,
An extrusion die characterized in that a fluid passage is provided through the gap between the mandrel and the mandrel ring from the outside of the mandrel at normal temperature, feeding fluid into the gap and discharging the fed fluid to the outside.

[2] When the clearance (X _T2 ) between the mandrel ring and the mandrel ring at the die temperature (T ₂ ) at the time of extrusion is expressed by the following formula in the portion where the gap at the normal temperature (T ₁ ) is minimized, In the preceding paragraph 1, the outer diameter (A _T1 ) of the mandrel and the inner diameter (B _T1 ) of the mandrel ring at (T ₁ ) are set so that the tightening allowance (X _T2 ) is 0 to 0.3% The extrusion die described.
X _T2 = {[A _T1 × (T ₂ −T ₁ ) × α ₁ + A _T1 ] / [B _T1 × (T ₂ −T ₁ ) × α ₂ + B _T1 ] −1} × 100
Where α ₁ : coefficient of thermal expansion of the material constituting the mandrel
α ₂ : coefficient of thermal expansion of the material constituting the base material of the mandrel ring (α ₁ > α ₂ )
T ₁ : normal temperature
T ₂ : Die temperature during extrusion (> T ₁ )
A _T1 : Outer diameter of the mandrel at normal temperature (T ₁ )
B _T1 : Inner diameter of mandrel ring at normal temperature (T ₁ ) (> A _T1 )

  [3] In the preceding item 1 or 2, a bolt portion having a diameter smaller than that of the mandrel is formed integrally with the mandrel at the tip of the mandrel, and a mandrel ring is restrained in the axial direction by screwing a nut into the bolt portion. Extrusion dies.

  [4] The extrusion die as recited in the aforementioned Item 3, wherein the fluid passage includes a bent hole that opens to a downstream end face of the bolt portion and opens to the outer peripheral surface of the mandrel through the bolt portion in the axial direction.

  [5] The extrusion die according to item 3 or 4, wherein the fluid passage includes a gap between the bolt portion and the nut.

  [6] The extrusion die according to [5], wherein the fluid gap is a groove provided in at least one of the outer peripheral surface of the bolt portion and the inner peripheral surface of the nut.

  [7] The extrusion die according to any one of [3] to [6], wherein the fluid passage includes a groove reaching the clearance between the mandrel ring and the mandrel ring from the outer peripheral edge on the upstream end surface of the nut.

  [8] The extrusion die according to any one of items 1 to 7, wherein a groove is provided along the axial direction on the outer peripheral surface of the mandrel.

  [9] The extrusion die according to any one of the preceding items 1 to 8, by sending a fluid from the outside through a fluid passage to the gap between the mandrel and the mandrel ring at normal temperature, A method for cleaning an extrusion die, comprising cleaning an inner peripheral surface of a mandrel ring.

  According to the invention described in [1] above, in the mandrel having the mandrel ring fitted on the mandrel, when the die reaches the temperature at the time of extrusion, there is a gap between the mandrel ring due to the difference in thermal expansion coefficient between the mandrel and the mandrel ring. The mandrel ring disappears and is fastened to the mandrel by being tightened by the radial force that the mandrel tries to expand. Thus, when extrusion is performed with the mandrel ring fixed to the mandrel, uneven thickness of the extruded material is suppressed, and a high-quality extruded material can be produced. In addition, since there is a gap between the mandrel ring and the mandrel ring at room temperature, the mandrel ring can be easily attached to and detached from the mandrel, and maintenance such as replacement of the mandrel ring can be easily performed. In addition, at normal temperature, the fluid is fed from the outside to the gap between the mandrel and the mandrel ring through the fluid passage to the mandrel, and the fluid is circulated through the gap by discharging the fed fluid. The outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring can be cleaned. Since the fluid flow into the gap is performed with the mandrel assembled, there is no need to disassemble the mandrel in order to clean the outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring. Maintenance can be performed.

According to the invention described in [2] above, since the tightening allowance (X _T2 ) between the mandrel ring and the mandrel ring at the die temperature at the time of extrusion is set in an appropriate range, a stable fixed state is obtained, In addition, breakage of the mandrel ring can be avoided.

According to the invention described in [3] above, since the mandrel ring is also fixed in the direction of the extrusion axis by the nut, the mandrel ring is prevented from falling off, and a more stable fixed state is obtained. Further, by suppressing the deviation of the extrusion axis by the nut, than when secured with only the tightening due to the expansion force of the mandrel, it is possible to reduce interference to (X _T2), interference of the (X _T2) The risk of breakage of the mandrel ring due to the increase can be avoided.

  According to the invention described in [4] above, fluid can be sent from the downstream end face of the mandrel into the gap through the bent hole, or discharged from the gap to the downstream end face of the mandrel through the bent hole.

  According to the invention described in [5] above, fluid is fed into the gap from the downstream end surface of the mandrel through the gap between the bolt part and the nut, or downstream of the mandrel through the gap between the bolt part and the nut. The fluid can be discharged to the side end face.

  According to the invention described in [6] above, since the cross-sectional area of the fluid passage is enlarged in the gap between the bolt portion and the nut, the amount of fluid flowing through the gap can be increased.

  According to the invention described in [7] above, the fluid passage is formed between the nut and the mandrel ring by the groove provided on the upstream end surface of the nut, and fluid is passed through the fluid passage from the side surface of the mandrel to the gap. The fluid can be discharged to the side surface of the mandrel from the gap through the fluid passage.

  According to the invention described in [8] above, since the distance between the outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring is increased by the groove provided on the outer peripheral surface of the mandrel, the amount of fluid flow is increased. be able to. Thereby, the distribution | circulation amount of the fluid distribute | circulated to a clearance gap can be increased.

  According to the invention described in [9] above, the fluid is sent from the outside through the fluid passage to the gap between the mandrel and the mandrel ring with the mandrel assembled, and the fluid is circulated through the gap. The outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring can be cleaned. For this reason, since it is not necessary to disassemble the mandrel for cleaning, die maintenance can be performed efficiently in a short time.

It is a disassembled perspective view which shows the porthole die provided with the male type | mold which is one Embodiment of this invention. It is sectional drawing which shows the assembly | attachment state of the porthole die of FIG. It is sectional drawing which shows the decomposition | disassembly state of the mandrel in the porthole of FIG. It is a figure which shows the relationship between temperature, the outer diameter of a mandrel, and the inner diameter of a mandrel ring. It is sectional drawing which shows the state at the time of normal temperature of the mandrel of FIG. It is sectional drawing which shows the state at the time of the die temperature at the time of extrusion of the mandrel of FIG. FIG. 4 is a cross-sectional view showing another state of the mandrel of FIG. 3 at room temperature. FIG. 4 is a cross-sectional view at normal temperature illustrating the restraint of the mandrel ring by a nut in the mandrel of FIG. 3. It is sectional drawing which shows the state in the die temperature at the time of extrusion of FIG. 6A. It is sectional drawing which shows the 1st channel | path for fluids. It is sectional drawing which shows the 2nd channel | path for fluids. It is sectional drawing which shows the 3rd channel | path for fluids. It is sectional drawing which shows the 4th channel | path for fluids.

  The port hole die (10) shown in FIGS. 1 and 2 is a combination of a female die (11) for molding the outer peripheral surface of the hollow extruded material (1) and a male die (20) for molding the inner peripheral surface. The male mold (20) is an embodiment of the extrusion die of the present invention.

  The female mold (11) has a bearing hole (12) in the center, a relief hole (13) is formed on the downstream side of the bearing hole (12), and a recess (14) for the welding chamber is formed on the upstream side. Is formed.

  The male mold (20) has a plurality of port holes (22) penetrating in the extrusion direction around the mandrel (30), with a mandrel (30) protruding downstream from the center of the die base (21). ing. Between adjacent port holes (22) and (22), leg portions (23) for supporting the mandrel (30) protruding downstream are supported at the base end portions.

  As shown in FIG. 3, in the mandrel (30), a mandrel (32) having a small diameter is integrally formed on the distal end side of a base (31) that continues integrally from the base portion (21) of the die, and the base (31 ) And the mandrel (32), a step (33) is formed between them. At the tip (downstream side) of the mandrel (32), a bolt part (34) having a smaller diameter than the mandrel (32) and having a helical thread groove formed on the outer peripheral surface is formed integrally with the mandrel (32). ing. The base (31), the mandrel (32) and the bolt part (34) are formed coaxially. The mandrel ring (35) is an annular body in which a bearing portion (36) for forming the inner peripheral surface of the extruded material (1) is projected on the outer peripheral surface. The nut (37) has a screw hole (38) to be screwed into the screw groove of the bolt part (34). Thus, the mandrel ring (35) is fitted onto the mandrel (32) and brought into contact with the stepped portion (33), and the screw hole (38) of the nut (37) is screwed into the bolt portion (34). The mandrel ring (35) is sandwiched between the step portion (33) and the nut (37), and is disposed at a predetermined position in the extrusion axis direction. The material properties and dimensions of the mandrel (32) and mandrel ring (35) will be described in detail later.

  When the female mold (11) and the male mold (20) are combined, the bearing portion (36) of the mandrel ring (35) of the male mold (20) is fitted into the bearing hole (12) of the female mold (11). An annular molding gap (not shown) is formed between them, and a part of the recess (14) for the welding chamber of the female mold (11) is blocked by the end face of the male mold (20), and the port hole ( 22) A welding chamber that communicates with is formed. Then, the extruded materials that have flowed into the respective port holes (22) merge in the welding chamber and are extruded from the forming gap as an extruded material (1) having a hollow portion (2).

  Further, the mandrel (30) is provided with a fluid passage through which a fluid flows so as to clean the mating surfaces without disassembling the mandrel (32) and the mandrel ring (35). This fluid passage will be described later.

[Mandrel shape]
The mandrel of the present invention has a gap between the mandrel ring and the mandrel at room temperature, and there is no gap at least in the axial direction of the mandrel at the die temperature during extrusion. As long as it is set to do, the shape of the outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring can be arbitrarily set. That is, the conditions regarding the shape of the mandrel in the present invention are the following (1) and (2).
(1) There is a gap that allows the mandrel ring to be fitted onto the mandrel at room temperature. (2) At the die temperature during extrusion, the mandrel ring comes into contact with the mandrel ring at least partly in the axial direction. The “die temperature during extrusion” in the present invention refers to the temperature at which the mandrel (32) and the mandrel ring (35) reach a predetermined temperature during high-temperature extrusion, and at that time.

3 and 5A are cross-sectional views of the main part of the mandrel (30) of the present embodiment at normal temperature (T ₁ ). This mandrel (30) is a mandrel constituting a part of the male die (20) of the extrusion die (10) shown in FIGS.

The mandrel (30) has an outer peripheral surface (32a) of the mandrel (32) and an inner peripheral surface (35a) of the mandrel ring (35) formed in parallel to the axis of the mandrel (30), and the outer diameter of the mandrel (32). (A _T1 ) and the inner diameter (B _T1 ) of the mandrel ring (35) are constant in the axial direction. When the mandrel ring (35) is externally fitted to the mandrel (32), a certain gap (S ₁ ) parallel to the axis exists between the two.

In the present invention, “there is a gap (S ₁ )” between the mandrel (32) and the mandrel ring (35) means that there is no contact between the mandrel (32) and the mandrel ring (35). And that the outer diameter (A _T1 ) of the mandrel at normal temperature (T ₁ ) and the inner diameter (B _T1 ) of the mandrel ring satisfy the relationship “B _T1 > A _T1 ”, and there is a clearance between them. means. Also, room temperature _{(T 1)} the difference between the outer diameter _{(A T1)} of the inner diameter of the magnitude mandrel ring gap _{(S 1)} when the _{(35) (B T1)} and the mandrel ₍₃₂₎ (B _{T1 -A} T1 ).

5A shows a state in which the distance between the inner peripheral surface (35a) of the mandrel ring (35) and the outer peripheral surface (32a) of the mandrel (32) is constant in the circumferential direction. At normal temperature (T ₁ ), the mandrel ring (35) and the mandrel (32) are not axially aligned, so the distance between them is not always constant in the circumferential direction. For example, when assembly is performed in a posture where the axis of the mandrel (30) is horizontal, as shown in FIG. 5C, the upper part of the inner peripheral surface (35a) of the mandrel ring (35) is the outer peripheral surface of the mandrel (32) ( The distance between the two in contact with the upper part of 32a) is zero, the distance between the two increases as it goes downward along the circumferential direction, and the distance becomes maximum at the lower part. In addition, since the mandrel ring (35) is in a state of being temporarily fastened by being tightened by the nut (37), there is a case where the two are not in contact with each other but the distance between them is uneven. . Accordingly, in the present invention, “there is a gap” does not mean the presence or absence of contact between the mandrel ring (35) and the mandrel (32), but the outer diameter (A) of the mandrel (32) at room temperature (T ₁ ). _T1 ) and the inner diameter (B _T1 ) of the mandrel ring (35) satisfy the relationship “B _T1 > A _T1 ”, which means that there is a clearance between them. In addition, in the case where the mandrel ring (35) and the mandrel (32) are in any of the above-described positional relationships, the size of the gap (S ₁ ) in the present invention is the same as the inner diameter (B _T1 ) of the mandrel ring (35). It is represented by a difference (B _T1 −A _T1 ) from the outer diameter (A _T1 ) of the mandrel.

Further, the present invention does not require that the outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring be parallel to the axis of the mandrel, and either one or both of the outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring are The present invention also includes a mandrel formed with a tapered surface inclined with respect to the axis, and a mandrel with a part of the axial direction formed with a tapered surface. Accordingly, the size of the gap between the two may change in the axial direction, and the gap (S ₁ ) in the present invention means the inner diameter (B _T1 ) of the mandrel ring and the outer diameter (A _T1 ) of the mandrel in the axial direction. Is a gap in a portion where the difference (B _T1 −A _T1 ) is minimum.

When assembling the mandrel (32) and the mandrel ring (35) at room temperature (T ₁ ), the mandrel (30) has a gap (S ₁ ) between the mandrel ring (35) and the mandrel ring (35). It is easy to fit on 32). Further, when the nut (37) is attached and tightened, the mandrel ring (32) generates a tensile force in the extrusion direction, and the mandrel ring (35) generates a compression force in the extrusion direction.

[Materials for mandrels]
The material constituting the mandrel ring (35) is excellent in wear resistance, and the thermal expansion coefficient (α ₂ ) thereof and the thermal expansion coefficient (α ₁ ) of the material constituting the mandrel (32) are α ₁ > α _2. As long as the above relationship is satisfied, there is no particular limitation. In the present embodiment, the portion including the mandrel (32) (hereinafter simply referred to as “mandrel”) is formed of tool steel, whereas the mandrel ring (35) is more resistant to wear than the tool steel. It is made of a super hard material. Examples of the cemented carbide material include cemented carbide alloys such as WC-Co, high-speed tool steel, powdered high-speed tool steel, and ceramics. Table 1 shows an example of these superhard materials and tool steels and their thermal expansion coefficients. In addition, since the thermal expansion coefficient of the base material of the mandrel (32) and the mandrel ring (35) only needs to satisfy the relationship of α ₁ > α ₂ , the exemplified materials are not limited to the uses described in Table 1. For example, a case where a mandrel ring of cemented carbide or ceramics is combined with a mandrel of powder high-speed tool steel is also included in the present invention.

  In the present invention, by using a material having a smaller thermal expansion coefficient than the mandrel as the mandrel ring, the expansion rate of the mandrel ring due to processing heat generated during extrusion is reduced, so that the extruded material can have a more stable size. it can. In other words, in the mandrel with a mandrel ring with a small thermal expansion coefficient combined with a mandrel (tool steel), the outer diameter difference between the unextruded and the maximum processing heat generation is larger than the outer diameter difference in the mandrel manufactured with only tool steel. Since it becomes smaller, the thickness of the extruded material is stabilized. And if the dimension of an extrusion material is stable, the product quality after post-processing will also become stable. For example, when drawing is performed after extrusion, if the extruded material has no uneven thickness and the thickness is constant, the thickness of the drawn material is also constant. In addition, if the thickness of the extruded material is constant, the length of drawing is also constant. Further, since the material of the mandrel ring has high wear resistance, the generation of wear powder is small, and the mixing of the wear powder into the extruded material is also reduced. If the die wear powder, which is a foreign substance, is mixed in the extruded material, the quality of the extruded material is deteriorated and it becomes a surface defect of the drawn material. If the amount of wear powder mixed into the extruded material is small, surface defects generated in the drawn material are also reduced. From these facts, the extruded material produced using the extrusion die of the present invention is excellent not only in quality as an extruded material but also in quality as a post-processing material.

[Fixing in the radial direction of the mandrel ring]
FIG. 4 shows changes in the outer diameter (A) of the mandrel (32) and the inner diameter (B) of the mandrel ring (35) with respect to temperature (T).

Both the mandrel (32) and the mandrel ring (35) expand in size due to thermal expansion (A _T , B _T ). As shown in this figure, at normal temperature (T ₁ ), the inner diameter (B _T1 ) of the mandrel ring is larger than the outer diameter (A _T1 ) of the mandrel, and there is a gap of B _T1 -A _T1 as an actual size. When the temperature (T) increases, the mandrel (32) and the mandrel ring (35) increase in diameter according to their respective thermal expansion coefficients (α ₁ ) (α ₂ ). T _2> outer diameter _{(A T2)} and the mandrel inside diameter of the ring (35) of the mandrel (32) at any temperature that satisfies _{T 1 (T 2) (B} T2) comprises the following formula (I) and (II ) Expression.

A _T2 = A _T1 × (T ₂ −T ₁ ) × α ₁ + A _T1 (I)
B _T2 = B _T1 × (T ₂ −T ₁ ) × α ₂ + B _T1 (II)
Where α ₁ : coefficient of thermal expansion of the material constituting the mandrel
α ₂ : Thermal expansion coefficient of the material constituting the base material of the mandrel ring
T ₁ : normal temperature
T ₂ : High temperature (> T ₁ )
A _T1 : Outer diameter of the mandrel at normal temperature (T ₁ )
B _T1 : Inner diameter of mandrel ring at normal temperature (T ₁ ) (> A _T1 )

As shown in FIG. 5A, if the inner diameter (B _T1 ) of the mandrel ring (35) is made larger than the outer diameter (A _T1 ) of the mandrel (32) at room temperature (T ₁ ), the mandrel is caused by the difference in both dimensions. Since there is a gap (S ₁ ) between the outer peripheral surface of (32) and the inner peripheral surface of the mandrel ring (35), it can be easily fitted.

As shown in FIG. 5B, when the die temperature rises, the outer diameter expansion amount of the mandrel (32) exceeds the inner diameter expansion amount of the mandrel ring (35), so that the gap (S ₁ ) decreases. When the gap (S ₁ ) disappears, the mandrel ring (35) is fixed to the mandrel (32).

Since the thermal expansion coefficient is α ₁ > α ₂ , as shown in FIG. 4, the outer diameter (A _TZ ) of the mandrel (32) and the mandrel ring (35) at the temperature (T _Z ) as the temperature rises. When the inner diameter (B _TZ ) becomes equal, the gap (S ₁ ) disappears, and the mandrel ring (35) does not come off the mandrel (32) and is fixed. When the temperature further increases, the outer diameter (A _T ) of the mandrel (32) exceeds the inner diameter (B _T ) of the mandrel ring (35). In the temperature range (T> T _Z ) where the outer diameter (A _T ) of the mandrel (32) exceeds the inner diameter (B _T ) of the mandrel ring (35), the expansion force of the mandrel (32) causes the mandrel ring (35) to move inward. Since it acts as a tightening force and a circumferential tensile force is applied to the mandrel ring (35), it is more difficult to come off the mandrel (32) and it is firmly fixed.

[Fixing allowance for mandrel and mandrel ring]
At the time of extrusion, the die is heated to a predetermined temperature and becomes higher than normal temperature (T ₁ ). Therefore, as shown in FIGS. 4 and 5B, at the die temperature (T ₂ ) during extrusion, is the outer diameter (A _T2 ) of the mandrel (32) equal to the inner diameter (B _T2 ) of the mandrel ring (35)? The outer diameter (A _T1 ) of the mandrel (32) at normal temperature (T ₁ ) and the mandrel ring so that the outer diameter (A _T2 ) of the mandrel (32) exceeds the inner diameter (B _T2 ) of the mandrel ring (35). If the inner diameter (B _T1 ) of (35) is set, extrusion can be performed with the mandrel ring (35) fixed to the mandrel (32). When extrusion is performed with the mandrel ring (35) fixed to the mandrel (32), uneven thickness of the extruded material (1) is suppressed, and a high-quality extruded material (1) can be produced. However, if the expansion force of the mandrel (32) becomes excessive and exceeds the limit of the tensile force of the mandrel ring (35), the mandrel ring (35) will be damaged, so the thermal expansion coefficient (α ₁ , α ₂ ) of the material Considering the die temperature (T ₂ ) at the time of extrusion, the outer diameter (A _T1 ) of the mandrel (32) at normal temperature (T ₁ ) and the mandrel ring (35) so as to generate an appropriate tensile force at high temperatures The inner diameter (B _T1 ) is set.

Here, the tightness and the looseness of the mandrel (32) and the mandrel ring (35) at an arbitrary temperature (T) are expressed as the outer diameter (A _T ) of the mandrel (32) and the inner diameter (B of the mandrel ring (35)). based on the ratio of _T), it is defined as the following formula (III) interference of the _{(X T).} When A _T <B _T , that is, when there is a gap between the two, X _T <0, indicating that the looseness increases as the tightening allowance (X _T ) value decreases. On the other hand, when A _T > B _T , that is, there is no gap between the two and the mandrel ring (35) is clamped to the mandrel (32) from the inside, X _T > 0 and the value of the tightening allowance (X _T ) The larger the is, the greater the tightening force. A _T = B _T (X _T = 0) is a state in which there is no gap between the two but the tightening force is not effective.
X _T (%) = (A _T / B _T −1) × 100 (III)

Furthermore, according to the formula (III), the allowance (X _T1 ) (X _T2 ) between the mandrel (32) and the mandrel ring (35) at normal temperature (T ₁ ) and high temperature (T ₂ ) (die temperature during extrusion) ) Are represented by the formulas (IV) and (V), respectively.
X _T1 (%) = (A _T1 / B _T1 −1) × 100 (IV)
X _T2 (%) = (A _T2 / B _T2 −1) × 100
= {[A _T1 × (T ₂ −T ₁ ) × α ₁ + A _T1 ] / [B _T1 × (T ₂ −T ₁ ) × α ₂ + B _T1 ] −1} × 100 (V)

Since the mandrel (32) and the mandrel ring (35) are manufactured so that A _T1 <B _T1 at room temperature (T ₁ ), X _T1 <0, and the tightening allowance (X _T1 ) has a gap between them. Shows a loose state. On the other hand, since there is no gap between the _two at the die temperature (T ₂ ) at the time of extrusion and A _T2 ≧ B _T2 , the tightening allowance (X _T2 ) is 0 or a positive value, and the tightening force is effective. Show. Further, X _T2 <0 indicates a state where the mandrel ring (35) is not fixed to the mandrel (32) due to the looseness even at the die temperature (T ₂ ) at the time of extrusion.

The greater the tightening allowance (X _T2 ), the stronger the tightening force becomes, and the mandrel ring (35) is firmly fixed and is difficult to come off. There is a fear. Further, during extrusion, a force in the extrusion direction is also applied due to the material flow. Taking these into account, the fastening allowance (X _T2 ) is preferably 0.3% or less. As long as the tightening allowance (X _T2 ) is 0 or a positive value, the lower limit value is not specified, but 0.05% or more is preferable in order to fix it securely. A particularly preferred interference (X _T2 ) is 0.15 to 0.25%. The appropriate range of the tightening allowance (X _T2 ) varies depending on the material of the mandrel (32) and the mandrel ring (35), the thickness of the mandrel ring (35), and the like.

Accordingly, the tightening allowance (X _T2 ) at the time of extrusion (T ₂ ) is 0 at the portion where the gap (S ₁ ) is minimum at normal temperature (T ₁ ) and the tightening force is maximum at the die temperature (T ₂ ) during extrusion. What is necessary is just to set the outer diameter (A _T1 ) of the mandrel (32) and the inner diameter (B _T1 ) of the mandrel ring (35) so as to be ˜0.3%. The tightening allowance in the other portions is a value corresponding to the size of the gap (S ₁ ) at normal temperature (T ₁ ).

Further, the tightening allowance (X _T1 ) at normal temperature (T ₁ ) is not limited as long as it is a negative value. Since the outer diameter (A _T1 ) of the mandrel (32) is smaller than the inner diameter (B _T1 ) of the mandrel ring (35), these assembling operations are easy. When the extrusion die is finished and cooled to room temperature (T ₁ ), it will come back to the tightening allowance (X _T1 ) at room temperature (T ₁ ) and loosen, so the mandrel ring (35) can be removed from the mandrel (32). Can be removed. Accordingly, maintenance such as removal of a worn mandrel ring and installation of a new mandrel ring can be easily performed.

[Fixing of the mandrel ring in the extrusion axis direction]
In the mandrel (30) of the above embodiment, a nut (37) having a diameter larger than the inner diameter of the mandrel ring (35) is detachably attached to the tip of the mandrel (32). The mandrel ring (35) at high temperature (T ₂ ) is clamped and fixed in the radial direction by the mandrel (32), but a downstream force is applied by the material flow during extrusion. Therefore, in the mandrel (30), the nut (37) is attached to reliably prevent the mandrel ring (35) from falling out and to improve the fixing stability. Also, by attaching a nut (37) and applying a restraining force in the direction of the extrusion axis, the tightening allowance (X _T2 ) can be made smaller than when fixing only by tightening with the expansion force of the mandrel (32). The risk of breakage of the mandrel ring (35) due to an increase in the tightening allowance (X _T2 ) can be avoided.

Further, in the mandrel (30) to which the nut (37) is attached, the dimensions in the direction of the extrusion axis of the mandrel (32) and the mandrel ring (35) are also different at normal temperature (T ₁ ), and high temperature (T ₂ ). It is sometimes preferred that the nut (37) contacts the mandrel ring (35) to ensure that the mandrel ring (35) is restrained by the nut (37).

5A and 5B show a preferred dimensional relationship in the direction of the extrusion axis of the mandrel (32) and the mandrel ring (35). At a normal temperature (T ₁ ) shown in FIG. 5A, the length of the mandrel (32) is shorter than the length of the mandrel ring (35), and the nut (37) screwed into the bolt part (34) is the mandrel ring (35 ) Is tightened. The mandrel ring (35) is constrained in the direction of the extrusion axis by applying a tensile force according to the gap (S ₂ ) between the mandrel (32) and the nut (37) to the mandrel (32). FIG. 5B is a diagram showing a state at the time of the die temperature (T ₂ ) at the time of extrusion in FIG. 5A, and shows a state where the mandrel (32) and the mandrel ring (35) are expanded. Since the mandrel (32) coefficient of thermal expansion (alpha ₁₎ and mandrel ring (35) coefficient of thermal expansion) (alpha ₂₎ have a relationship of α _1> α _2, the size expansion of the mandrel (32) is mandrel ring It exceeds the size expansion amount of (35), and the gap (S ₂ ) changes in the decreasing direction. By reducing this gap (S ₂ ), the tensile force applied to the mandrel (32) is reduced and the clamping force on the mandrel ring (35) is reduced, but as long as there is a gap (S ₂ ), the nut (37) Therefore, the mandrel ring (35) does not shift in the direction of the extrusion axis. That is, the mandrel ring (35) is constrained and fixed in both the radial direction and the extrusion axis direction. As described above, the restraint in the direction of the extrusion shaft is added, so that the fixing stability of the mandrel ring (35) can be maintained even if the above-described radial interference (X _T2 ) is reduced. As a result, the tensile force in the circumferential direction applied to the mandrel ring (35) can be reduced, and damage due to an increase in the tightening allowance (X _T2 ) can be avoided.

In contrast, in FIG. 6A, the lengths of the mandrel (32) and the mandrel ring (35) are equal at room temperature (T ₁ ), and there is no gap (S ₂ ) between the mandrel (32) and the nut (37). Indicates the state. FIG. 6B is a diagram showing a state at the die temperature (T ₂ ) at the time of extrusion shown in FIG. 6A. The mandrel ring (35) and the nut become longer than the mandrel ring (35) due to thermal expansion. There is a gap (S ₃ ) between (37) and (37). In such a state, the mandrel ring (35) is not restrained by the nut (37), and the fixing stability in the direction of the extrusion shaft is lowered. Further, in order to reliably prevent the mandrel ring (35) from shifting in such a state, it is necessary to sufficiently increase the radial tightening allowance (X _T2 ), and thus the mandrel ring (35) may be damaged. The sex also increases.

5A and 5B show the case where the mandrel (32) is shorter than the mandrel ring (35) at room temperature (T ₁ ), but the difference is small and the length is reversed at the die temperature (T ₂ ) during extrusion. If the mandrel (32) is longer than the mandrel ring (35), the nut (37) cannot be suppressed as shown in FIG. 6B.

Thus, to act nut (37) by clamping force to the mandrel ring (35) at a die temperature during the extrusion (T _2), ambient temperature (T ₁₎ when the mandrel (32) and the mandrel ring (35) It is preferable to set the dimension in the direction of the extrusion axis. With increasing temperature of the die, the nut (37) the mandrel ring (35) is so changed in the loosening direction, in order to cock reliably die temperature (T ₂₎ during the tightening force by the nut (37) at the time of extrusion The nut (37) needs to tighten the mandrel ring (35) at least at normal temperature (T ₁ ). At this time, the axial dimension is mandrel (32) <mandrel ring (35), and there is a gap (S ₂ ) between mandrel (32) and nut (37) (see FIG. 5A).

[Fluid passage]
As described above, the mandrel of the present invention has a gap (S ₁ ) between the mandrel and the mandrel ring at room temperature (T ₁ ). Then, having a fluid passage leading into the gap (S ₁₎ from outside of the mandrel, the fluid introduced liquid or gas from the outside through the fluid passage fed into the gap (S _1), the fluid passage fluid was pumped By discharging to the outside through the fluid, the fluid can be circulated in the gap (S ₁ ). Since the fluid flow to the gap by the fluid passage can be performed without disassembling the mandrel, the outer peripheral surface of the mandrel, which is the mating surface of the mandrel and the mandrel, and the inner peripheral surface of the mandrel ring are cleaned without disassembling the mandrel. be able to. For example, die washing after extrusion, in which the extruded material is dissolved with caustic liquid, the caustic liquid is removed by water washing, and further dried with air, can be performed in an assembled state without disassembling the mandrel.

  The fluid passage only needs to feed fluid from the outside into the gap between the mandrel and the mandrel ring, and discharge the fluid that has passed through the gap to the outside. A slight gap generated on the surface can be used as a fluid passage.

Hereinafter, various fluid passages will be described with reference to FIGS. The mandrels (30), (50), (60), and (70) illustrated in these figures have a longer mandrel ring (35) than the mandrel (32) in the axial direction at room temperature (T ₁ ), and the mandrel ( There is a gap (S ₂ ) between 32) and the nut (37). The fluid passage is provided in any one of the mandrel (32), the bolt part (34) integrally formed with the mandrel (32), or the nut (37) screwed into the bolt part (34). .

(First fluid passage)
FIG. 7 is an enlarged view of a main part of FIG. 5A.

In the mandrel (30), the fluid passage includes a bent hole (40) provided in the bolt part (34) and the mandrel (32), and a screwing gap between the bolt part (34) and the nut (37). (45) and a gap (S ₂ ) between the mandrel (32) and the nut (37).

One end of the bent hole (40) opens in the center of the downstream end face of the bolt part (34), and the first hole (41) penetrates the bolt part (34) and the mandrel (32) along the axis, 32) is bifurcated in the radial direction at the base end of the second hole (42) (42), and the tip of the second hole (42) (42) communicates with the outer peripheral surface (32a) of the mandrel (32). Yes. (43) is a downstream opening of the bending hole (40), and (44) is two communication ports to the gap (S ₁ ) between the mandrel (32) and the mandrel ring (35). On the other hand, the screwing gap (45) is a passage that directly uses a slight gap that is inevitably generated by screwing the bolt part (34) and the nut (37), and is downstream of the mandrel (30). An annular downstream opening (46) is formed at the end face. Also, the screwed gap (45) communicates with the gap (S ₂₎ between the upstream end and the mandrel (32) and nut (37), the mandrel through the gap a (S ₂₎ (32 ) and leads to a gap between the mandrel ring ₍₃₅₎ (S 1). (47) is a communication port to the gap (S ₂ ) of the screw gap (45).

In the mandrel (30), when the fluid (F) is fed from the downstream opening (43) of the bending hole (40), the fluid (F) travels upstream through the first hole (41) and the two second It branches into two holes (42), exits from the communication port (44) into the gap (S ₁ ), and diverts to both sides in the circumferential direction. The diverted fluid (F) also travels downstream while flowing in the gap (S ₁ ) in the circumferential direction, and the gap (S ₁ ) is filled with the fluid (F). Then, the fluid (F) proceeds to the clearance (S ₂ ) between the mandrel (32) and the nut (37), and further enters the screwing clearance (45) from the communication port (47) and proceeds to the downstream side. It is discharged from the side opening (46).

The bent hole (40) is branched into two second holes (42), but if there is at least one second radial hole (42), the fluid can be fed into the gap (S ₁ ). Therefore, the number of the second holes (42) can be arbitrarily set as long as the strength of the mandrel (32) can be secured. Also, the position of the gap (S ₁₎ communication port to (44) is not limited to the proximal end of the mandrel (32) (upstream), circulating the gap (S ₁₎ in uniform fluid (F) is The base end of the mandrel (32) that is the position farthest from the discharge passage (in this example, the screwing gap (45)) is preferable. Furthermore, radial holes may be provided at a plurality of locations in the axial direction.

5A and 7 showing the mandrel (30) at normal temperature (T ₁ ), the size of the screwing gap (45) is enlarged to illustrate the screwing gap (45) as a fluid passage. It is illustrated with emphasis. In contrast to FIG. 5B which shows the mandrel (30) at the time of extrusion (T ₂ ), it does not indicate the difference in the tightening degree of the nut (37) due to the temperature difference, and does not limit the tightening condition. Of course, the present invention does not limit the coefficient of thermal expansion or the difference between the material of the bolt part (34) and the material of the nut (37).

  In addition, in the mating surface of the bolt part (34) and the nut (37), one or more along the axial direction on one or both of the outer peripheral surface of the bolt part (34) and the inner peripheral surface of the nut (37) It is also possible to increase the cross-sectional area of the passage by providing a groove (see a fourth fluid passage described later and FIG. 10). If the passage cross-sectional area is enlarged, the discharge of the fluid is promoted and can be discharged from a specific location in the circumferential direction. Further, even when fluid circulation is difficult due to the absence or narrowness of the screwing gap, the fluid can be discharged from the downstream end face of the mandrel.

(Second fluid passage)
In the mandrel (50) shown in FIG. 8, the fluid passage includes a bent hole (40) provided in the bolt portion (34) and the mandrel (32), and a groove provided on the upstream end face of the nut (37) ( 51a) (51b).

The bent hole (40) is the same as the bent hole (40) in the mandrel (30) of FIG. On the upstream end face of the nut (37), that is, the face for suppressing the mandrel ring (35), two radial grooves (51a) (51b) are provided from the outer peripheral edge to the inner peripheral edge. These grooves (51a) and (51b) are holes whose upper surfaces of the grooves (51a) and (51b) are closed by the downstream end face of the mandrel ring (35) and both ends in the radial direction are opened by assembling the mandrels (50) ( 52a) (52b). (53a) and (53b) are openings on the outer peripheral side of the holes (52a) and (52b), and (54a) and (54b) are communication ports that lead to the gap (S ₁ ).

In the mandrel (50), when the fluid (F) is fed from the downstream opening (43) of the bending hole (40), the fluid (F) travels in the upstream direction through the first hole (41). It branches into two holes (42), exits from the communication port (44) into the gap (S ₁ ), and diverts to both sides in the circumferential direction. Then, the diverted fluid (F) flows to the downstream side while flowing in the gap (S ₁ ) in the circumferential direction, and directly flows into the communication ports (54a) and (54b) of the holes (52a) and (52a). flows into the communicating hole of the via _{(S 2) (54a) (} 54b), and is discharged from the hole (52a) outer peripheral side opening through (52b) (53a) (53b ).

The grooves (51a) and (51b) are formed so as to reach the inner peripheral edge from the outer peripheral edge of the nut (37), but in the gap (S ₁ ) between the mandrel ring (32) and the mandrel ring (35). If so, it can be a fluid passage. Therefore, it is a necessary condition that one end side of the grooves (51a) and (51b) reaches the outer peripheral edge on the upstream end face of the nut (37), but that the other end side reaches the inner peripheral edge is a necessary condition. Absent. The groove (51a) (51b) may be at least one, and providing a plurality of grooves is optional.

(Third fluid passage)
In the mandrel (60) shown in FIG. 9, the fluid passage is constituted by grooves (51a) (51b) provided on the upstream end face of the nut (37). Further, by providing grooves (61a) and (61b) on the outer peripheral surface of the mandrel (32), the amount of fluid flowing through the gap (S ₁ ) between the mandrel (32) and the mandrel ring (35) is increased. I am letting.

The two grooves (51a) (51b) provided in the nut (37) are provided at the same positions as the grooves (51a) (51b) of the nut (37) of the mandrel (50) in FIG. Two holes (52a) and (52b) are formed by the ring (35), and outer openings (53a) and (53b) are formed on one end side of the holes (52a) and (52b), and a gap (S ₁ ) It is common to form communication ports (54a) and (54b). In the present embodiment, one of the two holes (52a) and (52b) is used as the fluid introduction passage (52a), and the other (52b) is used as the fluid discharge passage.

  Further, on the outer peripheral surface of the mandrel (32), two grooves (61a) (61b) are provided at equal intervals in the circumferential direction along the axial direction. By these grooves (61a) and (61b), the distance between the outer peripheral surface of the mandrel (32) and the inner peripheral surface of the mandrel ring (35) is enlarged at two locations in the circumferential direction.

In the mandrel (60), when the fluid is introduced from one of the outer peripheral side openings (53a), the fluid (F) that has come out of the communication port (54a) through the hole (52a) is separated from the mandrel (32) and the mandrel ring. gap through the clearance (S ₂₎ between the fed into the gap (S ₁₎ and groove (61a), also a mandrel (32) and nut (37) between (35) (S ₁₎ and It is fed into the groove (61a), or is advanced in the circumferential direction through the gap (S ₂ ) and is fed into the gap (S ₁ ), and proceeds in the upstream direction and also in the circumferential direction. At this time, the flow amount of the fluid (F) fed into the gap (S ₁ ) from the communication port (54a) is increased by the groove (61a). Then, the fluid (F) that has been diverted to fill the gap (S ₁ ) joins at or near the other groove (61b), flows downstream along the groove (61b), and flows into the other communication port (54b). ) To the hole (52b) and discharged from the outer peripheral opening (53b).

  Thus, by forming the grooves (51a) and (51b) on the upstream end surface of the nut (37), the fluid (F) can be fed or discharged from the side surface of the mandrel (60).

(Fourth fluid passage)
In the mandrel (70) shown in FIG. 10, the fluid passage includes holes (72a) (72b) provided on the mating surfaces of the bolt part (34) and the nut (37), a mandrel (32), and a nut (37 ) To the gap (S ₂ ).

On the outer peripheral surface of the bolt part (34), grooves (71a) (71b) along the axial direction are provided at two locations in the circumferential direction, and the grooves (71a) (71b) are formed by screwing the nut (37). ) Is closed by the nut (37), and holes (72a) (72b) are formed in the downstream end face of the mandrel (70) and the upstream end face of the nut (37). (73a) and (73b) are downstream openings of the holes (72a) and (72b), and (74a) and (74b) are communication ports to the gap (S ₂ ). Further, the two grooves (61a) (61b) formed on the outer peripheral surface of the mandrel (32) are the same as the grooves (61a) (61b) of the mandrel (32) shown in FIG.

In the mandrel (70), when the fluid (F) is introduced from one of the downstream openings (73a), the fluid (F) enters the hole (72a) and proceeds upstream to the clearance (S ₂ ) Go out. Then, the fluid (F) is fed from the gap (S ₂ ) into the gap (S ₁ ) and the groove (61a), and is fed into the gap (S ₁ ) while proceeding circumferentially in the gap (S ₂ ). To the circumferential direction. At this time, the amount of fluid flowing into the gap (S ₁ ) from the communication port (74a) is increased by the groove (61a). Then, the fluid (F) that has been diverted to fill the gap (S ₁ ) joins at or near the other groove (61b), flows downstream along the groove (61b), and flows into the other communication port (74b). ) To the hole (72b) and discharged from the outer peripheral opening (73b).

As described above, the fluid (F) is fed into the gap (S ₁ ) between the mandrel (32) and the mandrel ring (35) by the fluid passage that opens to the outside, and the fed fluid (F) is discharged. Can do. Thus, by sending the fluid (F) into the gap (S ₁ ) and circulating it, the outer peripheral surface (32a) of the mandrel (32) and the inner peripheral surface (35a) of the mandrel ring (35) can be cleaned. . Since the fluid (F) can be circulated in the assembled state without disassembling the mandrels (30) (50) (60) (70), it is possible to work in a short time without the need for disassembly and assembly. . Therefore, in the die maintenance after extruding the metal using the extrusion die of the present invention, the fluid is supplied from the outside through the fluid passage to the gap between the mandrel and the mandrel ring in an assembled state without disassembling the mandrel. By feeding and circulating, the outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring can be cleaned, so that die maintenance can be performed efficiently in a short time.

  The fluid passages in the present invention are not limited to those described above. Further, the various introduction passages and discharge passages described above can be arbitrarily combined. Moreover, in any case of adopting any fluid passage, as shown in FIGS. 9 and 10, the flow amount of the fluid is increased by providing the grooves (61a) and (61b) on the outer peripheral surface of the mandrel (32). And the cleaning effect by the fluid can be enhanced.

The four types of mandrels (30), (50), (60), and (70) described above all have a mandrel (32) shorter than the mandrel ring (35) and between the mandrel (32) and the nut (37). A gap (S ₂ ) is exemplified, and this gap (S ₂ ) is used as a part of the fluid passage. However, the present invention does not require that the gap (S ₂ ) be used as a fluid passage. This is because even when the gap (S ₂ ) is narrow enough to make it difficult for fluid to flow, a passage can be secured by a method such as providing a groove on the upstream end face of the nut (37).

  Furthermore, the flow direction of the fluid is not limited to the direction of the embodiment described above. If there are a plurality of openings to the outside, it can be circulated in either direction. Therefore, any of the mandrels of the above-described embodiments can circulate in the opposite direction. In addition, when there are three or more openings, introduction and discharge from a plurality of openings are possible. In addition, the fluid is sent into the passage from the opening serving as the entrance, and the fluid is disposed at or near the opening serving as the entrance, and the fluid is drawn from the entrance by suctioning from the opening serving as the discharge port. May be.

  The extrusion die of the present invention can be applied not only to the extrusion of a hollow material having a closed hollow portion, but also to the extrusion of a semi-hollow material having a part of the hollow portion opened.

  Moreover, as long as the material shape | molded using the extrusion die of this invention is a metal, it will not be limited at all, and aluminum, copper, iron, and these alloys can be illustrated.

  The extrusion die of the present invention can be used for producing various extruded materials having a hollow portion or a semi-hollow portion.

1 ... Extruded material
10 ... Porthole Dice
11 ... Female
20 ... Male mold (extrusion die)
21 ... Dice base
30, 50, 60, 70 ... mandrels
32 ... Mandrel
34… Bolt part
35 ... Mandrel ring
37 ... Nut
40 ... Curved hole (fluid passage)
41 ... 1st hole
42 ... second hole
43… Opening
45 ... Screw gap (fluid passage)
46… Downstream opening
51a, 51b ... Groove (fluid passage)
61a, 61b ... groove
71a, 71b ... Groove (fluid passage)
S ₁ ... Gap S ₂ ... Gap (fluid passage)

Claims (9)

A mandrel that molds the inner surface of the extruded material has a mandrel and a mandrel ring fitted over the mandrel;
The mandrel ring is made of a material having a smaller coefficient of thermal expansion than the mandrel,
The outer peripheral surface of the mandrel and the inner peripheral surface of the mandrel ring are in a state where the mandrel ring is externally fitted to the mandrel, there is a gap between them at room temperature, and at the die temperature during extrusion, at least in the axial direction of the mandrel It is set so that the gap disappears and both come into contact,
An extrusion die characterized in that a fluid passage is provided through the gap between the mandrel and the mandrel ring from the outside of the mandrel at normal temperature, feeding fluid into the gap and discharging the fed fluid to the outside. When the clearance (X _T2 ) between the mandrel and the mandrel ring at the die temperature (T ₂ ) at the time of extrusion is expressed by the following formula in the portion where the gap at the normal temperature (T ₁ ) is the minimum, the normal temperature (T ₁ The outer diameter (A _T1 ) of the mandrel and the inner diameter (B _T1 ) of the mandrel ring at the time are set so that the tightening allowance (X _T2 ) is 0 to 0.3%. Extrusion die.
X _T2 = {[A _T1 × (T ₂ −T ₁ ) × α ₁ + A _T1 ] / [B _T1 × (T ₂ −T ₁ ) × α ₂ + B _T1 ] −1} × 100
Where α ₁ : coefficient of thermal expansion of the material constituting the mandrel
α ₂ : coefficient of thermal expansion of the material constituting the base material of the mandrel ring (α ₁ > α ₂ )
T ₁ : normal temperature
T ₂ : Die temperature during extrusion (> T ₁ )
A _T1 : Outer diameter of the mandrel at normal temperature (T ₁ )
B _T1 : Inner diameter of mandrel ring at normal temperature (T ₁ ) (> A _T1 )   The extrusion according to claim 1 or 2, wherein a bolt portion smaller in diameter than the mandrel is formed integrally with the mandrel at the tip of the mandrel, and the mandrel ring is restrained in the axial direction by screwing a nut into the bolt portion. dice.   4. The extrusion die according to claim 3, wherein the fluid passage includes a bent hole that opens to a downstream end surface of the bolt portion and opens to the outer peripheral surface of the mandrel through the bolt portion in the axial direction.   The extrusion die according to claim 3 or 4, wherein the fluid passage includes a gap between the bolt portion and the nut.   The extrusion die according to claim 5, wherein the fluid gap is a groove provided in at least one of an outer peripheral surface of the bolt part and an inner peripheral surface of the nut.   The extrusion die according to any one of claims 3 to 6, wherein the fluid passage includes a groove that reaches a gap between the mandrel and the mandrel ring from an outer peripheral edge on an upstream end surface of the nut.   The extrusion die according to any one of claims 1 to 7, wherein a groove is provided along an axial direction on an outer peripheral surface of the mandrel.   The extrusion die according to any one of claims 1 to 8, wherein the outer periphery of the mandrel and the mandrel ring are circulated by sending a fluid from outside through a fluid passage to a gap between the mandrel and the mandrel ring at room temperature. A method for cleaning an extrusion die, characterized in that an inner peripheral surface of the extrusion die is cleaned.

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