Sleeve for die casting

Abstract

This sleeve for die casting has an outer tube that is made of hot work tool steel and that has a sleeve rear portion including a molten metal supply port, and a composite inner tube that is provided inside the sleeve rear portion, wherein: the composite inner tube has ceramic inner tube with an L-shaped longitudinal cross section and having a front-end annular flange portion, and a high-strength material inner tube and a high-thermal expansion material inner tube provided in the length direction between the outer peripheral surface of the ceramic inner tube and the inner peripheral surface of the outer tube; and the high-strength material inner tube has a yield strength of 600 MPa or more, and the average thermal expansion coefficient of the high-thermal expansion material in the temperature range of 20 to 300°C is greater than that of the hot work tool steel.

Description

Die-casting sleeves

[0001] The present invention relates to a die-casting sleeve for injecting molten non-ferrous metals such as aluminum alloys into a die-casting mold.

[0002] A die-casting machine comprises an alloy steel sleeve having a molten metal supply port and a molten metal injection port, and a plunger that slides within the sleeve. Hot work tool steels such as SKD61 (JIS G 4404) and H13 (ASTM A681) are used as the alloy steel forming the sleeve. Molten metal is supplied to the sleeve from the molten metal supply port, injected by the plunger into a mold cavity communicating with the sleeve, and cooled and solidified to form a cast product. The inner surface of such a sleeve can be damaged by melting due to the molten metal or worn by the sliding of the plunger tip. When the inner surface of the sleeve is damaged by melting or wear, molten metal enters between the sleeve and the plunger tip, increasing the sliding resistance of the sleeve, which not only reduces the injection speed but also lowers the product quality.

[0003] To address these problems, die-casting sleeves have been proposed in which a ceramic inner sleeve is fitted inside an outer sleeve made of hot-work tool steel. For example, Japanese Patent Application Publication No. 2000-61604 (Patent Document 1) discloses a plunger sleeve for a die-casting machine having an outer cylinder with an opening for molten metal injection and an inner cylinder provided in the molten metal drop section of the outer cylinder, wherein the inner cylinder consists of a steel base material and a ceramic inner layer provided on the inner circumferential surface of the base material, and the inner cylinder is interchangeably fitted into the outer cylinder.

[0004] Furthermore, Japanese Patent Publication No. 2005-88016 (Patent Document 2) describes a device comprising a cylindrical body, a rear cylindrical body having a hot water inlet coaxially connected to the rear end of the cylindrical body, and a stopper plate attached to the rear end surface of the rear cylindrical body. The rear cylindrical body is a laminate consisting of an outer cylinder made of a low thermal expansion material and a ceramic inner cylinder shrink-fitted to the inside of the outer cylinder. The thermal expansion coefficient of the low thermal expansion material at room temperature to 600°C is 5 × 10⁻⁶. －6 ~7×10 －6 The temperature is / ℃, and the difference in thermal expansion coefficient between ceramics and low thermal expansion materials from room temperature to 600℃ is 2 × 10⁻⁶. －6~4.5 x 10 －6 A composite sleeve for a die-casting machine with a temperature of / ℃ is disclosed.

[0005] Furthermore, Japanese Patent Publication No. 2016-159333 (Patent Document 3) discloses a die-casting sleeve comprising a rear sleeve having a ceramic inner cylinder inside a metal outer cylinder, and a metal front sleeve fixed to one end of the rear sleeve, wherein the outer cylinder of the rear sleeve has an inner circumferential fitting surface and a female thread portion at its front end, and the front sleeve has an outer circumferential fitting surface that fits with the inner circumferential fitting surface of the outer cylinder and a male thread portion that screws into the female thread portion at its rear end, and the front sleeve is fixed to the rear sleeve by fitting the inner circumferential fitting surface of the outer cylinder and the outer circumferential fitting surface of the front sleeve, and by screwing the female thread portion of the outer cylinder and the male thread portion of the front sleeve together.

[0006] With the structure described in Patent Documents 1 to 3, when the inner cylinder made of ceramics is damaged at the rear of the sleeve where the molten metal supply port is provided, not only can only the inner cylinder be replaced with a new one, but it is also not necessary to construct the entire inner circumference of the sleeve from ceramics, thus reducing manufacturing costs.

[0007] Figures 1(a) and 1(b) show an example of a conventional die-casting sleeve 100 having an inner cylinder at the rear with a molten metal supply port. The die-casting sleeve 100 has an outer cylinder 10 made of hot tool steel having a molten metal supply port 11 at the rear and a molten metal injection port 12 at the front, a ceramic inner cylinder 2 provided on the inner circumference of the rear of the outer cylinder 10, and a rear end ring 5 that fixes the rear end of the ceramic inner cylinder 2. The outer cylinder 10 consists of a sleeve front part 10a having the molten metal injection port 12 and a sleeve rear part 10b having the molten metal supply port 11.

[0008] However, with such a die-casting sleeve 100, it has been found that when the temperature of the outer cylinder 10 rises during use, (a) a gap is likely to form between the front end surface 3 of the ceramic inner cylinder 2 and the inner circumferential step portion 13 of the outer cylinder 10 that the front end surface 3 contacts, and (b) a gap is also likely to form between the outer circumferential surface 4a of the ceramic inner cylinder 2 and the inner circumferential surface 14 of the rear sleeve portion 10b of the outer cylinder 10 that it contacts. If a gap (a) occurs, molten metal inside the sleeve may enter the gap, and the solidified molten metal may lead to damage to the ceramic inner cylinder 2. Also, if a gap (b) occurs, the ceramic inner cylinder 2 may shift radially relative to the outer cylinder 10, causing the central axis O2 of the ceramic inner cylinder 2 to shift from the central axis O1 of the outer cylinder 10. A plunger tip (not shown) sliding inside the outer cylinder 10 may catch on the step formed at the boundary between the outer cylinder 10 and the ceramic inner cylinder 2, potentially leading to damage to the ceramic inner cylinder 2.

[0009] The mechanism by which a radial gap is created between the ceramic inner cylinder 2 and the outer cylinder 10 will be explained with reference to Figure 2, which shows only the lower side of the die-casting sleeve 100 in Figure 1. For example, when the ceramic inner cylinder 2 is fitted into the outer cylinder 10 by shrink-fitting, not only can the ceramic inner cylinder 2 be easily fitted into the outer cylinder 10 which has expanded in diameter due to heating, but the inner diameter shrinks when the outer cylinder 10 is cooled after fitting, and the outer peripheral surface 4a of the ceramic inner cylinder 2 and the inner peripheral surface 14 of the sleeve rear portion 10b of the outer cylinder 10 are firmly fastened together.

[0010] However, in the temperature range from room temperature to the operating temperature (approximately 300°C), the average thermal expansion coefficient of the hot work tool steel forming the outer cylinder 10 is approximately 13 × 10⁻¹⁰ in the case of SKD61, for example. －6 While the temperature is / °C, the average thermal expansion coefficient of the ceramics forming the inner cylinder 2 is approximately 3 × 10 in the case of silicon nitride ceramics such as SiAlON. －6 The temperature is / ℃. Therefore, even if the shrink-fit is strong at room temperature, when the temperature of the sleeve rises during use, the inner diameter of the outer cylinder 10, which is made of hot-work tool steel, expands more than the ceramic inner cylinder 2 due to thermal expansion. As shown in Figure 2, this not only creates a radial gap G1 between the outer surface 4 of the ceramic inner cylinder 2 and the inner surface 14 of the outer cylinder 10, but also creates a step D1 between the inner surface 15 of the sleeve rear portion 10b of the outer cylinder 10 and the outer surface 4b of the ceramic inner cylinder 2.

[0011] Furthermore, the mechanism by which a longitudinal gap is created between the ceramic inner cylinder 2 and the outer cylinder 10 is as follows. The average thermal expansion coefficient of the ceramics forming the ceramic inner cylinder 2 is considerably smaller than that of the hot work tool steel forming the outer cylinder 10. Therefore, the outer cylinder 10 expands not only in the inner diameter but also in the longitudinal direction due to the rising temperature during use. Also, when the rear part of the sleeve of the outer cylinder 10 reaches a high temperature of 300°C, the fastening force due to shrink fitting is largely lost. As a result, the outer cylinder 10, which is made of hot work tool steel with high thermal expansion, is not constrained by the ceramic inner cylinder 2 with low thermal expansion and is prone to expanding significantly. Consequently, as shown in Figure 2, a longitudinal gap G2 is created between the front end surface 3 of the inner cylinder 2 and the inner circumferential step portion 13 of the outer cylinder 10, starting from the position of the rear end ring 5.

[0012] As a result of diligent research into means of suppressing the radial gap G1, it has been found that adjusting the fitting ratio [= (outer diameter of inner cylinder - inner diameter of outer cylinder) / inner diameter of outer cylinder)] and the shrink-fitting ratio, or setting the shrink-fitting temperature higher than the operating temperature of the die-casting sleeve, is effective in suppressing the radial gap G1. However, these methods cannot sufficiently suppress the longitudinal gap G2.

[0013] Japanese Patent Publication No. 2000-61604, Japanese Patent Publication No. 2005-88016, Japanese Patent Publication No. 2016-159333

[0014] Therefore, the object of the present invention is to provide a die-casting sleeve that sufficiently suppresses the formation of longitudinal and radial gaps between the outer cylinder made of hot-work tool steel and the inner cylinder made of ceramics at the operating temperature.

[0015] In view of the above objectives, the inventors have conducted diligent research and discovered that by arranging a high-strength material inner cylinder and a high-thermal-expansion material inner cylinder longitudinally between the ceramic inner cylinder and the outer cylinder, it is possible to sufficiently suppress the formation of longitudinal and radial gaps between the outer cylinder and the ceramic inner cylinder, leading to the present invention.

[0016] In other words, the die-casting sleeve of the present invention comprises a hot-work tool steel outer cylinder having a sleeve front portion having a molten metal injection port and a sleeve rear portion having a molten metal supply port, and a composite inner cylinder provided inside the sleeve rear portion, wherein the composite inner cylinder comprises a ceramic inner cylinder having an L-shaped longitudinal cross-sectional shape with a front end annular flange portion projecting outward, and a high-strength material inner cylinder and a high-thermal-expansion material inner cylinder provided longitudinally between the outer circumferential surface of the ceramic inner cylinder and the inner circumferential surface of the sleeve rear portion, wherein the high-strength material inner cylinder has a yield strength of 600 MPa or more, and the average thermal expansion coefficient of the high-thermal-expansion material in a temperature range of 20 to 300°C is greater than the average thermal expansion coefficient of the hot-work tool steel in a temperature range of 20 to 300°C.

[0017] The high-strength material inner cylinder has an L-shaped longitudinal cross-section with a rear annular flange portion that protrudes inward, and it is preferable that the ceramic inner cylinder and the high-strength material inner cylinder are in contact with each other with the front annular flange portion and the rear annular flange portion facing in opposite directions.

[0018] Preferably, the average thermal expansion coefficient Ch of the high thermal expansion material in the temperature range of 20 to 300°C is 1.3 to 2.3 times greater than the average thermal expansion coefficient Cs of the hot work tool steel in the temperature range of 20 to 300°C.

[0019] The longitudinal length L2 of the high thermal expansion inner cylinder is preferably 1 to 5 times the longitudinal thickness L1 of the front end annular flange portion of the ceramic inner cylinder.

[0020] It is preferable that the longitudinal length L2 of the inner cylinder of the high thermal expansion material and the longitudinal thickness L1 of the front annular flange portion of the ceramic inner cylinder before heating satisfy the following relationship: (α1 × L1) + (α2 × L2) > α3 × (L1 + L2) ... (1) (wherein α1 is the average thermal expansion coefficient of the ceramic in the temperature range of 20 to 300°C, α2 is the average thermal expansion coefficient of the high thermal expansion material in the temperature range of 20 to 300°C, and α3 is the average thermal expansion coefficient of the hot tool steel forming the outer cylinder in the temperature range of 20 to 300°C).

[0021] Preferably, the inner circumferential surface of the high-strength material inner cylinder that is in contact with the ceramic inner cylinder is grooved to reduce the contact area with the ceramic inner cylinder.

[0022] Before use (before heating), it is preferable that the diameter of the inner surface of the ceramic inner cylinder is larger than the diameter of the inner surface of the front part of the sleeve.

[0023] The die-casting sleeve of the present invention has a ceramic inner cylinder with an L-shaped longitudinal cross-section having a front annular flange portion that protrudes outward from a composite inner cylinder provided inside the rear of the sleeve, and a high-strength material inner cylinder and a high-thermal-expansion material inner cylinder provided longitudinally between the outer circumferential surface of the ceramic inner cylinder and the inner circumferential surface of the rear of the sleeve. Therefore, it is possible to suppress the formation of gaps in the longitudinal and radial directions between the composite inner cylinder and the outer cylinder.

[0024] This is a longitudinal cross-sectional view showing the overall structure of a conventional die-casting sleeve. This is a segmented cross-sectional view showing the outer and inner cylinders that constitute a conventional die-casting sleeve. This is a partial longitudinal cross-sectional view showing how a gap forms between the inner and outer cylinders due to thermal expansion at the rear of a conventional die-casting sleeve. This is a longitudinal cross-sectional view showing the overall structure of a die-casting sleeve according to one embodiment of the present invention. This is a longitudinal cross-sectional view showing the composite inner cylinder that constitutes the die-casting sleeve shown in Figure 3(a). This is a partial longitudinal cross-sectional view showing that a gap does not form between the composite inner cylinder and the outer cylinder at the rear of the die-casting sleeve shown in Figure 3, even with thermal expansion. This is a partial longitudinal cross-sectional view showing the composite inner cylinder that constitutes the die-casting sleeve of the present invention. This is a partial longitudinal cross-sectional view showing another example of the composite inner cylinder. This is a partial longitudinal cross-sectional view showing yet how the step difference between the inner surface of the composite inner cylinder and the inner surface of the outer cylinder is eliminated at the rear of the die-casting sleeve of the present invention due to thermal expansion. This is a longitudinal cross-sectional view showing a first partial model that mimics the structure of the rear of a die-casting sleeve. This is a longitudinal cross-sectional view showing a second partial model that simulates the rear structure of the die-casting sleeve of the present invention.

[0025] Embodiments of the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to these embodiments, and modifications, alterations, or improvements can be made without departing from the scope of the invention.

[0026] As shown in Figure 3(a), a die-casting sleeve 110 according to one embodiment of the present invention comprises a hot-work tool steel outer cylinder 10 having a sleeve front portion 10a with a molten metal injection port 12 and a sleeve rear portion 10b with a molten metal supply port 11, a composite inner cylinder 20 provided inside the sleeve rear portion 10b, and a rear end ring 5 that fixes the rear end of the composite inner cylinder 20. As shown in Figure 3(b), the composite inner cylinder 20 comprises a ceramic inner cylinder 6 with an L-shaped longitudinal cross-section having a front end annular flange portion 61 protruding outward, and a high-strength material inner cylinder 7 and a high-thermal-expansion material inner cylinder 8 provided longitudinally between the outer circumferential surface 62 of the ceramic inner cylinder 6 and the inner circumferential surface 14 of the sleeve rear portion 10b.

[0027] The inner circumferential surface 63 of the ceramic inner cylinder 6 constitutes the inner circumferential surface of the die-casting sleeve 110, and the front end surface 64 of the front annular flange portion 61 contacts the inner circumferential step portion 13 between the front portion 10a and the rear portion 10b of the sleeve. In the illustrated example, both the high-strength material inner cylinder 7 and the high-thermal-expansion material inner cylinder 8, which are fitted along the outer circumferential surface 62 of the ceramic inner cylinder 6, are I-shaped. In the illustrated example, the high-thermal-expansion material inner cylinder 8 is positioned in front of the high-strength material inner cylinder 7 (towards the front portion 10a of the sleeve), but this is not limited, and the high-strength material inner cylinder 7 may also be positioned in front of the high-thermal-expansion material inner cylinder 8.

[0028] The composite inner cylinder 20 is fitted into the die-casting sleeve 110 from the rear end and fixed to the outer cylinder 10 by the rear end ring 5. The front end surface 64 of the ceramic inner cylinder 6 is preferably located at the boundary between the front part 10a and the rear part 10b of the sleeve, and the boundary between the front part 10a and the rear part 10b of the sleeve is preferably located in front of the molten metal supply port 11 (towards the molten metal injection port 12).

[0029] (1) Suppression of radial gap To suppress the radial gap between the composite inner cylinder 20 and the sleeve rear portion 10b of the outer cylinder 10, it is effective to increase the fitting ratio, but in doing so, the high-strength material inner cylinder 7 must not deform. Furthermore, in order to maintain the fastening force due to fitting even when the temperature of the die-casting sleeve 110 reaches 300°C during use, it is preferable to set the fitting ratio (shrink fitting ratio) to 3.0 / 1000 or more, more preferably to 3.5 / 1000 or more, and most preferably to 4.0 / 1000 or more. A large fitting ratio generates a large fitting force on the fitting surface of the high-strength material inner cylinder 7.

[0030] Therefore, the high-strength inner cylinder 7 is required to have a high yield strength (0.2% proof stress) that does not undergo plastic deformation not only at room temperature but also at the operating temperature. When evaluated at room temperature (20°C), the yield strength of the high-strength inner cylinder 7 must be 600 MPa or higher. The yield strength is measured under the conditions of JIS Z 2241:2011. If the yield strength at room temperature is 600 MPa or higher, the high-strength inner cylinder 7 will not undergo plastic deformation even when under high stress before use or when at high temperatures during use, and the fastening force can be maintained. The yield strength of the high-strength inner cylinder 7 at room temperature is preferably 700 MPa or higher, more preferably 800 MPa or higher, and most preferably 900 MPa or higher. There is no upper limit to the yield strength, but around 11500 MPa is realistic. Hot work tool steel is preferred as the high-strength material.

[0031] The mechanism for suppressing radial gaps will be explained in detail below with reference to Figure 4, which shows only the rear part 10b of the sleeve and the lower part of the composite inner cylinder 20. When the temperature of the entire sleeve rises during use, the inner diameter of the high-strength material inner cylinder 7 tends to expand due to thermal expansion, so the fastening force between the ceramic inner cylinder 6 and the high-strength material inner cylinder 7 weakens. However, when the expanding high-strength material inner cylinder 7 presses against the outer cylinder 10 from the inside, the high-strength material inner cylinder 7 receives a reaction force from the outer cylinder 10 in the direction of pushing the ceramic inner cylinder 6. Therefore, even when the sleeve reaches a high temperature of 300°C, radial gaps are unlikely to occur between the outer circumferential surface 62 of the ceramic inner cylinder 6 and the inner circumferential surface 71 of the high-strength material inner cylinder 7, and between the outer circumferential surface 72 of the high-strength material inner cylinder 7 and the inner circumferential surface 14 of the rear part 10b of the sleeve of the outer cylinder 10, thus suppressing radial displacement of the composite inner cylinder 20 within the die-casting sleeve 110.

[0032] For suppressing the clearance in the radial direction, it is preferable to use shrink fitting for the fitting of the ceramic inner cylinder 6 and the high-strength material inner cylinder 7 because the fitting ratio (shrink fitting ratio) can be increased. In this case, as shown in Fig. 3(a), it is preferable that both ends in the longitudinal direction of the high-strength material inner cylinder 7 are positioned at positions sandwiching the molten metal supply port 11 from both sides. Note that shrink fitting may or may not be used for the fitting of the composite inner cylinder 20 and the outer cylinder 10.

[0033] (2) Suppression of longitudinal clearance When the temperature of the die casting sleeve during use reaches a high temperature, in order to prevent a longitudinal clearance from occurring between the front end face 64 of the ceramic inner cylinder 6 and the inner peripheral step portion 13 of the outer cylinder 10 due to the elongation of the outer cylinder 10 made of hot work tool steel in the longitudinal direction, the composite inner cylinder 20 of the present invention is characterized in that it has a high thermal expansion material inner cylinder 8 extending in the longitudinal direction between the outer peripheral surface 62 of the ceramic inner cylinder 6 and the inner peripheral surface 14 of the sleeve rear portion 10b.

[0034] Since the high thermal expansion material inner cylinder 8 presses the front end annular flange portion 61 of the L-shaped ceramic inner cylinder 6 in the direction of the sleeve front portion 10a when the temperature of the die casting sleeve rises, it is possible to suppress the occurrence of a longitudinal clearance between the front end annular flange portion 61 of the ceramic inner cylinder 6 and the inner peripheral step portion 13 of the outer cylinder 10. In order to sufficiently exhibit this pressing force, the average thermal expansion coefficient Ch of the high thermal expansion material 8 in the temperature range of 20 to 300 °C needs to be sufficiently larger than the average thermal expansion coefficient Cs of the hot work tool steel in the temperature range of 20 to 300 °C.

[0035] Since Ch > Cs, even if the outer cylinder 10 during use elongates in the longitudinal direction, the high thermal expansion material inner cylinder 8 elongates further and presses the front end of the ceramic inner cylinder 6 from the back side. As a result, the front end of the composite inner cylinder 20 can always be pressed against the outer cylinder 10, suppressing the occurrence of a longitudinal clearance.

[0036] As the average thermal expansion coefficient Ch of the high thermal expansion material increases, the pressing force increases. The average thermal expansion coefficient Cs of the hot work tool steel forming the outer cylinder 10 is, for example, 13 × 10 in the case of SKD61 －6Since it is about / °C, the average thermal expansion coefficient Ch of the high thermal expansion material is preferably 1.3 times or more, more preferably 1.4 times or more, still more preferably 1.5 times or more, and most preferably 1.6 times or more of Cs. The upper limit of the average thermal expansion coefficient Ch of the high thermal expansion material is not limited, but it is preferably 2.3 times, more preferably 2.2 times, still more preferably 2.1 times, and most preferably 2.0 times of Cs. Therefore, as an example of the range of Ch / Cs, 1.3 to 2.3 is preferable, 1.4 to 2.2 is more preferable, 1.5 to 2.1 is still more preferable, and 1.6 to 2.0 is most preferable. As such a high thermal expansion material, for example, stainless steel (18×10 －6 ~20×10 －6 / °C level), brass (18×10 －6 ~20×10 －6 / °C level), aluminum alloy (20×10 －6 ~22×10 －6 / °C level), etc. are preferable.

[0037] Considering the elongation amounts of the outer cylinder 10, the ceramic inner cylinder 6, and the high-strength material inner cylinder 7 when the sleeve for die casting is heated, it is preferable to adjust the longitudinal length L2 of the high thermal expansion material inner cylinder 8 in the sleeve for die casting before use (before heating) so as to satisfy the relationship represented by the following formula (1) with respect to the longitudinal thickness L1 of the front end annular flange portion 61 of the ceramic inner cylinder 6. (α1×L1) + (α2×L2) > α3×(L1 + L2) ···(1) α1: The average thermal expansion coefficient Cc of the ceramics in the temperature range of 20 to 300°C. α2: The average thermal expansion coefficient Ch of the high thermal expansion material in the temperature range of 20 to 300°C. α3: The average thermal expansion coefficient Cs of the hot work tool steel forming the outer cylinder 10 in the temperature range of 20 to 300°C.

[0038] For example, in the case of a combination of an outer cylinder 10 made of hot-work tool steel and a high-strength inner cylinder 7 also made of hot-work tool steel, the thermal expansion coefficients of both are almost the same. Therefore, when the die-casting sleeve is heated, the high-strength inner cylinder 7 and the outer cylinder 10 will expand by almost the same length without separating. Thus, when the die-casting sleeve is heated, the sum of the elongation of the front annular flange portion 61 of the ceramic inner cylinder 6 (α1 × L1) and the elongation of the high-thermal-expansion inner cylinder 7 (α2 × L2) should be greater than the elongation of the fitting portion of the outer cylinder 10 α3 × (L1 + L2).

[0039] If the longitudinal length L2 of the high thermal expansion material inner cylinder 8 is increased relative to the longitudinal thickness L1 of the front annular flange portion 61 of the ceramic inner cylinder 6, the total expansion amount (elongation) during use increases, and the force with which the front end surface 64 of the ceramic inner cylinder 6 presses against the outer cylinder 10 increases, which is advantageous in suppressing the occurrence of longitudinal gaps. However, it is not necessary to make the longitudinal length L2 of the high thermal expansion material inner cylinder 8 excessively large. By moderately limiting the longitudinal length L2 of the high thermal expansion material inner cylinder 8, the high-strength material inner cylinder 7 can be made longer, which increases the fitting area (tightening force) between the high-strength material inner cylinder 7 and the ceramic inner cylinder 6, which is advantageous in suppressing the occurrence of radial gaps. Preferably, the longitudinal length L2 of the high thermal expansion material inner cylinder 8 is 1 to 5 times the longitudinal thickness L1 of the front annular flange portion 61 of the ceramic inner cylinder 6, and more preferably 2 to 4 times.

[0040] As shown in Figure 5, the composite inner cylinder 21 according to another embodiment of the present invention comprises a high-strength material inner cylinder 7a having an L-shaped longitudinal cross-sectional shape with a rear end annular flange portion 73, the rear end annular flange portion 73 of the high-strength material inner cylinder 7a protruding in the opposite direction to the front end annular flange portion 61 of the ceramic inner cylinder 6. That is, the L-shaped structure of the high-strength material inner cylinder 7 and the L-shaped structure of the ceramic inner cylinder 6 are fitted together in an inverted manner. The front end surface 74 of the rear end annular flange portion 73 of the high-strength material inner cylinder 7a is in contact with the rear end surface 65 of the ceramic inner cylinder 6, and the inner circumferential surface 71 of the high-strength material inner cylinder 7a is in contact with the outer circumferential surface 62 of the ceramic inner cylinder 6. A high thermal expansion material inner cylinder 8 is fitted between the front end surface 75 of the high-strength material inner cylinder 7a and the inner end surface 66 of the rear end annular flange portion 61 of the ceramic inner cylinder 6. The thickness of the rear end annular flange portion 73 is preferably about 10 to 30% of the total length of the high-strength material inner cylinder 7a. With this structure, the rear end surface of the composite inner cylinder 20 fixed by the rear end ring 5 is made of high-strength material inner cylinder 7a (so the ceramics are not exposed), which not only allows for the application of a pushing force when inserting the composite inner cylinder 20, but also allows for the provision of screw holes for screws used when removing the composite inner cylinder 20.

[0041] As shown in Figure 6, in the composite inner cylinder 22 according to yet another embodiment of the present invention, the positional relationship between the high-strength material inner cylinder 7 and the high-thermal-expansion material inner cylinder 8 differs from that in Figure 3, with the high-thermal-expansion material inner cylinder 8 being positioned at the rear end of the high-strength material inner cylinder 7. Also, as shown in Figure 7, in the composite inner cylinder 23 according to yet another embodiment of the present invention, the high-strength material inner cylinder 7 is divided into multiple parts, and the high-thermal-expansion material inner cylinder 8 is positioned between the high-strength material inner cylinders 7, 7. In any case, the objective of the present invention can be achieved if the high-strength material inner cylinder 7 and the high-thermal-expansion material inner cylinder 8 are provided in the longitudinal direction between the outer circumferential surface 62 of the ceramic inner cylinder 6 and the inner circumferential surface 14 of the rear part 10b of the sleeve.

[0042] In this invention, shrink fitting may or may not be used to fit the high thermal expansion material inner cylinder 8 and the ceramic inner cylinder 6. However, in order to sufficiently suppress the occurrence of gaps in the longitudinal direction, it is preferable that the front end of the composite inner cylinder 20 is always pressing against the outer cylinder 10 during use (during heating). For this purpose, it is preferable that the end faces of the high thermal expansion material inner cylinder 8, the ceramic inner cylinder 6, and the high-strength material inner cylinder 7 are in close contact with each other from the state of the die-casting sleeve before use (before heating). In that case, in order to ensure dimensional accuracy, it is preferable not to use shrink fitting to fit the high thermal expansion material inner cylinder 8 and the ceramic inner cylinder 6.

[0043] As a means of suppressing the occurrence of gaps in the longitudinal direction, it is effective to lower the fitting resistance between the outer circumferential surface 62 of the ceramic inner cylinder 6 and the inner circumferential surface 71 of the high-strength material inner cylinder 7. By reducing the fitting resistance between the high-strength material inner cylinder 7 and the ceramic inner cylinder 6, the entire ceramic inner cylinder 6 moves more easily in the longitudinal direction, so even if the fitting ratio (shrink-fit ratio) is high, the high thermal expansion material inner cylinder 8, which expands in the longitudinal direction, can push and move the front annular flange portion 61 of the ceramic inner cylinder 6 from the back side. Note that when the entire ceramic inner cylinder 6 moves in the longitudinal direction, a gap may occur between the rear end of the ceramic inner cylinder 6 and the rear end ring 5 (in the case of Figure 5, between the rear end surface 65 of the ceramic inner cylinder 6 and the front end surface 74 of the rear annular flange portion 73 of the high-strength material inner cylinder 7), but this is not a problem as this part does not come into contact with the molten metal.

[0044] In the composite inner cylinder 24 of yet another embodiment of the present invention shown in Figure 8, one or more machined grooves 76 are formed on the inner circumferential surface 71 of the high-strength material inner cylinder 7 to reduce the fitting resistance between the outer circumferential surface 62 of the ceramic inner cylinder 6 and the inner circumferential surface 71 of the high-strength material inner cylinder 7. The reduction rate of the contact area by the machined grooves 76 is preferably 10 to 50% of the contact area when no grooves are machined. The shape, direction, depth, etc. of the machined grooves 76 are not limited as long as the contact resistance is reduced.

[0045] Before use (before heating), as shown in Figure 9, it is preferable that the diameter of the inner surface 63 of the ceramic inner cylinder 6 is larger than the diameter of the inner surface of the sleeve front 10a. Since the outer cylinder 10 is made of hot-work tool steel, as the die-casting sleeve heats up, the sleeve front 10a expands in diameter beyond the inner surface 63 of the ceramic inner cylinder 6, creating a step on the inner surface of the sleeve. Therefore, it is preferable to design the inner diameter of the ceramic inner cylinder 6 taking into account the amount of displacement in diameter expansion between the sleeve front 10a and the ceramic inner cylinder 6 caused by heating. The difference in inner diameter D2 between the sleeve front 10a and the ceramic inner cylinder 6 is preferably, for example, 0.05 to 0.5 mm, and more preferably 0.1 to 0.4 mm.

[0046] Reference Example 1 (1) Preparation of the first partial model Hot work tool steel SKD61 (average thermal expansion coefficient at 20-300°C: approximately 13 × 10) －6 The inner circumferential surface of a cylindrical body 30 (outer diameter 150 mm, inner diameter 90 mm, length 250 mm) made of a material (°C) was widened to 110 mm from one end to a depth of 150 mm by machining, and the widened portion 30b was made to resemble the rear part 10b of the sleeve.

[0047] The ceramic inner cylinder 6 is made of SiAlON (average thermal expansion coefficient Cc: approximately 3 x 10⁻¹⁰). －6 The high-strength inner cylinder 7 was formed using the following material (at / °C). The wall thickness of both inner cylinders 6 and 7 was set to 5 mm as the standard. The wall thickness was adjusted to achieve the desired shrink-fit ratio, and the high-strength inner cylinder 7 was shrink-fitted to the outer surface of the Sialon inner cylinder 6. The resulting composite inner cylinder 2 was fitted into the enlarged diameter portion 30b of the cylindrical body 30 to obtain the first partial model 120.

[0048] (2) Evaluation of radial gap While pulling the ceramic inner cylinder 6 upward with the handle 12, the partial model was gradually heated until it reached 300°C, and the size of the radial gap between the ceramic inner cylinder 6 and the high-strength material inner cylinder 7 was evaluated based on the temperature at which the ceramic inner cylinder 6 could be withdrawn.

[0049] Comparative Experiment 1: When the material of the high-strength inner cylinder 7 was brass (yield strength at room temperature (0.2% proof stress): approximately 350 MPa), the maximum shrink-fit ratio in which the brass inner cylinder 7 does not deform was estimated to be around 4.0 / 1000 by calculation. Therefore, the brass inner cylinder 7 was shrink-fitted to the outer surface of the Sialon inner cylinder 6 with a shrink-fit ratio of 3.0 / 1000 to create a composite inner cylinder 2. Under the same conditions as above, the composite inner cylinder 2 was fitted into the enlarged diameter portion 30b of the cylindrical body 30 to create the first partial model 120. While pulling the ceramic inner cylinder 6 upward with the handle 12, the first partial model 120 was gradually heated, and when it reached approximately 250°C, the Sialon inner cylinder 6 was pulled out from the brass inner cylinder 7.

[0050] Comparative Experiment 2: When the material of the high-strength inner cylinder 7 was stainless steel SUS304 (yield strength at room temperature (0.2% proof stress): approximately 400 MPa), the maximum shrink-fit ratio at which the SUS304 inner cylinder 7 does not deform was estimated to be approximately 2.7 / 1000 by calculation. Therefore, the SUS304 inner cylinder 7 was shrink-fitted to the outer surface of the Sialon inner cylinder 6 with a shrink-fit ratio of 3.0 / 1000 to create a composite inner cylinder 2. The composite inner cylinder 2 was fitted into the enlarged diameter portion 30b of the cylindrical body 30 to create the first partial model 120. Under the same conditions as above, the ceramic inner cylinder 6 was pulled upward with the handle 12 while the first partial model 120 was gradually heated, and at approximately 210°C, the Sialon inner cylinder 6 was pulled out from the SUS304 inner cylinder 7.

[0051] Even if the material of the high-strength inner cylinder 7 is an aluminum alloy (yield strength at room temperature (0.2% proof stress): approximately 200 MPa), the maximum shrink-fit ratio at which the aluminum alloy inner cylinder 7 does not deform can be estimated by calculation to be around 2.7 / 1000. Therefore, even if a pull-out test is performed on the composite inner cylinder 2 obtained by shrink-fitting the aluminum alloy inner cylinder 7 to the outer surface of the Sialon inner cylinder 6 with a shrink-fit ratio of 3.3 / 1000 under the same conditions as above, it is expected that the Sialon inner cylinder 6 will be pulled out of the aluminum alloy inner cylinder 7 at a temperature of less than 200°C.

[0052] Experimental Example 1: When the material of the high-strength inner cylinder 7 was SKD61 (yield strength at room temperature: approximately 800 MPa), calculations estimated that the SKD61 inner cylinder 7 would not deform even with a shrink-fit ratio of approximately 5.5 / 1000. Therefore, a composite inner cylinder 2 was fabricated by shrink-fitting the SKD61 inner cylinder 7 to the outer surface of the Sialon inner cylinder 6 with a shrink-fit ratio of approximately 4.0 / 1000, and the composite inner cylinder 2 was fitted into the outer cylinder 10 under the same conditions as above to obtain the first partial model 120. Under the same conditions as above, the first partial model 120 was heated to 300°C while pulling the ceramic inner cylinder 6 upward with the handle 12. Even at 300°C, it was not possible to pull the Sialon inner cylinder 6 out of the SKD61 inner cylinder 7.

[0053] From the above, it can be seen that by increasing the yield strength of the high-strength material inner cylinder 7, not only can the shrink-fit ratio (fitting ratio) between it and the ceramic inner cylinder 6 be increased, but it is also possible to suppress the formation of a radial gap between the ceramic inner cylinder 6 and the high-strength material inner cylinder 7 even when the die-casting sleeve is heated.

[0054] Example 1 (1) Fabrication of the second partial model A second partial model 130 shown in Figure 11 was fabricated by fitting the composite inner cylinder 20 described below into the bottomed cylindrical portion 31b of a bottomed cylindrical body 31 made of SKD61 having a bottom portion 32 (outer diameter 340 mm, inner diameter 260 mm, depth of the bottomed cylindrical portion 31b corresponding to the rear part 10b of the sleeve of the outer cylinder 10, which corresponds to 200 mm).

[0055] The composite inner cylinder 20 is an L-shaped Sialon inner cylinder 6 (average thermal expansion coefficient Cc: approximately 3 × 10°C at 20-300°C). －6 (°C) and an L-shaped inner cylinder 7 made of SKD61 (average thermal expansion coefficient Cs at 20-300°C: approximately 13 x 10) －6 It has a structure in which the front annular flange portion 61 of the inner cylinder 6 made of Sialon and the front end portion of the inner cylinder 7 made of SKD61 are fitted together in reverse. Between the front annular flange portion 61 of the inner cylinder 6 made of Sialon and the front end portion of the inner cylinder 7 made of SKD61 is a ring 8 made of SUS304 (average thermal expansion coefficient Ch at 20 to 300°C: approximately 18 × 10 －6 A (°C) is fitted into the socket.

[0056] The length of the composite inner cylinder 20 was set to 200 mm so that there was no step between it and the top surface of the bottomed cylindrical body 31. The length of the front annular flange portion 61 of the Sialon inner cylinder 6 and the rear annular flange portion 73 of the SKD61 inner cylinder 7 were both 20 mm. The length of the SKD61 inner cylinder 7 was 120 mm, and the length of the SUS304 ring 8 was 60 mm. Substituting these values ​​into the above formula (1) gives 1140 × 10 －6 > 1040 x 10 －6 Thus, we can see that it satisfies equation (1).

[0057] The standard wall thickness of the Sialon inner cylinder 6, the SKD61 inner cylinder 7, and the SUS304 ring 8 was 8 mm. By fine-tuning these wall thicknesses (fit), the SKD61 inner cylinder 7 was shrink-fitted into the Sialon inner cylinder 6 with a shrink-fit ratio of approximately 4.0 / 1000, without deformation of the SKD61 inner cylinder 7. The SUS304 ring 8 was also gap-fitted into the Sialon inner cylinder 6.

[0058] (2) Evaluation of the longitudinal gap The second partial model 130 was heated to 300°C, and the amount of step difference between the upper surface of the composite inner cylinder 20 and the upper surface of the bottomed cylindrical body 31 was measured. If a positive step difference is defined as the time when the upper surface of the composite inner cylinder 20 protrudes beyond the upper surface of the bottomed cylindrical body 31 which extends in the longitudinal direction, then the larger the positive step difference, the greater the force with which the front end (lower end in Figure 11) of the composite inner cylinder 20 presses down on the bottom 32 of the bottomed cylindrical body 31, and therefore the greater the effect of suppressing the longitudinal gap between the composite inner cylinder 20 and the outer cylinder 10.

[0059] Furthermore, if a longitudinal gap occurred between the rear end (upper end in Figure 11) of the Sialon inner cylinder 6 and the rear end annular flange portion 73 of the SKD61 inner cylinder 7, which constitute the composite inner cylinder 20, the amount of that gap was also measured.

[0060] The amount of step difference between the upper surface of the composite inner cylinder 20 and the upper surface of the bottomed cylindrical body 31 increased to the positive side in approximately proportion to the temperature rise of the second partial model 130, reaching +0.02 mm at 100°C, +0.03 mm at 200°C, and +0.04 mm when it reached 300°C. From the above results, it was confirmed that the composite inner cylinder 20 has a sufficient gap suppression effect to fill the gap value (-0.466 mm) expected when the entire composite inner cylinder 20 is made of Sialon and further push the outer cylinder.

[0061] The longitudinal gap between the rear end of the Sialon inner cylinder 6 and the rear end annular flange portion 73 of the SKD61 inner cylinder 7 was 0.12 mm at 100°C, 0.29 mm at 200°C, and 0.46 mm at 300°C. Since this portion does not come into contact with the molten metal, the above gap amounts are acceptable.

[0062] Based on the above results, the material of the inner cylinder 8 of the high thermal expansion material is stainless steel (average thermal expansion coefficient Ch: 18 × 10 at 20 to 300°C). －6 ~20 x 10 －6 (approximately / ℃), or brass (Ch: 18×10 －6 ~20 x 10 －6 (approximately / ℃), aluminum alloy (Ch: 20×10 －6 ~22×10 －6 Even if the temperature is changed to approximately [temperature], it is expected that the gap in the longitudinal direction can be sufficiently suppressed.

[0063] 110 Die-casting sleeve 10 Outer cylinder 10a Front part of the outer cylinder sleeve 10b Rear part of the outer cylinder sleeve 13 Inner circumferential step of the outer cylinder 14 Inner surface of the rear part of the sleeve 15 Inner surface of the front part of the sleeve 5 Rear end ring 20, 21, 22, 23, 24 Composite inner cylinder 6 Ceramic inner cylinder 61 Front annular flange of the ceramic inner cylinder 62 Outer surface of the ceramic inner cylinder 63 Inner surface of the ceramic inner cylinder 64 Front end surface of the front annular flange 65 Rear end surface of the ceramic inner cylinder 66 Inner end surface of the front annular flange 7, 7a High-strength material inner cylinder 71 Inner surface of the high-strength material inner cylinder 72 Outer surface of the high-strength material inner cylinder 73 Rear annular flange of the high-strength material inner cylinder 74 Front end surface of the rear annular flange 75 Front end surface of the high-strength material inner cylinder 76 Machined groove of the high-strength material inner cylinder 8 Inner cylinder of high thermal expansion material 12 Handle 120 First partial model 130 Second partial model 30 Cylindrical body 31 Bottomed cylindrical body 30b Enlarged diameter portion corresponding to the rear of the sleeve 31b Bottomed cylindrical portion corresponding to the rear of the sleeve 32 Bottom of the bottomed cylindrical body L1 Longitudinal thickness of the front annular flange portion L2 Longitudinal length of the inner cylinder of high thermal expansion material L4 Longitudinal length of the inner cylinder of high-strength material

Claims

1. A die-casting sleeve comprising a hot-work tool steel outer cylinder having a sleeve front portion with a molten metal injection port and a sleeve rear portion with a molten metal supply port, and a composite inner cylinder provided within the sleeve rear portion, wherein the composite inner cylinder comprises an L-shaped ceramic inner cylinder with an annular flange portion projecting outward from the front end, and a high-strength material inner cylinder and a high-thermal-expansion material inner cylinder provided longitudinally between the outer circumferential surface of the ceramic inner cylinder and the inner circumferential surface of the sleeve rear portion, wherein the high-strength material inner cylinder has a yield strength of 600 MPa or more, and the average thermal expansion coefficient of the high-thermal-expansion material in a temperature range of 20 to 300°C is greater than the average thermal expansion coefficient of the hot-work tool steel in a temperature range of 20 to 300°C.

2. A die-casting sleeve according to claim 1, wherein the high-strength material inner cylinder has an L-shaped longitudinal cross-section with a rear end annular flange portion projecting inward, and the ceramic inner cylinder and the high-strength material inner cylinder are in contact with each other with the front end annular flange portion and the rear end annular flange portion facing in opposite directions.

3. A die-casting sleeve according to claim 1, characterized in that the average thermal expansion coefficient of the high thermal expansion material in a temperature range of 20 to 300°C is 1.3 to 2.3 times the average thermal expansion coefficient of the hot work tool steel in a temperature range of 20 to 300°C.

4. A die-casting sleeve according to claim 1, characterized in that the longitudinal length L2 of the high thermal expansion material inner cylinder is 1 to 5 times the longitudinal length L1 of the front end annular flange portion of the ceramic inner cylinder.

5. A die-casting sleeve according to claim 1, characterized in that the longitudinal length L2 of the inner cylinder of the high thermal expansion material and the longitudinal thickness L1 of the front annular flange portion of the inner cylinder of the ceramic material in the die-casting sleeve before heating are related by the following formula (1): (α1 × L1) + (α2 × L2) > α3 × (L1 + L2) ... (1) (wherein α1 is the average thermal expansion coefficient of the ceramic in the temperature range of 20 to 300°C, α2 is the average thermal expansion coefficient of the high thermal expansion material in the temperature range of 20 to 300°C, and α3 is the average thermal expansion coefficient of the hot tool steel forming the outer cylinder in the temperature range of 20 to 300°C).

6. A die-casting sleeve according to claim 1, characterized in that the inner circumferential surface of the high-strength material inner cylinder that contacts the ceramic inner cylinder is grooved to reduce the contact area with the ceramic inner cylinder.

7. A die-casting sleeve according to any one of claims 1 to 6, characterized in that, before heating, the diameter of the inner surface of the composite inner cylinder is larger than the diameter of the inner surface of the front part of the sleeve.

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