JP2004050248A - Cylinder for metal injection molding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the breakage of a sleeve itself and the leakage of molten metal caused by a thermal expansion difference between a cylinder and the sleeve. <P>SOLUTION: Inside the front part of a cylinder 1 composed of a ferrous heat resistant alloy, a sleeve 11 made of a nonferrous heat resistant alloy is fitted in a sleeve fit hole 16 formed at a region to be slid with a counterflow prevention ring 8 and a piston ring 10 so that the fit at room temperature lies in the vicinity of the boundary between a clearance fit and a transition fit. The sleeve 11 is formed so that its thermal expansion coefficient is lower than that of the cylinder 1, and the total length L<SB>1</SB>is made shorter than the length L<SB>2</SB>in the axial direction of the sleeve fit hole. In the nose 11b of the sleeve and the heel 11c of the sleeve, slopes 18 and 18' cover the 1/2 to 4/5 of the thickness t of the sleeve, and are also formed at an angle α within the range of 30 to 60° to the axial center of the sleeve 11. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cylinder used for a metal injection molding machine for injection-molding a metal material such as an aluminum alloy or a magnesium alloy, wherein a cylinder body and a sleeve inserted into an inner surface of a tip portion thereof are made of different materials, and are resistant to erosion. The present invention relates to a cylinder which is excellent in heat resistance and thermal conductivity, has high wear resistance on the inner surface of the tip and is resistant to temperature changes.
[0002]
[Prior art]
Generally, in order to obtain a highly reliable metal injection molding machine, screws and cylinder members for the injection molding machine must be able to be used stably for a long period of time.
[0003]
The cylinder member for this injection molding machine requires the following conditions when, for example, a magnesium alloy is injection molded.
[0004]
1) Less erosion in contact with molten magnesium alloy.
[0005]
2) High temperature strength when heated to 580 to 630 ° C., which is the injection molding temperature of the molten magnesium alloy, is high and does not wear.
[0006]
3) In order to melt the magnesium alloy in the cylinder, it is necessary to transfer heat generated by a heater or the like mounted on the outer peripheral portion of the cylinder to the material through the cylinder, so that heat conduction is good.
[0007]
That is, it is a necessary condition that the cylinder member that comes into intense contact with the molten magnesium alloy has low melting loss, and is excellent in high-temperature strength, softening resistance during high-temperature heating, and thermal conductivity.
[0008]
Cylinders made of Ni-base heat-resistant alloy and coated with Co-base heat-resistant alloy on the surface of the contact part with the molten metal as those having excellent properties of high-temperature strength, softening resistance at high-temperature heating, and thermal conductivity Although disclosed in Japanese Patent Application Laid-Open No. 8-72110), the material cost is high, and problems remain in erosion and thermal conductivity.
[0009]
For this reason, a cylinder made of an iron-based material is effective as a material having excellent properties of erosion and heat conductivity, and a cylinder whose inner surface is coated with a non-ferrous heat-resistant alloy having excellent wear resistance. However, if the molding conditions are severe due to the difference in thermal expansion between the cylinder base material and the coating layer, the coating layer cannot withstand repeated heating and cooling and the injection internal pressure acting at high temperatures, causing cracking and falling off. May occur.
[0010]
In order to eliminate the destruction of the coating layer, a method of inserting and fixing a non-ferrous heat-resistant alloy or ceramic sleeve to the inner surface of a cylinder made of a ferrous material by shrink fitting has been attempted.
[0011]
FIG. 7 shows an injection device in which a sleeve made of a non-ferrous heat-resistant alloy is shrink-fitted on the inner surface of a cylinder made of a ferrous heat-resistant alloy.
[0012]
The rice-sized material chips put into the material hopper 105 drop onto the spiral grooves 113 on the surface of the screw 104 inserted into the cylinder 101. When the screw 104 rotates and moves backward by a driving device (not shown), the material chip is heated through the cylinder 101 by the heater 112 attached to the outer periphery of the cylinder 101 while being sent forward along the spiral groove 113, and melted. Alternatively, the molten metal is in a semi-molten state and stored in the front chamber 115 of the cylinder 101. This is called a weighing step.
[0013]
When the stored molten metal reaches a certain amount, the screw 104 moves forward at high speed by the driving device, and the molten metal stored in the front chamber 115 of the cylinder 101 is injected into the mold (not shown) through the nozzle 103 at high speed and high pressure. Is done. This is called an injection process.
[0014]
The molten metal filled in the cavity in the mold is cooled and solidified, and then the mold is opened to be taken out as a molded product. In the meantime, the next measuring step is executed, and after the mold is closed again, the next injection step is executed.
[0015]
In this injection step, when the screw 104 moves forward and the pressure of the molten metal in the front chamber increases, the molten metal tends to flow backward in the direction of the screw 104. In order to prevent this backflow, a backflow prevention device 106 including a backflow prevention ring 108, a reed 109 and a screw head 107 is attached to the tip of the screw 104. The outer diameter of the backflow prevention ring 108 is set so as to reduce the gap in order to prevent backflow from the gap with the inner surface of the cylinder 101, and a piston ring 110 is further mounted on the outer periphery of the backflow prevention ring 108, 101 is strongly pressed against the inner surface. Therefore, a sleeve 111 made of a non-ferrous heat-resistant alloy is inserted into the inner surface of the cylinder 101 on which the backflow prevention ring 108 and the piston ring 110 slide. The thermal expansion coefficient of the cylinder 101 is about 12 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the sleeve 111 is about 13 × 10 ⁻⁶ / ° C.
[0016]
The sleeve 111 is firmly fixed by shrink fitting to the cylinder 101, that is, by inserting the sleeve 111 at room temperature while the cylinder 101 is heated to a high temperature of 400 to 600 ° C.
[0017]
A method of shrink-fitting a sleeve of a different member to a cylinder and fixing the same is described in Japanese Patent Application Laid-Open Nos. 2-217216 and 6-79760.
[0018]
[Problems to be solved by the invention]
When an injection pressure is applied to the inner surface of the sleeve 111 in the injection process, it is necessary to hold the outer periphery of the sleeve 111 with the cylinder 101 in order to prevent damage due to excessive expansion of the sleeve 111.
[0019]
Further, it is necessary to press the cylinder head 102 against the sleeve 111 so that the molten metal does not leak from between the front part of the cylinder 101 and the cylinder head 102. In order to apply an appropriate surface pressure, it must be strongly tightened with a bolt 114 or the like.
[0020]
On the other hand, the cylinder 101 and the sleeve 111 are heated to about 600 ° C. during molding, and the temperature is lowered to room temperature after the machine is stopped, but a material having substantially the same thermal expansion coefficient as the cylinder 101 is used for the sleeve 111 having different required specifications. The choice is practically difficult.
[0021]
Therefore, the rise or fall of the temperature causes the influence of the difference in thermal expansion.
[0022]
If the sleeve 111 and the cylinder 101 are too tightly fitted in the radial direction, the sleeve 111 may be damaged. On the other hand, if it is too loose, a small gap may be formed.
[0023]
Also, when the axial length of the sleeve 111 relative to the sleeve insertion hole 116 of the cylinder 101 into which the sleeve 111 is inserted is relatively increased, the contact surface pressure increases, and the contact portion yields or the axial length decreases. When the contact pressure is relatively reduced, the contact surface pressure may be reduced and the molten metal may leak.
[0024]
Therefore, an object of the present invention is to provide a cylinder for a metal injection molding machine that is less likely to cause damage to the sleeve itself and leakage of molten metal due to a difference in thermal expansion between the cylinder and the sleeve.
[0025]
[Means for Solving the Problems]
In order to achieve the above object, a cylinder for a metal injection molding machine according to the present invention has a sleeve insertion hole for inserting a sleeve in a region where a backflow prevention ring of a backflow prevention device for preventing backflow of a molten material slides. In a cylinder for a metal injection molding machine to which a cylinder head can be attached at the tip, a material having a coefficient of thermal expansion larger than the coefficient of thermal expansion of the cylinder inside the sealing surface between the cylinder and the cylinder head, and from room temperature in the temperature range up to the molding temperature, the said short overall length L ₁ of the sleeve than the axial length L ₂ of the sleeve insertion hole from the seal faces the cylinder head is attached to the rear end face the sleeve insertion hole, at room temperature Is fitted with either a clearance fit or an intermediate fit.
[0026]
As described above, in the cylinder for a metal injection molding machine of the present invention, a sleeve having a thermal expansion coefficient of 1.03 to 1.50 times the thermal expansion coefficient of the cylinder is fitted in the sleeve insertion hole. For this reason, when the sleeve is shrunk due to the temperature drop due to the machine stoppage and becomes relatively shorter in the axial direction than the sleeve insertion hole of the cylinder, or conversely, the sleeve is extended due to the temperature rise during molding and the sleeve is relatively extended. When it becomes long, sliding with the sleeve insertion hole becomes easy. That is, since the sleeve and the cylinder are fitted to each other at room temperature with little clearance or loosely tightened, relative displacement in the axial direction between the sleeve and the cylinder due to a difference in thermal expansion is realized without resistance. Therefore, the end portion is not pressed against the cylinder or the cylinder head and is not damaged. Further, the fitting between the sleeve and the cylinder becomes tighter than the interference fit at the time of heating, and the outer periphery is held by the cylinder. Therefore, even if injection pressure acts on the inner surface of the sleeve in the injection process. , The destruction of the sleeve is prevented.
[0027]
Further, an inclined surface may be formed on the inner peripheral surface side of the sleeve front end and the sleeve rear end which are both ends of the sleeve. With this configuration, when the sleeve thermally expands, the inclined surfaces formed at both ends of the sleeve remove the deposits in the gap between the front end of the sleeve and the cylinder head or between the rear end of the sleeve and the cylinder. Thereby, it can be scraped out toward the inner surface of the sleeve. The height t ₁ of the inclined surface, accounting for 1 / 2-4 / 5 of the wall thickness t of the sleeve, and is formed at an angle α in the range of 30 to 60 ° with respect to the axis of the sleeve Is preferred.
[0028]
Further, the cylinder of the present invention may be one in which a seal ring made of a material having a hardness equal to or less than the hardness of the cylinder and the cylinder head is inserted into the seal surface.
[0029]
As described above, the cylinder for a metal injection molding machine of the present invention is configured to be sealed with a seal ring having a hardness equal to or less than that of the cylinder and the cylinder head. Even if it is damaged, the molten metal can be sufficiently sealed.
[0030]
Further, the cylinder for a metal injection molding machine of the present invention may be one in which a plurality of screw holes for extraction that penetrate the seal ring are formed in the seal ring. In this case, by inserting a bolt into these screw holes and pushing the front part of the cylinder, the seal ring can be easily pulled out.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
(1st Embodiment)
FIG. 1 is a side sectional view of a cylinder for a metal injection molding machine according to the present embodiment, and FIG. 2 is a partially enlarged view of a tip portion of the cylinder shown in FIG. It should be noted that numerical values and the like in the following description are merely examples, and the present invention is not limited to these.
[0032]
A screw 4 having a spiral groove 13 on its surface is inserted into the inner surface of the cylinder 1, a material hopper 5 is attached to the rear of the cylinder 1, and a heater 12 is attached to the outer periphery. A nozzle 3 is fixed to a front portion of the cylinder 1 via a cylinder head 2.
[0033]
A backflow prevention device 6 composed of a backflow prevention ring 8, a reed 9 and a screw head 7 is attached to the tip of the screw 4, and a piston ring 10 is attached to the outer periphery of the backflow prevention ring 8.
[0034]
A sleeve 11 made of a non-ferrous heat-resistant alloy is inserted into a portion of the inner surface of the cylinder 1 where the backflow prevention ring 8 and the piston ring 10 slide. Specifically, a sleeve 11 made of a Co-based heat-resistant alloy having a length L ₁ = 800 mm and a thickness t = 15 mm is fitted at room temperature to the inner surface of the front part of the cylinder 1 having an inner diameter of 110 mm made of an iron-based heat-resistant alloy. It is inserted with a tolerance H7 · js6 (an intermediate fit close to a clearance fit of −0.011 to +0.046). The cylinder 1 has a thermal expansion coefficient of 11 × 10 ⁻⁶ / ° C. at 20 to 600 ° C., and the sleeve 11 has a coefficient of thermal expansion of 13 × 10 ⁻⁶ / ° C. The material of the sleeve 11 is preferably selected so that the coefficient of thermal expansion of the sleeve 11 is in the range of 1.03 to 1.50 times the coefficient of thermal expansion of the cylinder 1. It is particularly preferred that it is within the range of 1.20 times.
[0035]
The sleeve 11 is lightly fixed to the cylinder 1 by lightly shrink fitting, that is, by inserting the sleeve 11 at room temperature while the cylinder 1 is heated to 150 to 200 ° C. That is, the fitting between the sleeve 11 and the cylinder 1 is such that there is almost no gap or loose tightening at room temperature, and the interference fit is close to 600 ° C.
[0036]
The length of the sleeve insertion hole 16 of the cylinder 1, i.e., the cylinder head 2 is mounted, the length L ₂ from the sealing surface 17 of the seal is made by abutting to the rear end face 22 is set to 802mm.
[0037]
In this embodiment, the length L ₁ of the sleeve 11 has become a 2mm shorter than the axial length L ₂ of the sleeve insertion hole 16. Thus, the length _{L 1} of the sleeve 11, the difference between the sleeve insertion hole _{L 2,} i.e., the gap 23 formed between the sleeve insertion hole 16 and the sleeve 11 is in the range of 0.5~10mm Is preferred, and it is particularly preferred that the thickness be in the range of 2 to 5 mm.
[0038]
Next, operations of the metal injection molding machine of the present embodiment at the time of metering and at the time of injection will be described.
[0039]
In the forming operation, the rice-sized material chips put into the material hopper 5 fall onto the spiral grooves 13 on the surface of the screw 4 inserted into the cylinder 1. When the screw 4 rotates backward (rightward in FIG. 1) by a driving device (not shown), the material chip is fed forward along the spiral groove 13 while being heated by the heater 12 attached to the outer periphery of the cylinder 1. , And becomes a molten or semi-molten state molten metal, and is stored in the front chamber 15 of the cylinder 1.
[0040]
When the stored molten metal reaches a certain amount, the screw 4 is advanced at a high speed by the driving device, and the molten metal stored in the front chamber 15 of the cylinder 1 is injected into the mold (not shown) through the nozzle 3 at a high speed and a high pressure. Is done.
[0041]
The molten metal filled in the cavity in the mold is cooled and solidified, and then the mold is opened to be taken out as a molded product. In the meantime, the next measuring step is executed, and after the mold is closed again, the next injection step is executed.
[0042]
In the injection process, when the screw 4 moves forward and the pressure of the molten metal in the front chamber 15 rises, the molten metal tends to flow backward in the direction of the screw 4, but the backflow prevention device including the backflow prevention ring 8, the oscillating 9 and the screw head 7. Blocked by 6.
[0043]
The outer diameter of the backflow prevention ring 8 is set so that the gap between the backflow prevention ring 8 and the inner surface of the cylinder 1 is reduced, and the piston ring 10 attached to the outer periphery of the backflow prevention ring 8 is strongly pressed against the inner surface of the cylinder 1. Backflow from the gap with the outer periphery of the backflow prevention ring 8 is prevented.
[0044]
In the case of the present embodiment, the sealing surface 17 at the front part of the cylinder 1 abuts on the cylinder head 2, and the molten metal is always sealed at this part. The sleeve 11 withstands the injection internal pressure of about 100 MPa by holding the outer periphery by the cylinder 1 at the time of molding, withstands high-speed sliding with the backflow prevention ring 8 and the piston ring 10 at a maximum speed of 5 m / s, and prevents the backflow of the molten metal. Can be blocked. Also, the sleeve 11 may be relatively shorter in the axial direction than the sleeve insertion hole 16 of the cylinder 1 (about 1 mm in the case of the present embodiment) due to the temperature drop due to the machine stop, or conversely, the temperature may increase due to the temperature rise during molding. When the sleeve 11 is relatively long, the sleeve 11 slides easily with the sleeve insertion hole 16, and the end portion is not strongly damaged by being pressed against the cylinder 1 or the cylinder head 2.
(Second embodiment)
FIG. 3A is a partially enlarged view of a tip portion of the cylinder for a metal injection molding machine according to the present embodiment, and FIG. 3B is an enlarged view of a portion A in FIG. 3A. It should be noted that numerical values and the like in the following description are merely examples, and the present invention is not limited to these.
[0045]
In the following description, a description of parts having the same functions as those in the first embodiment will be omitted, and only different points will be described. In addition, the same components as those in the first embodiment will be described. Description will be made using the same reference numerals. That is, the dimensional relationship between the sleeve 11a of this embodiment and the sleeve insertion hole 16 formed in the cylinder 1 and the relationship between the thermal expansion coefficient of the sleeve 11a and the cylinder 1 are the same as those of the first embodiment. It is.
[0046]
The inner circumferential surface 11d side of the sleeve front end 11a and the sleeve rear end 11b which is both ends of the sleeve 11a, with a length _{L 3} 10 mm, the inclined portion 18, 18 'is inclined an angle alpha = 45 ° with respect to the axis Is provided. In addition, it is preferable that the inclined portions 18 and 18 'are formed in a range where the angle α is 30 to 60 °. Further, it is preferable that the height t ₁ occupied by the inclined surfaces 18 and 18 ′ with respect to the thickness t of the sleeve 11 is within a range of ２〜 to ／ of the thickness t of the sleeve 11.
[0047]
When the temperature of the cylinder 1 rises and the sleeve 11a expands, the axial gap 23 between the sleeve front end 11b and the cylinder head 2 or the sleeve rear end 11c and the cylinder 1 decreases. At this time, undissolved deposits such as oxides and nitrides, which are part of the components in the molten metal, remain in the gaps 23 due to the inclined portions 18, 18 'provided on the inner surfaces of both ends of the sleeve 11a. It is scraped out in the inner surface direction of 11a.
[0048]
In addition, instead of providing the inclined portions 18 and 18 ′ on the inner surfaces of both ends of the sleeve 11 a, a similar inclined portion may be provided on a portion of the cylinder 1 or the cylinder head 2 facing the end surfaces 11 b and 11 c of the sleeve 11 a. The effect can be obtained.
[0049]
As described above, in the case of the present embodiment, the attached matter in the gap 23 is scraped toward the inner surface of the sleeve 11a by the inclined portions 18 and 18 'due to the thermal expansion of the sleeve 11a. By being buried, the sleeve 11a cannot absorb the difference in thermal expansion of the sleeve 11a and receives strong compression in the axial direction, so that the sleeve front end 11b or the sleeve rear end 11c buckles or collapses as a whole. Can be prevented. Further, similarly to the first embodiment, the sleeve 11a can withstand the injection internal pressure and the high-speed sliding with the backflow prevention ring 8 and the piston ring 10, and can prevent the backflow of the molten metal. Since the sliding with the cylinder head 16 is easy, the sleeve front end 11b or the sleeve rear end 11c is not pressed against the cylinder 1 or the cylinder head 2 and is not damaged.
(Third embodiment)
FIG. 4 is a partially enlarged view of the tip of the cylinder for a metal injection molding machine of the present embodiment, FIG. 5 is an enlarged view of the vicinity of the seal ring shown in FIG. 4, and FIG. The sectional views taken along the line B are shown. In the following description, description of portions having functions similar to those of the first and second embodiments will be omitted, and only different points will be described. In addition, the configuration shown in the first and second embodiments will be described. Elements that are the same as the elements will be described using the same reference numerals. Further, in each drawing, the sleeve 11a having the inclined surfaces 18 and 18 'shown in the second embodiment is illustrated as an example.
[0050]
In the case of this embodiment, a seal ring 19 made of an iron-based heat-resistant alloy having a slightly lower hardness than the cylinder 1 and the cylinder head 2 is inserted into an axial contact surface between the tip of the cylinder 1 and the cylinder head 2. . Therefore, even when the contact surface between the cylinder 1 and the cylinder head 2 is damaged during disassembly and cleaning, the molten metal can be sufficiently sealed by the seal ring 19.
[0051]
The outer edge portion 21 of the seal ring 19 is formed thinner than other portions, and a plurality of screw holes 20 are formed in the outer edge portion at equal intervals on the circumference. Therefore, by inserting a bolt into these screw holes 20 and pushing the front part of the cylinder 1, the seal ring 19 can be easily pulled out.
[0052]
As described above, in the case of the present embodiment, since the sealing is performed by the seal ring 19 made of an iron-based heat-resistant alloy having a hardness equal to or less than that of the cylinder 1 and the cylinder head 2, the contact between the cylinder 1 and the cylinder head 2 is performed. Even if the surface is damaged, the molten metal can be sufficiently sealed. Further, similarly to the first embodiment, the sleeve 11a can withstand the injection internal pressure and the high-speed sliding with the backflow prevention ring 8 and the piston ring 10, and can prevent the backflow of the molten metal. Since the sliding with the cylinder head 16 is easy, the sleeve front end 11b or the sleeve rear end 11c is not pressed against the cylinder 1 or the cylinder head 2 and is not damaged. Further, as in the second embodiment, the thermal expansion of the sleeve 11a scrapes off the deposits in the gap 23 toward the inner surface of the sleeve 11a by the inclined portions 18 and 18 '. By being buried, the sleeve 11a cannot absorb the difference in thermal expansion of the sleeve 11a, and the sleeve 11a is strongly compressed in the axial direction, and the sleeve front end 11b or the sleeve rear end 11c buckles or collapses as a whole. Can be prevented.
[0053]
【The invention's effect】
As described above, according to the present invention, the sleeve having a larger coefficient of thermal expansion than the coefficient of thermal expansion of the cylinder and shorter than the length of the sleeve insertion hole in the axial direction has almost no gap at room temperature or the cylinder is loosely tightened. , The axial relative displacement between the sleeve and the cylinder due to the difference in thermal expansion is realized without resistance, so that the end is not strongly pressed against the cylinder or the cylinder head and is not damaged. Further, this fitting is such that the sleeve is held on the outer periphery by the cylinder due to the tight fitting at the time of heating, which is more than the interference fit. Is prevented from being destroyed. Further, due to the inclined surfaces formed at both ends of the sleeve, it is possible to scrape off the deposits causing the buckling of the sleeve by the inclined portion.
[0054]
Further, in the configuration in which the gap between the cylinder and the cylinder head is sealed with a seal ring, the molten metal can be sufficiently sealed even if the contact surface between the cylinder and the cylinder head is damaged during disassembly and cleaning.
[Brief description of the drawings]
FIG. 1 is a side sectional view of a cylinder for a metal injection molding machine according to a first embodiment of the present invention.
FIG. 2 is a partially enlarged view of a tip portion of the cylinder shown in FIG.
FIG. 3 is an enlarged side sectional view of a part of a distal end portion of a cylinder for a metal injection molding machine according to a second embodiment of the present invention.
FIG. 4 is an enlarged side sectional view of a part of a distal end portion of a cylinder for a metal injection molding machine according to a third embodiment of the present invention.
FIG. 5 is an enlarged side sectional view of a part of a seal ring in which a screw hole is formed.
FIG. 6 is a sectional view taken along line BB of FIG. 5;
FIG. 7 is a side sectional view of a conventional example of a cylinder for a metal injection molding machine.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cylinder 2 Cylinder head 3 Nozzle 4 Screw 5 Material hopper 6 Backflow prevention device 7 Screw head 8 Backflow prevention ring 9 Oscillating 10 Piston ring 11, 11a Sleeve 11b Sleeve front end 11c Sleeve rear end 11d Inner peripheral surface 12 Heater 13 Spiral groove 14 Bolt 15 Front chamber 16 Sleeve insertion hole 17 Sealing surface 18, 18 'Inclined portion 19 Seal ring 20 Screw hole 21 Outer edge 22 Rear end surface 23 Clearance

Claims (6)

In a cylinder for a metal injection molding machine, a sleeve insertion hole for inserting a sleeve is formed in a region where a backflow prevention ring of a backflow prevention device that prevents backflow of a molten material slides, and a cylinder head can be attached to a tip thereof.
Inside the sealing surface (17) between the cylinder (1) and the cylinder head (2), a material having a larger coefficient of thermal expansion than the coefficient of thermal expansion of the cylinder (1), and a temperature range from room temperature to a molding temperature. in the cylinder head (2) said sealing surface (17) from the rear end face (22) to said axial length _{L 2} shorter overall length _{L 1} of the sleeve than the sleeve insertion hole (16) of which is mounted (11 ) Is fitted into the sleeve insertion hole (16) at room temperature by either a clearance fit or an intermediate fit. The cylinder for a metal injection molding machine according to claim 1, wherein the thermal expansion coefficient of the sleeve (11) is 1.03 to 1.50 times the thermal expansion coefficient of the cylinder (1). The inclined surface (18, 18 ') is formed on the inner peripheral surface (11d) side of the sleeve front end (11b) and the sleeve rear end (11c) which are both ends of the sleeve (11). 4. A cylinder for a metal injection molding machine according to claim 1. The height _{t 1} of the inclined surface (18, 18 ') is accounted for 1 / 2-4 / 5 of the wall thickness t of the sleeve (11), and 30 with respect to the axis of said sleeve (11) 4. The cylinder for a metal injection molding machine according to claim 3, wherein the cylinder is formed at an angle α in the range of 60 °. The seal ring (19) made of a material having a hardness equal to or less than the hardness of the cylinder (1) and the cylinder head (2) is inserted into the seal surface (17). 4. A cylinder for a metal injection molding machine according to claim 1. The cylinder for a metal injection molding machine according to claim 5, wherein a plurality of screw holes (20) for extraction are formed in the seal ring (19) so as to penetrate the seal ring (19).

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