JPH07115147B2 - Die-casting cylinders - Google Patents

Description

The present invention relates to a cylinder for injecting molten metal in a die casting machine for non-ferrous metals such as aluminum alloys, and more particularly to a die casting cylinder of a composite structure in which an inner cylinder made of a ceramic material is fitted into an outer cylinder made of a metal material.

BACKGROUND ART: Generally, the cylinder constituting the injection device of a cold chamber die casting machine has a horizontal axis and an inlet opening at the top of the side near the end face. Molten metal is supplied through the inlet and injected into the mold cavity connected to the cylinder by a piston sliding within the cylinder. Therefore, the inner surface of the cylinder, particularly directly below the inlet, is often subject to melting damage due to the molten metal directly falling and impacting it, and wear due to the sliding of the piston. Damage to the inner surface of the cylinder due to melting damage or friction can lead to the molten metal penetrating between the cylinder and the piston, increasing the sliding resistance of the piston and reducing the injection speed, leading to reduced product quality, reduced workability, and further damage to the inner surface of the cylinder. Furthermore, using a large amount of lubricant to reduce the sliding resistance between the cylinder and the piston or to prevent seizure is undesirable because it can cause impurities to be mixed into the molten metal, thereby reducing product quality.

For this reason, cylinders made of nitrided steel with a hardness of approximately H _R C65 (H _v 832) have been used up to now. Although the use of such nitrided steel cylinders reduces wear and erosion of the cylinder's inner surface, there are still some shortcomings in terms of the durability of the cylinders and the quality of products cast using these cylinders.

Therefore, a die-cast cylinder has been proposed in which a ceramic cylinder having heat resistance and wear resistance is fitted to the inner circumferential surface of a steel cylinder into which a piston is fitted.

U.S. Pat. No. 3,664,411 discloses a die-casting cylinder having a ceramic inner layer that is resistant to corrosion and thermal fatigue by molten metal and a metal casing, the ceramic inner layer having a slightly tapered outer surface and the casing having a complementarily tapered inner surface, and when the inner layer is assembled into the casing, the inner layer is radially pressed against the casing over its entire length.

In addition, Japanese Patent Application Laid-Open No. 53-70034 discloses a molten metal injection cylinder with
The present invention discloses a die casting device characterized by the fact that a plurality of split sleeves made of ceramic are combined together.

In addition, Japanese Patent Laid-Open No. 61-67555 discloses a molten metal injection sleeve having a double structure of an inner cylinder and an outer cylinder, and
The patent discloses a die-casting injection sleeve characterized in that a cooling water jacket is formed between the inner cylinder and the outer cylinder.

Furthermore, Japanese Patent Laid-Open No. 61-103658 discloses a method for fitting an inner cylinder made of a non-ferrous metal material having ultra-heat resistance and ultra-wear resistance, such as ceramics or cermet, to the inner circumferential surface of an outer cylinder into which a piston is fitted, at least in the vicinity of a molten metal injection hole, with an appropriate interference, and forming a hole in the outer cylinder through which a heat transfer medium can be introduced.
The present invention discloses an injection cylinder for a mold casting machine, characterized in that one or more injection cylinders are provided.

While the above-described construction in which a ceramic inner cylinder is fitted inside a cylinder is extremely effective in improving wear resistance and corrosion resistance, there is still room for improvement in the point that the temperature of the molten metal poured into the cylinder drops. In other words, since die casting generally tends to be performed at a temperature of the molten metal as close as possible to its solidification temperature, the cylinder is required to have excellent thermal insulation, i.e., heat retention, in addition to the above-described properties, in order to prevent the temperature drop of the molten metal. In this respect, a cylinder fitted with a ceramic inner cylinder has slightly improved thermal insulation and heat retention compared to a conventional steel cylinder, but it does not fully satisfy the requirements of die casting.

Furthermore, when molten metal is poured into the cylinder, the lower part in contact with the molten metal heats up first, causing the cylinder to bend upward due to the difference in thermal expansion. This has led to problems such as cracks and breakage in the ceramic cylinder. To solve this problem, it is necessary to improve its thermal insulation and heat retention. In other words, if the ceramic cylinder, which heats up when it comes into contact with the molten metal, is sufficiently insulated from the metal outer cylinder, the temperature rise in the metal outer cylinder will be minimal, and the degree of bending due to the difference in thermal expansion can be reduced.

In view of the above, an object of the present invention is to provide a composite die-casting cylinder consisting of a ceramic cylinder and a metal outer cylinder, which has a structure in which the thermal insulation and heat retention properties between the ceramic cylinder and the metal outer cylinder are improved.

DISCLOSURE OF THE INVENTION The die-casting cylinder of the present invention has a metal outer cylinder and a ceramic inner cylinder, and is characterized in that a plurality of voids are provided at the boundary between the outer cylinder and the inner cylinder, the voids being formed as grooves provided on the inner surface of the outer cylinder or the outer surface of the inner cylinder, and the ratio a/b of the width a of the grooves to the spacing b is within the range of 1:1 to 6:1.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view showing a die-casting apparatus having a die-casting cylinder according to one embodiment of the present invention; FIG. 2 is a partially enlarged sectional view showing a void at the boundary between the metal outer sleeve and the ceramic outer sleeve of a die-casting cylinder according to one embodiment of the present invention; FIG. 3 is a partially enlarged sectional view showing a void according to another embodiment of the present invention; and FIG. 4 is a graph showing the temperature drop of the ceramic cylinder and the metal outer sleeve, where (a) shows the case where there is no void, and (b) shows the temperature drop of the ceramic cylinder and the metal outer sleeve.
shows a case where there is a void portion, Figure 5(a) is a partial cross-sectional view showing an example where the outer surface of a ceramic cylinder is expanded at the cylinder tip portion 1, Figure 5(b) is a partial cross-sectional view showing an example where the inner surface of a metal outer cylinder is reduced in diameter at the cylinder tip portion 1, Figure 6 is a vertical cross-sectional view showing a die-casting apparatus having a die-casting cylinder according to yet another embodiment of the present invention, and Figure 7 is a vertical cross-sectional view showing a die-casting cylinder according to yet another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Fig. 1 shows a die casting machine having a die casting cylinder according to one embodiment of the present invention. The die casting machine comprises a stationary platen 1 and a cylinder 2 detachably fixed to the stationary platen 1.
The mold has a fixed mold 3 fixed to the fixed platen 1, and a movable mold 4 that is movable relative to the fixed mold 3. A cavity 5 is formed in the movable mold 4, and a sprue 6 that communicates with the cavity 5 and the cylinder 2 is provided in the fixed mold 3.

The cylinder 2 is composed of a metal outer cylinder 21 and a ceramic cylinder 22, and has a molten metal injection port 23 formed at the top near the rear end. A piston tip 7 is slidably inserted into the rear end of the cylinder 2, and the piston tip 7 is slidably moved back and forth within the cylinder 2 by a piston rod 8.

In the cylinder 2 having such a configuration, first, molten metal is poured into the cylinder 2 through the pouring port 23, and then the piston tip 7
The molten metal is pushed toward the mold by the piston tip 7 (see 7a). The pressure of the piston tip 7 causes the molten metal to enter the mold cavity 5, where it solidifies to obtain a molded product of the desired shape.

In the present invention, a metal outer cylinder 21 and a ceramic cylinder 22
A feature of this method is that a plurality of voids 24 are formed at the boundary between the adjacent voids. Fig. 2 shows a preferred example. In the example of Fig. 2, the voids 24 are grooves having a semicircular cross section, and the width (opening size) a of each void 24 is
It is preferable that the following relationship be satisfied between the distance b of the first and second electrodes 24 and the distance b of the second and third electrodes 24:

a/b = 1:1 to 6:1 (1) As a:b approaches 1, the heat insulating effect of the voids 24 decreases, and if a/b < 1:1, it becomes insufficient. On the other hand, as a:b increases, the shear force acting on the ceramic cylinder 22 increases due to the compressive force caused by the shrink fitting of the outer cylinder 21.
To prevent destruction, the upper limit of a/b is 6:1.

On the other hand, the relationship between the wall thickness t of the ceramic cylinder 22 and the width a of the hole 24 is preferably a≦t (2). If a>t, the shear force acting on the ceramic cylinder 22 will be too large, which may cause the inner cylinder 22 to break. On the other hand, if the hole 24 is too small, the heat insulation and heat retention will not be sufficient even if the above requirements are met. Therefore, the width (diameter) a of the hole 24 should be set to a value less than t.
It is desirable that the thickness is 1 mm or more.

The cavity 24 is preferably formed by grooves, which may be a plurality of circumferential grooves, a spiral groove, or a plurality of grooves extending in the longitudinal direction of the cylinder. In any case, it is preferable that the above requirements (1) and (2) are satisfied.

3 shows a cavity 25 according to another embodiment of the present invention. In this embodiment, the cavity 25 has a triangular cross section and is formed of circumferential grooves, spiral grooves or longitudinal grooves, as in FIG. 2.

Although preferred shapes of the grooves are shown in Figures 2 and 3, the present invention is not limited to these, and the voids can be formed by grooves having a cross section of, for example, a rectangular, square, trapezoidal, or other shape.

The width a and spacing b of each groove are set to satisfy the requirements of the above formulas (1) and (2). Specifically, the width a of each groove is 1 to 6 mm, the spacing b is about 1 to 3 mm, and the depth of the groove is 0.2 to 1.0 mm.
It is preferable to set it to mm.

The voids described above are preferably present along the entire length of the boundary between the metal outer cylinder 21 and the ceramic cylinder 22, but they may be provided only in areas where the temperature rise is particularly large. Also, while it is preferable for the voids to be formed on the inner surface of the metal outer cylinder for processing purposes, they may also be provided on the outer surface of the ceramic cylinder in some cases.

Fig. 4 shows the heat insulating effect of the pores. As shown in (a), when there are no pores, the ceramic cylinder
The temperature difference _ΔT0 between the inner surface of 22 and the outer surface of the metal outer cylinder 21 is not very large, but when the voids 24 are present ((b)), the temperature difference _ΔT1 becomes very large due to the insulating heat-retaining effect. Comparing the temperatures of the metal outer cylinder in cases (a) and (b), it can be seen that the temperature in case (b) is much lower. Therefore, in case (b), the thermal expansion of the metal outer cylinder is small, reducing the bending of the cylinder and therefore reducing the risk of damage to the ceramic cylinder 22.

The outer and inner cylinders 21 and 22 are shrink-fitted together at a shrink-fit ratio of 1/1000 to 6/1000. This configuration prevents loosening of the bond due to differential expansion between the inner and outer cylinders 22 and 22 when molten metal is poured into them. When the piston 7 is operated after pouring molten metal into the inner cylinder 22 shown in FIG. 1, the inner cylinder 22 is filled with molten metal, causing it to heat and expand. Furthermore, the outer cylinder 21 also heats and expands due to heat transfer. In this case, the thermal expansion coefficient of the metal outer cylinder 21 is higher than that of the ceramic inner cylinder 22, so the difference in expansion between the two cylinders causes the shrink-fit to loosen when heated. However, the shrink-fit ratio is set to absorb the difference in thermal expansion, preventing loosening of the bond between the outer and inner cylinders 21 and 22. Furthermore, in the cylinder of the present invention, the insulating and heat-retaining voids 24 are provided at the boundary between the inner cylinder 22 and the outer cylinder 21, so the temperature rise of the outer cylinder 21 is small, and therefore the thermal expansion is small. This further improves the function of preventing loosening between the two.

Furthermore, the shrink fit ratio imparts compressive stress to the inner cylinder 22, which acts to counteract the tensile stress acting on the inner cylinder 22 due to the hydraulic pressure generated when the molten metal is injected by the piston, thereby preventing cracks in the inner cylinder 22 caused by the tensile stress.

5(a) and (b) are cross-sectional views showing the shapes of an inner cylinder 22 and an outer cylinder 21 according to yet another embodiment of the present invention. In Fig. 5(a), the outer diameter of the tip portion 1 of the inner cylinder 22 is enlarged, and the outer diameters of other portions are gradually reduced.
On the other hand, the inner diameter of the outer cylinder (not shown) is made the same over the entire length, and in the range of the tip portion 1, a fitting ratio (shrink fitting ratio), for example, 2/1000 to 6/1000, sufficient to reinforce the inner cylinder 22 can be ensured. Therefore, the fitting ratio in the areas other than the tip portion 1 is slightly smaller than the above value.

By forming the cylinder 21 as described above, a sufficient fit between the inner and outer cylinders is ensured in the range of the tip portion l where injection pressure is applied, thereby providing reinforcement for the inner cylinder 22. This prevents tensile stress in the inner cylinder 22 due to the application of injection pressure, differences in thermal expansion, and other factors, thereby preventing cracks. Meanwhile, the fit in areas other than the tip portion is smaller than that in the range l, preventing cracks in the inner cylinder 22 near the injection port 23. Furthermore, after the molten metal is poured into the cylinder 2, the lower portion of the cylinder 2 is heated during the transition to injection, which causes a difference in thermal expansion between the outer cylinder 21 and the inner cylinder 22. However, the small fit between the inner and outer cylinders allows the difference in thermal expansion to be fully absorbed, preventing undesirable thermal stress.

Figure 5(b) shows a case where the inner diameter of the outer tube 21 is the same at the tip 1 and the inner diameter of other parts is gradually increased. In this case, the outer diameter of the inner tube (not shown) is the same over the entire length, and in the range of the tip 1,
The fitting rate must be sufficient to reinforce the inner cylinder. The operation of this configuration is the same as that of Fig. 5(a).

The above-described structure sufficiently reinforces the inner cylinder made of ceramic material while reducing the restraining force in the area where injection pressure is not applied, completely preventing cracks from occurring near the injection port. As a result, the inherent properties of ceramic material, such as wear resistance, corrosion resistance, and heat insulation, can be fully utilized, significantly contributing to improvements in the durability of the die-cast sleeve, the yield of die-cast products, and energy costs.

6 shows a die-casting cylinder according to yet another embodiment of the present invention, which has a metal inner cylinder at the tip. The die-casting cylinder 52 is detachably fixed to a fixed platen 51, to which a fixed mold 53 is fixed, and a movable mold 54 is provided so as to be able to open and close relative to the fixed mold 53. The cylinder 52 comprises a metal outer cylinder 59 and a ceramic inner cylinder 60.
It is a split type, and the tip portion is made up of a metal outer cylinder 61 having a tip flange 62 and a metal inner cylinder 63.

Molten metal 58 is poured into the cylinder from a ladle 56 and is forced into the cavity 55 by a piston 57. At this time, the pressure of the molten metal 58 pressed by the piston 57 becomes very high at the tip of the cylinder, which may cause damage to the inner cylinder. Therefore, in order to completely prevent damage to the tip,
It is preferable to use a metal inner tube at the tip portion, which also has the advantage of improving the cooling effect of the molten metal, shortening the solidification time of the molten metal in the cavity, and shortening the die casting cycle.

FIG. 7 shows a die-cast cylinder 71 in which a water channel 77 is provided inside a metal outer cylinder 72 to prevent the temperature of the metal outer cylinder 72 from rising.
An example of a cylinder 71 is shown in Figure 1. The basic structure of this cylinder 71 is the same as that shown in Figure 1, and it has a metal outer cylinder 72, a ceramic inner cylinder 73, and an inlet 74. A piston tip 75 fixed to the tip of a piston rod 76 slides inside the cylinder. The water channel 77 may be spiral, for example, or may extend in the longitudinal direction. Furthermore, if it extends in the longitudinal direction, the ends of adjacent water channels may be connected to form a single water channel as a whole. The cooling effect can be improved by providing two or more water supply and outlet ports for the water channel, if necessary.

Various ceramic materials can be used as the ceramic inner cylinder that constitutes the die-casting cylinder having the above structure, but from the standpoints of heat resistance, seizure resistance, thermal shock resistance, etc., those made of silicon nitride ceramic or sialon are preferred.

A typical composition of silicon nitride ceramic or _sialon is 70% by weight or more of _Si3N4 , 20% by weight or less of at least one oxide of an element from Group IIa or IIIa of the periodic table, 20% by weight or less _{of Al2O3} , and 10% by weight or less of an AlN solid solution (AlN- _Si3N4 - _{Al2O3 system} ) or _AlN , and is obtained by sintering these mixtures. The silicon nitride or sialon inner cylinder can be formed by molding the raw material powder using a cold isostatic press, sintering it at atmospheric pressure, and processing it to the specified dimensions. This ceramic inner cylinder has a bending strength of 50 kg/ ^mm2 or more,
It has a density of 90% or more of the theoretical density and a thermal shock resistance temperature ΔT of 300°C or more when dropped into water.

The outer cylinder is preferably made of tool steel, but may also be made of structural steel, alloy steel, non-ferrous metal, or the like.

Example 1 87% by weight of Si ₃ N ₄ , 6% by weight of Y ₂ O ₃ , 4% by weight of Al ₂ O ₃ and AlN
The inner cylinder (outer diameter 75 mm) was made of sialon and consisted of 3% by weight of solid solution.
mm, inner diameter 60 mm, length 230 mm) and an outer cylinder made of SKD-61 (outer diameter
The outer cylinder has a semicircular groove (width 2 mm, inner diameter 75 mm, length 250 mm) fixed to the inner surface by shrink fitting.
The cylinder was provided with 1 mm intervals around the circumference of the cylinder (0.5 mm deep, 0.5 mm in diameter). A molten metal injection port was provided at the top of the rear end of the cylinder.

The cylinder with this structure was attached to the die-casting machine (clamping force 800t) with the structure shown in Figure 1, and the casting was performed using molten aluminum alloy at 760°C with a casting cycle of 72 seconds and a hardening time of 20 seconds.
The die casting was carried out under the casting conditions of 100,000 seconds.
It was confirmed that the material can withstand more than 0 shots, with almost no damage, and has excellent heat insulation and heat retention properties.

Example 2 Using the same SiAlON inner cylinder and SKD-61 outer cylinder as in Example 1, the inner surface shape of the outer cylinder was designed as shown in Figure 5(b), so that the fitting ratio was 4/1000 at the tip portion 1 and 4/1000 to 1.5/1000 in other parts.

When die casting was carried out under the same conditions as in Example 1 using a cylinder of this structure, it was found to withstand over 150,000 shots without any cracks occurring near the injection port.

The die-casting cylinder of the present invention has excellent heat insulation properties due to the voids at the boundary between the metal outer cylinder and the ceramic inner cylinder, so that the temperature rise of the metal outer cylinder can be kept low even when molten metal is poured into it, thereby reducing the difference in thermal expansion between the lower part of the cylinder that comes into contact with the molten metal and the upper part that does not, and preventing the cylinder from warping upward, thereby effectively preventing damage to the ceramic inner cylinder.

Furthermore, due to the heat insulating effect, poor molten metal flow can be prevented even in cast products with thin-walled portions, making it possible to produce high-quality die-cast products.

Furthermore, since there is no need to increase the temperature of the molten metal more than necessary, defects such as oxidation of the molten metal or an increase in the gas content due to overheating, which have been experienced in the past, can be drastically reduced.

Furthermore, damage to the ceramic inner cylinder has been prevented,
This can significantly extend the life of the cylinder.

The die-casting cylinder of the present invention having the above-mentioned features is particularly suitable for use in a cold chamber type die-casting machine for non-ferrous metals such as aluminum alloys.

──────────────────────────────────────────────────── Continued from the front page (56) References: Japanese Patent Application Publication No. 109150 (JP, A) Japanese Patent Application Publication No. 44726 (JP, A) Japanese Utility Model Application Publication No. 140710 (JP, U) Japanese Utility Model Application Publication No. 177758 (JP, U) Japanese Patent Application Publication No. 31533 (JP, B1)

Claims (5)

[Claims] [Claim 1] A device having a metal outer cylinder and a ceramic inner cylinder, wherein a plurality of holes are provided at the boundary between the outer cylinder and the inner cylinder, and the holes are formed by grooves provided on the inner surface of the outer cylinder or the outer surface of the inner cylinder, and the width a of the grooves is
A die casting cylinder characterized in that the ratio a/b of the gap a to the gap b is in the range of 1:1 to 6:1. [Claim 2] A die-casting cylinder as described in claim 1, characterized in that the fit rate between the outer tube and the inner tube near the die cavity side end where injection pressure is applied is greater than the fit rate at other locations. 3. The die-casting cylinder according to claim 1 or 2, wherein the inner cylinder at the end on the die cavity side is made of metal. 4. A die-casting cylinder according to claim 1, wherein said metal outer cylinder has a cooling water passage therein. [Claim 5] A die-casting cylinder as described in any one of claims 1 to 4, characterized in that the ceramic inner tube is made of silicon nitride ceramic or sialon, has a bending strength of 50 kg/ ^mm2 or more, a density of 90% or more of the theoretical density, and a thermal shock resistance temperature ΔT of 300°C or more when measured by a water immersion method.