JPH0429462B2 - - Google Patents

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a pressure casting method and apparatus applied, for example, to the production of light alloy castings, and in particular improves the flow velocity control technology of pressurized molten metal in a cavity. This invention relates to a pressure casting method and apparatus. (Prior art) Conventionally, when producing high-quality light alloy castings, air or inert gas is supplied into a furnace containing molten metal to pressurize the molten metal in the furnace, thereby molding the molten metal into a mold. The low-pressure casting method, in which the metal is supplied into the cavity, is widely used. FIG. 3 shows a conventional pressure casting apparatus used to carry out such a casting method. As shown in FIG. 3, a crucible 2 is installed in a closed furnace 1 having a pressurized gas supply port 1a, and cavities 4a, 4b, 4c of a mold 4 are placed inside the crucible 2 and on the furnace 1. and are connected via an introduction pipe 5. During casting, pressurized gas is blown into the furnace 1 from the pressurized gas supply port 1a, and the molten metal 3 is introduced into the cavities 4a, 4b, 4c of the mold 4 through the introduction pipe 5 by the pressure.
to be pumped to. By the way, as is well known, when casting using a mold, heat transfer occurs at the interface between the mold and the molten metal, and the molten metal rises while forming a solidified layer on the inner surface of the cavity. The thickness δ of this solidified layer is a function of the cross-sectional area of the casting (the cross-sectional area of the cavity), the temperature of the molten metal, the temperature of the mold, the rising speed of the molten metal, etc., as expressed by the following equation (1). D: Cross-sectional area of casting λ: Thermal conductivity of solidified layer θ ₁ : Temperature of solidified layer θ ₂ : (Temperature of molten metal - solidification temperature) c: Specific heat v: Flow velocity When this solidified layer reaches a certain thickness, The flow of molten metal stops within the cavity, making it impossible to form a casting. Figure 4 shows experimental data showing the relationship between the cross-sectional area of the casting and the critical flow velocity at which the flow of the molten metal stops.
On the other hand, the flow rate has a relationship with the rate of increase in pressure in the furnace per unit time (hereinafter referred to as pressurization rate) as shown in equation (2) below. u=Pν×(V ₀ +V)+V/{(γ/1000)
×(H+V/A)×(V ₀ +V)+V}×H u: Flow rate of molten metal H: Filling height Pν: Pressurizing speed A: Pressurizing area of molten metal in the furnace V ₀ : Space volume in the furnace V : Filling volume γ: Specific gravity of the molten metal For this reason, for general castings with little variation in cross-sectional area, use Fig. 4 to determine the flow velocity V at which the molten metal does not stop, based on the typical cross-sectional area of the casting, and further (2) The rate of pressurization into the furnace can be set using the formula. However, in castings with large variations in cross-sectional area, when cast at a constant pressurizing speed, vortices are likely to form in the molten metal, as shown by the arrows in FIG. 5, especially in areas where the cross-sectional area of the cavity suddenly changes. When such a vortex is generated, gas defects due to oxide entrainment and air entrainment occur in the cast product. For this reason,
In areas where the cross-sectional area suddenly changes, it is necessary to change the pressurization rate to a flow rate that does not generate vortices. As a method of changing the pressurizing speed at a portion where the cross-sectional area changes, for example, as shown in FIG.
A commonly used method is to provide thermocouples 6a and 6b, detect when the molten metal reaches the cross-sectional area changing portion, and then change the pressurizing speed. Experimental results using such conventional pressure casting technology are shown below. FIG. 6 is a schematic diagram of the mold used in the experiment.
Upper cavity 4c (large cross-sectional area) and lower cavity 4b (small cross-sectional area)
The cross-sectional area ratio S ₂ /S ₁ was varied from 1.5 to 10.0, and the cross-sectional area S ₁ of cavity 4b was varied from 154 mm ² to 616 mm ² , and molten pure aluminum was cast. It was set according to the area using Fig. 4 and formula (2). Pressure switching was performed by a signal from a thermocouple 6b provided near the section where the cross-sectional area changed. In addition, the pressurization speed after pressure switching is 0.02Kg/cm ² /
It was held constant at sec. The experimental results are shown in Table 1 below.

[Structure of the invention]

(Means for Solving the Problems) The pressure casting method according to the present invention pressure-feeds molten metal from a furnace to a mold, and adjusts the flow rate of the molten metal in the mold to correspond to changes in the cross-sectional area of the cavity. In the controlled pressure casting method, infrared rays emitted from the molten metal itself are input to an infrared sensor embedded in the mold to detect the molten metal's approach to and passage of the cavity cross-sectional area change area, and based on the detected value. It is characterized by changing the flow rate of the molten metal. Further, the pressure casting apparatus according to the present invention includes a furnace for storing molten metal, a pressurizing means for pressurizing the molten metal in the furnace, and a mold having cavities with different cross-sectional areas.
A molten metal introduction pipe that connects the furnace and the mold and supplies pressurized molten metal to the mold, and is buried near the cavity cross-sectional area changing part in the mold to detect infrared rays emitted by the molten metal itself that approaches and passes through the said position. It is equipped with an infrared sensor and a pressure control device connected to the sensor and configured to set the flow rate of the molten metal corresponding to changes in the cross section of the cavity by changing the pressurizing pressure of the molten metal in the furnace. Features. (Function) According to the present invention, the proximity and passage of the molten metal to the portion where the cross-sectional area of the cavity changes is detected by inputting infrared rays emitted from the molten metal, so there is no delay in detection time and the speed of the molten metal can be controlled. You will be able to do it sharply and reliably. In other words, since the present invention detects infrared rays emitted from the molten metal itself using an infrared sensor installed at a certain location, when the molten metal is located away from the infrared sensor, it is detected by the same sensor. The amount of infrared rays is small, and as the molten metal approaches the infrared sensor, the amount of infrared rays detected gradually increases, and after reaching the sensor position, the amount of infrared rays detected remains approximately constant. Therefore, in the present invention, the approach of the molten metal to the sensor position can be detected by increasing the amount of infrared rays emitted from the molten metal itself and incident on the infrared sensor, and the passage of the molten metal can be detected by keeping the amount of incident light constant. By accurately and instantaneously detecting the approach and passage of the molten metal to the section where the cross-sectional area changes, the pressurization rate of the molten metal can be controlled more precisely. Therefore, the flow rate of the molten metal can be controlled appropriately, and high-quality castings without gas defects can be manufactured. (Example) Hereinafter, an example in which the present invention is applied to a low-pressure casting apparatus will be described with reference to FIGS. 1 to 3. First, the configuration of the pressure casting apparatus will be explained. As shown in FIG. 1A, compressed air introduction pipe 11a
A crucible 12 is housed in a closed furnace 11 having a molten aluminum (hereinafter referred to as
It contains 13 (simply referred to as molten metal). A metal mold 14 serving as an aluminum casting mold is installed above the furnace 11. Cavities 15a, 15b, and 15c having different cross-sectional areas are continuously formed in the mold 14 in the vertical direction. This mold 1
The cavity 15a of No. 4 and the crucible 12 are inserted into the introduction pipe 1.
6 and by applying pressure to the surface of the molten metal 13 in the crucible 12, the introduction pipe 16
The molten metal 13 is passed through the cavity 15a of the mold 14.
We are planning to introduce it to The mold 14 is provided with first and second infrared sensors 17 and 18 as detectors for detecting the approach and passage of the molten metal 13 to the portion where the cross-sectional area of the cavity changes. The first infrared sensor 17 is located in the lowest cavity (first large cross-sectional area) with a large cross-sectional area.
15a, and the molten metal 13 is placed in the middle second cavity (small cross-sectional area) with a small cross-sectional area.
15b and detects passing through that part. In addition, the second infrared sensor 18
is placed near the upper end of the small cross-sectional area portion 15b, and the molten metal 13 is placed in the uppermost cavity (second
(large cross-sectional area) 15c, and detects that the object passes through that part. FIG. 2 shows the configuration of the infrared sensors 17 and 18 in detail. Note that since the first infrared sensor 17 and the second infrared sensor 18 have substantially the same configuration, only the second infrared sensor 18 will be described. As shown in FIG. 2, a mounting hole 19 is formed extending from the outside of the mold 14 to the cavity 15b, and an infrared sensor 18 is embedded in this mounting hole 19. The infrared sensor 18 includes a window member 21, a condensing lens 22, and an optical fiber 23 in a cylindrical holder 20.
are housed coaxially, and the nut 2 is placed in the mold 14.
It is fixed via 4. The window member 21 has a convex shape, and together with the holder 20 forms a part of the peripheral wall of the small cross-sectional area portion 15b of the cavity. The window member 21 is made of a material with high heat resistance and transparency, such as quartz glass or sapphire single crystal, and has high mechanical strength against heat generated when the molten metal passes through it, and allows a large amount of light to enter. The condensing lens 22 is, for example, spherical, and the window member 21
The window member 21 is arranged adjacent to the window member 21 so that the light from the window member 21 is efficiently and uniformly collected. The optical fiber 23 is inserted into the holder 20 via a holding tube 25 and fixed with a set screw 20a, and the insertion end is adjacent to the lens 22, and the light focused by the lens 22 is transferred to the mold. 14 to the outside. An optical cable 27 held by a guide tube 26 is connected to the outer end of the optical fiber 23. A cooling air passage 28 for preventing thermal deterioration of the optical fiber 23 is formed on the outer peripheral side of the holding tube 25 for the optical fiber 23 . This air passage 28 has a double structure, with an inner passage part 28a connected to an air supply device (not shown) via an air inlet nozzle 29 provided at the outer end of the holder 20, and an outer passage part 28b connected to the inner passage part 28a. It communicates with the inner end of the holder 20 and is open to the atmosphere through an outlet hole 30. Note that there is also a gap 3 between the holder 20 and the mold 14.
1 to reduce heat transfer between them. As shown in FIG. 1A, the optical cable 27 is connected to a pressure control device 32 for pressurizing the molten metal. The pressure control device 32 branches and connects a plurality of vent branch pipes 36 with different diameters to a vent pipe 34 led out from the surge tank 33 via a pressure reducing valve 35, and each vent branch pipe 36 is provided with a solenoid valve 37, respectively. Furthermore, the ventilation branch pipe 36 is integrated into a throttle valve 38 and a check valve 3.
9, compressed air is introduced into the compressed air inlet 11a of the furnace 11. and,
An infrared fiber unit 40 and an infrared fiber unit are connected to the solenoid valve 37.
An optical cable 27 is connected via a CPU control unit 41. Next, the casting method will be explained. At the start of casting,
The pressure reducing valve 35 and the appropriate solenoid valve 37 open, and the compressed air in the surge tank 33 flows through the many ventilation branch pipes 36.
through the selected one of them, and further through the throttle valve 38.
and the check valve 39 in order to be supplied into the furnace 11 . As a result, the pressure inside the furnace 11 increases,
The molten metal 13 is pushed up. The pushed up molten metal 13 is guided through the introduction pipe 16 into the lowermost first cavity 15a, which is a large cross-sectional area. At this time, based on the relationship shown in FIG. 4, the flow rate of the molten metal 13 is controlled so that the flow of the molten metal 13 does not stop due to solidification in the first cavity 15a. This flow rate is set in the furnace 11 using compressed air.
This is done by appropriately setting the pressurization speed within. When the molten metal 13 almost completely fills the inside of the first cavity 15a and flows into the second cavity 15b, which is a small cross-sectional area, and from this second cavity 15b, the third cavity is a large cross-sectional area.
When the molten metal flows into the cavity 15c, the proximity and passage of the molten metal are detected by the first and second infrared sensors 17 and 18, respectively. This detection action will be explained with respect to the second infrared sensor 18 shown in FIG. 2. That is, the molten metal 13 emits infrared rays A based on the high heat.
is emitted. This infrared ray A is from cavity 15b.
It is reflected on the inner surface, emitted in the direction of molten metal flow (upward), passes through the window member 21, is focused by the lens 22, and enters the optical fiber 23. Thereafter, the infrared fiber unit 40 converts it into an electrical signal, and the combination of the solenoid valves 37 to be opened among the many solenoid valves 37 of the ventilation branch pipes 36 is changed according to instructions from the CPU control unit 41. The pressurization speed is controlled. This effect is illustrated in FIG. 1B. From the first cavity 15a to the second cavity 15
When flowing to b, the molten metal 13 rises to a predetermined flow rate that does not cause flow stoppage due to solidification. On the other hand, molten metal 1
3 almost completely fills the second cavity 15b with a small cross-sectional area, and the third cavity 15 with a large cross-sectional area
c, the second infrared sensor 1
8, the combination of the electromagnetic valves 37 is changed again, and the pressurization speed in the furnace 11 is reduced. For this reason,
The molten metal 13 flows into the third cavity 15c at a low flow rate that does not cause turbulence. And molten metal 13
After the third cavity 15c is completely filled and solidification of the molten metal 13 is completed, the supply of compressed air to the furnace 11 is stopped, and casting is thus completed. According to the above embodiment, the molten metal 13 is transferred from the first cavity 15a to the second cavity 15 having a small cross-sectional area.
Since the molten metal 13 rises at a high flow rate by increasing the speed when flowing into the molten metal b, the flow of the molten metal 13 does not stop due to solidification.
Moreover, the molten metal 13 is placed in the second cavity 1 with a small cross-sectional area.
When flowing from the molten metal 5b into the third cavity 15c having a large cross-sectional area, the flow velocity is reduced and the molten metal 13
Since the liquid flows into the third cavity 15c at a low flow rate, entrainment of oxides and air into the molten metal 13 is prevented, and the occurrence of gas defects is effectively prevented. In particular, in the embodiment described above, the approach of the molten metal 13 to the sensor position is detected by increasing the amount of infrared rays emitted from the molten metal 13 itself and incident on the optical fiber 23, and the passing of the molten metal 13 is detected by keeping the amount of incident light constant. be done. Therefore, in order to accurately and instantaneously detect the proximity and passage of the molten metal 13,
The pressurizing speed is controlled with almost no time delay relative to the point in time when the fluid flows into the small cross-sectional area or the large cross-sectional area. Therefore, the molten metal 13 flows into each cavity 15a, 15b, 1 at an appropriate flow rate from the beginning.
5c, it is possible to more reliably prevent the flow of molten metal from stopping, gas defects, etc., and form a high-quality casting. Table 2 below shows the experimental results in the above embodiment, which corresponds to Table 1 explaining the conventional example.

〔Effect of the invention〕

As explained above, according to the present invention, the approach and passage of the molten metal to the portion where the cross-sectional area of the cavity changes is instantly detected by the infrared light receiving means from the molten metal, so that pressure can be changed accurately and quickly. This makes it possible to produce high-quality light alloy castings.

[Brief explanation of drawings]

FIG. 1A is a configuration diagram showing an embodiment of the pressure casting apparatus according to the present invention, FIG. 1B is a graph showing the state of controlling the pressurization speed of the molten metal in the mold of FIG. 1A, and FIG. 1 is an enlarged cross-sectional view of the optical detection means shown in FIG. 1, FIG. 3 is a configuration diagram showing a conventional example, FIG. 4 is a graph showing the trend of the critical velocity of molten metal flow, and FIG. 5 is a graph showing the turbulence of molten metal. FIG. 6 is a cross-sectional view of a mold used to illustrate the problems in the conventional example.
FIG. 7 is a graph showing experimental results in the conventional example. 11... Furnace, 13... Molten metal, 14... Mold, 1
5a, 15b, 15c... Cavity, 17, 1
8... Infrared sensor, 21... Window member, 23...
optical fiber.

Claims (1)

[Claims] 1. In a pressure casting method in which molten metal is pumped from a furnace to a mold and the flow rate of the molten metal in the mold is controlled in accordance with changes in the cross-sectional area of the cavity, By inputting infrared rays into an infrared sensor embedded in the mold, the approach and passage of the molten metal to the cavity cross-sectional area changing part is detected, and the flow rate of the molten metal is changed based on the detected value. Pressure casting method. 2. A furnace that accommodates molten metal, a pressurizing means that pressurizes the molten metal in this furnace, a mold having cavities with different cross-sectional areas, and molten metal introduction that communicates the furnace and mold and supplies pressurized molten metal to the mold. an infrared sensor that is buried in the vicinity of the section where the cross-sectional area of the cavity changes in the mold and detects infrared rays emitted by the molten metal itself that approaches and passes through the said position; 1. A pressure casting apparatus comprising: a pressure control device that sets a flow rate of molten metal corresponding to a change in the cross section of a cavity by changing the flow rate of the molten metal. 3. The infrared sensor has a transparent window member made of heat-resistant material provided in the part facing the cavity in the mold, and through this window member, infrared rays emitted from the molten metal itself in the cavity are input via a spherical condensing lens. 3. A pressure casting apparatus according to claim 2, comprising a luminous optical fiber.