JPS61245955A - Method for controlling flow rate of molten metal in casting - Google Patents

Abstract

PURPOSE:To control effectively the flow rate of a molten metal by embedding blocks made of a good heat conductive material in the parts of a metallic mold where the sectional area of the cavity thereof changes, disposing thermosensors therein and changing the flow rate of the molten metal in accordance with the temp. detected by said sensors. CONSTITUTION:The compressed air in a surge tank 22 is supplied successively to the space in a furnace 13 via a throttle valve 27 and a check valve 22 when a reducing valve 23 and a reducing valve 25 are opened upon starting of casting. The molten metal 14 is forced upward by the resulted pressure increase by which the molten metal is successively forced upward into the 1st large area part 12a and 2nd large area part 12b of the cavity 12. The blocks 17, 18 made respectively of the good heat conductive material are embedded into the parts of the cavity 12 where the sectional area changes and the thermosensors 19, 20 are disposed therein. The feed rate of the compressed air from the tank 22 is changed according to the temp. increase detected by said sensors, by which the flow rate of the molten metal 14 is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for controlling the flow rate of molten metal when the molten metal is pressurized and supplied into a mold cavity for casting.

[Technical background of the invention and its problems] As a method for manufacturing high-quality light alloy castings, air or inert gas is supplied into the furnace to increase the internal pressure of the furnace, thereby pushing up the molten metal inside the furnace. The low-pressure casting method, in which the metal is supplied into the cavity of the mold, is widely used.

When casting using a mold in this manner, 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, and the rate of rise of the molten metal, as expressed by the following equation (1).

δ=(1/4)・(D-JF −(32・λ・θt/V・γ・C・θ2))...
...(1) However, D = Cross-sectional area of casting λ: Thermal conductivity of solidified layer θl: Temperature of solidified layer determined from mold temperature θ2: Temperature of molten metal - solidification temperature C: Specific heat γ: Specific gravity V: Flow rate solidification When the layers reach a certain thickness, the flow of the molten metal stops within the cavity, making it impossible to form a casting.

Figure 3 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 of the pressure in the furnace per unit time (hereinafter simply referred to as pressurization rate pv) as expressed by the following equation (2).

Ll = (PV - (V[l +V) +VJ/ ((
7/1000)・(H+V/A>(Vo +V)+V)
・H・・・・・・(2) However, U: Flow rate of molten metal H: Filling height PV: Pressurizing speed A: Pressurizing area of molten metal in the furnace vo: Space volume in the furnace V; Filling volume γ: Specific gravity of the molten metal For general castings whose cross-sectional area varies little, use Figure 3 to determine the flow velocity (■) at which the molten metal does not stop, based on the typical cross-sectional area of the casting, and then use equation (2) to determine All you have to do is set the rate of pressurization into the furnace. However, in castings with large variations in cross-sectional area, when cast at a constant pressurizing speed, vortices are likely to form, especially in areas where the cross-sectional area changes, as shown by the arrows in Figure 5. The entrainment of oxides causes gas defects due to air entrainment. For this reason,
In the portion where the cross-sectional area changes, it is necessary to change the pressurizing speed to a flow rate that does not generate vortices.

As shown in Fig. 4, a method of changing the pressurizing speed at a portion where the cross-sectional area changes is to install a thermocouple 3 near the portion where the cross-sectional area of the cavity 2 changes in the mold 1, and use this thermocouple 3 to control the molten metal. It is conceivable to detect that the pressure has reached the cross-sectional area changing portion and change the pressurizing speed.

The present inventor actually performed casting using this pressurization control method and conducted an experiment to determine whether gas defects would occur. According to this, when molten metal flows from a part with a small cross-sectional area to a part with a large cross-sectional area, if the ratio of the former cross-sectional area Al to the latter cross-sectional area A2 becomes 3 or more, the occurrence of gas defects will become significant. I understand.

This is because there is a time delay between when the molten metal reaches the area where the cross-sectional area changes and when the temperature of the area where the thermocouple is installed actually rises. This is because the time delay cannot be ignored, especially when the flow velocity of the molten metal in a portion where the cross-sectional area is small, such as when the ratio of the cross-sectional area AI to A2 is 3 or more, is extremely large.

[Object of the Invention] An object of the present invention is to provide a method for controlling the flow rate of molten metal in casting, which can minimize the time delay from the arrival of the molten metal until the thermosensor actually detects the molten metal.

[Summary of the invention] The present invention embeds a block made of a thermally conductive material in a mold and arranges a thermosensor inside the block, so that the temperature of the part where the thermosensor is installed quickly rises when molten metal arrives. It was designed to do so.

[Embodiment of the Invention] An embodiment in which the present invention is applied to a low-pressure casting apparatus will be described below with reference to FIGS. 1 and 2. In Figure 1,
Reference numeral 11 denotes a mold, and a cavity 12 formed in the mold has portions 12a and 12b with large cross-sectional areas on both upper and lower sides.
and a portion 12c with a small cross-sectional area that communicates with these large cross-sectional area portions 12a and 12b. Such mold 1
1 is communicated via an introduction pipe 16 with a crucible 15 which is disposed in a casing 13 and stores a molten aluminum 14. 17 and 18 are first and second blocks made of a thermally conductive material, such as copper, and these are placed in the cavity 1 of the mold 11.
It is buried in the part where the cross-sectional area of No. 2 changes. That is, the first block 17 is located at the boundary between the first large cross-sectional area 12a and the small cross-sectional area 12G, for example, the first large cross-sectional area 12a.
It is buried in the upper end portion of the first large cross-sectional area portion 12a so as to form a part of the side surface portion of the first large cross-sectional area portion 12a. Also, the second protrusion 1
8 is buried in the boundary between the small cross-sectional area 12G and the second large cross-sectional area 12b, for example, at the upper end of the small cross-sectional area 12C, so as to form part of the side surface of the small cross-sectional area 12c. ing. These first and second blocks 17 and 18
Inside are first and second thermocouples 19 as thermosensors.
and 20 are arranged. 21 is a compressed air supply device that supplies compressed air into the group 13 to push up the molten metal 14; in this supply device 21, 22 is a surge tank;
23 is a pressure reducing valve; 24 is a large number of ventilation pipes each having a solenoid valve 25 and having different diameters; 26;
27 is a throttle valve, and 27 is a check valve. Of these, each ventilation pipe 24
The solenoid valve 25 is controlled to open and close based on the detection operations of the first and second thermocouples 19 and 20, which will be described later.

Next, the process of forming a casting using the casting apparatus configured as described above will be explained. With the start of casting, the compressed air in the surge tank 22 flows through the pressure reducing valve 23. When the appropriate solenoid valve 25 is opened, the air is supplied into the class 13 through several vent pipes selected from the large number of vent pipes 24, the throttle valve 26, and the check valve 27 in order, thereby increasing the pressure inside the class 13. The molten metal 14 is pushed up. The pushed-up melt 414 is guided into the first large cross-sectional area portion 12a of the cavity 12 via the introduction pipe 16. At this time, the flow velocity of the molten metal 14 is such that the flow of the molten metal 14 does not stop due to solidification in the first large cross-sectional area portion 12a (this can be determined from FIG. 3).

This flow rate is set by appropriately setting the rate of pressurization in class 13 by compressed air shown in FIG.

Now, when the melt 114 almost completely fills the first large cross-sectional area section 12a and attempts to flow into the small cross-sectional area section 12c, the first thermocouple 19 detects this.

At this time, the first block 17 is connected to the first large cross-sectional area section 12.
Since it comes into direct contact with the molten metal 14 in a, the temperature of the first block 17 rises at the same time as the contact, causing the first thermocouple 19 to generate a predetermined electromotive force, that is, the first thermocouple Pair 19 performs a detection operation. Based on the detection operation of the first thermocouple 19, the combination of solenoid valves to be opened among the many solenoid valves 25 of the ventilation pipes 24 changes, and as a result, the pressurization speed in class 13 is increased. change in different ways. For this reason, molten metal 1
4 flows into the small cross-sectional area portion 12c and rises at a relatively high flow rate that does not cause flow stoppage due to solidification. Then, when the molten metal 14 almost completely fills the small cross-sectional area portion 12c and attempts to flow into the second large cross-sectional area portion 12b,
The second thermocouple 20 detects this. At this time as well, the second
Since the block 18 directly contacts the molten metal 14 in the small cross-sectional area portion 12C, the temperature of the second block 18 rises at the same time as the contact, and this causes the second thermocouple 20 to perform a detection operation. . Based on the detection operation of the second thermocouple 20, the combination of the solenoid valves to be opened among the many solenoid valves 25 of the ventilation pipes 24 changes again, and as a result, the pressurization speed in Class 13 is reduced to a low value. It changes as it becomes. Therefore, the molten metal 14 flows into the second large cross-sectional area portion 12b at a relatively low flow velocity that does not cause turbulence. Then, when the molten metal 14 completely fills the second large cross-sectional area portion 12b, the Class 1
The supply of compressed air into the chamber 3 is stopped, and casting is thus completed.

According to the above configuration, the melt 114 is formed in the first large cross-sectional area portion 12a.
When flowing into the small cross-sectional area section 12c from the molten metal 14, the velocity is increased so that the molten metal 14 rises inside the small cross-sectional area section 12c at a high flow velocity.
The thickness of the solidified layer formed on the inner surface of c can be suppressed to a certain thickness or less, and the flow of the molten metal will not stop due to solidification. Furthermore, when the molten metal 14 flows from the small cross-sectional area section 12c into the second large cross-sectional area section 12b, the flow rate is reduced so that the molten metal 14 flows into the second large cross-sectional area section 12b at a low flow rate. Since the molten metal 14 is configured to flow into the molten metal 14, the molten metal 14 does not entrain air, and gas defects can be prevented from occurring. Moreover, the change in the pressurizing speed, which is the source of changing the flow speed of the molten metal 14, is performed based on the detection operations of the first and second thermocouples 19 and 2o. These thermocouples 19
and 20 are disposed in the first and second blocks 17 and 18 made of copper, which is a good thermal conductor, so that the weld 14 does not enter the small cross-sectional area portion 12c or the second large cross-sectional area portion 12b. The first and second thermocouples 19 and 20 perform a detection operation, that is, a change in the pressurizing speed, with almost no time delay with respect to the time of inflow. Therefore, the molten metal 14 flows into the small cross-sectional area portion 12c or the second large cross-sectional area portion 12b at an appropriate flow rate from the beginning, and the occurrence of stoppage of flowing flow, gas defects, etc. is more reliably prevented. be able to.

By the way, Figure 2 shows the results of a comparative experiment to determine how much time delay the thermocouple starts to operate after passing through the thermocouple placement area between the case according to the present invention and the case shown in Figure 4. Therefore, it can be seen from FIG. 2 that the thermocouple detection operation starts earlier in the case of the present invention shown by characteristic curve A than in the case of FIG. 4 shown by characteristic curve 1iB. In addition, in FIG. 2, the vertical axis shows the temperature detected by the thermal lightning pair, and the horizontal axis shows the elapsed time from the point of passage of the molten metal.

Although the above embodiment has been described as being applied to a low-pressure casting apparatus, the present invention is not limited to this, and can be widely applied to casting by injecting molten metal into a mold.

[Effects of the Invention] As explained above, the present invention has the excellent effect of being able to detect that the molten metal has reached the part where the cross-sectional area of the cavity changes with as little time delay as possible. .

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a casting apparatus showing an embodiment of the present invention, Fig. 2 is a detection operation characteristic diagram of a thermocouple, Fig. 3 is an experimental result of the critical velocity for stopping the flow of molten metal, and Fig. 4 is a comparison diagram. FIG. 5 is a partial sectional view showing turbulence in the molten metal. In the figure, 11 is a mold, 12 is a cavity, 13 is a furnace, and 14
is the molten metal, 17.18 is the 1st. Second block, 19.2
0 is a first and second thermocouple (thermo sensor), and 21 is a compressed air supply device. Fig. 1 [] Fig. 2 Time (sec) Fig. 3

Claims (1)

[Claims] 1. In a device that pressurizes molten metal and supplies it into the cavity of a mold, a block made of a thermally conductive material is embedded in the part of the mold where the cross-sectional area of the cavity changes, and a thermostat is installed in this block. 1. A method for controlling the flow rate of molten metal in casting, characterized in that a sensor is provided, and the flow rate of the molten metal is changed by changing the pressure applied to the molten metal based on the detection of a temperature rise by the thermosensor.