JPS5841941B2 - Casting equipment for light alloys - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a casting apparatus for light alloys, and in particular, a casting apparatus for light alloys for strictly controlling the solidification conditions of the molten metal when the molten metal for casting is forcibly cooled with a cooling liquid. It is related to the device.

Among the terms used in this specification, ■ Molten metal cooling rate refers to the average cooling rate from a temperature 10°C higher than the freezing point of the molten metal to the freezing point temperature, and ■ Solidification section cooling rate refers to the period from the solidification start temperature of the molten metal to the end of solidification. The average cooling rate of Each means the speed at which it progresses toward a certain part.

If the molten metal, especially the molten non-ferrous light alloy, in the mold is cooled and solidified from a molten state at a cooling rate of 60°C/min or higher in the solidification zone, casting defects such as gas holes and shrinkage will be reduced, resulting in a sound and solid state. It is already known that castings with excellent strength can be obtained, and its practical use is progressing as a forced solidification casting method using a cooling liquid.

However, if the shape of the casting is complex and the wall thickness fluctuates widely, adjusting only the cooling rate in the solidification zone is insufficient, and the thick interior tends to have more defects than the thinner part, resulting in lower physical properties, especially toughness. Therefore, it cannot be said that a satisfactory effect is necessarily obtained in terms of the average strength and toughness of the casting as a whole.

In other words, the strength and toughness of a casting are determined by the strength and toughness of the thick interior where there are many defects.
This is because it depends on toughness etc.

Therefore, in order to effectively utilize the characteristics of the forced solidification casting method, it is desired to develop a casting method that can provide defect-free castings not only in thin-walled portions but also in thick-walled portions.

The present inventors focused on the above-mentioned circumstances and developed a casting method that can reliably increase the strength and toughness of each part regardless of the wall thickness, even when manufacturing castings with large wall thickness fluctuations. In anticipation of its development, various studies have been conducted for some time.

As a result, the molten metal in the cavity is heated by 20° below its freezing point.
The temperature was maintained at ~75°C, and the solidification direction was set to one direction, and the cooling rate of the solidification section was set to 1 to b seconds, respectively, and the ratio of the temperature gradient of each part of the molten metal in the cavity to the solidification interface advancement speed was set. I learned that the above objective can be achieved by differentially and systematically setting the temperature lowering and solidifying conditions for each part of the molten metal, such as setting the temperature to 0.5 to 2.

The grounds for the above numerical limitations are as shown below.

■ Set the temperature at the start of cooling to 20 to 75 degrees Celsius below the freezing point of the molten metal.
The temperature was set on the high temperature side because the above temperature range was optimal for maintaining the cooling efficiency of the coolant as constant as possible.

■ The cooling rate of the molten metal was set from 10°C above the freezing point to the freezing point temperature because the metal structure of the solidified material is strongly influenced by the cooling rate of the molten metal from just before solidification to when passing through the freezing point. This was determined based on the knowledge of

■ Cooling rate of molten metal from 1 to b When determining the metallographic structure of the casting, the cooling rate is important for refining all of the macrocrystal grains, microcrystalline grains, dendrite main axis spacing, dendrite secondary branch spacing, intermetallic compounds, etc. The cooling rate should be 1°C/sec or more, the tensile strength and yield strength improvement effect should be 1-b, the elongation improvement effect should be 4-b, and the upper limit of the cooling rate should be about 5°C/sec.
Based on experimental results such as

(2) The cooling rate in the solidification zone was set at 1-b because this significantly affects the tensile strength, yield strength, elongation, etc. of each part of the casting.

That is, in order to make these physical properties excellent, the cooling rate in the solidification section should be at least 1° C./second or higher.

The improvement effect of tensile strength and yield strength is 2-b. The improvement effect is 5-b. Therefore, the preferable solidification zone cooling rate is 1-b seconds, more preferably 5-b. Ratio 0.5~
2 was set based on the experimental results of the present inventors that the original objective could not be achieved only by setting the cooling start temperature, molten metal cooling rate, and solidification zone cooling rate in the above-mentioned condition sections.

That is, if the ratio is less than 0.5, the tensile strength, elongation, and yield strength of each part of the cast product will be poor.
When the value is 5 or more, the physical properties are significantly improved.

Further, the effect of improving the physical properties reaches a nearly saturated state when the ratio is in the range of 1 to 2.

In order to maximize the effects of the forced solidification casting method, it is necessary to control the cooling start temperature of the molten metal, the cooling rate of the molten metal, the cooling rate of the solidification zone, the temperature gradient of the molten metal within the cavity, and the rate of progress at the solidification interface. It is necessary to strictly control the ratio between No.

The apparatus of the present invention is advantageously applied to the above-mentioned controlled solidification casting method, and is configured to reliably and automatically control the cooling and solidification conditions of the molten metal. be.

That is, the light alloy casting apparatus according to the present invention is an apparatus for forced solidification casting of light alloy castings whose wall thickness varies continuously or intermittently in the vertical direction, and includes a permanent mold, a core,
The heating device is equipped with a heating device and a cooling device, and a temperature measuring device is attached to the core at a position corresponding to the change in wall thickness of the cast product. Heating elements that generate heat independently are arranged at positions corresponding to the respective positions, and the temperature measuring device and the heating device compare the heat removal rate with a preset and stored heat removal rate according to the wall thickness variation of the cast product. , is electrically connected via a heat removal rate control device that instructs temperature increase or decrease according to the difference, and furthermore, the permanent mold is immersed in the cooling medium sequentially from the bottom to cool the solidification interface of the molten metal in the cavity. The gist is that an adjustment device is provided to relatively adjust the rate of gradual increase in inverse proportion to the wall thickness of each part of the cast product.

The configuration and effects of the present invention will be explained below based on the drawings which are examples, but the following are only representative examples, and all modifications to the design and implementation in accordance with the spirit of the preceding and subsequent descriptions are entirely within the scope of the present invention. within the scope of the invention.

FIG. 1 is a schematic vertical cross-sectional view illustrating the casting apparatus of the present invention, in which a heating device 2 is disposed above a cooling liquid tank 1, and a permanent mold 3 is connected to a lifting drive source (e.g. It is arranged so that it can be moved up and down by a continuously variable speed servo motor (5).

A core 6 made of a sand mold, a metal mold, etc. is arranged inside the permanent mold 3, and a cavity 1 is formed in the gap between the permanent mold 3 and the core 6 according to the shape of the intended cast product. Sur.

The core 6 is provided with a temperature measuring device 8a such as a thermocouple at a position corresponding to the volume varying portion of the cavity 7, that is, the wall thickness varying portion of the cast product.
A large number of 8b, . . . are arranged to measure the temperature of the molten metal at each part of the cavity.

Further, the heating device 2 is the temperature measuring device 8a. 8b, -...
Heat generating elements 9a, 9b, .

And temperature measuring devices 8a, 8b,... and heating element 9a
j 9b t...- is a heat removal rate control device [for example, a device equipped with a 3-position (high, low, stop) control mechanism, which controls the heating element 9
When a gas burner is used as a, . . . , it is electrically connected via a device 10 that can automatically control the electric valve in the burner to fully open, half open, or close.

The heat removal rate control device 10 stores a program of optimal temperature lowering conditions for each part set according to the target cast product, and the temperature is sensed by the temperature measuring devices 8a, 8b, . . . Compare the molten metal temperature at each part of the same cavity with the temperature set in the program, and if the molten metal temperature is too low, increase the heating output of the heating element at the corresponding position, and if the molten metal temperature is too high, take appropriate action. The heating output of the heating element at the position is lowered, thereby adjusting the heat removal rate so that the molten metal at each part of the cavity is always at the optimum temperature.

Therefore, even if the target cast product has wall thickness variations in the vertical direction, the cooling start temperature and heat removal rate of each part can be accurately controlled according to the wall thickness.

The heating device 2 may be one that uses gaseous fuel such as city gas, propane gas, or natural gas, or liquid fuel such as light oil or heavy oil, a resistor, or electric heating using induced electromagnetism at high, medium, or low frequencies. It does not matter whether direct heating or indirect heating is used.

However, the figure shows an example in which a direct heating method using a gas body is adopted.

That is, the heating device 2 includes a mixer 11 such as a venturi structure.
A gas supply pipe 12 and an air supply pipe 13 are connected through the valve 14, and by opening and closing a valve 14 to adjust the gas supply amount, an appropriate amount of air is sucked and supplied to the mixer 11 portion.

This mixed gas is then supplied to each heating element 9a. 9b...
・Heat each part of the permanent mold from the outside.

If the amount of mixed gas ejected from each heating element 9a, sb, . . . is made adjustable, and the heating output of each part is adjusted according to the program, Regardless of whether the volume of molten metal in each part is large or small, it is possible to control the cooling rate at a constant rate.

After properly adjusting the solidification start temperature of the molten metal in this way,
The elevating drive source 5 is operated to immerse the permanent mold 3 in the cooling liquid in the cooling liquid tank 1 to solidify the molten metal. However, if the immersion speed is made constant, the cooling and solidification conditions will change due to volume fluctuations of various parts within the cavity. , it becomes impossible to obtain high-quality molds.

Therefore, in the present invention, regarding the dipping speed of the permanent mold 3,
It is designed to be able to be adjusted according to the volume fluctuations of each part inside the cavity.

That is, the lowering position of the permanent mold 3 can be detected by a position detecting device 15 (for example, a level meter similar to a dial gauge is used, and a device that converts the height position into an electrical signal), and this and the lifting drive source 5 A descending speed adjusting device (for example, a program controller manufactured by Fuji Electric Co., Ltd.) is used to program a reference descending speed in advance, and by comparing it with the actual descending speed, the rotational speed of the servo motor of the lifting drive source 5 is determined. control) 16.

The descending speed adjusting device 16 stores the optimum immersion speed according to the wall thickness variation of each part of the target cast product, and depending on the position of the volume variation in the cavity detected by the position detecting device 15, Adjust the immersion speed while controlling the descent speed.

As a result, the molten metal cooling rate, the solidification zone cooling rate, and the ratio of the temperature gradient to the solidification interface advancement speed of each part can be set strictly to the conditions described above, regardless of volume fluctuations in each part of the cavity.

The coolant is continuously supplied from a suitable location below the coolant tank 1, and is also continuously discharged from the overflow port 1a above, keeping the liquid level constant and the liquid temperature as constant as possible. make it possible.

FIG. 2 shows another embodiment of the invention, which is substantially the same as that of FIG. 1, except for slight changes in the cooling means.

That is, in this example, the coolant injection nozzle 17 is arranged above the coolant level in the coolant tank 1, and which nozzle 1
After the permanent mold 3 is cooled from the outer periphery by the cooling liquid injected from 7, it is immersed in the cooling liquid to solidify the molten metal.

This method is preferable because the liquid temperature at the start of cooling can be kept more constant, and the temperature control for cooling and solidification described above can be performed more accurately.

FIG. 3 is a further embodiment of the invention, illustrating an apparatus which may be advantageously used in obtaining large castings.

That is, if the cast product is large, large equipment and a driving source are required to raise and lower the permanent mold 3, which increases the economic burden.

Therefore, in this example, the permanent mold 3 (and the heating device 2) is fixedly arranged in the cooling liquid tank 1, and when cooling, the cooling liquid is supplied from the water supply port 1b at a constant rate to the cooling liquid tank 1.
The liquid level inside is raised to cool the permanent mold 3.

In this case, it is necessary to accurately control the rate of increase in the liquid level according to changes in the wall thickness of the cast product. Then, the liquid level rise rate control device (for example, the program controller described above) is used to control the liquid level rise rate control device (for example, the program controller) The water level rise speed is memorized graphically, the liquid level height detected by the liquid level gauge is compared, and the opening degree of the electric valve of the water piping is automatically controlled based on the difference result, and the amount of water supplied is adjustment) 20.

That is, the liquid level detector 18 detects the liquid level position using changes in liquid pressure that increase as the liquid level rises.

In addition, the liquid level rise rate control device 20 stores a cooling rate program that is preset according to the wall thickness variation of the target cast product, and also stores a cooling rate program that is set in advance according to the wall thickness variation of the target cast product. It is also equipped with a mechanism for comparing and calculating the rising speed, and is configured to appropriately control the liquid supply speed from the supply pump 19 accordingly.

□In addition to the liquid level detector 18 that uses liquid pressure as shown in the figure, a number of float type liquid level detectors are installed in the height direction of the liquid tank to continuously detect the liquid level. You can also use things, etc.

Further, in this example, since the heating device 2 is sequentially immersed in the liquid together with the permanent mold 3, each heating element 9a, 9 is immersed in the liquid as the liquid level increases.
Each heating element 9a, 9b2. . . . is also connected to the liquid level rise rate control device 20, and each heating element 9a,
It is desirable to be able to automatically control heating stop, etc. of 9b, . . . .

In this example, the profit of the cooling rate of the molten metal before cooling and the control of the cooling start temperature are performed in the same manner as in the example shown in FIG.

After cooling, the drain port 21 is opened to discharge the cooling liquid, and then the permanent mold 3 may be taken out from the cooling liquid tank 1 portion by an appropriate means.

This type of device is suitable for casting large-sized castings because it is not necessary to raise and lower the permanent mold 3 during the cooling and solidification process of the molten metal.

Although the present invention is roughly configured as described above, the specific configuration is not limited to the illustrated example, and the shape and structure of the permanent mold and core may vary depending on the shape of the intended cast product. The structure of the heating device, the heating means, the shape of the cooling liquid tank, etc. can be changed as appropriate depending on the situation at the site.

Further, a computer may be used for a mechanism for automatically controlling the rate of cooling of the molten metal and the cooling start temperature, a mechanism for automatically controlling the rate of descent of the permanent mold, or the rate of increase of the cooling liquid level.

The present invention is configured as described above, and includes temperature reduction rate, cooling start temperature, cooling rate, solidification zone cooling rate,
The ratio of the temperature gradient to the solidification interface advancement speed can be precisely and appropriately automatically controlled according to the wall thickness variation of the target cast product (i.e. the cavity volume variation), so it is possible to control the ratio of the temperature gradient and the solidification interface progress rate, etc. However, it is possible to obtain a product that is homogeneous throughout and has excellent physical characteristics, making it an extremely excellent casting device.

[Brief explanation of the drawing]

1 to 3 are schematic vertical cross-sectional explanatory views illustrating a casting apparatus according to the present invention. 1... Cooling liquid tank, 2... Heating device, 3
...Permanent mold, 6... Core, I...
...Cavity, 8at8b...1 temperature measuring device, 9a,,9b...Heating element, 10...
Heat removal rate control device, 15...Descent position detection device, 16...Descent rate control device, 18...
-Liquid level detector, 20---Liquid level rising speed control device.

Claims (1)

[Claims] 1. A device for forcibly solidifying and casting light alloy castings whose wall thickness varies continuously or intermittently in the vertical direction, and is equipped with a permanent mold, a core, a heating device, and a cooling device, and includes a permanent mold, a core, a heating device, and a cooling device. A temperature measuring device is attached to a position corresponding to the change in wall thickness of the cast product, and a heating device formed by inserting a permanent mold somewhere has a temperature measuring device attached at a position corresponding to the position of the temperature measuring device. A heating element that generates heat is arranged, and the temperature measuring device and the heating device compare the heat removal rate set and stored in advance according to the variation in the wall thickness of the cast product, and raise or lower the temperature according to the difference. electrically connected via a heat removal rate controller that directs the
Furthermore, when the permanent mold is sequentially immersed in a cooling medium from the bottom to gradually raise the solidification interface of the molten metal in the cavity, the rising speed is relatively adjusted in inverse proportion to the wall thickness of each part of the cast product. A casting device for light alloy, characterized in that it is equipped with a device.