JPH09225621A - Casting cooling method - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To shorten the unframe time of a casting and to improve the efficiency of the casting process. In addition, partial cooling is performed reliably and easily to improve the structure and prevent shrinkage cavities. After pouring a molten metal into a mold 2, a cooling liquid is supplied to the mold from a water pipe 10 or the like, and the cooling liquid is permeated into a molding sand 12. As a result, the high-temperature casting can be cooled rapidly, and the frame can be broken in a short time. In addition, the cooling with the cooling liquid is performed so that the temperature of the casting is up to the A1 transformation temperature and the A1 transformation temperature passing speed is slow. Therefore, it is possible to prevent the hardening of the structure and reduce the influence on the casting product. Further, the cooling liquid is partially supplied to accelerate the cooling rate at a desired location. As a result, the cast structure can be appropriately changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling method of supplying a cooling liquid into a mold and cooling a casting in the mold with the cooling liquid. Further, the present invention relates to a method for cooling a casting for preventing shrinkage cavities, seizure, and densification of a structure by cooling a cooling liquid.

[0002]

2. Description of the Related Art In conventional casting work, after pouring molten metal into a mold, cracks and deterioration in accuracy may occur. Therefore, the mold is left for a certain period of time to wait for the internal heat to naturally decrease. Was there. However, since the foundry sand itself has a heat insulating effect, when casting a large-sized foundry, it may take several weeks from pouring the molten metal to unraveling the mold. During that time, the mold must be stored in a state where it has been poured, and it occupies a large storage space, and since it cannot be used for other molding sands or flasks during the storage period, a large amount of molding sand and It required a frame and was not productive.

Therefore, the inventors of the present invention believe that if the time from pouring to the unraveling can be shortened, it is possible to improve the productivity of casting work by reducing the number of casting flasks and the molding sand. We focused on increasing the cooling rate of.

Regarding cooling of castings, conventionally, the amount of sand (the amount of sand covering the castings) is reduced to increase the amount of heat radiation from the mold, and after the frame is removed, mist-like water is sprayed on the castings, A method of rotating a product together with sand to radiate heat has been known.

The following applications have been filed regarding cooling of castings.

Invention in which a pipe is installed in a mold, and a cooling medium is passed through the pipe to cool the molding sand (Japanese Patent Laid-Open No. 57-103775), or air or a mist-like gas mixture of air and water. Is an invention (Japanese Patent Publication No. 4-45264) that cools the casting by sending the steel into a mold.

As means for partially cooling the casting,
There has also been a method in which a chiller is placed in a mold to cool it.

[0008]

However, even when the molding sand is reduced, the molding sand cannot be reduced below the required amount and the cooling capacity cannot be increased. In addition, generally, the frame is set at a temperature of 200 ° C. or lower, and if the frame opening time is set too early, dimensional change or deformation occurs, or cracking occurs due to internal stress. There was a fear.

Further, the invention of Japanese Patent Laid-Open No. 57-103775 discloses that a coolant is passed through the inside of a pipe or the like to locally accelerate the cooling rate to increase the hardness of the casting and the wear resistance thereof. Since it is performed indirectly and is partial, it does not remove the heat of the entire casting to lower the temperature, and the cooling rate of the entire casting cannot be shortened. In the invention of Japanese Patent Publication No. 4-45264, air or air containing water is blown to a specific portion of a casting through an air hole or the like so that the hardness of a desired portion can be improved in the same manner as the invention of JP-A-57-103775. There is a description that water is supplied to the casting after being contained in a gas, and that supplying water in a liquid state is prohibited from the viewpoint of preventing blowholes and the like. Therefore, even in such an invention, the heat of the casting cannot be removed from the entire casting to increase the cooling rate.

In particular, the invention of Japanese Patent Laid-Open No. 57-103775 has the purpose of preventing water from actively contacting the casting by using a pipe, and in the invention of Japanese Patent Publication No. 4-45264, direct water is also used. Injection is prohibited,
This point is a common idea in casting, such as green mold, where clay (bentonite) and water are mixed with sand to form a mold, and increasing the amount of mixed water causes pinholes, blowholes, etc. It was considered impossible to use large amounts of water in casting.

Further, regarding the cooling provided in the mold so as to be in contact with the molten metal, the cooling is
By directional solidification, the part where the sink mark is generated is moved to a place where it does not interfere or a part outside the product called the riser to prevent it, or by partially cooling it to densify the tissue,
It partially cools the casting to prevent shrinkage of the casting and partially densifies the structure.It does not cool the temperature of the entire casting, and it is necessary to apply a chill according to the shape. However, the work efficiency was very poor.

[0012]

According to the present invention, in order to solve the above-mentioned problems, a cooling liquid such as water is injected and permeated into a mold after pouring molten metal, and the casting is rapidly cooled by this cooling liquid. I decided. The cooling liquid is not applied directly to the casting, but is poured from above the casting mold in which the casting is immersed, so that the cooling liquid permeates the inside of the casting and removes the heat of the casting through the casting sand. At that time, not only the rise in water temperature but also about 540 cal / g
Utilizes the high latent heat of vaporization.

Water is injected after the pouring of the molten metal is completed.
If water is injected before pouring the molten metal or during pouring,
Turbulence occurs in the molten metal, and water molecules are entrained in the molten metal, causing blowholes and pinholes. The mold must be kept under the same conditions as before until the molten metal is completely fed into the mold. On the other hand, even if the cooling liquid is injected after pouring the molten metal, the surface of the molten metal is solidified by the cooling effect of the cooling liquid, and the cooling liquid is vaporized by the heat of the molten metal and evaporated, so that the liquid is directly liquefied in the molten metal. Blow holes and the like will not occur due to the invasion of the cooling liquid.

The cooling liquid is injected not only from above the mold,
A water pipe may be installed inside the mold, and the water pipe may be allowed to flow out of the water pipe so as to permeate into the casting sand. Further, a time difference may be provided so as to hit a specific portion of the casting, and the water may be partially injected first.

The casting is cooled with the cooling liquid until just before the surface temperature of the casting reaches the A1 transformation temperature. This is because if the A1 transformation temperature is passed in a short time by cooling water, the cooling rate becomes too fast and the structure hardens. That is, in the case of iron-based castings, the hardness due to the matrix structure is determined by the passage speed of the A1 transformation, and the cooling rate in austenite does not significantly affect the hardness of the matrix structure. In the case of cast iron, considering the equilibrium diagram, cementite eutectic (1148 ° C) and A
There is a gap of 425 ° C. between one transformation (723 ° C.), so that rapid cooling is possible for the temperature range of this austenite region. For cast steel products,
Since the structure and hardness are adjusted again by the heat treatment, a large temperature decrease in the austenite region does not cause any trouble.

Even if the surface temperature of the casting falls below the A1 transformation temperature, if the injection of water is stopped, the temperature inside the casting rises again to above the A1 transformation temperature.
The decrease to 1 transformation temperature or less is not a problem.

Further, when the cooling liquid is injected again after passing through the A1 transformation to cool the casting, the injection of the cooling liquid is limited to within the plastic region. In iron-based castings, the range of 550 ° C to 200 ° C is generally considered to be the area where internal stress is likely to accumulate and crack, so except for small articles and those with good wall thickness balance, rapid cooling in this range Will be refrained from. Preferably, water is not injected in the elastic region below the plastic region.

Further, by injecting water partially, the temperature of a specific part is lowered to densify the structure of a desired part,
The occurrence of shrinkage cavities may be prevented.

The foundry sand to be used may be an ordinary foundry sand, and at least water permeability and air permeability are required. Water permeability is
The reason for this is that water permeates into the inside of the mold, and the air permeability is required to allow steam to escape smoothly to the outside. Further, it is preferable that a drain hole for discharging excess water is formed in the lower part of the mold.

The cooling liquid may be only water or a mixed liquid obtained by mixing water with a rust preventive agent or other liquid. In addition to allowing the cooling liquid to naturally permeate, the injection may be performed by applying pressure into the mold. The cooling liquid may be injected after a lapse of a predetermined time from the molten metal or immediately after pouring, but it is not preferable that the injected water directly reaches the surface of the casting at least before the surface of the casting is solidified. However, even if the cooling liquid is injected immediately after pouring, it may be injected as long as the injection amount is appropriate and water is vaporized into steam before directly contacting the molten metal.

Further, from the viewpoint of the occurrence of seizure, when the injection of the cooling liquid is taken into consideration, it has been found by the inventors' experiments that when the temperature of the molding sand reaches about 600 ° C., the molten metal penetrates into the molding sand and seizure occurs. confirmed. Therefore, before the temperature of the foundry sand reaches the seizure occurrence temperature, the casting sand is cooled by the cooling liquid (steam) and injected so as not to exceed 600 ° C. According to the experiment, the molten metal starts to invade the casting sand (about 3 mm) for 2 to 3 minutes after pouring and 5 to 15 minutes if there is a coating mold, and cooling by the cooling liquid is started before that. It is preferable to suppress the temperature to 600 ° C. or lower from the viewpoint of preventing seizure.

Next, the operation of this casting cooling method will be described.

After the molten metal is completely poured into the mold, the cooling liquid is poured into the mold. The cooling liquid penetrates between the foundry sands and penetrates inside to reach the vicinity of the surface of the foundry. Since the temperature near the surface is several hundred degrees Celsius, it usually evaporates in the molding sand before directly contacting the surface, and the vapor that has deprived the vaporization heat from the surroundings is dissipated to the outside through the gap of the molding sand, Alternatively, it is cooled on the way and liquefied and permeates inside again. At that time, even if the surface of the casting is not solidified, it is considered that the cooling liquid does not come into direct contact with the surface of the casting at a normal permeation rate, and problems such as blow holes do not occur.

Therefore, by injecting the cooling liquid into the mold in this way, the heat of the casting can be rapidly taken away, the temperature lowering time can be shortened, the unraveling frame can be expedited, and the casting work efficiency can be improved. You can Further, since water is evaporated at 100 ° C., it does not stay on the surface of the casting for a long time in a water state, and vaporization and liquefaction are repeated in the casting sand, so that an appropriate cooling rate is maintained. Further, when the cooling liquid directly reaches the surface of the molten metal, a skin layer is formed on the surface of the casting, so that defects such as blowholes do not occur.

Further, by appropriately adjusting the supply of the cooling liquid, the change of the tissue can be set appropriately. Further, by partially cooling with a cooling liquid, it is possible to adjust hardness, prevent shrinkage cavities, and densify.

In the disappearance model casting method, a cooling means such as a chill cannot be used, but by using the cooling method of the present invention, a sufficient effect can be obtained as a substitute for the chill. Further, in the disappearing model casting method, since the coating is applied to the model side rather than the sand mold side, there is a problem of seizure due to the intrusion of the molten metal into the sand mold. The wearing phenomenon can be reduced.

A pressure reducing pump may be connected to the inside of the mold to reduce the pressure inside the mold with a pressure reducing pump or the like during cooling with the cooling liquid. When the pressure in the mold is reduced in this way, the generated steam is quickly discharged to the outside, does not create a back pressure on the casting side, and even if the injection pressure of water is high or the injection amount is excessive, the casting surface The cooling liquid is not sent to and the defects such as blow holes are not generated.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a mold for carrying out the cooling method according to the present invention will be described with reference to the drawings.

FIG. 1 shows a mold 2 using the cooling method of the present invention.
The vanishing model 8 is embedded in the casting frame 11 by the foundry sand 12. A sprue 15 is connected to the model 8, and a cracking test piece 9 is provided on the upper portion. A water pipe 10 is provided on the upper part of the mold 2, and a water pipe 13 is provided inside thereof, and holes through which water flows out are appropriately formed on the side surfaces of these water pipes 10, 13. A one-way valve or an on-off valve that is open to the outside at the bottom of the casting frame 11 (neither is shown)
The drainage pipe 19 having the above is attached, and the water accumulated inside the casting frame 11 flows out to the outside through the drainage pipe 19.
Further, water pipes 4 and 5 are provided in the lower portion of the mold 2, and a suction pipe 6 connected to a decompression pump (not shown) via a pipe 7 is provided on the side surface. The foundry sand 12 is a normally used foundry sand having air permeability.

After the molten metal is poured into the mold 2 through the sprue 15 to form a casting 18, the water pipe 10 or the water pipe 13 is formed.
From water, the temperature of casting 18 is A1 transformation temperature, about 730 ° C
The casting 18 is cooled by appropriately supplying, for example, intermittently until the casting 18 decreases. After the casting temperature reaches the A1 transformation temperature, natural cooling is performed.

When water is supplied to the mold 2 in this way, the water that has reached near the casting 18 becomes steam by the heat of the casting 18, removes a large amount of heat from the casting 18, and passes through the gap of the casting sand 12 to the outside. Dissipated.

As a result, the casting 18 is cooled by the cooling liquid, and it is possible to shorten the time until the frame is removed. Moreover, cooling with water is not performed during passage of the A1 transformation temperature and in the elastic region of the casting, and cooling is performed at a normal cooling rate in that range, so the hardness of the product is maintained at a desired value,
Further, it is possible to prevent the occurrence of cracks.

[0033]

Next, an experimental example will be described. In the experiment, the material was FC250, the weight of the product was about 800 kg, the molten metal was poured into the mold, and then water was intermittently sprinkled from the top until the casting temperature reached about 730 ° C. After the watering was stopped, it was cooled naturally. The water sprinkling was carried out by confirming that the injected water flowed out from the lower part of the mold and taking care not to collect water in the mold and prevent the casting from being submerged. The temperature of the casting was measured by abutting a plurality of thermometers directly on the surface of the casting to obtain the average surface temperature of the casting.

The results are shown in FIG. As shown in A of FIG. 2, the sprinkling time T was about 6 hours, and the casting decreased to 200 ° C. in about 54 hours. On the other hand, when the castings cast under the same conditions are naturally cooled, as shown in FIG.
It took 23 hours. Furthermore, when the hardness was measured,
Little difference from the naturally cooled product was seen.

Also, the material is changed to FC300, FCD45
The same effect could be obtained even when the FCD550 was set to 0.

Further, before cooling the entire casting with a cooling liquid, water is jetted from a water pipe 5 arranged at a position where shrinkage cavities are generated, such as the water pipe 5 shown in FIG. The whole was cooled by the cooling liquid. Then, the product did not have shrinkage cavities. Further, a large amount of water was partially supplied from the water pipe 4 shown in FIG. 1 to perform rapid cooling. As a result, it was possible to generate a dense structure at the surface of the water pipe 4.

Even when a large amount of cooling liquid was supplied, no blow hole or blow-back explosion was observed when the pressure inside the casting frame 11 was reduced from the suction pipe 6.

A similar experiment was conducted on cast steel. As a result, it became possible to densify the structure, prevent microshrinkage, prevent shrinkage cavities, shorten the cooling time, and prevent seizure. Further, it was found that in the case of cast steel, the problem of hardness unevenness does not occur because heat treatment is performed.

[0039]

According to the cooling method of the present invention, since the cooling liquid is supplied to the mold after pouring the molten metal to cool it, the cooling rate can be increased and the standing time can be shortened.

Further, since the cooling with the cooling liquid is performed up to the A1 transformation temperature, a normal casting can be manufactured in a short time without causing a change in the structure.

Further, since the cooling by the cooling liquid is limited to the plastic range, it is possible to cool in a short time without causing cracks and the like.

Further, by partially supplying the cooling liquid, it is possible to prevent the occurrence of shrinkage cavities and to arbitrarily increase the hardness of a desired portion.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a mold for carrying out a cooling method of the present invention.

FIG. 2 is a graph showing experimental results.

[Explanation of symbols]

 2 Molds 4, 5 10, 10 13 Water pipe 6 Suction pipe 7 Pipe 8 Disappearance model 9 Test piece 11 Casting frame 12 Casting sand 13 Drainage pipe 15 Gate 18 Casting

Claims (7)

[Claims] 1. After pouring a total amount of molten metal into a mold formed by using molding sand, a cooling liquid is permeated into the molding sand, and the casting cast in the mold is cooled by the cooling liquid. A method for cooling a casting characterized by the above. 2. The method for cooling a casting according to claim 1, wherein the cooling liquid is supplied from an upper portion of the mold to permeate the inside of the casting sand. 3. The method for cooling a casting according to claim 1, wherein the cooling liquid is supplied from a water pipe installed in the casting mold and permeates into the casting sand. 4. The cooling of the casting with the cooling liquid is performed when the temperature of the casting passes through the A1 transformation temperature and within the elastic region of the casting, and within these ranges by a cooling rate close to natural cooling. The method for cooling a casting according to claim 1, wherein the casting is cooled. 5. The method for cooling a casting according to claim 1, wherein air in the mold is sucked to reduce the internal pressure when the cooling liquid is supplied. 6. The method of cooling a casting according to claim 1, wherein the casting of the casting is a vanishing model casting method. 7. The method for cooling a casting according to claim 1, wherein the cooling liquid is water.