JP3505285B2 - Mold making method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the working environment at the time of molding and casting, or the filling property of the molding sand in the molding of a mold, and further to a method for molding a high quality casting casting.

[0002]

2. Description of the Related Art In recent years, molds using organic binders have been developed mainly for the production of small lots of various kinds, but most of the molding methods are manual work, inefficient, and automation has long been desired. As one of the means, a pressure reduction molding method and a VRH method (Vacuum Replace Hardening P
rocess) has been devised.

The characteristic feature of the pressure-sensitive molding method is that it uses a reduced pressure to fill the mold sand and to pass the hardening gas, and the clamping force of the mold can be suppressed to be small as compared with the pressure filling. Wooden molds can also be used, and there are merits such as automation of molding for low-volume high-mix production. As the type of binder used in the pressure-sensitive molding method, a gas-curable binder having a longer pot life than a self-curing binder is preferable. Conventionally, amine cold box method, water-soluble phenol-methyl formate are used. Method, water glass / CO ₂ method, etc.

On the other hand, in the VRH molding method, a molding sand is filled with a binder to fill a model, and the model is placed in an airtight container. After that, the pressure in the container is reduced to eliminate air in the mold, and then a hardening gas in the container is set. Is introduced, the gas is uniformly filled in the mold and reacts with the binder in the mold to uniformly cure the mold.

[0005]

Conventionally, when performing mold molding by such a reduced pressure molding method, the binder described above has been used, but the working environment at the time of molding, the filling property of the mold sand and the Improvement of casting quality has been desired.

For example, amines used in pressure absorption molding
In the cold box method, there is a concern about the working environment due to the odor and toxicity of amine gas, and in the water-soluble phenol / methyl formate method, there remain problems such as flammability of methyl formate and poor gas circulation at low sand temperatures.

In the water glass / CO ₂ method, there are problems such as a large amount of water glass to be added to the mold sand, and a high viscosity of the binder, which reduces the filling property of the mold sand into the model. To be

Regarding the casting quality, when casting was performed using a mold made by the amine cold box method, there were cases where blown by gas, surface defects due to lastras carbon and the like occurred.

As described above, the amine cold box method, the water-soluble phenol / methyl formate method, and the water glass / CO ₂ method which have been conventionally used in the pressure absorption molding method, the working environment, the filling property of the molding sand, and the casting quality. No performance satisfying the above conditions was obtained.

Conventionally, the amine cold box method or the water-soluble phenol-methyl formate method has been used as the binder used in the pressure-sensitive molding method as described above. However, such defects have occurred because the curing gas is liable to be uncured without rotating and the curing gas is likely to be condensed especially in the winter when the sand temperature is low. In addition, a scrubber must be installed to treat the remaining amine gas and methyl formate that have been aerated after molding the mold, and environmental measures must be taken.

The VRH molding method may be used in the amine / cold box method or the water-soluble phenol / methyl formate method of the binder, but water glass is generally used. Although the amount of water glass used in this molding method is relatively small, the resin viscosity is high, so that the filling property of the kneading sand is deteriorated. Therefore, in order to impart fire resistance to the finished mold, there are cases where a mold coating agent is applied and when it is cast without coating, but in particular, when casting is performed in a state where no coating agent is applied (hereinafter referred to as uncoated type), There were problems such as blowing by gas, surface defects due to lastras carbon, and seizure, and the quality of the finished casting (casting surface) was never satisfactory.

[0012]

Therefore, as a result of intensive studies to solve the above-mentioned problems, the present inventors have found that, in a vacuum molding method, a phenol-based formaldehyde resin, especially an organic carbon dioxide-curable binder, is used. By using an alkaline water-soluble phenolic resin consisting of phenols / formaldehyde resin, bisphenols / formaldehyde resin, or phenols / bisphenols / formaldehyde co-condensation resin as a binder for the reduced pressure molding method, during molding and casting. The present invention has been completed by finding that the characteristics such as the working environment at the time or the filling property of the mold sand can be improved and that a high-quality cast casting can be obtained.

That is, the present invention relates to a mold making method characterized by using an organic carbon dioxide-curable binder as a mold binder in a vacuum molding method.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The mold making method of the present invention will be described in detail below. In the present invention, examples of the reduced pressure molding method include a pressure absorption molding method and a VRH molding method.

Regarding the pressure molding method, see "JACT NEWS, P21
~ 26, 1983.9.20, About the pressure molding method ", Jikkou Sho 61-4
No. 5952, No. 61-45953, No. 61-45954, JP Sho
57-75248, JP-A-57-97840, JP-A-57-124549, etc., which will be described in detail below.

First, in the pressure absorption molding method, a gas-hardening mold sand is instantly filled in a flask or a core box at a high vacuum pressure of several tens torr, and subsequently, the hardening gas is charged into the main mold or the core under reduced pressure. It is a method of producing a mold by curing the resin. More specifically, as a molding method of the main mold, a casting frame is installed on a hollow pattern plate having a vent plug, and the present invention is provided in a hopper having a plurality of mold sand outlets thereon. When the mold sand in which the organic carbon dioxide-curable binder to be used is kneaded is put and placed on the flask, and air is instantly sucked by operating the valve on the pressure reducing side, the mold sand in the hopper instantly The flask is suction filled. Furthermore,
If you want to increase the filling degree, it is better to cover the upper surface of the mold sand with a film or flat plate and suck again. In this case, carbon dioxide gas in the air is shut off, which also has the advantage of extending the pot life of the mold sand. . Also, when molding the core,
A vertical split core box with a vent plug was installed on the inner surface of the mold cavity, and a hopper containing mold sand kneaded with an organic carbonic acid hardening type binder was placed on it, and the inside of the cavity was instantaneously operated by the operation of a pressure reducing valve. Upon suctioning, the mold sand in the hopper is vigorously filled in the core cavity.
Next, in order to ventilate carbon dioxide gas, a gassing lid or a film is put on the core box, and after suction from the core box, carbon dioxide gas is supplied to cure the mold sand.

The pressure molding method will be described in more detail with reference to FIG. The model stand (1) has a decompression chamber (2) inside, and communicates with the decompression chamber (2), and a ventilation hole (3) is provided at the center of the upper surface.
And a communication hole (4) near both ends, each of which is provided with a hollow cavity (5) vertically penetrating on the upper surface of the model base (1), and A model box (7) having a plurality of vertically penetrating holes (6) surrounding the (5) surrounds the cavity (5) and the through hole (6) by the vent hole (3) or the communicating hole. It is installed in communication with the decompression chamber (2) via (4).

The model lid (8) is provided with an annular groove (9), and is provided with a plurality of ventilation holes (9a) communicating from the horizontal part of the annular groove (9) to the lower surface, and the molding sand (organic system It is the one that penetrates the supply hole (10) for the mold sand of the carbonic acid hardening type binder,
The model lid (8) has a model box (7), a hopper (12) for storing the molding sand (11), a model lid (8), a connecting pipe (13) and an on-off valve (1).
It is installed so as to communicate with the hollow portion (5) via 4). A vent plug (15) is embedded in the lower end of the vent hole (9a) so as to be substantially flush with the lower surface of the model lid (8). A vacuum pump (19) is connected to the decompression chamber (2) via a conduit (16).

In the state of FIG. 1 constructed as described above, the vacuum pump (19) is operated to operate the conduit (16) and the decompression tank (1
8), the decompression chamber (2), the vent (3) and the communication hole (4) make the entire cavity (5) under negative pressure and open the on-off valve (14) to open the inside of the hopper (12). The uncured molding sand (11) coated with an organic carbon dioxide-curable binder is used as an opening / closing valve (14) and a connecting pipe (1).
It is suction-filled into the cavity (5) via 3). At this time, the through hole (6), the annular groove (9), and the vent hole are provided above the cavity (5).
Since negative pressure is exerted via (9a), the molding sand is well filled even in the upper part of the cavity (5), and the molding sand in the cavity (5) is uniformly filled. afterwards,
In order to cure the molding sand filled, the on-off valve (14) is closed and the on-off valve (17) is opened again to reduce the pressure, and the carbon dioxide gas cylinder (21) is opened.
The opening / closing valve (20) of (1) is opened and carbon dioxide gas is sent to ventilate the molding sand filled in the cavity (5).

The aeration conditions are not particularly limited, but as a guide, it is preferably 20 to 500 liters / minute, and the aeration pressure of carbon dioxide gas is preferably in the range of 0.1 to 5 atm, more preferably 0.5 to 3 atm. The amount of carbon dioxide gas used is preferably 5 to 300 parts by weight per 100 parts by weight of the binder. Cavity
The degree of pressure reduction of (5) is not particularly limited, but is preferably 0 to 700 torr, more preferably 1 to 300 torr. Here, such a molding method is called a pressure absorption molding method, and by molding using an organic carbon dioxide-curing binder, the filling property of the molding sand is further improved, and a mold of high strength is molded. Is possible. In addition, high quality castings can be produced by casting using an organic carbon dioxide-curable phenolic binder that cures using non-toxic carbon dioxide.

On the other hand, regarding the VRH molding method, "JACT N
EWS, P37 ~ 41, 1986.8.20, Vacuum displacement hardening (VRH)
However, it will be described in detail below.

In the VRH molding method, casting sand generally kneaded with a binder, which is water glass, is filled in a model, placed in a closed container, and then depressurized in the container to eliminate air in the mold. When the hardening gas in the rear container is introduced, the gas is uniformly filled in the mold and reacts with the binder in the mold to uniformly harden the mold. In the present invention, a high-quality cast casting can be produced by using a carbon dioxide-curable binder as the binder.

In the present invention, when the VRH molding method is used for molding, the mold sand filled with a carbon dioxide-curable binder is filled in a mold model, and the degree of pressure reduction after the mold sand is placed in a closed container is usually 0-.
400 torr is good, and practically preferably 10 to 100 torr. Also, the holding time is usually within 30 minutes, though it depends on the capacity of the closed container and the vacuum pump, and it reaches 10 torr within about 10 minutes after opening the pressure reducing valve leading to the vacuum pump of the closed container, and then the carbon dioxide. Replace the inside of the closed container with gas. The time required for this is from several seconds to several minutes, and the mold is taken out with the pressure in the closed container corresponding to about atmospheric pressure.

The organic carbon dioxide-curable binder used in the present invention is a phenol-formaldehyde resin, particularly phenol-formaldehyde resin, bisphenol-formaldehyde resin, or phenol-bisphenol-formaldehyde co-condensation resin. Alkaline water-soluble phenolic resin consisting of is mentioned, but these will be explained in detail below.

The above-mentioned organic carbon dioxide-curable binder used in the present invention is used in an alkaline water-soluble phenolic resin as described in JP-B-4-76947, JP-A-4-33953 and the like. Boric acid and boric acid compounds which are oxyanion compounds necessary for forming a cross-link, such as borax, or borate esters, or those containing salts such as aluminate compounds and stannic acid compounds, It is obtained by adding it at the time of reaction or compounding.

As the phenolic raw material of the phenol-formaldehyde resin, a formaldehyde resin using phenols or bisphenols alone or a formaldehyde co-condensation resin using phenols and bisphenols at the same time is prepared, and a predetermined organic carbonate is prepared. Although a gas-curable binder is obtained, a binder of bisphenol / formaldehyde resin or phenol / bisphenol / formaldehyde co-condensation resin is particularly preferable in the vacuum molding method. Since the fluidity of the kneading sand of the mold sand in which bisphenols / formaldehyde resin or phenols / bisphenols / formaldehyde co-condensation resin is kneaded is better than that of the homopolymer resin using phenols, the filling property is This is because it has excellent features such as improved mold strength, high mold strength, and long pot life.
Among these, phenol / bisphenol A /
A cresol-formaldehyde co-condensation resin is particularly preferred.

Phenols include phenol, cresol (ortho, meta, para), resorcin, and the like, and bisphenols include bisphenol A, bisphenol F, bisphenol S, bisphenol Z and the like.

In order to further enhance the mold strength, glycol ethers such as cellosolve, carbitol, triethylene glycol ethers may be added as an additive during the reaction of the resin or at the end of the reaction. Binder
The amount is 0.1 to 30 parts by weight, preferably 5 to 20 parts by weight, based on 100 parts by weight. Incidentally, the addition time may be added at the time of adjusting the kneading of the mold sand, or a silane coupling agent may be added.

Usually, the amount of the binder used in the reduced pressure molding method is 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the molding sand. Used and kneaded to obtain mold sand. The types of foundry sand that can be used here include imported silica sand, domestic silica sand, alumina sand, zircon sand, chromite sand, synthetic mullite sand (cera beads), olivine sand, metal powder, metal oxide powder, etc. The particle size and particle size distribution of the above are not particularly limited. Also,
The degree of reduced pressure in the reduced pressure molding is not particularly limited, and the amount and flow rate of the carbon dioxide gas used as the curing gas are not particularly limited. However, the proper amount of carbon dioxide gas used is 5 to 300 parts by weight, preferably 20 to 200 parts by weight, per 100 parts by weight of the binder.

[0030]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.

In Examples 1 to 3 and Comparative Examples 1 to 3, casting was carried out by a pressure molding method, and in Examples 4 to 6 and Comparative Example 4, casting was carried out by a VRH molding method.

In the molding method of the pressure absorption molding method, a casting frame is installed on a hollow pattern plate having a vent plug, and a poly film is cured with carbon dioxide gas in order to increase the pot life and the filling degree. Cover the mold sand mixed with the mold binder, put a hopper with multiple mold sand outlets on the mold, and operate the valve on the pressure reducing side to instantly suck in air. Was suction-filled. The degree of pressure reduction at this time was 60 torr. After the suction filling, the degree of reduced pressure becomes low, so that the degree of reduced pressure is maintained as it is, and then a valve of carbon dioxide gas is opened to feed a hardening gas to obtain a mold.

Example 1 3 kg of an organic carbon dioxide-curable binder composed of phenol / formaldehyde was kneaded with 100 kg of domestic silica sand No. 6 in a mold making mixer, and the kneaded sand was suction-molded by the above-mentioned process. A carbon dioxide gas valve was opened to feed carbon dioxide gas to obtain a carbon dioxide gas-curable binder mold.
The amount of carbon dioxide used for curing at this time is
Used 50% by weight. The ventilation pressure of carbon dioxide used for curing is 2
It was kgf / cm ² and was aerated at 150 l / min for 3 minutes.

Example 2 Except that an organic carbon dioxide-curable binder consisting of bisphenol A / formaldehyde co-condensation resin was used.
Molding was performed in the same manner as in Example 1 to obtain a carbon dioxide curable binder mold.

Example 3 A carbon dioxide gas-curable binder mold was prepared in the same manner as in Example 1 except that an organic carbon dioxide-curable binder consisting of phenol / bisphenol A / metacresol / formaldehyde co-condensation resin was used. Obtained.

Comparative Example 1 In a mold-making mixer, 0.8 kg of a cold box binder composed of a resole phenolic resin and an isocyanate oligomer was kneaded with 100 kg of domestic silica sand No. 6, respectively, and the kneaded sand was suction-molded by the above process. Then, the amine gas valve was opened and the amine gas was fed to obtain a mold. The amount of amine gas used for curing at this time was 50% by weight based on the resin.

Comparative Example 2 With a mixer for molding a mold, 1.5 kg of a water-soluble phenol / methyl formate curing binder composed of alkaline phenol / formaldehyde was kneaded with 100 kg of domestic silica sand No. 6, and the kneaded sand was suction-molded by the above process. Then, the valve for methyl formate was opened and methyl formate was fed to obtain a mold. The amount of methyl formate gas used for curing at this time was 50% by weight based on the resin.

Comparative Example 3 6 kg of water glass was kneaded with 100 kg of domestic silica sand No. 6 in a mold making mixer, and the kneaded sand was suction-molded by the above process, and then a carbon dioxide gas valve was opened to release carbon dioxide gas. It was sent and a mold was obtained. The amount of carbon dioxide gas used for curing at this time was 100% by weight based on the resin. The carbon dioxide gas used for curing was aerated at 150 l / min for 6 minutes.

Next, a mold was molded by the VRH molding method. The mold sands prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were used in a depressurizable closed container, and in order to obtain a VRH mold, a closed container having a volume of 100 liters was depressurized to 15 torr and carbonized after depressurization. The gas was sent to atmospheric pressure, and the mold was taken out from the closed container. The time required to reach 15 torr at this time is 3
The time required for sending carbon dioxide gas to reach normal pressure was 1 minute.

Example 4 2.5 kg of an organic carbon dioxide-curable binder consisting of phenol / formaldehyde was kneaded with 100 kg of domestic silica sand No. 6 with a mixer for molding a mold, and the kneaded sand was VRH molded by the above process.

Example 5 Molding was carried out in the same manner as in Example 4 except that an organic carbon dioxide-curable binder consisting of phenol / bisphenol A / formaldehyde co-condensed resin was used.

Example 6 Molding was performed in the same manner as in Example 4 except that an organic carbon dioxide-curable binder consisting of phenol / bisphenol A / formaldehyde co-condensation resin was used.

Comparative Example 4 Molding was carried out in the same manner as in Example 4 except that water glass was used instead of the organic carbon dioxide curable binder.

In the above-mentioned Examples 1 to 3, the odor during molding was subjected to a sensory evaluation, the packing density of the mold, and a casting of the material FCD-450 (the pouring temperature was 1410 ° C.) was not coated using the mold. After casting, the casting surface condition (casting defect) was observed. The results are shown in Table 1. In Comparative Examples 1 to 3, sensory evaluation of odor at the time of molding, filling density of the mold and casting using the mold with a material of FCD-450 (the pouring temperature is 1410 ° C.) without coating, The casting surface condition (casting defect) was observed. The results are shown in Table 1.

[0045]

[Table 1]

In Example 1, as compared with Comparative Examples 1 to 3, good results were obtained in terms of odor, filling property and casting surface condition during molding, and in Examples 2 and 3, all items were good or remarkable. It is clear that the results are excellent, and that it is remarkably excellent when the mold making method according to the present invention is carried out.

In the above Examples 4 to 6, the odor during molding was subjected to a sensory evaluation, the packing density of the mold, and a casting of the material FCD-450 (the pouring temperature was 1410 ° C.) was not coated using the mold. After casting, the casting surface condition (casting defect) was observed. In Comparative Example 4, the odor during molding was subjected to a sensory evaluation, the packing density of the mold and the mold used to cast a casting of material FCD-450 (the pouring temperature was 1410 ° C) without coating to obtain a casting surface. The state (casting defect) was observed.

[0048]

[Table 2]

Compared to Comparative Example 4, Example 4 gave good results in terms of filling property and casting surface condition, and further, Examples 5 and 6
Is a good or remarkably good result in all the items, and it is clear that it is remarkably excellent when the mold making method according to the present invention is carried out.

[0050]

According to the molding method of the present invention, it is possible to improve the work environment and the filling property of the molding sand and the casting quality,
Further, not only is it applicable to a wide range of applications such as main molds, cores, H process molds, and stack molds, but it is also useful for automating the casting manufacturing process and has a beneficial effect.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a pressure-molding method according to the present invention.

[Explanation of symbols] 1 model stand 2 decompression room 3, 9a vent 4 communication holes 5 cavity 6 through holes 7 model box 8 model lid 9 annular groove 11 Foundry sand 18 decompression tank 19 vacuum pump 21 Carbon dioxide cylinder

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A 61-273241 (JP, A) JP-A 6-210392 (JP, A) JP-A 7-185731 (JP, A) JP-A 57- 39058 (JP, A) JP-A-6-99248 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B22C 1/00-1/26 B22C 9/12

Claims (5)

(57) [Claims] 1. In a vacuum molding method, as a template binder , oxyanion compounds, aluminate compounds and
A method of molding a mold, which comprises molding using only an organic carbon dioxide-curable binder containing a compound selected from stannic acid compounds . 2. The mold making method according to claim 1, wherein the organic carbon dioxide-curable binder is a phenol-formaldehyde resin. 3. The mold making method according to claim 2, wherein the phenol-formaldehyde resin is a bisphenol-formaldehyde resin or a phenol-bisphenol-formaldehyde co-condensation resin. 4. The mold molding method according to claim 2, wherein the phenol-formaldehyde resin is a phenol-bisphenol A-cresol-formaldehyde co-condensation resin. 5. The mold molding method according to claim 1, wherein the reduced pressure molding method is a pressure absorption molding method or a VRH molding method.