JPH04100654A - Surface treating method for casting mold - Google Patents

Abstract

PURPOSE:To remove an excess coating material on a mold surface and to obtain the casting mold for manufacturing a product having good casting surface and releasing from the mold, etc., by fluidizing the medium material of the specific grain diameter of powdery body as main substance, arranging the mold in this fluidized bed, bringing it into contact with the medium material and removing a surface layer on the mold. CONSTITUTION:The medium materials 2 consisting essentially of the granular bodies having the average grain diameter to more than half of average hole diameter of gaps, which is present on the surface 4 in the casting mold, and smooth surface at least on a part of the surface, are fluidized with fluidized gas to form a fluidized bed. In the formed fluidized bed, the casting mold is arranged and the mold and the fluidized medium material 2 are relatively shifted and by bringing the mold into contact with the medium material 2, the surface layer 4 on the mold is removed. Then, as the furidized gas, air, nitrogen, oxygen or inert gas is used.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for surface treatment of a casting mold for improving the casting surface and mold separation of the product by removing the surface layer of the casting mold. Regarding.

(Prior Art) In molds for metal casting, for example, sand molds, the size of sand used is relatively coarse in view of the strength of the mold, air permeability, etc. Therefore, during casting, the molten metal is inserted into the gaps in the molding sand on the surface of the mold, causing "aiming", rough casting surfaces, and poor release from the mold. Furthermore, some castings are made into products with the surface as cast, that is, with the cast surface as is, and the roughness of the surface of the casting may affect its value. In general, the finer the grain, the more accurate it is.
The appearance is said to be good.

However, it is possible to uniformly process the complex-shaped mold surface,
Until now, there was no way to obtain fine-grained, high-precision molds.

Therefore, we add alcohol, water, etc. to fine sand, etc., and if necessary, add a binder to form a slurry, which is coated onto the surface of the mold in a wet manner by brushing, spraying, dipping, etc. This is a commonly used method to improve the casting surface.

However, when coating the mold surface with a wet coating material,
Although the casting surface becomes clean, a drying process is required, and cracks and blisters occur in the coating material during drying, making it easy for the coating material to peel off. Furthermore, in the case of a coating material that easily absorbs moisture, etc., the drying process is time-consuming, increasing the number of steps and increasing costs. Furthermore, if drying is insufficient, moisture etc. adsorbed in the coating material during casting may evaporate and gas defects may occur. In addition, there was a problem in that the coating material sagged at the edges of the mold due to surface tension, making it difficult for the coating material to have a uniform thickness, which affected the dimensional accuracy of the product.

Another method is to prepare a mold using molding sand coated with a room temperature curable resin or a thermosetting resin (hereinafter simply referred to as resin). However, in this case, if casting is performed using a molten metal such as aluminum, magnesium, or an alloy thereof, which has a relatively low casting temperature, the decomposition of these resins will be insufficient and tar will be generated. These resins adhere to gas vents and the like, causing clogging, and furthermore, the generated gas flows toward the cavity, leading to casting defects. In order to prevent this, the resin adhering to the vents must be cleaned frequently, which poses a problem of placing a heavy burden on maintenance.

To solve these problems, hydrated magnesium silicate,
A coating material made of a porous material such as activated carbon or activated alumina, a powder of clay minerals, natural minerals, artificial minerals, etc. is mixed with a coating medium of a larger diameter and made to flow, and the mold is moved vertically and back and forth within the coating material. There is a method of moving the mold in the direction or left and right to coat the surface of the mold with a coating material to improve the casting surface and further reduce the occurrence of tar (Japanese Patent Application Laid-Open No. 1-202336).
), is the most powerful means at this stage.

However, in this method, if the amount of coating material in the fluidized bed becomes too large, the mold surface may be coated with excess coating material, resulting in a layer of coating material being formed on the mold surface. This is because the coating medium in the fluidized bed hardly removes the excess coating material. Since no binder is used in these excessive coatings, they tend to peel off or fall off. These excess coatings are scraped away by the molten metal during casting and washed away to the mold surface, causing the problem that the casting surface in contact with the mold becomes rough.

Previously, excess coatings were removed by brushing or blowing with compressed air. However, with a brush, the coating is uneven after removal (and with compressed air, it is difficult to adjust the blowing method, so the excess coating may not be removed, or it may be too much and the coating may fill the gaps between the sand grains on the mold surface). This caused the problem of removing even the covering material.

Therefore, in order to make the most of the method of the above-mentioned application, it was necessary to treat the surface of the mold in some way.

[Purpose of the invention]

An object of the present invention is to provide a surface treatment method for uniformly and easily removing excessive coatings and other surface layers from a casting mold filled with a coating material deep into the gaps between sand grains on the mold surface. be.

[Structure of the invention]

The surface treatment method for a casting mold according to the present invention uses a fluidizing gas to form particles having a smooth surface on at least a part of the surface and having an average particle size that is half or more of the average pore size of the gaps existing on the surface of the casting mold. a step of fluidizing a medium containing as a main component to form a fluidized bed; arranging and holding the casting mold in the formed fluidized bed, and relative to the mold and the fluidized medium; and removing a surface layer of the mold by bringing the mold into contact with the medium.

The medium of the present invention may contain 1% by weight or less of a finely powdered mineral having a diameter of less than half the average pore diameter.

If 1% by weight or more of fine powder is contained, the removal effect of the fluidized bed is reduced.

As the fluidizing gas of the present invention, air, nitrogen, oxygen, or an inert gas is used.

Further, the average particle diameter of the medium is preferably at least half the average pore diameter of the gaps existing on the mold surface. If smaller than this,
Since the mass of the particles is small, the acting force is weak, and they are often trapped in small gaps and depressions on the mold surface, so they do not have a removal effect.

In the present invention, a mold is placed and held in a fluidized bed made of a removal medium, and the mold is moved relative to the medium to utilize the acting force of the medium in contact with the mold. Remove the surface layer uniformly.

That is, to remove the surface layer of the mold, the mold is placed in a fluidized bed of fluidized media. This arrangement is performed by hanging the mold, etc., and in order to perform uniform processing, the mold is repeatedly moved primarily in the vertical direction.

In addition, it can be moved not only in the vertical direction, but also in the front-back and left-right directions. Furthermore, when processing molds with complex shapes,
Combine many movements, not just one direction, to avoid any backlogs. Furthermore, if it is difficult to move the mold, the fluidized bed itself may be moved. Note that the mold may be placed in the fluidized bed not only after the formation of the fluidized bed as described above, but also before the formation of the fluidized bed before introducing the fluidizing gas.

Further, the casting surface to which the present invention can be applied is not particularly limited, such as a normal shell mold or a mold filled with a coating material.

For the coating material filling type, any surface texture can be applied as shown below.

In other words, the coating material is filled only into the depressions on the mold surface, and the coating material is filled into the depressions on the mold surface, and the coating material is further filled into at least part of the surface layer outside the depressions. The coating material is filled and coated over the entire desired part of the mold surface (including the fillet area) to form a thin coating layer.

[Action/effect of the invention]

The mechanism by which excess coating can be removed by the present invention is not clear, but a mechanism roughly shown in the accompanying drawings is conceivable. In the figure, number 1 indicates the covering material, 2 indicates the medium, 3 indicates the molding sand, and 4 indicates the mold surface.

When the medium is fluidized and the mold is moved within it, Figure (a)
-1-(b)-+ As shown in (C), the mold surface 4 and the medium 2 come into contact, and acting forces such as frictional force and impact force act,
It is believed that this force removes excess coating. Since the medium is progressing in contact with the mold surface, excess coating material is pushed along with the medium in the direction of movement of the medium or pushed into the cavity, so there is more coating material in the cavity. As well as being compacted, only the excess coating is removed from the top of the cavity after the medium has passed, thus forming a smooth surface embedded in the coating or coagulation.

If the surface treatment of the mold according to the present invention is carried out, a mold with a smooth mold surface 4 and good dimensional accuracy can be obtained as shown in FIG. The roughening of the casting surface in contact with the mold surface that occurs due to this process does not occur, and a casting with a clean casting surface can be obtained.

Further, according to the present invention, even the surface layer of a mold having a complicated shape can be removed evenly and uniformly.

Furthermore, the present invention does not require a drying step.

[Other inventions]

The particle size of the medium used in the present invention is preferably 70 μm to 5 μm.

When the diameter is less than 70 μm, it is difficult to fluidize and the ability to remove the surface layer is reduced, and since the amount of fluidizing gas is small, there is no adverse effect on the adhesion of media in the surface layer, residual slag, casting surface, and molten metal. vinegar.

When the amount of fluidizing gas increases, channeling occurs due to the gas, creating a non-uniform fluidization state and drastically reducing the removal power.

Furthermore, if the particle size is larger than 5 mm, the amount of fluidizing gas to be supplied for fluidizing the medium will be large, and the force applied to the mold will be large, and the mold will be easily damaged. Also,
Particulate media tends to scatter out of the fluidized bed. Furthermore,
It becomes difficult to move the mold.

The particle size of the fine powder that can be contained in the medium of the present invention at 1% by weight or less is considered to be suitably 50 μm or less.

When a medium is used to remove excess coating material from the mold surface, it is preferable to use a material with a density similar to or greater than that of the coating material and a particle size comparable to or greater than that of the coating medium. . When powdered minerals with a particle size of 50 μm or less are included, the content is preferably 1% by weight or less.

In the fluidized bed of the present invention, the medium is placed in a fluidized bed processing apparatus,
It is formed by introducing a fluidizing gas to fluidize the medium.

The fluidizing gas is preferably introduced at a superficial velocity of 0.03 to 0.15 m/sec. The amount of fluidizing gas varies depending on the particle size of the medium and the content of removed clay minerals, etc.In order to make the acting force work most effectively, regardless of these conditions, the amount of gas near the starting point of fluidization must be adjusted. It is desirable to flow the fluidizing gas so that

If the superficial velocity of the fluidizing gas is less than 0.03 m/sec, the medium will not be fluidized, and if it is more than 0.15 m/sec, the fluidization will be too intense and the removal power will be reduced.

Air, nitrogen, oxygen, or an inert gas is used as the fluidizing gas and is introduced from below the fluidizing device.

At this time, make sure that the covering material does not absorb moisture in the atmosphere. Dry air or hot air may be used for this purpose.

The medium of the present invention includes clay minerals, natural minerals, artificial minerals,
One or more powders of activated carbon are used.

The clay minerals used in the present invention include sepiolite,
Natural minerals such as palygorskite, diatomaceous earth, zeolite, and vermiculite include silica sand, chromite sand,
Suitable artificial minerals such as zircon sand and silica flour include alumina, synthetic mullite, and fused silica.

In order to improve the ability to remove the surface layer, it is best to use a medium with a coarse surface texture, such as a crushed one, which increases frictional force, but there is a risk that it will also scrape off the coating material filled in the holes of the mold. There is. A medium with some smooth areas is desirable to remove excess coating material and to obtain a smooth mold surface. Further, in order to firmly fill the coating material and obtain a smooth mold surface, a spherical shape is suitable.

〔Example〕

The present invention will be explained in detail below.

(Example 1) Two fluidized bed processing devices (hereinafter referred to as fluidized devices) were used, one of which was a coating fluidized device and the other was a removal fluidized device. Sepiolite powder (specific surface area approx. 28
0rd/g) to perform surface treatment of the mold.

That is, coating is performed using a coating flow device, and excess coating material is removed using a removal flow device. A fluidizing device for coating contains a mixed powder consisting of a coating material and a coating medium, and fluidizes it with a fluidizing gas such as air. Then, the mold is moved in the vertical direction, and also in the front, back, left and right directions, and the coating material is filled into the depressions on the surface of the mold. A fluidizing device for removal has a removing medium placed therein and fluidizes it with a fluidizing gas such as air. Then, the coated mold is moved in the removal flow device in the up-down direction, furthermore, in the front-back and left-right directions to remove the excess coating on the mold surface.

Concerning the above, specific examples are shown below. First, using resin-coated foundry sand (100 parts by weight of silica sand, 2 parts by weight of phenolic resin, particle size No. 6), the outer diameter of the upper part was 73 mm and the outer diameter of the lower part was 80 mm.
A hollow cylindrical mold having a height of 110 mm and a thickness of 10 mm was prepared.

Next, sepiolite 3 with a particle size of 50 μm or less was used as a coating material.
parts by weight and 100 parts by weight of spherical mullite having a particle size of 150 to 380 μm were mixed as a coating aid. Then, this mixture was prepared into a dish with internal dimensions of 300mm in length, 300mm in width, and 400mm in height.
- The mold was placed in the fluidizing device, and compressed air was introduced as a fluidizing gas to form a fluidized bed of the mixture.Then, the mold was placed therein and moved up and down 20 to 30 times.

Excess coating from the coated mold was then removed in a removal fluidizer.

As a removal medium, spherical mullite (particle size 100~
500 μm) (Table 1 Nα1 to 3),
Spherical mullite mixed with 0.4% by weight of the sepiolite (Table 1 N04-6), spherical mullite mixed with 0.6% sepiolite (Table 1 N07-9)
, 0.8% by weight (Nα10 in Table 1) was used, and compressed air was introduced as a fluidizing gas to fluidize it. The above-mentioned coated mold was placed in this and moved up and down 5 to 50 times. Table 1 shows the results of measuring the amount of excess coating before and after treatment and the amount removed.

In addition, as a comparative example, 1.0% sepiolite was added to spherical mullite.
Excess coating material was removed in the same manner as above using a fluidized bed for removal containing 0% by weight of the mixture.

The results are also shown in Table 1.

In addition, in the table, roJ indicates whether the mold surface after treatment is "good" or "
△” indicates that “some excess coating remains” on the surface, “×”
indicates that there is "significant excess coating remaining" on the surface.

As is clear from this example, when the content of sepiolite with a diameter of 50 μm or less is less than 1% by weight, the fluidized bed of this example has a surface layer of 10 g/rr of the mold. As a result, it was possible to obtain a mold that was uniform, clean, and had good dimensional accuracy.

When the fluidized bed of the comparative example was used, it was useless as a removal method because it had more of an adhesion effect than a removal effect.

Further, in this example, the amount of sepiolite in the fluidized bed for removal after 100 surface treatments was about 0.04% by weight, which corresponded to about 10% of the total amount removed.

From this, the fluidized bed for removal of this example has a service life of about 2,500 times.

(Example 2) After producing a coating mold in the same manner as in Example 1, the mold was taken out of the coating flow device, and excess coating material was removed in the removal flow device.

The fluidizing device for removal had the same structure and dimensions as the fluidizing device for coating. As removal media, spherical mullite (particle size 100 to 500 μm) with a particle size larger than half of the average pore size of 60 μm in the mold surface, spherical mullite (particle size 0.5 to InIn), and crushed silica sand (particle size 30-5
Compressed air was introduced as a fluidizing gas to fluidize the mold, and a coating mold coated in the same manner as in Example 1 was placed in the mold and moved up and down 1 to 10 times. .

The results of measuring the amount of coating before and after removing the excess coating material are shown in Table 2 together with the conditions of the removal medium, the flow rate of air as a fluidizing gas, and the number of vertical movements of the mold during the removal process.

In all cases, excess coating was uniformly removed from the surface of the mold obtained in this example, and a smooth mold surface was formed.

The present invention is not limited in any way by these Examples unless it goes beyond the gist thereof.

[Brief explanation of the drawing]

Figure (a) is the surface of the mold with excessive surface coating, Figure (b)
is a schematic diagram showing the effect of the medium on the mold surface, and FIG. (a) (b) (c)

Claims (1)

[Claims] The main component is a granular material that is produced by a fluidizing gas and has a smooth surface on at least a portion of the surface and has an average particle diameter that is half or more of the average pore diameter of the gaps existing on the surface of a casting mold. a step of fluidizing a medium to form a fluidized bed, and arranging and holding the casting mold in the formed fluidized bed and relatively moving the mold and the fluidized medium. , a step of removing a surface layer of the mold by contacting the mold with the medium; and a method for surface treatment of a casting mold.