JPS63224838A - Core for pressurized casting - Google Patents

Abstract

PURPOSE:To secure the good formability of shell core of blow forming, etc., and strength of the core and to improve the collapsibility of the shell core by packing the specific core sand base material and resin as binder in a forming mold. CONSTITUTION:The shell core 3 is formed as binding silica sand and water soluble salt grain with the resin. And, blending ratio of the silica sand and the water soluble salt grain is set to by wt.% of 60-75:25-40 and the resin to the core sand base material is blended to 1-5wt.% ratio. As a result, deterioration of the fluidity of silica sand, etc., caused by deliquenscence of the water soluble salt grain at the time of forming by blowing is prevented, and as the silica sand for the cores 1, 2 is firmly combined by the resin, after molding the lowering of the strength does not occurred, and after casting, as gap between the silica sand becomes large, caused by dissolving the water soluble salt grain by submerging the shell cores 1, 2 into the water, while the formability of shell core by the blow forming, etc., and strength of the shell cores 1, 2 are secured, the collapsibility of the shell core after casting is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a core used for pressure casting such as die casting.

(Prior art) Conventionally, such cores have been filled with shell sand (so-called resin-coated sand) in which sand grains are coated with phenolic resin into a mold heated to about 250'C and then fired. A shell core in which the phenolic resin on the surface of the shell sand is caked and hardened and then released from the mold is generally well known because of its excellent moldability.

By the way, when a cast product is cast using this shell core, the shell core contracts due to the action of molten metal pressure during casting. When the shell core shrinks in this way, the packing density of the shell sand that makes up the shell core increases, and even if the shell core is vibrated to remove it from the cast product after casting, The problem was that it was difficult to collapse.

In particular, when cast by a high-pressure casting method such as a molten metal forging method, the deterioration of the collapsibility of the shell core is remarkable. In addition, the decrease in the collapsibility of the shell core is due to the fact that as the packing density of the shell core increases, the porosity between the shell sand decreases and the air permeability deteriorates. This is also because the phenol resin coating the phenol resin has less contact with oxygen, making it difficult to thermally decompose the phenol resin.

Therefore, as a means for improving the disintegration properties of the shell core, for example, as disclosed in Japanese Patent Application Laid-open No. 53-95126, water-soluble starch, gelatin, etc. It has been proposed that a mold is formed by mixing an aqueous solution containing 0.1 to 2.0 parts by weight of a polymer and an aqueous solution containing 1 to 10 parts by weight of water-soluble salt particles.

(Problems to be Solved by the Invention) However, since the above-mentioned publication uses a water-soluble polymer and water-soluble salt particles as a binder to bind silica sand, it is difficult to solve the problem when a phenolic resin is used as a binder. In comparison, the bonding force is weaker, which causes the problem that the strength of the mold decreases. In addition, when using a mold or a core, the core is generally formed by blow molding or the like, or if water-soluble salt particles are used as a binder as described above, the fluidity of silica sand etc. is inhibited due to its deliquescent property. This may adversely affect the molding of the core.

The present invention has been made in view of the above, and its purpose is to use silica sand and water-soluble salt particles as the main constituents of the shell core, and a conventionally widely used resin such as phenol resin as the binder. We will use each. In this case, by specifying the blending ratio of the shell sand, water-soluble salt particles, and resin, it is possible to prevent the flowability of silica sand, etc. caused by deliquescence of the water-soluble salt particles during blow molding, etc., and the binding strength of silica sand, etc. without causing a decrease in the strength of the shell core after molding due to this, and furthermore, the gap between the silica sand can be enlarged by dissolving the water-soluble salt particles by infiltration of the shell core into water after casting,
This aims to improve the collapsibility of the shell core after casting while ensuring good moldability and strength of the shell core by blow molding or the like.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a core sand base composed of 60-75% by weight of silica sand and 25-40% by weight of water-soluble salt particles. The composition is such that a mixture of 1 to 5% by weight of resin as a binder to the material is filled into a mold and fired.

(Function) With the above configuration, in the present invention, the shell core is formed by bonding silica sand and water-soluble salt particles with resin, and the blending ratio of water-soluble salt particles to silica sand is 6% by weight.
0 to 75: 25 to 40, and the resin is blended at a ratio of 1 to 5% by weight with respect to this blend, that is, the core sand base material.

For this reason, the fluidity of silica sand etc. due to the deliquescence of the water-soluble salt particles during blow molding etc. is inhibited, and the silica sand etc. in the shell core that is opened after molding is tightly bound by the resin, reducing its strength. In addition, after casting, the shell core is immersed in water and the water-soluble salt particles are dissolved, so that the gaps between the silica sands are enlarged, which improves the moldability of the shell core by blow molding etc. Moreover, the collapsibility of the shell core after casting can be improved while ensuring the strength of the shell core.

(Example) Embodiments of the present invention will be described below based on the drawings.

Figures 1 and 2 show a pressure casting according to an embodiment of the present invention, which is a two-part type consisting of a first core 1 and a second core 2, which is applied when casting a rotor for a rotary piston engine of an automobile. A shell core 3 is shown, and since both boxes 1 and second cores 1 and 2 of the shell core 3 have the same structure except for different shapes, the first core 1 will be explained below. , regarding the second core 2, the same components are given the same reference numerals and detailed explanation thereof will be omitted.

The first core 1 is made by coating a core sand base material made of silica sand and water-soluble salt particles with a resin as a binder, and heating the core sand base material coated with this resin to about 250'C, for example. The first core 1 is molded by filling a held core mold (not shown) by blow molding or the like and firing it.

The composition of the silica sand constituting the core sand base material of the first core 1 is, for example, SiO293.36% by weight, A! 1203
5.19% by weight, Fe2030.97% by weight,
The water-soluble salt particles having a concentration of 0.48% by weight are used, for example, NaQρ or KCρ. Further, if the average particle size of these particles is, for example, 60 mesh for silica sand, it is preferable to use water-soluble salt particles having a slightly coarser mesh size of 40 mesh from the viewpoint of improving disintegrability. Furthermore, as a feature of the present invention, the blending ratio of silica sand and water-soluble salt particles constituting the core sand base material of the above-mentioned "first core" is 60 to 75% by weight for silica sand and 60 to 75% by weight for water-soluble salt particles Each is selected within this range of 25 to 40 uff1%.

In addition, phenolic resin is used as the resin as a binder, and in the novolak type, hexamethylenetetramine is added as a hardening agent to the phenol resin.
The one added at 0% by weight is used. Note that the resol type does not require a curing agent. Further, the blending ratio of the resin to the core sand W'tA is selected within the range of 1 to 5% by weight.

Further, a first coating layer 4 is provided on the outer surface of the first core 1 as a coating material layer, and the first coating layer 4 is made of a steel 1 containing powdered refractories, metal oxides, etc.
After applying the no-liquid solution to the outer surface of the first core 1, a drying process is carried out at a drying temperature of 150° C. and a drying time of 30 minutes to form a powder with a thickness of, for example, 100 to 350 μm.
The layer thickness is 7n. The reason why the thickness of the first coating layer 4 is set in the above range is that if it is less than 100 μm, cracks may occur due to the pressure of the molten metal during casting. This is because an infiltration prevention effect proportional to the increase cannot be expected, and the dimensional accuracy of the first core 10 may be adversely affected. The composition of the slurry liquid is, for example, S! O255゜5% by weight, A, Q 203
2. O condolence Wx%, re20g4. ()II%, Ca
O0.5% by weight, Mg025.0% by weight, ZrO2o,
5i hanging%, C6,0% by weight, its(l!26.5% by weight
is diluted to 50% with ethyl alcohol.

Further, a second coating layer 5 is provided as another coating material layer on the first coating layer 4 of the first core 1, and the second coating layer 5 is made of graphite.

By applying a solution containing fine particles or flat particles such as mica and then going through a drying process, for example, in the case of a graphite layer, the average particle size of 0.5 to 10 μm can be reduced to 10 to 50 μT.
In the case of a mica layer, those having an average particle size of 2 to 10 μm are formed to a layer thickness of 50 to 150 μm.

The reason why the particle diameters of the graphite and mica particles constituting the second coating layer 5 are set in the above range is that the lower limit is a manufacturing problem, and the upper limit is difficult to densify the layer and prevent molten metal infiltration. This is because there is always a risk of In addition, the reason why the layer thickness of graphite and mica is set within the above range is that if the graphite layer is less than 10 μm, there is a risk of cranking due to the hot water pressure during casting, whereas if the thickness exceeds 50 μm, the first This is because it is not possible to expect a prevention effect proportional to the increase in the layer thickness of the molten metal to the core 1, and in the case of a mica layer, there is a risk that cracks may occur due to the metal pressure during casting with a 50 μm end vortex, as with the graphite layer described above. On the other hand, if the thickness exceeds 150 μm, the effect of preventing the molten metal from penetrating in proportion to the increase in the layer thickness of the first core 1 cannot be expected.

For example, in the case of graphite, the solution containing fine particles or flat particles of graphite, mica, etc.
In the case of mica, a mixture of 80 weight % of mica particles and 20 weight % of water glass (thorium silicate) is used.

Note that the drying conditions for forming the second coating layer 5 are, for example, the drying temperature of 150° C. and the drying time of 30 minutes, as in the case of the first coating 1 and 4. The drying temperature and drying time are not limited to this, and any drying temperature and drying time may be used as long as the volatile components in the solutions constituting each of the layers 4 and 5 can be evaporated.

In this way, the first and second coating layers 4 and 5 are formed on the outer surfaces of the two cylinders 1 and the second cores 1 and 2, respectively, and the two cylinders 1 and the second cores 1 and 2 are combined. Two-split type pressure casting shell core 3 for pressure casting
or is formed.

Next, a method for manufacturing the shell core 3 for two-part type loaf horn casting according to the above embodiment and a case where a rotor for a rotary piston engine of an automobile is cast using the molten metal forging method will be specifically explained. .

First, 65% by weight of silica sand with an average particle size of 60 mesh, 35% by weight of N801 with an average particle size of 40 mesh, 2.0% by weight of novolak type phenolic resin, and 0.2% by weight of hexamethylenetetramine were placed in a mold by blow molding. After filling, the first and second cores 1 and 2 are molded by firing at a firing temperature of 250'C.

In order to investigate the molding state of the first and second cores 1 and 2 at this time, we prepared cylindrical shell cores 3 samples with a diameter of 20 m and a length of 50 m that were molded under various conditions.
Each sample was immersed in water for 10 hours and the rate of disintegration at that time was examined. The data at this time is shown in FIG. In the diagram, those marked with a Δ mark indicate that the amount of phenolic resin relative to the core sand base material must be 1°0% by weight, and those marked with an ○ mark indicate that the amount of phenolic resin must be 4°0% by weight. Those marked with . each represent 5.0% by weight. The lower limit of the allowable disintegration rate was set at 50%, at which the remainder could be easily removed by shaking out each sample taken out of the water and applying mechanical vibrations.

According to this data, those that satisfy the above criteria include those with a phenol resin content of 1.0% by weight based on the core sand base material, those with a blending ratio of Na (jl) of silica sand of 25% by weight or more, and those with a core sand content of 25% by weight or more. The amount of phenolic resin relative to the base material is 4.
If the amount of phenolic resin is 0% by weight, it is 30% by weight or more, and if the amount of phenolic resin is 5.0% by weight based on the core sand base material, it is 4% by weight.
It can be seen that 0% by weight or more of each is necessary. In addition, if the blending ratio of NaCβ to silica sand exceeds 40% by weight, the fluidity of silica sand etc. will be inhibited during blow molding due to the deliquescent nature of NaC, and the moldability of the core will deteriorate, so it should not be lower than this. It is appropriate and necessary to set it. therefore,
The mixing ratio of the water-soluble salt particles to the silica sand of the core sand base material is preferably set to 60-75:25-40 in weight percent.

Furthermore, if the amount of phenolic resin to the core sand base material is less than 1% by weight, the strength of the core may decrease and casting may be adversely affected, while if it exceeds 5% by weight, the collapse rate of the core will be 50%. %, it becomes impossible to satisfy the above criteria, so it is preferable to mix the resin in a ratio of 1 to 5% by weight with respect to the core sand base material.

Thereafter, the operation of immersing each of the first and second cores 1 and 2 in the slurry liquid blended as described above is repeated an appropriate number of times, so that the outer surface of each of the first and second cores 1 and 2 is After applying the slurry liquid by dip coating, each of the first and second cores 1.2 coated with the slurry liquid is carried into a drying process and dried under conditions of a drying temperature of 150°C and a drying time of 30 minutes. As a result, a first coating layer 4 having a layer thickness of 200 μm is formed on the outer surface of each of the first and second cores 1 and 2.

Next, the first and second cores 1 and 2 on which the first coating layer 4 has been formed are immersed in a solution containing graphite particles mixed as described above, and the same as in the case of forming the first coating layer 4. By drying under the drying conditions of
50 μm second coating layer 5 on coating layer 4
form.

As shown in FIG. A shell core 3 is formed by combining the first core 1 on top and the second core 2 on the bottom, and this shell core 3 is inserted into an upper mold 8 and a lower mold 9.
The molten SA of the aluminum alloy is placed in a mold 10 of 700 KFI/cM by the operation of the plunger 11.
The rotor 12 of a rotary piston engine as shown in FIG. 4 is cast by the molten metal forging method by injecting hot water into the mold 10 at a pressure of .

After casting the rotor 12 as described above, the rotor 12 is taken out from the mold 10 and immersed in water for 10 hours. At this stage, the shell core 3 in the hollow part of the rotor 12 is dissolved cause it to collapse by more than 50%.

Thereafter, the remaining core 3 is destroyed by applying mechanical vibration by knocking out, shaking out, etc., or it is heated and maintained under conditions of 400 to 500'C x 30 minutes to 1 hour. The phenolic resin is thermally decomposed or disintegrated and removed from the hollow portion of the rotor 12.

In the above embodiment, the second coating @5 is formed of graphite particles, but is not limited thereto, and may be formed of mica particles, for example.

Further, in the above embodiment, a two-piece type shell core 3 is shown in which the shell core 3 is composed of the first core 1 and the second core 2.
It is not necessary to limit it to the split type.

Furthermore, in the above embodiment, the rotor 12 of an automobile rotary piston engine is cast.
Needless to say, the present invention is not limited to this, and can also be applied to the casting of cylinder blocks, cylinder heads, and other cast products other than mountain vehicle parts.

(Effects of the Invention) As explained above, according to the present invention, the core sand base material, which is the main component of the core, is composed of silica sand and water-soluble salt particles, and the silica sand and water-soluble salt particles By appropriately setting the blending ratio of the resin and the blending ratio of the resin as a binder, it is possible to prevent the flowability of silica sand etc. during blow molding etc. and the strength reduction of the shell core after molding. By immersing the shell core in water, the water-soluble salt particles can be dissolved and the gaps between the silica sands can be enlarged;
This makes it possible to improve the disintegrability of the shell core after casting while ensuring good moldability and strength of the shell core by blow molding or the like.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of a pressure casting core according to an embodiment of the present invention, which is a two-split type applied to the casting of a rotor for a rotary piston engine of an automobile, and FIG. Fig. 3 is a longitudinal sectional front view showing the cast state of the rotor, Fig. 4 is a perspective view of the cast rotor, and Fig. 5 is data obtained by testing the collapsibility of the core sample by changing its structural conditions. 1...First core, 2...Second core, 3...Shell core. Figure 3 Figure 1 Figure 4 Figure 5 King Potato F? J'l - Harvesting salt coarse mixer 11 go (vehicle volume °l) Fig. 2

Claims (1)

[Claims] (1) 60-75% by weight of silica sand and 25-40% of water-soluble salt particles
A mold is filled with a core sand base material composed of 1% to 5% by weight, and a resin as a binder whose blending ratio to the core sand base material is set at 1 to 5% by weight. A pressure casting core characterized by: