JP2817206B2 - Self-hardening composite mold - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a mold using self-hardening mold sand.

(Prior art) Conventionally, a self-hardening mold has been frequently used as a casting mold. Regarding a binder for forming a self-hardening mold, regarding an inorganic binder and an organic binder, Various things are used. Regarding the organic binder, those using an organic acid, particularly an acid curing agent such as xylene sulfonic acid, as a furan resin and a curing agent thereof are used from the viewpoint of cost and workability. Self-hardening molds using furan resin have the advantage that mold sand is easy to regenerate and easy to disassemble. Recently, as a self-hardening mold,
A mold using an acetic acid ester curing agent and an alkali water-soluble phenol resin has been proposed.

On the other hand, silica sand is mainly used as mold sand, but special sand such as chromite sand is also used.

(Problems to be Solved by the Invention) However, a self-hardening mold using an acid curing agent such as a furan resin and an organic acid has the following problems.

When the molten metal is poured into a mold, nitrogen gas is generated from the nitrogen-containing furan resin, which causes gas defects in the cast product.

Since acid hardeners such as xylene sulfonic acid contain sulfur atoms, when casting a melt that requires a high temperature such as stainless steel or heat-resistant steel, a sulfurization phenomenon occurs on the casting surface to form metal sulfide at grain boundaries, There was a problem that a grain boundary crack was generated and the product had a crack on its surface.

Further, according to the above-described alkali water-soluble phenol resin molding method, there are the following problems.

During the regeneration of the mold sand, it is difficult to remove the binder coating the surface of the sand grains, and it is difficult to remove the binder by scrubbing the sand grains and obtain reusable sand grains. is there. In addition, it is possible to regenerate the mold sand by polishing the surface of the sand grains with a grindstone, but the yield of the reclaimed sand is poor and the cost is increased. Further, if the sand is made finer, the amount of the binder added must be increased, which increases the cost.

Since the phenol resin is water-soluble, the heat of pouring causes evaporation and condensation of water in the mold sand. For this reason, since the sand of the mold contains a large amount of water, it is difficult to transport the sand.

If the sand used is quartz sand, the required pressure resistance during pouring is 25 kg / cm ²
, The amount of phenolic resin added is required to be 1.2%, which is excessive compared to the required amount of furan resin of 0.4%, and the amount of phenolic resin equivalent to furan resin must be increased. However, there is a problem that the cost is greatly increased.

The present invention solves the above-mentioned problems by providing a two-layered mold using an expensive chromite sand alkaline water-soluble phenol type for skin sand and a silica sand furan type for back sand.

(Means for Solving the Problems) A self-hardening composite mold according to a first invention of the present invention for solving the above-mentioned problems is characterized in that a water-soluble phenol resin is added to chromite sand as skin sands of a main mold and a core, respectively. It is characterized by using a mold sand obtained by adding a hardening agent, and using a mold sand obtained by adding a furan resin and an acid hardener to silica sand as back sand.

The self-hardening composite mold according to the second invention of the present invention comprises a main mold and a core, and uses a mold sand obtained by adding a water-soluble phenol resin and a curing agent to chromite sand as a main mold sand. Mold sand made by adding furan resin and acid hardener to silica sand is used as the backing sand, and one or more of chromite sand, phenol resin mold, shell mold, silica sand zircon shell is used as the core .

The self-hardening composite mold of the third invention of the present invention uses a mold sand obtained by adding a water-soluble phenol resin and a hardening agent to chromite sand as a main mold sand, and furan resin to silica sand as a back mold sand of the main mold. And a mold sand to which an acid curing agent is added.

The reason for using chromite sand as sand for skin sand is
Since the furan resin is acidic and the phenolic resin is alkaline, if the furan resin and the phenolic resin are mixed, an insufficiently hardened portion occurs, and the mold sand cannot be recycled. However, since chromite sand can be used to separate mold sand once used by a magnetic separation device, it is possible to avoid mixing of chromite sand coated with phenolic resin into silica sand using furan resin during reuse. is there.

It is not necessary to completely separate the sand using the water-soluble phenolic resin and the sand using the furan resin, but the sand using the water-soluble phenolic resin is reduced to 20% by weight or less of the sand using the furan resin. If it is mixed, the sand pressure can be reduced to 25 kg / cm ² . Also,
The water-soluble phenol resin is preferably an alkali water-soluble phenol resin containing K or the like.

Further, the chromite sand water-soluble phenol resin template as the core may be a core cured by a curing agent or a core cured by a curing gas such as methyl formate gas. The shell mode as the core is preferably a silica sand shell mode, a mixed shell mold of silica sand and zircon sand, or a mullite sand shell mold.

(Example) As an example of the mold to which the first invention described above is applied, there is a mold including a main mold and a core as shown in FIG.

In FIG. 1, 1 is a metal frame, 2 is a casting cavity, 3 is a feeder, 4 is a feeder heat insulating sleeve, 5 is a sprue, 6 is a sprue sleeve (porcelain pipe), 7 is a weir, 8 is a main mold, 9 is core, 10 is skin sand,
11 shows back sand.

FIG. 2 shows an embodiment of a mold to which the second invention of the present invention is applied. The main form uses skin sand and back sand, and the core is made of skin sand and does not use back sand.

FIG. 3 shows an embodiment of a mold to which the third invention of the present invention is applied. There is no core, and skin sand and back sand are used for the main model.
2 and 3, components that are substantially the same as those in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted.

As the back sand used for the mold shown in FIGS. 1 to 3 described above, sand having a particle size index (AFS GS No.) of quartz sand of 50 or less is used. The smaller this value is, the coarser the grain size of the sand is.
This is because if the particle size of the silica sand is made coarse, the amount of the binder is small, and the amount of the furan resin added is reduced, so that the cost can be reduced. It is desirable that the amount of N in the furan resin added to the back sand be 4.5% or less.

A furan resin is added in an amount of 0.4 to 1.5% by weight to silica sand used for the back sand, and an acid (organic acid such as xylene sulfonic acid or paratoluene sulfonic acid or phosphoric acid) is added to the furan resin in an amount of 20 to 80% by weight. The counter pressure of the mold is preferably 15 kg / cm ² or more.

As for chromite sand used for skin sand, it is desirable to use sand having a particle size index (AFS GSNo) of 35 or more and 75 or less. This is because if the particle size index is less than 35, the sand space of the casting becomes excessively large and penetration (sintering) defects are likely to occur. If it exceeds 75, the specific surface area of the sand increases, so that the amount of the binder added increases and the cost increases.

It is desirable that the pressure against the skin sand be 25 kg / cm ² or more after the sand is put in a metal frame or a core mold and left for 24 hours. 25kg / cm ²
If it is less than 10 mm, the strength will be insufficient, and it will lose the pouring pressure, causing squaring, which will cause a sand jam defect.

An alkali water-soluble phenol resin is added in an amount of 0.7 to 1.7% by weight based on the chromite sand in order to secure the anti-pressure of skin sand. If the alkali water-soluble phenolic resin is less than 0.7% by weight, the mold strength is insufficient and there is a danger of mold breakage. If it exceeds 1.7% by weight, the mold strength becomes excessive and the product is cracked due to mold restraint. Further, an ester (γ-butyrolactone, propiolactone, caprolactone, triacetylene, methyl formate, or the like) is added to the phenol resin as a curing agent in an amount of 20 to 45% by weight to enhance the strength of the template.

A frame such as a metal frame or a wooden frame may or may not be used for the main mold. When the frame is attached, the transportability and the strength are enhanced.

As the gate, runner or weir of the mold, a ceramic tube made of a brick of chamotte, high Al ₂ O ₃ , zircon or the like may be used. For the gate, runner or weir, mold sand obtained by adding an alkali water-soluble phenol resin and a curing agent to chromite sand may be used.

The yield can be improved by using a heat-insulating or heat-generating or heat-dissipating sleeve in the feeder portion.

Alternatively, a mold coated with a coating agent may be used for the purpose of preventing seizure and improving the casting surface. Coated aggregate 75 for 350 mesh pass
% Is used. This reduces the voids in the mold. Coating molds are those using zircon flour as an aggregate and alcohol or water as a solvent, magnesia flour as an aggregate and alcohol as a solvent or
The MgO-Al ₂ O ₃ spinel Flower or mullite flour and aggregate, it is preferable to use a material obtained by using alcohol as a solvent.

In order to prevent the peeling of the skin sand and back sand of the mold described above,
It is also possible to use a mold provided with a connection as shown in FIG. 4 or FIG. In the mold 20 shown in FIG.
An uneven portion 10a is provided between the back sand 10 and the back sand 11 to prevent peeling of skin sand and back sand. In the mold 30 shown in FIG. 5, a drum-shaped sheet metal structure 32 made of, for example, mild steel, curved iron wires 34, 35, or an uneven pipe 36 may be used as a connection between the skin sand 10 and the back sand 11.

In the part of the back sand, it is also possible to remove the sand at a part where there is no problem in strength, it is possible to throw in franc block sand, or you may throw in a sheet metal sand stealing jig, Empty cans or the like may also be charged. As a result, the cost of the back sand portion can be reduced.

The thickness of the chromite sand on the sand skin should be at least 30 mm. This is to completely prevent the adverse effect of the pyrolytic gas of the silica sand to which the furan resin used for the back sand is added.
When the product thickness of the casting is thin and the shape is simple, a high quality casting can be obtained without coating.

Materials that can be cast into this mold are cast irons such as ordinary cast iron, ductile cast iron, high Cr cast iron, ordinary steel, low alloy steel, stainless steel, heat-resistant steel, high Mn steel, tool steel, wear-resistant steel, etc.
An Al alloy, a Cu alloy, a Co-based alloy, a Ni-based alloy, or the like can be used. Of these, the use of Ni-containing steel such as stainless steel, heat-resistant steel, Ni-based alloy and ductile cast iron is particularly effective because the sulfurization phenomenon is prevented.

The casting temperature is preferably raised by 30 to 50 ° C. from the ordinary casting temperature. This is because the use of chromite sand, which has a higher cooling rate than silica sand, as skin sand, prevents the occurrence of hot water defect.

(Effects of the Invention) As described above, according to the self-hardening composite mold of the present invention, N in the furan resin is prevented from acting on the surface of the casting, thereby preventing gas defects and curing. The generation of crack defects in the cast product due to S in the agent is reliably prevented.

In addition, when reclaiming mold sand, chromite sand using phenolic resin can be easily separated by a magnetic separator, so chromite sand coated with alkaline phenolic resin is excessively mixed with silica sand using acidic furan resin. And the quality of the regenerated silica sand can be ensured.

Furthermore, since phenol resin is adopted only for skin sand,
Almost all of the moisture in the binder evaporates, facilitating the transport of the sand by adhesion of moisture, and the sand can be easily collected.

[Brief description of the drawings]

FIG. 1 is a sectional view of a mold comprising a main mold and a core to which the present invention is applied, FIG. 2 is a sectional view showing a mold comprising a main mold and a core of another embodiment of the present invention, and FIG. FIG. 4 is a sectional view of a mold having a main mold, FIG. 4 is a sectional view showing a mold having a joint between skin sand and back sand, and FIG. 5 is another mold having a joint between skin sand and back sand. FIG. 8 ... main type, 9 ... core, 10 ... skin sand, 11 ... back sand.

Claims (3)

(57) [Claims] 1. A mold sand obtained by adding a water-soluble phenol resin and a hardening agent to chromite sand as skin sand for each of a main mold and a core, and a furan resin and an acid hardening agent are added to silica sand as back sand. A self-hardening composite mold characterized by using a mold sand consisting of: 2. A mold sand composed of a main mold and a core, which is obtained by adding a water-soluble phenol resin and a hardening agent to chromite sand as main mold skin sand, and furan resin and silica sand are used as back sand of the main mold. A self-hardening composite mold using a mold sand to which an acid hardener is added, and using at least one of (a) a chromite sand, a phenol resin mold, and (b) a shell mold as a core. 3. A main mold sand made by adding a water-soluble phenol resin and a hardening agent to chromite sand as a main form sand, and a furan resin and an acid hardener added to silica sand as a main back sand. Self-hardening composite mold characterized by using mold sand.