JPH0323253B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a suction mold, and particularly to a method for manufacturing a durable suction mold that has good air permeability throughout the mold and is highly effective in removing air and gas from the cavity.

Molten metals such as Al alloys, Zn alloys, Mg alloys, and Cu alloys, plastics, rubber, glass, or molten or softened plastic materials such as mortar and wax are poured by gravity into a mold with a cavity and then pressurized. Methods of forming (including casting, the same shall apply hereinafter) by methods involving inflow or plastic flow have been widely used in the past.

Generally, it is desirable that the mold used in this molding method satisfy the following requirements, but hitherto there has been no practical mold that can satisfy these various requirements.

It has sufficient strength characteristics to withstand the desired molding, can be used many times instead of requiring molding each time as is typical with sand molds, and has good transferability, making it possible to mold complex shapes and It is possible to handle thin-walled shapes, the mold can be easily enlarged and large molded products can be obtained, the mold does not produce pinholes or cavities on the surface or inside the molded product, and the mold is easy to manufacture and can be obtained at low cost. For example, a die-casting mold is used as a casting mold for forming (casting) molten metal such as Al alloy, and although this mold can satisfy the following conditions,
cannot meet the conditions. In particular, in die casting, molten metal is forced into a mold at high pressure and high speed, and the mold has no air permeability, resulting in porosity.
This tends to cause problems when performing airtightness, heat treatment, surface treatment, etc. Fixed molds and movable molds are also used to produce three-dimensional products such as rubber, and liquid or softened materials are charged into the mold and pressurized at a predetermined pressure to form them. However, it is difficult to meet the conditions because the air inside the cavity and the air trapped in the material cannot be removed, resulting in problems such as a decrease in the yield of good products and the need for complicated deburring work. Because the mold is made of metal, the following conditions cannot be met.

The present invention solves the above-mentioned problems of conventional molds, has sufficient strength and can be used many times, has good transferability and reproducibility, and is easily applicable to complex shapes, thin-walled shapes, and large shapes. In addition, the entire mold is breathable, and by applying suction force from desired locations, air and gas within the cavity and molding material can be effectively removed, and manufacturing is simple and inexpensive. The present invention aims to provide a method for manufacturing this type of durable mold.

To achieve this objective, the present invention has a particle size of 500 μm.
The aggregate is iron-based powder with a particle size of 300 μm or less and ceramic powder with a particle size of 300 μm or less, and a caking agent containing components that evaporate during the hardening process is mixed in a weight ratio of (1 to 5): (1 to 5).
5): 1 is mixed to make a slurry mixture, this slurry mixture is poured and solidified to form a mold surface, and after air drying and/or primary firing, the firing temperature is 600 ~ 600 in an oxidizing atmosphere. This method involves firing at 1000°C for 1 to 50 hours.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

1 to 3 illustrate a suction molding mold, which is made up of a composite fired body 1 made of iron-based powder and ceramic powder (refractory powder) as aggregates. This composite fired body 1 has a dense hardened layer 2 on the outer periphery including an arbitrary mold surface 11 such as a concave or convex shape, and has a backing layer 3 made of an unfired mixed structure inside this hardened layer 2. ing.

Figure 2 shows an example of a separate mold, where the mold surface 1
A runner 12 leading to the backing layer 1 is made of a hardened layer, and a pin hole 13 is formed through the hardened layer 2 and the backing layer 3. Further, if necessary, conduits and heaters 14 for mold cooling and heat retention are buried.

FIG. 3 shows another example of the present invention, which consists of a composite fired body 1 made of iron-based powder, ceramic powder (refractory powder), and steel fibers 4 as aggregates. Similar to the previous embodiment, this composite fired body 1' has a dense hardened layer 2 on the outer periphery and a backing layer 3 made of an unfired mixture inside the hardened layer 2. Steel fibers 4 are almost uniformly dispersed within each layer and at the boundaries between both layers, and these dispersed steel fibers 4 strengthen the unfired mixed structure constituting the backing layer 3 and also strengthen the hardened layer 2. By being passed between the backing layers 3, the adhesion between both layers is strengthened.

The hardened layer 2 is made of modified iron particles (a-Fe ₂ O ₃ ) 2 of iron-based powder dispersed in ceramic powder as shown in FIG. 4a.
0 and fired ceramic grains 21. The formation mechanism of this hardened layer 2 is not necessarily clear, but in general, the iron-based powder greatly increases in volume due to oxidation, and is sintered in a manner that envelops the ceramic particles, while the firing of the ceramic particles also progresses. This is thought to be the result of diffusion bonding at the interface. This hardened layer 2 has fine pores 22 (approximately 5 to 10 μm) due to evaporation of evaporation components contained in the binder during the drying process, primary firing process, and secondary firing process. These fine pores 22 form a porous yet dense and smooth surface.

On the other hand, the bucking layer 3 inside the hardened layer 2 is made of a mixed structure of unfired iron-based powder particles 20' and ceramic powder particles 21', as shown in FIG. 4b. Coarse pores 22' are formed at the interface of the grains 20' due to the previous evaporation of the caking agent. These pores 22' are the pores 2 of the hardened layer 2.
2, therefore, the composite fired body 1 has a porous ventilation structure as a whole. The pores 22, 2
2' is characterized by no cracks. The porosity depends on the composition and firing conditions described below, but it is generally between 1 and 2'.
The compressive strength is approximately 200 to 900.
Kg/cm ² characteristics.

Therefore, in order to obtain a suction molding mold as shown in FIGS. 1 to 4, the present invention mixes and kneads aggregate and caking material to form a slurry sample 5, and pours this slurry sample 5. The process of molding;
This method employs a process of drying or primary firing the mixed molded body, and a process of firing the product that has gone through this process under oxidizing atmosphere conditions.

First, the step of obtaining slurry sample 5 is to thoroughly mix and stir iron-based powder and ceramic powder or steel fibers, add a caking agent containing components that evaporate during the curing process, and thoroughly mix and stir. It consists of things.

Specifically, as the "iron-based powder", iron powder such as cast iron powder, electrolytic powder, pure iron powder, steel powder, etc. are used. Among these, cast iron powder has the advantage of promoting pore formation by burning free carbon during firing.

Ceramic powders include those that have a low deformation rate at high temperatures and are easy to bond with iron-based powders, such as neutral types such as mullite, calcined alumina, activated alumina, fused alumina, chromite, and sillimanite; Acidic materials such as fused silica, zirconium, and fused zircon are generally suitable, but basic materials such as magnesia and talc may also be used.

Furthermore, as the "steel fiber", stainless steel fibers are generally suitable. This is because stainless steel fibers do not disappear during the firing process, so they have a high reinforcing effect on both the hardened layer and the backing layer. Even if other steel fibers such as free-cutting steel are used, the reinforcing effect of the backing layer can be obtained, and the advantages of preventing cracks and preventing ceramic powder from falling off can also be obtained. Suitable steel fibers are ones that have high strength and a large surface area, such as those produced by a chatter vibration cutting method.

Next is "caking material containing components that evaporate during the curing process."
is used in the present invention to bond iron-based particles and ceramic particles and to create fine pores in the composite fired body. Specific examples include colloidal silica and ethyl silicate. The former is a stabilized silica colloidal liquid, in which water is the evaporated component. Also,
The latter is a mixture of a low condensate of orthoethyl silicate (approximately 40-42% effective silica), an alcoholic solvent (e.g., ethanol, isoprepanol), water, and an acid catalyst to accelerate the reaction and stabilize the sol. (for example, hydrochloric acid), mixed and hydrolyzed, and the evaporated component in this case is mainly alcohol.

The mixing ratio of the iron-based powder, ceramic powder, and binder;
The weight ratio is preferably (1-5):(1-5):1, and this blending ratio improves strength, air permeability, thermal conductivity,
Various properties such as surface texture can be obtained in a well-balanced manner. Here, the lower limit of the blending ratio was defined as
This is because it is necessary to obtain the minimum strength that can be used as a mold, and the reason why the upper limit was specified is that too much aggregate will reduce the covering ability of the caking material from the aspect of moldability, resulting in a decrease in strength. This is because it causes deterioration of the stability of the mold surface. The upper limit for iron-based powder was stipulated by
Even if the blend of ceramic powder and binder is appropriate, if iron-based powder is used in excess, sufficient strength will not be obtained, and the surface quality will deteriorate due to excessive porosity, which will impair transferability. It is. The reason why the upper limit of ceramic powder is limited is that the strength will be impaired if excessively blended. Caking agents are necessary for bonding aggregates together and are necessary to provide air permeability.

When steel fiber is used in combination, the amount added is approximately 1 to 1.
It should be 10vol%. If it is less than 1%, effects such as improved strength and dimensional stability cannot be expected. but
Addition of more than 10% tends to cause fiber balls and reduces moldability. In addition, excessive precipitation on the surface of the hardened layer results in poor skin quality and is also disadvantageous in terms of cost.

The particle size of the iron-based powder is preferably 500 μm or less, and the particle size of the ceramic powder is preferably 300 μm or less. If the maximum dimension exceeds 500 μm for iron-based powders and 300 μm for ceramic powders, the strength, that is, the bucking effect, will decrease and the mold surface will become excessively porous, resulting in a rough surface. Impairs transferability. Therefore, it has sufficient strength and durability and good transferability, and can be used for molding complex shapes, thin-walled shapes, and large shapes.Moreover, it has good air permeability throughout the mold, so it can be easily used inside the cavity or during molding. This makes it impossible to achieve the purpose of producing a mold that allows gas and air in the material to be easily removed by suction. Therefore, the upper limit of particle size was specified. Under the conditions of this maximum particle size, the particle size may be selected so that strength, transferability, and porosity can be obtained according to the purpose and application of the mold. From the viewpoint of mold surface roughness, which affects transferability, the finer the particle size, the better; however, if it is extremely fine, cracks are likely to occur during the drying and firing processes. Therefore, the minimum grain size may be appropriately selected to avoid the occurrence of cracks during actual mold manufacturing. The steel fibers may be appropriately selected, for example, from a length of 1 to 30 mm and a thickness of 20 to 400 μm depending on the size of the mold.

Next, the slurry sample 5 is solidified and molded into a desired shape. This is done, for example, by pouring the previous slurry sample 5 into a mold 6 in which a model or actual object 4 is set as shown in Fig. 5, and leaving it for the required time. It is also effective to apply vibration or squeeze to promote filling properties. Second
When using a suction mold as shown in the figure, this can be easily carried out by inserting pins and pipes into the mold during the casting process.

Next, in the present invention, after the molded body 1' obtained in the previous step is removed from the mold 6, it is air-dried and/or subjected to primary firing. This is to prevent cracking and distortion, as well as to make the binder more porous by evaporating the alcohol contained in it. Select appropriately from. The latter primary firing may be performed by directly igniting the molded body 1' with a torch lamp or the like.

The molded product after this natural drying and/or primary firing process has air permeability throughout and can be used as it is for pressureless casting. However, since the mechanical strength is low and the durability does not deteriorate, the present invention subjects the molded body 1' that has been dried and/or primary fired to secondary firing in an oxidizing atmosphere. The oxidizing atmosphere may be air or may be so-called oxygen-enriched air in consideration of oxygen supply. Firing conditions depend on the blending ratio, mold dimensions, and desired porosity, but generally the firing temperature is 600 to 1000℃,
The baking time should be at least 1 hour.

The lower limit of firing temperature is 600℃, the lower limit of firing time is 1
The reason why the time is set is because the firing is insufficient and a dense hardened layer, which is a feature of the present invention, is not formed, and the strength necessary for a durable type cannot be obtained. The reason why the upper limit of the firing temperature was set at 1000°C is that although a hardened layer is formed, the surface becomes rough and transferability is impaired. The longer the firing time, the higher the strength.
The hardened layer does not grow beyond its limit, and instead causes surface roughness and reduced productivity. Although it depends on the mold dimensions, etc., the maximum time should be 50 hours.

In this secondary firing step in an oxidizing atmosphere, firing of the ceramic powder and oxidation sintering of the iron-based powder dispersed in the molded body proceed, and as shown in Figure 6, a dense hardened layer is formed from the surface to the inside. 2 is gradually produced, and at the same time, the volatile components of the caking agent remaining in the molded body are burned and removed, so that the formation of porosity is promoted.
Upon completion of the secondary firing, a durable suction mold made of the composite fired body 1 as shown in FIGS. 1 to 3 is obtained. .

In addition, in the present invention, in order to adjust the air permeability (porosity), the type, particle size, blending ratio of iron powder and ceramic powder, vibration and squeezing conditions during pour molding, firing conditions, etc. are adjusted by adjusting the required strength, etc. It may be set arbitrarily while taking into consideration.

Figure 16 shows the relationship between the mixing ratio of iron-based powder (for example, cast iron powder) and ceramic powder (iron-based powder/ceramic powder) and porosity. To increase the porosity, increase the mixing ratio of iron-based powder. I know it's good. 17th
The figure shows the relationship between the blending ratio of binder and aggregate (iron powder + ceramic powder) and porosity, and it can be seen that the lower the aggregate blending ratio, the higher the porosity tends to be.

Next, we will explain how the suction molding mold is used and how it works.

Figures 7 to 9 show examples of how the suction molding mold manufactured according to the present invention is used.
Applied when forming liquid or slurry material W such as refractories by non-pressure suction method, No. 8
The figure is applied to molding a liquid or slurry material W, typically molten metal, using a low-pressure suction method. Figure 9 shows rubber, glass, plastic,
An example in which this method is applied to pressurized suction molding of liquid or soft material W' such as metal with plastic flow will be shown.

Molding by the non-pressure suction method shown in FIG. 7, for example, is divided into a fixed mold 1a and a movable mold 1b,
1 and 11 are coated with a mold coating agent and a mold release agent, and incorporated into a molding device to perform pouring and mold release.For this molding, suction parts are placed in advance at desired locations on the fixed mold 1a and the movable mold 1b. 8, 8 are provided, and the suction parts 8, 8 are connected to a pressure reducing device 9 such as a vacuum pump via a hose or the like, and a suction force is applied from the time of injection of the material W to the time of molding.

In the case of molding by the low pressure suction method, a fixed mold 1a and a movable mold 1b made of the composite fired body 1 are used instead of the molds in a known vacuum casting apparatus as illustrated in FIG. and suction parts 8, 8 are provided at desired locations on the movable mold 1b, and the suction parts 8,
8 to the pressure reducing device 9 as in the case of FIG. 7,
The piston rod 16 of the mold opening/closing cylinder 15 may be connected to the movable mold 1b. For molding, the material W is charged into the crucible 17, a molten metal is made in the holding furnace 18, and the material W is inserted into hot water by pressurizing gas through the air introduction hole 25 provided in the airtight lid 19 above the crucible. The fixed mold 1a and the movable mold 1b are connected through the conduit 26
The hot water is pushed up into the cavity 10 of the hot water tank, and at the same time, a suction force is applied through the suction parts 8, 8 by the pressure reducing device 9.

Furthermore, when forming with plastic flow,
As shown in Fig. 9, suction molding molds 1a and 1b of the composite fired body produced according to the present invention are used instead of the conventional male mold, and a fixed mold 1a corresponding to the female mold is fixed to the pressbed side. However, the movable mold 1b corresponding to the male mold is attached to the press slide side, and the suction parts 8, 8 are provided at desired parts of both molds 1a, 1b and connected to a pressure reducing device. For molding, fill the mold surface of the fixed mold 1a with material W',
Next, the movable die 1b is operated to apply the necessary pressure to the material W' while sucking air through the suction parts 8, 8.

In each of the above-mentioned moldings, according to the present invention, the mold is composed of a composite fired body 1 made of iron-based powder and ceramic powder as aggregates, and this composite fired body 1 is made of a hardened layer 2 made of oxidized iron-based powder. Because it forms the outer periphery, the mold has a strength of 200 kg/cm ² or more, which is necessary for a durable mold, and there is no cracking, chipping, or crumbling even after repeated rapid heating and cooling. In this case, important corner chipping does not occur. In particular, when steel fibers are used as an aggregate, characteristics such as high bending strength and little dimensional change can be obtained.
Moreover, in addition to having the strength as a durable type, the outer hardened layer 2 and the inner backing layer 3 that make up the composite fired body 1 are porous, consisting of fine pores 22, 22'. It consists of
The entire mold has good ventilation. Furthermore, although the cured layer 2 that constitutes the mold surface has suction holes, it is dense and has small surface roughness, and since it is made by pour molding, it has good transferability and mold reproducibility. ing.

Therefore, as shown in FIGS. 7 to 9, by applying suction from a desired location during the molding process, the entire cavity or mold surface can be made to have a uniform negative pressure. It is possible to fill the material evenly and provide good transferability, and at the same time, it is possible to quickly and reliably eliminate air in the cavity, air caught in when filling the material, or gas released from the material. Moreover, the mold manufactured according to the present invention has a lower thermal conductivity than a metal mold, and has a low velocity of molten metal.
Even with low-pressure inflow, hot water flows well. For these reasons, molded products with complex shapes and thin shapes without pinholes or cavities on the surface or inside can be molded very easily.

In addition, the suction parts 8, 8 in the above example may be obtained by inserting an intake pipe into a mold during casting molding, or may be provided after secondary firing. For the outer surface other than the suction part, methods such as applying a sealing material as appropriate, attaching it to an airtight casing, or joining a planar body may be used. Of course, the entire mold can also be used as a suction part. In the above example, both of the split molds are composed of composite fired bodies, and each mold is inhaled, but in some cases, only one of the divided molds may be made of a composite fired body, or only one of them may be inhaled. .

Next, specific examples of the present invention will be shown.

Example: Cast iron powder (particle size under 100 μm) was used as the iron-based powder, synthetic mullite powder (particle size under 100 μm) was used as the ceramic powder, and ethyl silicate was used as the binder, with a weight mixing ratio of 3:3:1. A slurry-like material A was obtained by uniformly mixing and stirring the mixture.

In addition, stainless steel fiber (length 7
mm, thickness 0.19 mm) was added and mixed at 1 to 4 vol%,
A slurry sample B was obtained.

Next, slurry samples A and B were respectively poured into molds containing models (sewing machine parts, automobile parts), and the solidified molded bodies were removed from the molds, ignited, and subjected to primary firing for 0.5 hours, and then loaded into a firing furnace. Then, secondary firing was performed at a firing temperature of 900℃ under air conditions.
Suction molding molds A′ and B′ were obtained.

For each suction molding mold A' and B', the relationship between firing time and compressive strength is shown in Figure 10, and the relationship between firing time and weight increase is shown in Figure 11.
As shown in the figure. Compressive strength and weight increase with increasing firing time. This is due to the formation of a hardened layer due to oxidation of the iron-based powder.

The results of a bending strength test and measurements of dimensional changes for the suction mold B' are shown in FIGS. 12 and 13. From FIG. 12 and FIG. 13, it can be seen that when steel fibers are added, the bending strength is significantly improved and changes in mold dimensions are suppressed, and therefore it is suitable for use as a large mold. Recognize.

In order to examine the effects of rapid heating and cooling on suction molding molds A' and B', repeated heating and cooling tests were conducted using a cycle of heating at 800°C for 5 minutes and cooling at room temperature for 5 minutes. As a result, no cracks or chips were observed even after 100 cycles.

FIG. 14 shows the results of examining the relationship between firing time, hardened layer thickness, and porosity under conditions of constant firing temperature for suction molding molds A' and B'. In the case of the present invention, the entire mold has at least 5
% or more.

Using a suction molding mold A′ with a porosity of 20%, coat the mold surface with graphite alcohol solution, attach a suction pipe to the side of the mold, select the other surface, and assemble it into the casting machine to form the aluminum alloy ADC. -700 mmHg through the suction tube while performing gravity casting of -12
suction was performed. The casting conditions are the casting temperature
700℃, casting time 3-5 seconds, mold release time 15-50
I was there in seconds.

As a result, not only was it possible to perform good casting with good melt flow and no sinkage, but the transferability (casting surface) of the casting was significantly better than with simple gravity casting, and casting accuracy was improved. At the same time, a good casting with low density and no cavities was obtained not only on the surface but also inside. At the same time, we performed casting with a wall thickness of 1.5 mm.
The hot water spread to every corner, and a good thin-walled cast product with no defects was obtained. As for durability, no damage to the mold was observed even after 70 castings, and a considerable number of castings were still possible.

Using a suction mold B′ with a porosity of 25%, an Al alloy was cast by a low-pressure casting method, and at this time a suction force of 700 mmHg was applied through suction pipes attached to the sides of the movable mold and the fixed mold. As a result, in addition to the characteristics of low-pressure casting, casting accuracy has been improved to the same level as die casting.

In addition, using other suction molding molds A' and B',
When used as a mold for pressure molding of rubber products, glass products, and plastic products, including shoe sole materials, good durability was obtained, and
Uniform suction force acts on the cavity, resulting in very good transferability and adhesion to the mold, and since air and gas inside the cavity are effectively removed, good quality products without air bubbles can be obtained. I understand. At the same time, material efficiency has been improved because burrs do not need to be generated as in the conventional method. 15th
The figure shows the surface roughness measurement results of the master model, suction molding mold, and molded product. It can be seen from FIG. 15 that the present invention provides excellent transferability.

According to the first aspect of the present invention explained above, it has strength and durability for mass production, and
It has good transferability, has air permeability throughout the mold, can provide an extremely simple and effective deaeration effect to the entire cavity, is easy to upsize, and has a simple and short process. It is possible to provide a method for manufacturing a suction molding mold that can be manufactured in short manufacturing time and at low cost.

The suction molding mold produced according to the present invention is suitable for gravity suction casting and low pressure suction casting of aluminum alloys, Zn alloys, Mg alloys, Cu alloys, ordinary cast iron, ductile cast iron, etc., as well as wax, rubber, glass, etc. It can be used for any type of molding that requires degassing, such as pressurized suction molding that involves plastic flow, such as plastics and metals. It can also be used as a mold with high degassing and dehydration properties in the molding of ceramics, mortar, refractories, etc. In each of these molds, it is possible to inexpensively mass-produce molded products with complex shapes, thin walls, and tightness and precision. can. .

[Brief explanation of the drawing]

Figures 1 to 3 are cross-sectional views showing examples of durable molds, Figures 4 a and b are cross-sectional views schematically showing the structure of durable suction molds, and Figures 5 and 6 are suction molds. 7 to 9 are cross-sectional views showing examples of the use of the suction molding mold. FIG. 10 is a graph showing the relationship between the strength and firing time of the suction molding mold according to the present invention. The figure is a graph showing the relationship between firing time and weight increase, Figure 12 is a graph showing the relationship between fiber inclusion rate and bending strength, Figure 13 is a graph showing the relationship between fiber inclusion rate and dimensional change, and Figure 14 is a graph showing the relationship between fiber inclusion rate and dimensional change. Graph showing the relationship between time, porosity, and hardened layer, 1st
Figure 5 is a graph showing the transferability of the suction mold, No. 16
The figure is a graph showing the relationship between the blending ratio of aggregate and porosity, and FIG. 17 is a graph showing the relationship between the blending ratio of caking material and aggregate and porosity. 1... Composite fired body, 2... Hardened layer, 3... Unfired backing layer.

Claims (1)

[Claims] 1 Iron-based powder with a particle size of 500 μm or less and ceramic powder with a particle size of 300 μm or less are used as aggregates, and a caking agent containing components that evaporate during the hardening process is mixed in a weight ratio of (1 to 30 μm).
5): (1 to 5): 1 is mixed to make a slurry mixture, this slurry mixture is poured and solidified to form a mold surface, and after air drying and/or primary firing, it is placed in an oxidizing atmosphere. Firing temperature in 600
A method for producing a durable suction mold, characterized by firing at ~1000°C for 1 to 50 hours.