JPH0153140B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing composite durable molds.

BACKGROUND ART Metal molds are generally used as molds for obtaining aluminum alloy castings, especially as molds that can withstand multiple uses. Molds require a lot of effort and time to manufacture and are extremely expensive, but they are also highly used as molds for mass production because of their good durability. However, in high-mix low-volume production or prototyping, even if it is not as durable as a mold,
Durable molds that are inexpensive and easy to manufacture are desired. Many ceramic durable molds have been proposed as durable molds for such purposes, but due to reasons such as insufficient mold strength, poor casting surface, and not necessarily easy manufacturing methods, The reality is that it has hardly been put into practical use.

The present invention was created after repeated research in view of the above-mentioned circumstances, and its purpose is to easily cast products with complex shapes that have sufficient strength and durability, as well as good mold surfaces and casting surfaces. To provide a method by which a durable composite mold can be produced relatively efficiently and inexpensively through simple steps.

Another object of the present invention is to provide a method for manufacturing this type of composite durable mold which has even better strength properties such as bending strength in addition to the above properties and has less dimensional change.

In addition, in obtaining a durable mold, the present invention uses iron-based powder with a particle size of 500 μm or less, refractory powder with a particle size of 300 μm or less, and a caking agent in a weight ratio of (1 to 5): (1 to 5).
5): Add steel fiber to 1 or further add steel fiber to 1 to 1.
Add 10% by volume to make a slurry-like mixture, mold this by pouring as appropriate, and dry this molded product naturally and/or after primary firing, in an oxidizing atmosphere.
This method involves firing at 600 to 1000°C.

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

1 to 3 show an example of a composite durable type manufactured according to the present invention, which is composed of a composite fired body 1 made of iron-based powder and refractory powder as aggregates. In this composite fired body 1, a dense hardened layer 2 is formed on the outer periphery, a backing layer 3 made of an unfired mixture is formed inside this hardened layer 2, and a mold surface 5 and a runner 6 are formed. and the sprue 7 are each composed of the hardened layer 2, and the hardened layer 2 and the backing layer 3.
A pin hole 8 is formed through it. This hardened layer 2
Alternatively, the backing layer 3 may include mold cooling,
A conduit or a heater 4 for heat retention may be embedded.

As shown in FIG. 3a, the hardened layer 2 is composed of iron oxide particles (α-
It consists of a bonding structure of Fe ₂ O ₃ ) 20 and fired refractory particles 21. The formation mechanism of the hardened layer 2 is not necessarily clear, but since no special composite product is observed other than the change of Fe to α-Fe ₂ O ₃ ,
Iron-based powder changes to iron oxide and the volume increases greatly,
This is thought to be the result of sintering of the refractory particles while enclosing the refractory particles, and diffusion bonding at the interface with the refractory particles.

On the other hand, the backing layer 3 inside the hardened layer 2 is
As shown in Figure 3b, unfired iron powder particles 2
It consists of a mixed structure of 0' and refractory particles 21'.

FIG. 4 shows another embodiment of a composite durable mold manufactured according to the present invention, which is composed of a composite fired body 1c made of iron-based powder, refractory particles, and steel fibers 9 as an aggregate. This composite fired body 1c is composed of a dense hardened layer 2 on the outer periphery and a backing layer 3 made of an unfired part inside the hardened layer 2, as in the above embodiment.
Steel fibers 9 are dispersed between the hardened layer 2 and the backing layer 3, and the dispersed steel fibers 9 strengthen the mixed structure that constitutes the backing layer 3, and also bridge the hardened layer 2 and the backing layer 3. It has increased their adhesion.

Next, a method of manufacturing a composite durable mold according to the present invention will be explained as shown in FIGS. 5 to 7.

That is, in order to obtain the desired composite durable mold, first, iron-based powder and refractory powder are mixed, and when steel fiber is used, this is mixed with the aggregate,
A caking agent is added to this, and the mixture is thoroughly mixed and stirred to obtain a slurry-like mixed material 10. As the caking agent, a known material such as pentonite can be used, or a material having a component that evaporates during the curing process, such as silica sol, can also be used.

As the "iron-based powder", iron powder such as cast iron powder, pure iron powder, electrolytic powder, or steel powder can be used.

In addition, as a "refractory powder", it has a high degree of fire resistance,
Materials with low deformation rate at high temperatures and easy to bond with iron-based powders, such as mullite, zirconium,
Any of the following materials may be used: fused silica, fused zircon, sillimanite, kyanite, chromite, high alumina syamoto, diatomaceous earth, perlite, talc magnesia, and the like. When the binder is something like silica sol, it is stable at pH 2 to 3, so neutral or acidic refractory powder is appropriate.

Although free-cutting steel can be used as the "steel fiber," stainless steel is preferably used. Since stainless steel fibers do not disappear due to oxidation during firing, they have a high reinforcing effect on both the hardened layer and the backing layer. Of course, the reinforcing effect of the buckling layer can also be obtained by using free-cutting steel, etc.
It has the advantage of preventing electric cracking and preventing refractory powder from falling off. Preferably, the steel fiber itself is high in strength and has a large surface area, such as one produced by chatter vibration cutting.

The appropriate mixing ratio of the iron-based powder, refractory powder, and binder is generally about (1-5):(1-5):1 by weight. This blending ratio makes it possible to achieve a good balance of properties such as strength, thermal conductivity, and skin texture. The lower limit of the mixing ratio was set at 1:1:1 in order to obtain the minimum strength that can be used as a mold, and the upper limit was set because of the moldability of the mold, if too much aggregate is used. This is because the covering ability of the caking material is reduced, resulting in a reduction in strength and deterioration in stability of the mold surface. The reason for setting the upper limit for iron-based powder is that if too much iron-based powder is added, the mold will not have sufficient strength, and the surface quality of the mold surface will deteriorate, impairing transferability. The reason why the upper limit for the amount of refractory powder was specified was that the strength would be impaired.

When steel fibers are used in combination, the appropriate amount is 1 to 10% by volume. If it is less than 1%, no effect on strength improvement or dimensional stability can be expected. In addition, the upper limit is 10%
This is because fiber balls are likely to occur, making it difficult to obtain a good slurry material, and excessive precipitation on the surface of the hardened layer will worsen the texture, and it is also disadvantageous in terms of cost. be.

In addition, the particle size of iron-based powder is generally 50~50 in the maximum dimension.
The particle size of the refractory powder is preferably in the range of 50 to 300 μm in the maximum dimension. The reason is,
A small particle size is desirable from the standpoint of preventing surface roughness on the mold surface and improving transferability, but on the other hand, this makes it easier for cracks to form.The upper limit was set from the standpoint of strength and mold surface properties. When using steel fibers, the length may be 1 to 30 mm and the thickness may be 20 to 400 μm depending on the dimensions of the mold to be manufactured.
It is sufficient to use one with specifications such as .

Next, in the present invention, the slurry-like mixed material 10 obtained as described above is molded into a desired shape. This is done by pouring the mixed material 10 into a mold 11 in which a model or actual object 12 is set, as shown in FIG.
This is done by leaving it for a predetermined period of time. At this time, it is also effective to add a curing agent to promote solidification, to apply vibration to promote filling properties, or to squeeze.

By inserting pins and pipes into the mold during this molding, pin holes 8 and embedding mechanisms 4 for cooling and heat retention are obtained.

The molded body 13 thus obtained is placed in the formwork 11.
After demolding, air drying is performed for 1 to 48 hours to prevent cracks and distortion. If necessary, such as when the binder contains an evaporative component, primary firing may be performed by directly igniting the molded body 13 in place of or in addition to natural drying.

Next, the molded body 13 that has completed this step is fired in an oxidizing atmosphere. The oxidizing atmosphere may be air or may be so-called oxygen-enriched air supplied with oxygen. Firing conditions depend on the blending ratio, particle size, mold dimensions, etc., but generally the firing temperature is around 600-1000℃,
It is best to use a firing time of 1 to 50 hours. The reason why the lower limit of the firing temperature was set to 600° C. and the lower limit of the firing time was set to 1 hour is that the firing would be insufficient and the hardened layer, which is a feature of the present invention, would not be generated. The upper limit of the firing temperature was set at 1000°C because although a hardened layer is formed, the surface becomes rough and damages the casting surface. In addition, the upper limit of the firing time was set at 50 hours because although the longer the firing time, the stronger the strength, the hardened layer will not grow beyond the limit and will instead cause surface roughness, which is disadvantageous and will also reduce productivity. It is. Through this firing step, the hardened layer 2 is gradually formed by firing the refractory powder and progressing the oxidation of the iron-based powder.

Through the above steps, a composite durable mold as shown in FIGS. 1 to 4 is completed. So all that is left is mold surface 5.
All you have to do is apply a mold to the mold, attach it to a casting machine, pour the molten metal, and release the mold. In this casting, since the mold is made by pour molding, the transferability to the model is extremely good, and since the mold surface becomes a dense hardened layer 2 by firing, the casting surface is also good.
Furthermore, since the hardened layer 2 made of oxidized iron-based powder forms the outer periphery of the mold, the mold strength is high and the thermal conductivity is also good, preventing cracks and chips from being caused by rapid heating or cooling.
There is no occurrence of crumbling, and no chipping of important corner parts of the mold occurs. When steel fibers are also used as aggregate, the strength becomes higher and dimensional changes are reduced. Furthermore, the composite durable mold manufactured according to the present invention has a lower thermal conductivity than a metal mold, and the molten metal flows well even when the molten metal flows in at a low speed. Therefore, even with low pressure and low speed casting, complex shapes or thin wall shapes can be cast.

Although any casting apparatus may be used to incorporate the composite durable mold manufactured according to the present invention, the apparatus used in the casting experiment described later is shown in FIG. 8. That is, this casting device has front and rear fixed tables 1 on the underframe 15.
6a and 16b are provided, and a composite durable mold 1a, which is a composite fired body, is mounted on one fixed base 16a via a frame 17.
Install. Guide rods 18, 18 are fixed to both sides of the underframe 15, and two mounting plates 19a, 19b are inserted through these guide rods 18, 18 with their ends, and both mounting plates 19
A and 19b are connected by a spacer 25 such as a roller bearing, and a composite durable mold 1b is attached via a frame 17 to one mounting plate 19a facing the fixed base 16a.

A piston rod 27 of a cylinder 26 for opening and closing the mold provided on the underframe 15 is connected to the back of the other mounting plate 19b, and a movable plate 28 is arranged on the front of the mounting plate 19b. The ends of the extrusion pins 29, 29 corresponding to the pin holes 8, 8 of the composite durable mold 1b are fixed, and the movable plate 2 is normally placed around these extrusion pins 29, 29.
8 is interposed between the springs 30 and 30 that press the mounting plate 19b against the front surface of the mounting plate 19b. Further, on the rear side of the movable plate 28, protruding pins 31, 31 are provided that penetrate through the thickness of the mounting plate 19b.

When this structure is adopted, when the cylinder 26 is actuated to open the mold from the mold closing and casting state shown in the figure, the movable plate 28 is attached by the ejecting pins 31, 31 coming into contact with the fixed base 16b. Board 1
9b is moved forward, thereby moving the push-out pins 29, 29 in the axial direction to make a rough shape of the product attached to the mold surface. Therefore, it is possible to accurately set the mold release time and to perform mold release smoothly without applying any partial load.

Next, examples of the present invention will be described.

Examples Cast iron powder (particle size under 100 μm) was used as iron-based powder, synthetic mullite powder (particle size
(under 100μ), and ethyl silicate as a binder, with a weight mixing ratio of 3:
The mixture was mixed and stirred at a ratio of 3:1 to obtain Mixed Material A.
In addition, stainless steel fibers with a length of 7mm and a thickness of 0.19mm were added and kneaded in a range of 1 to 4% by volume to form mixed material B.
I got it. Each of the mixed materials A and B is poured into a mold containing a model (sewing machine parts, automobile parts) and molded, the solidified molded body is removed from the mold, ignited and subjected to primary firing for 0.5 hours, and then fired in a firing furnace. Secondary firing was performed at a firing temperature of 900°C in an acidic atmosphere to obtain composite durable molds A and B of 170 x 170 x 50 mm.

The relationship between firing time and compressive strength and the relationship between firing time and weight increase are shown in Figures 9 and 10 for composite durable molds A (without steel fiber addition) and B (with steel fiber addition). As the firing time increases, the compressive strength increases and the weight also increases. This is because the iron-based powder in the mixed material was oxidized and a hardened layer was formed.

Next, regarding composite durable mold B (steel fiber addition),
The results of the bending strength test and the measurement of dimensional changes are shown in FIGS. 11 and 12.

It can be seen from FIGS. 11 and 12 that when steel fibers are added, the bending strength is significantly improved and the change in mold dimensions (elongation) is significantly suppressed.

In addition, in order to see the effect of rapid heating and cooling, the
Repeated heating and cooling tests were conducted with a cycle of heating for 5 minutes and cooling at room temperature for 5 minutes, but cracks still appeared after 24 cycles.
No occurrence of chipping was observed.

The obtained composite durable molds A and B were coated with a graphite alcohol solution, and installed in the experimental casting apparatus shown in Fig. 8 to form an aluminum alloy.
Performed gravity casting of ADC-12. The casting conditions are
The casting temperature was 700°C, the casting time was 3 to 5 seconds, and the mold release time was 15 to 50 seconds. As a result, good casting was possible without insufficient flow or sinkage, and the casting surface was also good. As for durability, no damage to the mold was observed even after 50 castings, and a considerable number of castings were still possible.

The durable mold manufactured according to the present invention can be used for casting not only aluminum alloys but also Zn alloys, Mg alloys, Cu alloys, ordinary cast irons, ductile cast irons, and the like.

According to the first aspect of the present invention described above, iron-based powder with a particle size of 500 μm or less and refractory material with a particle size of 300 μm or less are used as aggregate, and a caking agent is added to this in a weight mixing ratio of (1 to 5): 1 to 5): 1 is mixed and stirred to make a slurry mixture, this slurry mixture is poured and solidified to form a mold surface, and the molded body is air-dried and/or after primary firing, in an oxidizing atmosphere.
Because we adopted a firing process at 600-1000℃,
It is possible to obtain a durable mold that has sufficient strength and durability, has a good mold surface and casting surface, and can easily cast products with complex shapes. Furthermore, since the mold surface is formed by pour molding, fine irregularities on the master model etc. can be easily and faithfully transferred. Therefore, according to the present invention, it is possible to produce a durable mold having the above-mentioned favorable characteristics simply, inexpensively, and efficiently.

Further, according to the second aspect of the present invention, the first aspect
Since 1 to 10% by volume of steel fibers are added to the mold material of the invention, it is possible to manufacture durable molds with improved bending strength due to the reinforcing effect of the steel fibers.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of a composite durable mold manufactured according to the present invention, FIG. 2 is an enlarged sectional view thereof, and FIG. 3a is a partially enlarged view of the hardened layer in FIG.
FIG. 3b is a partially enlarged view of the backing layer in FIG. 2, FIG. 4 is a sectional view showing another embodiment of the present invention, and FIGS. 5 to 7 are manufacturing steps of a composite durable mold according to the present invention. FIG. 8 is a cross-sectional view showing an example of a casting apparatus using a mold manufactured according to the present invention, FIG. 9 is a graph showing the relationship between firing time and compressive strength in the present invention, and FIG. Figure 11 is a graph showing the relationship between firing time and weight change, Figure 11 is a graph showing the relationship between bending strength and addition rate when steel fiber is added, and Figure 12 is a graph showing the relationship between steel fiber addition rate and dimensional change. This is a graph showing. 1, 1'... Composite fired body, 2... Hardened layer, 3...
...Batting layer.

Claims (1)

[Claims] 1. Iron-based powder with a particle size of 500 μm or less and refractory material with a particle size of 300 μm or less are used as aggregate, and a caking agent is added to this in a weight mixing ratio of (1 to 5): (1 to 5): 1 is mixed and stirred to obtain a slurry-like mixture, this slurry-like mixture is poured and solidified to form a mold surface, and the molded body is air-dried and/or after primary firing, in an oxidizing atmosphere.
A method for manufacturing a composite durable mold characterized by firing at 600-1000℃. 2 Iron-based powder with a particle size of 500 μm or less and refractory material with a particle size of 300 μm or less are used as aggregates, and a caking agent is mixed therein in a weight ratio of (1 to 5): (1 to 5): 1, and Add 1 to 10% by volume of steel fibers, mix and stir to obtain a slurry mixture, pour and solidify this slurry mixture to form a mold surface, air dry the molded body and/or after primary firing, in an oxidizing atmosphere
A method for manufacturing a composite durable mold characterized by firing at 600-1000℃.