JPH0252606B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a breathable mold.

The inventors of this application filed a patent application in 1983 in an earlier patent application.
- No. 62784 (see Japanese Patent Application Laid-Open No. 60-6242)
58-71258 (see JP-A-60-6241), JP-A-58-71259 (see JP-A-60-46213), and JP-A-58-80943 (see JP-A-60-6243) As disclosed in Japanese publications, etc., metal powder and ceramic powder are used as aggregates, and a binder containing components that evaporate or burn out during the hardening and firing process is added, as well as steel fibers as necessary. We have proposed a mold with an air-permeable structure, which is made of a composite fired body obtained by this process, and has a dense hardened layer containing at least a metal oxide on its surface. However, this mold can be used for molding processes that require air permeability and water permeability, such as vacuum molding molds, blow molding molds, casting molds, etc., as well as molds for metal casting, slippers for ceramics, etc. When used in molds for staining, etc., it is necessary to adjust the air permeability, and the air permeability needs to be controlled by the particle size distribution of metal powder and ceramic powder, the blending ratio, or the amount of binder added. However, this is complex and requires advanced technology. For example, in ceramic casting molds, if the air permeability, or water permeability, differs depending on the part of the mold, the thickness of the ceramic raw material deposited on the mold will differ. This causes some inconvenience, and it is necessary to make the air permeability constant depending on the part of the mold. For this purpose, the thickness must be constant along the shape of the mold, but if the wall thickness is thin, there are problems such as distortion and cracks occurring during the drying and firing process, so a shell-shaped mold with a constant thickness is used. It was difficult to make. Another problem was that the air permeability could not be changed depending on the part of the mold.

The present invention has been made in view of these problems, and its purpose is to provide a structure that does not have any problems in terms of strength, has excellent breathability, thermal conductivity, etc., and has functions appropriate to the intended use. The purpose of the present invention is to manufacture a breathable mold.

The present invention will be explained in detail below based on examples. As shown in Fig. 1, reference numeral 1 denotes a porous composite fired body with a recess 1a in the center.This composite fired body 1 is made of metal powder and ceramic powder, and has a dense hardened body on the outer periphery including the mold surface. It has a layer 2, and a backing layer 3 made of an unfired mixed structure inside the hardened layer 2.

The hardened layer 2 consists of a bonding structure of metal oxide particles dispersed in ceramic powder and fired ceramic particles. Although the formation mechanism of this hardened layer 2 is not necessarily clear, it is generally considered to be the result of oxidation of metal powder and diffusion bonding at the interface with ceramic particles.

In this hardened layer 2, the binder is evaporated or burned away during the drying process and the firing process in an oxidizing atmosphere, resulting in fine particles (about 5 to 10 μm).
These fine pores form a porous yet dense and smooth surface. On the other hand, the backing layer 3 located inside the hardened layer 2
It consists of a mixed structure of metal powder and ceramic powder that have not been sufficiently fired, and pores are formed at the interface of these metal powders or ceramic powders due to evaporation or burning of the previous binder. .
The pores of this backing layer 3 communicate with the pores of the hardened layer 2, so that the entire composite fired body 1 has a porous ventilation structure.

Such a porous composite fired body 1 is produced by mixing and kneading aggregate and a binder to obtain a slurry sample, pouring and molding the slurry sample, and drying or primary firing the molded body. The product obtained through this step is then fired in an oxidizing atmosphere.

First, the process of obtaining a slurry sample involves thoroughly mixing and stirring metal powder and ceramic powder or steel fibers, and then adding a binder containing components that evaporate during the curing process, such as silica sol such as ethyl silicate or colloidal silica. and thoroughly mix and stir. Next, the slurry sample is solidified and molded into a desired shape to obtain a molded body. This is done, for example, by setting a model or actual object inside a mold, pouring the slurry sample into the mold, and leaving it for the required time. Adding vibration to promote filling properties,
Squeezing is also effective.

Specifically, as the "metal powder", iron powder such as cast iron powder, electrolytic powder, pure iron powder, etc., and non-ferrous metal powder such as nickel powder, copper 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 small deformation rate at high temperatures and are easily bonded to metal powders, such as neutral types such as mullite, calcined alumina, activated alumina, fused alumina, chromite, sillimanite, etc. Acidic materials such as 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.

The mixing ratio of the metal powder, ceramic powder, and binder is preferably approximately (1-5):(1-5):1 by weight. Here, the lower limit of the mixing ratio of metal powder, ceramic powder, and binder is specified because it is necessary to obtain the minimum usable mold strength.

The upper limit was specified because too much aggregate would reduce the coating ability of the binder from the viewpoint of moldability, resulting in a decrease in strength and deterioration of the stability of the mold surface.

Next, after removing the molded body obtained in the previous step from the mold, natural drying and/or primary firing is performed,
Further, the molded body is subjected to secondary firing under oxidizing atmosphere conditions. The oxidizing atmosphere may be air or may be so-called oxygen-enriched air in consideration of oxygen supply. Firing conditions vary depending on the blending ratio of aggregates and binders, mold dimensions, target porosity, and production aspects, but in general, a firing temperature of 400 to 1500°C and a firing time of 1 hour or more are appropriate. However, the temperature and time are not limited to these, and as the firing time becomes longer, the hardened layer will grow and increase in size. Therefore, if you want to make the hardened layer thicker, you just need to lengthen the firing time, and if you want to make it thinner, you can shorten the firing time. In this secondary firing step in an oxidizing atmosphere, firing of the ceramic powder and oxidation sintering of the metal powder dispersed in the molded body proceed, and a dense hardened layer 2 is gradually generated from the surface toward the inside. At the same time, the volatile components of the binder remaining in the molded body are burned off to promote porosity, and upon completion of the secondary firing, a porous composite fired body 1 as shown in FIG. can get.

Next, the composite fired body 1 shown in Fig. 1 was cut at the A-A' position to expose the unfired backing layer 3, and it was masked with a rubber plate so that the mold surface would not be damaged even if shot particles hit the mold surface. After that, the unfired backing layer 3 is thoroughly removed by projecting a shot material such as shot grains toward the backing layer 3 from a projection device, and a cavity 4a is formed on the back side as shown in FIG.
A hollow mold 4 was obtained, which had a hardened layer 2 on its outer periphery. At this time, only the backing layer 3 is removed cleanly, leaving only the hardened layer 2 with a uniform thickness, without causing molding or cracking due to shot particles projected from a projection device (not shown). Ta.

In addition to the above-mentioned projection device, the means for removing the backing layer 3 may be a sandblasting device, a sander, a grinder, a drill, etc., and when the hardened layer 2 is to be removed, it may be scraped off with a sander, grinder, cutter, etc.

Next, a furan-based resin containing a curing catalyst as a binder was added to the cavity 4a of the hollow mold 4, and the mixed particulate matter 5 was filled as a backup and cured to obtain an air-permeable mold 6. In addition, if thermal conductivity, strength, and heat resistance are required as particulate matter 5, it may be made of aluminum alloy, copper alloy, iron-based material, etc. with a relatively small particle size of about 100 μ to 3 mm, or simply If breathability is important,
A relatively large particle size of about 1 mm to 10 mm is preferable. If you want to make the mold even lighter, plastic resins such as vinyl chloride resin, A/B/S resin, or styrene resin are suitable. It also has breathability, thermal conductivity,
Inorganic compounds such as silicon oxide, zirconium silicate, aluminum oxide, and glass can also be used as materials that averagely satisfy a wide range of requirements such as heat resistance, weight, and price.

In addition to the above, as a means for curing the particulate matter 5, adding a urethane resin as a binder,
After filling the mixed particulate matter 5, a method of curing by passing amine gas through the air, or a method of using sodium silicate as a binder and curing by bubbling carbon dioxide gas after filling, and a thermosetting method. A phenolic resin may be used as a binder, and after filling, it may be heated and cured at a temperature of 150 to 180°C. Next, specific examples of the present invention will be shown.

(Example) Cast iron powder (particle size under 44μ) as metal powder and synthetic mullite powder (particle size under 75μ) as ceramic powder were uniformly mixed at a weight ratio of 1:1, and a curing catalyst was further added as a binder. Containing ethyl silicate based on the total weight of cast iron powder and synthetic mullite powder
Add 25wt% and mix and stir thoroughly to obtain a slurry sample. Next, this slurry-like sample was poured into the mold with the model set while applying vibrations, left to stand for a predetermined period of time, solidified, and molded. After releasing the solidified molded product, it was left in the air for 24 hours to allow it to grow naturally. dry. Next, it was charged into a firing furnace and subjected to secondary firing at a firing temperature of 900° C. for 4 hours in an oxidizing atmosphere to obtain a composite fired body.

Next, the back side of this composite fired body is cut to expose the internal unfired backing layer, and after masking with a rubber plate or the like so that the mold surface will not be damaged even if shot particles hit the mold surface, the unfired backing layer is removed. Shot grains with a diameter of 0.5 mm are projected onto the layer from a projection device at a projection speed of 70 m/sec so that the shot density is 100 Kg/m ² to cleanly remove the unfired backing layer and form a cavity. At the same time, a furan-based resin containing a curing catalyst as a binder was added in advance to this cavity, and mixed aluminum alloy particulate matter 7 with a particle diameter of 1.5 mm was filled as a backup and hardened to obtain a breathable mold 8. . Next, as shown in FIG. 4, this breathable mold 8 is placed in a frame 9 of a vacuum forming apparatus having an opening on one side and a plurality of ventilation holes 9a leading to the outside on the other side wall. After fitting with the back side facing the opening side and the back side facing the ventilation hole 9a, suction is applied from the back side of the breathable mold 6 through the ventilation hole 9a with a vacuum pump (not shown), and the mold is heated to 120°C. 0.5
A resin product made of vinyl chloride sheet of mm was suctioned and molded in about 6 seconds.

(Comparative example) The back side of a composite fired body made of the same ingredients and conditions as in the above example was cut in the same manner as in the above example, and the backing layer 3 was left intact.The body was fitted into the frame 9 and heated to 120°C. When a resin product made of 0.5mm vinyl chloride sheet is molded in the same manner as above, approximately 11
It took seconds.

As described above, when the air-permeable mold 8 manufactured according to the present invention was used, the molding time was shortened and productivity was greatly improved compared to when the backing layer 3 was left as it was. .

This is due to the use of aluminum alloy particles, which are coarser in size and have better thermal conductivity than metal powder or ceramic powder, in the back-up, which improves the air permeability and thermal conductivity of the mold, and the gap between the vinyl chloride sheet and the mold surface. The trapped residual air is efficiently discharged through the gaps between the particles of the mold 8, which has good air permeability, and the speed at which the vinyl chloride sheet is attracted to the mold surface becomes faster, and its thermal conductivity improves. This is thought to be because the surface temperature of the mold no longer rises, and the time required for cooling and releasing the mold after molding is shortened.

In addition, FIG. 5 shows a composite fired body 1 having a convex shape, and when vacuum forming is performed using a mold having such a shape, it takes time for the synthetic resin sheet to adhere to the corner A by suction. Requires high breathability,
In addition, the side surface portion B does not require much air permeability, because if the sheets come into close contact with each other in the initial stage of molding, stretching will be inhibited and the thickness of the resin product will likely fluctuate. In such a case, when removing the backing layer 3', the hardened layer 2' near the corner A is scraped off to make it thinner, and the backing layer 3' at the area corresponding to the vicinity of the side surface B is intentionally removed. It is necessary to leave it in the

Incidentally, it is manufactured according to the present invention. Breathable molds include, in addition to the vacuum forming in the above embodiments, resin molding molds such as blow molding molds and injection molding molds, and molds for casting low alloy metals such as aluminum alloys and zinc alloys.
It can also be used as a mold for press molding, roller machine molding, slurry casting molding, etc. in ceramic molding.

As is clear from the above description, it is manufactured according to the present invention. Air-permeable molds allow you to control the air permeability throughout the mold or in each part as needed without compromising mold strength, and by using metal etc. as particulate matter, thermal conductivity is improved. Furthermore, particulate matter from plastic resin can be used to make the mold lighter, and by using various particulate matter according to each purpose, the function of the mold can be improved, resulting in better quality products. It is expected that the molding of resin products will be possible, and productivity will be greatly improved, and the effect of contributing to this type of industry will be significant.

[Brief explanation of the drawing]

Figures 1 to 3 show the manufacturing process of the present invention. Figure 1 is a cross-sectional view of the composite fired body, and Figure 2 is a cross-sectional view of the composite fired body in Figure 1 after cutting the back side and removing the backing layer. Figure 3 is a cross-sectional view of a breathable mold in which the back cavity of the hollow mold is filled with particulate matter. FIG. 5 is a sectional view showing another embodiment of the composite fired body. 1, 1': Composite fired body, 2, 2': Hardened layer, 3,
3': unfired backing layer, 4: hollow mold, 5,
7: Particulate matter, 6, 8: Breathable mold.

Claims (1)

[Scope of Claims] 1. A sample made of metal powder and ceramic powder as aggregate, mixed with a caking agent containing components that evaporate or burn out, is molded and fired to form a dense hardened material containing metal oxides in the outer periphery. A process of obtaining a composite fired body consisting of a layer and an unfired backing layer, and a step of cutting a part of this composite fired body, leaving only a dense hardened layer containing metal oxide at the outer periphery and cutting the inner unfired backing layer. An air-permeable mold comprising the steps of: forming a cavity by removing the binder, and filling the cavity with particulate material mixed with a binder and forcibly hardening it to make it back up. Production method. 2. The breathable molding according to claim 1, characterized in that when removing the backing layer to form the cavity, a projection material such as a shot is projected onto the backing layer using a projection device. Mold manufacturing method.