JPH0453686B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a breathable mold useful for injection molding of metal or synthetic resin, and a method for manufacturing the same.

[Prior Art] Air entrainment during injection molding has a large effect on the product. To address this issue, air-permeable metal such as air vents and air vent pieces are attached to some parts of the mold, but this cannot be said to be a complete countermeasure.
There are also vacuum injection machines, but they pose a cost problem.

[Problems to be solved by the invention] Currently, the air-permeable metals on the market lack the mechanical strength of air vent pieces for injection molding, and cannot be directly used to form cavities. However, it is not suitable for injection molds. An injection mold must have two points: it must be capable of three-dimensional die engraving, and it must have mechanical properties that can withstand injection.

The present invention provides a mold that fully satisfies these two requirements for an injection mold and is breathable, making it possible to obtain a product without air entrainment without using a vacuum injection machine. That is.

[Means for Solving the Problems] The first invention of the present invention is a molded sintered body of stainless steel powder and boron or metal boride, which has a dense layer on the inner surface of the mold and a coarse layer on the outer surface. This is a breathable mold characterized by a porous ventilation structure divided into two parts.

The above-mentioned metal borides include Ti, Zr of group a,
Borides of Nb and Ta from the Va group, Cr, Mo, and W from the a group are used.

The amount of boron and metal boride used is suitably in the range of 0.1 to 6 wt%. Furthermore, it is desirable to use particles with a particle size of 10μ or less. The stainless steel powder may be martensitic, austenitic, or ferrite. For example, precipitation hardening type
Use SUS630, hardened and tempered SUS440, etc. Stainless steel powder should preferably pass 400 meshes to avoid clogging when used as a mold.

In addition, since this mold is made by pouring slurry and vibration, which will be described later, a dense layer 1 is formed near the bottom of the mold as shown in Figure 1, and a coarse layer 2 is formed near the pouring surface, which is the so-called double layer. becomes.

If a mold is made with the surface of the dense layer 1 facing the inner surface during injection molding, the injection melt will be less likely to enter the holes and cause clogging, and the mechanical strength will be high, so it will be easier to use during injection molding. Will not be damaged by pressure. Furthermore, by forming the rough layer 2 on the outer surface of the mold, air permeability is improved.

In the second invention, a slurry made by mixing a mixture of stainless steel powder and boron or metal boride with a binder that evaporates during the drying and solidification process is poured into a mold, and the bottom of the mold becomes tightly sealed by applying vibrations. This is a method for manufacturing an air-permeable mold, which is characterized by solidifying and molding the layer so that the layer is rough near the pouring surface, and after drying, sintering in a vacuum.

That is, in the invention of this manufacturing method, the raw material mixture is molded by slurry casting, so if dimensional shrinkage after firing is taken into consideration, a product with dimensions close to the final mold size can be obtained, and the amount of processing can be kept to a minimum.
Furthermore, if a model is available, it can be transferred, and a mold that can be used as a durable injection mold can be obtained without performing die carving such as electric discharge machining or cutter machining.

Then, as shown in FIG. 2, slurry is poured into the mold 3 held by the elastic body 4, and solidified while being vibrated by an eccentric weight (not shown). Due to the vibration, materials with relatively high specific gravity in the slurry gather at the bottom of the mold 3, forming a dense layer 1, and near the pouring surface, many materials with relatively low specific gravity form a coarse layer 2. In this case, there is a correlation between the vibration time and the depth of the generated dense layer. One test result is shown in Figure 3. Figure 3 shows the case where stainless steel powder that passed 400 mesh was used and a block height of 18 m/m was cast.

When such a molded body is vacuum sintered after drying, a dense layer 1 is formed.
After sintering, the mechanical strength is strong and the porosity is small, and the rough layer 2 has a low mechanical strength but a large porosity. Sintering temperature is 1160 ~
A range of 1200℃ is appropriate.

As a binder that is evaporable during the drying and solidification process used in plaster, silica gel or colloidal silica, typified by ethyl silicate, is used.

Normally, in the case of plaster casting, water absorption is required, so a material with a high water absorption rate such as a plaster mold is used as a mold, but in the case of the present invention, silica sol or colloidal silica is used. It has a fast curing speed and can be used with all types of wood, whether it is wood or metal.

Since sludge is used, if dimensional shrinkage after firing is taken into account, dimensions close to the final mold can be obtained, and the amount of processing can be kept to a minimum. Furthermore, if a model is available, it can be made and transferred, and there is no need to carry out die carving such as electric discharge machining or cutter machining, so it can be used as a durable injection mold.

[Example] Next, examples and comparative examples will be described.

Example 1 SUS630 powder is used as the stainless steel powder. The particle size used was one that passed through 400 mesh, and 350 g of mixed powder to which 0.9 wt% B was added and mixed was used.

Add ethyl silicate to the above mixed powder (e.g.
The amount of silicic acid sol obtained by mixing HC1) with respect to the amount of powder
A slurry was formed by mixing 15 to 30 wt%, which was poured into a mold with a volume of 80 mm x 80 mm x 40 mm, and was molded to a thickness of 15 mm while being vibrated for 6 minutes. At this time, the depth of the dense layer formed at the bottom of the mold was 4 mm.

After drying, this was demolded and sintered in a vacuum at 1190°C for 1 hour.

Comparative Example 1 A molded article was obtained in the same manner as in Example 1 except that B was not added.

FIG. 4 is a graph showing the relationship between sintering temperature and porosity of the products in Example 1 and Comparative Example 1. In the case of Example 1, sintering progresses at a lower temperature than in Comparative Example 1, resulting in a low porosity. Further, FIG. 5 is a graph showing the relationship between sintering temperature and resistance after precipitation hardening treatment. In the case of Example 1, the resistance is improved at low temperatures compared to the case of Comparative Example 1.

Next, zinc die casting was performed using the molds prepared in Example 1 and Comparative Example 1. Die engraving was performed on each surface, but in the case of Example 1, engraving was performed on the dense layer side.

The product of Example 1 could be injection molded more than 20,000 times without breaking, but the product of Comparative Example 1 showed breakage in the fine part of the mold engraving.

In addition, in the case of Example 1, because of its air permeability, injection was possible even at a lower pressure than with ordinary steel molds, and the casting surface of the molded product was also good.

Example 2 The same procedure as Example 1 was carried out except that 3 wt% of TiB ₂ was added instead of B. In this case as well, the same results as in Example 1 were obtained.

Example 3 The same procedure as Example 1 was carried out except that 3 wt% of WB was added instead of B. In this case as well, the same results as in Example 1 were obtained.

Although the above embodiments have been described mainly for injection molding, the mold according to the present invention is also effective for press molding of soft materials such as aluminum. In other words, in presses, etc., if oil drainage holes are not provided in the mold, cutting oil will be present in the die engraving area, which has the disadvantage that the mold surface shape cannot be accurately transferred.However, the mold according to the present invention In this case, the above-mentioned drawback can be compensated for because oil can be released.

[Effects of the Invention] The mold according to the present invention has a porous ventilation structure divided into a dense layer and a coarse layer, and if fine engraving is applied to the dense layer side, the strength is increased, so it can withstand repeated use. It will not lose its shape even when worn. In addition, the injection molten material is less likely to enter the holes on the mold surface and cause clogging, and since the rough layer side has high air permeability, there is no air left inside the mold surface, and the mold surface can be used for injection molded products. It can be precisely transferred to the surface.

In addition, since the method of the present invention is manufactured by plaster casting, if dimensional shrinkage after firing is anticipated in advance, dimensions close to the final mold size can be obtained, and the final processing amount can be kept to a minimum. be. Then, by vibration molding, it can be easily molded into a molded body consisting of a coarse layer and a dense layer.

By using boron or metal boride with stainless steel powder, ideal porosity and high mechanical strength can be obtained at lower temperatures.

Normally, in the case of plaster casting, water absorption is required, so a material with a high water absorption rate, such as a plaster mold, is used as the mold, but in the case of the present invention, silicate sol is used as the hardening agent. It has a fast curing speed and can be used with all mold materials, including wooden molds and metal molds.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of an example of the mold of the present invention, Fig. 2 is an explanatory diagram of the same manufacturing method, Fig. 3 is a graph showing the relationship between vibration time and dense layer depth in the inventive manufacturing method, and Fig. 4 is an explanatory diagram of an example of the mold of the present invention. Graph showing the relationship between sintering temperature and porosity, fifth
The figure is a graph showing the relationship between sintering temperature and transverse rupture strength. 1...Dense layer, 2...Coarse layer, 3...Formwork, 4...
Elastic body.

Claims (1)

[Claims] 1. A molded sintered body of stainless steel powder and boron or metal boride, which has a porous ventilation structure divided into a dense layer on the inner surface of the mold and a coarse layer on the outer surface. A breathable mold characterized by: 2 A slurry made of a mixture of stainless steel powder and boron or metal boride mixed with a binder that evaporates during the drying and solidification process is poured into a mold, and while being vibrated, the bottom of the mold becomes a dense layer. A method for producing a breathable mold, which is characterized by solidifying and molding so that the layer near the pouring surface becomes a rough layer, drying, and then sintering in a vacuum.