KR20020074851A - manufacture method of open-cell type matal preform - Google Patents

Abstract

PURPOSE: A manufacturing method of an open-cell type metal preform is provided which easily produces the open-cell type metal preform durability and compression strength of which are substantially improved, and which has various densities. CONSTITUTION: The manufacturing method of an open-cell type metal preform comprises coating process of drying the metal powder coated polyurethane foam after coating a specific metal powder selected from copper, nickel and titanium powder on a polyurethane foam which is formed in a three-dimensional network structure having a porosity ranging from 50 to 98%, and on the surface of which a liquid phase polyurethane resin is coated; preform manufacturing process of impregnating the polyurethane foam passing the coating process into a slurry in which the same metal powder selected and used in the coating process, a water soluble PVA binder and ethyl alcohol are mixed in a weight ratio of 100:10-50:1-10 so that the surface of the polyurethane foam is coated with the slurry, removing the excess slurry by pressing the slurry coated polyurethane foam, and then drying the slurry coated polymer resin foam at a temperature of about 50 to 150 deg.C for more than 3 hours; oxidation process of removing pyrolytic organic constituents such as urethane and PVA binder by maintaining the foam at the maximum temperature for 1 to 5 hours and air cooling the heated foam after positioning the foam passing the foam manufacturing process in a furnace chamber and heating the air to a temperature of about 300 to 600 deg.C as continuously flowing air into the furnace chamber; and reduction and powder sintering process of sintering the resulting material by maintaining the reduced metal powder at a temperature of about 800 to 1000 deg.C for 3 to 6 hours after reduction treating the oxidized metal powder by applying a heating temperature of about 300 to 800 deg.C to the metal powder oxidized in the oxidation process in a reduction atmospheric chamber in which a mixed gas of hydrogen and argon is continuously flows.

Description

Manufacturing method of open cell foam {manufacture method of open-cell type matal preform}

The present invention relates to a method for producing an open-type metal foam, and more particularly, a porous three-dimensional net structure, wherein the metal powder arrives on a polyurethane foam in which a liquid polyurethane resin arrives on the surface thereof. Urethane foam is impregnated into the slurry containing the metal powder, and after the slurry arrives, it is heated to a certain temperature to remove the thermally decomposable resin, and the oxidized metal powder is reduced in the reducing atmosphere of the hydrogen mixed gas and then sintered at a certain high temperature. It provides a method for producing an open metal foam through a process, and relates to a method of manufacturing an open metal foam to facilitate the production of an open metal foam of various densities with significantly improved durability and compressive strength.

Porous foam material having a general three-dimensional cell structure has a higher porosity and easier control of the porosity than a bulk material.

Thus, porous materials can be lightweight, have high stiffness, and exhibit mixed properties of metals and pore structures, making them widely used for cushioning, insulation, vibration damping, construction, filtration, catalysts, and many other applications. It is becoming.

As such, foams used in various fields are classified into closed-cell type and open-cell type. In the case of alveolar type, they are mainly used in structures such as architecture, automobiles, and aircraft. In the case of an open cell type, heat energy or material flow is possible through contacting pores, and a wide surface area can be contacted, so it is widely used as a noise and sound absorbing material, a filter, an electrode, a heat exchanger, an adsorption material, and a structural material.

In addition, the method of manufacturing the metal foam is largely by a direct casting method of permeating a gas or granular material in the molten metal state, an indirect casting method of casting a liquid metal around a polymer foam or a solid filling material, sputtering method Metal deposition methods for depositing metals, and powder sintering methods for heating a metal powder to a urethane polymer.

Here, the direct casting method for directly preparing a foam from molten metal is mainly for forming a closed alveolar metal foam, which is largely used as a method of adding a foam forming element into a molten metal instead of the MMC molten metal method.

The first of these two methods, the MMC molten metal method, was developed by Cymat in Canada and Hydro Aluminum in Norway. In the first step, SiC, Al ₂ O ₃ or MgO particles are used to make aluminum molten metal and increase the viscosity of the molten metal. Add.

In the second step, a foam is formed by blowing air nitrogen or argon gas using a rotating impeller to the liquid MMC molten metal.

This process is easy to manufacture foam and has the advantage of producing a large amount of low-density foam having a porosity of about 80 to 97% at a relatively low cost, while it is difficult to control the porosity, and also has the disadvantage of uneven pore structure.

In addition, while the pores are large in the center of the foam, the density increases in the cooling wall, and also the disadvantages of collapse of the foam because the foam forming element is added at a high temperature.

The method of adding a foam forming element in the molten metal instead of the gas decomposes the element forming the foam through heat and promotes the formation of the foam through the blowing gas.

It is a process commercialized by the Shiko Wire Company in Japan, which uses calcium (Ca) to stabilize the molten metal and uses TiH ₂ as an element to form a foam to release hydrogen gas upon heating. The metal foam produced by this method has the disadvantage that the pore structure is uniform, but more expensive than the MMC foam.

Metal foams can also be prepared indirectly by investment casting using polymeric foams.

The manufacturing process is a process of filling and drying a polymer foam having an open-type structure with a heat-resistant slurry, which is a mixture of mullite, phenolic resin and calcium carbide, and drying the molten metal into the same pores as the original foam structure formed by removing the polymer. It is composed of a process of producing metal foam that is exactly the same as the original polymer by filling the mold and removing the mold material by hydraulic pressure.

Representative products produced by such indirect casting method is DUOCEL produced by ERG company in the United States, and produces foams with various densities of 10 ~ 40 PPI.

In addition, the metal deposition method for depositing metal by sputtering method is composed of three steps such as stiffening and electrodeless plating. In the final step, a metal such as copper (Cu) or nickel (Ni) is required for the pre-plated urethane foam. Electroplate to thickness.

Metal foams produced by metal plating have the disadvantage of being very uniform and having excellent porosity, while having high manufacturing cost of foams.

On the other hand, the powder sintering method of heating the metal powder to the urethane polymer, there is a Fraunhofer process for producing a foam by mixing the metal powder with the foam forming element and the polymer sintering method to reach the slurry to the polymer sponge.

Fraunhofer's production process is a method of forming foams by mixing metal powders with foam-forming elements, compressing them into dense semi-molded products, and then heat-treating them near the melting point temperature of the base metal material.

In the heat treatment process, the elements forming the foam are decomposed to release the gas into the base metal, thereby expanding the filled P / M material to form a porous foam structure.

The shape and structure of the cells produced by this method are irregular and are mainly applied to the production of aluminum foam.

In the polymer powder sintering method, a polymer sponge such as urethane having a three-dimensional net structure is impregnated with a metal powder slurry to reach the surface of the resin, and then heated to remove binder and organic substances, and heated to a high temperature to sinter the metal powder. That's how.

Powder metallurgy using the polymer sponge is easy to control the porosity, and can be applied in various fields because it is possible to apply a variety of metal powders, such as copper, nickel, iron and stainless steel.

However, the powder metallurgy method using the polymer sponge as described above has a problem in that the application of metal slurry on the surface of the polyurethane foam having a triangular shape contracted inwards cannot be effectively taken as shown in FIGS. 8 and 9. Was doing.

That is, the metal powder which reaches relatively to the edge surface of a polyurethane foam by the heating taken in order to remove a thermally decomposable resin in an oxidation process reduces the overall strength of a foam.

Due to such a problem, the powder sintering process caused a problem of reducing the sintering speed of the metal even when high heat was applied, and also, as shown in FIG. 10, cracks caused by sintering shrinkage seriously occurred in the powder sintering process. To prevent the formation of dense metal sintering on the surface of the polyurethane foam, resulting in the production of copper-based metal foams with poor durability and compressive strength, and to easily produce copper-based metal foams of various densities. It caused a problem that could not be.

The present invention has been made in view of the conventional problems as described above, the object of which is to take a porous three-dimensional net structure, the metal powder in the polyurethane foam is a liquid polyurethane resin has arrived on the surface When the polyurethane foam is impregnated into the slurry containing the metal powder, the slurry is arrived and heated to a predetermined temperature to remove the thermally decomposable resin, and the oxidized metal powder is reduced in the reducing atmosphere of the hydrogen mixed gas. By providing a method for producing an open metal foam through a step of sintering at a constant high temperature, a method of manufacturing an open metal foam to easily produce an open metal foam of various densities with greatly improved durability and compressive strength. To provide.

The above object of the present invention is a method for producing an open metal foam used in silencers, heat exchangers and purifiers,

It has a three-dimensional net structure with porosity in the range of 50 to 98%, and arrives by selecting a specific metal powder among copper, nickel or titanium powder in the polyurethane foam where the liquid polyurethane resin arrives on the surface. An arrival step of drying;

A slurry in which the same metal powder, water-soluble PVA binder, and ethyl alcohol are used to have a weight ratio of 100: 10 to 50: 1 to 10. Forming a slurry on the surface by impregnation, and compressing and removing the excess slurry, and then drying the polymer resin foam in which the slurry arrives at about 50 to 150 ° C. for at least 3 hours;

After placing the foam through the above-mentioned foam manufacturing process in the furnace chamber, while continuously flowing air in the furnace chamber, it is heated to about 300 ~ 600 ℃ while maintaining the maximum temperature for 1 to 5 hours and air-cooled urethane An oxidation step of removing pyrolytic organic components such as PVA binder;

The metal powder oxidized in the above-described oxidation process was reduced by applying heat of about 300 to 800 ° C. in a reducing atmosphere chamber in which a mixed gas of hydrogen and argon flowed continuously, and then reduced to about 3 to 6 hours at about 800 to 1000 ° C. It characterized in that it comprises a reduction and powder sintering process to maintain and sinter.

1 is a manufacturing process diagram showing a step-by-step method of manufacturing an open metal foam according to the present invention,

Figure 2 is a cross-sectional view showing a cross-sectional state of the copper-based metal foam prepared by the method of manufacturing an open-cell metal foam according to the present invention.

Figure 3a, Figure 3b is a photograph showing the appearance state of the foam after the arrival process when manufacturing a copper-based metal foam through the method of manufacturing an open-type metal foam according to the present invention,

Figure 4 is a photograph showing the appearance state of the foam after the foam manufacturing process when manufacturing a copper-based metal foam through the method of manufacturing an open-type metal foam according to the present invention,

Figure 5 is a photograph showing the appearance state of the foam after the oxidation, reduction and powder sintering process when manufacturing the copper-based metal foam through the method for producing an open-type metal foam according to the present invention,

6 is a diagram illustrating a comparison of compressive strength after reduction and sintering of a conventional simple metal slurry coated specimen and a specimen produced by the manufacturing method of the present invention;

7 is a diagram showing the weight change of copper oxide when heated in a hydrogen mixed gas atmosphere,

8 is a cross-sectional view showing a cross-sectional state of the polyurethane foam;

9 is a cross-sectional view showing an outer surface of the polyurethane foam;

10 is a photograph showing the appearance state of the foam after the oxidation, reduction and powder sintering process when manufacturing a copper-based metal foam through a conventional open-type metal foam manufacturing method,

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, an open-cell metal foam manufacturing method as follows.

1 is a manufacturing process diagram showing a step-by-step manufacturing method of the open-cell metal foam according to the present invention, Figure 2 shows a cross-sectional state of the copper-based metal foam prepared by the method of manufacturing a open-type metal foam according to the present invention. It is a cross section.

The open-type copper-based metal foam of the present invention as shown is first, taking a three-dimensional net structure having a porosity in the range of 50 ~ 98%, copper on the polyurethane foam in which a liquid polyurethane resin arrived on the surface And an arrival process of selecting a specific metal powder from among nickel or titanium powder and arriving thereafter, followed by drying.

Polyurethane foam, which has undergone such an arrival process, is mixed with the same metal powder used in the arrival process, water-soluble PVA binder, and ethyl alcohol to have a weight ratio of 100: 10 to 50: 1 to 10. The slurry is impregnated to reach the surface, and the excess slurry is compressed and removed, followed by a foam manufacturing process of drying the polymer resin foam in which the slurry arrives at about 50 to 150 ° C. for at least 3 hours.

Then, the foam having been subjected to the above-mentioned foam manufacturing process is placed in a furnace chamber, and then heated to about 300 to 600 ° C. while continuously flowing air in the furnace chamber, and maintained at a maximum temperature for 1 to 5 hours and air-cooled. By the oxidation process to remove thermally decomposable organic components such as urethane and PVA binder.

In addition, the metal powder oxidized in the above-described oxidation process is subjected to a reduction process by applying heat of about 300 to 800 ° C. in a reducing atmosphere in which a mixed gas of hydrogen and argon flows continuously, and then reducing the amount to 3 to about 800 to 1000 ° C. It is manufactured through a reduction and powder sintering process of sintering by holding for 6 hours.

On the other hand, the present invention is produced by reducing and sintering using a graphite plate in which a circle of about 1 cm diameter is uniformly perforated during the process of reducing and sintering at a temperature of about 300 to 1000 ° C as described above.

When described with reference to the accompanying drawings, the present invention manufactured through such a process as follows.

Figure 3a, Figure 3b is a photograph showing the appearance state of the foam after the arrival process when manufacturing the copper-based metal foam through the method of manufacturing the open-cell metal foam according to the present invention, Figure 4 is an open-type metal foam according to the present invention When manufacturing a copper-based metal foam through the manufacturing method is a photograph showing the appearance state of the foam after the foam manufacturing process, Figure 5 is an oxidation, when producing a copper-based metal foam through the manufacturing method of the open-type metal foam according to the present invention, Figure 6 is a photograph showing the appearance of the foam after the reduction and powder sintering process, Figure 6 after the reduction and sintering treatment of the conventional simple metal slurry coating and the specimen produced by the production method of the present invention under the same conditions FIG. 7 is a diagram illustrating a comparison of compressive strength, and FIG. 7 is a diagram illustrating a change in weight of copper oxide when heated in a hydrogen mixed gas atmosphere.

First, as shown in FIGS. 3a and 3b, after the first arrival process, the polyurethane foam of the triangular shape contracted inward is transformed into a more complementary triangular shape or a circular shape to improve its durability. To achieve this.

In addition, in the foam manufacturing process that arrives to the metal slurry, as shown in Figure 4, it is possible to achieve the action to achieve a dense coating of the metal slurry as a whole, as well as the oxidation process as shown in FIG. In the reduction and powder sintering process, the generation of cracks due to sintering shrinkage is hardly generated and the metal sintering of the surface can be made more compact than the existing technology.

Therefore, the porosity can be easily controlled and manufactured so that metal foams of various densities can be easily produced, and the foaming can be produced at a relatively low cost, with the foamed foam having improved durability and compressive strength significantly. It becomes possible.

In addition, as described above, in the process of reducing and sintering, a graphite plate in which a circle having a diameter of about 1 cm is uniformly perforated can be used to prevent the metal foam from sticking to the support.

This will be described in more detail through experimental examples as follows.

First, it has 10 PPI with porosity of 95%, and the liquid polyurethane resin arrives on the surface, but it is water-soluble and has a viscosity of 1.3 Pa.s (3 cm net structure cut to 19cm × 25cm × 3cm). A polyvinyl alcohol having a temperature of 20 ° C.) was used to obtain a 300-mesh copper powder on the surface, and a drying process was performed at about room temperature for about 5 hours.

As the solvent and viscosity regulator of the powder slurry, industrial ethyl alcohol is used, and the copper powder, the PVA binder, and the ethyl alcohol are mixed in a slurry having a weight ratio of 100: 20: 5 to form a polymer foam that has undergone the above-mentioned arrival process. After impregnation, the compressed copper powder was pressed to allow the slurry to flow into the polymer foam and dried at 60 ° C. for 3 hours or more.

The polymer foam, which has undergone such a manufacturing process, has a temperature of about 600 ° C., but is charged for about 3 hours in a chamber of a furnace where air is continuously flowing, followed by air cooling to thermally decompose urethanes and binders. An oxidation process was performed to remove the organic component.

Then, the polymer foam subjected to such an oxidation process has a temperature of about 950 ° C., and charged in air for about 4 hours in a chamber of a furnace in which an atmosphere of hydrogen (4%) and argon mixed gas flows continuously. During the heat treatment, a reduction and sintering process of reducing and sintering the oxidized copper powder was performed.

For reference, the copper oxide undergoing the reduction process as described above does not change in weight from room temperature to about 400 ° C. as shown in FIG. 7, but when the temperature increases above about 450 ° C., the weight begins to decrease at a constant rate. Decreased to about 780 ° C.

In this temperature range, the copper oxide reduced by about 12% as it was reduced by the surrounding hydrogen gas.

However, at temperatures above about 800 ° C., the weight of the copper metal no longer decreased.

Based on the thermal analysis results above, the oxidized copper metal powder was heated to 800 ° C. at a rate of 100 ° C./h from room temperature in a mixed atmosphere of hydrogen and argon to reduce the copper oxide powder, and then the temperature was continuously increased to 950 ° C. Sintering was carried out to raise and hold for 9 hours.

At this time, the foam size after the above-described reduction and sintering process was modified as shown in the table below.

Foam Original Size 15 × 10 × 2 (Cm) = 300Cm³ After reduction and sintering 13.0 × 8.64 × 1.52 (Cm) = 170.7Cm ³ Volumetric shrinkage after sintering 43.3%

In addition, the copper-based metal foams prepared by performing the above-described process showed the surface of the copper metal color gloss.

In addition, as a result of observing with a scanning electron microscope to observe the sintered state of the metal foam, as shown in Figure 5 the surface of the foam showed a dense structure with little pores.

In addition, the compressive strength of the specimen produced through the process of the present invention as described above was shown to increase the strength of about 5 times or more compared to the foam produced through the conventional process as shown in FIG.

On the other hand, the present invention can be produced in a variety of fields because it is possible to manufacture a variety of metal-based metal foam by applying a variety of metal powders, such as nickel and iron, stainless steel and titanium in place of the copper powder in the sludge used in the foam manufacturing process The action that can be applied is achieved.

As described above, the present invention has a porous three-dimensional net structure, but the metal powder arrives on the polyurethane foam in which the liquid polyurethane resin has arrived on the surface, and the polyurethane foam is mixed with the metal powder. After impregnating the slurry into a slurry, the slurry is heated to a predetermined temperature to remove the thermally decomposable resin, and the oxidized metal foam is formed by reducing the oxidized metal powder in a reducing atmosphere of hydrogen mixed gas and then sintering at a certain high temperature. By providing a method of manufacturing, it is possible to easily produce a copper-based metal foam of various densities with significantly improved durability and compressive strength, as well as a relatively low cost of open-type copper-based metal foam with significantly improved durability and compressive strength It is effective to provide as.

In addition, in the process of reducing and sintering, using a graphite plate having a uniformly rounded diameter of about 1 cm, the metal foam is prevented from adhering to the support.

Claims (2)

In the manufacturing method of an open cell metal foam used in a silencer, heat exchanger and purifier, It has a three-dimensional net structure with porosity in the range of 50 to 98%, and arrives by selecting a specific metal powder among copper, nickel or titanium powder in the polyurethane foam where the liquid polyurethane resin arrives on the surface. An arrival step of drying; A slurry in which the same metal powder, water-soluble PVA binder, and ethyl alcohol are used to have a weight ratio of 100: 10 to 50: 1 to 10. Forming a slurry on the surface by impregnation, and compressing and removing the excess slurry, and then drying the polymer resin foam in which the slurry arrives at about 50 to 150 ° C. for at least 3 hours; After placing the foam through the above-mentioned foam manufacturing process in the furnace chamber, while continuously flowing air in the furnace chamber, it is heated to about 300 ~ 600 ℃ while maintaining the maximum temperature for 1 to 5 hours and air-cooled urethane An oxidation step of removing pyrolytic organic components such as PVA binder; The metal powder oxidized in the above-described oxidation process was reduced by applying heat of about 300 to 800 ° C. in a reducing atmosphere chamber in which a mixed gas of hydrogen and argon flowed continuously, and then reduced to about 3 to 6 hours at about 800 to 1000 ° C. Method for producing an open metal foam comprising a reduction and powder sintering step of maintaining and sintering. The method of claim 1, wherein the reduction and sintering process using a graphite plate in which a circle of about 1 cm diameter is uniformly perforated during the process of reducing and sintering at a temperature of 300 ~ 1000 ℃ manufacturing of open cell type metal foam Way.