JP4616220B2 - Method for producing hollow metal body - Google Patents

Description

  The present invention relates to a production method for producing a hollow metal body at low cost by a powder sintering method.

Examples of the method for producing the hollow metal sphere include a method of sintering powder, a method of spraying and dispersing on a substrate, a method of plating on a substrate, a method of directly producing from a molten metal, and a method of foaming a metal. Among these methods, there is a method of sintering powder as a method for producing individual hollow metal spheres. In the case of this production method, a central core material that becomes a substrate in some form is used in order to form the raw material powder into a single hollow metal sphere. There are a method of removing the central core substance in the course of manufacturing the hollow metal sphere alone and a method of remaining in the manufactured hollow metal sphere alone.
The present invention relates to a production method for removing central core material in the course of production of a single hollow metal sphere. In Patent Document 1, a metal compound such as a metal oxide is used as a starting material, and an envelope layer is placed on a support element, and the green body is heat-treated in a reducing atmosphere of 1500 ° C. or less. A technique for thermally decomposing, reducing, and sintering a binder therein is disclosed.

  Patent Document 2 discloses the following method. Substantially spherical blowing agent particles are coated with a solid powder / binder layer while stirring in a flow reactor. The coated foaming agent particles are thermally decomposed while being stirred at a temperature of 400 to 500 ° C. after drying, whereby the coating layer becomes a shell surrounding the cavity. Furthermore, it is the manufacturing method of the hollow metal ball | bowl that a sintered layer is formed by heat-processing, stirring at the temperature of 1000-1500 degreeC.

However, in the actual manufacturing process, the intermediate product before sintering after decomposition and evaporation of the core material and the binder contained in the coating layer (hereinafter, unsintered hollow sphere) Is very thin, fragile, and if handled with extreme care, the spherical shell will easily break. Therefore, it was found that a sound final product could not be obtained, and this method was not suitable for mass production. Patent Document 2 discloses a method for ensuring the strength of the unsintered hollow sphere by coating the powder layer thickly. However, if the coating layer is simply thickened, the bulk specific gravity of the completed hollow metal sphere is disclosed. Becomes too large, and the advantage of the hollow metal sphere that it is light weight and low specific gravity is lost. Further, Patent Document 2 discloses a method for enhancing the strength of unsintered hollow spheres by obtaining a reinforced oxide film on the surface of metal powder particles by “pyrolytically decomposing the core core material under light oxidation conditions”. Although disclosed, when the metal oxide powder that is the subject of the present invention is used as the starting material, such an effect cannot be expected, and the strength of the unsintered hollow sphere is still insufficient. The problem remained.
Special table 2003-531287 gazette Japanese Patent Application Laid-Open No. 64-56137

The present invention has been made to solve the above-described problems, and provides a method for producing a hollow metal body having a good shape with few cracks and defects.

In order to solve the problem, the present invention has the following configuration.
(1) The method for producing a hollow metal body according to the first invention is a method for producing a hollow metal body comprising a sintered metal,
After coating a solution containing a metal oxide powder raw material and a binder on the outer surface of the central core material, and drying, a coating layer of the powder raw material is formed on the outer surface of the central core material And the core material having the coating layer of the powder raw material is heated in the temperature range of 250 to 400 ° C. in the atmosphere or in an inert gas atmosphere not containing a reducing gas, Pyrolysis / vaporization process of the central core material to obtain a hollow shell body by the remaining coating layer that has disappeared by pyrolysis / vaporization, and the shell body obtained by the pyrolysis / vaporization process in the atmosphere or oxidation Roasting step of heating in a temperature range of 800 to 1100 ° C. in a reactive gas atmosphere, and the shell subjected to the roasting step in a reducing gas atmosphere containing hydrogen and / or carbon at 1000 to 1300 ° C. Reduce and sinter by heating in the temperature range And a reduction / sintering step for producing a hollow metal body.
(2) The method for producing a hollow metal body according to the second invention is a method for producing a hollow metal body comprising a sintered metal,
After coating a solution containing a metal oxide powder raw material and a binder on the outer surface of the central core material, and drying, a coating layer of the powder raw material is formed on the outer surface of the central core material And the core material having the coating layer of the powder raw material is heated in the temperature range of 250 to 400 ° C. in the atmosphere or in an inert gas atmosphere not containing a reducing gas, Pyrolysis / vaporization process of the central core material to obtain a hollow shell body by the remaining coating layer that has disappeared by pyrolysis / vaporization, and the shell body obtained by the pyrolysis / vaporization process in the atmosphere or oxidation A roasting step of heating in a temperature range of 800 to 1100 ° C. in a reactive gas atmosphere, and immersing the shell obtained in the roasting step in an aqueous solution containing 0.1 to 1 mol / liter of phosphate ions And then dipping and drying steps to dry, and the soaking -It has a reduction / sintering step of heating and reducing / sintering the shell obtained in the drying step in a reducing gas atmosphere containing hydrogen and / or carbon in a temperature range of 1000 to 1300 ° C. It is the manufacturing method of the hollow metal body characterized.

(3) In the method for producing a hollow metal body according to the third invention, the powder raw material consists of one or more of Fe ₂ O ₃ or Fe ₃ O ₄ , and the total content thereof is 98 mass% or more of iron oxide 1st invention or 2nd invention characterized by consisting of 1 type, or 2 or more types of powder chosen from powder, or the alloy steel oxide powder whose sum of the oxide powder of Fe and an alloy component is 98 mass% or more It is a manufacturing method of the hollow metal body as described in above.

  (4) The hollow metal body according to any one of the first to third inventions, wherein the hollow metal body according to the fourth invention has a specific surface area diameter of the raw material powder of 1.0 μm or less. It is a manufacturing method of a body.

  (5) The method for producing a hollow metal body according to the fifth aspect of the present invention is such that the powder raw material is iron oxide powder and / or alloy steel oxide powder, copper powder, nickel powder, phosphorus powder, copper oxide powder, nickel oxide powder. Of the first to fifth inventions, characterized by comprising one or more powders selected from phosphorus pentoxide powder, ferrocopper powder, ferronickel powder, ferroline powder, molybdenum powder and molybdenum trioxide powder It is a manufacturing method of the hollow metal object in any one.

  (6) In the method for producing a hollow metal body according to the sixth invention, the component composition of the hollow metal body is mass%, P: 0.01 to 1%, Cu: 0.5 to 5%, Ni: 0. .2 to 10% and Mo: containing one or more selected from 0.2 to 10%, the balance being iron and inevitable impurities, and the porosity of the sintered layer of the hollow metal body being 10 vol It is a manufacturing method of the hollow metal body in any one of the 1st-5th invention characterized by the above-mentioned.

  The present invention can provide a hollow metal body having a good shape with few defects such as cracks in a spherical shell.

  As a result of intensive studies, the inventors of the present invention have produced a method for producing a hollow metal body by coating a powder raw material on the core, thermal decomposition / vaporization of the core material at a predetermined temperature and atmosphere, and roasting, It has been found that a hollow metal body having a good shape and few cracks and defects can be produced by treating each step of reduction and sintering, and the present invention has been completed. Furthermore, it has been found that an excellent spherical shell with higher strength can be produced by immersing the shell body in a solution containing phosphate ions between the roasting treatment step and the reduction / sintering step. This invention has been completed.

  The manufacturing process of the present invention will be specifically described with reference to FIG.

1. About a manufacturing process (1) Coating process of powder raw material to central core substance The material used as a central core substance should just have the function to thermally decompose and vaporize in the temperature range of 250-400 degreeC, for example, in resin, Foamed polymers, plastics and the like are suitable, and waste plastics can also be used. Moreover, the shape should just be similar to the shape of a final product, and is not limited to spherical shape, A rugby ball shape, a cylindrical shape, and a dice shape may be sufficient. The dimension is preferably 1 to 20 mm. Furthermore, when applied to shock absorbers, or for light-weight applications with a specific gravity of 1 or less, the size must be at least 2 mm, depending on the outer shell thickness of the sphere, and the shell at the time of manufacture In order to avoid damage to the sphere, it is preferably 8 mm or less corresponding to the diameter of the sphere.

  As the powder raw material, iron oxide powder is mainly used, but a mixed powder of metal iron powder and iron oxide powder may be used. Moreover, the combination using the oxide powder of alloy steel instead of the iron oxide powder and the alloy steel powder instead of the metal iron powder is also possible. If the purity of iron in the powder (in the oxide, the ratio of iron oxide to the total weight) is 98 mass% or more, preferably 99 mass% or more, a hollow iron sphere having high strength after sintering can be obtained. Further, the specific surface area diameter of these powder raw materials is 1.0 μm or less, more preferably 0.8 μm or less, which is an important condition for obtaining a hollow iron ball having higher strength.

  In addition to iron oxide powder and / or alloy steel oxide powder, copper powder, nickel powder, phosphorus powder, copper oxide powder, nickel oxide powder, phosphorus pentoxide powder, ferrocopper powder, ferronickel powder, ferroline powder, molybdenum powder Further, by adding one or more kinds of powders selected from molybdenum trioxide powder as a sintering aid, a hollow iron sphere having higher strength can be obtained. As specific addition amounts to the iron oxide powder and the like, phosphorus is preferably 1 mass% or less, copper is 5 mass% or less, nickel is 10 mass% or less, and molybdenum is 10 mass% or less. The metal raw material powder is described based on iron, but metal powders such as Ni, Cu, Cr, Mo, Al, and Ti can be appropriately used depending on the application of the product.

  When the powder is coated on the surface of the central core material, the binder serving as a binder also plays an important role. As a binder, water-soluble resins such as vinyl alcohol copolymers such as polyvinyl alcohol, starch pastes such as dextrin, glue, and starch, gum arabic, casein, and glue are used.

  Using the above raw materials, a dispersion solution in which powder raw materials and a binder are dispersed on the outer surface of the central core material is uniformly coated using a drum or a fluidized bed. The thickness of the coating layer when dried is 0.01 mm to 1 mm, preferably 0.04 mm to 0.2 mm. The ratio of the binder is preferably 1 to 1.5 mass%.

  Next, the coating layer is preferably dried at a temperature not higher than the temperature at which the thermal contraction of the central core material does not start. Drying may be performed using a fluidized bed or may be allowed to stand in a drying furnace. In addition, if the temperature is increased while the outer shell coating layer is still dry, the central core material rapidly contracts and cracks and the like are generated in the outer shell. Therefore, it is important that the outer shell coating layer is sufficiently dried.

(2) Thermal decomposition / vaporization step of central core material Next, the central core material is thermally decomposed / vaporized in a temperature range of 250 to 400 ° C. to eliminate the central core material. In this temperature range, the atmosphere of the heating furnace is the air or an inert gas atmosphere that does not contain a reducing gas so that the outer shell, which is the coating layer, is not reduced or sintered. If the reduction and sintering of the outer shell proceeds simultaneously with the thermal decomposition of the core, the pyrolysis gas of the core material is trapped in the shell and the shell may explode at that pressure, so the heating temperature should be as low as possible. Better. In this process, before the outer surface of the outer shell starts to sinter, the outer shell, which is the coating layer, will not crack, the outer shell will not explode, and no residue will remain in the center. It is necessary to dissipate gas.

  Therefore, after drying, the temperature is raised to 250 ° C., and then up to 400 ° C., for example, the temperature rise is interrupted in increments of 30 ° C. and maintained at that temperature for 10 minutes or more, or the temperature is maintained as high as possible. It is preferable that the thermal rate and the vaporization of the central core material are gradually advanced by slowing down the temperature rate to about 0.5 ° C./min to about 10 ° C./min.

  By this step, as shown in FIG. 2B, a hollow shell body with the remaining coating layer is obtained. FIG. 3 shows changes in diameter and weight when the foamed polymer is used alone and held at each heating temperature. According to this, melting of the foamed polymer starts at 100 ° C. or higher, and almost all of the polymer melts at around 200 ° C. Then, the vaporization starts at about 250 ° C. or more, and the vaporization is completed at about 400 ° C. Therefore, by selecting the central core material, a hollow shell body covered with the coating layer at 400 ° C. or lower can be obtained.

(3) Roasting step Next, the shell obtained in the above step is heated to a temperature range of 800 to 1100 ° C. in the air or in an oxidizing gas atmosphere, and further held if necessary (roasting treatment). This increases the strength of the shell and improves the shape retention. The shell from which the central core has disappeared by the pyrolysis / vaporization process is made of a thin film of metal oxide and has a very weak shape retention. Therefore, when this spherical shell is transported and loaded into the heating furnace for the subsequent reduction / sintering process, it can be damaged, broken or crushed to obtain a healthy metal sphere. This is not possible, and the yield (ratio of the number of healthy metal balls to the total number of metal balls) becomes low.

(4) Reduction / sintering process The shell after the roasting process was oxidized by raising the temperature to 1000 to 1300 ° C. in a reducing gas atmosphere containing hydrogen and / or carbon. Perform metal reduction. At the same time, the sintering of the metal particles proceeds, and the strength as a hollow metal body is imparted, and a hollow metal body excellent in impact force absorption is obtained.

As the reducing gas, generally known H ₂ , CO, CH _{4 and the} like can be considered. Further, the “coke oven gas” by-produced in the iron making process contains about 50 vol.% Of H ₂ and about 30 vol.% Of CH ₄ , and natural gas known as fuel contains CH 2 ₄ is 90 vol.%, H ₂ is included about 5 vol.%, propane, butane, etc. are also used as a reducing gas. The iron powder surface is covered with decomposed carbon, and the reduction also proceeds by carburizing inside. Furthermore, the decomposed H ₂ further accelerates the reduction. Practically, there is no need to use pure methane. Except for unnecessary components such as coke oven gas or CO ₂ in the coke oven gas, those with increased CH ₄ concentration can be used as reducing gas. . Moreover, if moisture or the like is contained in the reducing gas, there is a concern that reoxidation occurs immediately after the reduction, and it is preferable to supply a gas having a dew point of −20 ° C. or less.

  The reason why the lower limit of the reduction / sintering temperature is 1000 ° C. is that sufficient sintering strength cannot be obtained below that temperature, and the reason why the upper limit temperature is 1300 ° C. is higher than 1300 ° C. This is because the crystal grain size becomes too coarse and the strength of the sintered metal sphere, particularly the shock absorbing ability, is impaired.

(5) Phosphoric acid aqueous solution immersion step After the roasting step described in the above item 3, the dried spherical shell is immersed in an aqueous solution (for example, phosphoric acid aqueous solution) containing 0.1 to 1 mol / liter of phosphate ions. A stronger hollow iron sphere can be obtained by impregnating phosphorus into an unsintered hollow sphere, drying it, and reducing and sintering it. This is because, in the sintering process after the reduction, phosphorus reacts with iron to generate a low melting point compound and promotes sintering by the appearing liquid phase.

  In particular, by combining with a roasting step, it is possible to promote the penetration of phosphorus into the unsintered hollow sphere, which is very efficient. An unsintered hollow sphere that has not been roasted has poor wettability, hardly penetrates the aqueous solution containing phosphate ions, and it is difficult to uniformly add phosphorus. When the concentration of phosphate ions is less than 0.1 mol / liter, the concentration of phosphorus is too small and there is no effect of adding phosphorus. On the other hand, when the concentration of phosphate ions exceeds 1 mol / liter, the concentration of phosphorus becomes too high and the strength of the reduced hollow iron sphere becomes too high and becomes brittle, which is not practical. Instead of the aqueous phosphoric acid solution, an aqueous solution of potassium phosphate or sodium phosphate may be used.

2. The purity of the raw material iron powder, the particle size for the raw material iron powder in Fe content 98Mass% or more, the total content of Fe ₂ O ₃ or Fe ₃ O ₄ in the iron oxide powder is 98Mass% or more, of the alloy steel oxide powder in When the total of Fe and the oxide powder of the alloy component is 98 mass% or more, since there are few impurity components, sintering becomes stronger and high hollow metal sphere strength is obtained. The reason why the specific surface area diameter is 1.0 μm is to obtain higher sintering strength, and more preferably 0.8 μm or less.

3. Reasons for limiting component composition Reasons for limiting the amount of sintering aid added to the raw material powder will be described below. Mass% represents mass% of each element in the completed hollow metal body.

P: 0.01-1 mass%
The reason why the lower limit is set to 0.01 mass% is that if it is less than 0.01 mass%, the effect of promoting the sintering cannot be obtained, and the reason why the upper limit is set to 1 mass% is to add more than 1 mass%. This is because not only the effect of promoting the sintering is saturated but also the sintered body becomes too hard and brittle. In addition, the phosphorus concentration in the hollow metal sphere that has undergone the step of immersing in an aqueous solution containing phosphate ions as described in claim 2 is the phosphorus added to the powder and the phosphorus absorbed from the phosphate ion aqueous solution. Needless to say, it refers to the total concentration.

Cu: 0.5-5 mass%
The reason why the lower limit is set to 0.05 mass% is that the effect of promoting the sintering cannot be obtained if it is less than 0.5 mass%, and the reason why the upper limit is set to 5 mass% is to add more than 5 mass%. This is because the sintering promoting effect is saturated.

Ni: 0.2-10 mass%
The reason why the lower limit is set to 0.05 mass% is that if it is less than 0.2 mass%, the effect of promoting the sintering cannot be obtained, and the reason why the upper limit is set to 10 mass% is to add more than 10 mass%. This is because the sintering promoting effect is saturated.

Mo: 0.2-10 mass%
The reason why the lower limit is set to 0.2 mass% is that an effect of promoting sintering cannot be obtained if it is less than 0.2 mass%, and the reason why the upper limit is set to 10 mass% is to add more than 10 mass%. This is because the sintering promoting effect is saturated.

4). About the porosity of a sintered layer The reason for setting the porosity of a sintered layer to 10 vol.% Or less is described below.

  The porosity affects the mechanical properties of the molded body, particularly the strength and impact absorption capacity. If the porosity exceeds 10%, the strength and impact absorption capacity deteriorate significantly, so the lower limit of the porosity is 10%. It was as follows. More preferably, the content is 5% or less. In this range, the mechanical properties are further improved, and when the porosity is 2% or less, the mechanical properties are almost saturated.

Using 200 g of iron oxide (Fe ₂ O ₃ ) having a purity of 99.5 mass% and a specific surface area of 0.7 μm as a raw material, about 1 mass% of a commercially available detergent is used as a surfactant in 50 g of 5 mass% polyvinyl alcohol (PVA) aqueous solution. Used, in a Henschel mixer, foamed polystyrene (central core material) having a diameter of 5 mm was mixed, and the surface of the foamed polystyrene was coated with iron oxide powder. This was first pre-dried at 60 ° C. in the atmosphere, and further heated to 120 ° C. to perform main drying. By doing this, bumping due to rapid heating of moisture in the binder from the iron oxide powder layer formed on the outer shell was prevented, and cracking of the outer shell was prevented.

  Subsequently, the temperature was raised at 5 ° C./min in the atmosphere, and the temperature was maintained at 280 ° C., 330 ° C., 360 ° C., and 400 ° C. for 30 minutes each, and the internal polystyrene was pyrolyzed and vaporized. Subsequently, in the same furnace, the temperature was raised to a predetermined roasting temperature (700 ° C., 850 ° C., 1000 ° C.) shown in Table 1 at a heating rate of 5 ° C./min in the atmosphere, and after holding for 1 hour, Cooled down. The shell (unreduced hollow body) obtained by heating at 850 ° C. and 1000 ° C., which are the temperature ranges of the present invention, is treated without causing explosions and almost no cracks or defects. Was able to finish. Incidentally, in the case of heating from room temperature to 700 ° C. at a rate of 5 ° C./min, cracks and explosions occurred and a hollow body with a good shape could not be obtained.

Next, 50 vol.% H ₂ is added to N ₂ and the shell is heated to the predetermined reduction and sintering temperatures shown in Table 1 (850 ° C., 1100 ° C., 1450 ° C.) and held at that temperature for 1 hour. Then, H ₂ was stopped and only N ₂ was supplied to perform furnace cooling. When the temperature dropped to room temperature, the sample was taken out of the furnace and subjected to the following evaluation tests. 30 balls were selected at random, and the number of each was measured by dividing into broken, cracked, and healthy spheres, and the non-defective product rate = (number of healthy spheres) ÷ 30. Those that were not subjected to roasting after pyrolysis and vaporization of the central core material were significantly cracked and damaged, and the yield rate was low.

In addition, for each condition, the porosity of the sintered layer was measured by the area method for 5 balls selected at random separately using an image analyzer attached to the optical microscope. Furthermore, the crushing load of 10 single particles selected at random was measured with a compression tester. It can be seen that the production conditions within the scope of the present invention have a low porosity and a high crushing load.
The test results in Example 1 are shown in Table 1.

  In the thermal decomposition / vaporization process, in No. 1-7 held at 500 ° C. × 1 Hr, which is outside the scope of the present invention, the coating layer is cracked or explosive, and a spherical shell can be obtained. was difficult. On the other hand, in No. 1-1 to No. 1-6 which were pyrolyzed in the temperature range of the present invention, shell bodies having a good appearance shape were obtained.

  Next, No. 1-2 to No. 1-6 from which shells having a good appearance were obtained were subjected to roasting treatment at temperatures of 700 ° C., 850 ° C. and 1000 ° C. shown in Table 1, and then , 850 ° C., 1100 ° C., and 1450 ° C. were subjected to reduction and sintering treatments. In order to confirm the effect of the roasting treatment and the effect of the reduction / sintering temperature, the one not subjected to the roasting treatment (No. 1-1), the one subjected to the reduction / sintering treatment at 1450 ° C. (No 0.1-6) was used as a comparative material.

  No. 1-1 was subjected to reduction / sintering treatment without performing the roasting treatment, and the crushing load of the healthy hollow metal sphere was not different from that subjected to the roasting treatment. However, the non-defective product rate was extremely low as compared with the examples of the present invention. No. 1-2, which was roasted at 700 ° C. outside the scope of the present invention, obtained a crushing load equivalent to that of the present invention example as in No. 1-1, but the yield rate was good. Similar to No. 1-1, it is low and practically problematic.

  No.1-4 and No.1-5, which were subjected to pyrolysis / vaporization treatment, roasting treatment, and reduction / sintering treatment under the conditions of the present invention, gave good values for both the yield rate and crushing load. The effectiveness of the present invention has been demonstrated. No. 1-3 whose reduction / sintering temperature is 850 ° C. below the lower limit of the scope of the present invention and No. 1-6 which is 1450 ° C. exceeding the upper limit of the scope of the present invention are both non-defective. Although not different from the invention example, the crushing load is lower than that of the invention example. As a result of microstructural observation, it was considered that the former was due to incomplete sintering and a large number of voids remaining, and the latter was due to coarsening of the microstructure due to high-temperature sintering. No. 1-4 and No. 1-5, which are in the range of the present invention having a sintering temperature of 800 ° C. to 1100 ° C., have a non-defective rate of 97% and a crushing load of 88 to 98 N (9 to 10 kgf). It was in the range, and sufficient strength was obtained as a shock absorber.

In Example 2, the purity of iron oxide (mixture of Fe ₂ O ₃ and Fe ₃ O ₄ ) was shown in Example 1 using four kinds of powder raw materials having 99 mass%, 98 mass%, 97 mass%, and 95 mass%. By the test method, the influence of the purity of the iron oxide powder was examined. The specific surface area diameter was 0.7 μm in all cases. The roasting temperature is 900 ° C. and the reduction / sintering temperature is constant at 1100 ° C., so that the influence of these processing temperatures is excluded, and other test conditions are the same as those in Example 1.

  The result of the measurement of the crushing load was 93 N (9.5 kgf) at the purity of 99.5 mass% used in Example 1, whereas it was 89 N (9.1 kgf) at the purity of 99 mass% and the purity of 98 mass%. It was 75 N (7.6 kgf) at 84 N (8.6 kgf), purity 97 mass%, and 60 N (6.1 kgf) at purity 95 mass%.

  That is, when there are many impurity components, it turned out that sinterability worsens and the intensity | strength of a sintered compact tends to fall. It is considered that the impact absorbing material targeted by the present invention requires a crushing load of at least 78 N (8 kgf) or more, and the purity is preferably 98 mass% or more.

In Example 3, six types of powders having specific surface area diameters of iron oxide (Fe ₂ O ₃ ) powders of 0.7 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.5 μm, and 2.0 μm were used. The effect of powder particle size was investigated. The purity of the iron oxide (Fe ₂ O ₃ ) powder was 99.5 mass%, and comparison was made with hollow metal bodies that were roasted at 950 ° C. and reduced and sintered at 1100 ° C. As an evaluation index, the crushing load of monocytes was measured in order to see whether the sintering was sufficiently performed. When the specific surface area diameter is 0.7 μm, the crushing load is 93 N (9.5 kgf), when the specific surface area diameter is 0.9 μm, the crushing load is 83 N (8.5 kgf), and when the specific surface area diameter is 1.0 μm, the crushing load is 79 N (8 0.1 kgf), crushing load is 74 N (7.5 kgf) at a specific surface area diameter of 1.2 μm, crushing load is 68 N (6.9 kgf) at a specific surface area diameter of 1.5 μm, and crushing load at a specific surface area diameter of 2.0 μm. Was 60 N (6.1 kgf). It turns out that sintering is not progressing, so that a powder particle size is large. As described in Example 2, it is considered that the impact absorbing material targeted by the present invention requires a crushing load of at least 78 N (8 kgf) or more. Therefore, the specific surface area diameter is preferably 1.0 μm or less.

In Example 4, the influence of the sintering aid added to the powder raw material was examined using iron oxide (Fe ₂ O ₃ ) powder having a specific surface area diameter of 0.9 μm. The purity of Fe ₂ O ₃ was 99.4 mass%.

  The added sintering aid was ferroline powder, and the amount added was varied over five types, and the concentration of phosphorus in the obtained hollow metal body was analyzed. As a result, 0.005 mass%, 0.05 mass%, and 0.3 mass%, respectively. 0.8 mass% and 1.2 mass%. The roasting temperature is 900 ° C., the reduction / sintering temperature is constant at 1050 ° C., and other test conditions are the same as those in Example 1.

  As a result of measuring the crushing load, when the phosphorus concentration was 0.005 mass%, it was 81 N (8.3 kgf), whereas the phosphorus concentration was 0.05 mass%, 0.3 mass%, and 0.2%. In the case of 8 mass%, larger values of 86N (8.8 kgf), 93N (9.5 kgf), and 100N (10.2 kgf) were obtained, respectively, and it was confirmed that the sinterability was improved. When the phosphorus concentration was 1.2 mass%, the crushing load was 99 N (10.1 kgf), and the effect of adding phosphorus was saturated. As a result, it is understood that the addition amount of phosphorus is preferably 0.005 mass% or more and 1 mass% or less. Similarly, an improvement in the crushing load was recognized even in a sintered body to which a predetermined amount of copper oxide powder, nickel metal powder, and ferromolybdenum was added.

In Example 5, the influence of phosphorus addition by immersing in an aqueous phosphoric acid solution was examined. Using 200 g of iron oxide (Fe ₂ O ₃ ) having a purity of 99.5 mass% and a specific surface area of 0.7 μm as a raw material, predrying at 60 ° C. in the atmosphere, and further heating to 120 ° C. went. Subsequently, it was heated in the air at a heating rate of 5 ° C./min, and kept at 280 ° C., 330 ° C., 360 ° C., and 400 ° C. for 30 minutes each so that the internal polystyrene was thermally decomposed and vaporized. . In the same furnace, the temperature was raised to 900 ° C. at a temperature raising rate of 5 ° C./min in the atmosphere, held for 1 hour, and then cooled. This hollow body was immersed in a 5 mass% phosphoric acid aqueous solution for 1 minute, quickly pulled up, and dried at 60 ° C.

Next, the green hollow body is heated to N ₂ up to 50 vol.% Of H ₂ 1100 ° C. is a predetermined sintering temperature added, and held at that temperature for one hour, stopped then H _2, N ₂ Only the furnace was cooled. When it fell to room temperature, it removed from the furnace and measured the crushing load.
Table 2 shows the test results in Example 5.

After performing the roasting process which is an example of the present invention, it was immersed in a phosphoric acid aqueous solution and subjected to reduction / sintering treatment. No. 5-3 was No. 5 which was not immersed in phosphoric acid aqueous solution. A crushing load better than that of 5-4 was obtained. On the other hand, no. 5-1. In No. 5-2, the crushing load was No. 5 after roasting treatment even when immersed in a phosphoric acid aqueous solution (No. 5-2). The value was lower than 5-4.

  Various metal powders and powder metal hollow metal bodies can be produced by the production method of the present invention, and the obtained hollow metal bodies can be used as shock absorbing materials for automobiles and the like. It can also be used as a vibration absorbing material for various sports equipment such as golf clubs and softball bats, and as a sound absorbing material for railway vehicles.

It is a flowchart explaining a manufacturing process. It is explanatory drawing which shows the production | generation process of a hollow metal body, (a) is a figure which shows the state which coat | covered the metal powder on the outer surface of a central core, (b) is a figure which shows the outer shell after thermal decomposition of a central core, (C) is a figure which shows the hollow metal body after this sintering. It is a figure explaining a diameter change and a weight change when a foamed polymer is heated.

Explanation of symbols

1 Core material 2 Metal powder / binder layer 3 Pre-sintered layer 4 Cavity 5 Sintered layer

Claims (6)

A method for producing a hollow metal body made of sintered metal,
After coating a solution containing a metal oxide powder raw material and a binder on the outer surface of the central core material, and drying, a coating layer of the powder raw material is formed on the outer surface of the central core material And the core material having the coating layer of the powder raw material is heated in the temperature range of 250 to 400 ° C. in the atmosphere or in an inert gas atmosphere not containing a reducing gas, Pyrolysis / vaporization process of the central core material to obtain a hollow shell body by the remaining coating layer that has disappeared by pyrolysis / vaporization, and the shell body obtained by the pyrolysis / vaporization process in the atmosphere or oxidation Roasting step of heating in a temperature range of 800 to 1100 ° C. in a reactive gas atmosphere, and the shell subjected to the roasting step in a reducing gas atmosphere containing hydrogen and / or carbon at 1000 to 1300 ° C. Reduce and sinter by heating in the temperature range A method for producing a hollow metal body comprising a reduction / sintering step. A method for producing a hollow metal body made of sintered metal,
After coating a solution containing a metal oxide powder raw material and a binder on the outer surface of the central core material, and drying, a coating layer of the powder raw material is formed on the outer surface of the central core material And the core material having the coating layer of the powder raw material is heated in the temperature range of 250 to 400 ° C. in the atmosphere or in an inert gas atmosphere not containing a reducing gas, Pyrolysis / vaporization process of the central core material to obtain a hollow shell body by the remaining coating layer that has disappeared by pyrolysis / vaporization, and the shell body obtained by the pyrolysis / vaporization process in the atmosphere or oxidation A roasting step of heating in a temperature range of 800 to 1100 ° C. in a reactive gas atmosphere, and immersing the shell obtained in the roasting step in an aqueous solution containing 0.1 to 1 mol / liter of phosphate ions And then dipping and drying steps to dry, and the soaking -It has a reduction / sintering step of heating and reducing / sintering the shell obtained in the drying step in a reducing gas atmosphere containing hydrogen and / or carbon in a temperature range of 1000 to 1300 ° C. A method for producing a hollow metal body. The powder raw material is composed of one or more of Fe ₂ O ₃ or Fe ₃ O ₄ , and the total content thereof is 98 mass% or more, or the total of Fe and alloy component oxide powder is 98 mass. 3. The method for producing a hollow metal body according to claim 1, comprising at least one powder selected from alloy steel oxide powders of at least%.   The method for producing a hollow metal body according to any one of claims 1 to 3, wherein the powder material has a specific surface area of 1.0 µm or less.   The powder raw material is iron oxide powder and / or alloy steel oxide powder, copper powder, nickel powder, phosphorus powder, copper oxide powder, nickel oxide powder, phosphorus pentoxide powder, ferrocopper powder, ferronickel powder, ferroline powder The method for producing a hollow metal body according to any one of claims 1 to 4, wherein the hollow metal body is composed of one or more powders selected from molybdenum powder and molybdenum trioxide powder.   The component composition of the hollow metal body is mass%, selected from P: 0.01 to 1%, Cu: 0.5 to 5%, Ni: 0.2 to 10%, and Mo: 0.2 to 10%. 1 or 2 or more types, the balance is iron and inevitable impurities, and the porosity of the sintered layer of the hollow metal body is 10 vol.% Or less. The manufacturing method of the hollow metal body in any one.

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