KR101223750B1 - Hollow parts and method for preparing the same - Google Patents

Abstract

Method for producing a hollow part of the present invention is to install the core for inserting the core, powder injection molding, degreasing, sintered hollow structure in the mold; Injecting the feedstock mixed with the raw material powder and the binder into the mold to produce a molded body with the core inserted therein; Contacting the molded body with an acid to remove the core; And degreasing and sintering the molded body from which the core is removed, and the binder may include a polyacetal-containing composite resin, paraffin wax, carnauba wax, amorphous polyalphaolefin, and propylene-based polymer. . The method can be applied to manufacturing a product having a through hole or a closed hole, especially a hole having an undercut or a radius of curvature, a hole having an irregular shape, and which cannot be manufactured by general machining. .

Description

Hollow Parts and Manufacturing Method {HOLLOW PARTS AND METHOD FOR PREPARING THE SAME}

The present invention relates to a method for producing a hollow part having an internal shape. More specifically, the present invention relates to a component having a through hole or a closed hole having a curvature or irregular shape therein and a method of manufacturing the same.

In the case of Elbow parts used as joints in the tubular structure, it is necessary to give a smooth curvature inside to smooth the flow of the fluid. However, it is only possible to have a right angle or a specific angle through mechanical machining in the manufacture of such parts, and it is impossible to smooth the curvature of the encountering part. Therefore, the flow of the fluid is rapidly changed and has been a problem such as being subjected to flow resistance or turbulence.

In addition, in the case of parts such as fuel injection nozzles, holes of 0.1 to 0.2 mm exist at an angle, which are usually manufactured through processing using Fine Drill. However, due to the limitation of the drilling process, the diameter is limited to about 0.08mm, the diameter of the hole is so small that the drill is easily broken, and there is a problem that it is not easy to process while giving various angles in the product. Recently, various studies have been conducted to improve fuel efficiency and reduce exhaust gas by controlling the amount of fuel injected into the combustion chamber, but since the manufacturing process depends on precision processing, the manufacturing cost is high and the size and direction of the hole (angle There is also a technical limitation in controlling).

In order to solve the above problem, a bending processing method has been proposed. However, there is a problem in that the bending of the cross-section thickness is reduced by plastic working, and in the case of a high-strength material, there is a problem that the tube bursts during bending due to the deterioration of formability. Moreover, the manufacture of hollow articles with irregularly shaped through holes or in particular closed internal structures was almost impossible.

Although some methods, such as disappearing molds, are applied through casting methods such as precision casting, there are problems in productivity due to complicated process steps.

On the other hand, relatively recently commercially available powder injection molding methods use an organic binder as a carrier and prepare a feedstock having fluidity capable of injection molding by mixing metal or ceramic powder, and using it as a raw material for injection molding. Therefore, since sufficient fluidity is provided by the organic binder, it is possible to manufacture a product having a complicated shape by applying injection molding. In addition, a hollow product can be manufactured by installing an insert core made of a polymer material which can be subsequently removed in the injection molding step into a mold, and then injection molding the outer surface with a feedstock and then removing it in a debinding process. have.

 Conventionally, a solvent extraction method using an organic solvent, a method of removing in a sintering process, a method of removing by heating, and the like have been proposed as the process of removing the core.

However, when removing the core by the above method, there is a problem that the surface characteristics such as wrinkles are observed on the surface of the penetrating portion, there is a problem that causes many problems in the dimensional control.

It is an object of the present invention to provide a hollow component having various shapes therein-having a gentle curvature or even an undercut shape-and a method of manufacturing the same.

Another object of the present invention is to provide a hollow part having a through hole and a closed hole therein and a method of manufacturing the same.

Still another object of the present invention is to provide a method for manufacturing a hollow part, which is advantageous in terms of processing time and energy.

Still another object of the present invention is to provide a method for manufacturing a hollow part having excellent surface properties.

Still another object of the present invention is to provide a method of manufacturing a hollow component in which a slumping phenomenon does not occur during a degreasing process.

Technical problems to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

One aspect of the invention relates to a method of manufacturing a hollow part. The method includes installing a core for forming a hollow structure in a mold; Injecting the feedstock mixed with the raw material powder and the binder into the mold to produce a molded body with the core inserted therein; Contacting the molded body with an acid to remove the core; And degreasing and sintering the molded body from which the core is removed, and the binder may include a polyacetal-containing composite resin, paraffin wax, carnauba wax, amorphous polyalphaolefin, and propylene-based polymer. .

The core may be one that is a resin molded product decomposable to an acid.

In an embodiment, the resin molded body may include polyacetal (POM).

The feedstock may have a solid phase of 40 to 70%.

The feedstock may be 50 to 70% by volume of the raw powder.

The raw material powder may have an average particle size of 0.5 to 30 ㎛.

The raw powder may be a ceramic powder, a metal powder or a mixture thereof.

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In an embodiment, the binder is 10 to 50% by weight of a composite resin containing polyacetal, 20 to 60% by weight of paraffin wax, 1 to 20% by weight of carnauba wax, 1 to 20% by weight of amorphous polyalphaolefin and propylene polymer It may include 10 to 30% by weight.

The composite resin containing polyacetal may include polyacetal, linear low density polyethylene, and styrene resin.

The acid may be selected from one or more of the group consisting of sulfuric acid, nitric acid, hydrochloric acid, oxalic acid and phosphoric acid.

In embodiments, the core may be removed by maintaining the temperature in the temperature range of 100-150 ° C. for 1 to 24 hours in an acid atmosphere.

In embodiments, the binder may be sintered after removing the binder from the molded body from which the core is removed.

Another aspect of the invention relates to a hollow part produced by the method. The hollow part has a hollow surface roughness Rmax in the range of 1 to 10 s, preferably 3 to 7 s.

The hollow part is not particularly limited and may have a hollow shape having various shapes therein, such as an elbow for connecting a tube, a fuel injection nozzle for automobiles, various valves, a liner motion guide having various flow paths therein, or various hydraulic parts. It may have a gentle curvature or even have an undercut shape.

The present invention can provide a component having a structure of a through hole or a closed hole therein, which has a free curvature or irregular shape, which cannot be manufactured by conventional machining, and is advantageous in terms of processing time and energy. The present invention has the effect of providing a method for producing a hollow part having excellent surface properties and no slumping phenomenon during the degreasing process.

1 is a schematic process diagram of the present invention.
2 is a photograph of the insertion center used in Example 1. FIG.
3 shows a heating schedule of Example 1. FIG.
Figure 4 shows a photograph of the hollow part produced in Example 1.
Figure 5 shows the internal cross-sectional shape photograph of the hollow part produced in Example 1.
Figure 6 shows the internal cross-sectional shape picture of the hollow part produced in Comparative Example 1.
Figure 7 shows the shape of the core used in Example 2.
8 shows a heating schedule of Example 2. FIG.
9 is a photograph showing a cross-sectional view and an appearance of a fuel injection nozzle manufactured in Example 2. FIG.

The hollow component of the present invention is a powder injection molding to which metal or ceramic powder is applied, and is characterized by containing a through-hole or a closed hole having a curved surface or a free shape therein.

1 is a schematic process diagram of the present invention.

In the manufacturing method of the hollow part, a core for forming a hollow structure is installed in a mold, a feedstock including a raw material powder and a binder is introduced into the mold to prepare a molded body having a core inserted therein, and the molded body Contacting the acid to remove the core, and sintering the molded body from which the core has been removed.

In mold  Middle character installation

Mold apparatus that can be applied in the present invention can be applied to all the powder injection molding machine for a general hollow product, there is no particular limitation.

The core is a molded body for forming a hollow shape in the hollow part of the present invention and is referred to as a core or an insert core.

In the present invention, since the core is removed by an acid, a resin capable of decomposing in the acid may be used for the core material.

In the present invention, as the resin, a resin containing polyacetal (POM) may be preferably applied. Polyacetal (POM) has high mechanical strength and elastic modulus, high creep resistance, good elastic recovery, good fatigue resistance, good resistance to shock and vibration, self-lubrication and excellent friction resistance, and surface hardness High and excellent, chemical resistance, practical in a wide range of temperature, little influence of humidity and moisture, heat resistance, high dimensional stability and excellent molding processability, high degreasing rate and post ash decomposition There is an advantage that (Ash) does not remain.

The polyacetal may be used oxymethylene homopolymer, oxymethylene copolymer or a mixture thereof. In embodiments, the polyacetal may contain oxymethylene units and oxyalkylene units having 2 to 8 carbon atoms. In embodiments, the polyacetal may include 60 to 100 wt% of oxymethylene units and 0 to 40 wt% of oxyalkylene units having 2 to 8 carbon atoms. Preferably 75 to 95% by weight of oxymethylene units and 5 to 25% by weight of oxyalkylene units having 2 to 8 carbon atoms.

The polyacetal can be prepared by a known production method. In one embodiment, the oxymethylene homopolymer may be prepared by adding anhydrous formaldehyde to an organic solvent containing a basic polymerization catalyst such as an organic amine, and stabilizing the polymer obtained by acetylating an acetic anhydride, for example. Can be. The oxymethylene copolymer can also be directly polymerized with trioxane anhydride and a copolymerization component such as ethylene oxide or 1,3-dioxolane or a Lewis acid catalyst such as boron trifluoride in a solvent such as cyclohexane or benzene. It can be prepared by polymerization and decomposition using diethyl etherate followed by removal of unstable ends with a basic compound.

In another embodiment, one kind of thermoplastic resin, such as polyethylene (PE), polypropylene (PP), polystyrene (PS), polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), and polycarbonate (PC) together with the polyacetal (POM) It can be used by mixing the above.

The method of forming the core is not particularly limited, and all methods such as extrusion molding, injection molding and blow molding may be applied. Among these, injection molding is preferable.

Feedstock  Input and Molded body  Produce

The feedstock is a mixture of the raw material powder and the binder, any feedstock for powder injection can be applied.

The raw material powder may be a ceramic powder, a metal powder or a mixture thereof.

The raw material powder may have an average particle size of 0.5 to 30 ㎛, preferably 1 to 20 ㎛, more preferably 5 to 15 ㎛. When the feedstock manufactured using the powder in the above range is used, it provides excellent fluidity during injection molding, and has excellent injection property and high sinterability due to high specific surface area, thereby facilitating densification during sintering and high sintering by pure densification. There is an advantage that it is possible to manufacture a sintered body having a density.

In preparing the feedstock, it is advantageous to increase the volume ratio (solid phase ratio) between the alloy powder and the organic binder as long as the fluidity required for injection molding is ensured. The reason is that it can promote sinterability by increasing the contact frequency between alloy powders, and above all, the addition amount of organic binder can be reduced, which can shorten the degreasing process and lower the defect rate during degreasing process, which is advantageous for producing a healthy sintered body. Because. The solid phase ratio suitable for the present invention may vary depending on the shape of the alloy powder, the average particle size, the particle size distribution and the viscosity of the organic binder. In a specific embodiment, the solid phase rate of the feedstock may be prepared in a state in which the volume of the alloy powder is about 5% to 10% lower than the solid phase rate corresponding to the tap density of the alloy powder, thereby securing fluidity required in injection molding. In another embodiment, the solid phase rate is 40 to 70%, preferably 50 to 65%. If the solidity rate is excessively high, the fluidity decreases due to the high viscosity, and the injection property is drastically decreased. On the other hand, if the solidity rate is too low, the strength of the injection molded product is reduced due to the excessively added organic binder, resulting in shape deformation or injection molding. The extra binder separates the metal powder particles to form a non-uniform injection molded part, which may cause problems in dimensional control. In addition, the gap between the alloy powders is increased due to the excess organic binder, so the slumping phenomenon may occur because the body is not able to withstand its own weight during the degreasing process. Furthermore, excessively long degreasing time causes a problem that productivity is lowered. In addition, during the sintering process, the shrinkage rate increases, which greatly deviates from the expected shrinkage rate during mold design, which causes many problems in dimensional control.

In embodiments, the feedstock may be 50 to 70% by volume of the raw powder.

In one embodiment, the raw powder is a metal powder, chromium 10-40% by weight, nickel 10-40% by weight, niobium 0.01-7% by weight, carbon 0.1-1.2% by weight, hafnium, titanium, molybdenum, vanadium , Tungsten and zirconium may contain 0.2 to 5% by weight of at least one metal selected from the group consisting of, the remainder may be made of iron. In the case of the composition may have excellent heat resistance.

In another embodiment, the raw powder is a metal powder, chromium 10-40% by weight, nickel 10-40% by weight, molybdenum 0.2-5% by weight, silicon 0.01-2% by weight, manganese 0.01-2% by weight, copper 0.005 to 0.5% by weight of carbon, 0.005 to 0.3% by weight of carbon, phosphorus, sulfur, and at least one selected from 0.001 to 0.05% by weight of metal, the remainder may be made of iron.

In another embodiment, the raw material powder is a metal powder, nickel 45-80% by weight, chromium 5-20% by weight, aluminum 1-10% by weight, molybdenum 1-7% by weight, niobium 0.01-5% by weight 0.1 to 2% by weight of titanium, 0.05 to 1% by weight of oxygen, 0.05 to 1% by weight of carbon, 0.05 to 1% by weight of zirconium, and 0.001 to 0.05% by weight of boron. It may have excellent heat resistance in the composition.

The metal or ceramic powder is kneaded with a binder, made into a feedstock, and then injection molded.

In embodiments, the binder may be a conventional thermoplastic organic binder capable of powder injection molding. Although not particularly limited in the present invention, a wax-based organic binder may be preferably used.

In one embodiment, the binder may comprise a composite resin containing polyacetal, paraffin wax, carnauba wax, amorphous polyalphaolefin and propylene-based polymer.

Preferably, the binder is 10 to 50% by weight of a composite resin containing polyacetal, 20 to 60% by weight of paraffin wax, 1 to 20% by weight of carnauba wax, 1 to 20% by weight of amorphous polyalphaolefin and propylene polymer 10 To 30% by weight. Higher compatibility with the raw material powder in the composition can significantly reduce the incidence of defects, it is possible to produce a healthy injection molded body of precise shape and to obtain a good degreasing effect in the subsequent process, high temperature acid during the core removal process The effect of preventing the corrosion of the metal powder is excellent.

The composite resin may include polyacetal, linear low density polyethylene, and styrene resin. In an embodiment, the composite resin may include 30 to 80 wt% of polyacetal, 10 to 60 wt% of linear low density polyethylene, and 1 to 30 wt% of styrene resin. Preferably, the composite resin may include 40 to 70% by weight of polyacetal, 20 to 40% by weight of linear low density polyethylene, and 5 to 20% by weight of styrene resin. Excellent injection property in the above range does not occur heat deformation during degreasing.

The linear low density polyethylene (hereinafter referred to as LLDPE) may have a density of 0.913 to 0.923 g / cm 3.

The styrene-based resin is a polymer containing styrene in the main chain, polystyrene, styrene-acrylonitrile copolymer, styrene- (meth) acrylate copolymer may be used. Of these, polystyrene (GPPS) may be preferably used, which has a high pyrolysis temperature and excellent thermal stability and meltability during dissolution.

The main component of the paraffin wax is composed of linear paraffinic hydrocarbons CH ₃ (CH ₂ ) _n CH ₃ , and the number of carbon atoms is distributed in 16 to 40, especially those of 20 to 30 can be preferably used.

The carnauba wax may include 80 to 85% by weight of fatty acid ester, 10 to 16% by weight of fatty alcohol, 3 to 6% by weight of fatty acid, and 1 to 3% by weight of hydrocarbon. The carnauba wax may have a melting point of 60 to 90 ° C., preferably 80 to 90 ° C.

The amorphous polyalphaolefin (hereinafter, Amorphous Poly-alpha-olefin, APAO) is substantially amorphous and does not have crystallinity. The amorphous polyalphaolefin may include a polymer of ethylene, propylene and butene or a copolymer thereof or a mixture thereof. Embodiments may include APP (amorphous polypropylene) and amorphous butene polymer, and mixtures thereof may also be used. The amorphous polyalphaolefin may have a melt viscosity of 300 to 30,000 cP at 190 ° C. and a number average molecular weight of 1,000 to 30,000. In other embodiments, softening points of 100 to 170 ° C. may be used. The APAO can be prepared by polymerizing α olefins using a Ziegler-Natta catalyst.

The propylene polymer may include isotactic propylene homo polymers, ethylene-propylene blocks or random copolymers, rubber modified polypropylenes, or mixtures thereof. The rubber-modified polypropylene is a polypropylene modified with rubber such as ethylene propylene rubber (EPR) containing a olefin component, EPDM, branched olefin rubber EOR, EBR, and block copolymer type olephine rubber. The propylene-based polymer may have a melt index (MI) of 1 to 20 g / 10 minutes (ASTM D1238, 230 ° C.). When using a polypropylene having the above range, it can have excellent injection workability.

In a specific embodiment, the kneading of the raw material powder and the binder may be kneaded at 120 ° C. to 190 ° C. for 1 hour to 6 hours to prepare a feed stock.

In order to prepare the feedstock, a feedstock for metal injection molding is commonly used, such as a double planetary mixer, a twin screw mixer, a twin cam kneader, and a kneader extruder. Any kind of kneader used in the production may be used. The feedstock prepared in this way may be used in the form of granules uniformly to have a size of about 5mm diameter using an extruder or the like, or may be used in the form of granules using a crusher after hardening into a block.

The feedstock prepared by kneading the ceramic or metal powder and the binder may be charged into an injection molding machine and then injected at an injection temperature of 130 to 180 ° C., preferably 140 to 170 ° C., thereby producing a molded article having a desired part shape. . At this time, the injection pressure may be prepared under the conditions of 2 to 30 MPa, holding pressure 0.5 to 10 MPa.

Core removal

The injection molded body has a middle core inserted therein and may remove the inserted middle core through a middle core removing process. Conventionally, in the removal of the core, a solvent extraction using an organic solvent such as hexane or heptane, a method of heating and removing in an inert gas, etc. have been used.

In the present invention, the binder component in the feedstock may also be removed by the catalyst extraction method using an acid and the sintering process may be immediately performed.

In embodiments, the core may be removed by contacting an acid with a powder-injected molded body having a core inserted therein.

In embodiments, the core may be removed by maintaining the temperature in the temperature range of 100-150 ° C. for 1 to 24 hours in an acid atmosphere. In a preferred embodiment, the core can flow nitrogen together while maintaining a temperature of 100 ° C.-130 ° C. to vaporize 98% nitric acid in the Oven, so that the insertion cores present in the product can be easily decomposed.

That is, the POM (Polyacetal), which is included as a component of the core, is disconnected from the CO by the heated acid to form HCHO, and the HCHO may be decomposed into CO ₂ or H ₂ O.

In addition, POM (Polyacetal) is also included in the binder included in the feedstock, which is advantageous when the degreasing and sintering processes are shortened after being decomposed and removed together during the insertion core removal.

The acid may be selected from one or more of the group consisting of sulfuric acid, nitric acid, hydrochloric acid, oxalic acid and phosphoric acid. Preferably nitric acid can be applied.

Degreasing and Sintering

The molded body from which the core is removed may remove the organic binder component through a degreasing process. In addition, the degreasing process may be carried out in a single heating process continuously with the sintering process.

The organic binder component may be removed by a solvent extraction method using a hexane or heptane solvent, a vacuum degreasing technique in which the carrier gas is degassed while heating in a vacuum, or the organic binder component is evaporated by heating while flowing in an inert gas nitrogen or argon gas. Or it can be carried out by applying a variety of known degreasing process, such as heating degreasing method to remove by decomposition (degradation). The degreasing process is a process that requires special attention to shape retention as the binder in the injection molded product is pulled out. Therefore, the degreasing process should be carefully scheduled in consideration of the characteristics of the thermoplastic binder and the metal powder characteristics. If the degreasing process is not completed before sintering, the binder filled with 30 to 50% by volume of the feedstock is easily pulled out and defects easily occur in the weakened molded body. Degreasing is one of the very difficult techniques, as it must go through several very delicate steps to get out.

In one embodiment of the invention the degreasing can be degreased by heating under an inert gas. Preferably, it can be degreased by heating while flowing nitrogen gas or argon gas up to 900 degreeC.

In addition, when the core contains other thermoplastic resins such as PE (Polyethylene), PP (Polypropylene), PS (Polystyrene), PMMA (Polymethyl methacrylate), TPU (Thermo-plastic Polyurethane), and PC (Polycarbonate), The 700 ° C. section may be removed during the heating in an inert gas atmosphere at a heating rate of 0.1-1 ° C./min.

The molded product that has been subjected to the degreasing step is subjected to a sintering step. In embodiments, the sintering may be sintered at a temperature of 5 ° C. to 100 ° C., preferably 20 ° C. to 80 ° C., lower than the liquidus temperature of the metal or ceramic powder.

In one embodiment, the sintering may be performed at 1100 to 1500 ° C, preferably at 1200 to 1400 ° C, more preferably at 1250 to 1350 ° C for 1 to 4 hours, preferably 1.5 to 3.5 hours. In this range, it is possible to achieve a high density of 93 to 99% and preferably 95 to 99% of the relative density and excellent production capacity. In another embodiment, the sintering may be carried out by heating while initially maintaining a vacuum or low argon partial pressure at the sintering temperature. In a specific embodiment, the argon partial pressure may be sintered in a vacuum adjusted to a range of 0.5 to 50 torr, preferably 1 to 10 torr, and more preferably 2 to 5 torr.

In the present invention, the density of the sintered compact can be increased by suitably controlling the atmosphere gas during the sintering step.

The hollow part that can be applied in the present invention is not particularly limited, and may have a hollow shape having various shapes therein, and may have a smooth curvature or even an undercut shape. For example, elbows for connecting tubes, fuel injection nozzles for automobiles having fine holes, various valves, liner motion guides having complicated flow paths, and various hydraulic components can be manufactured.

In addition, the hollow part of the present invention has a smooth surface with a surface roughness Rmax of the hollow part in the range of 1 to 10 s, preferably 3 to 7 s. Rmax is the difference between the maximum peak and the lowest valley.

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.

Example 1

The injection core having the shape of FIG. 2 was injection molded using a POM (Polyacetal) pellet and mounted on a pre-fabricated injection molding die. The feedstock prepared by the following method was introduced into the mold.

Feedstock manufacturing

As shown in Table 1, a stainless steel alloy powder having a SUS316L composition, a spherical shape, and having an average particle size of 8 µm was used as a raw material, paraffin wax 35%, carnauba wax 5%, and polyalphaolefin (amorphous) 10%. The feedstock was prepared by pressure kneading at 160 DEG C using a wax-based thermoplastic organic binder having a composition of 20% propylene polymer and 30% polyacetal-containing composite resin. The solid phase rate was 63% at this time. The prepared feedstock was crushed into granules using a crusher and then charged into an injection molding machine to perform powder injection molding.

Ingredient, weight percent C Si Mn P S Ni Cr Mo Cu Fe 0.026 0.77 0.79 0.016 0.008 12.55 16.45 2.10 0.04 bal

The injection molded product prepared in the above process was charged to Oven, and 10 g / min of nitrogen gas was injected, while 0.7 g / min of purity 98% nitric acid was injected to remove the core inserted into the product. At this time, the atmosphere temperature is maintained at 130 ° C. for 5 hours. In this way, after removing the insertion core, the organic binder was removed by heating to 600 ° C. while adjusting the temperature increase rate according to the heating schedule shown in FIG. 3 so that defects such as swelling or cracking did not occur.

Subsequently, the degreasing body from which the organic binder was removed was heated to 1350 ° C., which is a sintering temperature, by the heating schedule of FIG. 3 to induce densification. At this time, heating was performed under a vacuum of 10 ⁻³ torr or less to promote sintering. Since sintering under high vacuum may cause excessive volatilization of the chromium component in the alloy component, argon gas was charged to maintain about 10 to 50 torr to prevent this. Thus, a high density sintered body having a density of 97.3% was produced. At this time, the player rate was 14.5%.

4 shows the shape of the sintered body which has been sintered by the above method. 5 is a photograph showing a cross section of the component, it can be seen that the through-hole with a gentle curvature was formed by completely removing the middle core. The surface roughness of the through hole was measured using a surface roughness measuring instrument (CD-120) manufactured by Mahr, and the measured Rmax was 6.3 s.

Comparative Example  One

The same procedure as in Example 1 was carried out except that the treatment for removing the insertion core with nitric acid was not performed. A cross-sectional photograph of the manufactured part is shown in FIG. 6. The surface roughness of the through hole was measured by using a surface roughness measuring instrument (CD-120) manufactured by Mahr, and the measured Rmax was 12.5 s.

For the parts manufactured in Example 1 and Comparative Example 1, the inside of the through hole was observed. In Example 1 (FIG. 5), the surface of the through hole was very smooth (Rmax: 6.3 s). In Fig. 6), it can be seen that the case of Example 1, in which some wrinkles are observed (Rmax: 12.5 s), is superior to the surface characteristics of the through-holes compared to Comparative Example 1.

Example  2

The injection core having the shape of FIG. 7 was injection molded using POM (Polyacetal) Pellet and mounted on a pre-fabricated injection molding die. The feedstock prepared by the following method was introduced into the mold.

Feedstock manufacturing

As shown in Table 2, a raw material of Inconel713 heat-resistant steel having a near-spherical shape and having an average particle size of 8 μm as a raw material, 35% paraffin wax, 5% carnauba wax, and 10% polyalphaolefin (amorphous) The feedstock was prepared by pressure kneading at 160 DEG C using a wax-based thermoplastic organic binder having a composition of 20% propylene polymer and 30% polyacetal-containing composite resin. At this time, the solid phase rate was 60%. The prepared feedstock was crushed into granules using a crusher and then charged into an injection molding machine to perform powder injection molding.

Ingredient, weight percent C O Cr Mo Al Ti B Zr Nb Ni 0.15 0.28 12.7 4.43 6.13 0.96 0.014 0.14 2.4 72.796

The injection molded product prepared in the above process was charged to Oven, and 10 g / min of nitrogen gas was injected, while 0.7 g / min of purity 98% nitric acid was injected to remove the core inserted into the product. At this time, the atmosphere temperature is maintained at 130 ° C. for 6 hours. In this way, after removing the insertion core, the organic binder was removed by heating to 600 ° C. while adjusting the temperature increase rate according to the heating schedule shown in FIG. 8 so as not to cause swelling or cracking.

Subsequently, the degreasing body from which the organic binder was removed was heated to 1300 ° C., which is a sintering temperature, by the heating schedule of FIG. 8 to induce densification. At this time, heating was performed under a vacuum of 10 ⁻³ torr or less to promote sintering. Since sintering under high vacuum may cause excessive volatilization of the chromium component in the alloy component, argon gas was charged to maintain about 10 to 50 torr to prevent this. Thus, a high density sintered body having a density of 96.5% was produced. At this time, the players' rate was 15.3%.

Fig. 9 shows the shape of the fuel injection nozzle which has been sintered by the above method and finished up to the outer surface processing.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings and the table, the present invention is not limited to the above embodiments, but may be manufactured in various forms, and common knowledge in the art to which the present invention pertains. Those skilled in the art can understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (14)

Installing a core for forming the hollow structure in the mold;
Injecting the feedstock mixed with the raw material powder and the binder into the mold to produce a molded body with the core inserted therein;
Contacting the molded body with an acid to remove the core; And
Degreasing and sintering the molded body from which the core is removed;
Including the steps,
The binder is a manufacturing method of a hollow component, characterized in that it comprises a polyacetal-containing composite resin, paraffin wax, carnauba wax, amorphous polyalphaolefin and propylene polymer.
The method for manufacturing a hollow part according to claim 1, wherein the core is a resin molded product decomposable to an acid.
3. The method of claim 2, wherein the resin molded body comprises polyacetal (POM).
The method of claim 1, wherein the feedstock has a solid phase of 40 to 70%.
The method of claim 1, wherein the feedstock is a raw material powder manufacturing method of the hollow component, characterized in that 50 to 70% by volume.
6. The method of claim 5, wherein the raw material powder has an average particle size of 0.5 to 30 ㎛.
The method of claim 1, wherein the raw material powder is a ceramic powder, a metal powder or a mixture thereof.
delete The method of claim 1, wherein the binder is 10 to 50% by weight of a composite resin containing polyacetal, 20 to 60% by weight of paraffin wax, 1 to 20% by weight of carnauba wax, 1 to 20% by weight of amorphous polyalphaolefin and propylene. Method for producing a hollow component, characterized in that it comprises 10 to 30% by weight of the polymer.
The method of claim 1, wherein the polyacetal-containing composite resin comprises polyacetal, linear low density polyethylene, and styrene resin.
The method of claim 1, wherein the acid is at least one selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, oxalic acid and phosphoric acid.
The method of claim 1, wherein the core is removed by maintaining for 1 to 24 hours in a temperature range of 100-150 ° C. in an acid atmosphere.
The hollow part manufactured by the method of any one of Claims 1-7 and 9-12.
The hollow component of claim 13, wherein the hollow component has a hollow surface roughness Rmax of 1 to 10 s.

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