Method for manufacturing high-toughness, high-strength silicon nitride balls

Abstract

The present invention relates to a method for manufacturing a silicon nitride ball with high toughness and high strength, and more specifically, to a method for manufacturing a silicon nitride ball as follows: the production output of the silicon nitride ball can be greatly improved, and the reaction between the silicon nitride ball and carbon can be controlled during sintering, so that the silicon nitride ball with high strength and high toughness can be manufactured.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a silicon nitride ball with high toughness and high strength, and more specifically, to a method for manufacturing a silicon nitride ball as follows: the production output of the silicon nitride ball can be greatly improved, and the reaction with carbon can be controlled during sintering, so that the silicon nitride ball with high strength and high toughness can be manufactured. Background Art

[0002] Ceramic materials are suitable for various machine parts due to their low density and thermal expansion coefficient, high hardness and excellent heat resistance.

[0003] Due to such characteristics, ceramics are widely used as a material for bearing balls used under severe conditions.

[0004] At present, most of the bearing balls used under acidic and alkaline conditions are ZrO2 series and Si3N4 series. As high-temperature and high-speed bearing balls, Si3N4 series or Al2O3 series with relatively low specific gravity are mainly used.

[0005] ZrO2, a general material for corrosion-resistant bearing balls, undergoes three types of crystal structure phase transitions (monoclinic → tetragonal → cubic) as the sintering temperature rises. When cooling after sintering, it also undergoes a phase transition from tetragonal to monoclinic. At this time, the sample is damaged by a volume expansion of about 4%, making it difficult to sinter alone.

[0006] Therefore, in order to improve sinterability, one selected from Y2O3, CeO2, and MgO is added to ZrO2 as a stabilizer. Here, when Y2O3 is added to ZrO2, although the mechanical properties are excellent, the corrosion resistance decreases, and it is mainly used in general wear-resistant products such as cutting tools (Cutter). When CeO2 or MgO is added, although the corrosion resistance is excellent, the mechanical properties are insufficient due to excessive grain growth. On the other hand, in the case of Al2O3, although it is an economical material with excellent hardness and corrosion resistance, its strength and wear resistance are lower than other ceramic materials Si3N4 and ZrO2, so it is difficult to use as a bearing ball. Summary of the invention

[0007] Technical issues

[0008] The present invention has been developed to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing a silicon nitride ball having high toughness and high strength for use as a bearing ball.

[0009] In addition, another object of the present invention is to provide a method for manufacturing silicon nitride balls that can significantly improve manufacturing yield.

[0010] Means of solving problems

[0011] In order to achieve the above-mentioned purpose, the present invention provides a method for manufacturing silicon nitride balls, characterized in that it includes the following steps: preparing silicon powder; adding a solvent and an organic binder to the above-mentioned silicon powder to form a slurry; thermally spray drying the above-mentioned slurry to produce particles (granules) with a specified particle size; press-molding the above-mentioned particles to produce silicon balls; so that the above-mentioned silicon balls are located in each hole of a soft porous foam; placing the porous foam with a plurality of silicon balls in a plastic bag and sealing it by vacuum exhausting; placing the sealed plastic bag in a hydrostatic press to perform hydrostatic molding; degreasing after obtaining the above-mentioned hydrostatically molded silicon balls; and nitriding and sintering the degreased silicon balls to produce silicon nitride balls.

[0012] In a preferred embodiment, the porous foam is PE foam, each hole is formed into a circle or a polygon and is open through the upper and lower surfaces of the porous foam, and the maximum width of each hole is greater than the diameter of the configured silicon ball.

[0013] In a preferred embodiment, the porous foam is PE foam, each hole is formed into a circle or a polygon and is only open to the upper surface of the porous foam, and a silicon ball is installed inside each hole.

[0014] In a preferred embodiment, the degreasing process further includes a step of coating boron nitride on the outer surface of the hydrostatically pressed silicon spheres, thereby controlling the silicon spheres to react with carbon inside a furnace during degreasing and sintering.

[0015] In a preferred embodiment, the boron nitride is in the form of a slurry and is wet-coated onto the outer surface of the hydrostatically pressed silicon sphere.

[0016] Effects of the Invention

[0017] The present invention has the following excellent effects.

[0018] According to the method for producing silicon nitride balls of the present invention, a plurality of silicon balls can be placed in porous foam and then packaged for hydrostatic pressure molding, thus having the advantage of being able to significantly increase the yield of silicon nitride ball production.

[0019] In addition, according to the method for manufacturing silicon nitride balls of the present invention, boron nitride is coated on the outer surface of the hydrostatic pressure molded silicon ball, and the reaction with carbon can be controlled during degreasing and sintering, thereby having the advantage of being able to manufacture silicon nitride balls with high toughness and high strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flowchart of a method for manufacturing silicon nitride balls according to an embodiment of the present invention.

[0021] Figure 2This is a diagram illustrating a porous foam used in hydrostatic molding in a method for producing a silicon nitride ball according to an embodiment of the present invention.

[0022] Figure 3 This is a diagram showing a silicon sphere formed by hydrostatic pressure in a method for producing a silicon nitride sphere according to an embodiment of the present invention.

[0023] Figure 4 FIG. 1 is a diagram showing silicon spheres coated with boron nitride in a method for producing silicon nitride spheres according to an embodiment of the present invention.

[0024] (Explanation of symbols)

[0025] 100: Silicon nitride ball 200: Porous foam

[0026] 210: hole 300: plastic bag

[0027] 310: Encapsulated plastic bag 320: Hydrostatically pressed silicon ball

[0028] 400: Silicon sphere coated with boron nitride DETAILED DESCRIPTION

[0029] Regarding the terms used in the present invention, general terms that are currently widely used have been selected as much as possible. However, in specific cases, there are also terms that are arbitrarily selected by the applicant. In such cases, the meaning of the term should not be simply considered, but the meaning recorded or used in the detailed description of the invention should be considered to understand its meaning.

[0030] Hereinafter, the technical structure of the present invention will be described in detail with reference to the preferred embodiments shown in the accompanying drawings.

[0031] However, the present invention is not limited to the embodiments described herein, and may be implemented in other ways. Throughout the specification, the same symbols represent the same constituent elements.

[0032] Figure 1 The present invention is a flowchart of a method for manufacturing a high-toughness, high-strength silicon nitride ball according to an embodiment of the present invention.

[0033] Reference Figure 1 A method for manufacturing high-toughness, high-strength silicon nitride balls according to one embodiment of the present invention is a method for manufacturing silicon nitride balls inserted into machine devices such as bearings to reduce contact friction.

[0034] First, silicon powder is prepared ( S1000 ).

[0035] The silicon powder used is obtained by pulverizing metal silicon scrap to control impurities and particle size.

[0036] The silicon powder has a smaller particle size as possible, but a silicon powder having an average particle size of 1 μm to 10 μm can be used for mixing with a sintering additive and final refinement.

[0037] Then, a solvent and an organic binder are added to the silicon powder to form a slurry ( S2000 ).

[0038] In addition, there is no particular limitation on the types of the above-mentioned solvent and organic adhesive, but as the above-mentioned solvent, it is preferred to use one or more selected from ethanol, methanol, isopropyl alcohol, distilled water and acetone, and as the above-mentioned organic adhesive, it is preferred to use a polyvinyl butyral (PVB)-based adhesive.

[0039] Then, the slurry is thermally spray-dried to produce granules having a predetermined particle size (S3000).

[0040] In addition, regarding the particles obtained by thermal spray drying, in order to prevent the inside of the particles from being hollow or forming donut-shaped particles, the internal temperature of the chamber was fixed at 120°C, the temperature of the external chamber was fixed at 90°C, and the atomizer speed was set at 8,000 rpm to 15,000 rpm.

[0041] In addition, the average particle size of the particles produced in this way is 60 μm to 120 μm, preferably 80 μm to 120 μm.

[0042] Then, the granules are press-molded to produce silicon balls 100 ( S4000 ).

[0043] In addition, the molding pressure of the above-mentioned press molding is preferably set to 20 kg / cm 3 Up to 50kg / cm 3 , so that when performing the following hydrostatic forming, uniform pressure is applied and it is easy to handle after forming.

[0044] Then, the silicon balls 100 are positioned in the respective pores 210 of the soft porous foam 200 ( S5000 ).

[0045] In addition, the porous foam 200 is a PE foam having a plurality of pores 210 separated from each other. Figure 2 As shown in (b), the hole 210 is formed in a circular shape or as Figure 2 As shown in (a), the hole 210 is formed in a polygonal shape.

[0046] In addition, the holes 210 may be punched through the upper and lower surfaces of the porous foam 200 , or may be recessed into a groove shape with the lower surface blocked and open only to the upper surface.

[0047] In addition, the maximum width of the hole 210 should be greater than the diameter of the silicon ball 100 .

[0048] This is to allow the silicon ball 100 to pass through when it is located in the hole 210 and minimize the contact with the PE foam.

[0049] However, the size needs to be adjusted so that only one silicon ball 100 is arranged in one hole 210 .

[0050] That is, the porous foam 200 functions as a jig capable of placing a plurality of silicon balls.

[0051] In order to set the silicon balls 100 in the holes 210 of the porous foam 200 , a plurality of silicon balls 100 are placed on the porous foam 200 and shaken left and right using a vibrator, thereby causing the silicon balls 100 to be stuck in the holes 210 .

[0052] In addition, the thickness of the porous foam 200 should be smaller than the diameter of the silicon ball 100 , preferably 20% to 50% of the diameter of the silicon ball 100 .

[0053] Then, the porous foam 200 in which the silicon balls 100 are placed is placed in a plastic bag 300 and vacuum-exhausted, thereby packaging ( S6000 ).

[0054] In addition, the plastic bag 300 may be made of any material or shape as long as it can withstand the pressure in the hydrostatic pressure molding described below.

[0055] On the other hand, the applicant previously placed a silicon ball in a rubber bag, sealed it, and molded it using a hydrostatic press, so the output was low. However, by using the above-mentioned porous foam 200 to encapsulate multiple silicon balls at one time and then perform hydrostatic pressure molding, the output was greatly improved.

[0056] Then, the sealed plastic bag 310 is put into a hydrostatic press to perform hydrostatic molding (S7000).

[0057] In addition, the pressure applied during the hydrostatic pressure molding is preferably maintained at 200 atm to 400 atm, and the application time is preferably about 30 minutes to 60 minutes.

[0058] Then, if Figure 3 As shown, the hydrostatically pressed silicon ball 320 is taken out of the plastic bag and then subjected to degreasing (S9000) and sintering (S9100) processes to complete the manufacture of high-toughness and high-strength silicon nitride balls.

[0059] In addition, the above degreasing is a process of removing organic matter including silicon powder in an unoxidized state, and the temperature is kept at 450°C, the heating rate is maintained at 0.11°C / min to 1°C / min, and it is kept in an oxidizing environment for 2 hours to 10 hours. The residual carbon that is not completely removed is degreased at 900°C for 1 hour to 10 hours in a nitrogen environment.

[0060] In addition, the sintering is a process of sintering and nitriding the silicon balls by using a gas pressure sintering (GPS) method, and the temperature is kept at 0.1°C / min to 2°C / min until 1400°C, and the nitrogen pressure is kept at 1.0 atmosphere to 1.8 atmosphere for 0.5 to 10 hours. For the final sintering, the temperature is kept at 1°C to 5°C until 1900°C, and the nitrogen pressure is kept at 9 atmospheres for 1 to 10 hours.

[0061] On the other hand, after the hydrostatic pressure forming, before the degreasing step, a process of coating the silicon sphere with boron nitride may be added (S8000).

[0062] in addition, Figure 4 The silicon sphere is coated with boron nitride.

[0063] In addition, regarding the boron nitride, a solvent is added to a boron nitride powder to form a slurry, and then the boron nitride slurry is applied to the silicon nitride spheres in a wet process.

[0064] In addition, as the above-mentioned solvent, water is preferably used.

[0065] In addition, the reason for using water as the above-mentioned solvent is as follows: when performing thermal spray drying, a polyvinyl butyral (PVB)-based binder is used as an organic binder. When an organic solvent other than water is used, the polyvinyl butyral (PVB)-based binder on the surface of the silicon sphere melts and reacts with boron nitride. In this case, it is difficult to achieve refinement during sintering.

[0066] In addition, in the boron nitride slurry, the specific gravity of water relative to the boron nitride powder is 50 wt% to 98 wt%. Because when the weight ratio decreases, the viscosity of the slurry becomes higher, the coating thickness is too thick, and the thermal conductivity is low during sintering, which leads to different structures between the surface and the inside, thereby reducing the strength of the ball.

[0067] In addition, regarding the thickness of the boron nitride coating, when the coating thickness is 5 μm to 20 μm, the reaction at the interface between the silicon balls can be suppressed during the sintering process, and the growth of particles on the surface can be suppressed.

[0068] Then, the silicon balls coated with the boron nitride slurry are dried, and then the degreasing step ( S9000 ) is performed, and sintering ( S9100 ) is performed to complete the manufacture of the silicon nitride balls with high toughness and high strength.

[0069] In addition, the moisture content of the dried silicon balls is preferably within 5%, because the moisture volatilized during the high-pressure gas pressure sintering process will oxidize the graphite heating element inside the equipment or the parts made of graphite inside the cavity into carbon monoxide or carbon dioxide, thereby causing damage to the equipment and products.

[0070] Thus, when degreasing and sintering the silicon balls coated with boron nitride, if the reaction with carbon inside the furnace is not controlled, the carbon will penetrate into the silicon balls and synthesize into silicon carbide, making it difficult to manufacture high-toughness and high-strength silicon nitride balls. Therefore, it is very important to control the carbon well to prevent the formation of silicon carbide.

[0071] As described above, the present invention has been illustrated and described by taking preferred embodiments as examples, but the present invention is not limited to the above embodiments, and those skilled in the art may make various changes and modifications without departing from the spirit of the present invention.

Claims

1. A method for manufacturing silicon nitride balls, characterized in that: The steps include: preparing silicon powder; Adding a solvent and an organic binder to the silicon powder to form a slurry; The slurry is subjected to thermal spray drying to produce particles having a predetermined particle size; Pressing and molding the above particles to produce silicon balls; The silicon balls are placed in the pores of the soft porous foam; The porous foam equipped with a plurality of silicon balls is placed in a plastic bag and vacuum-exhausted for packaging; The sealed plastic bag is placed in a hydrostatic press to be hydrostatically pressed; After obtaining the hydrostatically pressed silicon balls, degreasing is performed; and The degreased silicon balls are nitrided and sintered to produce silicon nitride balls. The size of each hole of the porous foam is adjusted so that only one silicon ball is arranged in one hole.

2. The method for manufacturing silicon nitride balls according to claim 1, characterized in that: The porous foam is PE foam, each hole is formed into a circle or a polygon and penetrates the upper surface and the lower surface of the porous foam to be open, and the maximum width of each hole is larger than the diameter of the arranged silicon ball.

3. The method for manufacturing silicon nitride balls according to claim 1, characterized in that: The porous foam is PE foam, each hole is formed into a circular or polygonal shape and is open only to the upper surface of the porous foam, and a silicon ball is installed inside each hole.

4. The method for manufacturing silicon nitride balls according to any one of claims 1 to 3, characterized in that: The degreasing process also includes a step of coating the outer surface of the hydrostatically pressed silicon sphere with boron nitride, thereby controlling the silicon sphere to react with carbon inside the furnace during degreasing and sintering.

5. The method for manufacturing silicon nitride balls according to claim 4, characterized in that: The boron nitride is wet-coated in the form of slurry onto the outer surface of the hydrostatically pressed silicon sphere.

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