A method of manufacturing a textured nut

Abstract

The application discloses a preparation method of a textured nut and belongs to the field of high-temperature metallurgical connecting structural member preparation. The application is characterized in that long strip beta-silicon nitride whiskers and wax-based binders are added into heated ceramic slurry, the ceramic slurry is shaped by a low-temperature wax-based auxiliary agent, and tapping is performed on the shaped ceramic slurry by a mold. During the tapping process, micro-texture effects are formed on the surface of the thread, so that the shear force of the thread part of the prepared nut is higher than that of a conventional ceramic thread, a certain degree of damage to the ceramic structure is avoided during the processing, and the quality of the thread part is affected.

Description

Technical Field

[0001] This invention relates to the field of high-temperature metallurgical connection structure preparation, and in particular to a method for preparing a textured nut. Background Technology

[0002] Silicon nitride screws and nuts, with their core advantages of high temperature resistance, thermal shock resistance, and chemical inertness, have become an ideal fastener solution for the extreme environments of metal smelting. The combination of their low coefficient of thermal expansion and high hardness ensures dimensional stability at high temperatures while significantly extending equipment maintenance cycles through excellent wear resistance and impact toughness. Furthermore, the lightweight nature and self-lubricating properties of silicon nitride further optimize safety and reliability in high-frequency vibration scenarios, making them particularly suitable for critical components such as continuous casting machines and high-temperature reactors. Although the initial investment is higher, their long lifespan reduces overall lifespan costs, driving the metallurgical industry towards high efficiency and low carbon emissions.

[0003] Traditional ceramic screws and nuts are manufactured by first preparing the screw and nut bodies, and then machining the threads. Because the threads of screws and nuts are very fine, extremely high precision is required during machining, resulting in very high costs. Furthermore, the machining process causes some damage to the ceramic structure, affecting the quality of the threaded portion and leading to a high scrap rate. Summary of the Invention

[0004] The innovation of this invention lies in adding long strips of β-silicon nitride whiskers and wax-based sintering aids to heated ceramic slurry. The ceramic slurry is shaped by a low-temperature wax-based binder, and then tapped by a mold. During the tapping process, a micro-texture effect is formed on the thread surface, which can be divided into the following two points.

[0005] Innovation in green body machinability: A specific type and proportion of wax-based binder is introduced into silicon nitride powder. Through thermal mixing, the binder melts and uniformly binds the powder, which then solidifies upon cooling to form a green body with suitable mechanical strength. This green body has a hardness far lower than sintered ceramics, allowing for high-precision, low-damage thread tapping using conventional carbide taps, completely solving the machining challenges of hard and brittle ceramic threads.

[0006] Structure-performance integrated innovation: Flaky or rod-shaped β-silicon nitride whiskers are introduced into the formulation as texture inducers. These whiskers align under shear force. During subsequent high-temperature sintering, they guide the preferential growth of silicon nitride grains along specific directions, ultimately forming a textured microstructure with anisotropic characteristics.

[0007] A method for preparing a textured nut, characterized by the following steps:

[0008] S1. Preparation of mixed slurry: Silicon nitride powder with α phase content higher than 85%, rare earth element compound, β-silicon nitride whisker powder, dispersant, and wax-based binder are mixed and heated by ball milling until all particles have a particle size of 0.05-1.5μm, thus completing the preparation of the hot mixed slurry.

[0009] S2. Place the hot-mixed slurry into the nut mold, cool the hot-mixed slurry to room temperature, and prepare a nut blank without threads;

[0010] S3. At room temperature, the nut blank is processed to produce threads; the processing method is spiral cutting or tapping. During the thread processing, the processing part performs thread processing in a unidirectional spiral manner to complete the preparation of the thread blank.

[0011] S4. The threaded blank is degreased, sintered, and then processed into a silicon nitride nut through secondary thread processing.

[0012] Preferably, the hot-mixed slurry in step S1 is prepared by hot mixing at 60-80°C for 2-4 hours.

[0013] Preferably, the mass parts of silicon nitride powder, rare earth element compound, β-silicon nitride whisker powder, dispersant, and wax-based binder in step S1 are 70-90 parts, 2-11 parts, 3-20 parts, 3-12 parts, and 2-6 parts, respectively.

[0014] Preferably, the wax-based binder in step S1 is one, two, or three of paraffin wax and microcrystalline wax.

[0015] Preferably, before the hot-mixed slurry is placed into the nut mold, a cylinder with a nut hole is inserted along the center line.

[0016] Preferably, after the thread is machined in step S3, the center hole of the thread blank is transferred to a graphite screw for shaping.

[0017] Preferably, the degreasing process in step S4 involves placing the threaded blank in a degreasing furnace, heating it to 500-600°C at a rate of 0.5-2°C / min, and holding it at that temperature.

[0018] Preferably, the sintering process in step S4 involves placing the furnace in a nitrogen atmosphere and performing pressure sintering at 1750-1850℃ for 1-4 hours.

[0019] Preferably, the secondary thread processing in step S4 is a grinding process. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.

[0021] Figure 1 Here is a structural diagram of the nut;

[0022] Figure 2 This refers to the machining method for the threaded portion of a nut. Detailed Implementation

[0023] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0024] Material Selection: Silicon nitride powder: α-silicon nitride content ≥92%, average particle size 0.5-1.5μm, oxygen content ≤1.5%. Sintering aids: Yttrium oxide, MgO, alumina, etc., purity ≥99.9%, average particle size 0.5-2μm. Texture inducer: Flaky or high aspect ratio rod-shaped β-silicon nitride whiskers, long diameter 5-20μm, short diameter 0.5-2μm. Binder: Paraffin wax, galvanized paraffin wax, microcrystalline wax, melting point 40-80℃.

[0025] Formulation design (mass percentage): Silicon nitride powder: 75%-90%, sintering aid: 3%-10% (e.g., yttrium oxide: 2%-6%, MgO: 1%-4%), texture inducer (β-silicon nitride whiskers): 5%-14%, wax-based binder: 1%-4%.

[0026] Mixing and molding: The powder and molten wax-based binder are hot-mixed at 60-80℃ for 2-4 hours to form a uniform plastic agglomerate. The agglomerate is injected into a preheated nut blank mold while hot and pressed to obtain a nut blank with a central smooth hole and no threads, which is then cooled and solidified.

[0027] Blank processing: such as Figure 2 As shown, at room temperature, a processing device is used to tap a solidified green blank to produce a complete thread. The tapping process is smooth with good chip removal. During the tapping process, the rotary table must maintain a single direction for tapping. As the rotary table rotates and taps, it causes the β-silicon nitride whiskers in the thread green blank to fall horizontally, producing a texturing effect and generating a textured layer on the thread surface. After sintering, this textured layer can provide shear force for the threaded portion.

[0028] Mold shaping: Insert a threaded graphite rivet into the tapped blank to shape the nut blank.

[0029] Debinding and sintering: The tapped green body is placed in a debinding furnace and heated to 500-600℃ at a slow heating rate (0.5-2℃ / min) and held at that temperature to completely remove the organic binder. Then it is placed in a nitrogen atmosphere sintering furnace and sintered under gas pressure at 1750-1850℃ for 1-4 hours to finally obtain a fully dense textured silicon nitride ceramic nut.

[0030] Specific implementation examples:

[0031] Example: The formulation consists of 82% silicon nitride, 5% yttrium oxide, 2% MgO, 8% rod-shaped β-silicon nitride whiskers, and 3% paraffin wax. After hot mixing, the mixture is molded, the blank is tapped, degreased, and sintered at 1800℃ for 2 hours.

[0032] Comparative example: The formula is the same as in Example 1, but without wax and whiskers. After dry pressing, the powder is directly sintered to obtain a dense, threadless hollow ceramic column. Then, internal threads are machined on the sintered body using a diamond grinder.

[0033] The machining process requires extremely low feed rates and adequate cooling. This step is inefficient, causes significant tool wear, and is highly susceptible to introducing imperceptible microcracks and other machining damage at the thread root. The test results of the examples and comparative examples are as follows.

[0034] project β-silicon nitride percentage paraffin percentage Axial tensile strength (MPa) Creep strain (%) at 1100℃ / 100h Thermal shock resistance (ΔT_c, water cooling) Thread integrity Example 8 3 850 <0.2 >600℃ Smooth, free of machining microcracks Comparative example 0 0 780 0.5 >450℃ Localized microcracks are visible (which become sources of high-temperature fatigue).

[0035] The test results above show that introducing long-grained β-phase silicon nitride whiskers increases the proportion of long grains in both the horizontal and vertical directions of the ceramic substrate. Due to the directional pressure of the casting squeegee, the distribution of long grains along the casting direction is even higher. This structure is significantly beneficial to improving the toughness of the ceramic substrate. Simultaneously, the formation of a textured structure with A-type long grains in the horizontal direction is also observed.

[0036] Test results: The density of the nut in the example is greater than 3.25 g / cm³, and the thread size accuracy reaches IT7 grade. Microscopic observation shows that the long columnar crystals of β-silicon nitride are significantly oriented along the plane perpendicular to the axis of the nut. This texture direction is beneficial to improving the wear resistance and shear resistance of the thread surface.

Claims

1. A method for preparing a textured nut, characterized in that: the steps include: S1. Preparation of the mixed slurry: Silicon nitride powder with an α-phase content higher than 85%, rare earth element compounds, β-silicon nitride whisker powder, dispersant, and wax-based binder are mixed and heated by ball milling until all particles have a particle size of 0.05-1.5μm, thus completing the preparation of the hot mixed slurry; the mass parts of silicon nitride powder, rare earth element compounds, β-silicon nitride whisker powder, dispersant, and wax-based binder are 70-90 parts, 2-11 parts, 3-20 parts, 3-12 parts, and 2-6 parts, respectively. S2. Place the hot-mixed slurry into the nut mold, cool the hot-mixed slurry to room temperature, and prepare a nut blank without threads; S3. At room temperature, the nut blank is processed to produce threads; the processing method is spiral cutting or tapping. During the thread processing, the processing part performs thread processing in a unidirectional spiral manner to complete the preparation of the thread blank. S4. The threaded blank is degreased, sintered, and then processed into a silicon nitride nut through secondary thread processing.

2. The method for preparing a textured nut according to claim 1, characterized in that: The hot-mixed slurry described in step S1 is prepared by hot mixing at 60-80℃ for 2-4 hours.

3. The method for preparing a textured nut according to claim 1, characterized in that: The wax-based binder mentioned in step S1 is one, two, or three types of paraffin wax or microcrystalline wax.

4. The method for preparing a textured nut according to claim 1, characterized in that: In step S2, before the hot mixed slurry is placed into the nut mold, a cylinder with a nut hole is inserted into the center line.

5. The method for preparing a textured nut according to claim 1, characterized in that: After the thread is machined in step S3, the center hole of the thread blank is transferred to a graphite screw for shaping.

6. The method for preparing a textured nut according to claim 1, characterized in that: The degreasing process described in step S4 involves placing the threaded blank in a degreasing furnace, heating it to 500-600℃ at a rate of 0.5-2℃ / min, and holding it at that temperature.

7. The method for preparing a textured nut according to claim 1, characterized in that: The sintering process described in step S4 involves placing the furnace in a nitrogen atmosphere and performing pressure sintering at 1750-1850℃ for 1-4 hours.

8. The method for preparing a textured nut according to claim 1, characterized in that: The secondary thread processing described in step S4 is a grinding process.

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