A method of manufacturing a powder metallurgical mill disc

Abstract

This invention discloses a method for manufacturing a powder metallurgy grinding disc, comprising the following steps: Step S01: Selecting raw materials, the raw materials comprising, by weight percentage: 13%-19% chromium powder, 0.5%-1.0% carbon powder, 0.8%-1.0% lubricant, and the remainder being iron powder; mixing the raw materials; Step S02: Selecting a mold corresponding to the grinding disc body, and forming a blank in a forming machine using the mixed powder raw materials; Step S03: Placing the blank on a ceramic plate, with adjacent blanks spaced apart; Step S04: Transferring the blank to a first sintering furnace for primary sintering; Step S05: Transferring the blank after primary sintering to a second sintering furnace for secondary sintering; Step S06: Immersing the cooled blank after secondary sintering in oil; Step S07: Grinding the oil-immersed blank, and cleaning it after grinding to obtain the finished product; This invention not only shortens the production cycle and reduces the cost of tool procurement and wear, but also achieves high tooth shape consistency, thereby improving product quality.

Description

Technical Field

[0001] This invention relates to the technical field of grinding disc manufacturing methods, and in particular to a powder metallurgy grinding disc manufacturing method. Background Technology

[0002] As a key component of a grinder, the grinding disc is commonly used for grinding bean-shaped materials (such as coffee beans and peanuts). The grinding disc is fixedly assembled to the grinder's rotating shaft via a flat surface. During operation, it rotates at high speed with the shaft and relies on the cutting teeth on its blade surface to grind the workpiece. Currently, grinding discs are generally manufactured using traditional machining methods.

[0003] Because the cutting teeth need to be distributed around the center of the grinding disc, multi-axis linkage with radial feed and circumferential indexing is required during machining. After each cutting of a cutting tooth, the workpiece needs to be precisely rotated to fix the indexing angle, and the tool needs to synchronously switch the radial feed trajectory to adapt to the machining position of the next cutting tooth. Due to the narrow spacing between the cutting teeth, the tool is prone to collision and interference with adjacent cutting teeth that have already been machined. Therefore, multiple small-diameter tools need to be pre-assembled in the machine tool's tool magazine, and the tool type needs to be frequently changed during machining. This not only increases the cost of tool procurement and wear, but also increases the machining time of a single grinding disc, resulting in a significant decrease in production efficiency. At the same time, each tool change will generate a positioning reference deviation, and after multiple changes, it is easy to form a cumulative error, resulting in a large tooth pitch deviation, poor tooth profile consistency, and even tooth surface scratches, which reduces product quality. Summary of the Invention

[0004] The purpose of this invention is to provide a method for manufacturing powder metallurgy grinding discs, which can not only shorten the production cycle, but also achieve high tooth profile consistency of the cutting teeth, thereby improving product quality.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for manufacturing a powder metallurgy grinding disc includes the following steps:

[0007] Step S01: Select raw materials, which include the following by weight percentages: 13%-19% chromium powder, 0.5%-1.0% carbon powder, 0.8%-1.0% lubricant, and the balance being iron powder; mix the raw materials.

[0008] Step S02: Select a mold corresponding to the grinding disc body and form the mixed powder raw material into a blank in the molding machine;

[0009] Step S03: Place the blanks on the ceramic plate, with adjacent blanks spaced apart;

[0010] Step S04: Transfer the blank to the first sintering furnace for a first sintering;

[0011] Step S05: Transfer the blank after the first sintering to the second sintering furnace for the second sintering;

[0012] Step S06: Immerse the blank after secondary sintering and cooling in oil;

[0013] Step S07: Polish the oil-soaked blank, and clean it after polishing to obtain the finished product.

[0014] Based on the above technical solution, the present invention can be improved as follows:

[0015] Furthermore, in step S01, the particle size of the iron powder is 50-100 mesh, the particle size of the chromium powder is 80-120 mesh, and the particle size of the carbon powder is 200-300 mesh.

[0016] Furthermore, in step S01, the raw material also includes 0.2% nickel powder by weight, with a particle size of 80-150 mesh.

[0017] Further, in step S02, the molding pressure of the molding machine is 35-45 MPa, the holding time is 6-8 seconds, and the density of the molded preform is measured to be 6.4-6.6 g / cm³. 3 .

[0018] Furthermore, in step S03, on the ceramic plate, the distance between two adjacent blanks is 1-3mm, and the cutting tooth surface of the blank faces upward and the flat surface faces downward, fitting against the ceramic plate.

[0019] Furthermore, in step S04, the temperature of the first sintering furnace is 1120°C, and after holding at that temperature for 1 hour, it is cooled to room temperature along with the furnace.

[0020] Further, in step S05, the temperature of the second sintering furnace is 1120℃, and after holding at that temperature for 3 hours, it is cooled to room temperature with the furnace; the density of the blank is measured to be ≥7.2 g / cm³. 3 .

[0021] Furthermore, in step S06, rust-preventive oil is selected, the oil bath temperature is 50-60℃, the immersion time is 15-20 minutes, the hardness of the blank is tested to be ≥35HRC, and unqualified blanks are screened out.

[0022] Further, in step S07, rough grinding is performed first to remove 0.2-0.3mm of machining allowance; then fine grinding is performed to remove 0.05-0.1mm of allowance to obtain the finished product; the finished product is cleaned for 12-15 minutes, the surface roughness of the finished product is tested to be Ra1.6MAX, and unqualified blanks are screened out.

[0023] Furthermore, it also includes:

[0024] Step S08: Demagnetize the finished product for 5-10 seconds; clean and dry after demagnetization.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The present invention uses powder metallurgy technology to manufacture grinding discs, which can directly press and form blanks that are highly matched with the structure of the grinding disc. Afterwards, only targeted grinding is needed to remove the surface micro-excess and simultaneous cleaning of residual iron filings to obtain the finished product. This not only saves the tedious process of frequent tool changes and multiple clamping in traditional machining, shortens the production cycle, and reduces the cost of tool procurement and wear, but also reduces the manufacturing cost from the source. Moreover, the blank is formed in one step, avoiding the cumulative error caused by multiple tool changes and positioning deviations in traditional machining. The tooth shape of the cutting edge is highly consistent, thereby improving the product quality.

[0027] (2) The present invention adopts a manufacturing method of two sintering without oil immersion between sintering. On the one hand, the absence of oil immersion can completely avoid the interference of additional carbon source introduced by oil. On the other hand, after the first sintering is completed, the blank does not need to be cooled and is directly transferred to the second sintering furnace. With the help of the stable reducing gas environment in the furnace, the trace amount of lubricant decomposition gas and air in the pores remaining from the first sintering can be quickly discharged, effectively avoiding gas retention that hinders the densification of powder particles and improving the density of the blank. The manufacturing method can accurately control the stability of the free chromium content in the blank. Under the high temperature of the second sintering, the chromium element reacts fully with the matrix and trace oxygen elements in the furnace to form a continuous and uniform Cr-Ni-O composite passivation film. This passivation film tightly covers the surface of the grinding disc and the gap between the cutting teeth, effectively isolating the contact between the humid air and the metal matrix, significantly increasing the hardness of the grinding disc by 20% and enhancing the corrosion resistance of the grinding disc, thus extending its service life. Attached Figure Description

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] Figure 1 A schematic diagram of the structure of the grinding disc manufactured in the invention;

[0030] Figure 2 This is a flowchart of the powder metallurgy grinding disc manufacturing method in the invention.

[0031] The markings on the attached diagram are: 1. Grinding disc body; 2. Cutting teeth. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. These descriptions are intended to aid in understanding the present invention but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] See Figure 1 This embodiment relates to a powder metallurgy grinding disc manufacturing method. The manufactured grinding disc includes a disc-shaped grinding disc body 1. One end of the grinding disc body 1 is a cutting tooth surface with multiple cutting teeth 2 arranged around the center of the grinding disc body. The other end of the grinding disc body is a flat surface.

[0034] See Figure 2 The powder metallurgy grinding disc manufacturing method of this embodiment includes the following steps:

[0035] Step S01: Select raw materials, which include the following by weight percentages: 13%-19% chromium powder, 0.5%-1.0% carbon powder, 0.8%-1.0% lubricant, and the balance being iron powder; mix the raw materials.

[0036] Step S02: Select a mold corresponding to the grinding disc body and form the mixed powder raw material into a blank in the molding machine;

[0037] Step S03: Place the blanks on the ceramic plate, with adjacent blanks spaced apart;

[0038] Step S04: Transfer the blank to the first sintering furnace for primary sintering at a temperature of 1120℃;

[0039] Step S05: Transfer the blank after the first sintering to the second sintering furnace for a second sintering at a temperature of 1120℃.

[0040] Step S06: Separate the blank after secondary sintering and cooling from the ceramic plate, and impregnate it with oil until the hardness is ≥38HRC;

[0041] Step S07: Transfer the oil-soaked blank to a grinding machine for grinding to obtain the finished product. Clean the finished product to remove iron slag and iron filings.

[0042] Step S08: Demagnetize, clean, and dry the finished product;

[0043] Step S09: Inspect the finished products and screen out the unqualified products;

[0044] Step S10: Package the qualified finished products.

[0045] In step S01 of this embodiment, the particle size of iron powder is 50-100 mesh, the particle size of chromium powder is 80-120 mesh, and the particle size of carbon powder is 200-300 mesh; a double cone mixer is used with a speed of 30-40 r / min and a mixing time of 25-30 min; the mixed powder is sealed and stored in a dry silo.

[0046] Using chromium powder can improve the corrosion resistance of the matrix, while carbon powder can optimize the martensite content. Mixing with a double cone mixer can avoid powder agglomeration and ensure the consistency of the density of subsequent blanks. Sealed and dry storage can prevent the powder from absorbing moisture and affecting the molding density and sintering quality.

[0047] Furthermore, the raw materials also include, by weight percentage: 0.2% nickel powder, with a particle size of 80-150 mesh. The nickel powder can fill the gaps between iron and chromium particles, reducing powder agglomeration and effectively reducing the segregation of chromium powder due to density differences, thereby improving the flowability of the mixed powder. The nickel particles can bridge adjacent iron and chromium particles through plastic deformation, which can improve the green strength of the blank and reduce the impact and breakage of the blank during the process of taking it out of the molding machine and transferring it to the ceramic plate.

[0048] In step S02 of this embodiment, the mold cavity is matched with the main body of the grinding disc in size, and the surface roughness of the cavity is Ra0.8μm; a molding machine is used, the molding pressure is 35-45MPa, the holding time is 6-8s, and the density of the molded blank is measured to be 6.4-6.6g / cm³. 3 .

[0049] In step S03 of this embodiment, the spacing between two adjacent blanks on the ceramic plate is 1-3mm, and the cutting tooth surface of the blank faces upward and the flat surface faces downward, and they are attached to the ceramic plate.

[0050] By placing the cutting teeth face upwards, the sintering heat field is applied evenly to the complex cutting tooth structure, reducing stress concentration and improving the integrity of the cutting teeth forming.

[0051] In step S04 of this embodiment, the first sintering furnace is a horizontal sintering furnace, and a thermocouple is installed inside the furnace to monitor the temperature in real time; the first sintering is carried out at 1120°C, and after holding at that temperature for 1 hour, the furnace is cooled to room temperature.

[0052] The use of a reducing gas environment can isolate oxygen and prevent oxidation and discoloration of the blank; the segmented heating and low-temperature holding can completely eliminate lubricant volatiles and reduce the occurrence of pores and cracks; the initial sintering at 1120℃ can form a stable matrix framework, laying the foundation for densification in the secondary sintering and avoiding deformation caused by direct high-temperature sintering.

[0053] In step S05 of this embodiment, the second sintering furnace is the same horizontal sintering furnace as the first sintering furnace. The second sintering is performed at 1120°C, held for 3 hours, and then cooled to room temperature with the furnace. The density of the blank is measured to be ≥7.2 g / cm³. 3 To ensure that the densification standard is met.

[0054] This embodiment employs a two-stage sintering process. By extending the holding time of the second sintering at the same sintering temperature, diffusion sintering and pore closure between powder particles can be promoted, significantly increasing the shrinkage rate of the blank and reducing the porosity of the microstructure, thereby optimizing the product density. During the furnace cooling process, the carbide phase is fully refined and evenly distributed, which not only improves the overall hardness of the blank but also synergistically improves the sharpness and wear resistance of the grinding disc teeth. After testing, the density of the blank after this process is ≥7.2 g / cm³, indicating that the densification process has fully met the standards.

[0055] In step S06 of this embodiment, compressed air is used to blow away the floating dust on the surface of the blank, rust-preventive oil is selected, the oil bath temperature is 50-60℃, and the oil immersion time is 15-20 minutes, so that the oil penetrates into the micropores to form a rust-preventive protective film; Rockwell hardness tester is used to select 3 test points evenly on the flat surface of the blank, and the average value is taken to ensure that the hardness is ≥38HRC, and unqualified blanks are screened out.

[0056] It should be noted that in this embodiment, the carbon content of the grinding disc needs to be controlled at 0.5%-0.8% to ensure the subsequent formation of a uniform martensite and chromium carbide structure. The core component of the rust-preventive oil is hydrocarbons, which undergo violent pyrolysis under the high temperature of 1120℃ during secondary sintering. While low-boiling-point components can be discharged through the furnace exhaust system, high-boiling-point components will carbonize to generate free carbon, which then penetrates into the loose pores of the blank after primary sintering. The purpose of secondary sintering is to promote the full diffusion of iron, chromium, and nickel atoms through the high temperature of 1120℃, forming a continuous Fe-Cr-Ni solid solution and a dispersed Cr... 23 C6 strengthening phase; abnormally increased free carbon accumulates in the pores of the blank, forming a carbon film that encapsulates metal particles, blocking the diffusion channels of iron and chromium atoms, leading to insufficient alloying and the appearance of local unalloyed areas (such as chromium particle agglomeration areas); excessive carbon combines with chromium to form coarse Cr7C3 carbides. These carbides are enriched at grain boundaries, easily causing microcracks after secondary sintering and reducing the toughness of the blank; after the first sintering, the blank has a large number of micron-sized pores with a porosity of 8%-10%. During oil immersion, the rust-preventive oil will penetrate into the pores and adhere to the particle surface; during the secondary sintering heating stage (800-1200℃), although the rust-preventive oil will pyrolyze into gas, the gas escape rate is too fast at high temperatures, easily forming bubble-type pores inside the blank; these pores cannot be eliminated by subsequent high-temperature holding, ultimately resulting in the blank density after secondary sintering only reaching 6.8-7.0 g / cm³. 3 The material is below the design standard, which directly weakens the hardness and wear resistance of the grinding disc. Therefore, it is not suitable to soak it in oil between the two sintering processes.

[0057] In this embodiment, no oil immersion is performed after the first sintering, which completely avoids the interference of the carbon source of the rust-preventive oil. During the second sintering, the carbon element can react with iron and chromium in a preset ratio to form a uniform martensitic matrix and dispersed Cr. 23 The C6-reinforced phase exhibits no coarse carbides or carbon segregation. After the first sintering, the blank is directly transferred to the second sintering stage, which can quickly remove trace amounts of gas remaining from the first sintering stage and prevent gas from hindering particle bonding. The free chromium content is stable, and a continuous and uniform Cr-Ni-O composite passivation film can be formed after the second sintering, effectively isolating humid air from contact with the substrate.

[0058] In step S07 of this embodiment, a CNC surface grinder is used, and a white corundum grinding wheel is selected, with a grinding wheel speed of 1800-2000 r / min;

[0059] First, perform rough grinding to remove 0.2-0.3mm of machining allowance and correct dimensional deviations after sintering;

[0060] After fine grinding, remove 0.05-0.1mm of excess material and control the surface roughness to Ra1.6MAX;

[0061] The finished product after fine grinding is cleaned with a cleaning agent, which is a mixture of water and rust inhibitor; the cleaning time is 12-15 minutes to remove iron slag and iron filings from the surface; then it is dried with compressed air.

[0062] In step S08 of this embodiment, a demagnetizer is used with a demagnetization intensity of 6000-8000 A / m. The finished product passes through the demagnetization area at a constant speed of 50-100 mm / s for 5-10 seconds.

[0063] After demagnetization, clean again for 8-10 minutes to remove any trace iron filings that may have been adsorbed during the demagnetization process.

[0064] A hot air circulating oven is used, with a drying temperature of 90±5℃, an air velocity of 1.5m / s, and a drying time of 25-30min. After drying, the product is cooled to room temperature.

[0065] In step S09 of this embodiment, a coordinate measuring machine is used to detect key dimensions such as the outer diameter, inner diameter, and thickness of the grinding disc, and the tolerances must meet the design requirements; visual inspection is performed to ensure there are no cracks, burrs, or scratches; and hardness testing is performed again.

[0066] This invention uses powder metallurgy technology to manufacture grinding discs, which can directly press and form blanks that are highly matched to the structure of the grinding disc. Subsequent processing only requires targeted grinding to remove trace amounts of surface residue and simultaneous cleaning of residual iron filings to obtain the finished product. This not only eliminates the tedious process of frequent tool changes and multiple clamping in traditional machining, shortening the production cycle and reducing tool procurement and wear costs, but also avoids the cumulative errors caused by multiple tool changes and positioning deviations in traditional machining, resulting in high tooth profile consistency and thus improving product quality.

[0067] This invention employs a manufacturing method involving two sintering processes without oil immersion between sintering. On one hand, the absence of oil immersion completely avoids interference from additional carbon sources introduced by the oil. On the other hand, after the first sintering, the blank does not require cooling and is directly transferred to the second sintering furnace, which can quickly expel the residual trace amounts of lubricant decomposition gases and air in the pores from the first sintering, effectively preventing gas retention from hindering the densification of powder particles and improving the density of the blank. This manufacturing method can precisely control the stability of the free chromium content in the blank. Under the high temperature of the second sintering, chromium reacts fully with the substrate and trace amounts of oxygen in the furnace to form a continuous and uniform Cr-Ni-O composite passivation film. This passivation film tightly covers the surface of the grinding disc and the gaps between the cutting teeth, effectively isolating the contact between humid air and the metal substrate, significantly enhancing the grinding disc's corrosion resistance and extending its service life.

[0068] The above embodiments of the present invention are not intended to limit the scope of protection of the present invention. The implementation of the present invention is not limited thereto. All other modifications, substitutions or alterations made to the above structure of the present invention based on the above content of the present invention, in accordance with ordinary technical knowledge and common practice in the field, without departing from the basic technical idea of ​​the present invention, shall fall within the scope of protection of the present invention.

Claims

1. A powder metallurgy mill disc manufacturing method, characterized by, The method comprises the following steps: Step S01: selecting raw materials, the raw materials comprising, by weight percentage: 13%-19% chromium powder, 0.5%-1.0% carbon powder, 0.8%-1.0% lubricant, and the balance being iron powder; mixing the raw materials; Step S02: selecting a mold corresponding to the main body of the grinding disc, and molding the mixed powder raw materials into blanks in a molding machine; Step S03: placing the blanks on a ceramic plate, and spacing the adjacent two blanks; Step S04: transferring the blanks to a first sintering furnace for primary sintering; Step S05: transferring the blanks after primary sintering to a second sintering furnace for secondary sintering; Step S06: immersing the blanks after secondary sintering and cooling in oil; Step S07: polishing the blanks after oil immersion, cleaning the blanks after polishing to obtain finished products; In the step S01, the raw materials further comprise, by weight percentage, 0.2% nickel powder, and the particle size is 80-150 mesh; In the step S02, the molding pressure of the molding machine is 35-45 MPa, the pressure maintaining time is 6-8 s, and the density of the molded blank is 6.4-6.6 g / cm 3； In the step S04, the temperature of the first sintering furnace is 1120°C, and the furnace is cooled to room temperature after holding for 1h; In the step S05, the second sintering furnace temperature is 1120°C, and the temperature is kept for 3 hours, and then the furnace is cooled to room temperature. The density of the blank is ≥7.2 g / cm 3 .

2. The powder metallurgy mill disc manufacturing method according to claim 1, characterized by, In the step S01, the particle size of the iron powder is 50-100 mesh, the particle size of the chromium powder is 80-120 mesh, and the particle size of the carbon powder is 200-300 mesh.

3. The powder metallurgy mill disc manufacturing method according to claim 2, characterized by, In the step S03, the distance between the adjacent two blanks on the ceramic plate is 1-3mm, the blade surface of the blank faces upward, the flat surface faces downward, and the blank is attached to the ceramic plate.

4. The powder metallurgy pan manufacturing method according to claim 3, characterized by, In the step S06, rust-proof oil is selected, the oil bath temperature is 50-60°C, and the oil immersion time is 15-20min.

5. The powder metallurgy mill disc manufacturing method according to claim 4, characterized by, In the step S07, first, coarse grinding is performed to remove 0.2-0.3mm of machining allowance; then, fine grinding is performed to remove 0.05-0.1mm of allowance to obtain finished products; and the finished products are cleaned for 12-15min.

6. The powder metallurgy pan manufacturing method according to claim 5, characterized by, Further comprising: Step S08: demagnetizing the finished products for 5-10s; After demagnetization, cleaning and drying are performed.

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