Production process for preventing semi-sintering cracking of large pre-sintered board

Abstract

The invention relates to the technical field of hard alloy material production, in particular to a production process for preventing semi-sintering cracking of a large pre-sintered board, which comprises the following steps: S1, selecting the dosage ratio of paraffin according to the thickness of the board, weighing raw material components, and preparing into a mixture; s2, the mixture prepared in the step S1 is put into a mold to be mechanically pre-pressed, and a green body is formed; s3, putting the green body prepared and formed in the step S2 into a high-pressure container, and preparing a compact pre-sintered green body by adopting a cold isostatic pressing process; and S4, putting the pre-sintered blank prepared in the step S3 into a sintering furnace, carrying out a fixed pre-sintering process, cooling and discharging after sintering to obtain a large pre-sintered plate, and carrying out appearance detection. According to the production process, large-product pre-sintered boards can be stably prepared on a large scale, and the production rate and the yield of the boards can be improved; the problem that in the prior art, due to a pre-sintering production mode, plates crack and are scrapped is solved.

Description

Technical Field

[0001] The invention relates to the technical field of hard alloy material production, and in particular to a production process for preventing half-burned cracking of pre-burned plates of large products. Background Art

[0002] Cemented carbide is an alloy material made of hard compounds of refractory metals and bonding metals through powder metallurgy. Cemented carbide has a series of excellent properties such as high hardness, wear resistance, good strength and toughness, heat resistance, and corrosion resistance. It is used to manufacture cutting tools, knives, cobalt tools, and wear-resistant parts, and is widely used in military industry, aerospace, mechanical processing, metallurgy, oil drilling, electronic communications, and other fields.

[0003] With the development of high-tech and market needs, the market demand for cemented carbide continues to increase, and the requirements for the quality of cemented carbide products are getting higher and higher. The production scale of cemented carbide enterprises is also expanding, and the production technology is constantly improving.

[0004] Subfine-grained cemented carbide, with a grain size of ≤0.8um, has smaller grains than ordinary cemented carbide, which can increase the surface area between hard phase crystals and enhance the bonding force between crystals, thereby increasing its bending strength against plastic deformation; compared with ordinary cemented carbide, subfine-grained cemented carbide has higher strength under the same hardness conditions; under the same strength conditions, it has higher hardness; and subfine-grained cemented carbide is widely used in automatic CNC machining industry, especially in the electronics industry and precision parts processing fields due to its excellent comprehensive performance. Therefore, the stable development of low-cost subfine-grained cemented carbide is of great significance.

[0005] Cemented carbide plates have good durability and strong impact resistance, and can be used in hardware and standard stamping dies. Subfine grain (≤0.8um grain size) cemented carbide non-standard large products and cemented carbide plates are introduced below using "plates" as an example. The mainstream technical direction is to use 2.5 to 3.0 parts of wax ratio, that is, the amount of paraffin wax, through the "mechanical pre-pressing plate-C IP-pre-burning" process, and then machined into non-standard parts and then pressurized sintered or pre-burned plates and then pressurized sintered into alloy plates for customers to use for wire cutting. However, if Figure 1As shown, this pre-burning production method, with a temperature of 640℃~720℃, will cause cracking and scrapping of sub-fine-grained boards with a blank thickness greater than and / or equal to 60mm. If the blank is not pre-burned, it will not have strength and cannot be processed. Research has found that the main reason for half-burned cracking is that during the pre-burning process, the molding agent paraffin in the sub-fine-grained board needs to be removed; if the rate of paraffin removal is too fast, a large amount of steam pressure will be generated to squeeze the blank product by air pressure; and the thicker the blank thickness, the more difficult it is for the paraffin vapor in the blank to be discharged, and the easier it is for the blank product to crack during pre-burning, which leads to low board production efficiency, unstable board quality, and high defective rate, thereby increasing the production cost of the board. The present invention provides a production process for preventing half-burned cracking of pre-burned large-scale products, so as to solve the problem that the pre-burning production method in the prior art will cause sub-fine-grained boards with a blank thickness greater than and / or equal to 60mm to crack and be scrapped. Summary of the invention

[0006] The purpose of the present invention is to provide a production process for preventing half-burned cracking of pre-burned large-scale products, so as to solve the problem that the pre-burning production method in the prior art will cause the sub-fine-grained plates with a rough thickness greater than and / or equal to 60mm to crack and be scrapped.

[0007] The technical solution of the present invention is: a production process for preventing half-burned cracking of pre-burned large-scale products, comprising the following steps:

[0008] S1. According to the thickness of the plate, select the dosage ratio of paraffin wax, weigh the raw material components, and prepare a mixture;

[0009] S2, placing the mixture prepared in step S1 into a mold for mechanical pre-pressing to form a green body;

[0010] S3, placing the green body prepared in step S2 into a high-pressure container, and preparing a dense pre-sintered green body by cold isostatic pressing;

[0011] S4, placing the pre-sintered green body prepared in step S3 into a sintering furnace for a fixed pre-sintering process. After sintering, naturally cool to 50° C. and then take it out of the furnace to obtain a large pre-sintered plate product, and perform an appearance inspection;

[0012] Wherein, the raw material components include tungsten carbide powder, cobalt powder, additives and paraffin;

[0013] Calculated as a percentage of the total mass of the raw material components, the maximum thickness of the plate is ≤130 mm, and the amount of the paraffin wax that matches the thickness of the plate is 0.3%-2.0%;

[0014] The maximum thickness of the plate is inversely proportional to the amount ratio of the paraffin wax.

[0015] Preferably, in the raw material components, the amount ratio of the cobalt powder is 4%-15%, the amount ratio of the additive is 0.2%-0.8%, and the amount ratio of the tungsten carbide powder is 82.2%-95.5%.

[0016] Preferably, calculated based on the mass percentage of the raw material components, the maximum thickness of the plate is 60 mm-130 mm, and the amount of the paraffin matching the thickness of the plate is 0.5%-1.5%;

[0017] Preferably, the grain size of the tungsten carbide powder is ≤0.8um; the grain size of the cobalt powder is ≤1.0um

[0018] Preferably, the paraffin wax is paraffin wax powder; the crystal size of the paraffin wax powder is ≤1.5um.

[0019] Preferably, the preparation of the mixture comprises the following steps:

[0020] a: According to the thickness of the plate, select the dosage ratio of paraffin wax, weigh tungsten carbide powder, cobalt powder and additives, and add them into the ball mill for ball milling;

[0021] b: Weigh the paraffin wax and add it into the ball mill for ball milling;

[0022] c: The ball-milled slurry is sieved, dried and granulated to prepare a mixed material.

[0023] Preferably, the fixed pre-firing process includes: a negative pressure dewaxing stage and a vacuum pre-firing stage;

[0024] The temperature of the negative pressure dewaxing stage is set to 20°C-500°C; the temperature of the vacuum pre-burning stage is set to 640°C-720°C, and the pre-burning insulation time is 20-100min; after the negative pressure dewaxing stage is completed, the temperature in the sintering furnace rises uniformly to the temperature of the vacuum pre-burning stage, and the heating rate is 1.0-3.0°C / min.

[0025] Preferably, the negative pressure dewaxing stage includes three stages: the first stage is that the temperature in the furnace is increased from 20°C to 200°C, and is kept constant for 1 hour, and the heating rate is 0.8-3.0°C / min; the second stage is a continuous heating-constant temperature stage, the temperature is increased from 200°C to 400°C, and the temperature is kept constant for 1 hour every time the temperature rises by 50°C, and the heating rate is 0.05-1.0°C / min; the third stage is that the temperature in the furnace is increased from 400°C to 500°C, and the heating rate is 0.5-3.0°C / min.

[0026] Preferably, the heating rate of the first stage is 1.0-3.0°C / min; the heating rate of the second stage is 0.1-1.0°C / min; the heating rate of the third stage is 0.1-1.0°C / min.

[0027] Preferably, the pressure in the negative pressure dewaxing stage is 0-500 Pa; in the vacuum sintering stage, the vacuum degree is controlled at 0-50 Pa, and the pre-burning insulation time is 30-60 min.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] (1) The present invention provides a production process for preventing large pre-burned plates from cracking during half-burning. In order to effectively prevent the plates from cracking during the half-burning process, the production process controls the dosage ratio of cobalt powder and additives in the raw material components, selects the dosage ratio of paraffin that matches the maximum thickness of the plates, and prepares large pre-burned plates by sintering using a fixed sintering process. The production process can stably produce large-scale pre-burned plates, whose maximum thickness is inversely proportional to the paraffin dosage ratio. A matching paraffin dosage ratio can be selected according to the thickness of the plate, thereby reducing the amount of paraffin used; the smaller the amount of paraffin used, the less paraffin content in the plate, which is more conducive to the discharge of paraffin; at the same time, the internal vapor pressure of the plate is relatively reduced during the dewaxing process, and the extrusion of the plate by the internal vapor pressure of the plate is weakened, thereby effectively preventing the plate from cracking during the semi-burning process; at the same time, the toughness of the plate is improved, the residual stress of the plate is reduced, and the probability of the plate breaking during use is reduced; the production process can stably and in large quantities prepare large-scale pre-burned plates, which can effectively improve the productivity and finished product rate of large-scale pre-burned plates, and save the production cost of large-scale pre-burned plates; and solve the problem in the prior art that the pre-burning production method will cause the sub-fine-grained plates with a blank thickness greater than and / or equal to 60 mm to crack and be scrapped.

[0030] (2) The present invention provides a production process for preventing half-burned cracking of pre-fired large-scale product plates. The fixed sintering process of the production process is divided into a negative pressure dewaxing stage and a vacuum pre-burning stage. Among them, the negative pressure dewaxing stage is also carried out in stages, which can not only effectively control the rate of paraffin volatilization, but also make the plate heated more evenly, so that the plate allows the paraffin gas to be slowly discharged in a first and then a later order, effectively avoiding the simultaneous volatilization of the paraffin inside and outside the plate, which may cause the plate to crack. In the first stage, the temperature is raised uniformly from room temperature to make the paraffin begin to volatilize, and the heating rate is controlled so that the volatilization rate of the paraffin gradually increases, and the slope of the gradual increase tends to be stable, so as to achieve the purpose of controlling the volatilization rate of the paraffin. The constant temperature for 1 hour can make the heating of the inside and outside of the board more uniform; the second stage includes multiple continuous heating-constant temperature processes, and the heating rate is significantly lower than that of the first stage. These slow heating-constant temperature processes are conducive to better controlling the volatilization rate of the paraffin, so that the volatilization rate of the paraffin is gradually and stably increased, which can effectively prevent the volatilization rate of the paraffin from suddenly increasing. The constant temperature process can also make the heating of the inside and outside of the board more uniform, so that the paraffin gas is slowly discharged in the order of first and then, avoiding the occurrence of the phenomenon of gas pressure squeezing and cracking of the board due to the excessive discharge rate and the generation of a large amount of steam pressure; in the third stage, the temperature is raised uniformly and kept warm for 1 hour, while controlling the volatilization rate of the paraffin, the paraffin in the pre-burned blank is further discharged, so that the paraffin in the pre-burned blank is completely discharged.

[0031] (3) The present invention provides a production process for preventing half-burned cracking of pre-fired plates for large products. The production process uses paraffin wax powder as a molding agent. Compared with the traditional method of melting paraffin wax and adding it to a mixture, adding uniform powdered paraffin wax to the mixture can effectively solve the problem of uneven mixing and uneven shape of the mixture caused by paraffin wax agglomeration, making the density of the pre-fired blank more uniform and avoiding the occurrence of pores, holes, pits, and cobalt segregation inside the plate after sintering.

[0032] (4) The present invention provides a production process for preventing large pre-burned plates from cracking during half-burning. The production process can control the sintering process to be fixed and the amount of paraffin in the mixture as a single variable to produce large pre-burned plates of different thicknesses, thereby effectively preventing the plates from cracking during the half-burning process; the production process can be accurately implemented and is easy to control the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0034] Figure 1 This is a photo of the appearance of a large product plate in the prior art described in the present invention;

[0035] Figure 2 This is a photo of the appearance of the pre-sintered green body of the present invention when it is loaded into the furnace;

[0036] Figure 3 This is a photo of the appearance of the large product plate prepared in Example 1 of the present invention;

[0037] Figure 4 This is a photo of the appearance of the large product plate prepared in Example 2 of the present invention;

[0038] Figure 5 This is a photograph of the appearance of the large product plate prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with specific embodiments:

[0040] It should be further explained that the "mass ratio, mass parts" in the present invention correspond to the dry weight of the raw materials and the initial state of each additive; the "parts" in the embodiments of the present invention are parts by mass, and the mass of each part can be confirmed according to actual needs. For example, in each embodiment, each "part" can be calibrated as 1Kg, and then 40 parts are 40Kg, 0.1 parts are 0.1Kg, and other parts by mass are the same.

[0041] Example 1

[0042] A production process for preventing half-burned cracking of pre-burned large-scale products comprises the following steps:

[0043] S1. According to the thickness of the plate, select the amount ratio of paraffin wax, weigh the raw materials, and prepare a mixture;

[0044] a: Select the amount ratio of paraffin wax to be 1.5%, weigh 5 parts of cobalt powder, 0.4 parts of additives and 93.1 parts of tungsten carbide powder, and add them into a ball mill for ball milling; wherein the grain size of tungsten carbide powder is 0.6um, and the grain size of cobalt powder is 0.8um;

[0045] b: Weigh 1.5 parts of paraffin powder and add it into the above ball mill for ball milling;

[0046] c. Screening, drying and granulating the ball-milled slurry to obtain a mixed material;

[0047] S2, placing the mixture prepared in step S1 into molds of different sizes for mechanical pre-pressing to form a green body;

[0048] S3, placing the green body prepared in step S2 into a high-pressure container, and performing a cold isostatic pressing process under the conditions of holding the pressure at 150 MPa for 3 minutes, holding the pressure at 100 MPa for 2 minutes, and holding the pressure at 50 MPa for 1 minute to obtain a dense pre-sintered green body;

[0049] The specifications of the pre-fired green body (length*width*thickness) are: 210mm*210mm*60mm, 210mm*210mm*75mm;

[0050] S4, such as Figure 2 As shown, the pre-fired green body prepared in step S3 is placed in a sintering furnace and arranged neatly for a fixed pre-fired process; the fixed pre-fired process includes a negative pressure dewaxing stage and a pre-fired stage; in the negative pressure dewaxing stage: first, the temperature of the sintering furnace is uniformly increased from room temperature to 200°C, and kept constant for 1 hour, and the heating rate is 1.2°C / min, and negative pressure dewaxing is performed; then a continuous heating-constant temperature process is performed, so that the temperature in the sintering furnace is uniformly increased from 200°C to 400°C, and the heating rate is 0.125°C / min, so as to control the dewaxing speed of the pre-fired green body, and the temperature in the sintering furnace is kept constant for 1 hour every time it increases by 50°C, and then the temperature is continuously increased, that is, the temperature is first increased from 200°C to 250°C and then kept constant for 1 hour, and then the temperature is increased from 200°C to 250°C. The temperature is raised from 250℃ to 300℃ and kept constant for 1h, then the temperature is raised from 300℃ to 350℃ and kept constant for 1h, and finally the temperature is raised from 350℃ to 400℃ and kept constant for 1h; finally the temperature is raised from 400℃ to 500℃ and kept constant for 1h, the heating rate is 0.65℃ / min, and the paraffin in the pre-burned body is further discharged, so that the paraffin in the pre-burned body is completely discharged; after the dewaxing stage is completed, the sintering furnace is evacuated, and the temperature in the furnace is raised to 720℃ at the same time, the heating rate is 2.0℃ / min, and it is kept warm for 40 minutes to carry out the vacuum pre-burning stage; after the sintering is completed, it is naturally cooled to 50℃ and then taken out of the furnace to obtain a large pre-burned plate, and the appearance inspection is carried out.

[0051] The paraffin wax volatilization temperature is 370-380°C; however, the paraffin wax volatilization process does not occur suddenly, but gradually as the temperature rises, and as the temperature rises, the paraffin wax volatilization rate gradually increases, reaching a maximum value at 370-380°C. The present application controls the wax discharge rate by controlling the heating rate in the dewaxing stage and dewaxing in stages, thereby preventing the discharge rate from being too fast, and preventing the paraffin wax discharge from generating a large amount of steam pressure that squeezes and cracks the pre-sintered green body.

[0052] In different embodiments, the changes in each temperature section during the fixed pre-firing process can be adjusted according to actual needs and equipment level, and the temperature, heating rate, and holding time of each temperature section during the fixed pre-firing process can also be adjusted according to the specifications of the pre-firing plates of large products, the amount of furnace loading, the grain size of each component in the raw material components, etc. In general, the larger the specifications of the plates, the more furnace loading, and the finer the material particle size, the heating time or the holding time will be slightly adjusted, and the time will be increased by 30-120 minutes.

[0053] Example 2

[0054] The difference between this embodiment and embodiment 1 is that the dosage ratio of the selected paraffin wax is different, the dosage ratio of each component in the raw material is different, the grain size of some components in the raw material components is different, and in the fixed sintering process, the heating rate in the dewaxing stage, the heating rate in the vacuum pre-burning stage and the sintering temperature are different.

[0055] A production process for preventing half-burned cracking of pre-burned large-scale products comprises the following steps:

[0056] S1. Select the amount ratio of paraffin wax according to the thickness of the plate, weigh the raw materials, and prepare a mixture;

[0057] a: Select the amount of paraffin wax as 0.8%, weigh 8 parts of cobalt powder, 0.5 parts of additives and 90.7 parts of tungsten carbide powder, and add them into a ball mill for ball milling; wherein the grain size of tungsten carbide powder is 0.7um, and the grain size of cobalt powder is 0.6um;

[0058] b: Weigh 0.8 parts of solid paraffin wax and add it into the above ball mill for ball milling;

[0059] c. Screening, drying and granulating the ball-milled slurry to obtain a mixed material;

[0060] S2, placing the mixture prepared in step S1 into molds of different sizes, and pre-pressing in the same manner as in Example 1 to form a green body;

[0061] S3, preparing the green body prepared in step S2 by the same cold isostatic pressing process as in Example 1 to obtain a dense pre-sintered green body;

[0062] The specifications (length*width*thickness) of the pre-sintered green body are: 210mm*210mm*60mm, 210mm*210mm*75mm, 210mm*210mm*90mm, 210mm*210mm*100mm, 210mm*210mm*110mm;

[0063] S4, the pre-sintered green body prepared in step S3 is placed in a sintering furnace, and sintered using the same fixed pre-sintering process as in Example 1. First, the temperature of the sintering furnace is uniformly increased from room temperature to 200°C, and the temperature is kept constant for 1 hour at a heating rate of 1.1 / min, and negative pressure dewaxing is performed; then a continuous heating-constant temperature process is performed, so that the temperature in the sintering furnace is uniformly increased from 200°C to 400°C at a heating rate of 0.1°C / min, so as to control the dewaxing speed of the pre-sintered green body, and the temperature in the sintering furnace is kept constant for 1 hour every time the temperature rises by 50°C , and then continue to heat up; finally, raise the temperature from 400℃ to 500℃, and keep the temperature constant for 1h, with a heating rate of 0.6℃ / min, and further discharge the paraffin in the pre-burned body, so that the paraffin in the pre-burned body is completely discharged; after the dewaxing stage is completed, evacuate the sintering furnace, and at the same time raise the temperature in the furnace to 640℃, with a heating rate of 1.4℃ / min, and keep warm for 50 minutes, and carry out the vacuum pre-burning stage; after sintering is completed, naturally cool to 50℃ and then take out of the furnace to obtain a large pre-burned plate, and conduct appearance inspection. In this application, the molding agent paraffin can be selected from different forms of paraffin, such as solid paraffin, liquid paraffin or powdered paraffin, etc. Powdered paraffin is preferred, and the crystal size of the paraffin is preferably not more than 1.5um.

[0064] Example 3

[0065] The difference between this embodiment and embodiment 1 is that the dosage ratio of the selected paraffin wax is different, the dosage ratio of each component in the raw material is different, the grain size of some components in the raw material components is different, and in the fixed sintering process, the heating rate in the dewaxing stage, the heating rate in the vacuum pre-burning stage and the sintering temperature are different.

[0066] A production process for preventing half-burned cracking of pre-burned large-scale products comprises the following steps:

[0067] S1. Select the amount ratio of paraffin wax according to the thickness of the plate, weigh the raw materials, and prepare a mixture;

[0068] a: Select the amount of paraffin wax to be 0.5%, weigh 12 parts of cobalt powder, 0.52 parts of additives and 87 parts of tungsten carbide powder, and add them into a ball mill for ball milling; wherein the grain size of tungsten carbide powder is 0.8um, and the grain size of cobalt powder is 0.6um;

[0069] b: Weigh 0.5 parts of paraffin wax and add it into the above ball mill for ball milling;

[0070] c. Screening, drying and granulating the ball-milled slurry to obtain a mixed material;

[0071] S2, placing the mixture prepared in step S1 into molds of different sizes, and pre-pressing in the same manner as in Example 1 to form a green body;

[0072] S3, preparing the green body prepared in step S2 by the same cold isostatic pressing process as in Example 1 to obtain a dense pre-sintered green body;

[0073] The specifications (length*width*thickness) of the pre-sintered green body are: 210mm*210mm*60mm, 210mm*210mm*75mm, 210mm*210mm*90mm, 210mm*210mm*100mm, 210mm*210mm*110mm; 210mm*210mm*130mm;

[0074] S4, the pre-sintered green body prepared in step S3 is placed in a sintering furnace, and sintered using the same fixed pre-sintering process as in Example 1. First, the temperature of the sintering furnace is uniformly increased from room temperature to 200°C, and the temperature is kept constant for 1 hour at a heating rate of 1.15 / min, and negative pressure dewaxing is performed; then a continuous heating-constant temperature process is performed, so that the temperature in the sintering furnace is uniformly increased from 200°C to 400°C at a heating rate of 0.25°C / min, so as to control the dewaxing speed of the pre-sintered green body, and the temperature in the sintering furnace is kept constant for 1 hour every time the temperature rises by 50°C. , and then continue to heat up; finally, the temperature is raised from 400℃ to 500℃ and kept constant for 1h at a heating rate of 0.7℃ / min to further discharge the paraffin in the pre-burned body, so that the paraffin in the pre-burned body is completely discharged; after the dewaxing stage is completed, the sintering furnace is evacuated, and the temperature in the furnace is raised to 720℃ at a heating rate of 2.2℃ / min, and kept warm for 30 minutes to carry out the vacuum pre-burning stage; after sintering is completed, it is naturally cooled to 50℃ and then taken out of the furnace to obtain a large pre-burned plate, and an appearance inspection is carried out.

[0075] Example 4

[0076] The difference between this embodiment and embodiment 1 is that the dosage ratio of the selected paraffin wax is different, the dosage ratio of each component in the raw material is different, the grain size of some components in the raw material components is different, and in the fixed sintering process, the heating rate in the dewaxing stage, the heating rate in the vacuum pre-burning stage and the sintering temperature are different.

[0077] A production process for preventing half-burned cracking of pre-burned large-scale products comprises the following steps:

[0078] S1. Select the amount ratio of paraffin wax according to the thickness of the plate, weigh the raw materials, and prepare a mixture;

[0079] a: Select the amount of paraffin wax to be 0.6%, weigh 10 parts of cobalt powder, 0.45 parts of additives and 88.95 parts of tungsten carbide powder, and add them into a ball mill for ball milling; wherein the grain size of tungsten carbide powder is 0.7um, and the grain size of cobalt powder is 0.8um;

[0080] b: Weigh 0.6 parts of paraffin wax powder and add it into the above ball mill for ball milling; the particle size of the paraffin wax is 1.5 um;

[0081] c. Screening, drying and granulating the ball-milled slurry to obtain a mixed material;

[0082] S2, placing the mixture prepared in step S1 into molds of different sizes for mechanical pre-pressing to form a green body;

[0083] S3, preparing the green body prepared in step S2 by the same cold isostatic pressing process as in Example 1 to obtain a dense pre-sintered green body;

[0084] The specifications (length*width*thickness) of the pre-sintered green body are: 210mm*210mm*60mm, 210mm*210mm*75mm, 210mm*210mm*90mm, 210mm*210mm*100mm, 210mm*210mm*110mm; 210mm*210mm*130mm;

[0085] S4, the pre-sintered green body prepared in step S3 is placed in a sintering furnace, and sintered using the same fixed pre-sintering process as in Example 1. First, the temperature of the sintering furnace is uniformly increased from room temperature to 200°C, and the temperature is kept constant for 1 hour at a heating rate of 1.2 / min, and negative pressure dewaxing is performed; then a continuous heating-constant temperature process is performed, so that the temperature in the sintering furnace is uniformly increased from 200°C to 400°C at a heating rate of 0.125°C / min, so as to control the dewaxing speed of the pre-sintered green body, and the temperature in the sintering furnace is kept constant for 1 hour every time the temperature rises by 50°C , and then continue to heat up; finally, the temperature is raised from 400℃ to 500℃, and kept at a constant temperature for 1h, with a heating rate of 0.67℃ / min, to further discharge the paraffin in the pre-burned body, so that the paraffin in the pre-burned body is completely discharged; after the dewaxing stage is completed, the sintering furnace is evacuated, and the temperature in the furnace is raised to 680℃, with a heating rate of 1.8℃ / min, and kept warm for 60 minutes, and the vacuum pre-burning stage is carried out; after the sintering is completed, it is naturally cooled to 50℃ and then taken out of the furnace to obtain a large pre-burned plate, and the appearance inspection is carried out.

[0086] Example 5

[0087] The difference between Example 5 and Example 4 is that the dosage ratio of the selected paraffin is different; the dosage ratio of the paraffin selected in this embodiment is 0.9%, and the corresponding dosage ratio of tungsten carbide is 88.65; the above method is used to prepare pre-fired blanks of different sizes, and the pre-fired blanks are placed in a sintering furnace for a fixed pre-fired process; after sintering is completed, they are naturally cooled to 50°C and then taken out of the furnace to obtain large pre-fired plates, and an appearance inspection is performed.

[0088] In this embodiment, the specifications (length*width*thickness) of the pre-sintered green body are: 210mm*210mm*60mm, 210mm*210mm*75mm, 210mm*210mm*90mm, 210mm*210mm*100mm;

[0089] Example 6

[0090] The difference between Example 6 and Example 4 is that the dosage ratio of the selected paraffin is different; the dosage ratio of the paraffin selected in this embodiment is 1.2%, and the corresponding dosage ratio of tungsten carbide is 88.35; the above method is used to prepare pre-fired blanks of different sizes, and the pre-fired blanks are placed in a sintering furnace for a fixed pre-fired process; after sintering is completed, they are naturally cooled to 50°C and then taken out of the furnace to obtain large pre-fired plates, and an appearance inspection is performed.

[0091] In this embodiment, the specifications (length*width*thickness) of the pre-sintered green body are: 210mm*210mm*60mm, 210mm*210mm*75mm, 210mm*210mm*90mm;

[0092] The large pre-burned plates prepared in Examples 1-6 of the present invention were subjected to appearance inspection. At the same time, in order to reduce the error, under the conditions of the same embodiment, 4 samples were prepared at the same time for each specification of pre-burned blank, and a fixed pre-burning process was carried out under the same conditions. After sintering, the plates were cooled and taken out of the furnace for appearance inspection. The inspection results are shown in Table 1. The large pre-burned plates prepared in each embodiment were tested starting from the pre-burned blank thickness of 60 mm, and gradually increased until the pre-burned blank thickness was 130 mm. As long as one of the 4 samples had cracks, the inspection was stopped. The paraffin dosage ratio can be obtained to effectively prevent half-burned cracking, corresponding to the limit value of the thickness of the large pre-burned plates. Among them, the maximum thickness of the large pre-burned plates tested was 130 mm, and large pre-burned plates greater than 130 mm had no practical production significance.

[0093] Table 1. Cracking of large pre-sintered plates prepared in Examples 1-6

[0094]

[0095]

[0096] As shown in Table 1, the amount of paraffin wax in Example 1 is 1.5%, and the pre-sintered green body prepared is sintered in a fixed sintering process, cooled and taken out of the furnace, and an appearance inspection is performed; Figure 3As described above, the pre-burned body with a thickness of 75mm has cracks; it can be seen that when the amount of paraffin wax is 1.5%, the thickness limit of the large pre-burned plate prepared by the above process without cracking is less than 75mm, that is, when the amount of paraffin wax is 1.5%, the large pre-burned plate prepared by the above process, in order to prevent the plate from half-burning and cracking, its maximum thickness should be less than 75mm. In Example 2, the amount of paraffin wax is 0.8%, and the pre-burned body prepared is sintered in a fixed sintering process, cooled and taken out of the furnace, and an appearance inspection is performed; Figure 4 As described above, the pre-burned body with a thickness of 100mm has cracks; therefore, when the amount of paraffin wax is 0.8%, the thickness limit of the large pre-burned plate prepared by the above process without cracking is less than 110mm, that is, when the amount of paraffin wax is 0.8%, the large pre-burned plate prepared by the above process, in order to prevent the plate from half-burning and cracking, its maximum thickness should be less than 110mm. Similarly, in Example 3, the amount of paraffin wax is 0.5%, and the pre-burned body prepared is sintered in a fixed sintering process, cooled and taken out of the furnace, and an appearance inspection is performed; as Figure 5 It is described that no cracked pre-burning was found in the pre-burned blanks with a thickness of 60-130 mm; it can be seen that when the dosage ratio of paraffin is 0.5%, the thickness limit of the large pre-burned plate prepared by the above process without cracking can reach at least 130 mm, that is, when the dosage ratio of paraffin is 0.5%, the large pre-burned plate prepared by the above process, in order to prevent the plate from half-burning and cracking, its thickness should not exceed 130 mm. Therefore, it can be seen from Examples 1-3 that in order to prevent the large pre-burned plate from half-burning and cracking, the large pre-burned plate is prepared stably and with high yield. When the above production process is adopted, the larger the dosage ratio of paraffin is selected, the smaller the maximum thickness that can be achieved; conversely, the smaller the dosage ratio of paraffin is selected, the larger the maximum thickness range that can be achieved; that is, in order to effectively prevent the plate from half-burning and cracking, the maximum thickness that can be achieved by the large pre-burned plate is inversely proportional to the dosage ratio of paraffin.

[0097] It can be seen from Examples 4-6 that when the dosage ratio of paraffin is selected as a single variable, the dosage ratio of the corresponding tungsten carbide is different; the dosage ratio of cobalt powder and the dosage ratio of additives are controlled to be fixed values, and the grain size of the raw material is controlled to be fixed values; the above production process is used to prepare large-scale pre-burned plates, and in the fixed sintering process, the heating rate in the dewaxing stage is the same, and the heating rate, sintering temperature and insulation time in the vacuum pre-burning stage are the same; as shown in Table 1, when the dosage ratio of paraffin is 0.6%, the maximum thickness that can be achieved by the large-scale pre-burned plate is less than 130mm; when the dosage ratio of paraffin is 0.9%, the maximum thickness that can be achieved by the large-scale pre-burned plate is less than 100mm; when the dosage ratio of paraffin is 1.2%, the maximum thickness that can be achieved by the large-scale pre-burned plate is less than 90mm. Therefore, it can be further explained that in order to effectively prevent the half-burned cracking of the plate, the maximum thickness that can be achieved by the prepared large-scale pre-burned plate is inversely proportional to the dosage ratio of paraffin.

[0098] Embodiment 7-11

[0099] In Examples 7-11, the dosage ratio of cobalt powder and additives is set to a fixed value under the same conditions, the dosage ratio of paraffin is adjusted, and the rest is tungsten carbide; and the grain size of each raw material component is set to a fixed value; the above production process is used to prepare large pre-burned plates with a thickness of 70 mm, and the heating rate in the dewaxing stage is set to be the same in the fixed sintering process, and the heating rate, sintering temperature and holding time in the vacuum pre-burning stage are the same. In Examples 7-11, 4 samples are prepared at the same time, and appearance and performance tests are performed on them respectively. The test results are shown in Table 2.

[0100] Table 2. Performance test results of large pre-sintered plates prepared in Examples 7-11

[0101]

[0102]

[0103] As can be seen from Table 2, in Examples 7-11, the dosage ratio of cobalt powder, the dosage ratio of additives and the fixed sintering process are all set to be the same, and large-scale pre-burned plates of the same thickness are prepared under different paraffin dosage ratios; in the prepared large-scale pre-burned plates, the lower the dosage ratio of paraffin, the less paraffin remains in the plate after the sintering process is completed, and the lower the residual carbon content in the plate, thereby significantly reducing the carbon gradient of the plate after sintering; thereby improving the toughness of the plate, reducing the residual stress of the plate, effectively preventing the half-burned cracking of the plate, and reducing the probability of the plate collapsing during use; however, in the preparation of large-scale pre-burned plates of the same thickness, the lower the dosage ratio of the selected paraffin, the lower the residual carbon content in the plate after sintering, and the lower the carbon gradient of the plate, which will cause the magnetic saturation of the plate to be significantly reduced, thereby deteriorating the magnetic properties of the plate and affecting the use effect of the plate. Therefore, when preparing large pre-burned plates of the same thickness, in order to effectively prevent the plates from cracking and reduce the probability of plate breakage, and to ensure that the plates have good magnetic properties, the amount of paraffin used should be as large as possible.

[0104] Example 12

[0105] The difference between Example 12 and Example 4 is that the dosage ratio of the selected paraffin wax is different; the dosage ratio of the paraffin wax selected in this embodiment is 2.0%, and the rest is tungsten carbide; the above method is used to prepare pre-fired blanks of different sizes, and the pre-fired blanks are placed in a sintering furnace for a fixed pre-fired process; after sintering is completed, they are naturally cooled to 50°C and then taken out of the furnace to obtain large pre-fired plates, and the appearance and performance tests are performed on them respectively. The test results data are shown in Table 3.

[0106] In this embodiment, the thickness of the pre-sintered green body is 5 mm, 10 mm, 30 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, and 80 mm, respectively.

[0107] Table 3. Performance test results of large pre-sintered plates of different specifications prepared in Example 12

[0108]

[0109]

[0110] It can be seen from Table 3 that in Example 12, the dosage ratio of cobalt powder, the dosage ratio of additives, and the dosage ratio of paraffin are set as fixed values, and under the same fixed sintering process conditions, large-scale pre-burned plates with different thicknesses are prepared; in the prepared large-scale pre-burned plates, the thinner the thickness of the plate, the less paraffin remains in the plate after the sintering process is completed; as the thickness of the plate increases, the amount of paraffin remaining in the plate gradually increases. It can be seen that when the amount ratio of paraffin wax is a fixed value, under the same fixed sintering process conditions, the thinner the prepared large product pre-burned plate, the lower the residual carbon content in the plate, and the carbon gradient of the plate after sintering is significantly reduced; thereby improving the toughness of the plate, reducing the residual stress of the plate, effectively preventing the half-burned cracking of the plate, and reducing the probability of the plate breaking during use; similarly, when preparing large product pre-burned plates of the same thickness, when the amount ratio of the selected paraffin wax is the same, the thinner the thickness of the plate, the lower the residual carbon content in the plate after sintering, and the lower the carbon gradient of the plate, which will lead to a significant reduction in the magnetic saturation of the plate, thereby deteriorating the magnetic properties of the plate and affecting the use effect of the plate. Therefore, under the same amount ratio of paraffin wax, when preparing large product pre-burned plates of different thicknesses, in order to effectively prevent the cracking of the plate and reduce the probability of the plate breaking, and to ensure that the plate has good magnetic properties, the thickness of the plate should be as thick as possible.

[0111] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description, and it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention.

Claims

1. A production process for preventing half-burned cracking of pre-burned large-scale products, characterized in that: The following steps are involved: S1. According to the thickness of the plate, select the dosage ratio of paraffin wax, weigh the raw material components, and prepare a mixture; S2, placing the mixture prepared in step S1 into a mold for mechanical pre-pressing to form a green body; S3, placing the green body prepared in step S2 into a high-pressure container, and preparing a dense pre-sintered green body by cold isostatic pressing; S4, placing the pre-sintered green body prepared in step S3 into a sintering furnace for a fixed pre-sintering process. After sintering, naturally cool to 50° C. and then take it out of the furnace to obtain a large pre-sintered plate product, and perform an appearance inspection; Wherein, the raw material components include tungsten carbide powder, cobalt powder, additives and paraffin; Calculated as a percentage of the total mass of the raw material components, the maximum thickness of the plate is ≤130 mm, and the amount of the paraffin wax that matches the thickness of the plate is 0.3%-2.0%; The maximum thickness of the plate is inversely proportional to the amount ratio of the paraffin wax.

2. A production process for preventing half-burned cracking of pre-burned large-scale products according to claim 1, characterized in that: In the raw material components, the usage ratio of the cobalt powder is 4%-15%, the usage ratio of the additive is 0.2%-0.8%, and the usage ratio of the tungsten carbide powder is 82.2%-95.5%.

3. A production process for preventing half-burned cracking of pre-burned large-scale products according to claim 2, characterized in that: Calculated based on the mass percentage of the raw material components, the maximum thickness of the plate is 60 mm-130 mm, and the amount of the paraffin wax that matches the thickness of the plate is 0.5%-1.5%.

4. A production process for preventing half-burned cracking of large pre-burned plates according to claim 2, characterized in that: The grain size of the tungsten carbide powder is ≤0.8um; the grain size of the cobalt powder is ≤1.0um.

5. A production process for preventing half-burned cracking of large pre-burned plates according to claim 4, characterized in that: The paraffin wax is paraffin wax powder; the crystal size of the paraffin wax powder is ≤1.5um.

6. A production process for preventing half-burned cracking of large pre-burned plates according to claim 2 or 3, characterized in that: The preparation of the mixed material comprises the following steps: a: According to the thickness of the plate, select the dosage ratio of paraffin wax, weigh tungsten carbide powder, cobalt powder and additives, and add them into the ball mill for ball milling; b: Weigh the paraffin wax and add it into the ball mill for ball milling; c: The ball-milled slurry is sieved, dried and granulated to prepare a mixed material.

7. A production process for preventing half-burned cracking of large pre-burned plates according to claim 6, characterized in that: The fixed pre-burning process includes: a negative pressure dewaxing stage and a vacuum pre-burning stage; The temperature of the negative pressure dewaxing stage is set to 20°C-500°C; the temperature of the vacuum pre-burning stage is set to 640°C-720°C, and the pre-burning insulation time is 20-100min; after the negative pressure dewaxing stage is completed, the temperature in the sintering furnace rises uniformly to the temperature of the vacuum pre-burning stage, and the heating rate is 1.0-3.0°C / min.

8. A production process for preventing half-burned cracking of pre-burned large-scale products according to claim 7, characterized in that: The negative pressure dewaxing stage includes three stages: the first stage is that the temperature in the furnace rises from 20°C to 200°C and is kept constant for 1 hour, and the heating rate is 0.8-3.0°C / min; the second stage is a continuous heating-constant temperature stage, the temperature rises from 200°C to 400°C, and is kept constant for 1 hour every time the temperature rises by 50°C, and the heating rate is 0.05-1.0°C / min; the third stage is that the temperature in the furnace rises from 400°C to 500°C, and the heating rate is 0.5-3.0°C / min.

9. A production process for preventing half-burned cracking of large pre-burned plates according to claim 8, characterized in that: The heating rate of the first stage is 1.0-3.0°C / min; the heating rate of the second stage is 0.1-1.0°C / min; the heating rate of the third stage is 0.1-1.0°C / min.

10. A production process for preventing half-burned cracking of pre-burned large-scale products according to claim 8, characterized in that: The pressure of the negative pressure dewaxing stage is 0-500Pa; the vacuum degree of the vacuum sintering stage is controlled within 0-50Pa, and the pre-firing insulation time is 30-60min.

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