A method for reducing sintering distortion of large hard metal articles

Abstract

The application belongs to the technical field of hard alloy and particularly relates to a method for reducing sintering deformation of large hard alloy products, which comprises the following steps: S1, obtaining hard alloy mixture, filling the hard alloy mixture into a mold through a blanking net disc for pressing to obtain a pressed compact, the density of the pressed compact gradually increases from the center point to the outermost edge in the horizontal direction; S2, loading the pressed compact into a furnace for sintering to obtain a large hard alloy product. The blanking net disc can change the density difference between the outer part and the center part of the pressed compact in the pressing process, reduce defects such as cracks, and make the shrinkage rate of the outer part during sintering faster, thereby reducing the bottom concave deformation caused by the large volume; two thin groove boats are used to clamp the pressed compact, and a layer of ashless paper is placed between the thin groove boats and the pressed compact, so that the alloy has the same dewaxing condition and heat load during sintering, and the above optimization is performed during the pressing and sintering processes of the hard alloy, so that the sintering deformation of the large hard alloy product is reduced.

Description

Technical Field

[0001] This application relates to the field of cemented carbide technology, specifically, to a method for reducing the sintering deformation of cemented carbide in large products. Background Technology

[0002] Cemented carbide, prepared using powder metallurgy, is a composite material consisting of a refractory metal hard phase and a metal binder phase. This material possesses excellent properties such as high hardness, high wear resistance, and high elastic modulus, holding an irreplaceable position in advanced manufacturing and often referred to as the "teeth of industry." Cemented carbide for large-scale products is a common category, suitable for various processing scenarios such as grinding, stamping, and mold making, and is widely used in the machinery manufacturing and metal processing industries.

[0003] Dimensional accuracy is one of the key quality indicators of cemented carbide, especially for high-precision alloy products. During the blank manufacturing process, the final dimensions of the alloy are determined through a sintering process. This process transforms porous powder compacts into dense materials with microstructures and properties that meet design requirements. After sintering, the hardness and strength of the alloy are significantly improved, and the dimensions are fixed. If the sintering deformation is too large, subsequent grinding will be extremely difficult and the cost will be far higher than the previous process.

[0004] Compared to standard-sized products, large-sized cemented carbide products (such as standard-sized plates and large cold heading dies) are prone to uneven powder density distribution during the pressing stage due to their larger volume. During sintering, dewaxing and shrinkage occur gradually from the surface inwards, leading to inconsistent shrinkage in different areas. Under the combined effect of these two factors, large products are more susceptible to sintering deformation, correspondingly increasing subsequent processing costs. To effectively control the production cost of large-sized cemented carbide products, optimization of the pressing and sintering processes is necessary to reduce deformation and improve dimensional stability. Therefore, there is an urgent need to develop a method to reduce sintering deformation in large-sized cemented carbide products. Summary of the Invention

[0005] To solve the above-mentioned technical problems, this application provides a method for reducing the sintering deformation of large cemented carbide products, comprising the following steps: S1, obtaining a cemented carbide mixture, loading the cemented carbide mixture into a mold through a feeding tray for pressing to obtain a compact, wherein the density of the compact gradually increases from the center point to the outermost edge in the horizontal direction; S2, loading the compact into a furnace and sintering to obtain large cemented carbide products.

[0006] As a preferred embodiment of the method for reducing sintering deformation of large cemented carbide products described in this application, in step S1, the material of the feeding mesh includes stainless steel.

[0007] As a preferred embodiment of the method for reducing sintering deformation of large cemented carbide products described in this application, in step S1, the shape of the feeding mesh is the same as the shape of the filling port of the mold, and the area of ​​the feeding mesh is slightly smaller than the area of ​​the filling port of the mold.

[0008] As a preferred embodiment of the method for reducing sintering deformation of large cemented carbide products described in this application, in step S1, the feeding screen has sieve holes of the same size, the diameter of the sieve holes is 2-4 mm, and the distribution of the sieve holes is as follows: the feeding screen is divided into four regions at equal distances along a straight line from the center point to the outermost edge, and the sieve holes are evenly distributed in each of the four regions. The distance between the sieve holes in different regions is different. Specifically, the distance between the sieve holes in each region from the center point to the outermost edge becomes smaller and smaller, and the ratio of the distance between the sieve holes in each region from the center point to the outermost edge is (1.3-1.4):(1.2-1.3):(1.1-1.2):(1-1.1).

[0009] As a preferred embodiment of the method for reducing sintering deformation of large cemented carbide products according to this application, in step S1, the filling method is as follows: the screen holes of the feeding tray are closed and blocked by a pallet, the cemented carbide mixture is evenly and flatly spread in the feeding tray, the feeding tray is then transferred to the filling port of the mold, the pallet is removed, and the feeding tray is quickly placed into the mold, and the cemented carbide mixture enters the mold through the screen holes.

[0010] As a preferred embodiment of the method for reducing sintering deformation of large cemented carbide products described in this application, in step S2, the furnace loading method is as follows: two grooved boats are used to clamp the compact, the working surface of the grooved boat is in contact with the upper and lower surfaces of the compact, a layer of ashless paper is placed on the contact surface of the grooved boat and the compact, and then the furnace loading is completed.

[0011] As a preferred embodiment of the method for reducing sintering deformation of large cemented carbide products described in this application, in step S2, the substrate material of the fine groove boat is graphite, and the working surface of the fine groove boat has a coating, the material of which includes MgO.

[0012] As a preferred embodiment of the method for reducing sintering deformation of large cemented carbide products described in this application, in step S2, the ashless paper comprises cellulose.

[0013] As a preferred embodiment of the method for reducing sintering deformation of large cemented carbide products described in this application, in step S2, the working surface of the fine groove boat is uniformly distributed with elongated strip grooves, the dimensions of the strip grooves are: width: 1-3mm, depth: 1-2mm, and the interval between the strip grooves is 2-5mm.

[0014] As a preferred embodiment of the method for reducing sintering deformation of large cemented carbide products according to this application, in step S2, the cemented carbide of the large product includes WC-Co series cemented carbide; the dimensions of the cemented carbide of the large product are: length ≥ 100 mm, width ≥ 100 mm, height ≥ 25 mm or diameter ≥ 100 mm, height ≥ 25 mm; the height deformation of the cemented carbide of the large product is ≤ 1.5 mm.

[0015] The beneficial effects of this application are as follows:

[0016] This application proposes a method for reducing the sintering deformation of large cemented carbide products, and designs and uses a feeding tray and a fine-groove boat.

[0017] 1. The feeding tray is made of stainless steel, which will not react with the hard alloy mixture and contaminate the raw materials. It is easy to clean and store after use. Its shape should be the same as the filling port of the pressing mold, but its area should be slightly smaller to allow it to be fully inserted into the mold. The feeding tray has sieve holes of the same size, with a diameter of 2-4mm, distributed in four equal parts from the inside out. The ratio of the distance between the sieve holes in each area from the center to the outermost area is (1.3-1.4):(1.2-1.3):(1.1-1.2):(1-1.1). In use, use a support plate to seal the sieve holes of the feeding tray, evenly and flatly spread the mixture required for pressing the compact in the feeding tray, then transfer the feeding tray above the mold filling port, remove the support plate, and quickly place the feeding tray into the mold. The mixture will then begin to enter the mold through the sieve holes. After the mixture is filled with feed mesh, it has passed through the sieve holes at different distances in each area, forming a material pile with different densities on the outside and in the center. After pressing, there is a density difference from the outside to the center of the compact, and the overall density of the compact gradually increases from the center to the outside.

[0018] 2. Fine-groove boat-shaped vessel, with graphite as the base material, is used in conjunction with ashless paper. It can withstand the high-temperature sintering temperature of cemented carbide without deformation and is often used as a carrier for cemented carbide sintering. The working surface has evenly distributed strip grooves, and a spray coating is applied to the working surface. It can withstand the high temperature of sintering and isolate the cemented carbide blank, so that the cemented carbide blank will not stick to the boat, carburize, or decarburize during the sintering process. The main component of ashless paper is cellulose, and its combustion is essentially a process of cellulose oxidation. After the ashless paper is fully burned, it mainly produces carbon dioxide and water vapor, leaving only trace amounts of inorganic salt paper ash, which will not react with the alloy or damage the coating. In use, two grooved boats are used to clamp the compact, with the working surface of the grooved boats in contact with the top and bottom surfaces of the compact. A layer of ashless paper is placed between them. After combustion, this paper layer provides a medium, reducing the frictional resistance between the compact shrinking and the grooved boats during sintering, thus reducing the risk of deformation and cracking. Simultaneously, using grooved boats ensures that the top and bottom surfaces of the compact have the same dewaxing area during sintering and dewaxing. The grooves in the grooved boats can also serve as vents, and the boats can act as heat carriers during sintering. Compared to traditional flat boats placed on the bottom of the compact, using grooved boats for sintering ensures that the alloy has the same dewaxing conditions and heat carrier during sintering, resulting in a more uniform atmosphere and temperature across the upper and lower parts. The addition of ashless paper and the grooved structure also facilitates shrinkage, dewaxing, and venting, reducing deformation during these processes and thus minimizing sintering deformation in large-scale alloy products.

[0019] This application utilizes a feeding tray to alter the density difference between the outer and central parts of the pressed blank during the pressing process. A better external density results in greater external strength, reducing defects such as cracks, and accelerating the external shrinkage rate during sintering. This also reduces the inward deformation of the bottom surface caused by large-volume gradient sintering during overall cemented carbide sintering. This application uses two fine-groove boats to clamp the pressed blank, placing a layer of ashless paper between the boats and the blank. This ensures uniform dewaxing and heat bearing during alloy sintering, resulting in a more uniform atmosphere and temperature across the upper and lower parts. The addition of ashless paper and the fine-groove structure also facilitates shrinkage, dewaxing, and venting, reducing deformation during these processes. By implementing these optimizations in the cemented carbide pressing and sintering processes, this application reduces the sintering deformation of large cemented carbide products. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the feeding mesh structure in this application;

[0022] Figure 2 This is a schematic diagram illustrating the use of the material feeding network disk in this application;

[0023] Figure 3 This is a schematic diagram of the fine-groove boat structure in this application;

[0024] Figure 4 This is a schematic diagram illustrating the use of the fine-groove vessel in this application.

[0025] The attached diagram is labeled as follows: 1. Feeding tray; 2. Pressing mold; 3. Mixing material; 4. Fine groove boat; 5. Ash-free paper; 6. Large product cemented carbide blank.

[0026] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0027] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0028] This application provides a method for reducing sintering deformation of large cemented carbide products, comprising the following steps:

[0029] S1. Obtain cemented carbide mixture, and fill the cemented carbide mixture into the mold through the feeding mesh to press it into a compact. The density of the compact gradually increases from the center point to the outermost edge in the horizontal direction.

[0030] The material of the feeding screen includes stainless steel. The shape of the feeding screen is the same as the shape of the filling port of the mold. The area of ​​the feeding screen is slightly smaller than the area of ​​the filling port of the mold. The feeding screen has screen holes of the same size, with a diameter of 2-4 mm. The distribution of the screen holes is as follows: the feeding screen is divided into four regions at equal distances along a straight line from the center point to the outermost edge. The screen holes are evenly distributed in each of the four regions, and the distance between the screen holes is different in different regions. Specifically, the distance between the screen holes in each region decreases from the center point to the outermost edge, and the ratio of the distance between the screen holes in each region from the center point to the outermost edge is (1.3-1.4):(1.2-1.3):(1) .1-1.2): (1-1.1); The method of dividing into four areas is as follows: For a circular feeding tray with a diameter of 100mm, it is divided into four areas: a circular area with a diameter of 0 to 25mm, an annular area with a diameter of 25mm to 50mm, an annular area with a diameter of 50mm to 75mm, and an annular area with a diameter of 75mm to 100mm; The filling method is as follows: the screen holes of the feeding tray are closed and blocked by a pallet, the cemented carbide mixture is evenly and flatly spread in the feeding tray, the feeding tray is then transferred to the filling port of the mold, the pallet is removed, and the feeding tray is quickly placed into the mold, and the cemented carbide mixture enters the mold through the screen holes;

[0031] S2. The pressed billet is loaded into a furnace and sintered to obtain a large cemented carbide product.

[0032] The furnace loading method is as follows: two grooved boats are used to clamp the compact, with the working surface of the grooved boats in contact with the upper and lower surfaces of the compact. A layer of ashless paper is placed on the contact surface between the grooved boats and the compact, and then the furnace loading is completed. The base material of the grooved boats is graphite, and the working surface of the grooved boats has a coating, the coating material of which includes MgO. The ashless paper is composed of cellulose. The working surface of the grooved boats has uniformly distributed elongated strip grooves, the dimensions of which are: width: 1-3mm, depth: 1-2mm, and the interval between the strip grooves is 2-5mm. The cemented carbide of the large product includes WC-Co series cemented carbide; the dimensions of the cemented carbide of the large product are: length ≥100mm, width ≥100mm, height ≥25mm or diameter ≥100mm, height ≥25mm; the height deformation of the cemented carbide of the large product is ≤1.5mm.

[0033] Please see Figure 1 , Figure 1 This is a schematic diagram of the feeding mesh structure in this application; Figure 1This indicates that the feeding screen has a structure with protrusions on the outer edge and screen holes on the inner working plane. The working plane is divided into four regions at equal distances from the center point to the outermost edge. The screen holes are evenly distributed in the four regions. The distance between the screen holes is different in different regions. The distance between the screen holes is larger in the central region and smaller in the outer regions. That is, the screen holes are denser in the outer regions.

[0034] Please see Figure 2 , Figure 2 This is a schematic diagram illustrating the use of the material feeding network disk in this application; Figure 2 This indicates the following usage scenario when using the feeding screen 1 for pressing: During filling, the screen holes of the feeding screen 1 are sealed with a pallet. The mixture 3 required for pressing is evenly and flatly spread in the feeding screen 1. Then, the feeding screen 1 is transferred to the filling port of the pressing mold 2, the pallet is removed, and the feeding screen 1 is quickly placed into the pressing mold 2. The mixture 3 begins to enter the pressing mold 2 through the screen holes. After being filled by the feeding screen 1, the mixture 3 has passed through the screen holes at different distances in different areas, forming a material pile with different densities at the outside and center. After pressing, there is a density difference from the outside to the center of the pressed blank, and the overall density of the pressed blank gradually increases from the center to the outside.

[0035] Please see Figure 3 , Figure 3 This is a schematic diagram of the fine-groove boat structure in this application; Figure 3 This indicates that the strip-shaped grooves are evenly distributed on the surface of the fine-groove vessel.

[0036] Please see Figure 4 , Figure 4 This is a schematic diagram illustrating the use of the fine-groove boat in this application; Figure 4 This indicates that when sintering using two fine-groove boats 4, the large cemented carbide blank 6 is sandwiched between the two fine-groove boats 4 during sintering. The working surfaces of the two fine-groove boats 4 are in contact with the upper and lower surfaces of the large cemented carbide blank 6, and a layer of ashless paper 5 is placed between them.

[0037] The technical solution of this application will be further described below with reference to specific embodiments.

[0038] Example 1

[0039] S1. Select a cemented carbide of grade YG15, 200mm×200mm×30mm, to be produced. This material is a WC-15%Co cemented carbide with a WC grain size of approximately 1.0-1.5μm and a cobalt content of 10wt.%. Referring to the die drawing for this type of cemented carbide, the die filling orifice size is known to be 250mm×250mm. Determine that the feed tray for producing this type of compact is 240mm×240mm. Design and manufacture the feed tray for this large cemented carbide product. The feed tray is square, with the same shape as the filling orifice of the die, and a size of 240mm×240mm, allowing it to be fully inserted into the die. The feed tray contains sieve holes of the same size, with a diameter of 3mm, evenly divided into four sections from the inside out. The ratio of the distance between the sieve holes in each section is 1.3:1.2:1.1:1.

[0040] S2. Using a feeding tray to assist in pressing. During pressing, the mixture is filled into the mold cavity using a feeding tray, and then pressed. The screen holes of the feeding tray are sealed with a support plate, and the mixture required for pressing is evenly and flatly spread in the feeding tray. The feeding tray is then transferred to above the mold filling port, the support plate is removed, and the feeding tray is quickly placed into the mold. The mixture enters the mold cavity through the screen holes. After being filled using the feeding tray, the mixture has passed through screen holes at different distances in different areas, forming a material pile with different densities at the outside and center. After pressing, the overall density of the 200mm×200mm×30mm compact gradually increases from the center to the outside.

[0041] S3. Use two grooved boats to clamp a 200mm×200mm×30mm blank. The working surface of the grooved boat has a coating made of MgO. The working surface of the grooved boat has evenly distributed elongated grooves with dimensions of 2mm width and 2mm depth, and the interval between the grooves is 4mm. The working surface of the grooved boat is in contact with the top and bottom surfaces of the blank, and a layer of ashless paper is placed between the grooved boat and the blank for sintering.

[0042] S4. Measure the dimensions of the 200mm×200mm×30mm cemented carbide blank. The lowest height dimension is 31.5mm and the highest is 32.3mm. Subtracting the lowest from the highest is 0.8mm, so the height deformation is 0.8mm. In Comparative Example 1, the lowest height dimension of the blank is 31.2mm and the highest is 33.0mm. Subtracting the lowest from the highest is 1.8mm, so the height deformation is 1.8mm. The height deformation in this embodiment is reduced by 1.0mm compared to Comparative Example 1. The sintering deformation of the 200mm×200mm×30mm product is reduced by this method.

[0043] Example 2

[0044] S1. Select a cemented carbide of grade YG20, Ø120mm×Ø60mm×50mm, to be produced. This material is a WC-20%Co cemented carbide with an average WC grain size of approximately 1.8μm and a cobalt content of 20wt.%. Referring to the die drawing for this type of cemented carbide, the die filling orifice size is known to be Ø150mm×Ø75mm. Determine the blanking tray for producing this type of compact to be Ø140mm×Ø85mm. Design and manufacture the blanking tray for this large cemented carbide product. The blanking tray has the same circular shape as the filling orifice of the die, with dimensions of Ø140mm×Ø85mm, allowing it to be fully inserted into the die. The blanking tray contains sieve holes of the same size, with a diameter of 3mm, evenly divided into four sections from the inside out. From the central area to the outermost area, the ratio of the distance between the sieve holes in each area is 1.4:1.3:1.2:1.1.

[0045] S2. Using a feeding tray to assist in pressing. During pressing, the feeding tray is used to fill the mold cavity with the mixture before pressing. A support plate is used to seal the sieve holes of the feeding tray, and the mixture required for pressing the compact is evenly and flatly spread in the feeding tray. The feeding tray is then transferred to above the mold filling port, the support plate is removed, and the feeding tray is quickly placed into the mold. The mixture enters the mold cavity through the sieve holes. After being filled using the feeding tray, the mixture has passed through sieve holes at different distances in different areas, forming a material pile with different densities at the outside and center. After pressing, the overall density of the Ø120mm×Ø60mm×50mm compact gradually increases from the center to the outside.

[0046] S3. Use two grooved boats to clamp a Ø120mm×Ø60mm×50mm blank. The working surface of the grooved boat has a coating made of MgO. The working surface of the grooved boat has evenly distributed elongated grooves with dimensions of 2mm width and 2mm depth, and the interval between the grooves is 4mm. The working surface of the grooved boat is in contact with the top and bottom surfaces of the blank, and a layer of ashless paper is placed between the grooved boat and the blank for sintering.

[0047] S4. Measure the dimensions of the Ø120mm×Ø60mm×50mm cemented carbide blank. The lowest height dimension is 52.1mm and the highest is 52.7mm. Subtracting the lowest from the highest value results in a height deformation of 0.6mm. In Comparative Example 2, the lowest height dimension is 52.1mm and the highest is 53.9mm. Subtracting the lowest from the highest value results in a height deformation of 1.8mm. The height deformation in this embodiment is reduced by 1.2mm compared to Comparative Example 2. The sintering deformation of the Ø120mm×Ø60mm×50mm product is reduced by this method.

[0048] Comparative Example 1

[0049] Select a cemented carbide blank of grade YG15, 200mm×200mm×30mm, and refer to the pressing die drawing for this type of cemented carbide. During pressing, the mixture should be filled into the die as evenly as possible. During sintering, the cemented carbide blank is placed on a flat boat. During the sintering process, the dimensions of the 200mm×200mm×30mm cemented carbide blank are affected by factors such as the density of the blank itself, the sintering atmosphere, and uneven temperature. The minimum height dimension is 31.2mm and the maximum height is 33.0mm. Subtracting the minimum height from the maximum value, which is 1.8mm, the height deformation is 1.8mm.

[0050] Comparative Example 2

[0051] Select cemented carbide of grade YG20, model Ø120mm×Ø60mm×50mm, and refer to the pressing die drawing for this model. During pressing, the mixture should be filled into the die as evenly as possible. During sintering, the cemented carbide blank is placed on a flat boat. During the sintering process, the blank's density, sintering atmosphere, and temperature are all affected. Measure the dimensions of the Ø120mm×Ø60mm×50mm cemented carbide blank. The lowest height is 52.1mm and the highest is 53.9mm. Subtracting the lowest from the highest is 1.8mm, so the height deformation is 1.8mm.

[0052] Comparative Example 3

[0053] S1. Refer to the drawing of the pressing die for producing YG15 grade cemented carbide in 200mm×200mm×30mm sizes. Given that the die filling inlet size is 250mm×250mm, determine that the blanking tray for this type of compact should be 240mm×240mm. Design and manufacture the blanking tray for this large cemented carbide product. The blanking tray is square, with the same shape as the filling inlet of the pressing die, and its size is 240mm×240mm, allowing it to be fully inserted into the die. The blanking tray has sieve holes of the same size, with a diameter of 3mm, distributed in four equal parts from the inside out, from the center to the outermost area. The distance between the sieve holes in each area is 1.8:1.6:1.3:1.

[0054] S2. Using a feeding tray to assist in pressing. During pressing, the feeding tray is used to fill the mold cavity with the mixture before pressing. A support plate is used to seal the sieve holes of the feeding tray, and the mixture required for pressing is evenly and flatly spread in the feeding tray. The feeding tray is then transferred to above the mold filling port, the support plate is removed, and the feeding tray is quickly placed into the mold, allowing the mixture to enter the mold cavity through the sieve holes. After being filled using the feeding tray, the mixture has passed through sieve holes at different distances in each area, forming material piles with different densities at the outside and center. After pressing, the overall density of the 200mm×200mm×30mm compact shows a trend of gradually increasing from the center to the outside. However, testing revealed that the density difference of the compact was too large, and the mixture in the center was not completely pressed and bonded together, resulting in a noticeable granular texture. This is a substandard compact and should not be sintered; it should be treated as PR material.

[0055] Comparative Example 4

[0056] S1. Refer to the drawing of the pressing die for producing YG15 grade cemented carbide in 200mm×200mm×30mm sizes. Given that the die filling inlet size is 250mm×250mm, determine that the blanking tray for this type of compact should be 240mm×240mm. Design and manufacture the blanking tray for this large cemented carbide product. The blanking tray should be square, with the same shape as the filling inlet of the pressing die, and a size of 240mm×240mm, allowing it to be fully inserted into the die. The blanking tray should have sieve holes of the same size, with a diameter of 3mm, distributed in four equal parts from the inside out. From the center area to the outermost area, the ratio of the distance between the sieve holes in each area is 1.3:1.2:1.1:1.

[0057] S2. Using a feeding tray to assist in pressing. During pressing, the mixture is filled into the mold cavity using a feeding tray, and then pressed. The screen holes of the feeding tray are sealed with a support plate, and the mixture required for pressing is evenly and flatly spread in the feeding tray. The feeding tray is then transferred to above the mold filling port, the support plate is removed, and the feeding tray is quickly placed into the mold. The mixture enters the mold cavity through the screen holes. After being filled using the feeding tray, the mixture has passed through screen holes at different distances in different areas, forming a material pile with different densities at the outside and center. After pressing, the overall density of the 200mm×200mm×30mm compact gradually increases from the center to the outside.

[0058] S3. During sintering, the cemented carbide blank is placed on a flat boat for sintering;

[0059] S4. Measure the dimensions of the 200mm×200mm×30mm cemented carbide blank. The lowest height dimension is 31.4mm and the highest is 33.0mm. Subtracting the lowest from the highest value results in a height deformation of 1.6mm. In Comparative Example 1, the lowest height dimension is 31.2mm and the highest is 33.0mm. Subtracting the lowest from the highest value results in a height deformation of 1.8mm. The height deformation in this comparative example is 0.2mm less than that in Comparative Example 1. The sintering deformation of the 200mm×200mm×30mm product is reduced by this method, but the improvement is not very significant.

[0060] As can be seen from the above embodiments and comparative examples, adjusting the density difference between the outside and inside of the cemented carbide compact using a feeding mesh increases the external density, improves the external strength of the compact, and accelerates the external shrinkage rate during sintering, thus reducing the influence of the sintering gradient on large cemented carbide products. The sintering method using a fine-groove boat with clamping and ashless paper to reduce resistance ensures that the alloy exhibits uniform dewaxing and heat-carrying properties during sintering, resulting in more uniform atmosphere and temperature between the upper and lower parts. The ashless paper and fine-groove structure also facilitate shrinkage, dewaxing, and venting, reducing deformation caused by uneven atmosphere and temperature during sintering.

[0061] This application proposes a method for reducing the sintering deformation of large cemented carbide products, and designs and uses a feeding tray and a fine-groove boat.

[0062] 1. The feeding tray is made of stainless steel, which will not react with the hard alloy mixture and contaminate the raw materials. It is easy to clean and store after use. Its shape should be the same as the filling port of the pressing mold, but its area should be slightly smaller to allow it to be fully inserted into the mold. The feeding tray has sieve holes of the same size, with a diameter of 2-4mm, distributed in four equal parts from the inside out. The ratio of the distance between the sieve holes in each area from the center to the outermost area is (1.3-1.4):(1.2-1.3):(1.1-1.2):(1-1.1). In use, use a support plate to seal the sieve holes of the feeding tray, evenly and flatly spread the mixture required for pressing the compact in the feeding tray, then transfer the feeding tray above the mold filling port, remove the support plate, and quickly place the feeding tray into the mold. The mixture will then begin to enter the mold through the sieve holes. After the mixture is filled with feed mesh, it has passed through the sieve holes at different distances in each area, forming a material pile with different densities on the outside and in the center. After pressing, there is a density difference from the outside to the center of the compact, and the overall density of the compact gradually increases from the center to the outside.

[0063] 2. Fine-groove boat-shaped vessel, with graphite as the base material, is used in conjunction with ashless paper. It can withstand the high-temperature sintering temperature of cemented carbide without deformation and is often used as a carrier for cemented carbide sintering. The working surface has evenly distributed strip grooves, and a spray coating is applied to the working surface. It can withstand the high temperature of sintering and isolate the cemented carbide blank, so that the cemented carbide blank will not stick to the boat, carburize, or decarburize during the sintering process. The main component of ashless paper is cellulose, and its combustion is essentially a process of cellulose oxidation. After the ashless paper is fully burned, it mainly produces carbon dioxide and water vapor, leaving only trace amounts of inorganic salt paper ash, which will not react with the alloy or damage the coating. In use, two grooved boats are used to clamp the compact, with the working surface of the grooved boats in contact with the top and bottom surfaces of the compact. A layer of ashless paper is placed between them. After combustion, this paper layer provides a medium, reducing the frictional resistance between the compact shrinking and the grooved boats during sintering, thus reducing the risk of deformation and cracking. Simultaneously, using grooved boats ensures that the top and bottom surfaces of the compact have the same dewaxing area during sintering and dewaxing. The grooves in the grooved boats can also serve as vents, and the boats can act as heat carriers during sintering. Compared to traditional flat boats placed on the bottom of the compact, using grooved boats for sintering ensures that the alloy has the same dewaxing conditions and heat carrier during sintering, resulting in a more uniform atmosphere and temperature across the upper and lower parts. The addition of ashless paper and the grooved structure also facilitates shrinkage, dewaxing, and venting, reducing deformation during these processes and thus minimizing sintering deformation in large-scale alloy products.

[0064] This application utilizes a feeding tray to alter the density difference between the outer and central parts of the pressed blank during the pressing process. A better external density results in greater external strength, reducing defects such as cracks, and accelerating the external shrinkage rate during sintering. This also reduces the inward deformation of the bottom surface caused by large-volume gradient sintering during overall cemented carbide sintering. This application uses two fine-groove boats to clamp the pressed blank, placing a layer of ashless paper between the boats and the blank. This ensures uniform dewaxing and heat bearing during alloy sintering, resulting in a more uniform atmosphere and temperature across the upper and lower parts. The addition of ashless paper and the fine-groove structure also facilitates shrinkage, dewaxing, and venting, reducing deformation during these processes. By implementing these optimizations in the cemented carbide pressing and sintering processes, this application reduces the sintering deformation of large cemented carbide products.

[0065] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method of reducing sintering distortion of large cemented carbide articles, characterized in that, The method comprises the following steps: S1, obtaining a cemented carbide mixture, and filling the cemented carbide mixture into a mold through a blanking screen disc to obtain a compact by pressing, wherein the density of the compact gradually increases from the center point to the outermost edge in the horizontal direction; S2, sintering the compact to obtain a large product cemented carbide. In the step S1, the blanking screen disc has screen holes of the same size, and the screen holes are uniformly distributed in four regions divided by the blanking screen disc according to linear distance equidistance from the center point to the outermost edge, and the distances between the screen holes in different regions are different, specifically, the distances between the screen holes in each region from the center point to the outermost edge are smaller and smaller, and the ratio of the distances between the screen holes in each region from the center point to the outermost edge is (1.3-1.4):(1.2-1.3):(1.1-1.2):(1-1.1). In the step S2, the size of the large product cemented carbide is: length≥100mm, width≥100mm, height≥25mm or diameter≥100mm, height≥25mm; and the height deformation of the large product cemented carbide is≤1.5mm.

2. A method of reducing sinter distortion of large cemented carbide articles according to claim 1, characterized in that, In the step S1, the material of the blanking screen disc is stainless steel.

3. A method of reducing sinter distortion of large cemented carbide articles according to claim 1, characterized in that, In the step S1, the shape of the blanking screen disc is the same as that of the filling port of the mold, and the area of the blanking screen disc is slightly smaller than that of the filling port of the mold.

4. A method of reducing sinter distortion of large cemented carbide articles according to claim 1, characterized in that, In the step S1, the diameter of the screen hole is 2-4mm.

5. A method of reducing sinter distortion of large cemented carbide articles according to claim 4, characterized in that, In the step S1, the filling mode is that the screen holes of the blanking screen disc are blocked by a supporting plate, the cemented carbide mixture is evenly and flatly laid in the blanking screen disc, the blanking screen disc is transferred above the filling port of the mold, the supporting plate is removed, and the blanking screen disc is quickly put into the mold, and the cemented carbide mixture enters the mold from the screen holes.

6. A method of reducing sinter distortion of large hard metal articles according to claim 1 wherein, In the step S2, the loading mode is that the compact is clamped by two fine groove boats, the use surface of the fine groove boat is in close contact with the upper and lower surfaces of the compact, a layer of ash-free paper is placed on the contact surface of the fine groove boat and the compact, and then the loading is completed.

7. A method of reducing sinter distortion of large cemented carbide articles according to claim 6, characterized in that, In the step S2, the base material of the fine groove boat is graphite, the use surface of the fine groove boat has a coating, and the material of the coating comprises MgO.

8. A method of reducing sinter distortion of large cemented carbide articles according to claim 6, characterized in that, In the step S2, the composition of the ash-free paper comprises cellulose.

9. A method of reducing sinter distortion of large cemented carbide articles according to claim 6, characterized in that, In the step S2, the use surface of the fine groove boat is uniformly distributed with a longitudinal strip-shaped groove, the size of the strip-shaped groove is: width: 1-3mm, depth: 1-2mm, and the interval between the strip-shaped grooves is 2-5mm.

10. A method of reducing sinter distortion of large cemented carbide articles according to claim 1, characterized in that, In the step S2, the large product cemented carbide is a WC-Co cemented carbide.

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