Production process of moire cooker

Abstract

The production process comprises the following steps: a casting step: smelting raw materials into molten iron, casting the molten iron in a mold, gathering cold and heat to form a moire on a casting tool, and taking out a casting after cooling; a post-treatment step: annealing, polishing and sandblasting the casting in sequence to form the cooker; heat treatment: placing the cooker in a heat treatment furnace; the temperature in the furnace is increased to 530 DEG C, and heat preservation is conducted for Cooling by spraying water on the cooker and exhausting; raising the temperature in the furnace to 500 DEG C, spraying water on the cooker for cooling and exhausting; the temperature in the furnace is increased to 550 DEG C, and 10 m < 3 > of ammonia gas is introduced; the pressure in the furnace is maintained to be 490 pa; the temperature in the furnace is increased to 560 DEG C, heat preservation is conducted for 240 min, and 0.5 m < 3 > of ammonia gas is introduced; the temperature in the furnace is maintained, heat preservation is conducted for 120 min, 14 m < 3 > of ammonia gas and 0.5 m < 3 > of carbon dioxide are introduced, and the ventilation time is 120 min; dropping blackening liquid into the furnace, and oxidizing for 80 minutes; and cooling to 200 DEG C by air cooling in the furnace, emptying the furnace pressure, and discharging the finished product out of the furnace. The problem that the distribution effect of a nitriding layer is poor due to the fact that moire patterns are different in depth and uneven in distribution in an existing scheme is solved.

Description

Technical Field

[0001] This invention relates to the field of cookware manufacturing, and more particularly to a manufacturing process for a tortoise-patterned cookware. Background Technology

[0002] Cookware cast using clay molds develops a tortoise-shell pattern on its surface, which provides a non-stick surface and even heat distribution. However, the depth and distribution of this pattern vary, limiting its non-stick properties and making the cookware prone to rust and wear.

[0003] Therefore, cookware undergoes nitriding for rust prevention and wear resistance. However, due to the varying depth and uneven distribution of the tortoise-shell pattern, the nitriding layer is unevenly distributed. In areas with deep and dense patterns, the cookware surface is prone to rust and chipping. In areas with shallow and sparse patterns, the nitriding layer is evenly distributed, providing rust prevention and wear resistance. This significantly affects the usability of tortoise-shell cookware.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a manufacturing process for tortoise-pattern cookware, so as to solve the problem that the tortoise pattern is uneven in depth and distribution, resulting in poor nitriding layer distribution.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A manufacturing process for a tortoise-patterned cookware; Includes the following steps: Casting process: The raw materials are melted into molten iron at 1650℃. The molten iron is poured into the mold. The heat and cold combine to form a tortoise shell pattern on the casting. The casting is removed after cooling. Post-processing steps: The castings are annealed, polished and sandblasted in sequence to form cookware; Heat treatment steps: The cookware is placed in a heat treatment furnace with a pressure of 4 MPa. First stage of heating in the furnace: The furnace temperature is raised to 530℃ and held for 50 minutes; the cookware is sprayed with water to cool it down and the exhaust is vented. The second stage of heating inside the furnace: the furnace temperature is raised to 500℃, the cookware is sprayed with water to cool it down and the exhaust is vented; the temperature is maintained for 50 minutes, the furnace temperature is raised to 550℃, and 10m³ of ammonia gas is introduced. 3 The furnace pressure is maintained at 490 Pa. The third stage of heating inside the furnace: The furnace temperature is raised to 560℃, held for 240 minutes, and 0.5 m³ of ammonia gas is introduced. 3 Maintain the furnace temperature for 120 minutes, then introduce 14m³ of ammonia gas. 3and carbon dioxide 0.5m 3 Ventilation time: 120 min; blackening solution dripped into the furnace, oxidation for 80 min; furnace pressure maintained at 490 Pa. The furnace is cooled to 200°C by air cooling, and the finished product is discharged after the furnace pressure is released.

[0007] A further technical solution is to use 26# pig iron as the raw material in the casting process.

[0008] A further technical solution is that, in the casting step: the mold includes mutually cooperating modules; the module includes a main mold, a clay mold layer, and a fan installed on the main mold; the main mold forms a contour surface on the side near the casting, and protrusions are formed side by side on the contour surface; the clay mold layer is formed on the contour surface and covers the protrusions; the working end of the fan cools the main mold.

[0009] A further technical solution is that the protrusion length matches the texture path of the cookware; a vibration device is also installed on the main body mold, and the vibration end of the vibration device acts on the main body mold.

[0010] A further technical solution is as follows: In the heat treatment step: the first stage of heating in the furnace: the furnace is heated to 450°C at a first rate, and then heated to 530°C at a second rate. The cookware is sprayed with water for the first time to cool down and exhaust the air. The furnace is kept warm for 50 minutes, and the cookware is sprayed with water for the second time to cool down and exhaust the air. The second stage of heating in the furnace: The furnace temperature rises to 500℃, and the cookware is sprayed with water for the third time to cool down and exhaust the air; The first spray volume is greater than the second spray volume, and the third spray volume is greater than the second spray volume; the first spray temperature is less than the second spray temperature, and the third spray temperature is less than the second spray temperature.

[0011] A further technical solution is that, in the heat treatment step: the furnace is cooled by air cooling and the furnace is pressurized by nitrogen alternately, the furnace temperature is gradually reduced to 200°C, and the finished product is discharged from the furnace after the furnace pressure is vented.

[0012] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) The casting step involves cooling the main mold and heating the molten iron to form coarse lines with controllable paths on the surface of the casting; during the heat treatment step, water is sprayed in the furnace to cool down the heat treatment process in the furnace, and fine lines are formed on the surface of the cookware through three water spraying processes, which also deepens the coarse and fine lines; during the three different amounts of ammonia gas introduced in the heat treatment step, the nitriding layer is bonded to the cookware substrate, and then a three-layer structure of nitriding layer, co-diffusion layer and oxide film is formed on the surface of the cookware through the oxidation process, which protects the co-diffusion layer and ensures the hardness and wear resistance of the cookware surface; during the three cooling processes in the heat treatment step, thermal stress and structural stress are avoided in the cookware, and deformation of the cookware is avoided.

[0013] (2) The protrusion length of the protrusions at different positions controls the formation position of the tortoise shell pattern on the casting surface, and the tortoise shell pattern is evenly distributed on the casting surface; the water content of the clay mold layer is high, and the clay mold layer cools down quickly to achieve a cooling effect; the molten iron is poured between the modules, and the temperature of the molten iron is high to achieve a heat-gathering effect; the temperature difference between the modules and the molten iron causes the tortoise shell pattern to form on the casting surface; after the molten iron is poured, the vibration device drives the main mold to vibrate to ensure the formation of cracks on the clay mold layer, and the molten iron adheres better to the clay mold layer under vibration to ensure the formation of the tortoise shell pattern on the casting; the temperature difference between the molten iron and the clay mold layer is large, and the molten iron cools down quickly. After the molten iron is vibrated, it can quickly expel air bubbles to avoid the formation of cavities in the casting; during the solidification process of the molten iron, the growing grains are broken under the action of vibration and the grains are refined; under vibration, some of the stress generated by the solidification shrinkage of the molten iron can be offset, and the residual internal stress of the casting can be eliminated by the annealing process in the subsequent post-processing steps.

[0014] (3) A large flow rate of low-temperature water medium is sprayed into the furnace. After the cookware surface is cooled, fine lines are formed on the outer periphery of the coarse lines. The fine lines are relatively short. The cookware surface is cooled by the first water spray, and it is impossible to form obvious fine lines by continuing to spray water medium. The cookware is cooled by the second water spray and the air is vented. A small flow rate of low-temperature water medium is sprayed into the furnace. After the cookware surface is cooled, the length of the fine lines is extended. The fine lines and coarse lines form the initial tortoise shell pattern. The third water medium can affect both fine lines and coarse lines at the same time, but the effect is small. It can deepen the formation of fine lines and coarse lines, making the tortoise shell pattern of the cookware clear.

[0015] (4) Ammonia gas is then introduced at an extremely high rate, and the ammonia gas is fully saturated in a short time, which can rapidly increase the nitrogen potential in the furnace. A large number of nitrogen atoms quickly penetrate into the surface of the cookware, initially forming a nitrided layer. A small amount of ammonia gas is introduced to maintain the nitrogen potential in the furnace, and the supply to the outside of the cookware is reduced. Nitrogen atoms on the surface of the cookware gradually diffuse into the interior of the cookware, so that the surface of the cookware gradually transitions from high hardness to high toughness, improving the bonding force between the nitrided layer and the substrate. By creating a high nitrogen potential environment in the furnace, the porosity of the nitrided layer increases. The filling process makes the nitrided layer more compact, improving the cookware's rust resistance. When ammonia is introduced, a small amount of carbon dioxide is simultaneously introduced, allowing carbon and nitrogen atoms to diffuse into the cookware surface and combine with the iron atoms, achieving carbon-nitrogen co-diffusion. The blackening solution reacts with the cookware surface to form an oxide film, which covers the pores of the co-diffusion layer. This creates a three-layer structure on the cookware surface—the nitrided layer, the co-diffusion layer, and the oxide film—from the inside out, protecting the co-diffusion layer and ensuring the cookware's surface hardness and wear resistance.

[0016] (5) Avoid sudden drops in furnace temperature through three cooling processes. After a certain temperature drop, pressurize the furnace to maintain stable pressure and temperature, and keep the cookware structure stable before cooling. After the furnace temperature drops, the surface temperature of the cookware drops. At this time, pressurize the furnace to maintain the temperature. The temperature inside the cookware is transferred to the surface of the cookware, so that the temperature difference between the inside and outside of the cookware is controlled within a certain range, avoiding thermal stress. After the furnace temperature drops, nitrogen atoms cannot be released from the cookware in time, which leads to increased surface lattice distortion. At the same time, the shrinkage rate of carbon and nitrogen compounds inside and outside the cookware is mismatched. At this time, pressurize the furnace to maintain the temperature, providing environmental conditions for nitrogen atom release and carbon and nitrogen compound shrinkage rate adjustment, avoiding structural stress. Attached Figure Description

[0017] Figure 1 A schematic diagram of the structure of a module according to an embodiment of the present invention is shown.

[0018] Figure 2 It shows Figure 1 A magnified view of the structure at the location of the main body model.

[0019] The attached diagram is labeled as follows: 1. Module; 11. Main mold; 12. Clay mold layer; 13. Protrusion; 131. Edge; 14. Fan; 15. Vibration device. Detailed Implementation

[0020] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0021] Figure 1 A schematic diagram of the structure of a module according to an embodiment of the present invention is shown. Figure 2 It shows Figure 1 A magnified view of the central main body structure. (Combined with...) Figure 1 and Figure 2 As shown, the present invention discloses a manufacturing process for a tortoise-shell patterned cookware, comprising the following steps: Casting steps: The raw material is 26# pig iron, which is melted into molten iron at 1650℃. The molten iron is poured into the mold, and the heat and cold combine to form a tortoise shell pattern on the casting. The casting is removed after cooling.

[0022] In the casting process: The mold consists of interlocking modules 1. Module 1 includes a main mold 11, a clay mold layer 12, and a fan 14 mounted on the main mold 11. The two sets of modules 1 are fitted vertically together. The side of the main mold 11 closest to the casting forms a contoured surface; the contoured surface of the upper main mold 11 bulges downwards, while the contoured surface of the lower main mold 11 is recessed downwards. When the modules 1 are fitted together, a space is formed between the contoured surfaces of the main mold 11, and molten iron is poured into this space to complete the casting process.

[0023] Protrusions 13 are formed side-by-side on the contoured surface, with their extension length matching the textured path of the cookware. Some protrusions 13 extend longer, inserting deeper into the clay mold layer 12, resulting in a thinner protrusion above the protrusions. These protrusions enhance the structural strength of the clay mold layer 12 at that location, preventing cracks. Other protrusions 13 extend shorter, inserting shallower into the clay mold layer 12, resulting in a thicker protrusion above the protrusions. These protrusions have less impact on the clay mold layer 12, making it easier for cracks to form.

[0024] By controlling the extension length of the protrusions 13 at different positions, the formation position of the mottled pattern on the casting can be controlled, resulting in a uniform distribution of the mottled pattern on the casting surface. By changing different main molds 11, the extension length of the protrusions 13 and the thickness of the clay mold layer 12 from the end face of the protrusions 13 can be controlled, thereby controlling the formation depth of the mottled pattern on the casting. The thicker the clay mold layer 12 is from the end face of the protrusions 13, the deeper the mottled pattern on the casting. The thinner the clay mold layer 12 is from the end face of the protrusions 13, the shallower the mottled pattern on the casting.

[0025] An edge 131 is formed on the side of a portion of the protrusion 13. Cracks in the clay mold layer 12 start to form from the edge 131. By changing the orientation of the edge 131, the formation angle of the crack is changed, so that the tortoise shell pattern on the surface of the casting is evenly distributed.

[0026] A clay mold layer 12 is formed on the contoured surface and covers the protrusions 13. The clay mold layer 12 comprises refractory clay as raw material, quartz sand as aggregate, and coke powder, binder, and release agent as auxiliary materials. To achieve the effect of heat and cold coagulation, the clay mold layer 12 has a high moisture content. The moisture content varies at different locations within the clay mold layer 12. The clay mold layer 12 covering part of the protrusions 13 has a moisture content of 24-26%, while the clay mold layer 12 covering another part of the protrusions 13 has a moisture content of 25.5-27%. The moisture content of the clay mold layer 12 covering part of the protrusions 13 is lower than that covering another part of the protrusions 13. Compared to the traditional cookware production process, which requires controlling the moisture content of the clay blank to a low range, this application improves the structural strength of the clay mold layer 12 due to the insertion of the protrusions 13, preventing collapse of the clay mold layer 12 during the casting process.

[0027] The working end of fan 14 cools the main mold 11, causing rapid cooling of the main mold 11 and protrusion 13. Due to the high moisture content of the clay mold layer 12, the rapid cooling of the clay mold layer 12 achieves a cooling effect. After the modules 1 are in place, molten iron is poured between the modules 1, and the high temperature of the molten iron achieves a heat-concentrating effect. The temperature difference between the modules 1 and the molten iron causes the surface of the casting to form a crackle pattern.

[0028] A vibration device 15 is also installed on the main mold 11, and the vibration end of the vibration device 15 acts on the main mold 11. The vibration of the vibration device 15 is a low-frequency vibration of 25-50 Hz, and the vibration time of the vibration device 15 is 8-12 minutes. After the molten iron comes into contact with the clay mold layer 12, due to the large temperature difference and the high moisture content of the clay mold layer 12, a large amount of steam will be generated, and the molten iron will cover the steam to form bubbles.

[0029] After the molten iron is poured into the casting module 1, the vibration device 15 drives the main mold 11 to vibrate, ensuring the formation of cracks on the clay mold layer 12. Under vibration, the molten iron adheres better to the clay mold layer 12, ensuring the formation of the tortoise shell pattern on the casting. The temperature difference between the molten iron and the clay mold layer 12 is large, and the molten iron cools rapidly. After vibration, the molten iron can quickly expel air bubbles, preventing the formation of cavities inside the casting.

[0030] During the solidification process of molten iron, the vibrating impact of the vibration device 15 breaks up the growing grains, resulting in grain refinement. Under vibration, some of the stress generated by the solidification shrinkage of the molten iron can be offset, and the residual internal stress of the casting can be eliminated by the subsequent annealing process.

[0031] The crackle pattern formed on the surface of cookware includes coarse and fine lines. Coarse lines are distributed on the surface of the cookware, while fine lines form near and connect with the coarse lines. During the casting process, coarse lines with controllable paths are formed on the surface of the casting, while subsequent heat treatment processes form fine lines on the surface of the cookware and deepen both the coarse and fine lines.

[0032] Post-processing steps: The castings are annealed, polished and sandblasted in sequence to form cookware; The casting is placed in an annealing furnace and heated to 900-910℃, held for 1.5 hours, with a heating rate of 125-130℃ / h. The casting is then cooled in the furnace to 735-740℃, held for 1.5 hours, and then cooled in the furnace to 200℃ before being removed from the furnace.

[0033] During the casting process, the vibration of the vibration device 15 enhances atomic diffusion, causing carbon atoms to migrate, aggregate, and precipitate into graphite, thus reducing the formation of hard and brittle cementite. During annealing at 900-910℃, the free cementite and eutectic cementite in the casting fully decompose, forming austenite and graphite. A short holding time of 1.5 hours can eliminate the hard and brittle cementite.

[0034] During the annealing process, at 735-740℃, a short holding time can further decompose the secondary cementite from the austenite into ferrite and graphite, resulting in a microstructure with ferrite as the matrix and graphite uniformly distributed.

[0035] In the post-processing steps, the casting is first polished to remove burrs, flash, protrusions, and other defects. Then, sandblasting is used to unify the surface of the casting, eliminate polishing marks, and remove the oxide layer on the surface of the casting, making it easier to treat the surface of the cookware in the subsequent heat treatment steps.

[0036] Heat treatment steps: Place the cookware in the heat treatment furnace, turn off the heat treatment furnace, and set the pressure inside the furnace to 4 MPa.

[0037] First stage of heating in the oven: The oven temperature is raised to 530℃ and held for 50 minutes. The cookware is then cooled by spraying water and the exhaust is vented.

[0038] Specifically: The oven temperature is raised to 450℃ at a first rate, then to 530℃ at a second rate. The first rate is 150-160℃ / h, and the second rate is 80-90℃ / h. When the cookware reaches 530℃, it needs to be cooled by spraying water. By rapidly raising the temperature to 450℃ and then slowly raising it to 530℃, the temperature inside and outside the cookware is made uniform when it reaches 530℃. The cookware then undergoes its first water cooling process and venting.

[0039] The first water spray volume is greater than the second water spray volume, and the first water spray temperature is lower than the second water spray temperature. A large flow of low-temperature water is sprayed into the oven. As the cookware surface cools, fine, interconnected lines form around the coarse lines. At this point, the lines are relatively short. The first water spray effectively cools the cookware surface, making it impossible to form noticeable fine lines with continued water spraying. At this point, water spraying stops to allow venting, releasing the steam generated by the water spraying.

[0040] The cookware is kept warm in the oven for 50 minutes. After this time, the heat is transferred to the cookware, and the temperature inside and outside the cookware reaches the same level again. The cookware is then sprayed with water a second time to cool it down and release the air. A small flow of low-temperature water is sprayed into the oven. As the cookware surface cools, the length of the fine lines lengthens, at which point the fine and coarse lines form the initial textured pattern. The difference in the water medium between the first and second sprays means that the second spray only affects the fine lines and not the coarse lines.

[0041] The second stage of heating inside the furnace: The furnace temperature rises to 500℃, and the cookware is sprayed with water for the third time to cool down and exhaust the gas.

[0042] After the second water spray for cooling, the temperature of the cookware and the oven decreases. The oven temperature is then raised to 500℃ via a second-stage heating process, followed by a third water spray for cooling. The water medium sprayed in the third spray needs to affect both fine and coarse textures simultaneously. Therefore, the volume of water sprayed in the third spray is greater than that of the second spray, but less than that of the first spray. The temperature of the third spray is lower than that of the second spray, but greater than that of the first spray. This allows the water medium sprayed in the third spray to affect both fine and coarse textures simultaneously, but with a smaller impact, thus deepening the formation of both and making the tortoise-shell pattern on the cookware clearer.

[0043] Hold at this temperature for 50 minutes, then raise the furnace temperature to 550℃ and introduce 10m³ of ammonia gas. 3 The pressure inside the furnace is maintained at 490 Pa.

[0044] Ammonia gas is introduced into the furnace at a first rate. When the ammonia gas supply reaches 70%, it is introduced at a second rate, with the first rate being lower than the second. Initially, the ammonia gas is introduced slowly, gradually dispersing within the furnace and slowly expelling the air. At high temperatures, the ammonia decomposes within the furnace, gradually forming a stable nitrogen potential. Then, the ammonia gas is introduced at an extremely high rate, quickly saturating the furnace and rapidly increasing the nitrogen potential. A large number of nitrogen atoms quickly penetrate the surface of the cookware, initially forming a nitrided layer.

[0045] The third stage of heating inside the furnace: The furnace temperature is raised to 560℃, held for 240 minutes, and 0.5 m³ of ammonia gas is introduced. 3 At this point, the ammonia gas flow rate is drastically reduced to prevent excessively high nitrogen potential inside the furnace and to avoid the formation of a brittle, shiny white layer on the cookware surface, which would affect its usability. By introducing a small amount of ammonia to maintain the nitrogen potential inside the furnace, the supply from outside the cookware is reduced, and nitrogen atoms on the cookware surface gradually diffuse into the interior. This causes the cookware surface to gradually transition from high hardness to high toughness towards the interior, improving the bonding strength between the nitrided layer and the substrate.

[0046] Maintain the furnace temperature for 120 minutes, then introduce 14m³ of ammonia gas. 3 and carbon dioxide 0.5m 3 Ventilation time: 120 minutes.

[0047] As nitrogen atoms on the cookware surface gradually diffuse into the interior, the nitrogen concentration on the surface decreases. By introducing a large amount of ammonia gas to replenish the nitrogen concentration on the cookware surface, the hardness of the surface is increased, thus fixing the tortoise-shell pattern. By creating a high-nitrogen potential environment inside the furnace, the pores of the nitrided layer are filled, making the nitrided layer structure denser and improving the cookware's rust resistance.

[0048] When ammonia is introduced, a small amount of carbon dioxide is also introduced. Carbon and nitrogen atoms diffuse to the surface of the cookware and combine with the iron atoms in the cookware to achieve carbon-nitrogen co-infiltration.

[0049] By controlling the aeration time, sufficient time is allowed for the ammonia gas to reform a high-nitrogen potential environment within the furnace. Simultaneously, the small amount of carbon dioxide allows for the full diffusion of carbon atoms, resulting in a better composite diffusion layer.

[0050] Blackening solution was dripped into the furnace and oxidized for 80 minutes, while the pressure inside the furnace was maintained at 490 Pa.

[0051] After nitriding and carburizing, the furnace environment is pure and oxygen-free. Following carbonitriding, the oxidation and blackening process takes place directly in the high-temperature furnace environment, preventing the cookware from contacting air. The blackening solution reacts with the cookware surface to form an oxide film. This oxide film covers the pores of the co-diffusion layer, creating a three-layer structure on the cookware surface: a nitriding layer, a co-diffusion layer, and an oxide film. This protects the co-diffusion layer and ensures the hardness and wear resistance of the cookware surface.

[0052] The furnace is cooled by air cooling, and the heat inside the furnace is discharged by a fan, causing the furnace temperature to drop. Then, nitrogen is used to pressurize the furnace, and the furnace temperature is maintained. The furnace cooling and nitrogen pressurization are carried out alternately, and the furnace temperature drops stepwise to 200°C. After the furnace pressure is released, the finished product is discharged from the furnace.

[0053] Specifically, it includes three cooling processes: First cooling: The furnace is cooled to 450°C by air cooling, and the nitrogen is pressurized to 490 Pa and maintained in the furnace for 10 minutes. Second cooling: The furnace is cooled to 330°C by air cooling, and the nitrogen is pressurized to 490 Pa and maintained in the furnace for 10 minutes; The third cooling process involves air cooling inside the furnace to 200°C, followed by venting the furnace pressure and then removing the finished product from the furnace.

[0054] During the process of the oven temperature dropping from 560℃ to 200℃, the carbonitride compounds on the surface of the cookware will coarsen, reducing the cookware's hardness and wear resistance. Expelling heat from the oven using a fan allows for rapid cooling, enabling the cookware to cool down in a shorter time and preventing carbonitride grain coarsening. However, rapid cooling in the oven can also induce thermal and structural stress in the cookware, leading to deformation.

[0055] This application employs a three-stage cooling process to prevent a sudden drop in furnace temperature. After a certain temperature decrease, the furnace is pressurized to maintain stable pressure and temperature, ensuring the stability of the cookware structure before further cooling. The decrease in furnace temperature causes a drop in the surface temperature of the cookware. Pressurization at this point maintains the temperature, transferring heat from the interior to the surface, thus controlling the temperature difference between the inside and outside of the cookware within a certain range and preventing thermal stress. Furthermore, the inability of nitrogen atoms to precipitate from the cookware promptly after the furnace temperature drops leads to increased surface lattice distortion and a mismatch in the shrinkage rates of carbonitrides inside and outside the cookware. Pressurization at this point maintains the temperature, providing the necessary environmental conditions for nitrogen atom precipitation and regulating the shrinkage rate of carbonitrides, thus preventing structural stress.

[0056] In this application, the cooling of the main mold 11 and the heating of the molten iron during the casting process create controllable coarse textures on the surface of the casting. During the heat treatment process, water is sprayed into the furnace for cooling during the heating phase. This three-stage water spraying process creates fine textures on the cookware surface and deepens both the coarse and fine textures. The three-stage ammonia gas introduction process during the heat treatment process allows the nitrided layer to bond with the cookware substrate. Then, through an oxidation process, a three-layer structure—a nitrided layer, a co-diffused layer, and an oxide film—is formed on the cookware surface from the inside out. This protects the co-diffused layer and ensures the hardness and wear resistance of the cookware surface. The three cooling processes during the heat treatment process prevent thermal and structural stresses from forming in the cookware, thus avoiding deformation.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A manufacturing process for a tortoise-shell patterned cookware, characterized in that, Includes the following steps: Casting process: The raw materials are melted into molten iron at 1650℃. The molten iron is poured into the mold. The heat and cold combine to form a tortoise shell pattern on the casting. The casting is removed after cooling. Post-processing steps: The castings are annealed, polished and sandblasted in sequence to form cookware; Heat treatment steps: The cookware is placed in a heat treatment furnace with a pressure of 4 MPa. First stage of heating in the furnace: The furnace temperature is raised to 530℃ and held for 50 minutes; the cookware is sprayed with water to cool it down and the exhaust is vented. The second stage of heating inside the furnace: the furnace temperature is raised to 500℃, the cookware is sprayed with water to cool it down and the exhaust is vented; the temperature is maintained for 50 minutes, the furnace temperature is raised to 550℃, and 10m³ of ammonia gas is introduced. 3 The furnace pressure is maintained at 490 Pa. The third stage of heating inside the furnace: The furnace temperature is raised to 560℃, held for 240 minutes, and 0.5 m³ of ammonia gas is introduced. 3 Maintain the furnace temperature for 120 minutes, then introduce 14m³ of ammonia gas. 3 and carbon dioxide 0.5m 3 Ventilation time: 120 min; blackening solution dripped into the furnace, oxidation for 80 min; furnace pressure maintained at 490 Pa. The furnace is cooled to 200°C by air cooling, and the finished product is discharged after the furnace pressure is released.

2. The manufacturing process of the tortoise-patterned cookware as described in claim 1, characterized in that, The raw material used in the casting process is 26# pig iron.

3. The manufacturing process of the tortoise-patterned cookware as described in claim 2, characterized in that, In the casting process: the mold includes mutually cooperating modules (1); the module (1) includes a main mold (11), a clay mold layer (12) and a fan (14) installed on the main mold (11); the main mold (11) forms a contour surface on the side near the casting, and protrusions (13) are formed side by side on the contour surface; the clay mold layer (12) is formed on the contour surface and covers the protrusions (13); the working end of the fan (14) cools the main mold (11).

4. The manufacturing process of the tortoise-patterned cookware as described in claim 3, characterized in that, The protrusion (13) extends to match the tortoise-shell pattern of the cookware; a vibration device (15) is also installed on the main body mold (11), and the vibration end of the vibration device (15) acts on the main body mold (11).

5. The manufacturing process of the tortoise-patterned cookware as described in claim 2, characterized in that, In the heat treatment process: the first stage of heating in the furnace: the furnace is heated to 450°C at the first rate, and then heated to 530°C at the second rate. The cookware is sprayed with water to cool down and exhaust air for the first time. Keep the oven warm for 50 minutes, then spray water on the cookware a second time to cool it down and release the vents. The second stage of heating in the furnace: The furnace temperature rises to 500℃, and the cookware is sprayed with water for the third time to cool down and exhaust the air; The first spray volume is greater than the second spray volume, and the third spray volume is greater than the second spray volume; the first spray temperature is less than the second spray temperature, and the third spray temperature is less than the second spray temperature.

6. The manufacturing process of the tortoise-patterned cookware as described in claim 2, characterized in that, In the heat treatment process: air cooling and nitrogen pressurization are carried out alternately in the furnace, and the furnace temperature is gradually reduced to 200°C. After the furnace pressure is released, the finished product is taken out of the furnace.

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