One-time forming process of large steel casting

Abstract

The invention relates to a one-time forming process of a large steel casting, which comprises the following steps: S1, according to one-time forming requirements, melting each component into molten steel liquid by using an electric furnace, and pouring the molten steel liquid into a heat preservation furnace for heat preservation; s2, after chemical components of a full furnace are prepared and qualified, the chemical components are poured into steel ladles respectively; s3, argon blowing and calming are conducted on the steel ladle, and carbonized rice husks are scattered into the steel ladle; s4, after sedation is finished, the steel ladle is baked through a fuel gas ladle baking device, and when the temperature rises to the pouring temperature, molten steel is poured into the sand mold; s5, pouring is stopped when the distance between the molten steel liquid level in the molten steel liquid and the bottom of the steel ladle is a set height, all links are reasonably controlled, all technological parameters conforming to the technology are set, meanwhile, the tapping temperature is calculated through the tapping distance pouring time and the steel ladle cooling rate, and finally the pouring temperature is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of cast steel, and particularly relates to a one - step forming process for large - scale cast steel parts. Background Art

[0002] During the pouring process, the control of the pouring process has a very important impact on the quality of cast steel parts. Improving the quality of cast steel parts requires not only strict control of the smelting process but also the control of the pouring process. If abnormalities occur during the pouring process, it will have an irreparable impact on the cast steel parts and even lead to the scrapping of the cast steel parts. The factors affecting the quality of cast steel parts generally include the total amount of molten steel, pouring temperature, pouring time, and abnormal situations such as slagging. Conventional pouring methods are just simple filling processes and do not pay attention to pouring temperature, killed molten steel, pouring time, and abnormal phenomena generated during the pouring process, resulting in defective or scrapped cast steel parts, increasing production costs, and causing waste of resources. Summary of the Invention

[0003] (I) Object of the Invention

[0004] In order to overcome the above - mentioned deficiencies, the object of the present invention is to provide a one - step forming process for large - scale cast steel parts to solve the above - mentioned technical problems.

[0005] (II) Technical Solution

[0006] To achieve the above object, the technical solution provided by the present application is as follows:

[0007] A one - step forming process for large - scale cast steel parts includes the following steps:

[0008] S1, according to the one - step forming requirements, melt each component into molten steel with an electric furnace and pour it into a holding furnace for heat preservation;

[0009] S2, after the full - furnace chemical composition is prepared and qualified, pour it into a ladle respectively;

[0010] S3, blow argon for ladle calming and sprinkle carbonized rice husk;

[0011] S4, after calming, bake the ladle with a gas - fired ladle heater. When the temperature rises to the pouring temperature, pour the molten steel into the sand mold;

[0012] S5, stop pouring when the liquid level of the molten steel in the molten steel is at a set height from the bottom of the ladle. The set height is H, H = 1.5d, where d is the diameter of the sliding gate. The remaining steel in the molten steel ladle = H×π×(1 / 2D)²×ρ, H is the set height of the molten steel liquid level from the bottom of the ladle, D is the diameter of the bottom of the ladle, ρ is the density of the molten steel liquid, and π is a constant coefficient.

[0013] Preferably, the components in S1 include C, Si, Mn, S, P and AI.

[0014] Preferably, the proportions of the components in S1 are respectively C: 0.17-0.21Si: 0.60-0.8Mn: 1.1-1.2S, P≤0.025AI: 0.02-0.03.

[0015] Preferably, in S3, argon gas is connected through the argon gas interface of the casting mechanism for argon blowing and sedation, and the argon gas pressure is 0.1MPa-0.2MPa. The ladle is provided with a sliding nozzle that can open and close automatically, and drainage sand is simultaneously poured into the sliding nozzle of the ladle through the casting mechanism. The filling height of the drainage sand is 30-50mm lower than the upper end surface of the sliding nozzle seat of the ladle.

[0016] Preferably, before adding the carbonized rice husks into S3, the slag above the molten steel is cleaned by a slag scraper, and the thickness of the carbonized rice husks is 50-200 mm.

[0017] Preferably, during pouring in S3, the distance between the sliding nozzle of the ladle and the intersection cup is 150-200 mm.

[0018] Preferably, the pouring temperature in S4 is 1560-1580°C.

[0019] Preferably, the ladle in S2 is baked before pouring molten steel, and the baking temperature setting value is greater than 500°C.

[0020] Preferably, the temperature of the insulation in the insulation furnace in S1 is the molten steel tapping temperature, which is the process pouring temperature + tapping distance pouring time × ladle cooling rate. The ladle cooling rate varies slightly due to the amount of molten steel, air temperature, and ladle smelting time, and should be adjusted in time. The tapping temperature in winter is 2-5°C higher than the normal temperature.

[0021] Preferably, the ladle is of bottom leakage type, a sliding water gate is arranged at the bottom of the ladle, and the sliding water gate adopts a hydraulically controlled sliding mechanism to close or open the water gate, which is a control device for the molten steel during the pouring process.

[0022] Beneficial effects:

[0023] The present invention reasonably controls each link and sets various process parameters that meet the process, mainly focusing on the total weight of molten steel, pouring temperature, pouring time and reducing the occurrence of abnormal situations during the pouring process. At the same time, the tapping temperature is calculated through the tapping distance, pouring time and the cooling rate of the molten steel ladle, and the pouring temperature is finally ensured; a series of protective pouring methods are applied during the pouring process to prevent the secondary oxidation of molten steel; at the same time, a scientific excess steel calculation method is adopted, which can save costs and ensure the pouring quality. Specific Embodiment

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the drawings. It should be understood that these descriptions are exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0025] A one-time forming process for large cast steel parts includes the following steps:

[0026] S1. According to the one-time forming requirements, each component is melted into molten steel liquid using an electric furnace. The components include C, Si, Mn, S, P, and Al. Preferably, the ratios of each component in S1 are as follows: C: 0.17 - 0.21, Si: 0.60 - 0.8, Mn: 1.1 - 1.2, S, P ≤ 0.025, Al: 0.02 - 0.03. Then, it is poured into a holding furnace for heat preservation. The temperature for heat preservation in the holding furnace is the tapping temperature of the molten steel. The tapping temperature of the molten steel = the process pouring temperature + the tapping distance pouring time × the temperature reduction rate of the ladle. The temperature reduction rate of the ladle varies slightly due to the amount of molten steel liquid, air temperature, and ladle smelting time, and should be adjusted in a timely manner. The tapping temperature in winter is 2 - 5°C higher than normal.

[0027] S2. Bake the ladle at least 30 minutes in advance. The set baking temperature is greater than 500°C. After the full furnace chemical composition is prepared and qualified, pour it into the ladle respectively.

[0028] S3. Connect argon through the argon interface of the pouring mechanism to perform argon blowing for calming. The argon blowing pressure is 0.1MPa - 0.2MPa. There is a sliding nozzle on the ladle that can automatically open and close. The distance between the sliding nozzle of the ladle and the pouring cup is 150 - 200mm. At the same time, pour drainage sand into the sliding nozzle of the ladle through the pouring mechanism. The filling height of the drainage sand is 30 - 50mm lower than the upper end face of the sliding nozzle seat of the ladle. Clean the steel slag above the molten steel liquid with a slag skimmer and sprinkle carbonized rice husk. The thickness of the carbonized rice husk is 50 - 200mm.

[0029] S4. After calming, bake the ladle with a gas baking burner. When the temperature rises to the pouring temperature, pour the molten steel liquid into the sand mold. The pouring temperature is 1560 - 1580°C.

[0030] S5. Stop pouring when the liquid level of the molten steel liquid in the molten steel liquid reaches the set height from the bottom of the ladle. The set height is H, and H = 1.5d, where d is the diameter of the sliding nozzle. The remaining steel amount in the molten steel ladle = H × π × (1 / 2D)² × ρ, where H is the set height of the molten steel liquid level from the bottom of the ladle, D is the diameter of the bottom of the ladle, ρ is the density of the molten steel liquid, and π is a constant coefficient.

[0031] The ladle adopts bottom leakage type, and a sliding nozzle is set at the bottom of the ladle. During the pouring process, the sliding nozzle of the ladle opens automatically to prevent inclusions from entering the sand mold. The sliding nozzle uses a hydraulically controlled sliding mechanism to close or open the nozzle. It is a control device for molten steel during the pouring process. It can accurately adjust the flow of molten steel from the ladle to the sand mold to balance the inflow and outflow of molten steel, making the pouring operation easier to control.

[0032] After the molten steel ladle is baked to the set temperature, argon is connected to the bottom sliding nozzle structure, and drainage sand is poured into the sliding nozzle of the molten steel ladle. After the tapping temperature reaches the standard, the molten steel is tapped into the molten steel ladle for sedation. After sedation, pouring is performed. Baking before filling can prevent the drainage sand from sintering and wrapping. The baking temperature setting value is greater than 500℃ to prevent the molten steel from absorbing air and oxidizing during the tapping process, and the molten steel sticks to the inner wall of the ladle. The filling height of the drainage sand is 30-50mm lower than the upper end surface of the sliding nozzle seat of the molten steel ladle. If the distance is too small, the drainage sand will easily rush into the molten steel, causing inclusion defects in the steel casting; if the distance is too large, the sintered layer of the drainage sand will be too thick, resulting in the need for manual drainage after the water inlet is opened, and the sintered drainage sand will easily be washed into the sand mold. In this way, the water inlet on the hydraulic mechanism can automatically flow down after opening, without the need for manual drainage. At the same time, it can prevent the sintered drainage sand from being washed into the sand mold during pouring due to the drainage sand being sintered too thickly.

[0033] The thickness of the carbonized rice husk before the molten steel is tapped is 50-200mm, which can prevent the molten steel from being exposed to the air during the tapping and pouring period, causing secondary oxidation of the molten steel. The set height is H, H = 1.5d, d is the diameter of the sliding nozzle. If the excess steel is less than the set height value, the steel slag will be drawn into the sand mold. That is, the 200T molten steel ladle is 180mm; the 130T molten steel ladle is 165mm; and the 70T molten steel ladle is 150mm.

[0034] The remaining steel volume in the ladle = H×W x (1 / 2D)2×ρ, H is the set height of the molten steel surface from the bottom of the ladle, D is the inner diameter of the bottom of the ladle, ρ is the density of the molten steel, and W is the constant coefficient ≈ 3.14. That is, the remaining molten steel volume of a 200T ladle is 6.9T molten steel, the remaining molten steel volume of a 130T ladle is 5T molten steel, and the remaining molten steel volume of a 70T ladle is 2.36T molten steel. Because the density of impurities is less than the density of molten steel, the impurities float on the molten steel.

[0035] During pouring, the distance between the sliding nozzle of the ladle and the pouring cup is 150-200mm to prevent the molten steel from inhaling air and causing secondary oxidation during the pouring process. At the same time, during the pouring process, the steel flow should be in the middle of the sprue to prevent the molten steel from flushing the sprue. During the pouring process, the sliding nozzle of the ladle opens automatically to prevent inclusions from entering the sand mold; the sliding nozzle is a control device for the molten steel during the pouring process, which can accurately adjust the flow of molten steel from the ladle to the sand mold, so that the inflow and outflow of molten steel are balanced, making the pouring operation easier to control.

[0036] During pouring, the pouring temperature of molten steel is 1560-1580℃. The pouring time and pouring temperature are obtained by process simulation. The pouring time is determined according to the inner gate flow rate, and the inner gate flow rate is 0.3-0.6m / s; the pouring temperature is determined according to the liquidus temperature of the casting, which is 20-40℃ higher than the liquidus temperature. Too high or too low temperature will affect the quality of the casting. Too high temperature will cause the casting to absorb air and increase the tendency of sand sticking. Too low temperature will make it difficult for inclusions to float up, resulting in casting defects such as cold shut.

[0037] The tapping temperature of the molten steel is estimated based on the cooling rate of the molten steel ladle, the tapping distance pouring time and the product process pouring temperature. Tapping temperature = process pouring temperature + tapping distance pouring time x molten steel ladle cooling rate. The tapping distance pouring time is the time from the molten steel being taken out of the furnace to being poured. The cooling rate of the molten steel ladle varies slightly due to the amount of molten steel, air temperature and smelting time of the molten steel ladle, and should be adjusted in time. The tapping temperature in winter is 2-5℃ higher than the normal temperature.

[0038] The present invention reasonably controls each link and sets various process parameters that meet the process, mainly focusing on the total weight of molten steel, pouring temperature, pouring time and reducing the occurrence of abnormal situations during the pouring process. At the same time, the tapping temperature is calculated through the tapping distance, pouring time and the cooling rate of the molten steel ladle, and the pouring temperature is finally ensured; a series of protective pouring methods are applied during the pouring process to prevent the secondary oxidation of molten steel; at the same time, a scientific excess steel calculation method is adopted, which can save costs and ensure the pouring quality.

[0039] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A one-step forming process for large steel castings, characterized in that: It includes the following steps: S1. According to the requirements of one-time forming, each component is melted into molten steel liquid by an electric furnace and poured into a holding furnace for heat preservation. S2. After the chemical components of the full furnace are prepared and qualified, they are respectively poured into a ladle. S3. Argon blowing is carried out for ladle calming, and carbonized rice husk is scattered. S4. After the calming is completed, the ladle is baked by a gas ladle heater. When the temperature rises to the pouring temperature, the molten steel liquid is poured into the sand mold. S5. When the liquid level of the molten steel liquid in the molten steel liquid is at a set height from the bottom of the ladle, the pouring stops. The set height is H, and H = 1.5d, where d is the diameter of the sliding gate. The remaining steel in the ladle = H×π×(1 / 2D)²×ρ, where H is the set height of the molten steel liquid level from the bottom of the ladle, D is the bottom diameter of the ladle, ρ is the density of the molten steel liquid, and π is a constant coefficient.

2. A one-step forming process for large steel castings according to claim 1, characterized in that: The components in S1 include C, Si, Mn, S, P, and Al.

3. A one-step forming process for large steel castings according to claim 2, characterized in that: The respective ratios of the components in S1 are: C: 0.17 - 0.21, Si: 0.60 - 0.8, Mn: 1.1 - 1.2, S, P ≤ 0.025, Al: 0.02 - 0.

03.

4. A one-step forming process for large steel castings according to claim 1, characterized in that: In S3, argon is connected through the argon interface of the pouring mechanism for argon blowing and ladle calming. The argon blowing pressure is 0.1 MPa - 0.2 MPa. A sliding gate that can automatically open and close is provided on the ladle. At the same time, pouring sand is poured into the sliding gate of the ladle through the pouring mechanism. The filling height of the pouring sand is 30 - 50 mm lower than the upper end face of the sliding gate seat of the ladle.

5. The one-step forming process of a large steel casting according to claim 1, characterized in that: Before putting carbonized rice husk in S3, the slag above the molten steel liquid is cleaned up by a slag skimmer. The thickness of the carbonized rice husk is 50 - 200 mm.

6. A one-step forming process for large steel castings according to claim 1, characterized in that: In S3 during pouring, the distance between the sliding gate of the ladle and the runner cup is 150 - 200 mm.

7. A one-step forming process for large steel castings according to claim 1, characterized in that: The pouring temperature in S4 is 1560 - 1580 °C.

8. The one-step forming process of a large steel casting according to claim 1, characterized in that: Before pouring the molten steel liquid into the ladle in S2, the ladle is baked first, and the set value of the baking temperature is greater than 500 °C.

9. A one-step forming process for large steel castings according to claim 1, characterized in that: The heat preservation temperature in the holding furnace in S1 is the tapping temperature of the molten steel. The tapping temperature of the molten steel = the process pouring temperature + the tapping distance pouring time × the ladle cooling rate. The ladle cooling rate varies slightly due to the amount of molten steel liquid, air temperature, and ladle smelting time, and should be adjusted in time. The tapping temperature in winter is 2 - 5 °C higher than the normal temperature.

10. The one-step forming process of a large steel casting according to claim 1, characterized in that: The ladle adopts a bottom leakage type. A sliding gate is provided at the bottom of the ladle. The sliding gate uses a hydraulic control sliding mechanism to close or open the gate, which is a control device for molten steel during the pouring process.