Method for cleaning condensed slag eave outside insertion pipe of RH vacuum furnace and slag melting agent

Abstract

The invention relates to the technical field of RH (Ruhrstahl Heraeus) vacuum refining furnaces, in particular to a method for cleaning a coagulated slag eave outside an insert tube of an RH vacuum furnace and a slagging agent. The slagging agent comprises the following chemical components in percentage by weight: 29.18 + / -1.5% of CaO; siO2: 31.6 + / -1.5%; the content of Al2O3 is 3.16 + / -1.2%; fe2O3: less than or equal to 1.25%; 3.87 + / -1.2% of MgO (magnesium oxide); f-: 8.55 + / -1.2%; 8.05 + / -1.2% of Na2O + K2O (sodium oxide + potassium oxide); on the basis that the efficient production rhythm of the RH furnace is guaranteed, the slag eave of the outer shell of the insertion pipe is safely and rapidly cleaned. The method has the beneficial effects that the problem of condensed slag eaves outside the RH furnace insertion pipe can be rapidly and safely solved, the quality of vacuum molten steel is effectively improved, pollution hazards are reduced, meanwhile, the method is good in operability and small in interference on the production rhythm, and the labor intensity of workers is not increased.

Description

Technical Field

[0001] This invention relates to the field of RH vacuum refining furnace technology, and in particular to a method for cleaning the slag rim outside the insertion tube of an RH vacuum furnace and a slag-reducing agent. Background Technology

[0002] During the operation of the RH vacuum refining furnace, its insertion tube needs to be immersed in the molten steel ladle, which causes slag to condense on the outer wall of the insertion tube to form a slag rim shell. The volume of the slag rim shell will continue to grow as the number of production ladles increases, increasing the equipment load and the burden on equipment operation.

[0003] The slag sheath outside the insert tube is mainly composed of converter slag, containing a large amount of harmful substances such as sulfur, phosphorus, and inclusions. When these harmful substances are impregnated into the molten steel ladle, they can directly enter the molten steel, contaminating it and causing steel scrapping accidents. During the RH treatment process, the slag sheath outside the insert tube absorbs heat from the molten steel, causing abnormal temperature drops and endangering production safety. Therefore, there is an urgent need for an effective technical method to clean the slag sheath of the RH furnace insert tube. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention provides a method and slag-removing agent for cleaning the slag rim on the outside of the insertion tube of an RH vacuum furnace. While ensuring the efficient production rhythm of the RH furnace, it achieves safe and rapid cleaning of the slag rim on the outer shell of the insertion tube, and the detached slag rim material is reasonably disposed of, eliminating its hazards and ultimately restoring the normal production capacity of the RH furnace.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for cleaning the slag rim on the outside of the insert tube of an RH vacuum furnace, the specific method including the following:

[0007] S1. Add slag dissolving agent to the cleaning tank.

[0008] After the slag-reducing agent is added to the molten steel in the cleaning tank, it is placed in the RH refining furnace processing station. The cleaning tank is lifted so that the distance between the slag surface of the cleaning tank and the vacuum chamber is close to the safe margin height. The safe margin height H1 = the safe limit immersion position of the insertion tube - the maximum splash height H2.

[0009] Turn on bottom-blown argon stirring to quickly slag; bottom-blown argon flow rate: 100~120NL / min; the slag surface moves slightly and has pores with a diameter ≤100mm, until the slag-forming agent is completely slag-forming.

[0010] S2. Insert the tube and clean it;

[0011] Perform regular, instantaneous switching between two states of bottom-blowing argon flow rate:

[0012] a. Initial bottom blowing argon high flow rate stirring state: Instantly increase the argon flow rate to cause slag surface to surge around the insertion tube. The height of the slag surface surge is 150±50mm. Then, a stable tumbling is formed around the insertion tube. The height of the slag surface tumbling is 100±20mm. This continues until the entire slag edge surface is sprayed with the first slag-removing agent.

[0013] b. Bottom-blown argon with low flow rate stirring: Reduce the bottom-blown argon flow rate to keep the slag surface around the insertion tube slightly moving, with pores of diameter ≤100mm, and continue until the slag-forming agent on the slag edge loses its fluidity;

[0014] c. Resume high-flow-rate argon stirring until the slag-removing agent on the slag edge surface regains its fluidity;

[0015] d. Observe whether the slag edge of the insertion tube has fallen off. If it has not fallen off, repeat steps b and c until the slag edge has completely fallen off.

[0016] Furthermore, in step S1, the molten steel in the cleaning tank has S < 0.015%, P < 0.015%, C < 0.045%, and a temperature ≥ 1620℃.

[0017] Furthermore, in step S1, the net clearance height of the molten steel in the cleaning tank meets the requirement that after the insertion pipe and slag edge are fully inserted, the height of the slag surface after rising + H2 < the safe loading height of the tank, and also meets the height requirements for normal RH treatment.

[0018] Furthermore, in step S1, the ladle used for cleaning is a continuous turnover ladle with a continuous turnover time of ≥24 hours. The molten steel loaded in the previous furnace is low-carbon, low-silicon, and aluminum-killed steel with a turnover interval of ≤30 minutes, and there is no residual steel or slag at the bottom of the ladle. The amount of slag carried by the molten steel from the cleaning ladle is ≥70% of the ladle opening area, and the slag thickness is ≤100mm.

[0019] Furthermore, in step S1, after the slag-reducing agent in the molten steel is completely melted, a liquid slag layer is formed on the surface of the molten steel, and the thickness of the slag layer is ≥200mm.

[0020] Furthermore, in step S4, the large and small flow rates of bottom-blown argon are switched regularly and instantaneously, with the large flow rate of bottom-blown argon being 300-400 NL / min and the small flow rate being 100-120 NL / min.

[0021] A method for cleaning the slag rim on the outside of the insert tube of an RH vacuum furnace using a slag-removing agent, wherein the chemical composition percentage of the slag-removing agent is as follows: CaO: 29.18±0.5%; SiO2: 31.6±0.5%; Al2O3: 3.16±0.2%; Fe2O3: ≤1.25%; MgO: 3.87±0.2%; F-: 8.55±0.2%; Na2O+K2O: 8.05±0.2%; the remainder being impurities.

[0022] Furthermore, the alkalinity of the slag-reducing agent is less than or equal to 0.92.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] This method provides a quick and safe solution to the problem of slag rimming outside the insert tube of an RH furnace. After cleaning, it increases the decarburization of RH-treated steel by 1–1.5 ppm; S, P, O, and N are reduced by 3–15 ppm compared to before cleaning, effectively improving the quality of vacuum steel. After the slag rim is eliminated, the temperature drop of molten steel during RH treatment is reduced by 1.5–5℃, macroscopic inclusions are basically eliminated, effectively reducing the harm of slag rim pollution. At the same time, this method is easy to operate, has little impact on the production rhythm, and does not increase the labor intensity of workers. Attached Figure Description

[0025] Figure 1 This is the flow rate diagram for bottom-blown argon cleaning as described in this invention.

[0026] Figure 2 This is a safety margin height diagram. Detailed Implementation

[0027] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0028] The cleaning time is related to the volume of the slag edge. The larger the volume of the slag edge, the longer it takes to melt and clean, and the greater the disruption to the production rhythm. Therefore, the optimal implementation method is: slag edge diameter > 1.5 × insertion tube diameter; slag edge thickness > 400 mm, clean once.

[0029] The cleaning time is related to the slag edge temperature. The higher the slag edge temperature, the shorter the cleaning melting time. Therefore, it is necessary to shorten the time interval between the last heat of RH production and the start of cleaning as much as possible to reduce the temperature drop of the slag edge. Similarly, increasing the temperature of the molten steel in the cleaning ladle can improve the cleaning effect.

[0030] Slag rim components contaminate molten steel. Therefore, when producing steel grades with stringent requirements for S, P, C, O, and inclusions in an RH furnace, the cleaning frequency should be increased. The optimal implementation method is: slag rim diameter > insertion tube diameter + 200mm; slag rim thickness > 300mm, clean once.

[0031] Examples: The chemical composition of the slag-reducing agent in the embodiments of the present invention is shown in Table 1; the beneficial effects of the embodiments of the present invention are shown in Table 2.

[0032] Table 1 shows the chemical composition (wt, %) of the slag-reducing agent of the present invention:

[0033]

[0034] This invention employs a 180t molten steel ladle and an RH vacuum furnace with a rotary table structure. The molten steel ladle at the processing station has a lifting function and a bottom-blown argon stirring system with adjustable flow rate. When the bottom-blown argon flow rate is 300–400 NL / min, the controllable splash height on the slag surface is 150 mm. When the bottom-blown argon flow rate is 100–120 NL / min, the slag surface exhibits slight movement and pores with a diameter ≤100 mm. The safe limit immersion position of the insertion tube is 600 mm, and the insertion depth under operating conditions is 300–500 mm. The safe loading height (clearance height) of the molten steel ladle is >200 mm, and the normal RH processing requires a clearance height of 800–1000 mm. Due to continuous production, a slag rim has formed on the outside of the insertion tube, with a diameter >1.5 times the diameter of the insertion tube and a thickness >400 mm.

[0035] When using conventional industry methods, such as high-temperature molten steel pipe cleaning, which involves molten low-carbon, low-silicon, and aluminum-killed steel arriving at a temperature above 1650℃ and then being vacuum-circulated in the furnace to clean the insertion tube and residual steel and slag in the vacuum chamber, this conventional method effectively cleans and heats the insertion tube and the inner wall of the vacuum chamber. However, the slag rim that forms on the outside of the insertion tube cannot be fully immersed in the high-temperature molten steel due to its high slag formation position and the limitation of the insertion tube's safe immersion position. Furthermore, the slag rim is mainly composed of converter slag, which has high basicity and a high melting point. As a result, the high-temperature molten steel pipe cleaning operation is ineffective in cleaning the slag rim, and the slag rim may even continue to grow due to the circulation effect of the vacuum furnace.

[0036] Example 1:

[0037] A method for cleaning the slag rim on the outside of the insert tube of an RH vacuum furnace, the specific method including the following:

[0038] Preparation of molten steel for cleaning ladle:

[0039] The molten steel in the cleaning ladle is low-carbon, low-silicon, aluminum-killed steel, with a steel composition of S: 0.012%, P: 0.01%, and C: 0.035%. The net height of the molten steel in the cleaning ladle is 850mm. The molten steel ladle used in the cleaning ladle is a continuous turnover ladle with a continuous turnover time of 26 hours. The molten steel loaded in the previous heat is low-carbon, low-silicon, aluminum-killed steel, and the turnover interval is 28 minutes. There is no residual steel or slag at the bottom of the ladle. Slag is blocked during the tapping process of the molten steel in the cleaning ladle. The amount of slag carried by the molten steel at the tapping of the cleaning ladle is ≥70% of the ladle opening area, and the slag thickness is 85mm.

[0040] After adding slag-forming agent to the molten steel in the cleaning tank, it is positioned in the RH vacuum furnace treatment station. The cleaning tank is then lifted so that the slag surface and insertion depth reach a safe margin height. The safe margin height H1 = (safe limit immersion position of the insertion tube - maximum controllable splash height H2) = 600mm - 150mm = 450mm. This height ensures that most of the slag edge on the insertion tube surface is in contact with or immersed in the slag surface, while the portion of the slag edge above the slag surface is <100mm. Bottom-blown argon is activated for slag agitation. The flow rate of bottom-blown argon for slag agitation is sufficient for rapid slag agitation under the insertion tube's insertion state. The bottom-blown argon for slag agitation flow rate Q1 = 120NL / min. Under this state, the slag surface of the slag agent floating below the slag edge of the insertion tube experiences slight movement and gradually develops pores with a diameter ≤100mm. Slag agitation continues under this state for 5 minutes to completely slag the slag agent and simultaneously allow the slag edge on the insertion tube surface to be fully baked and preheated. After the slag agent is completely melted, a liquid slag layer with a thickness of 200mm is formed on the surface of the molten steel.

[0041] like Figure 1 As shown, cleaning:

[0042] Based on the bottom-blown argon cleaning flow rate Figure 1 As shown, by rapidly switching between two states of large and small bottom-blown argon flow rate, impact force and impact vibration are generated, which accelerates the cleaning effect of the slag-removing agent.

[0043] a. Bottom-blown argon high-flow-rate stirring state: Instantly increase the argon flow rate from 120NL / min to 400NL / min, causing slag to surge around the insertion tube. The slag surge rises and falls to a height of 150mm, and then forms a stable tumbling around the insertion tube. Utilize the tumbling and undulating slag surface around the insertion tube to coat the slag-forming agent with the slag edge surface of the insertion tube. The first bottom-blown argon high-flow-rate stirring lasts for 2 minutes, completing the first slag-forming agent spraying on the entire slag edge surface.

[0044] b. Bottom-blown argon low-flow stirring state: restore the bottom-blown argon flow rate to 120NL / min to keep the slag surface around the insertion tube slightly moving, with pores of diameter ≤100mm, for 40s. At this time, the slag-forming agent on the slag edge surface loses its fluidity.

[0045] c. Resume high-flow-rate argon stirring, each time lasting 40 seconds. During this process, under the action of steel slag splashing and high-temperature molten steel baking, the slag-forming agent on the slag edge surface resumes flow and fully reacts chemically with the slag edge, reducing the basicity of the slag edge, thereby lowering the melting point of the slag edge, causing the slag edge to melt and soften, and then fall off under the impact and vibration of the steel slag.

[0046] d. Observe whether the slag edge of the insertion tube has fallen off. If it has not fallen off, repeat steps b and c until the slag edge has completely fallen off.

[0047] Post-cleaning treatment:

[0048] e. After cleaning the slag edge of the insertion tube, reduce the bottom blowing argon flow rate to 120NL / min, so that the slag surface around the insertion tube remains slightly moving and has pores with a diameter ≤100mm. Continue for 2 minutes to promote the slag formation of the detached material.

[0049] Turn off bottom blowing argon, rotate the rotary table, and move the cleaning tank from the processing position to the standby position to lift it out;

[0050] If the volume of unmelted slag ≥ 400×400mm in the cleaning tank, slag removal should be performed; otherwise, it should be hoisted to the LF furnace for further processing.

[0051] Example 2:

[0052] A method for cleaning the slag rim on the outside of the insert tube of an RH vacuum furnace, the specific method including the following:

[0053] When using conventional industry methods, after the high-temperature molten steel pipe rinsing operation, the slag edge of the inserted pipe was not effectively cleaned. The slag edge diameter was greater than the inserted pipe diameter + 200 mm, and the slag edge thickness was greater than 300 mm, even though the molten steel had already completed its circulation at the working position.

[0054] 1. Measure the temperature of the molten steel; the temperature should be >1620℃.

[0055] 2. Add the slag dissolving agent directly into the molten steel ladle for pipe cleaning;

[0056] 3. Reduce the height of the molten steel ladle to the safe margin height H1 from its current processing state.

[0057] 4. Clean according to the steps in Example 1.

[0058] Example 3:

[0059] A method for cleaning the slag rim on the outside of the insert tube of an RH vacuum furnace, the specific method including the following:

[0060] In the newly installed insertion tube, during normal production, after the molten steel enters the processing station and is positioned, a slag-reducing agent is added. Then, the large ladle is lifted, and the slag-reducing agent is coated onto the surface of the insertion tube during the lifting / lowering process of the large ladle, which can effectively eliminate the possibility of slag condensation.

[0061] Table 2 shows the beneficial effects of the embodiments of the present invention.

[0062]

[0063] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for cleaning the slag rim on the outside of the insertion tube of an RH vacuum furnace, characterized in that, The specific methods include the following: S1. Add slag dissolving agent to the cleaning tank. After the slag-reducing agent is added to the molten steel in the cleaning tank, it is placed in the RH refining furnace processing station. The cleaning tank is lifted so that the distance between the slag surface of the cleaning tank and the vacuum chamber is close to the safe margin height. The safe margin height H1 = the safe limit immersion position of the insertion tube - the maximum splash height H2. Turn on bottom-blown argon stirring to quickly slag; bottom-blown argon flow rate: 100~120NL / min; the slag surface moves slightly and has pores with a diameter ≤100mm, until the slag-forming agent is completely slag-forming. S2. Insert the tube and clean it; Perform regular, instantaneous switching between two states of bottom-blowing argon flow rate: a. Initial bottom blowing argon high flow rate stirring state: Instantly increase the argon flow rate to cause slag surface to surge around the insertion tube. The height of the slag surface surge is 150±50mm. Then, a stable tumbling is formed around the insertion tube. The height of the slag surface tumbling is 100±20mm. This continues until the entire slag edge surface is sprayed with the first slag-removing agent. b. Bottom-blown argon with low flow rate stirring: Reduce the bottom-blown argon flow rate to keep the slag surface around the insertion tube slightly moving, with pores of diameter ≤100mm, and continue until the slag-forming agent on the slag edge loses its fluidity; c. Resume high-flow-rate argon stirring until the slag-removing agent on the slag edge surface regains its fluidity; d. Observe whether the slag edge of the insertion tube has fallen off. If it has not fallen off, repeat steps b and c until the slag edge has completely fallen off.

2. The method for cleaning the slag rim outside the insertion tube of an RH vacuum furnace according to claim 1, characterized in that, In step S1, the molten steel in the cleaning tank has S < 0.015%, P < 0.015%, C < 0.045%, and a temperature ≥ 1620℃.

3. A method for cleaning the slag rim outside the insertion tube of an RH vacuum furnace according to claim 1, characterized in that, In step S1, the net clearance height of the molten steel in the cleaning tank meets the requirement that after the insertion pipe and slag edge are fully inserted, the height of the slag surface after rising + H2 is less than the safe loading height of the tank, and also meets the height requirements for normal RH treatment.

4. The method for cleaning the slag rim outside the insertion tube of an RH vacuum furnace according to claim 1, characterized in that, The molten steel ladle used in step S1 is a continuous turnover ladle with a continuous turnover time of ≥24 hours. The molten steel loaded in the previous furnace is low-carbon, low-silicon, and aluminum-killed steel with a turnover interval of ≤30 minutes. There is no residual steel or slag at the bottom of the ladle. The amount of slag carried by the molten steel from the cleaning ladle is ≥70% of the ladle opening area, and the slag thickness is ≤100mm.

5. A method for cleaning the slag rim outside the insertion tube of an RH vacuum furnace according to claim 1, characterized in that, In step S1, after the slag-reducing agent in the molten steel is completely melted, a liquid slag layer is formed on the surface of the molten steel, and the thickness of the slag layer is ≥200mm.

6. A method for cleaning the slag rim outside the insertion tube of an RH vacuum furnace according to claim 1, characterized in that, In step S4, the large and small flow rates of bottom-blown argon are switched regularly and instantaneously. The large flow rate of bottom-blown argon is 300-400 NL / min, and the small flow rate is 100-120 NL / min.

7. A slagging agent for cleaning the external slag rim of the insert tube of an RH vacuum furnace according to claim 1, characterized in that, The chemical composition percentages of the slag-reducing agent are as follows: CaO: 29.18±0.5%; SiO2: 31.6±0.5%; Al2O3: 3.16±0.2%; Fe2O3: ≤1.25%; MgO: 3.87±0.2%; F － : 8.55±0.2%; Na2O+K2O: 8.05±0.2%; the remainder are impurities.

8. The slag-removing agent used in the method for cleaning the slag rim outside the insertion tube of the RH vacuum furnace according to claim 7, is characterized in that... The alkalinity of the slag-reducing agent is less than or equal to 0.92.

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