Direct forming method for liquid die forging of carbon steel valve plate

Abstract

The invention discloses a direct forming method for liquid die forging of a carbon steel valve plate in the technical field of valve plate die forging, and the direct forming method for liquid die forging of the carbon steel valve plate comprises the following steps: S1, pretreatment of a carbon steel raw material: carrying out surface cleaning and drying preheating on the carbon steel raw material at the drying temperature of 200-300 DEG C; s2, metal smelting is conducted, specifically, the pretreated raw materials are added into smelting equipment to be heated to be in a liquid state, and the smelting temperature is controlled to be 1650-1700 DEG C; according to the forming method, molten metal is accurately injected into the specially-made precision mold, extremely high pressure is immediately applied, solidification crystallization and trace plastic deformation of the metal are completed under the pressure, the grain structure is remarkably refined, the mechanical property of the valve plate is close to that of a forged piece, and therefore the valve plate can be manufactured. And meanwhile, complex geometrical characteristics are reserved, near-net forming is achieved, the sealing performance is excellent, the pressure-resistant grade is high, and the service life is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of valve plate die forging, in particular to a direct forming method of liquid die forging of carbon steel valve plate. BACKGROUND

[0002] The valve plate is the core functional component of various valves such as stop valves, gate valves and compressor valves, and its structural integrity and performance stability directly determine the sealing accuracy, pressure rating, service life and operation reliability of the valve, and it is widely used in key fields such as industrial pipelines, energy equipment and general machinery.

[0003] At present, the mainstream forming methods of valve plate mainly include two types: one is the traditional casting process, represented by ordinary sand casting and investment casting, which is the main choice for early valve plate production due to its flexibility and low initial investment; the other is forging process, including free forging and die forging, which can densify the metal organization through plastic deformation and significantly improve the mechanical properties of the valve plate.

[0004] However, the existing forming methods have obvious technical shortcomings: the valve plate produced by casting process is prone to form pores, shrinkage holes, inclusions and other defects, which can easily evolve into fatigue cracks and leakage channels under harsh working conditions such as alternating pressure and medium corrosion, leading to premature failure of the valve plate and threatening the safety of the pipeline system; although the forging process can optimize the material organization, it is difficult to achieve near-net shaping of complex structures for valve plates with complex flow channels, sealing grooves or irregular geometric shapes, and a large amount of mechanical processing is required afterwards, which not only reduces production efficiency but also causes serious material waste. SUMMARY

[0005] The purpose of the present application is to provide a direct forming method of liquid die forging of carbon steel valve plate to solve the problem of existing forming methods being only complex in process, high in mold cost, and difficult to achieve near-net shaping of complex structures, and a large amount of mechanical processing and serious material waste afterwards.

[0006] To achieve the above purpose, the present application provides the following technical solution: a direct forming method of liquid die forging of carbon steel valve plate, the direct forming method of liquid die forging of carbon steel valve plate comprising:

[0007] S1: carbon steel raw material pretreatment: surface cleaning and drying preheating of carbon steel raw material, drying temperature is 200-300 DEG C;

[0008] S2: metal smelting: the pretreated raw material is added into the smelting equipment and heated to liquid state, and the smelting temperature is controlled at 1650-1700℃;

[0009] S3: mold and ladle pretreatment: the valve plate mold is cleaned, coated and preheated, the preheating temperature is 250-500℃; the ladle is lined, coated and dried and preheated;

[0010] S4: pouring: the molten steel after deslagging is poured into the pretreated ladle, and then poured into the mold cavity;

[0011] S5: pressure holding: the mold forging press applies a one-way pressure to the steel liquid in the cavity, the pressure is 26-30MPa, and the pressure holding time is 25-35s;

[0012] S6: sample removal: the mold is opened after pressure holding to remove the formed valve plate.

[0013] Preferably, in the carbon steel raw material pretreatment in step S1, ultrasonic cleaning is used for surface cleaning, and the drying and preheating holding time is 15-25min.

[0014] Preferably, the smelting equipment in step S2 is a medium frequency furnace, the furnace mouth diameter of the medium frequency furnace is 140-160mm, and the added carbon steel raw material is a small size billet.

[0015] Preferably, the smelting process in step S2 includes the following steps:

[0016] First heat to metal melting, then add the furnace charge to the liquid level, gradient heating during smelting, 15-25min holding time per stage, metal melting, 1500-1700HZ low frequency current holding, and temperature measurement frequency is 4-6min / time.

[0017] Preferably, in the mold pretreatment of step S3, the cavity and the key mating surface are thoroughly cleaned, and a high-temperature metal ceramic heat preservation coating is sprayed.

[0018] Preferably, the mold preheating temperature in step S3 is controlled at 250-300℃, and gradient heating is used for preheating.

[0019] Preferably, the ladle pretreatment in step S3 includes the following steps:

[0020] The ladle lining is made of refractory mortar, the working layer thickness is 18-22mm, after knotting, it is dried by carbon fire, then coated with high-temperature heat preservation coating and graphite emulsion in turn, and finally dried by secondary carbon fire.

[0021] Preferably, the pouring process of step S4, the ladle is transported to the top of the mold for 2-4s, the pouring action is completed for 4-6s, and the temperature of the molten steel during pouring is controlled between 1650-1700℃.

[0022] Preferably, in the pressurizing and holding step of step S5, the upper die punch is pressed to contact the molten steel for 2-4s after pouring, the applied unidirectional pressure is 26-30MPa, and the holding time is 25-35s.

[0023] Preferably, the slag removal process of step S4 includes the following steps:

[0024] Before pouring, a steel slag removal agent is added to the surface of the molten steel for slag removal treatment;

[0025] After slag removal, the flowability of the molten steel is checked, and if the flowability of the molten steel is poor, the molten steel is reheated to the process interval of 1650-1700℃ before pouring.

[0026] Compared with the prior art, the beneficial effects of the present application are: the forming method accurately injects molten metal into a specially designed precision mold and immediately applies extremely high pressure, so that the metal completes solidification and crystallization and micro plastic deformation under pressure, significantly refines the grain structure, makes the valve plate obtain mechanical properties close to forgings, while retaining its complex geometric characteristics, realizes near-net forming, has excellent sealing performance, high pressure resistance level, and prolongs the service life. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The forming method flowchart of the present application. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0029] The present application provides a direct forming method for liquid die forging of carbon steel valve plate, which accurately injects molten metal into a specially designed precision mold and immediately applies extremely high pressure, so that the metal completes solidification and crystallization and micro plastic deformation under pressure, significantly refines the grain structure, makes the valve plate obtain mechanical properties close to forgings, while retaining its complex geometric characteristics, realizes near-net forming, has excellent sealing performance, high pressure resistance level, and prolongs the service life.

[0030] Equipment and raw materials:

[0031] Medium frequency melting furnace (furnace mouth diameter 150 mm, power 500 kW);

[0032] Four-column die forging press (maximum pressure 50 MPa, with stroke limiting device);

[0033] Ultrasonic cleaner (power 600 W, frequency 40 kHz);

[0034] Fast thermocouple (temperature measurement range 1000-2000℃, accuracy ±5℃);

[0035] Surface roughness meter (accuracy 0.01 μm);

[0036] Universal material testing machine (maximum test force 1000 kN);

[0037] Industrial CT detector (detection accuracy 0.02 mm);

[0038] Q235 carbon steel billet (specification 50 mm x 50 mm x 50 mm, purity ≥99.5%);

[0039] Steel slag remover (particle size 0.1-0.3 mm);

[0040] High-temperature resistant metal ceramic heat preservation coating (main component Al2O3-ZrO2, solid content ≥60%), graphite milk (carbon content ≥98%);

[0041] Fire clay (refractoriness ≥1800℃);

[0042] Example 1

[0043] Equipment pretreatment: start the water circulation system, keep the water level at 3 / 4 of the water tank volume, and control the water temperature at 45℃;

[0044] Raw material pretreatment: select 10 kg of Q235 carbon steel billet, put it into the ultrasonic cleaner for cleaning for 15 min, and remove the surface oil and impurities;

[0045] Subsequently, put it into the oven, dry preheat at 250℃, and keep for 20 min. After the end of the heat preservation, take it out for standby, remove the water and oil adsorbed on the surface of the material, prevent it from entering the steel liquid to produce gas and cause pores in the casting, and at the same time avoid the cold material directly added into the molten metal to cause violent spatter and temperature fluctuation, improve the production safety;

[0046] Metal smelting: add the pretreated billet into the medium frequency furnace in batches, first add 5 kg of billet, and do not fill the billet to prevent the metal from lapping near the furnace mouth surface and blocking the furnace mouth. After the metal is melted, continue to add the furnace charge until it is flat with the surface;

[0047] The gradient temperature rising is first from room temperature to 800°C, then from 800°C to 1200°C, and finally from 1200°C to 1680°C, and each stage is kept for 20 minutes to ensure the uniformity of the temperature in the furnace;

[0048] After the metal is melted, the current frequency is adjusted to 1600 Hz for heat preservation, the temperature is measured once every 5 minutes by a rapid thermocouple, the temperature of the molten steel is maintained at 1680°C, the temperature is too high to avoid the knot material from melting into slag, 10-15 minutes after the temperature is stable, the remaining 5 kg of blank is added to the liquid level to be flat with the furnace mouth, after the feeding is completed, the heat preservation is continued for 5 minutes to ensure that the blank is completely melted and the temperature of the molten steel rises to 1680°C±5°C, then 0.3 kg of steel deslagging agent is put in, and the deslagging is stirred for 2 minutes, and after 3 minutes of standing, it is ready for pouring;

[0049] Mold pretreatment: clean the mold cavity and matching surface, the valve plate mold must be thoroughly cleaned before the mold is heated, to ensure that there is no dust, oil stains, residual release agent or other impurities, so as to avoid affecting the adhesion of the coating or causing surface defects of the casting, after cleaning, evenly spray 0.4mm thick high temperature metal ceramic heat preservation coating with a special spray gun, the coating has excellent heat insulation performance, which can effectively slow down the heat exchange rate between the molten metal and the mold, thereby preventing "cold separation" or "insufficient pouring" and other filling defects in thin-walled or complex features, at the same time, good heat preservation effect helps the molten metal to solidify smoothly in sequence, reduces the organizational stress and shrinkage resistance caused by quenching, and finally significantly improves the surface finish, dimensional accuracy and internal uniformity of the valve plate forging;

[0050] The mold is preheated by gradient temperature rising, first from room temperature to 150°C, kept for 15 minutes, then from 150°C to 250°C, kept for 20 minutes, and the preheating temperature is stabilized at 250°C±5°C, to eliminate the residual water in the mold, improve the flowability of the molten metal, and avoid forming defects caused by quenching, and ensure uniform distribution of thermal stress in the mold;

[0051] Pretreatment of pouring ladle: the pouring ladle is knotted with refractory lining, the working layer thickness is 20mm to ensure good heat preservation effect and structural strength, after knotting, the carbon fire drying treatment must be carried out first, the physical water in the refractory is fully evaporated by low temperature slow baking, to avoid cracking of the lining due to rapid vaporization of water during subsequent high temperature baking;

[0052] After drying for 75 min, brush the high-temperature heat preservation coating and graphite emulsion each once. The heat preservation coating aims to further improve the heat insulation performance of the ladle and reduce the heat loss of the molten metal. The graphite emulsion plays a lubricating and isolating role, effectively preventing the adhesion of the molten metal and the ladle lining. After brushing, carbon fire is used for baking again to completely remove volatile substances in the coating and sinter and solidify it to form a dense working surface. The second carbon fire baking is 60 min until completely dry.

[0053] Temperature measurement: After the mold is adjusted and preheated to the specified temperature, the final temperature of the molten steel after melting needs to be measured. When the temperature of the molten steel stabilizes near the upper limit of the appropriate interval of 1680℃, pouring can be carried out. This temperature interval aims to ensure that the molten steel has excellent fluidity, can smoothly complete the filling of the complex mold cavity, and at the same time avoid excessive oxidation of the molten metal, increase of gas solubility or thermal shock to the mold heat preservation coating due to too high temperature. Pouring operation should be rapid and smooth to minimize heat loss and ensure that the molten steel completes the filling and pressure crystallization at the best viscosity.

[0054] Pouring and pressure coordination operation: Pour the deslagged molten steel into the preheated and thoroughly dried ladle. During pouring, the flow state of the molten steel needs to be closely observed. If the flowability is poor, the surface oxidation film is too thick, or there are obvious film formation signs, stop transporting immediately and reheat the molten steel to the process window. Directly pouring is strictly prohibited to avoid solidification or clogging of the pouring gate in the ladle. If the molten steel has good flowability and meets the pouring requirements, pouring operation should be carried out quickly. The whole process requires close connection. The transfer from the ladle to the upper part of the press mold should be completed within 3 seconds. The pouring action itself should be completed within 5 seconds at one time, and sufficient filling should be ensured to minimize the temperature drop and oxidation of the molten steel.

[0055] After pouring, start the hydraulic press to perform mold closing and pressure. The time for the upper punch to contact the molten metal should be controlled within 3 seconds. Then enter the pressure maintaining stage, apply 28 MPa unidirectional pressure, and set the pressure stroke limit device to 15 mm.

[0056] Pressure maintaining and part taking: maintain 28 MPa pressure for 30 s to make the valve plate forge piece complete crystallization and solidification under continuous isostatic pressure, thereby obtaining an internal dense and size accurate formed part. Then open the mold to take out the formed valve plate and naturally cool to room temperature.

[0057] Example 2

[0058] Equipment pretreatment: start the water circulation system, keep the water level at 3 / 4 of the water tank volume, and control the water temperature at 45℃.

[0059] Raw material pretreatment: select Q235 carbon steel billet 10 kg, put it into the ultrasonic cleaner for 15 min to remove surface oil and impurities.

[0060] Subsequently put into the oven, 300℃ drying preheat, 25min, after the end of the heat preservation, remove the material surface adsorbed moisture and oil dirt, prevent its into the molten steel after the production of gas, resulting in casting pore, at the same time, avoid cold material directly into the molten metal caused by violent spatter and temperature fluctuations, improve the production safety;

[0061] Metal smelting: the pretreated billet batch into the intermediate frequency furnace, first add 5kg billet, billet not to fill, to prevent the surface metal near the mouth of the lap, block the mouth, after the metal melt, can continue to add charge until the surface flat;

[0062] Gradient heating, first from room temperature to 800℃, then from 800℃ to 1200℃, finally from 1200℃ to 1700℃, each stage 20min, ensure the temperature uniformity in the furnace;

[0063] After the metal melt, adjust the current frequency to 1700Hz, 4min with a fast thermocouple temperature measurement, maintain the liquid temperature 1700℃, avoid high temperature, resulting in knot material melting into slag, after the temperature stabilizes 10-15min, add the remaining 5kg billet to the liquid surface with the mouth flat, after the completion of the material continue to heat preservation 5min, ensure the billet completely melted and the liquid temperature back to 1700 0 -5 ℃, then put into the steel deslagging agent 0.3kg, stirring deslagging 2min, 3min after standing for pouring;

[0064] Mold pretreatment: clean the mold cavity and the matching surface, the valve plate mold before the mold heating, must be thoroughly cleaned on the cavity and the key matching surface, to ensure that there is no dust, oil, residual release agent or other impurities, to avoid affecting the coating adhesion or cause casting surface defects, after cleaning, evenly spray 0.5mm thick high temperature metal ceramic insulation coating with a special spray gun, the coating has excellent thermal insulation performance, can effectively slow down the heat exchange rate between the metal liquid and the mold, thereby preventing the thin wall or complex features from being "cold" or "under-pouring" and other filling defects, at the same time, good insulation effect helps the metal liquid to solidify smoothly in sequence, reduces the organizational stress and shrinkage resistance caused by quenching, ultimately significantly improves the surface finish, dimensional accuracy and internal uniformity of the valve plate forging;

[0065] Using gradient heating method to preheat the mold, first from room temperature to 150℃, 15min, then from 150℃ to 300℃, 20min, the preheating temperature is stable at 300℃±5℃, to eliminate the residual moisture in the mold, improve the metal liquid filling flowability, and avoid forming defects caused by quenching, ensure the uniform distribution of thermal stress of the mold;

[0066] Ladle pre-treatment: The ladle is given a refractory lining to ensure good insulation and structural strength. After the lining is completed, it must first be dried with charcoal fire. The physical moisture in the refractory is fully evaporated through low-temperature slow baking to avoid cracking of the lining due to rapid vaporization of moisture during subsequent high-temperature baking.

[0067] After drying for 90 minutes, apply a high-temperature insulation coating and graphite emulsion each once. The insulation coating aims to further improve the ladle's thermal insulation performance and reduce heat loss from the metal liquid. The graphite emulsion serves as a lubricant and insulator, effectively preventing the metal liquid from sticking to the ladle lining. After applying the coating, the ladle is baked again with charcoal fire to completely remove volatile substances in the coating and sinter and solidify it, forming a dense working surface. The second charcoal baking lasts for 60 minutes until complete drying.

[0068] Temperature measurement: After the mold is adjusted and preheated to the specified temperature, the final temperature of the molten steel is measured. When the temperature of the molten steel stabilizes at 1700°C, pouring can begin. This temperature range ensures that the molten steel has good fluidity, enabling smooth filling of complex mold cavities while avoiding excessive oxidation of the metal liquid, increased gas solubility, or thermal shock to the mold insulation coating. Pouring should be rapid and smooth to minimize heat loss and ensure that the molten steel fills the mold and undergoes pressure crystallization at the optimal viscosity.

[0069] Pouring and pressure coordination: Pour the deslagged steel liquid into the preheated and thoroughly dried ladle. Observe the flow state of the steel liquid during pouring. If the fluidity is poor, the surface oxidation film is too thick, or there are obvious signs of film formation, stop the transfer immediately and reheat the steel liquid to the process window. Do not use it directly for pouring to avoid solidification in the ladle or clogging of the pouring gate. If the steel liquid has good fluidity and meets the pouring requirements, pour it quickly. The entire process requires close coordination, with the transfer from the ladle to the mold above the press completed within 2 seconds. The pouring action itself must be completed within 4 seconds, and sufficient filling must be ensured to minimize temperature drop and oxidation of the steel liquid.

[0070] Immediately after pouring, start the hydraulic press to perform mold closing and pressurization. The time for the upper punch to contact the metal liquid should be controlled within 3 seconds. Then enter the pressure maintaining phase, apply a 30 MPa unidirectional pressure, and set the press travel limit device to 15 mm of pressurization travel.

[0071] Pressure maintaining and part removal: Maintain a pressure of 30 MPa for 35 seconds to allow the valve plate forging to complete crystallization and solidification under continuous isostatic pressure, resulting in a compact and accurately sized formed part. Then open the mold to remove the formed valve plate and allow it to cool naturally to room temperature.

[0072] Example 3

[0073] Device pretreatment: turn on the water circulation system, the water level is kept at 4 / 5 of the water tank volume, and the water temperature is controlled at 45°C;

[0074] Raw material pretreatment: select Q235 carbon steel billet 10 kg, put into ultrasonic cleaner for 15 min, remove surface oil and impurities;

[0075] Then put it into the oven, dry preheat at 200°C for 15 min, take it out after the end of insulation, remove the water and oil absorbed on the surface of the material, prevent it from entering the molten steel to produce gas, cause the casting to produce pores, at the same time, avoid the cold material directly added into the molten metal to cause violent spatter and temperature fluctuation, improve the production safety;

[0076] Metal smelting: add the pretreated billet into the intermediate frequency furnace in batches, first add 5 kg of billet, the billet does not need to be filled, in order to prevent the surface metal near the furnace mouth from lapping and blocking the furnace mouth, after the metal is melted, continue to add the furnace charge until it is flat with the surface;

[0077] Gradient heating, first from room temperature to 800°C, then from 800°C to 1200°C, finally from 1200°C to 1650°C, each stage is kept for 20 min to ensure uniform temperature in the furnace;

[0078] After the metal is melted, adjust the current frequency to 1500 Hz for insulation, measure the temperature every 6 min with a rapid thermocouple, maintain the steel liquid temperature at 1650°C, avoid high temperature, cause the knot material to melt into slag, after the temperature is stable, add the remaining 5 kg of billet to the liquid surface and the furnace mouth after 10-15 min, continue to keep for 5 min after the feeding is completed, ensure that the billet is completely melted and the steel liquid temperature rises to 1650°C±5°C, then put in 0.3 kg of steel material deslagging agent, stir for 2 min, and wait for 3 min before pouring;

[0079] Mold pretreatment: clean the mold cavity and matching surface, the valve plate mold must be thoroughly cleaned before the mold is heated, ensure that there is no dust, oil, residual release agent or other impurities, so as to avoid affecting the adhesion of the coating or causing surface defects of the casting, after cleaning, evenly spray 0.3 mm thick high temperature resistant metal ceramic insulation coating with special spray gun, the coating has excellent heat insulation performance, which can effectively slow down the heat exchange rate between the metal liquid and the mold, thereby preventing "cold separation" or "underfilling" and other filling defects in thin-walled or complex feature parts due to excessive heat loss, at the same time, good insulation effect helps the metal liquid to solidify smoothly in sequence, reduces the organizational stress and shrinkage resistance caused by quenching, finally significantly improves the surface finish, dimensional accuracy and internal uniformity of the valve plate forging;

[0080] The mold is preheated by gradient heating, first from room temperature to 150℃, holding for 15 minutes, then from 150℃ to 250℃, holding for 20 minutes, and the preheating temperature is stable at 250℃±5℃, so as to eliminate the residual moisture in the mold, improve the flowability of the molten metal, avoid forming defects caused by quenching, and ensure uniform distribution of thermal stress of the mold;

[0081] Pre-treatment of ladle: The ladle is troweled with refractory lining to ensure good heat preservation effect and structural strength. After troweling, carbon fire drying treatment must be carried out first to make the physical moisture in the refractory fully evaporate through low-temperature slow baking, avoiding cracking of the lining due to rapid vaporization of moisture during subsequent high-temperature baking.

[0082] After drying for 60 minutes, high-temperature insulation coating and graphite emulsion are each applied once. The insulation coating aims to further improve the heat insulation performance of the ladle and reduce heat loss of the molten metal, while the graphite emulsion plays a lubricating and isolating role to effectively prevent the molten metal from adhering to the lining. After coating, carbon fire baking is required again to completely remove volatile substances in the coating and sinter and solidify them to form a dense working surface. Secondary carbon fire baking is performed for 60 minutes until complete drying.

[0083] Temperature measurement: After the mold is completed and preheated to the specified temperature, the final temperature of the molten steel after smelting needs to be measured. When the temperature of the molten steel stabilizes near the upper limit of the appropriate interval of 1680℃, pouring can be carried out. This temperature interval aims to ensure that the molten steel has good flowability to successfully complete the filling of complex mold cavities, while avoiding excessive oxidation of the molten metal, increased gas solubility, or thermal shock to the mold insulation coating due to excessively high temperature. Pouring operation should be rapid and smooth to minimize heat loss and ensure that the molten steel completes the filling and pressure crystallization at the best viscosity.

[0084] Pouring and pressure coordination operation: Pour the deslagged molten steel into the preheated and thoroughly dried ladle. During pouring, the flow state of the molten steel needs to be closely observed. If the flowability is poor, the surface oxidation film is too thick, or there are obvious signs of film formation, the molten steel should be immediately returned to the furnace for re-heating to the process window. Direct pouring is strictly prohibited to avoid solidification or clogging of the pouring gate in the ladle. If the molten steel has good flowability and meets the pouring requirements, pouring operation should be carried out quickly. The entire process requires close coordination, and the transfer from the ladle to the mold above the press should be completed within 4 seconds. The pouring action itself must be completed within 6 seconds, and sufficient filling is ensured to minimize temperature drop and oxidation of the molten steel.

[0085] Immediately after pouring is completed, the hydraulic press is started to perform mold closing and pressurization. The time for the upper punch to contact the molten metal should be controlled within 3 seconds, followed by the pressure holding stage, during which a 26MPa unidirectional pressure is applied. The press travel limiting device is set to a pressurization travel of 15mm.

[0086] Pressure and pick-up: maintain 26MPa pressure for 25s, make the valve plate forge complete crystallization and solidification under continuous isostatic pressure, so as to obtain internal dense, size accurate forming parts, then open the mold to take out the formed valve plate, and naturally cool to room temperature.

[0087] Comparison dimension Example 1 Example 2 Example 3 Core process parameters Preheating temperature 250℃ Steel liquid temperature 1680℃ Pressurizing pressure 28MPa Pressure holding time 30s Coating thickness 0.4mm Preheating temperature 300℃ Steel liquid temperature 1700℃ Pressurizing pressure 30MPa Pressure holding time 35s Coating thickness 0.5mm Preheating temperature 250℃ Steel liquid temperature 1650℃ Pressurizing pressure 26MPa Pressure holding time 25s Coating thickness 0.3mm Internal defect rate 0.8% 0.6% 1.2% Tensile strength (MPa) 502 510 495 Yield strength (MPa) 285 290 280 Elongation rate (%) 24.5 25.2 24.1 Surface roughness (μm) 4.8 4.2 5.3 Processing allowance (mm) 1.5 1.2 1.8 Single piece production cost (yuan) 230 245 215

[0088] The core advantage of Example 1 is the highest comprehensive cost performance, with an internal defect rate of only 0.8%, and mechanical properties at a high level, which can meet the core needs of high-end valves for valve plate pressure sealing and fatigue resistance, while avoiding the increase in energy consumption caused by the upper limit of parameters, with a surface roughness of 4.8μm and a machining allowance of 1.5mm, which can greatly reduce the subsequent machining workload, with a material utilization rate of more than 90%, a single piece production cost of 230 yuan, a saving of 6.1% compared with Example 2, suitable for large-scale production scenarios, taking into account production efficiency, product quality and economy;

[0089] Example 2 focuses on the high performance requirements of high-end scenarios, with higher mold preheating temperature, steel liquid temperature and pressurizing pressure, combined with a thicker heat preservation coating, making the steel liquid flowability optimal, effectively avoiding complex runner "cold separation" defects, with an internal defect rate of 0.6%, mechanical properties reaching the peak, with a tensile strength of 510MPa, a yield strength of 290MPa and an elongation of 25.2%, a surface roughness of 4.2μm and a machining allowance of only 1.2mm, almost realizing "near net shaping", this scheme is suitable for harsh working conditions such as high pressure, high frequency opening and closing, strong corrosion, etc., such as industrial pipeline high pressure stop valve, compressor core valve plate, etc. The performance requirements of extreme scenarios;

[0090] The core advantage of Example 3 is the lowest production cost, with a single piece cost of only 215 yuan, a saving of 6.5% compared with Example 1 and a saving of 12.2% compared with Example 2, although the parameters are the lowest among the three examples, but still can stably meet the basic performance requirements, with an internal defect rate of 1.2%, a tensile strength of 495MPa, an elongation of 24.1%, a surface roughness of 5.3μm and a machining allowance of 1.8mm, completely meeting the use standards of ordinary working conditions valves, this scheme does not need to increase energy consumption and material cost, suitable for scenarios with moderate performance requirements and pursuing large-scale low-cost production, such as domestic pipeline gate valve, general mechanical supporting valve plate, etc., which can control cost while significantly improving the product quality of traditional casting process.

[0091] Control group 1

[0092] Using ordinary sand casting, Q235 carbon steel raw material is directly melted after simple oil removal, with a melting temperature of 1550℃, no mold preheating, natural pouring, no pressurizing and pressure maintaining step, cooling to room temperature after casting and taking out, and subsequent mechanical machining to remove 5mm allowance.

[0093] Control group 2

[0094] The Q235 carbon steel blank is heated to 1100 DEG C (forging temperature), and is initially formed by free forging, and then is die forged by a special die, the pressing pressure is 40 MPa, the pressure maintaining time is 15 s, and the subsequent mechanical processing removes a 3 mm excess amount.

[0095] Group Internal defect rate Tensile strength (MPa) Yield strength (MPa) Elongation rate (%) Surface roughness (μm) Processing allowance (mm) Single piece production cost (yuan) Example 1 0.8% 502 285 24.5 4.8 1.5 230 Example 2 0.6% 510 290 25.2 4.2 1.2 245 Example 3 1.2% 495 280 24.1 5.3 1.8 215 Control group 1 18.5% 385 235 21.3 18.6 5.0 205 Control group 2 2.3% 475 272 23.0 8.5 3.0 380

[0096] The defect rate of the embodiments 1-3 of the application is only 0.6%-1.2%, which is far lower than that of the control group 1 (18.5%) and the control group 2 (2.3%), the reason is that the high-pressure pressure maintaining (26-30 MPa) eliminates the pores and shrinkage in the solidification process of the molten steel, and the die coating and precise temperature control are combined to avoid the organization defects caused by rapid cooling;

[0097] The tensile strength (495-510 MPa), yield strength (280-290 MPa) and elongation rate (24.1%-25.2%) of the application are all better than those of the control group 1 (385 MPa, 235 MPa, 21.3%) and the control group 2 (475 MPa, 272 MPa, 23.0%), which benefits from the low-frequency heat preservation grain refinement and the densification effect of crystallization under pressure;

[0098] The surface roughness Ra of the application is only 4.2-5.3 mu m, and the processing excess amount is 1.2-1.8 mm, compared with the control group 1 (18.6 mu m, excess amount 5 mm) and the control group 2 (8.5 mu m, excess amount 3 mm), the mechanical processing amount is significantly reduced, and the material utilization rate is increased by more than 30%;

[0099] The single-piece cost of the application is 215-245 yuan, which is slightly higher than that of the control group 1, but the performance is significantly improved, which is reduced by more than 35% compared with the control group 2, and the synergistic optimization of high performance and low cost is realized.

[0100] Although the application has been described with reference to the embodiments above, various improvements can be made thereto, and equivalent replacements can be made to the components therein without departing from the scope of the application. In particular, as long as there is no structural conflict, each feature in the disclosed embodiments of the application can be combined with each other in any way, and the combinations are not exhaustively described in the specification only for the consideration of saving space and resources. Therefore, the application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A direct forming method for liquid forging of carbon steel valve plates, characterized in that: The direct forming method of this carbon steel valve plate by liquid forging includes: S1: Carbon steel raw material pretreatment: The carbon steel raw material is surface cleaned and preheated, and the drying temperature is 200-300℃. S2: Metal smelting: The pretreated raw materials are added to the smelting equipment and heated to a liquid state. The smelting temperature is controlled at 1650-1700℃. S3: Mold and ladle pretreatment: Clean, coat and preheat the valve plate mold to 250-500℃; line the ladle, coat and preheat it. S4: Casting: After slag removal, the molten steel is poured into the pretreated ladle and then poured into the mold cavity; S5: Pressure application and holding: Apply unidirectional pressure to the molten steel in the cavity through a die forging press. The pressure is 26-30MPa, and the holding time is 25-35s. S6: Sample removal: After the pressure holding period is over, open the mold and remove the formed valve plate.

2. The direct forming method for liquid forging of carbon steel valve plates according to claim 1, characterized in that: In the carbon steel raw material pretreatment in step S1, the surface cleaning is performed by ultrasonic cleaning, and the drying, preheating and heat preservation time is 15-25 minutes.

3. The direct forming method for liquid forging of carbon steel valve plates according to claim 1, characterized in that: The smelting equipment in step S2 is a medium-frequency furnace with a furnace opening diameter of 140-160mm, and the added carbon steel raw material is a small-sized billet.

4. The direct forming method for liquid forging of carbon steel valve plates according to claim 1, characterized in that: The smelting process in step S2 includes the following steps: First, heat the metal until it melts, then add more charge until the liquid level is reached. During the smelting process, the temperature is increased gradually, and each stage is held for 15-25 minutes. After the metal melts, it is held at a low frequency current of 1500-1700 Hz, and the temperature is measured every 4-6 minutes.

5. The direct forming method for liquid forging of carbon steel valve plates according to claim 1, characterized in that: In the mold pretreatment of step S3, after the cavity and key mating surfaces are thoroughly cleaned, a high-temperature resistant metal ceramic heat-insulating coating is sprayed on.

6. The direct forming method of carbon steel valve plate by liquid forging according to claim 1, characterized in that: In step S3, the mold preheating temperature is controlled at 250-300℃, and a gradient heating method is used for preheating.

7. The direct forming method for liquid forging of carbon steel valve plates according to claim 1, characterized in that: The ladle pretreatment in step S3 includes the following steps: The ladle lining is made of refractory clay with a working layer thickness of 18-22mm. After bridging, it is dried over charcoal fire, then coated with a high-temperature insulating coating and graphite emulsion, and finally baked over charcoal fire a second time until completely dry.

8. The direct forming method for liquid forging of carbon steel valve plates according to claim 1, characterized in that: During the pouring process in step S4, the time for the ladle to be transferred to the mold is 2-4 seconds, the pouring action is completed in 4-6 seconds, and the temperature of the molten steel is controlled between 1650-1700℃.

9. The direct forming method of carbon steel valve plate by liquid forging according to claim 1, characterized in that: In the pressurization and pressure holding step S5, after the pouring is completed, the upper die punch is pressed down to contact the molten steel for 2-4 seconds, the applied unidirectional pressure is 26-30 MPa, and the pressure holding time is 25-35 seconds.

10. The direct forming method of carbon steel valve plate by liquid forging according to claim 1, characterized in that: The slag removal process in step S4 includes the following steps: Before pouring, a steel slag remover is added to the surface of the molten steel to remove slag. After slag removal, check the fluidity of the molten steel. If the fluidity is poor, return it to the furnace and heat it to the process range of 1650-1700℃ before casting.

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