A casting method for alloy cast steel components for the front disc of a coal mill fan in a thermal power plant.

Abstract

This invention discloses a casting method for alloy cast steel parts of the front plate of a coal mill fan in thermal power generation, belonging to the field of mechanical manufacturing technology. This invention employs an open bottom-pouring gating system process, changing the ratio of F_straight:F_horizontal:F_internal to 1:12.5:4.5, resulting in stable mold filling, slow filling speed, and convenient venting. The gating system is designed according to the principle of sequential solidification, yielding a dense casting. This process effectively solves the problem of smoothly, continuously, and uniformly introducing molten metal into the mold cavity, avoiding mold damage and secondary oxidation defects. The gating system design minimizes the molten metal injection path, reducing heat loss and temperature differences between different parts of the casting. Using chills accelerates solidification, dividing the feeding zone, and adding insulating risers prolongs the molten metal solidification time, improves the feeding effect, and prevents casting defects. This invention provides a highly efficient, stable, and high-quality casting method for alloy cast steel parts of the front plate of a coal mill fan in thermal power generation, possessing extremely high market value and application prospects.

Description

Technical Field

[0001] This invention relates to the field of mechanical manufacturing technology, specifically to a method for casting alloy cast steel parts for the front disc of a coal mill fan in a thermal power plant. Background Technology

[0002] A fan-driven coal mill is a type of high-speed mill, similar in structure to a blower. It is primarily used in large, medium, and small thermal power plants to provide boilers with pulverized coal of a certain fineness. Due to its simple structure, ability to use hot flue gas as a drying medium, and strong explosion-proof properties, the fan-driven coal mill is particularly suitable for grinding lignite with high moisture content. A significant feature of the fan-driven coal mill is its centrifugal fan characteristic, which eliminates the need for a separate blower in the pulverizing system. The drying medium is introduced into the mill using the air pressure generated by the mill itself. During this process, the raw coal and the high-temperature drying medium are thoroughly mixed in the drying section, drying off some of the surface moisture of the raw coal. Then, the coal enters axially from the mill's gate into the impact wheel area for further crushing. The crushed coal powder remains suspended inside the mill, allowing the drying and crushing processes to occur simultaneously.

[0003] When raw coal is subjected to strong impacts from the crushing wheel, it is continuously dried. The surface moisture of the dried coal particles evaporates, causing cracks that facilitate further crushing in the next impact. The drying and crushing processes alternate continuously. The dried and crushed coal powder is continuously fed into a separator for filtration. Qualified coal powder is sent to the boiler furnace for combustion, while unqualified coal powder is returned to the mill for further crushing via a return cone. Fan mills, due to their mature design and stable operation, are widely used in the power generation industry and are an important pulverizing equipment. The front disc, as a core component of the fan mill, is in direct contact with the processed material and bears significant wear and load during operation, thus requiring regular replacement, resulting in a huge market demand. In recent years, some defects in the existing alloy cast steel front disc manufacturing process have failed to meet higher standards. Currently, the manufacturing process for alloy cast steel front discs involves first casting a front disc blank, and then machining the outer surface to the dimensions shown in the drawings.

[0004] However, existing front plate casting processes often result in localized discontinuous defects in the finished product during ultrasonic testing. These defects, with an area exceeding 15,000 mm², fail to meet the GB / T7233 testing standard. The reasons for these defects are analyzed as follows:

[0005] Splashing and secondary oxidation of molten steel during casting: During the casting of molten steel, the molten metal splashes and is prone to secondary oxidation, which can lead to inclusion defects.

[0006] An unreasonable gating system gating system: An unreasonable gating system layout will cause the molten metal to generate a large impact force during the pouring process, which will impact the core, cause sand washing and gas entrapment, resulting in inclusions and porosity defects.

[0007] Insufficient riser feeding: The existing process has insufficient riser feeding effect, resulting in defects such as shrinkage cavities and porosity inside the casting.

[0008] To address the aforementioned problems, this invention provides an optimized casting method for the alloy cast steel front plate of a coal mill fan in thermal power generation. Summary of the Invention

[0009] The purpose of this invention is to provide a method for casting alloy cast steel parts for the front disc of a coal mill fan in thermal power generation, so as to solve the problems mentioned above.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a method for casting alloy cast steel parts for the front disc of a coal mill fan in a thermal power plant, characterized by comprising the following steps:

[0011] a) Raw material preparation: Alloy cast steel is selected, with a composition including 10%~15% chromium, 8%~12% nickel, 2%~5% molybdenum, 0.5%~1.5% vanadium, etc.

[0012] b) Melting treatment: Melting is carried out in an electric arc furnace, with the melting temperature controlled at 1600°C~1650°C and the melting time strictly controlled to ensure uniform alloy composition.

[0013] c) Casting process: An open bottom-pouring casting process is adopted, specifically including:

[0014] c1) The front plate of the casting adopts an open bottom pouring process;

[0015] c2) The sprue is made of a single Φ80 ceramic tube;

[0016] c3) The horizontal runner uses 8 Φ60 ceramic tubes and 8 Φ80 ceramic tubes, which are evenly distributed in the gating system;

[0017] c4) The ingate uses eight Φ60 ceramic tubes. The reasonable arrangement of the ingate makes the flow of molten metal more uniform.

[0018] c5) Eight waist-shaped heating risers are evenly distributed on the top of the front plate of the casting;

[0019] c6) The chills are evenly placed between the two concealed risers, with 3 chills placed in total, for a total of 24 chills at 600;

[0020] d) Heat treatment process: High-temperature annealing and quenching are carried out to further improve the mechanical properties and wear resistance of the castings;

[0021] e) Quality inspection: A combination of X-ray inspection and ultrasonic testing is used to conduct comprehensive quality inspection of the castings to ensure that there are no defects such as cracks or porosity inside or outside the castings;

[0022] f) Finished product processing: Precision machining is performed on the qualified castings to ensure the dimensional accuracy and surface quality of the front plate of the casting.

[0023] Preferably, in the above-mentioned casting method for the alloy cast steel front plate of a coal mill fan for thermal power generation, the riser cross-section is 300mm×150mm and the height is 350mm to 400mm to ensure uniform temperature distribution inside the front plate of the casting.

[0024] Preferably, in the above-mentioned method for casting alloy cast steel parts for the front plate of a coal mill fan in a thermal power plant, the chills have the following specifications: 150mm×120mm×110mm, and the spacing between each group of chills is 20mm. The reasonable arrangement of the chills effectively controls the solidification speed and shape of the front plate of the casting.

[0025] Preferably, in the above-mentioned method for casting alloy cast steel parts for the front plate of a coal mill fan in a thermal power plant, the casting pressure of the vacuum negative pressure casting technology in step c) of the casting process is between 0.05MPa and 0.1MPa to ensure the density and internal defects of the casting front plate.

[0026] Preferably, in the above-mentioned casting method for the alloy cast steel front plate of a coal mill fan for thermal power generation, in the heat treatment process step d), the annealing temperature is 750°C~800°C, the annealing time is 2 hours~4 hours, and the quenching temperature is 900°C~950°C. The heat treatment process step d) can effectively reduce the residual stress inside the front plate of the casting.

[0027] Preferably, in the above-mentioned method for casting alloy cast steel parts for the front plate of a coal mill fan in a thermal power plant, the quality inspection step e) includes using a combination of X-ray inspection and ultrasonic inspection to perform non-destructive testing on the internal and surface of the casting to ensure the quality of the front plate.

[0028] Preferably, in the above-mentioned casting method for the alloy cast steel front plate of a coal mill fan in a thermal power plant, in the quality inspection step (e), further metallographic testing and mechanical property testing are conducted to improve the evaluation of the internal microstructure and mechanical properties of the casting, so as to ensure the performance stability and reliability of the casting front plate in actual use.

[0029] Preferably, in the above-mentioned casting method for the alloy cast steel front plate of a coal mill fan for thermal power generation, the finished product processing step f) includes three processing methods: turning, milling and grinding. Through two roughing processes and three finishing processes, the dimensional accuracy and surface quality of the casting front plate are finally ensured to meet the usage requirements.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. This invention adopts an open bottom-pouring gating system process, changing the F-direction:F-horizontal:F-internal ratio to 1:12.5:4.5, which makes the filling system of the gating system stable, slow in filling speed, and convenient in venting. The gating system is set according to the principle of sequential solidification to obtain a dense casting. This process effectively solves the problem of introducing molten metal into the cavity smoothly, continuously and uniformly, avoiding mold damage and secondary oxidation defects. The gating system design minimizes the molten metal injection path, reducing heat loss and temperature differences between different parts of the casting. The use of chills accelerates the solidification speed, and the division of feeding zones and the addition of heat-insulating risers can prolong the solidification time of the molten metal, improve the feeding effect, and prevent casting defects.

[0032] 2. This invention uses CAE software to simulate and analyze the casting system, avoiding the shortcomings of existing processes. The first prototype was successfully produced. The material is 17CrMo55, and the quality grade meets the GB / T7233 standard after ultrasonic flaw detection. Through precise heat treatment process, residual stress is effectively reduced, and the mechanical properties and wear resistance of the casting are improved. This gives the front plate a longer service life under high temperature, high pressure and wear environment. This improves the stability of equipment operation, reduces downtime losses caused by frequent replacement and maintenance, and significantly reduces maintenance costs. Quality inspection is carried out by a combination of X-ray and ultrasonic methods to ensure that the casting meets the GB / T7233 testing standard and ensure product quality.

[0033] 3. During the finished product processing, the present invention employs multiple precision machining processes (turning, milling, and grinding) to ensure the dimensional accuracy and surface quality of the casting front plate, optimize production efficiency, and improve product consistency and traceability. Overall, through the series of optimization measures described above, the present invention provides a highly efficient, stable, and high-quality casting method for alloy cast steel parts of the front plate of a coal mill fan for thermal power generation. It is suitable for a wide range of industrial applications and has extremely high market value and application prospects. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a front view of an embodiment of the present invention;

[0036] Figure 2 This is a top view of an embodiment of the present invention.

[0037] The attached diagram lists the components represented by each number as follows:

[0038] 100, front plate of casting; 200, sprue; 300, gating; 400, ingate; 500, riser; 600, chill. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Please see Figure 1-2 A method for casting alloy cast steel parts for the front disc of a coal mill fan in a thermal power plant is characterized by the following steps:

[0041] a) Raw material preparation: Alloy cast steel is selected, with a composition including 10%~15% chromium, 8%~12% nickel, 2%~5% molybdenum, 0.5%~1.5% vanadium, etc.

[0042] b) Melting treatment: Melting is carried out in an electric arc furnace, with the melting temperature controlled at 1600°C~1650°C and the melting time strictly controlled to ensure uniform alloy composition.

[0043] c) Casting process: An open bottom-pouring casting process is adopted, specifically including:

[0044] c1) The front plate 100 of the casting adopts an open bottom pouring process;

[0045] c2) The sprue 200 uses a single Φ80 ceramic tube;

[0046] c3) The horizontal runner 300 uses 8 Φ60 ceramic tubes and 8 Φ80 ceramic tubes, which are evenly distributed in the gating system;

[0047] c4) The 400 ingate uses eight Φ60 ceramic tubes. The reasonable arrangement of the ingate makes the flow of molten metal more uniform.

[0048] c5) Eight waist-shaped heating risers are evenly distributed on the top of the front plate of the casting (100mm);

[0049] c6) Place chills 600 evenly between two concealed risers 500, and place 3 chills 600 in total, for a total of 24 chills 600;

[0050] d) Heat treatment process: High-temperature annealing and quenching are carried out to further improve the mechanical properties and wear resistance of the castings;

[0051] e) Quality inspection: A combination of X-ray inspection and ultrasonic testing is used to conduct comprehensive quality inspection of the castings to ensure that there are no defects such as cracks or porosity inside or outside the castings;

[0052] f) Finished product processing: Precision machining is performed on the qualified castings to ensure the dimensional accuracy and surface quality of the front plate 100 of the casting.

[0053] The riser 500 has a cross-section of 300mm × 150mm and a height of 350mm to 400mm to ensure uniform temperature distribution inside the front plate 100 of the casting.

[0054] The chills 600 have the following specifications: 150mm×120mm×110mm. The spacing between each set of chills 600 is 20mm. The reasonable arrangement of chills 600 effectively controls the solidification speed and shape of the front plate 100 of the casting.

[0055] c) The casting pressure of the vacuum negative pressure casting technology in the casting process is between 0.05MPa and 0.1MPa to ensure the compactness and internal defects of the front plate 100 of the casting.

[0056] d) In the heat treatment process, the annealing temperature is 750°C~800°C, the annealing time is 2 hours~4 hours, and the quenching temperature is 900°C~950°C. The heat treatment process can effectively reduce the residual stress inside the front plate 100 of the casting.

[0057] e) The quality inspection steps include using a combination of X-ray inspection and ultrasonic inspection to perform non-destructive testing on the internal and surface of the castings to ensure 100% quality of the castings.

[0058] e) In the quality inspection step, further metallographic testing and mechanical property testing are conducted to improve the evaluation of the internal microstructure and mechanical properties of the casting, so as to ensure the performance stability and reliability of the casting front plate 100 in actual use.

[0059] f) The finished product processing steps include three processing methods: turning, milling and grinding. Through two roughing operations and three finishing operations, the dimensional accuracy and surface quality of the casting front plate 100 are finally ensured to meet the usage requirements.

[0060] Example 1

[0061] Raw material preparation: The alloy cast steel selected has the following composition: 12% chromium, 10% nickel, 3% molybdenum, 1% vanadium, and the remainder is iron and impurities.

[0062] Melting process: The alloy cast steel raw material is placed in an electric arc furnace, and the melting temperature is controlled at 1625°C for 40 minutes. The uniformity of the alloy composition is confirmed by spectral analysis, with the error controlled within ±0.1%.

[0063] Casting process:

[0064] Direct casting run 200: One Φ80 ceramic pipe with a length of 1.2 meters is installed;

[0065] Horizontal runner 300: 8 Φ60 ceramic tubes with a length of 0.8 meters and 8 Φ80 ceramic tubes with a length of 0.7 meters are evenly distributed;

[0066] Inner gating 400: Equipped with 8 Φ60 ceramic tubes, each 0.6 meters long;

[0067] During the pouring process, the vacuum level was maintained at 90 Pa, the pouring pressure was 0.08 MPa, and the pouring speed was 4.0 liters per minute.

[0068] Heat treatment process:

[0069] Annealing temperature 780°C, annealing time 3 hours;

[0070] Quenching temperature 920°C, quenching time 40 minutes, cooling rate 18°C ​​per minute;

[0071] Quality inspection: X-ray and ultrasonic testing are used to ensure that the castings are free of cracks and porosity.

[0072] Metallographic testing indicators include grain size, phase distribution, and inclusion grade;

[0073] The hardness test result was HRC60, and the tensile test results showed a yield strength of 450MPa and a tensile strength of 700MPa.

[0074] Finished product processing: Machining such as turning, milling and grinding are performed, with dimensional accuracy controlled within ±0.1mm and surface finish reaching Ra0.8μm.

[0075] Example 2

[0076] Raw material preparation: The composition of alloy cast steel is: 12% chromium, 9% nickel, 4% molybdenum, 1% vanadium, with the remainder being iron and impurities.

[0077] Melting process: Melting is carried out in an electric arc furnace at a temperature controlled at 1630°C for 35 minutes. The alloy composition is homogenized by spectral analysis, with the error controlled within ±0.1%.

[0078] Casting process: 200mm straight gating system: Φ80 ceramic tube, 1.3 meters in length;

[0079] 300mm horizontal runner: 8 Φ60 ceramic tubes and 8 Φ80 ceramic tubes, each with a length of 0.9m and 0.6m respectively;

[0080] Ingate 400: 8 Φ60 ceramic tubes, each 0.7 meters long;

[0081] The vacuum level was maintained at 85 Pa, the pouring pressure was 0.07 MPa, and the pouring speed was 3.8 liters per minute.

[0082] Heat treatment process: Annealing temperature is 790°C, and annealing time is 2.5 hours;

[0083] The quenching temperature is 930°C, the quenching time is 35 minutes, and the cooling rate is 17°C per minute.

[0084] Quality inspection: X-ray and ultrasonic testing are used to ensure there are no internal defects;

[0085] Metallographic analysis was performed to achieve the standards of fine grain size and uniform phase distribution.

[0086] Hardness and tensile tests were conducted, and the yield strength was 470 MPa and the tensile strength was 720 MPa.

[0087] Finished product processing: Processed using high-precision CNC equipment to ensure that dimensions and surface quality meet design requirements.

[0088] Through the detailed process flow and specific parameter control described above, this invention can effectively improve the mechanical properties and wear resistance of the alloy cast steel front plate of the coal mill fan in thermal power generation, meeting the GB / T7233 testing standard and other relevant industry standards, thereby significantly improving the service life and reliability of the front plate.

[0089] In summary, through optimized raw material selection, smelting process, casting process, heat treatment process, and quality inspection methods, this invention provides an efficient and stable casting method for alloy cast steel parts of the front plate of a coal mill fan in thermal power generation. This method overcomes several defects in the prior art, ensures the excellent performance of the front plate under high temperature, high pressure, and wear environments, and is widely applicable to practical applications in large, medium, and small thermal power plants.

[0090] Working Principle: The present invention relates to a casting method for the alloy cast steel front plate of a coal mill fan in a thermal power plant. The casting process employs an open bottom-pouring method. The straight runner 200, horizontal runner 300, and ingate 400 are designed with a F_straight:F_horizontal:F_ingate ratio of 1:12.5:4.5, using Φ80 and Φ60 ceramic tubes respectively to ensure smooth, slow, and convenient venting of the molten metal. Eight Φ60 ceramic tubes are used in the ingate to optimize the distribution of the molten metal. Eight waist-shaped heating risers 500 are provided at the top, arranged according to the solidification principle. Chips 600 are evenly distributed between the hidden risers, with a total of 24 chills. Vacuum negative pressure casting technology is used to ensure the metal... The molten metal rapidly fills the mold in a vacuum environment, avoiding the generation of porosity and inclusions, and minimizing the injection path of the molten metal to reduce heat loss and temperature difference. The heat treatment process includes high-temperature annealing and quenching, with annealing temperatures of 750°C~800°C and quenching temperatures of 900°C~950°C, further improving the mechanical properties and wear resistance of the casting. Quality inspection uses a combination of X-ray and ultrasonic methods for comprehensive non-destructive testing, and metallographic testing and mechanical property testing are conducted to ensure the internal quality and microstructural stability of the casting. Finally, qualified castings undergo precision machining such as turning, milling, and grinding to ensure the dimensional accuracy and surface quality of the front plate.

[0091] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0092] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for casting alloy cast steel parts for the front disc of a coal mill fan in a thermal power plant, characterized in that: Includes the following steps: a) Raw material preparation: Alloy cast steel is selected, with a composition including 10%~15% chromium, 8%~12% nickel, 2%~5% molybdenum, 0.5%~1.5% vanadium, etc. b) Melting treatment: Melting is carried out in an electric arc furnace, with the melting temperature controlled at 1600°C~1650°C and the melting time strictly controlled to ensure uniform alloy composition. c) Casting process: An open bottom-pouring casting process is adopted, specifically including: c1) The front plate of the casting (100) adopts an open bottom pouring process; c2) The direct sprue (200) uses a single Φ80 ceramic tube; c3) The horizontal runner (300) uses 8 Φ60 ceramic tubes and 8 Φ80 ceramic tubes, which are evenly distributed in the gating system; c4) The ingate (400) uses 8 Φ60 ceramic tubes. The reasonable arrangement of the ingate makes the flow of molten metal more uniform. c5) The top of the front plate (100) of the casting has 8 waist-shaped heating risers evenly distributed; c6) Place chills (600) evenly between two dark risers, and place 3 chills (600) in total, for a total of 24 chills (600). d) Heat treatment process: High-temperature annealing and quenching are carried out to further improve the mechanical properties and wear resistance of the castings; e) Quality inspection: A combination of X-ray inspection and ultrasonic testing is used to conduct comprehensive quality inspection of the castings to ensure that there are no defects such as cracks or porosity inside or outside the castings; f) Finished product processing: Precision machining is performed on the qualified castings to ensure the dimensional accuracy and surface quality of the front plate (100) of the casting.

2. The casting method for the alloy cast steel front plate of a coal mill fan in a thermal power plant according to claim 1, characterized in that: The riser has a cross-section of 300mm × 150mm and a height of 350mm to 400mm to ensure a uniform temperature distribution inside the front plate (100) of the casting.

3. The casting method for the alloy cast steel front plate of a coal mill fan in a thermal power plant according to claim 2, characterized in that: The chills (600) have the following specifications: 150mm×120mm×110mm. The spacing between each set of chills (600) is 20mm. The reasonable arrangement of the chills (600) effectively controls the solidification speed and shape of the casting front plate (100).

4. The casting method for the alloy cast steel front plate of a coal mill fan in a thermal power generation system according to claim 3, characterized in that: The casting pressure of the vacuum negative pressure casting technology in step c) of the casting process is between 0.05MPa and 0.1MPa to ensure the compactness and internal defects of the front plate (100) of the casting.

5. The casting method for the alloy cast steel front plate of a coal mill fan in a thermal power generation system according to claim 4, characterized in that: In the heat treatment process step d), the annealing temperature is 750°C~800°C, the annealing time is 2 hours~4 hours, and the quenching temperature is 900°C~950°C. The heat treatment process step d) can effectively reduce the residual stress inside the front plate (100) of the casting.

6. The casting method for the alloy cast steel front plate of a coal mill fan in a thermal power generation system according to claim 5, characterized in that: The quality inspection step e) includes using a combination of X-ray inspection and ultrasonic inspection to perform non-destructive testing on the internal and surface of the casting to ensure the quality of the front plate (100) of the casting.

7. The casting method for the alloy cast steel front plate of a coal mill fan in a thermal power generation system according to claim 6, characterized in that: In the quality inspection step described in e), further metallographic inspection and mechanical property testing are conducted to improve the evaluation of the internal microstructure and mechanical properties of the casting, so as to ensure the performance stability and reliability of the casting front plate (100) in actual use.

8. The casting method for the alloy cast steel front plate of a coal mill fan in a thermal power generation system according to claim 7, characterized in that: The f) finished product processing steps include three processing methods: turning, milling and grinding. Through two roughing processes and three finishing processes, the dimensional accuracy and surface quality of the casting front plate (100) are finally ensured to meet the usage requirements.

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