Method for preparing diesel engine flywheel by using vermicular graphite cast iron

Abstract

The invention discloses a method for preparing a diesel engine flywheel by using vermicular graphite cast iron, and belongs to the technical field of vermicular graphite cast iron smelting, and the method comprises the following steps: S1, preparing furnace burden, equipment and technical files; s2, the chemical component range of the vermicular graphite cast iron flywheel casting is determined; s3, determining a melting process procedure of the vermicular graphite cast iron flywheel casting; s4, the pouring technological procedure of the vermicular graphite cast iron flywheel casting is determined; s5, the molten iron melting process is controlled according to the technological procedure requirements, then the chemical components and temperature of the molten iron are detected, and whether the molten iron meets the technological requirements or not is judged; s6, the molten iron meeting the requirements is discharged out of the furnace and subjected to vermicularizing-inoculation treatment; and S7, casting pouring is conducted, and after pouring is completed, quality inspection is conducted on the casting. According to the vermicular graphite cast iron flywheel casting iron liquid and the vermicular graphite cast iron flywheel casting, precious metal such as Cu, Sn and Cr is not used in the vermicular graphite cast iron flywheel casting iron liquid and the vermicular graphite cast iron flywheel casting, and therefore the production cost of a finally produced vermicular graphite cast iron flywheel can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting vermicular cast iron, and in particular relates to a method for preparing a diesel engine flywheel by using vermicular cast iron. Background Art

[0002] Diesel engines have large torque and good economic performance, and are widely used in large and medium-sized trucks, agricultural machinery, and construction machinery. Traditionally, flywheels, which are core components of diesel engines, are mostly made of high-strength alloy cast iron. During the smelting and pouring of flywheel molten iron, alloying is usually used to improve the mechanical properties by adding alloy elements such as copper Cu, molybdenum Mo, and chromium Cr to the molten iron. However, the prices of these alloy materials are very high, which will significantly increase the production cost of engine flywheel castings. Therefore, vermicular graphite cast iron is used instead of alloy gray cast iron to manufacture diesel engine flywheels.

[0003] Since the creeping window of vermicular graphite cast iron is relatively narrow, the content of creeping elements needs to be precisely controlled, so the preparation of vermicular graphite cast iron is very difficult, and people have been exploring and optimizing the preparation process of vermicular graphite cast iron. China Invention Publication Patent CN110894582A discloses a high-strength and high-thermal-conductivity vermicular graphite cast iron and its preparation method: C: 3.5-4.2%, Si: 1.0-1.8%, Mn: 0.2-0.3%, P<0.06%, S<0.02%, V: 0.02-0.05%, Cu: 0.5-1.0%, Sn: 0.03-0.05%, Sb: 0.004-0.028%, Mg: 0.016-0.022%, RE: 0.005-0.015%, which is used by using the proportion of components and the proportion of creeping agent inoculant to obtain a vermicular graphite cast iron with high strength and excellent thermal conductivity.

[0004] China Invention Publication Patent CN107619989A discloses a casting process for high-strength vermicular graphite cast iron: C: 3.3-3.8%, Si: 2.0-2.5%, S: 0.010-0.020%, Mn: 0.3-0.5%, Cu: 0.7-1.1%, Cr<0.15%, Sn: 0.07-0.10%. The final vermicular graphite cast iron has good performance and low shrinkage tendency by means of impact vermicularization, use of calcium-barium inoculant, secondary inoculation and other means.

[0005] The above patent documents still use a large amount of precious metals such as Cu and Sn, which leads to a high production cost of compacted graphite iron castings. Summary of the invention

[0006] In order to solve the problem of high production cost of prior art vermicular graphite cast iron castings, the present invention provides a method for preparing a diesel engine flywheel using vermicular graphite cast iron. Compared with the original alloy gray cast iron flywheel, the vermicular graphite cast iron flywheel produced by the present invention can reduce costs while ensuring that the product quality is stable and meets the technical requirements.

[0007] The technical solution adopted by the method for preparing a diesel engine flywheel using compacted graphite cast iron of the present invention is:

[0008] A method for preparing a diesel engine flywheel using compacted graphite cast iron comprises the following steps:

[0009] S1. Prepare furnace charge, equipment and technical documents;

[0010] S2. Determine the chemical composition range of the compacted graphite iron flywheel casting;

[0011] S3. Determine the melting process specification of the compacted graphite cast iron flywheel casting;

[0012] S4. Determine the pouring process specification of the vermicular graphite cast iron flywheel casting;

[0013] S5. Control the melting process of the molten iron according to the process regulations, then detect the chemical composition and temperature of the molten iron to determine whether the molten iron meets the process requirements;

[0014] S6, taking out the molten iron that meets the requirements and performing creeping-inoculation treatment;

[0015] S7. Pour the casting and inspect the quality of the casting after pouring is completed.

[0016] A further improvement of the technical solution of the present invention is that the charge in step S1 includes pig iron, scrap steel, return charge, alloy charge and auxiliary materials; wherein, return charge refers to metal charge returned to the furnace and re-melted, including casting risers of the same material, scrapped castings, and ingots of residual molten iron from previous furnaces; alloy charge refers to various metal charges added in small amounts such as ferromanganese, ferrosilicon, ferrochrome, electrolytic copper, vermicularizing agent and inoculant used to adjust the chemical composition of molten iron or treat molten iron; auxiliary materials refer to non-metallic auxiliary materials such as carburizers, refining agents, covering agents, and slag agglomerating agents used in small amounts in cast iron melting operations.

[0017] A further improvement of the technical solution of the present invention is that the chemical composition mass percentage content in the vermicular graphite cast iron flywheel casting in step S2 is: 3.6% to 3.8% C, 2.3% to 2.8% Si, 0.3% to 0.5% Mn, ≤0.05% P, ≤0.02% S, 0.01% to 0.02% Mg, and 0.015% to 0.03% RE.

[0018] A further improvement of the technical solution of the present invention is that the chemical composition mass percentage content in the vermicular graphite cast iron flywheel casting in step S2 is: 3.5% to 3.7% C, 2.2% to 2.7% Si, 0.4% to 0.6% Mn, ≤0.05% P, ≤0.02% S, 0.015% to 0.03% Mg, and 0.02% to 0.05% RE.

[0019] A further improvement of the technical solution of the present invention is that step S3 includes the following steps:

[0020] S3.1. Determine the chemical composition of the molten iron in the furnace and the chemical composition of the compacted graphite iron flywheel casting;

[0021] S3.2. Determine the melting batching process sheet and charge adding sequence of compacted graphite cast iron flywheel cast iron;

[0022] S3.3. Determine the sampling temperature, furnace temperature, processing temperature and pouring temperature requirements;

[0023] S3.4. Determine the method of creep-inoculation treatment of molten iron in the furnace and when it is discharged from the furnace.

[0024] A further improvement of the above technical solution of the present invention is that the chemical composition of the molten iron in the furnace in step S3.1 is as follows: 3.6% to 3.8% C, 1.8% to 2.1% Si, 0.3% to 0.5% Mn, ≤0.05% P, ≤0.02% S in weight percentage.

[0025] A further improvement of the above technical scheme of the present invention is that: the mass percentage content of each ingredient in the melting batching process sheet of vermicular graphite cast iron flywheel cast iron in step S3.2 is: 60% to 70% pig iron, 10% to 20% scrap steel, 10% to 30% recycled materials, 0.25% to 0.45% ferromanganese, 0.5% to 0.8% ferrosilicon, 0 to 0.2% carbon powder, 0.4% to 0.6% inoculant, and 0.9% to 1.1% vermicular agent.

[0026] A further improvement of the above technical solution of the present invention is that the chemical composition of the molten iron in the furnace in step S3.1 is as follows: 3.5% to 3.7% C, 1.7% to 2.0% Si, 0.4% to 0.6% Mn, ≤0.05% P, ≤0.02% S in weight percentage.

[0027] A further improvement of the above technical solution of the present invention is that: the mass percentage content of each ingredient in the melting batching process sheet of vermicular graphite cast iron flywheel cast iron in step S3.2 is: 60% to 70% pig iron, 10% to 20% scrap steel, 10% to 30% recycled materials, 0.3% to 0.5% ferromanganese, 0.55% to 0.85% ferrosilicon, 0 to 0.2% carbon powder, 0.45% to 0.65% inoculant, and 1% to 1.2% vermicular agent.

[0028] A further improvement of the technical solution of the present invention is that the specific steps of the molten iron creep-inoculation treatment in step S6 are:

[0029] S6.1. Put all the baked vermicularizer into the pit at the bottom of the ladle and tamp it, then put 2 / 3 of the total amount of the baked inoculant and tamp it, then cover it tightly with an appropriate amount of covering agent, and then cover it with a cast iron plate with a thickness of 2.5mm to 4.5mm, and then cover the surrounding and upper part of the cast iron plate tightly with covering agent;

[0030] S6.2. The first tapping amount is 2 / 3 of the ladle volume. After the creep reaction is over, add the remaining 1 / 3 of the inoculant and tap until the ladle is full of liquid iron.

[0031] Due to the adoption of the above technical solution, the technical advances achieved by the present invention include:

[0032] The technical method for melting and pouring the cast vermicular graphite cast iron flywheel casting designed by the present invention provides a set of systematic and complete chemical composition determination, alloy melting proportioning and molten iron vermicularization-inoculation treatment technology and casting pouring operation control method for the cast vermicular graphite cast iron flywheel casting, which changes the existing commonly used operation method of "cast iron alloying to produce high-strength cast iron flywheel castings", making the chemical composition determination of the cast vermicular graphite cast iron flywheel casting, molten iron melting proportioning and molten iron vermicularization-inoculation treatment, and pouring operation control more accurate, rapid, reasonable and feasible.

[0033] The present invention clearly stipulates the control range of the molten iron and casting chemical composition of common vermicular graphite cast iron flywheel castings, the cast iron melting ingredient ratio, the casting casting technical parameters, the operation process and technical requirements, which changes the traditional empirical exploration method and makes the production of vermicular graphite cast iron flywheels more accurate, fast, reasonable and feasible.

[0034] At the same time, the molten iron and the casting of the compacted graphite cast iron flywheel of the present invention do not use precious metals such as Cu, Sn, Cr, etc., so the compacted graphite cast iron flywheel finally produced by the present invention can reduce production costs. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with specific implementation methods. In the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0036] The present invention provides a method for preparing a diesel engine flywheel using compacted graphite cast iron, comprising the following steps:

[0037] S1. Prepare furnace charge, equipment and technical documents.

[0038] Specific contents: Prepare various furnace materials such as pig iron, scrap steel, returned materials, alloy materials, auxiliary materials, etc. required for cast iron melting production; check and prepare various equipment required for smelting such as medium-frequency electric furnace, iron ladle, overhead crane, tools, and testing equipment; prepare various technical documents such as standards, manuals, process procedures, operating instructions, batching process sheets, etc. required for cast iron smelting operations.

[0039] The above-mentioned return materials refer to metal materials that are returned to the furnace and re-melted for use, generally including casting risers of the same material, scrapped castings, ingots of remaining molten iron from previous furnaces, etc.

[0040] The above alloy charge refers to various metal charges such as ferromanganese, ferrosilicon, ferrochrome, electrolytic copper, vermicularizing agent and inoculant used to adjust the chemical composition of molten iron or treat molten iron, which are added in relatively small amounts.

[0041] At the same time, the above-mentioned auxiliary materials refer to non-metallic auxiliary materials such as carburizers, refining agents, covering agents, slag aggregation agents, etc. used in small quantities in cast iron melting operations.

[0042] S2. Determine the chemical composition range of the compacted graphite iron flywheel casting.

[0043] In order to ensure that the material and performance of the vermicular graphite cast iron flywheel casting meet the technical requirements, the reasonable chemical composition range of the vermicular graphite cast iron flywheel casting should be determined first. For the cast vermicular graphite cast iron flywheel casting, according to the technical requirements of the cast iron material, various factors such as the wall thickness, weight, size of the casting are comprehensively considered, and the successful experience in the past is referred to to determine the suitable chemical composition control range of the flywheel casting. The present invention selects two common vermicular graphite cast iron models, RuT350 and RuT400, for the production of diesel engine flywheels. The chemical composition control range of the vermicular graphite cast iron flywheel casting produced by the above two models of vermicular graphite cast iron is shown in Table 1 below.

[0044] Table 1 Control range of chemical composition of molten iron and castings in common cast-state vermicular graphite cast iron flywheel furnace

[0045]

[0046]

[0047] S3. Determine the melting process regulations for compacted graphite cast iron flywheel castings.

[0048] After the chemical composition control range of the as-cast vermicular graphite cast iron flywheel casting is determined, the next step is to compile the cast iron melting process specification. The main steps of the cast iron melting process specification include:

[0049] S3.1. Determine the chemical composition of the molten iron in the furnace and the chemical composition of the compacted graphite cast iron flywheel casting; wherein, the control range of the chemical composition of the molten iron in the furnace of the compacted graphite cast iron flywheel casting is shown in the above Table 1.

[0050] S3.2. Determine the melting batching process sheet and charge adding sequence of compacted graphite cast iron flywheel cast iron.

[0051] Specifically, according to the material and chemical composition requirements of the cast iron parts, the chemical composition and reserve of the existing furnace charge, the characteristics of the melting equipment, the oxidation and burning rate of various metal elements and other factors are comprehensively considered, and combined with previous successful experience, the cast iron melting batching ratio of the vermicular graphite cast iron flywheel is determined. The iron melt batching ratio of the vermicular graphite cast iron flywheel produced using two common vermicular graphite cast iron types, RuT350 and RuT400, in the present invention is shown in Table 2 below.

[0052] Table 2 Melting ingredient ratio of common cast-state vermicular graphite cast iron flywheel castings

[0053]

[0054] Note: As the wall thickness of the casting increases, the proportion of pig iron and ferrosilicon decreases, and the proportion of scrap steel and other alloy charges increases.

[0055] At the same time, the above-mentioned vermicular graphite cast iron flywheel cast iron melting batching process sheet should clearly specify the following contents: ① the material grade, product name and code of the casting to be produced;

[0056] ② The specifications and model of the melting equipment to be used and the total weight of the molten iron;

[0057] ③ Specifications and addition amounts of various furnace charges;

[0058] ④Control range of chemical composition of molten iron before furnace;

[0059] ⑤ The order in which various materials are added into the furnace;

[0060] ⑥ Date of preparation and validity period of the process sheet.

[0061] S3.3. Determine the sampling temperature, furnace temperature, processing temperature and pouring temperature requirements.

[0062] S3.4. Determine the method of creep-inoculation treatment of molten iron in the furnace and when it is discharged from the furnace.

[0063] S4. Determine the casting process regulations for the compacted graphite cast iron flywheel casting.

[0064] The above-mentioned process regulations include: S4.1, pouring and cooling process of as-cast vermicular graphite cast iron flywheel castings; specifically including: ① determining the appropriate furnace temperature and pouring temperature according to the material and structural characteristics of the castings;

[0065] ② Determine the tooling preparation requirements before pouring the as-cast vermicular graphite cast iron flywheel casting;

[0066] ③ Implement the casting of vermicular graphite cast iron flywheel castings and the vermicularization-inoculation treatment;

[0067] ④ Pour the casting and control the cooling process inside the casting mold after pouring.

[0068] The above-mentioned process regulations also include: S4.2, casting and cooling technical requirements for as-cast vermicular graphite cast iron flywheel castings; specifically including: ① strictly controlling the casting temperature, single casting time and total casting time of each package of molten iron and other process parameters in accordance with the process specification requirements;

[0069] ② After the casting is completed, wait for the mold to cool to room temperature before unpacking and taking out the parts.

[0070] The casting process parameters that need to be determined in the casting process specification of the above-mentioned vermicular graphite cast iron flywheel casting generally include: molten iron temperature out of the furnace, start casting temperature, end casting temperature, single casting time and cooling time, etc. The above-mentioned process parameters are generally clearly marked in the process documents and can be determined based on the actual situation of cast iron production and drawing on previous successful technical experience.

[0071] S5. Control the molten iron melting process according to the process regulations, then detect the chemical composition and temperature of the molten iron to determine whether the molten iron meets the process requirements.

[0072] The above main steps include: S5.1, prepare materials, load materials and heat and melt according to the requirements of the cast iron melting batching process sheet; specifically, according to the requirements of the cast iron melting batching process sheet, accurately weigh the various furnace materials required for the melting operation, place them neatly in different areas, and mark them to prevent misuse or confusion. Then, according to the production operation plan and process requirements, add various furnace materials such as pig iron, scrap steel, recycled materials, ferroalloys, etc. into the furnace in turn, and supply electricity to heat the furnace materials so that the furnace materials are melted one after another.

[0073] S5.2. Take samples of the molten iron for pre-furnace chemical composition analysis. Specifically, according to the requirements of the process documents, after all kinds of furnace materials are added into the furnace, completely melted and homogenized, samples are taken to detect the chemical composition of the molten iron in the furnace. The sampling temperature range should be 1350℃-1450℃.

[0074] According to the requirements of the process documents, a direct reading spectrometer is usually used to quickly and accurately detect the chemical composition of the molten iron before the furnace, and issue a furnace chemical composition analysis report.

[0075] According to the requirements of the process documents, check whether the chemical composition analysis results before the furnace meet the requirements of various process parameters, and determine whether the chemical composition test results of the molten iron are qualified.

[0076] S5.3. Adjust the chemical composition of the molten iron in front of the furnace; specifically, if the test results of the chemical composition of the molten iron do not meet the process requirements, it is necessary to adjust the chemical composition in front of the furnace. Common methods for adjusting the chemical composition in front of the furnace include adding the same alloy method, adding pig iron or carburizer method, adding scrap steel method, iron re-matching method, delayed burning loss method, etc. One or more appropriate adjustment methods can be selected according to the specific situation of the excessive chemical composition in front of the furnace.

[0077] Refer to the common methods for adjusting the chemical composition before the furnace, select the most suitable method for adjustment, calculate the weight of the furnace charge to be added, and weigh and prepare the materials. After weighing and preparing the various furnace charges to be added, add all the various furnace charges to be added into the furnace in the method and order required by the process.

[0078] After adding the charge, the molten iron should continue to be heated to ensure that the added charge is fully melted and homogenized, and then a second sampling is performed to detect the chemical composition of the molten iron. According to the chemical composition test results, the measured contents of various chemical elements in the molten iron are compared with the process requirements. If the contents of various chemical elements are within the range of the process parameter requirements, it is determined that the chemical composition analysis results meet the process requirements, and subsequent operations can be carried out. If unqualified, the chemical composition adjustment should be continued.

[0079] S6. The molten iron meeting the requirements is discharged from the furnace and subjected to a creeping-inoculating treatment. Specifically, in general, the molten iron is discharged from the furnace and subjected to a creeping-inoculating treatment at the same time.

[0080] Vermicularizing-inoculating treatment usually adopts the ladle flushing method, which is carried out at the same time as the molten iron is discharged from the furnace. The baked vermicularizing agent and inoculant (the dosage is shown in the ingredient list) are added into the ladle according to the process requirements. The specific operation method and technical requirements are as follows:

[0081] S6.1. First, put all the baked vermicular agent into the pit at the bottom of the ladle and tamp it, then put in 2 / 3 of the total amount of the baked inoculant and tamp it, then cover it tightly with an appropriate amount of covering agent, and then cover it with a cast iron plate with a thickness of 2.5mm to 4.5mm, and then cover the surrounding and upper part of the cast iron plate tightly with covering agent.

[0082] S6.2. The first tapping amount is about 2 / 3 of the ladle volume. After the creep reaction is over, add the remaining 1 / 3 of the inoculant and tap until the ladle is full of molten iron. When tapping, the liquid flow should be stable and uniform, with a moderate flow rate to prevent interruption or splashing.

[0083] During the above-mentioned creeping process, the creeping reaction time of each package of molten iron is generally 1min to 2min. During the creeping reaction, the package mouth is covered with a package cover to alleviate the oxidation and loss of the molten iron. After the creeping reaction is completed, the package cover should be removed in time, the molten iron in the package should be fully stirred with a stirring rod, and the slag on the surface of the molten iron should be removed. Then, the remaining 1 / 3 of the inoculant is added for secondary inoculation, and the molten iron in the package is filled up, and stirred and slag is removed again.

[0084] After the creep-inoculation treatment of the molten iron is completed, the temperature of the molten iron should be ensured to be no less than 1390℃, and the molten iron should be allowed to stand in the ladle for 1-2 minutes before pouring the casting to facilitate the floating of slag inclusions in the molten iron, and measures should be taken to strengthen slag blocking and slag removal during the pouring process.

[0085] At the same time, the quality of the ladle should be checked during the creeping and inoculation process, with emphasis on whether the shape and size of the creeping reaction chamber are appropriate. It should be ensured that it can accommodate all the creeping-inoculant materials, and no bulges should occur after loading. If it does not meet the requirements, it should be cleaned and repaired in time to avoid affecting the creeping quality.

[0086] S7. Pour the casting and inspect the quality of the casting after pouring is completed.

[0087] Specifically, before the molten iron is poured out of the furnace, a special ladle for vermicular iron shall be prepared according to the process requirements. The ladle shall be well maintained on a daily basis. The slag on the ladle mouth and the inner cavity surface shall be cleaned before use, and it shall be baked to dark red. Vermicularization-inoculation treatment shall be carried out while the molten iron is out of the furnace. After completion, the casting shall be poured, and the casting and cooling process parameters shall be controlled according to the process requirements. The specific operation process and technical requirements are shown in Table 3 below.

[0088] Table 3 Casting and cooling technical requirements for common as-cast vermicular graphite cast iron flywheel castings

[0089]

[0090]

[0091] The steps for quality inspection of castings include:

[0092] When pouring castings, standard single casting samples should be poured. If required, castings should be dissected according to product drawings to make body samples. According to the requirements of casting acceptance technical documents, the chemical composition, metallographic structure, tensile strength, yield strength, elongation, hardness and other material properties of castings should be tested to ensure that the inspection results meet the technical requirements.

[0093] If the inspection results do not meet the technical requirements, the chemical composition of the cast iron, the melting and batching process, and the molten iron melting and creeping-inoculation, pouring and cooling processes should be optimized and adjusted.

[0094] The following is an example of the production of diesel engine flywheel casting No. 3 made of RuT400 vermicular graphite cast iron. The casting material of No. 3 flywheel was originally alloy gray cast iron, which belongs to the thick-walled gray cast iron part of the wheel type. The main wall thickness is 35-55mm, the casting blank size is Ф500x130mm, and the casting weight is about 80Kg. The mechanical properties of the casting body are required: the tensile strength is not less than 300Mpa, and the hardness is required to be 200-240HB. Casting defects that affect the strength and appearance quality of the casting are not allowed. After analysis and research, the casting material of No. 3 flywheel was changed to RuT400, which can not only meet the technical requirements of flywheel product design, but also solve the problem of high casting cost caused by the addition of alloy materials.

[0095] The melting equipment for producing the No. 3 flywheel casting of vermicular cast iron is a 0.5t medium frequency electric furnace. The furnace materials used for melting cast iron include: Wu'an Q10 pig iron, scrap steel is low-carbon steel scraps from the steel rolling mill, and various ferroalloys are purchased in accordance with international standards. According to the technical requirements for casting acceptance and combined with production practice, the production processes of the above-mentioned castings are compiled, and various casting molds are made. Furan resin self-hardening sand is used for manual shaping and core making.

[0096] According to the technical requirements of cast iron materials, comprehensive consideration of various factors such as casting wall thickness, weight, size, etc., combined with previous successful experience, and referring to the control range of chemical composition of common cast vermicular graphite cast iron flywheel castings in Table 1 above, the chemical composition of the cast vermicular graphite cast iron flywheel casting is determined. The chemical composition control of flywheel castings made of alloy gray cast iron and RuT400 vermicular graphite cast iron is shown in Table 4 below:

[0097] Table 4 Comparison of chemical composition of RuT400 vermicular graphite cast iron and alloy gray cast iron flywheel castings

[0098]

[0099] Note: 1. The data in the table are the average values ​​of the physical and chemical test results of 10 batches of castings;

[0100] 2. In the chemical composition of RuT400 vermicular graphite cast iron casting, the contents of residual rare earth and magnesium are 0.031% and 0.023% respectively;

[0101] 3. Depending on the specific situation, the alloying element Mo may need to be added during the smelting of the alloy gray cast iron flywheel molten iron if necessary, and its content is usually 0.3-0.6%.

[0102] The scientific rationality of the design of the "Melting and Proportioning Process Sheet" is crucial to ensure that the chemical composition and mechanical properties of the castings meet the technical requirements. In the production process of cast iron parts, the appropriate cast iron melting and proportioning process is usually determined based on the technical requirements of the cast iron material, taking into account the chemical composition and reserve of the existing furnace charge, the characteristics of the melting equipment, the oxidation and burning rate of various metal elements and other factors.

[0103] The following is the "Cast Iron Melting Ingredients Process Sheet" for RuT400 vermicular graphite cast iron and alloy gray cast iron flywheel castings

[0104] Cast iron melting batching process sheet 1

[0105] Product: No. 3 flywheel (0.5t furnace) Material brand: RuT400 Date: xx / xx / xxxx

[0106]

[0107]

[0108] Cast iron melting batching process sheet 2

[0109] Product: No. 3 flywheel (0.5t furnace) Material brand: Alloy gray cast iron xxxx year xx month xx

[0110]

[0111] Then refer to the contents of S4 above to determine the pouring process specification of the compacted graphite cast iron flywheel casting.

[0112] Then, according to the process regulations, all the charges are added into the furnace, completely melted and homogenized, and then samples are taken to detect the chemical composition of the flywheel iron liquid. The sampling temperature range should be 1350℃-1450℃.

[0113] After sampling, a direct reading spectrometer is used to quickly and accurately detect the chemical composition of the molten iron in front of the furnace, and the analysis results are compared with the process requirements to verify whether the content of chemical elements in the flywheel molten iron meets the process technical requirements.

[0114] If the test results of the chemical composition of the molten iron do not meet the process requirements, it is necessary to adjust the chemical composition in front of the furnace. The commonly used methods for adjusting the chemical composition in front of the furnace include adding the same alloy method, adding pig iron or carburizer method, adding scrap steel method, iron re-matching method, delayed burning loss method, etc. One or more appropriate adjustment methods can be selected according to the specific situation of the excessive chemical composition in front of the furnace.

[0115] Then the molten iron that meets the requirements is discharged from the furnace and subjected to vermicularization-inoculation treatment. In the present invention, the molten iron of the vermicular graphite cast iron flywheel is discharged from the furnace and subjected to vermicularization-inoculation treatment at the same time, and the vermicularization-inoculation treatment of the molten iron is carried out by a ladle-injection method. The vermicularizing agent adopts a rare earth magnesium-titanium vermicularizing agent (its main chemical components (ω%) are: Si: 48-52, Mg: 4.5-5.0, Ti: 8.5-10.5, Ce: 0.25-0.35, Cu: 4.0-5.5, Al: 1.0-1.5, and the remainder is Fe), the particle size is 5mm-15mm, and the amount added is 1.1%-1.2% of the weight of the molten iron in the ladle, and the vermicularizing agent is all added to the ladle at one time. The inoculant is BS-I or BS-IA produced in Wuxi, with a particle size of 3mm to 10mm. The added amount is 0.55% to 0.65% of the weight of the molten iron in the ladle. The inoculant is added to the ladle twice, 2 / 3 of the total amount is added for the first time, and 1 / 3 is added for the second time.

[0116] Creeping agent and inoculant must be preheated and dried before use. The preheating temperature is 300℃~350℃, and the holding time is 1h~2h. Other materials such as covering agent should also be kept dry. The molten iron ladle for creeping reaction should use a special ladle for vermicular iron or ductile iron castings. A cylindrical pit is built in the middle of the bottom of the ladle with refractory materials as a creeping-inoculation treatment reaction chamber. The ladle should be maintained in time, and the ladle mouth and inner wall should be kept dry and clean. It should be preheated by baking before each shift to prevent the molten iron in the ladle from cooling too much during the creeping reaction.

[0117] The specific operation method of creep-inoculation treatment is as follows:

[0118] First, put all the prepared vermicular agent into the pit at the bottom of the ladle and tamp it, then put 2 / 3 of the total amount of inoculant and tamp it, then cover it tightly with an appropriate amount of covering agent, and then cover it with a ductile iron plate with a thickness of 2.5mm to 4.5mm, and then cover the surrounding and upper part of the ductile iron plate with covering agent. The first tapping amount is about 2 / 3 of the amount of the ladle. After the creeping reaction is over, continue tapping until the ladle is full of molten iron. The tapping liquid flow should be stable and uniform, with a moderate flow rate to prevent interruption or splashing.

[0119] The creeping reaction temperature of each package is generally controlled at 1510℃~1430℃, and the creeping reaction time is generally 1min~2min. During the creeping reaction, the ladle mouth is covered with a ladle cover to alleviate the oxidation and loss of molten iron. After the creeping reaction of each package is completed, the ladle cover should be removed in time, the molten iron in the ladle should be fully stirred with a stirring rod, and the slag on the surface of the molten iron should be removed. Then, the remaining 1 / 3 of the inoculant is added for secondary inoculation, and the molten iron in the ladle is filled up, and stirred and slag is removed again.

[0120] After the above creep-inoculation process is completed, the sample should be immediately cast into the furnace test block, and the fracture morphology of the test block should be observed to judge the creep quality of the molten iron. If it is qualified, the casting can be cast; if the molten iron creeps poorly or not, the casting shall not be cast, and the molten iron in the ladle shall be combined into ingots or returned to the furnace for adjustment.

[0121] Then the casting is poured. Combined with the characteristics of the flywheel casting as well as the quality and output requirements, a special vermicular iron ladle with a specification of 500Kg can be selected. The operator will check the quality of the ladle before each shift, focusing on whether the shape and size of the creeping reaction chamber are appropriate. It should be ensured that it can accommodate all the creeping-inoculating materials, and no bulges should occur after loading. If it does not meet the requirements, it should be cleaned and repaired in time to avoid affecting the creeping quality.

[0122] In the present invention, the size of the sand mold (sand box) for flywheel casting production is 750X750mm, each mold iron liquid weighs about 100Kg, the main wall thickness of the casting is ≥40mm, and the ladle specification can be selected as a 500Kg ductile iron ladle. The temperature of the flywheel iron liquid out of the furnace is preferably: 1500-1520℃, the starting pouring temperature is: 1410℃, the ending pouring temperature is: 1360℃, and the single piece pouring time is: 10-15s. The cooling time of the flywheel casting in the sand mold is generally more than 8 hours.

[0123] Before production and use, the slag at the mouth and inner cavity of the flywheel ladle should be thoroughly cleaned, and the defective parts of the ladle lining should be repaired. The flywheel ladle should be baked to dark red at a temperature of 600-650℃ and kept warm for 20-30 minutes.

[0124] Before production, prepare the auxiliary materials such as slag aggregation agent, covering agent, refractory clay, etc. required for flywheel melting and pouring operations, and prepare tools such as slag rod, stirring rod, sampling spoon, temperature measuring tube and coupler head to ensure smooth production operation and inspection.

[0125] After confirming that the temperature of the flywheel molten iron in the ladle meets the process requirements, start pouring the flywheel casting blank. The pouring operation should be smooth and continuous to prevent the molten iron from splashing, interrupting or overflowing. During the pouring process, a group of operators should cooperate and coordinate, pay attention to adjusting and controlling the molten iron flow rate, flow rate, pressure head height and other factors at any time, and take timely measures to properly handle the phenomenon of sparking, box expansion, etc.

[0126] After the cooling time of the casting in the mold reaches the process requirements, the casting can be unpacked and sand removed. Then, the flywheel blank is shot blasted according to the process requirements to remove the sand on the surface of the casting. Then, grinding and finishing are performed with tools such as grinders and angle grinders to remove the flash and burrs on the surface of the blank, and the remaining roots of the pouring and riser are ground flat to keep the surface of the casting smooth and flat. The technical requirements for the surface quality acceptance of the casting are met.

[0127] When pouring the flywheel casting, a set of standard single casting samples should be poured. According to the flywheel product drawing and the acceptance technical conditions, the casting body should also be dissected and sampled to check the metallographic structure and mechanical properties of the casting body. According to the requirements of the casting acceptance technical documents, the chemical composition, tensile strength, hardness and other material properties of the casting should be tested to ensure that the inspection results meet the technical requirements.

[0128] The mechanical properties test results of the flywheel casting produced by the technical method of the present invention and the flywheel using alloy gray cast iron are shown in the following table:

[0129]

[0130] Note: 1. The data in the table are the average values ​​of the physical and chemical test results of 10 batches of castings;

[0131] 2. The single cast test bar is a standard tensile specimen, and the bulk mechanical properties specimen is sampled and processed according to technical requirements.

[0132] It can be seen from the above table that the tensile strength, Brinell hardness and other mechanical properties inspection results of RuT400 vermicular graphite cast iron flywheel all meet the product technical quality requirements.

[0133] At the same time, after calculation, the metal material cost per ton of flywheel casting is as follows:

[0134] The metal material cost per ton of alloy gray cast iron flywheel casting is 4220 yuan / ton, and the metal material cost of a single alloy gray cast iron flywheel casting is 422 yuan / piece;

[0135] The metal material cost per ton of RuT400 vermicular graphite cast iron flywheel casting is 3032 yuan / ton, and the metal material cost of a single RuT400 vermicular graphite cast iron flywheel casting is 303.2 yuan / piece;

[0136] After the diesel engine flywheel material is improved from alloy gray cast iron to RuT400 vermicular graphite cast iron, on the basis of ensuring stable product quality and meeting technical requirements, the material cost can be saved by 1,188 yuan per ton of casting and 118.8 yuan per flywheel blank.

[0137] It can be seen that the use of compacted graphite iron technology to manufacture diesel engine flywheel castings can achieve good practical results.

[0138] In the above embodiment, the present invention provides a method for preparing a diesel engine flywheel using vermicular cast iron. The present invention determines appropriate melting ingredients and smelting process, and performs inoculation-vermicularization treatment on ordinary molten iron with suitable chemical composition. Without adding precious metal elements such as copper, tin, and chromium, flywheel castings that meet the technical quality requirements can be produced, and the product quality is relatively stable, which can significantly reduce the casting cost.

[0139] The above-described embodiments are merely descriptions of preferred implementations of the present invention, and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made by ordinary persons in the art to the technical solution of the present invention should fall within the protection scope of the present invention, and the technical contents for which protection is sought in the present invention have been fully recorded in the claims.

Claims

1. A method for preparing a diesel engine flywheel using compacted graphite cast iron, characterized in that: The following steps are involved: S1. Prepare furnace charge, equipment and technical documents; S2. Determine the chemical composition range of the compacted graphite iron flywheel casting; S3. Determine the melting process specification of the compacted graphite cast iron flywheel casting; S4. Determine the pouring process specification of the vermicular graphite cast iron flywheel casting; S5. Control the melting process of the molten iron according to the process regulations, then detect the chemical composition and temperature of the molten iron to determine whether the molten iron meets the process requirements; S6, taking out the molten iron that meets the requirements and performing creeping-inoculation treatment; S7. Pour the casting and inspect the quality of the casting after the pouring is completed.

2. A method for preparing a diesel engine flywheel using compacted graphite cast iron according to claim 1, characterized in that: The charge in step S1 includes pig iron, scrap steel, return charge, alloy charge and auxiliary materials; wherein, return charge refers to the metal charge returned to the furnace and re-melted, including casting risers of the same material, scrapped castings, and ingots of residual molten iron from previous furnaces; alloy charge refers to various metal charges added in small amounts such as ferromanganese, ferrosilicon, ferrochrome, electrolytic copper, vermicularizing agent and inoculant used to adjust the chemical composition of molten iron or treat molten iron; auxiliary materials refer to non-metallic auxiliary materials such as carburizer, refining agent, covering agent and slag aggregation agent used in small amounts in cast iron melting operations.

3. The method for preparing a diesel engine flywheel using compacted graphite cast iron according to claim 1, characterized in that: The chemical components in the vermicular graphite cast iron flywheel casting in step S2 are as follows: 3.6% to 3.8% C, 2.3% to 2.8% Si, 0.3% to 0.5% Mn, ≤0.05% P, ≤0.02% S, 0.01% to 0.02% Mg, and 0.015% to 0.03% RE.

4. The method for preparing a diesel engine flywheel using compacted graphite cast iron according to claim 1, characterized in that: The chemical composition mass percentage content in the vermicular graphite cast iron flywheel casting in step S2 is: 3.5% to 3.7% C, 2.2% to 2.7% Si, 0.4% to 0.6% Mn, ≤0.05% P, ≤0.02% S, 0.015% to 0.03% Mg, and 0.02% to 0.05% RE.

5. The method for preparing a diesel engine flywheel using compacted graphite cast iron according to claim 1, characterized in that: Step S3 includes the following steps: S3.

1. Determine the chemical composition of the molten iron in the furnace and the chemical composition of the compacted graphite iron flywheel casting; S3.

2. Determine the melting batching process sheet and charge adding sequence of compacted graphite cast iron flywheel cast iron; S3.

3. Determine the sampling temperature, furnace temperature, processing temperature and pouring temperature requirements; S3.

4. Determine the method of creep-inoculation treatment of molten iron in the furnace and when it is discharged from the furnace.

6. A method for preparing a diesel engine flywheel using compacted graphite cast iron according to claim 5, characterized in that: The chemical composition of the molten iron in the furnace in step S3.1 is as follows: 3.6% to 3.8% C, 1.8% to 2.1% Si, 0.3% to 0.5% Mn, ≤0.05% P, ≤0.02% S by weight.

7. A method for preparing a diesel engine flywheel using compacted graphite cast iron according to claim 6, characterized in that: Step S3.2 The mass percentage content of each ingredient in the melting batching process sheet of vermicular graphite cast iron flywheel cast iron is: 60% to 70% pig iron, 10% to 20% scrap steel, 10% to 30% recycled materials, 0.25% to 0.45% ferromanganese, 0.5% to 0.8% ferrosilicon, 0 to 0.2% carbon powder, 0.4% to 0.6% inoculant, and 0.9% to 1.1% vermicular agent.

8. The method for preparing a diesel engine flywheel using compacted graphite cast iron according to claim 5, characterized in that: The chemical composition of the molten iron in the furnace in step S3.1 is as follows: 3.5% to 3.7% C, 1.7% to 2.0% Si, 0.4% to 0.6% Mn, ≤0.05% P, ≤0.02% S by weight.

9. A method for preparing a diesel engine flywheel using compacted graphite cast iron according to claim 8, characterized in that: Step S3.2 The mass percentage content of each ingredient in the melting batching process sheet of vermicular graphite cast iron flywheel cast iron is: 60% to 70% pig iron, 10% to 20% scrap steel, 10% to 30% recycled materials, 0.3% to 0.5% ferromanganese, 0.55% to 0.85% ferrosilicon, 0 to 0.2% carbon powder, 0.45% to 0.65% inoculant, and 1% to 1.2% vermicular agent.

10. The method for preparing a diesel engine flywheel using compacted graphite cast iron according to claim 1, characterized in that: The specific steps of the molten iron creep-inoculation treatment in step S6 are: S6.

1. Put all the baked vermicularizer into the pit at the bottom of the ladle and tamp it, then put 2 / 3 of the total amount of the baked inoculant and tamp it, then cover it tightly with an appropriate amount of covering agent, and then cover it with a cast iron plate with a thickness of 2.5mm to 4.5mm, and then cover the surrounding and upper part of the cast iron plate tightly with covering agent; S6.

2. The first tapping amount is 2 / 3 of the ladle volume. After the creep reaction is over, add the remaining 1 / 3 of the inoculant and tap until the ladle is full of liquid iron.

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