Manufacturing method of high-nickel austenite nodular cast iron valve casting

Abstract

The invention discloses a manufacturing method of a high-nickel austenite nodular cast iron valve casting. The manufacturing method comprises the following steps: manufacturing a casting mold by using resin sand according to the shape of the valve casting; pig iron, waste steel, foundry returns, nickel plates, ferromanganese and ferrosilicon are adopted as raw materials for reasonable proportioning, and an electric furnace is adopted for melting to obtain base iron; pouring base iron with qualified components and the temperature of 1490-1500 DEG C into a prepared spheroidizing bag, and carrying out spheroidizing reaction for nearly 2 minutes; then at least 0.3% of an inoculant containing 75% of Si is added for inoculation treatment; after the spheroidizing reaction is finished, adding a small amount of slag remover, stirring, removing slag, and casting the treated molten iron into a valve casting mold cavity to obtain a valve casting; and a finished product is obtained, specifically, the valve casting is cooled, taken out and subjected to shot blasting, and the finished valve casting is obtained. The high-nickel austenite nodular cast iron manufactured through the method is good in heat resistance and corrosion resistance, the service life of a valve is prolonged, and the problem that a casting is loose is solved.

Description

Technical Field

[0001] This invention relates to a method for manufacturing high-nickel austenitic ductile iron valve castings. Background Technology

[0002] High-nickel austenitic ductile iron contains a large number of alloying elements, such as Ni and Cr, which form more compounds in the matrix.

[0003] ASTM A439 D2-B austenitic ductile iron has a high nickel content (18-22%), and the graphitization of nickel during the smelting process can easily lead to unstable spheroidization. Large valves larger than 78 inches have the risk of pump pressure leakage. Traditional processes are prone to shrinkage porosity and other defects in key parts such as valve plate sealing grooves and shaft holes. In existing technologies, resin sand casting produces a large amount of gas during the pouring of high-nickel molten iron, which can easily lead to porosity defects.

[0004] Therefore, a method for manufacturing high-nickel austenitic ductile iron valve castings is provided. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a method for manufacturing high-nickel austenitic ductile iron valve castings, which solves the problem of casting porosity defects and reduces repair costs.

[0006] The technical solution to achieve the above objectives is:

[0007] A method for manufacturing high-nickel austenitic ductile iron valve castings includes:

[0008] Step S1, Molding and Core Making: According to the shape of the valve casting, a mold is made with resin sand, with a resin addition amount of 1.2% and a curing agent addition amount of 35% of the resin amount;

[0009] Step S2, preparing molten iron: using pig iron, scrap steel, recycled materials, nickel plates, ferromanganese, and ferrosilicon as raw materials, and melting them in an electric furnace to obtain raw molten iron;

[0010] Step S3, spheroidizing treatment: Pour the qualified raw iron at a temperature of 1490℃-1500℃ into the prepared spheroidizing ladle, and the spheroidizing reaction lasts for nearly 2 minutes.

[0011] Step S4, inoculation treatment: When the original molten iron is poured into the spheroidizing ladle to 2 / 3-3 / 4 full, add at least 0.3% of an inoculant containing 75% Si for inoculation treatment.

[0012] Step S5: After the spheroidizing reaction is completed, add a small amount of slag remover, stir, remove the slag, and then pour the treated molten iron into the valve mold cavity to obtain the valve casting.

[0013] Step S6, Obtain the finished product: Cool the valve casting, remove it, and then shot blast it to obtain the finished valve casting.

[0014] Preferably, in step S1, the molding sand is made of resin sand, with a resin addition amount of 1.2% and a curing agent addition amount of 35% of the resin amount; the molding sand is subjected to a compressive strength test using Ф50mm test blocks, the final strength of the sand mold after 24 hours is >2.8Mpa, and the loss on ignition of the resin sand is controlled within 3.5%.

[0015] Preferably, in step S1, conformal chills are placed on the core of the valve casting shaft hole and the shaft hole flange. The thickness of the chills is 40mm and the gap between the chills is ≤25mm. Chills are placed at the valve plate sealing groove of the valve body casting. The thickness of the chills is 100mm and the gap between the chills is ≤25mm.

[0016] Preferably, in step S1, the valve mold is equipped with a plug-out head for casting, the diameter of its sprue is Ф80mm, the sprue is a two-layer trapezoidal sprue, the two layers of sprue are the upper box and the lower box respectively, a filter screen is placed between the two layers of sprue, and the inner sprue uses 10 φ30 ceramic tubes for casting.

[0017] Preferably, in step S1, the cover surface of the valve mold has four Ф80mm necked heat-generating risers with a height of 300mm, two of which are concealed risers.

[0018] Preferably, in step S2, the raw molten iron has a C content of ≤2.6-3.0%, a Si content of 1.9-2.3%, a Mn content of 0.8-1.15%, a Cr content of ≤1.85-2.25%, a Cu content of ≤0.5%, and a Ni content of 19-21%.

[0019] Preferably, in step S2, the melting temperature of the electric furnace is 1550-1560℃.

[0020] Preferably, in step S2, a sample of the original molten iron is taken for spectral analysis. Based on the spectral analysis results, it is determined whether the composition of the original molten iron needs to be adjusted. For the original molten iron with qualified composition, the temperature is controlled at 1550±5℃, and the slag is removed after standing for 5 minutes, and the spheroidization process is awaited.

[0021] Preferably, in step S3, the weight of the spheroidizing agent in the spheroidizing ladle is 1.0-1.4% of the original weight of the molten iron, and the spheroidizing reaction should last for nearly 2 minutes.

[0022] Preferably, in step S3, the spheroidizing agent is covered with 0.2%-0.25% of Si and Ba inoculants and rust-free iron sheets.

[0023] Preferably, in step S5, the molten iron casting temperature is 1400℃-1410℃.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention uses resin sand molding to make valve castings, the final strength of the sand mold after 24 hours is >2.8 MPa, the resin sand ignition loss is controlled within 3.5%, reducing the amount of gas generated by the resin sand and avoiding porosity, and using high-nickel austenitic ductile iron instead of traditional copper alloys and other materials to make valve castings. Since high-nickel austenitic ductile iron has good heat resistance and corrosion resistance, it can improve the service life of valves, solve the problem of casting porosity defects, and reduce repair costs. Attached Figure Description

[0025] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0026] Figure 1 This is a flowchart of a method for manufacturing a high-nickel austenitic ductile iron valve casting according to the present invention. Detailed Implementation

[0027] 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.

[0028] like Figure 1 As shown, a method for manufacturing a high-nickel austenitic ductile iron valve casting includes:

[0029] Step S1, Molding and Core Making: According to the shape of the valve casting, a mold is made with resin sand, with a resin addition amount of 1.2% and a curing agent addition amount of 35% of the resin amount.

[0030] In the embodiment, resin sand was used for molding, with a resin addition of 1.2% and a curing agent addition of 35% of the resin amount; the molding sand was subjected to a compressive strength test using Ф50mm test blocks, and the final strength of the sand mold after 24 hours was >2.8Mpa, and the loss on ignition of the resin sand was controlled within 3.5%.

[0031] In this embodiment, because the structure of the valve casting is relatively simple, in order to ensure the internal quality of the casting, conformal chills are placed on the shaft hole core and shaft hole flange. The thickness of the chills is 40mm and the gap between the chills is ≤25mm. In addition, chills are also placed at the valve plate sealing groove of the valve body casting. The thickness of the chills is 100mm and the gap between the chills is ≤25mm.

[0032] In this embodiment, the valve mold is equipped with a plug-out head for casting. The diameter of its sprue is Ф80mm. The sprue is a two-layer trapezoidal sprue (upper bottom 70, lower bottom 80, height 95). The two layers of sprues are respectively the upper and lower boxes. In order to prevent slag, a filter screen is placed between the two layers of sprues. The inner sprue uses 10 φ30 ceramic tubes for casting.

[0033] In the embodiment, because the shrinkage rate of ASTM A439 D2-B material is relatively large, in order to ensure the internal quality of the casting, the cover surface of the valve mold is evenly distributed with four Ф80mm necked heat risers with a height of 300mm, two of which are concealed risers.

[0034] Step S2, preparing molten iron: using pig iron, scrap steel, recycled materials, nickel plates, ferromanganese, and ferrosilicon as raw materials, and melting them in an electric furnace to obtain raw molten iron.

[0035] In this embodiment, the melting temperature of the electric furnace is 1550-1560℃.

[0036] In this embodiment, a sample of the original molten iron is taken for spectral analysis. Based on the spectral analysis results, it is determined whether the composition of the original molten iron needs to be adjusted. For the original molten iron with qualified composition, the temperature is controlled at 1550±5℃, and the slag is removed after standing for 5 minutes, and the spheroidization process is awaited.

[0037] In the examples, the original molten iron had a C content of ≤2.6-3.0%, a Si content of 1.9-2.3%, a Mn content of 0.8-1.15%, a Cr content of ≤1.85-2.25%, a Cu content of ≤0.5%, and a Ni content of 19-21%.

[0038] Step S3, spheroidizing treatment: Pour the qualified raw iron at a temperature of 1490℃-1500℃ into the prepared spheroidizing ladle, and the spheroidizing reaction lasts for nearly 2 minutes.

[0039] In the embodiment, the weight of the spheroidizing agent in the spheroidizing ladle is 1.0-1.4% of the original weight of molten iron, and the spheroidizing reaction lasts for nearly 2 minutes.

[0040] In the examples, the spheroidizing agent is covered with 0.2%-0.25% of Si and Ba inoculants and rust-free iron sheets.

[0041] Step S4, inoculation treatment: When the original molten iron is poured into the spheroidizing ladle to 2 / 3-3 / 4 full, add at least 0.3% of an inoculant containing 75% Si for inoculation treatment.

[0042] Step S5: After the spheroidizing reaction is complete, add a small amount of slag remover, stir, remove the slag, and then pour the treated molten iron into the valve mold cavity to obtain the valve casting.

[0043] In this embodiment, the molten iron casting temperature is 1400℃-1410℃.

[0044] Step S6, Obtain the finished product: Cool the valve casting, remove it, and then shot blast it to obtain the finished valve casting.

[0045] After adopting the above process, the performance of the test bar meets the requirements of ASTM A439 D2-B material, no defects were found in the valve after processing, and the pump pressure test was also passed.

[0046] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for manufacturing high-nickel austenitic ductile iron valve castings, characterized in that, include: Step S1, Molding and Core Making: According to the shape of the valve casting, a mold is made with resin sand, with a resin addition amount of 1.2% and a curing agent addition amount of 35% of the resin amount; Step S2, preparing molten iron: using pig iron, scrap steel, recycled materials, nickel plates, ferromanganese, and ferrosilicon as raw materials, and melting them in an electric furnace to obtain raw molten iron; Step S3, spheroidizing treatment: Pour the qualified raw iron at a temperature of 1490℃-1500℃ into the prepared spheroidizing ladle, and the spheroidizing reaction lasts for nearly 2 minutes. Step S4, Inoculation treatment: When the original molten iron is poured into the spheroidizing ladle to 2 / 3-3 / 4 full, add at least 0.3% of an inoculant containing 75% Si for inoculation treatment. Step S5: After the spheroidizing reaction is completed, add a small amount of slag remover, stir, remove the slag, and then pour the treated molten iron into the valve mold cavity to obtain the valve casting. Step S6, Obtain the finished product: Cool the valve casting, remove it, and then shot blast it to obtain the finished valve casting.

2. The method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S1, resin sand is used for molding, with a resin addition of 1.2% and a curing agent addition of 35% of the resin amount; the molding sand is subjected to a compressive strength test using Ф50mm test blocks, and the final strength of the sand mold after 24 hours is >2.8Mpa, and the loss on ignition of the resin sand is controlled within 3.5%.

3. The method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S1, conformal chills are placed on the core of the valve casting shaft hole and the shaft hole flange. The thickness of the chills is 40mm and the gap between the chills is ≤25mm. Chills are placed at the valve plate sealing groove of the valve body casting. The thickness of the chills is 100mm and the gap between the chills is ≤25mm.

4. The method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S1, the valve mold is equipped with a plug-out head for pouring. The diameter of its sprue is Ф80mm. The sprue consists of two trapezoidal sprues, with the upper and lower sprues respectively. A filter screen is placed between the two sprues. The inner sprue uses 10 φ30 ceramic tubes for pouring.

5. The method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S1, four Ф80mm necked heat-generating risers with a height of 300mm are evenly distributed on the cover surface of the valve mold, two of which are concealed risers.

6. The method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S2, the raw molten iron obtained has a C content of ≤2.6-3.0%, a Si content of 1.9-2.3%, a Mn content of 0.8-1.15%, a Cr content of ≤1.85-2.25%, a Cu content of ≤0.5%, and a Ni content of 19-21%.

7. The method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S2, the melting temperature of the electric furnace is 1550-1560℃.

8. The method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S2, a sample of the original molten iron is taken for spectral analysis. Based on the spectral analysis results, it is determined whether the composition of the original molten iron needs to be adjusted. For the original molten iron with qualified composition, the temperature is controlled at 1550±5℃, and the slag is removed after standing for 5 minutes, and the spheroidization process is waited for.

9. A method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S3, the weight of the spheroidizing agent in the spheroidizing ladle is 1.0-1.4% of the original weight of the molten iron, and the spheroidizing reaction should last for nearly 2 minutes.

10. A method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S3, the spheroidizing agent is covered with 0.2%-0.25% of Si and Ba inoculants and rust-free iron sheets.

11. The method for manufacturing a high-nickel austenitic ductile iron valve casting according to claim 1, characterized in that, In step S5, the molten iron casting temperature is 1400℃-1410℃.

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