A method for producing nodular cast iron pipe fittings under clay wet sand process conditions

Abstract

The application provides a method for producing nodular cast iron pipe fittings under clay wet sand process conditions and relates to the technical field of nodular cast iron pipe fitting production processes. The method comprises the following steps: S1, batching: proportionally configuring pig iron, scrap steel, return-to-furnace material, silicon iron and silicon carbide raw materials; S2, smelting: placing the raw materials into a medium-frequency electric furnace for melting; S3, primary molten iron inoculation: placing primary inoculants in a tapping spout for primary inoculation of the molten iron when the molten iron is tapped; S4, spheroidizing treatment: an automatic wire feeder enters the molten iron at a certain feeding speed and spheroidizing line length to perform spheroidizing treatment on the molten iron, and the wire feeder leaves the spheroidizing station after the residual magnesium and the residual rare earth in the molten iron reach the specified range; S5, secondary inoculation; S6, pouring; and S7, cooling and sand dropping. The application solves the technical problem of excessive cementite and pearlite, can make the elongation reach the process specified requirements, and has good machining performance in the as-cast state.

Description

Technical Field

[0001] This invention relates to the field of ductile iron pipe fitting manufacturing technology, and more specifically, to a method for producing ductile iron pipe fittings under clay wet sand process conditions. Background Technology

[0002] Current Chinese casting or mechanical design literature stipulates that the minimum allowable wall thickness for sand-cast ductile iron parts (maximum outer contour dimension of casting < 200mm) is 3-4mm. Therefore, castings with a wall thickness of 2.4-3.4mm, especially those cast in the as-cast state under clay wet sand casting conditions, present significant technical challenges.

[0003] Sand casting involves three processes: wet clay sand, dry clay sand, and chemically hardened sand. Because the cooling rate of the wet clay sand process is faster than the other two, the microstructure and properties of the castings are more difficult to control. The technical challenge in mass-producing 2.4–3.4 mm thick as-cast parts under wet clay sand conditions lies in:

[0004] 1. Cementite content is very likely to exceed the standard (≤1%); 2. Pearlite content is very likely to exceed the standard (≤40%); Elongation is difficult to meet the process specifications (process specifications ≥12%). Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing ductile iron pipe fittings under clay wet sand process conditions. This method addresses the shortcomings of existing technologies by solving the technical problem of excessive cementite and pearlite content. The elongation can meet the process requirements, the casting performance is stable and meets the standards, and the casting has good machinability in the as-cast state.

[0006] The technical solution adopted in this invention is as follows:

[0007] This application provides a method for producing ductile iron pipe fittings under clay wet sand process conditions, comprising the following steps:

[0008] S1. Ingredients:

[0009] Pig iron, scrap steel, recycled materials, ferrosilicon, and silicon carbide raw materials are mixed in the following weight ratios, wherein: carbon accounts for 3.85%, silicon accounts for 2.12%, manganese accounts for ≤0.2%, sulfur accounts for ≤0.02%, and phosphorus accounts for ≤0.05%.

[0010] S2, Smelting:

[0011] The prepared pig iron, scrap steel, recycled materials, ferrosilicon, and silicon carbide raw materials are placed in an induction furnace for melting. The molten iron in the furnace is pretreated. The molten iron can be tapped from the furnace only after the temperature of the molten iron reaches 1560℃ and the chemical composition is qualified.

[0012] S3, One-time molten iron incubation:

[0013] When molten iron is tapped from the furnace, an inoculant is placed in the tapping trough to inoculate the molten iron once.

[0014] S4. Spheroidizing treatment:

[0015] The molten iron, after being inoculated once, is transported to the spheroidizing station. An automatic wire feeder enters the molten iron at a certain feeding speed and spheroidizing line length to perform spheroidizing treatment on the molten iron, so that the residual magnesium and rare earth content in the molten iron reaches the specified range before leaving the spheroidizing station.

[0016] S5, Secondary Pregnancy:

[0017] The molten iron from the spheroidizing station is poured into the ladle of the casting machine. At the same time as the molten iron is poured, a secondary inoculant is added along with the molten iron to perform a secondary inoculation treatment on the molten iron.

[0018] S6. Pouring:

[0019] The secondary inoculation molten iron is automatically poured into the mold cavity made of clay wet sand by a casting machine. At the same time as the secondary inoculation molten iron is poured into the sand mold cavity, the tertiary inoculant is added to the molten iron along with the flow of molten iron.

[0020] S7, Cooling and Sand Removal:

[0021] After the sand mold is poured, it is left to stand for a certain period of time for sand-iron separation, i.e., cooling and sand removal. The sand enters the sand treatment system for secondary use, and the poured castings enter the casting and gating system and enter the separation section.

[0022] Furthermore, in some embodiments of the present invention, the process after cooling and removing the sand further includes the following steps:

[0023] S8. Casting Inspection:

[0024] In the casting and gating / riser separation section, gating / risers and scrap castings enter the conveying system for secondary use, while qualified castings are put into storage.

[0025] Furthermore, in some embodiments of the present invention, the above-mentioned steps after casting inspection further include the following:

[0026] S9. Surface cleaning and secondary inspection:

[0027] The surface of the casting is polished in a shot blasting machine, and the polished casting undergoes a second inspection.

[0028] Furthermore, in some embodiments of the present invention, after surface cleaning and secondary inspection, the following steps are also included:

[0029] S10, hot-dip galvanized:

[0030] After the second inspection, the castings enter the hot-dip galvanizing department for surface galvanizing.

[0031] S11, Machining:

[0032] After hot-dip galvanizing, the casting is finished by flattening and threading.

[0033] S12, Final Inspection and Packaging:

[0034] After machining, the castings are inspected, and the qualified products are packaged and put into storage.

[0035] Furthermore, in some embodiments of the present invention, the primary inoculant used in the primary inoculation of molten iron includes a silicon-calcium alloy and silicon carbide, wherein the weight percentage of the silicon-calcium alloy relative to the molten iron is 0.3%, and the weight percentage of the silicon carbide relative to the molten iron is 0.2%.

[0036] Furthermore, in some embodiments of the present invention, the specified ranges for the residual magnesium and rare earth content in the molten iron during the spheroidizing process are as follows: the residual magnesium content relative to the weight of the molten iron is 0.025 to 0.035%, and the residual rare earth content relative to the weight of the molten iron is 0.008 to 0.015%.

[0037] Furthermore, in some embodiments of the present invention, the secondary inoculant used in the secondary inoculation process includes a silicon-calcium-barium alloy, wherein the weight percentage of the silicon-calcium-barium alloy relative to the molten iron is 0.4-0.6%.

[0038] During casting, the three inoculants include a silicon-calcium-barium alloy, wherein the silicon-calcium-barium alloy accounts for 0.15% of the weight of the molten iron.

[0039] Furthermore, in some embodiments of the present invention, the carbon equivalent in the molten iron is controlled to be 4.6% to 4.7% of the weight of the molten iron during casting.

[0040] Furthermore, in some embodiments of the present invention, the silicon-to-carbon ratio in the molten iron is ≥0.83 during casting.

[0041] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0042] Pre-treatment of the molten iron involves adding silicon carbide into the furnace to purify the iron and increase graphite crystallization nuclei.

[0043] Enhanced inoculation effect and significantly increased graphite sphere count: While improving the effect of secondary and in-flow inoculation, in-depth research and multiple experiments were conducted on primary inoculation. Without increasing production costs, a composite inoculation method was adopted, which increased the graphite sphere count by more than 30% on the original basis.

[0044] The technical problem of excessive cementite and pearlite has been solved, the elongation can meet the process requirements, the casting performance is stable and meets the standards, and it has good machinability in the as-cast state. Detailed Implementation

[0045] Example

[0046] This embodiment provides a method for producing ductile iron pipe fittings under clay wet sand process conditions, including the following steps:

[0047] S1. Ingredients:

[0048] Pig iron, scrap steel, recycled materials, ferrosilicon, and silicon carbide raw materials are mixed in the following weight ratios, wherein: carbon accounts for 3.85%, silicon accounts for 2.12%, manganese accounts for ≤0.2%, sulfur accounts for ≤0.02%, and phosphorus accounts for ≤0.05%.

[0049] S2, Smelting:

[0050] The prepared pig iron, scrap steel, recycled materials, ferrosilicon, and silicon carbide raw materials are placed in an induction furnace for melting. The molten iron in the furnace is pretreated. The molten iron can be taken out of the furnace only after the temperature of the molten iron reaches 1560℃ and the chemical composition is qualified. By adding silicon carbide in the furnace to pretreat the molten iron, the molten iron is purified and graphite crystallization nuclei are increased.

[0051] S3, One-time molten iron incubation:

[0052] When molten iron is tapped from the furnace, a primary inoculant is placed in the tapping trough to inoculate the iron. The primary inoculant consists of a silicon-calcium alloy and silicon carbide, with the silicon-calcium alloy accounting for 0.3% of the weight of the molten iron and the silicon carbide accounting for 0.2%. This composite inoculation method, without increasing production costs, increases the number of graphite spheres by more than 30%.

[0053] S4. Spheroidizing treatment:

[0054] The molten iron, after being inoculated once, is transported to the spheroidizing station. An automatic wire feeder enters the molten iron at a certain feeding speed and spheroidizing line length to perform spheroidizing treatment on the molten iron, so that the residual magnesium and rare earth content in the molten iron reaches the specified range before leaving the spheroidizing station.

[0055] The specified ranges for residual magnesium and rare earth elements in molten iron are as follows: the residual magnesium content relative to the weight of molten iron is 0.025% to 0.035%, and the residual rare earth elements relative to the weight of molten iron is 0.008% to 0.015%.

[0056] S5, Secondary Pregnancy:

[0057] Molten iron from the spheroidizing station is poured into the ladle of the casting machine. At the same time as the molten iron is poured, a secondary inoculant is added along with the molten iron to perform a secondary inoculation treatment. The secondary inoculant includes a silicon-calcium-barium alloy, wherein the silicon-calcium-barium alloy accounts for 0.4-0.6% of the weight of the molten iron.

[0058] S6. Pouring:

[0059] The secondary inoculation molten iron is automatically poured into a mold cavity made of clay wet sand by a casting machine. At the same time as the secondary inoculation molten iron is poured into the sand mold cavity, the tertiary inoculator is added to the molten iron along with the molten iron flow. The tertiary inoculator includes a silicon-calcium-barium alloy, in which the silicon-calcium-barium alloy accounts for 0.15% of the weight of the molten iron.

[0060] During casting, the carbon equivalent in the molten iron is controlled to be 4.6%–4.7% of its weight. The carbon equivalent is the sum of one-third the weight of silicon and the weight of carbon, relative to the weight of the molten iron. The silicon-to-carbon ratio in the molten iron is ≥0.83.

[0061] S7, Cooling and Sand Removal:

[0062] After the sand mold is poured, it is left to stand for a certain period of time for sand-iron separation, i.e., cooling and sand removal. The sand enters the sand treatment system for secondary use, and the poured castings enter the casting and gating system and enter the separation section.

[0063] S8. Casting Inspection:

[0064] In the casting and gating / riser separation section, gating / risers and scrap castings enter the conveying system for secondary use, while qualified castings are put into storage.

[0065] S9. Surface cleaning and secondary inspection:

[0066] The surface of the casting is polished in a shot blasting machine, and the polished casting undergoes a second inspection.

[0067] S10, hot-dip galvanized:

[0068] After the second inspection, the castings enter the hot-dip galvanizing department for surface galvanizing.

[0069] S11, Machining:

[0070] After hot-dip galvanizing, the casting is finished by flattening and threading.

[0071] S12, Final Inspection and Packaging:

[0072] After machining, the castings are inspected, and the qualified products are packaged and put into storage.

[0073] Thus, the method for producing ductile iron pipe fittings under clay wet sand process conditions provided in this application pre-treats the original molten iron by adding silicon carbide in the furnace to pre-treat the molten iron, thereby purifying the molten iron and increasing the graphite crystallization nuclei.

[0074] Enhanced inoculation effect and significantly increased graphite spheroid count: While improving the effects of secondary and in-flow inoculation, in-depth research and multiple experiments were conducted on primary inoculation. A composite inoculation method was adopted without increasing production costs, resulting in an increase of over 30% in the graphite spheroid count. The technical problem of excessive cementite and pearlite was solved, the elongation met the process requirements, the casting performance was stable and up to standard, and it exhibited good machinability in the as-cast state.

[0075] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and that the present application can be implemented in other specific forms without departing from the spirit or basic characteristics of the present application.

[0076] Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of this application is defined by the appended claims rather than the foregoing description, and thus all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the protection scope of this invention.

Claims

1. A method of producing nodular cast iron pipe fittings under clay wet sand process conditions, characterized in that: It comprises the following steps: S1, batching: The pig iron, scrap steel, recycled material, ferrosilicon and silicon carbide raw material are configured in the following weight ratio, wherein: the carbon accounts for 3.85%, the silicon accounts for 2.12%, the manganese accounts for ≦0.2%, the sulfur accounts for ≦0.02%, and the phosphorus accounts for ≦0.05%; S2, smelting: The prepared pig iron, scrap steel, recycled material, ferrosilicon and silicon carbide raw material are put into the intermediate frequency electric furnace for melting, and the molten iron in the furnace is pretreated. When the temperature of the molten iron reaches 1560℃ and the chemical composition is qualified, the molten iron can be discharged; S3, primary molten iron inoculation: When the molten iron is discharged, the primary inoculant is placed in the iron discharge slot to inoculate the molten iron; S4, spheroidizing treatment: The molten iron after primary inoculation is transported to the spheroidizing station, and the automatic wire feeder enters the molten iron at a certain feeding speed and spheroidizing line length to spheroidize the molten iron. After the residual amount of magnesium and rare earth in the molten iron reaches the specified range, the molten iron leaves the spheroidizing station; S5, secondary inoculation: The molten iron from the spheroidizing station is poured into the pouring ladle of the pouring machine. While the molten iron is poured, the secondary inoculant is added into the molten iron flow to inoculate the molten iron for the second time; S6, pouring: The secondary inoculated molten iron is automatically poured into the clay wet sand made cavity by the pouring machine. While the secondary inoculated molten iron is poured into the sand mold cavity, the tertiary inoculant is added into the molten iron along with the molten iron flow; S7, cooling and sand separation: After the pouring is completed, the sand mold is cooled and separated from the iron after a certain period of time. The sand enters the sand treatment system for secondary utilization, and the castings poured out enter the casting and pouring head separation department.

2. A process for producing nodular cast iron pipe fittings under clay wet sand process conditions as claimed in claim 1 wherein: After cooling and sand separation, it further comprises the following steps: S8, casting inspection: In the casting and pouring head separation department, the pouring head and waste castings enter the conveying system for secondary utilization, and the qualified castings are put into the warehouse.

3. A method of producing nodular cast iron pipe fittings under clay wet sand process conditions according to claim 2, characterized in that: After the casting inspection, it further comprises the following steps: S9, surface cleaning and secondary inspection: The surface of the casting is polished in the shot blasting machine, and the polished casting is subjected to secondary inspection.

4. A method of producing nodular cast iron pipe fittings under clay wet sand process conditions according to claim 3, characterized in that: After the surface cleaning and secondary inspection, it further comprises the following steps: S10, hot galvanizing: The casting after the secondary inspection enters the hot galvanizing department to galvanize the surface of the casting; S11, machining: After the hot galvanizing is completed, the casting is flat-faced and threaded; S12, final inspection and packaging: The machined casting is inspected, and the qualified products are packaged and put into the warehouse.

5. A method of producing nodular cast iron pipe fittings under clay wet sand process conditions as claimed in claim 1, wherein: In the primary molten iron inoculation, the primary inoculant includes silicon calcium alloy and silicon carbide, wherein the weight ratio of silicon calcium alloy to molten iron is 0.3%, and the weight ratio of silicon carbide to molten iron is 0.2%.

6. A method of producing nodular cast iron pipe fittings under clay wet sand process conditions as claimed in claim 1, wherein: In the spheroidizing treatment, the specified range of residual amount of magnesium and rare earth in the molten iron is: the weight ratio of residual amount of magnesium to molten iron is 0.025-0.035%, and the weight ratio of residual amount of rare earth to molten iron is 0.008-0.015%.

7. A method of producing nodular cast iron pipe fittings under clay wet sand process conditions as claimed in claim 1, wherein: In the secondary inoculation, the secondary inoculant includes silicon calcium barium alloy, wherein the weight ratio of silicon calcium barium alloy to molten iron is 0.4-0.6%; In the pouring, the tertiary inoculant includes silicon calcium barium alloy, wherein the weight ratio of silicon calcium barium alloy to molten iron is 0.15%.

8. A method of producing nodular cast iron pipe fittings under clay wet sand process conditions as claimed in claim 1, wherein: At the time of pouring, the carbon equivalent in the molten iron is controlled to 4.6-4.7% by weight.

9. A method of producing nodular cast iron pipe fittings under clay wet sand process conditions according to claim 1, characterized in that: At the time of pouring, the silicon-carbon ratio in the molten iron is >= 0.83.