Method of manufacturing an axle housing
By performing spheroidization treatment of molten iron and using inoculants in the tidal sand casting process, combined with riser design, the problem of coarse grains in bridge shells during tidal sand casting was solved, and the high strength and toughness of the bridge shells were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FAW CASTING CO LTD
- Filing Date
- 2026-03-19
- Publication Date
- 2026-06-05
Smart Images
Figure CN122142234A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of casting technology, and more specifically, to a method for manufacturing a bridge shell. Background Technology
[0002] In related technologies, cast iron parts such as bridge housings often employ the wet-sand casting process. This process offers advantages such as high production efficiency and low production costs. However, the cooling rate of wet-sand casting is relatively slow, which is not conducive to the refinement of metal grains. This can easily lead to coarse grains and microporous structures inside the casting, especially in thicker areas such as the central body of the bridge housing. Consequently, this results in defects such as low strength and stiffness, and insufficient toughness in the casting. Summary of the Invention The present invention aims to at least partially solve one of the aforementioned technical problems in the prior art. To this end, the present invention proposes a method for manufacturing a bridge shell, which can improve the tensile strength and toughness of the bridge shell.
[0003] According to an embodiment of the present invention, a bridge housing manufacturing method includes the following steps: mold manufacturing, using wet molding sand to manufacture a mold; metal smelting, smelting raw materials to obtain molten iron, pouring the molten iron into a ladle, and subjecting the molten iron in the ladle to spheroidization treatment; casting, pouring the spheroidized molten iron from the ladle into the cavity of the mold, and using an inoculant during casting to form ductile iron; cooling and unpacking, unpacking the ductile iron in the mold when it is in the austenitizing temperature range to remove the bridge housing.
[0004] According to the axle housing manufacturing method of the present invention, the axle housing of a vehicle can be manufactured using a wet molding sand process. During manufacturing, the molten iron is first spheroidized, and an inoculant is used during pouring. The ductile iron in the mold is placed in the austenitizing temperature range to improve the tensile strength and toughness of the axle housing.
[0005] According to some embodiments of the present invention, the mold has multiple risers and multiple exothermic risers.
[0006] According to some embodiments of the present invention, the raw materials for smelting include: a carbonizer, ferrosilicon, ferromanganese, electrolytic copper, tin ingots, scrap steel, and recycled materials, wherein the molten iron contains, by mass percentage: C: 3.65% to 3.70%, Si: 1.85% to 1.95%, Mn: 0.38% to 0.45%, P: less than 0.06%, S: less than 0.2%, Cu: 0.4% to 0.5%, Sn: 0.02% to 0.025%, with the remainder being Fe.
[0007] According to some embodiments of the present invention, the heating power for smelting the raw materials is gradually increased from 500 kW to 1200 kW within 1.2 hours.
[0008] According to some embodiments of the present invention, before pouring the molten iron into the ladle, the bridge shell manufacturing method further includes: adding 75% ferrosilicon to the bottom of the ladle, wherein the mass of the 75% ferrosilicon is 0.55% to 0.65% of the mass of the molten iron.
[0009] According to some embodiments of the present invention, the ductile iron contains, by weight percentage, 3.65% to 3.70% C, 2.48% to 2.52% Si, 0.40% to 0.44% Mn, less than 0.06% P, less than 0.2% S, 0.43% to 0.47% Cu, 0.02% to 0.025% Sn, 0.04% to 0.05% Mg, with the balance being Fe.
[0010] According to some embodiments of the present invention, when the spheroidized molten iron is poured into the cavity of the mold from the ladle, the pouring temperature is 1420°C to 1440°C.
[0011] According to some embodiments of the present invention, the tidal sand contains, by weight percentage: mud: 8% to 13%, bentonite: 4.94% to 6.08%, water: 1.7% to 2.7%, with the remainder being sand.
[0012] According to some embodiments of the present invention, the compaction rate of the wet molding sand is 36% to 46%, the hot wet tensile strength is greater than or equal to 2.7 kPa, and the wet compressive strength is greater than or equal to 0.08 MPa.
[0013] According to some embodiments of the present invention, after the bridge housing is removed, the surface of the bridge housing is further subjected to shot blasting.
[0014] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description
[0015] Figure 1 This is a flowchart of a bridge housing manufacturing method according to an embodiment of the present invention; Figure 2 This is a schematic diagram showing the positional relationship between the bridge shell and multiple risers on the mold according to an embodiment of the present invention; Detailed Implementation Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.
[0016] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0017] The bridge housing manufacturing method according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.
[0018] Reference Figure 1 As shown, the bridge housing manufacturing method includes the following steps: Step S1, mold making, using wet sand to make the mold.
[0019] The upper and lower mold boxes both employ wet sand molding, and the sand cores in the mold can be manufactured using a fully automated core-making machine. These sand cores offer high dimensional accuracy and strength. Molding can be performed using a fully automated hydrostatic molding line to achieve efficient and stable molding. Using wet sand to manufacture molds offers high production efficiency, low production costs, and good casting quality, making it suitable for large-scale production.
[0020] Step S2, metal smelting, smelting raw materials to obtain molten iron, pouring the molten iron into a ladle, and performing spheroidizing treatment on the molten iron poured into the ladle.
[0021] Molten iron is a liquid metal whose main component is iron. Molten iron can be poured into a ladle with a capacity of 1500 kg. Using a wire feeder, a metal-coated wire with a spheroidizing agent (such as MgFeSi) inside is inserted vertically into the bottom of the ladle at a certain speed. By controlling the wire feeding speed and length, the amount of spheroidizing agent added can be precisely controlled to ensure the stability of the spheroidizing effect. After the spheroidizing treatment, the carbon in the molten iron can precipitate in the form of spheroidal graphite, so as to obtain high-quality ductile iron.
[0022] Step S3, casting and molding: the spheroidized molten iron is poured into the mold cavity from the ladle, and an inoculant is used during pouring to form ductile iron.
[0023] The inoculant can be a sulfur-oxygen inoculant. During the process of pouring the spheroidized molten iron from the ladle into the mold cavity, a flow-fed inoculant feeder can be used to evenly sprinkle the sulfur-oxygen inoculant into the molten iron flow. This allows for inoculation just before pouring, maximizing the effect of the inoculant, increasing the number of graphite spheres, refining the sphere diameter, preventing white cast iron, and making the graphite spheres more evenly distributed, thereby improving the strength and toughness of ductile iron.
[0024] Step S4, cooling and unpacking: The ductile iron in the mold is unpacked when it is in the austenitizing temperature range to remove the bridge housing.
[0025] After casting, the ductile iron can be cooled for 30 to 40 minutes before being removed from the mold, for example, 37 minutes. This allows the ductile iron in the mold to be removed when it is in the austenitizing temperature range (870°C to 950°C), which can control the formation ratio and morphology of pearlite and ferrite. After the bridge shell is removed from the mold, it can be exposed to air to cool, which can refine the microstructure and reduce or eliminate brittle eutectic carbides (such as cementite), thereby improving the strength, stiffness and toughness of the bridge shell and ensuring that the performance grade of the bridge shell meets the design requirements. The ductile iron grade of the bridge shell can be QT700-8, that is, the tensile strength is not less than 700MPa and the elongation after fracture is not less than 8%.
[0026] According to the axle housing manufacturing method of the present invention, the axle housing of a vehicle can be manufactured using a wet molding sand process. During manufacturing, the molten iron is first spheroidized, and an inoculant is used during pouring. The ductile iron in the mold is placed in the austenitizing temperature range to improve the tensile strength and toughness of the axle housing.
[0027] In some embodiments of the present invention, reference is made to... Figure 2 As shown, the mold has multiple risers 1 and multiple exothermic risers. Both risers 1 and exothermic risers can effectively feed the bridge shell 20 to prevent internal defects such as shrinkage cavities and porosity from occurring in the bridge shell 20, thereby obtaining a dense casting.
[0028] Since ductile iron undergoes volume shrinkage during solidification from liquid to solid, the mold can be equipped with a corresponding riser 1 or a heating riser above each hot section of the bridge shell 20 as a reservoir for liquid ductile iron, ensuring that it always contains high-temperature liquid ductile iron. The bridge shell 20 can solidify before the riser 1 and the heating riser, thereby introducing shrinkage cavities into the riser 1 rather than into the interior of the bridge shell 20 casting.
[0029] Specifically, riser 1 mainly relies on its large volume and heat dissipation area to extend the liquid state time by utilizing the sensible heat of the molten metal itself, thereby feeding the bridge shell 20 below. The heating riser, on the other hand, is based on riser 1, with its inner wall lined or top covered with a sleeve composed of heating agent (such as aluminum powder, iron oxide powder), heat preservation agent, etc. After pouring, it is ignited and an exothermic chemical reaction occurs. This not only significantly slows down the heat dissipation rate of the molten metal in the heating riser, but also maintains a high temperature or even local remelting for a very long time through active heating, thereby improving the feeding efficiency.
[0030] In some embodiments of the present invention, the mold can cast two bridge shells 20 at one time. The number of risers 1 can be twelve, and the number of heating risers can also be twelve. That is, each bridge shell 20 corresponds to six risers 1 and six heating risers. The six risers 1 can respectively correspond to the shrinkage of the shaft head (one riser 1 on each side), the leaf spring seat (one riser 1 on each side), and the inner support (one riser 1 on each side) of the bridge shell 20. The six heating risers can respectively correspond to the shrinkage of the round flange (one heating riser on each side) and the outer support (two heating risers on each side) of the bridge shell 20.
[0031] In some embodiments of the present invention, the raw materials for smelting include: carbon raiser, ferrosilicon, ferromanganese, electrolytic copper, tin ingots, scrap steel and recycled materials, and the molten iron contains, by mass percentage: C: 3.65% to 3.70%, Si: 1.85% to 1.95%, Mn: 0.38% to 0.45%, P: less than 0.06%, S: less than 0.2%, Cu: 0.4% to 0.5%, Sn: 0.02% to 0.025%, with the remainder being Fe.
[0032] Specifically, a medium-frequency induction furnace with a capacity of 12,000 kg can be used to heat and melt the raw materials. The weighed carbon raiser, ferrosilicon, ferromanganese, electrolytic copper, tin ingots and scrap steel are added into the medium-frequency induction furnace for heating. The feeding sequence is as described above. After the molten iron is clear, the recycled materials and the remaining scrap steel are added one after another until all the furnace materials are added. Then, the furnace is kept warm until all the furnace materials are completely melted.
[0033] When the molten iron temperature reaches 1270℃, a sample is taken from the furnace for spectral analysis. Based on the spectral results, the composition of the molten iron is adjusted. The molten iron obtained from the smelting raw materials is required to contain C (carbon): 3.65% to 3.70%, Si (silicon): 1.85% to 1.95%, Mn (manganese): 0.38% to 0.45%, P (phosphorus): less than 0.06%, S (sulfur): less than 0.2%, Cu (copper): 0.4% to 0.5%, Sn (tin): 0.02% to 0.025%, with the remainder being Fe (iron). This composition design lays an ideal foundation for spheroidization treatment. The combination of high carbon and low silicon in its components can effectively suppress the spontaneous precipitation of graphite before spheroidization treatment, thus preserving a sufficient carbon source for the subsequent spheroidization reaction. The precise ratio of manganese, copper, and tin constitutes a stable pearlite-forming element system. Copper, along with trace amounts of tin, works synergistically to ensure a stable pearlite-dominated matrix structure during subsequent cooling. The low phosphorus content aims to minimize grain boundary brittle phosphorus eutectic, ensuring the toughness of the casting. The low sulfur content removes most interference from subsequent spheroidizing desulfurization.
[0034] In some embodiments of the present invention, the heating power of the smelting raw materials is gradually increased from 500kw to 1200kw within 1.2 hours. The gradual increase in heating power can protect the furnace lining of the medium-frequency furnace, extend the service life of the medium-frequency furnace and reduce the risk of furnace leakage. At the same time, the gradual increase in heating power can gradually raise the temperature inside the furnace, which is conducive to the slow and uniform heating of large scrap steel and recycled materials, prevents local overheating, and reduces the oxidation and burning loss of elements such as silicon and carbon, providing high-quality molten iron with highly stable composition and temperature for subsequent spheroidization inoculation.
[0035] In some embodiments of the present invention, before pouring molten iron into the ladle, the bridge shell manufacturing method further includes: adding 75% ferrosilicon to the bottom of the ladle, wherein the mass of 75% ferrosilicon is 0.55% to 0.65% of the mass of the molten iron.
[0036] Specifically, 75% ferrosilicon (FeSi75) has a silicon content of about 75%, and its mass is 0.55% to 0.65% of the mass of molten iron. For example, if the mass of molten iron is 1000 kg, then the mass of 75% ferrosilicon is 5.5 kg to 6.5 kg.
[0037] Before pouring molten iron into the ladle, a certain amount of 75% ferrosilicon is placed at the bottom of the empty ladle. When the high-temperature molten iron is poured into the ladle, the 75% ferrosilicon at the bottom will melt rapidly, increasing the silicon content and forming a large number of silicon-enriched areas before the spheroidizing treatment. These silicon-enriched areas can serve as potential nucleation sites for subsequent graphite precipitation, laying a good foundation for subsequent processing and making graphite nucleation more complete. This helps to obtain smaller and rounder graphite spheres. At the same time, the melting of 75% ferrosilicon absorbs heat, which helps to lower the temperature of the molten iron and create a more suitable temperature window for subsequent spheroidizing treatment.
[0038] In some embodiments of the present invention, the ductile iron contains, by weight percentage, 3.65% to 3.70% C, 2.48% to 2.52% Si, 0.40% to 0.44% Mn, less than 0.06% P, less than 0.2% S, 0.43% to 0.47% Cu, 0.02% to 0.025% Sn, 0.04% to 0.05% Mg, with the balance being Fe.
[0039] Specifically, after spheroidizing and inoculation treatment, the resulting ductile iron has the following composition: C (carbon): 3.65% to 3.70%, Si (silicon): 2.48% to 2.52%, Mn (manganese): 0.40% to 0.44%, P (phosphorus): less than 0.06%, S (sulfur): less than 0.2%, Cu (copper): 0.43% to 0.47%, Sn (tin): 0.02% to 0.025%, with the remainder being Fe (iron). The introduction of magnesium is crucial for successfully completing the spheroidization reaction and transforming the graphite morphology from flakes to spheres, thus giving the ductile iron high strength and toughness. The silicon content is significantly increased through inoculation, which on the one hand promotes graphitization, prevents the tendency for white iron formation caused by magnesium addition, refines the graphite spheres, and makes their distribution more uniform. On the other hand, the increased silicon dissolved in ferrite effectively improves the strength and hardness of the matrix. The advantages of the original alloy system (Cu, Sn, Mn) are fully preserved. They will work synergistically with the new spheroidal graphite and silicon-reinforced matrix to ensure that the castings achieve a high spheroidization rate while forming an ideal reinforced matrix structure dominated by fine and uniform pearlite with an appropriate amount of ferrite, thereby stably meeting the comprehensive mechanical property requirements of QT700-8.
[0040] In some embodiments of the present invention, when the spheroidized molten iron is poured into the mold cavity, the pouring temperature is 1420°C to 1440°C to ensure that the molten iron has good fluidity and can completely fill the complex bridge shell cavity, avoiding defects such as cold shuts and incomplete filling. Combined with a reasonable riser and heating riser design, internal defects such as shrinkage porosity and shrinkage cavities can be significantly reduced. Furthermore, this process allows the casting to achieve a tensile strength of not less than 700 MPa and an elongation of not less than 8% directly in its as-cast matrix structure without heat treatment after solidification, achieving a balance between high strength and good toughness.
[0041] In some embodiments of the present invention, the tidal sand contains, by weight percentage: mud: 8% to 13%, bentonite: 4.94% to 6.08%, water: 1.7% to 2.7%, with the remainder being sand.
[0042] Specifically, 8% to 13% clay provides basic binding and plasticity, ensuring the basic shaping of the sand mold. 4.94% to 6.08% bentonite, as the core binder, guarantees the wet strength and thermal stability of the sand mold to withstand the erosion of high-temperature molten iron. 1.7% to 2.7% water, meaning the moisture content of the mold sand is 1.7% to 2.7%, activates the binding properties of the bentonite, ensuring sufficient strength of the sand mold while maximizing excellent permeability. This helps to expel gases generated during pouring and prevents porosity defects in the casting. This formulation of mold sand combines good formability, sufficient strength, ideal collapsibility, and excellent permeability, making it suitable for ductile iron castings such as bridge housings, which require high surface quality and internal density.
[0043] In some embodiments of the present invention, the compaction rate of the wet molding sand is 36% to 46%, the hot wet tensile strength is greater than or equal to 2.7 kPa, and the wet compressive strength is greater than or equal to 0.08 MPa.
[0044] Specifically, a compaction rate of 36%-46% allows the wet molding sand to achieve good plasticity and strength while maintaining excellent permeability, which is beneficial for venting. A hot wet tensile strength greater than or equal to 2.7 kPa ensures strong resistance to cracking of the surface layer when in contact with molten iron, maintaining the integrity of the mold cavity. A wet compressive strength greater than or equal to 0.08 MPa ensures sufficient overall hardness of the sand mold during demolding, handling, and mold assembly, resisting deformation and ensuring dimensional accuracy of the casting.
[0045] In some embodiments of the present invention, the loss on ignition of the mold sand is 2.5% to 5.5%, that is, the total amount of all organic or inorganic substances in the mold sand that can burn, volatilize, and decompose at high temperature is 2.5% to 5.5%. When the loss on ignition is 2.5% to 5.5%, defects such as porosity and surface roughness in the casting can be avoided.
[0046] In some embodiments of the present invention, after the bridge housing is removed, the surface of the bridge housing is shot blasted. Specifically, after the housing is opened, the riser can be removed by air hammer and manual grinding, and then shot blasting is performed by a fully automatic shot blasting machine to improve the surface quality of the bridge housing.
[0047] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," 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, the 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. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.
[0048] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.
Claims
1. A method for manufacturing a bridge shell, characterized in that, Includes the following steps: Mold manufacturing, using wet molding sand to create the mold; Metal smelting, melting raw materials to obtain molten iron, pouring the molten iron into a ladle, and performing spheroidizing treatment on the molten iron poured into the ladle; The casting process involves pouring the spheroidized molten iron from the ladle into the cavity of the mold, and using an inoculant during pouring to form ductile iron. Cooling and unpacking: When the ductile iron in the mold is in the austenitizing temperature range, unpack the mold to remove the bridge housing.
2. The bridge housing manufacturing method according to claim 1, characterized in that, The mold has multiple risers and multiple exothermic risers.
3. The bridge housing manufacturing method according to claim 1, characterized in that, The raw materials used in the smelting include: carbon raiser, ferrosilicon, ferromanganese, electrolytic copper, tin ingots, scrap steel, and recycled materials. The molten iron contains, by mass percentage, 3.65% to 3.70% C, 1.85% to 1.95% Si, 0.38% to 0.45% Mn, less than 0.06% P, less than 0.2% S, 0.4% to 0.5% Cu, 0.02% to 0.025% Sn, with the remainder being Fe.
4. The bridge housing manufacturing method according to claim 3, characterized in that, The heating power for smelting the raw materials was gradually increased from 500kw to 1200kw within 1.2 hours.
5. The bridge housing manufacturing method according to claim 3, characterized in that, Before pouring the molten iron into the ladle, the bridge shell manufacturing method further includes: adding 75% ferrosilicon to the bottom of the ladle, wherein the mass of the 75% ferrosilicon is 0.55% to 0.65% of the mass of the molten iron.
6. The bridge housing manufacturing method according to claim 5, characterized in that, The ductile iron contains, by weight percentage, 3.65% to 3.70% C, 2.48% to 2.52% Si, 0.40% to 0.44% Mn, less than 0.06% P, less than 0.2% S, 0.43% to 0.47% Cu, 0.02% to 0.025% Sn, 0.04% to 0.05% Mg, with the balance being Fe.
7. The bridge housing manufacturing method according to claim 1, characterized in that, When the spheroidized molten iron is poured into the mold cavity from the ladle, the pouring temperature is 1420°C to 1440°C.
8. The bridge housing manufacturing method according to claim 1, characterized in that, The tidal sand contains, by weight percentage: mud: 8% to 13%, bentonite: 4.94% to 6.08%, water: 1.7% to 2.7%, with the remainder being sand.
9. The bridge housing manufacturing method according to claim 8, characterized in that, The compaction rate of the wet molding sand is 36% to 46%, the hot and wet tensile strength is greater than or equal to 2.7 kPa, and the wet compressive strength is greater than or equal to 0.08 MPa.
10. The method for manufacturing a bridge housing according to any one of claims 1-9, characterized in that, After the bridge housing is removed, its surface is shot blasted.