Knowledge

I. Cast Iron Materials and Production Methods

1. Gray Cast Iron

Material Characteristics: It has excellent casting properties, shock absorption, wear resistance, and machinability. It is relatively low-cost and widely used in general-purpose reducer housings. Its graphite is distributed in flake form, which weakens the continuity of the matrix, resulting in relatively lower strength and toughness. However, it can meet the requirements of most medium and low-speed reducers with small loads.

Production Methods:

-Melting: It is melted using cupola furnaces, electric furnaces, or a combination of both. Cupola furnaces are cost-effective and suitable for large-scale production; electric furnaces can better control the chemical composition and temperature of the molten iron. Raw materials such as pig iron, scrap steel, and return materials are added to the furnace in a certain proportion. During the melting process, the chemical composition of the molten iron, such as carbon, silicon, manganese, phosphorus, and sulfur, is controlled by adjusting the ratio of the charge and the blast volume. Generally, the carbon content is between 2.7% and 3.6%, the silicon content is between 1.0% and 2.8%, and the manganese content is between 0.5% and 1.3%, to ensure the desired mechanical and casting properties.

-Molding: Common molding methods include sand casting, including manual molding and machine molding. Manual molding offers greater flexibility and is suitable for single-piece and small-batch production; machine molding is highly efficient and has high dimensional accuracy, making it suitable for large-scale production. During the molding process, a pattern is made according to the shape of the reducer housing, and the pattern size should consider the shrinkage rate of the casting. The molding sand is compacted around the pattern to form the casting cavity, and the gating and riser systems are set up to ensure smooth entry of the molten iron into the cavity and to compensate for the shrinkage during the solidification process of the casting.

-Pouring: When the molten iron temperature reaches the appropriate range (generally between 1350 and 1450°C), the molten iron is slowly and steadily poured into the casting cavity through a ladle. The pouring speed and temperature have a significant impact on the quality of the casting. Pouring too fast can cause defects such as sand washing and slag inclusion, while pouring too slowly may result in underfilling. High temperatures can increase defects such as shrinkage and porosity in the casting, while low temperatures can lead to poor fluidity of the molten iron, also causing underfilling and cold shuts.

-Cleaning and Machining: After the casting cools and solidifies, the molding sand and gates are removed, and the surface of the casting is cleaned to remove adhering sand and burrs. Then, mechanical processing is carried out according to the design requirements, such as turning, milling, drilling, and boring of installation surfaces and holes, to ensure dimensional accuracy and surface roughness, meeting the assembly requirements of the reducer.

2. Ductile Iron

Material Characteristics: The graphite is distributed in spherical form, significantly improving the mechanical properties of the cast iron. Its strength, toughness, and plasticity are much higher than those of gray cast iron, and it has better comprehensive mechanical properties. It can be used in reducer housings that bear larger loads and higher speeds, and can partially replace cast steel materials while being relatively cheaper than cast steel.

Production Methods:

-Melting: Similar to gray cast iron, but with stricter requirements for the chemical composition of the molten iron. Typically, the carbon content is between 3.6% and 4.0%, and the silicon content is between 2.0% and 2.8%, with low sulfur and phosphorus content in the molten iron to ensure the spheroidization effect. The melting equipment can also use cupola furnaces, electric furnaces, or a combination of both.

-Spheroidization and Inoculation: These are the key steps in the production of ductile iron. Spheroidization involves adding a spheroidizing agent (such as magnesium alloys) to the molten iron to make the graphite crystallize in a spherical form. Inoculation is carried out after spheroidization by adding an inoculant (such as ferrosilicon) to the molten iron to promote graphitization, increase the number of graphite spheres, refine the graphite spheres, and improve the microstructure and properties of the casting. The amount, timing, and method of adding the spheroidizing agent and inoculant have a significant impact on the spheroidization effect and the quality of the casting, and must be strictly controlled. §Molding and Pouring: The molding and pouring processes are basically the same as those for gray cast iron. However, due to the slightly poorer fluidity of ductile iron molten metal, the pouring temperature is slightly higher, generally between 1400 - 1480℃. Meanwhile, during the molding process, attention should be paid to the permeability of the molding sand to prevent defects such as porosity caused by poor gas venting.

-Cleaning and Machining: Similar to gray cast iron, the castings are cleaned and then mechanically processed to achieve the required dimensional accuracy and surface quality. Due to the better mechanical properties of ductile iron, the processing difficulty may be slightly higher than that of gray cast iron, and appropriate cutting tools and parameters need to be selected.

II. Cast Steel Materials and Production Methods

1. Carbon Cast Steel

Material Characteristics: It has high strength, toughness, and plasticity, capable of withstanding large loads and impacts. It is suitable for reducer housings with high mechanical performance requirements, such as in heavy machinery and mining machinery. However, its casting performance is not as good as that of cast iron, and the cost is relatively high, with a tendency to produce casting defects.

Production Methods:

-Melting: Generally, electric furnaces are used for melting, such as electric arc furnaces. Scrap steel, pig iron, and other raw materials are added to the electric furnace, and the raw materials are melted by the high temperature generated by the electric arc between the electrodes. During the melting process, the chemical composition of the molten steel must be strictly controlled, and the contents of carbon, manganese, silicon, and other elements should be adjusted. For example, for commonly used carbon cast steel, the carbon content is generally between 0.15% - 0.60%, and the specific content is determined according to different usage requirements. Deoxidizers such as aluminum and ferrosilicon are added to remove oxygen from the molten steel to prevent defects such as porosity.

-Molding: Sand casting can be used, and for castings with higher precision requirements, investment casting and other methods can also be adopted. For sand casting, the strength and permeability of the molding sand are required to be higher to accommodate the higher pouring temperature of cast steel. The shrinkage rate of the casting should also be considered when making the pattern. The linear shrinkage rate of cast steel is generally larger than that of cast iron, approximately 1.8% - 2.5%. A reasonable gating and risering system should be set up during the molding process to ensure the filling and feeding of the molten steel.

-Pouring: The pouring temperature is relatively high, generally between 1550 - 1650℃, with the specific temperature determined by the composition of the molten steel and the structure of the casting. The pouring speed should be appropriate; too fast can cause splashing and porosity, while too slow may result in insufficient filling. During pouring,

-Cleaning and Machining: After the casting cools, the molding sand and gates and risers are removed, and the surface is cleaned. The cleaning of cast steel castings is relatively more difficult and may require multiple methods such as shot blasting and grinding to remove adhering sand and burrs. Due to the higher hardness of cast steel, appropriate cutting tools and parameters should be selected during machining, and the machining allowance is usually larger than that of cast iron to ensure machining accuracy and surface quality.

2. Alloy Cast Steel

Material Characteristics: On the basis of carbon cast steel, one or more alloy elements such as chromium, nickel, molybdenum, and vanadium are added, further enhancing the strength, toughness, wear resistance, and corrosion resistance of the steel. It is suitable for reducer housings operating in harsh conditions, such as in chemical and marine environments, meeting higher performance requirements, but the cost is also relatively higher.

Production Methods:

-Melting: Electric furnaces are also used for melting, and the addition method and timing of alloy elements should be determined based on their characteristics. Generally, alloy elements with higher melting points and less susceptibility to oxidation, such as chromium and molybdenum, are added first, and elements that are more prone to oxidation, such as aluminum and titanium, are added later in the melting process. The chemical composition and temperature of the molten steel must be strictly controlled to ensure the uniform distribution of alloy elements and obtain good mechanical properties. For example, for chromium-nickel-molybdenum alloy cast steel, the chromium content should be precisely controlled between 1.0% - 2.0%, the nickel content between 0.5% - 1.5%, and the molybdenum content between 0.15% - 0.30%, etc. §Molding and Pouring: Similar to carbon cast steel, the addition of alloying elements may affect the fluidity and shrinkage characteristics of the molten steel, so the molding and pouring process parameters need to be adjusted appropriately. The pouring temperature may vary depending on the alloy composition, generally ranging from 1500 to 1650℃. At the same time, it is necessary to prevent the oxidation and segregation of alloying elements during the pouring process.

-Cleaning and Machining: The cleaning and machining processes are similar to those of carbon cast steel. However, due to the mechanical properties and microstructure characteristics of alloy cast steel, the machining difficulty may be greater, and more suitable cutting tools and machining processes need to be selected to ensure machining quality and efficiency. Sometimes special heat treatments, such as quenching and tempering, are required to further improve the performance of the castings.

III. Aluminum Alloy Materials and Production Methods

1. Cast Aluminum Alloys

Material Properties: It has the advantages of low density, light weight, high specific strength, good thermal conductivity, and corrosion resistance. It is suitable for the production of reducer housings where weight is a concern, such as in the aerospace and automotive industries, which can effectively reduce the weight of equipment and improve energy utilization efficiency. At the same time, aluminum alloys have good casting properties and can produce complex-shaped castings.

Production Methods:

-Melting: Common melting equipment includes resistance furnaces and gas furnaces. Add aluminum alloy ingots, recycled materials, etc. to the furnace. During the melting process, the temperature must be strictly controlled, and the melting temperature of general aluminum alloys is 700 - 750℃. At the same time, add refining agents for refining treatment to remove gases and inclusions in the aluminum liquid and improve the purity of the aluminum liquid. The refining agents are generally salt mixtures, such as zinc chloride and hexachloroethane. After refining, perform modification treatment. For some aluminum alloys, such as aluminum-silicon alloys, add modification agents (such as sodium salts, etc.) to refine the silicon phase and improve the mechanical properties of the alloy.

-Molding: Various methods such as sand casting, permanent mold casting, and low-pressure casting can be used. Sand casting is suitable for single-piece and small-batch production; permanent mold casting has high production efficiency, high dimensional accuracy of castings, and good surface quality, suitable for large-batch production; low-pressure casting allows the aluminum liquid to fill the mold smoothly under low pressure, which is conducive to obtaining high-quality castings and is often used to produce some aluminum alloy reducer housings with high internal quality requirements. During the molding process, select appropriate molding sand or permanent mold materials according to different casting methods and set up a reasonable gating and risering system.

-Pouring: Control the pouring temperature and speed according to different casting methods. For example, the pouring temperature for sand casting is generally 680 - 730℃, while for permanent mold casting and low-pressure casting, it is slightly lower, around 650 - 700℃. The pouring speed should be moderate to ensure that the aluminum liquid can smoothly fill the mold cavity, while preventing the entrainment of gases and the formation of oxide inclusions.

-Cleaning and Machining: After the casting cools, remove the molding sand or permanent mold and clean the gates and risers. The cleaning of aluminum alloy castings is relatively easy and can be done by mechanical or chemical methods. During machining, since aluminum alloys have low hardness, the cutting speed can be appropriately increased, but attention should be paid to preventing tool wear and workpiece deformation. Reasonably select the geometric parameters of the cutting tool and cutting fluid to ensure machining accuracy and surface quality.

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