Cast Iron Parts Machining for Rail Transit

Cast iron parts machining for rail transit refers to the process of manufacturing cast iron components for rail transit systems (such as subways, high-speed railways, and railways). These parts are widely used in railway tracks, vehicle components, and related infrastructure, requiring high strength, wear resistance, and high precision to ensure safety and durability.

Cast iron parts are mainly used in the following areas in rail transit:

• Track System:
  • Fastening System: Such as fasteners, rail joint bars (fishplates), and baseplates, used to fix rails and ensure track stability.
  • Switch Components: Such as cast manganese steel frogs and switch plates, used for train switching.
  • Other Track Materials (OTM): Such as tie plates, buffers, and inert retarders, used to enhance track performance.
• Vehicle Components:
  • Wheels and Hubs: Bear the weight of the train and transmit power, requiring high strength and wear resistance.
  • Braking System: Such as brake shoes, providing friction for deceleration or stopping.
  • Car Body Connectors: Such as drawbar pockets and chassis connectors, requiring resistance to heavy loads and impacts.
• Infrastructure:
  • Support Structures: Such as grillage column bases and brackets, used for foundation pit support or station structures.
  • Other: Such as maintenance equipment parts and pipe fittings.

Cast Iron Parts Machining Process

The machining of cast iron parts for rail transit needs to meet high precision and strict quality requirements. The process flow is as follows:

• Design and Mold Making:
  • According to design drawings (in accordance with the "Railway Track Design Code" GB50090-2006, etc.), make high-precision sand molds or metal molds.
  • Use CAD/CAM software to optimize the casting structure and reduce defects such as shrinkage cavities and porosity.
• Smelting and Casting:
  • Material Smelting: Use a medium-frequency induction furnace to melt gray cast iron or ductile iron, control the carbon equivalent (CE) and spheroidizing agent (such as magnesium) ratio to ensure material performance.
  • Casting Process: Commonly use sand casting (resin sand or coated sand) or static pressure casting (such as the process of Huyong Group) to ensure the surface finish and dimensional accuracy of the castings.
  • Parameter Control:
    • Casting temperature: 1350-1450°C (gray cast iron), 1450-1500°C (ductile iron).
    • Cooling rate: Control the cooling time to optimize the graphite morphology (such as the spheroidization rate of ductile iron ≥90%).
• Machining:
  • CNC Machining: Use CNC machine tools (lathes, milling machines, drills) for precision machining to ensure tolerances (such as CT8 level) and surface roughness (Ra6.3-25μm).
  • Swiss-type Machining: Used for high-precision, small-batch parts, such as pins and fasteners.
  • Surface Treatment: Shot blasting, heat treatment (such as austenitizing or normalizing) to improve wear resistance and strength.