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Process Flow

Process Flow

Flange forging is a process in which a metal billet is heated and subjected to compressive forces to induce plastic deformation, thereby achieving the desired shape, dimensions, and mechanical properties. The core process involves Raw material preparation → Heating → Forging → Heat treatment → Machining → Inspection and packaging , suitable for high-pressure, high-temperature, and high-seal-purity pipeline connection applications.
 

I. Raw Material Preparation and Inspection

 
  1. Material Selection
    • Carbon steel: A105, 20#, Q235; suitable for medium- and low-pressure, ambient-temperature applications.
    • Alloy steels: F11, F22, and 16Mn, suitable for high-temperature and high-pressure applications.
    • Stainless steels: 304, 316, and 321, suitable for applications involving corrosive media.
  2. Cutting the material
    • Use a band saw, flame cutting, or plasma cutting to cut bar stock or steel ingots into fixed-length billets, leaving a 10%–15% allowance. Machining allowance and weight deviation shall be controlled within Within ±1%**.
  3. Reinspection
    • Chemical composition analysis, mechanical property testing, and spectroscopic inspection confirm that the material complies with GB, ANSI, and ASME standards.
 

II. Heating

 
  • Equipment: gas chamber furnace, medium-frequency induction furnace, electric furnace.
  • Temperature: Carbon Steel 1100-1200℃ , stainless steel / alloy steel 1150-1250℃ , strictly control temperature to prevent overheating and burnout.
  • Objective: To enhance ductility, reduce deformation resistance, and remove a portion of the surface oxide scale.
 

III. Forging and Forming (Core Process)

 

1. Free Forging (Small Batch, Large Size)

 
  • Process steps: upsetting → drawing out → punching → reaming → shaping.
  • Equipment: air hammer, hydraulic press.
  • Applicable to: non-standard and extra-large flanges (e.g., DN2000 and above).
 

2. Forging / Die Forging (High Volume, High Precision)

 
  • Pre-forging: preliminary shaping, metal distribution, and scale removal.
  • Final forging: precise forming of the flange, neck, and boss.
  • Trimming / Punching: Remove flash and sprue, and form the central hole.
  • Ring rolling (ring forging): Specifically for ring-shaped flanges, it achieves hole expansion and shaping, resulting in a uniform microstructure and material savings.
 

3. Key Controls

 
  • Forging ratio ≥ 3: refines grain structure and eliminates porosity and segregation.
  • Initial forging / final forging temperature: final forging shall not be lower than 800°C , crack-resistant.
 

IV. Heat Treatment

 
  • Normalizing/Annealing: Relieve residual stresses, homogenize the microstructure, and improve machinability (commonly used for carbon steels).
  • Quenching and tempering: enhances strength, hardness, and toughness (for high-pressure flanges).
  • Solution treatment + aging: prevents intergranular corrosion in stainless steel and stabilizes the microstructure.
  • Objective: To stabilize dimensions and ensure mechanical properties (HB 160–220).
 

V. Machining

 
  1. Turning : External diameter, internal bore, sealing surfaces (RF/FF/MFM/TG), shoulder, and chamfer.
  2. Drilling : Drilling machine / machining center for drilling bolt holes, ensuring hole position accuracy.
  3. Fine processing : Polishing/honing of the sealing surface to ensure a surface roughness of Ra ≤ 3.2 μm.
 

VI. Inspection and Surface Treatment

 
  1. Inspection
    • Dimensions: calipers, three-coordinate measuring machine, and templates.
    • Performance: hardness, tensile strength, impact resistance.
    • Non-destructive testing: UT (internal), MT/PT (surface cracks), hydrostatic test.
  2. Surface Treatment
    • Carbon steel: rust-preventive paint, blackening, galvanizing.
    • Stainless steel: pickling, passivation, polishing.
  3. Labeling and Packaging
    • Stamping: material, pressure, specifications, batch number, and standard.
    • Packaging: Rust-preventive oil + wooden crate/pallet.
 

VII. Finished Goods Receipt

 
  • Qualified finished products shall be stored separately by category and accompanied by certificates of quality assurance (material, heat treatment, non-destructive testing, and hydrostatic pressure test reports).
 

Process Comparison

 
  • Free forging : Flexible, low cost, low efficiency, and large margin.
  • Forging : High efficiency, high precision, dense microstructure, and suitable for mass production.
  • Ring rolling : Optimal for ring-shaped components, with continuous flow lines, material savings, and high strength.