F&D (Flanged and Dished) heads are typically manufactured through a series of forming, machining, and finishing processes tailored to their low-to-moderate pressure application requirements. Below is the standard manufacturing workflow:
1. Material Selection & Cutting: Choose suitable materials (e.g., carbon steel, stainless steel) based on the vessel’s service conditions (pressure, temperature, corrosiveness). Cut the material into a circular blank using plasma cutting, laser cutting, or shearing.
2. Forming the Dish: Shape the circular blank into the "dished" (curved) portion. Common methods include:
Spin Forming: For smaller diameters, the blank is rotated on a lathe while a tool presses it into a curved mold.
Press Forming: For larger diameters, the blank is pressed between a male and female die using a hydraulic press to achieve the desired curve.
3. Forming the Knuckle & Flange: The transition between the dish and the straight flange (called the "knuckle") is formed, followed by the straight flange. This is often done via additional press forming or rolling to create the flat, bolt-ready flange.
4. Trimming & Machining: Excess material is trimmed from the flange edge. The flange surface may be machined (e.g., faced or drilled) to add bolt holes and ensure a tight seal when connected to the vessel shell.
5. Inspection & Finishing: The F&D head is inspected for dimensional accuracy (e.g., curvature, flange flatness), wall thickness uniformity, and surface defects. It may undergo surface treatments like painting, galvanizing, or pickling/passivation (for stainless steel) to resist corrosion.
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