III. Feature Description

A. Midline (Concentric) Design: Low Torque & Uniform Sealing

• Uniform Seat Contact: The disc’s central alignment ensures even pressure distribution across the PTFE seat, eliminating uneven wear and extending seal life by 2–3× compared to offset designs in low-pressure corrosive service.
• Low Operational Torque: Concentric alignment reduces friction between the disc and seat, enabling manual lever operation for DN150 PN10 models—no specialized tools or actuators required for basic on-off control.
• Full-Bore Flow: The central disc position ensures the valve’s bore matches the pipeline diameter, minimizing pressure drop and energy consumption (critical for pumping corrosive fluids, which often have high viscosity).

B. Full PTFE Lining: Universal Chemical Compatibility

• Media Isolation: The lining completely encapsulates the GGG40 body, disc face, and stem (where it contacts fluid), preventing direct exposure to aggressive chemicals. In a seawater desalination plant, this design prevented body corrosion—unlike unlined ductile iron valves, which failed within 12 months.
• Broad Compatibility: PTFE resists all common industrial corrosives, including hydrochloric acid (HCl), sulfuric acid (H₂SO₄), sodium hydroxide (NaOH), chlorine solutions, and hydrocarbons. This eliminates the need for application-specific alloy valves (e.g., Hastelloy), reducing costs by 30–50%.
• Smooth Flow Path: The PTFE lining’s smooth surface (Ra ≤0.8μm) minimizes fluid turbulence and prevents particulate buildup—ideal for slurry or viscous corrosive media (e.g., chemical pigments, mining tailings).

C. 2507 Duplex Steel Disc: Strength & Corrosion Resistance

• High Strength: With tensile strength ≥800MPa, 2507 duplex steel is 2× stronger than 316L stainless steel, enabling it to withstand pressure spikes or fluid hammer in chemical process lines.
• Corrosion Resistance: The alloy’s high chromium (25%) and molybdenum (4%) content resists pitting, crevice corrosion, and stress corrosion cracking in saline media (e.g., seawater) or acidic environments (e.g., pH 1–3). In a coastal wastewater treatment plant, 2507 discs showed no corrosion after 5 years—compared to 316L discs, which required replacement after 18 months.
• Wear Resistance: The disc’s polished surface (Ra ≤0.4μm) reduces friction with the PTFE seat, extending both disc and seal life in high-cycle applications (e.g., batch chemical processing).

D. PTFE Soft Seal: Bubble-Tight Leakage

• ANSI/FCI Class VI Sealing: The soft, elastic PTFE material conforms to minor surface imperfections, achieving near-zero leakage (≤60 mm³/min for DN150 liquid media). This is critical for hazardous corrosive fluids (e.g., toxic solvents) or 洁净 pharmaceutical processes (e.g., sterile drug manufacturing).
• Temperature Stability: PTFE maintains its sealing properties between -20℃ and 120℃, covering most ambient and moderately heated corrosive applications (e.g., heated chemical baths).
• Non-Stick Properties: PTFE’s non-adhesive surface prevents media buildup (e.g., chemical sludge), reducing maintenance frequency and ensuring consistent flow.

IV. Manufacturing Process

A. Material Inspection & Preparation

• GGG40 Ductile Iron Verification: Castings undergo spectral analysis (XRF) to confirm chemical composition (C: 3.2–3.6%, Si: 2.2–2.8%) and ultrasonic testing (UT) to detect internal defects (porosity, cracks). Mechanical testing (tensile, impact) ensures compliance with ASTM A536.
• 2507 Duplex Steel Testing: Disc blanks are tested for chromium, nickel, and molybdenum content (via XRF) and hardness (HRC 28–32) to confirm corrosion and strength properties. Salt spray testing (ASTM B117) verifies resistance to saline corrosion.
• PTFE Lining Validation: PTFE resin is tested for purity (≥99.5% PTFE), tensile strength (≥20MPa), and thermal stability (no degradation at 120℃) to ensure compliance with ASTM D4894.

B. Valve Body Machining & Surface Preparation

• Body Casting & Machining: GGG40 castings are shot-blasted to remove surface scale, then machined via 3-axis CNC centers. Wafer flange faces are precision-machined to ASME B16.5 flatness (≤0.05mm/m) and surface finish (Ra ≤3.2μm) for proper gasket seating. The body’s interior is machined to a uniform diameter to accommodate the PTFE lining.
• Surface Activation for Lining: The body’s interior, disc face, and stem contact areas are grit-blasted (SA 2.5) to create a rough surface (Ra 12.5–25μm). This enhances adhesion between the GGG40 substrate and PTFE lining, preventing delamination under pressure or temperature fluctuations.

C. PTFE Lining Application

• Primer Coating: A fluoropolymer primer (compatible with GGG40 and PTFE) is applied to the blasted surfaces and cured at 80℃ for 1 hour to create a bonding layer.
• PTFE Molding: PTFE resin (in granular form) is loaded into a mold that matches the valve’s interior geometry. The mold is heated to 370–390℃ (PTFE’s melting point) and pressurized to 10–15 MPa to form a seamless lining.
• Sintering & Curing: The lined body is heated to 380℃ in a controlled-atmosphere oven for 4 hours (sintering), then cooled slowly (2℃/minute) to room temperature. This process eliminates internal stresses and ensures the PTFE adheres uniformly to the substrate.
• Finishing: The lined interior is machined to a smooth surface (Ra ≤0.8μm) and inspected for pinholes or delamination using a high-voltage spark test (10kV) to confirm integrity.

D. Disc & Stem Fabrication

• 2507 Disc Processing: 2507 bar stock is cut to size, then turned and milled via CNC lathes to the midline disc profile. The disc’s sealing surface is polished to Ra ≤0.4μm to minimize friction with the PTFE seat. Post-machining, the disc undergoes solution annealing (1050–1100℃, water-quenched) to restore its duplex microstructure and corrosion resistance.
• 316L Stem Manufacturing: 316L bar stock is turned to size, with a keyway machined to connect to the disc. The stem’s fluid-contacting surface is coated with PTFE (via electrostatic spraying) to prevent corrosion, then cured at 200℃ for 1 hour.

E. Assembly & Quality Testing

• Stem & Disc Assembly: The PTFE-coated stem is inserted into the lined body, then the 2507 disc is keyed to the stem. PTFE packing (graphite-impregnated) is installed around the stem to minimize fugitive emissions.
• Seat & Body Finalization: The PTFE seat is pressed into the lined body’s seat pocket, with a preload applied to ensure initial Class VI sealing.
• Hydrostatic Testing (API 598):
  • Shell Test: 1.5× rated pressure (1.5MPa for PN10) for 30 minutes, with no leakage or lining delamination.
  • Seat Test: 1.1× rated pressure (1.1MPa for PN10) for 15 minutes, with leakage measured via bubble counting (≤1 bubble/minute for Class VI).
• Operational Testing: 50 open-close cycles to verify torque consistency (≤80 N·m for DN150 PN10) and smooth disc movement.
• Spark Testing: The PTFE lining is tested with a 10kV spark detector to confirm no pinholes or defects.