Detailed Explanation of Forged Flange Production Process

Forged flanges are flange components produced through a forging process. Compared to cast flanges, they have advantages such as low carbon content, resistance to rust, dense structure, and superior mechanical properties, but the cost is higher. The forging process ensures that the internal structure of the flange is uniform and free of defects such as pores or inclusions, making it suitable for high-pressure and high-strength applications. The production process generally includes stages such as raw material preparation, heating, forging, heat treatment, machining, and inspection. Depending on the size, batch size, and precision requirements of the flange, methods such as free forging, die forging, or mandrel forging can be used. The following is a detailed description of the process flow, based on industry standards and typical production practices.

1. Raw Material Receiving and Inspection

Step Description: First, raw materials (such as stainless steel, carbon steel, or alloy steel bars, plates, or billets) are received at the factory. The materials must comply with national standards (such as GB/T 9112-2010, etc.).

Key Operations: Perform chemical composition analysis, mechanical property testing, and visual inspection to ensure there are no defects such as cracks or inclusions. Store in the warehouse after passing inspection.

Purpose: To ensure material quality and avoid subsequent defects.

2. Blanking (Cutting)

Step Description: According to the flange design specifications (such as diameter and thickness), use sawing, shearing, or plasma cutting to cut the raw materials into the required blanks.

Key Operations: Consider forging allowance (usually 5-10mm) during cutting to compensate for forging shrinkage and machining losses. For large flanges, plate cutting or bar cutting may be used.

Purpose: To prepare blank sizes suitable for heating and forging.

3. Heating

Step Description: Place the cut blanks into a heating furnace and heat to the forging temperature (usually 950-1250℃ for carbon steel, 800-1100℃ for stainless steel, depending on the material).

Key Operations: Use a medium-frequency furnace or gas furnace for heating, ensuring uniform heating to avoid overheating or decarburization. The heating time depends on the size of the blank.

Purpose: To soften the material and increase plasticity, facilitating subsequent forming.

4. Forging

Step Description: Place the heated blank on a forging machine for deformation. This is the core stage, divided into free forging, die forging, etc., depending on the method.

Free Forging: Suitable for small-batch, multi-variety flanges. Basic processes include:

Upsetting: Compress the blank axially to reduce height and increase cross-section, used for disc-shaped flanges.

Drawing Out: Extend the length of the blank and reduce the cross-section, used for shaft-like parts.

Punching: Use a punch to create through holes or blind holes to form the flange center hole.

Bending: Bend the blank to a specified angle.

Twisting: Rotate part of the blank to form a specific shape.

Cutting: Remove excess material.

Die Forging: Suitable for large-batch, high-precision flanges. Forge the blank in a mold, including pre-forging, final forging, flash removal, and trimming. Equipment such as die forging hammers and hot die forging presses.

Mandrel Forging: Between free forging and die forging, using simple molds for assistance.

Key Operations: Control temperature, deformation, and hammering force during forging to avoid coarse grains or cracks. For large flange rings, processing may be segmented: precise bending, end removal, weld beveling, and welding into a circle.

Purpose: To form the flange blank and ensure a dense internal structure.

5. Post-Forging Cooling and Heat Treatment

Step Description: Cool immediately after forging (air cooling, water cooling, or oil cooling), and then perform heat treatment such as normalizing, annealing, quenching and tempering.

Key Operations: Control the cooling rate to prevent cracking. Adjust heat treatment temperature and time according to the material (e.g., carbon steel normalizing at 850-900℃).

Purpose: To improve mechanical properties, eliminate internal stress, and refine grain size.

6. Machining

Step Description: Send the forged blank to the machining workshop and use lathes, milling machines, and other equipment to precisely machine the shape, plane, and sealing surface.

Key Operations: Machining tolerances comply with standards (such as ANSI B16.5), surface roughness Ra1.6-6.3μm.

Purpose: To achieve precise dimensions and finish.

7. Drilling

Step Description: Drill mounting holes (such as bolt holes) on the flange using drilling machines or CNC machine tools.

Key Operations: High hole position accuracy, hole diameter and spacing comply with design drawings.

Purpose: To facilitate flange connection.

8. Inspection and Non-Destructive Testing

Step Description: Perform dimensional measurements, hardness testing, ultrasonic testing (UT), magnetic particle testing (MT), or radiographic testing (RT).

Key Operations: Check for internal defects and surface cracks to ensure compliance with national standards.

Purpose: To ensure product quality, with a typical pass rate requirement of over 99%.

9. Marking and Packaging

Step Description: Use steel stamps to mark specifications, materials, batch numbers, and other information, then brush with anti-rust paint and package (wooden boxes or pallets).

Key Operations: Clear marking, moisture-proof and impact-resistant packaging.

Purpose: To facilitate traceability and transportation.

Notes and Variations

Specific Process for Welding Neck Flanges: First, longitudinally forge to increase the cross-section, then draw out to increase the length, and finally vertically punch holes.

Large Flange Rings: Due to the large size, they may be bent and welded in segments.

Comparison with Other Flange Types: Forged flanges have higher strength than cast flanges (which are prone to porosity), but are less flexible than welded flanges. Pay attention to safety and environmental protection during production, such as exhaust gas treatment.

Equipment Examples: Forging hammers, heating furnaces, CNC lathes, flaw detectors, etc.

The entire process cycle depends on the scale, ranging from a few days for small batches to several weeks for large batches. In actual production, parameters can be adjusted according to specific standards (such as national standards, American standards).