Flange Manufacturing Process | Forged & Cast Flanges Guide

A flange connection involves first securing two pipelines, pipe fittings, or equipment components to separate flange discs; then, a flange gasket is placed between the two flange discs, and the assembly is fastened together with bolts to complete the connection. Some pipe fittings and equipment components already incorporate integrated flange discs, which also constitute a flange connection. Flange connections are a critical method of connection in pipeline construction; they are easy to install and capable of withstanding high pressures. In industrial piping systems, where pipe diameters are small and operating pressures are low, flange connections may not be readily apparent; however, in boiler rooms or production facilities, flange-connected pipelines and equipment are ubiquitous.

1. Based on the connection method, flange connections can be classified into the following types: plate-type flat-weld flanges, flanges with necks, butt-weld flanges with necks, socket-weld flanges, threaded flanges, flange covers, flanges with necks and loose-welded rings, flat-weld rings with loose sleeves, ring-slot flanges with flange covers, large-diameter flat flanges, large-diameter high-neck flanges, T-shaped blind plates, and butt-weld flanges with loose rings, among others.

2. According to chemical industry standards (HG), flange types include: integral flanges (IF), threaded flanges (Th), plate-type flat-weld flanges (PL), flanges with necks (WN), flanges with necks and flat welds (SO), socket-weld flanges (SW), butt-weld flanges with loose rings (PJ/SE), flat-weld flanges with loose rings (PJ/RJ), lined flange covers (BL(S)), and flange covers (BL).

3. According to petrochemical industry standards (SH), flange types include: threaded flanges (PT), butt-weld flanges (WN), flat-weld flanges (SO), socket-weld flanges (SW), loose-welded flanges (LJ), and flange covers (no specific notation provided).

4. Classification according to mechanical (JB) industry standards: integral flange, butt-welded flange, plate-type flat-welded flange, butt-welded ring-plate loose-fitting flange, flat-welded ring-plate loose-fitting flange, flanged ring-plate loose-fitting flange, flange cover.

5. Classification according to national (GB) standards: integral flange, threaded flange, butt-welded flange, flange with neck for flat welding, flange with neck for socket welding, butt-welded ring-plate loose-fitting flange with neck, plate-type flat-welded flange, butt-welded ring-plate loose-fitting flange, flat-welded ring-plate loose-fitting flange, flanged ring-plate loose-fitting flange, flange cover.

Production Processes: The production processes are primarily categorized into four types:

forging, casting, cutting, and rolling.

(1) Casting and Forging Flanges: Cast flanges feature accurately shaped and dimensioned blanks, require minimal machining, and offer lower production costs; however, they may exhibit casting defects (e.g., porosity, cracks, inclusions). Additionally, castings often exhibit inferior grain flow structures (this is even more pronounced in machined components). Forged flanges generally contain lower carbon content than cast flanges, making them less prone to rust. Forged parts also demonstrate superior grain flow structures, a denser microstructure, and better mechanical properties compared to cast flanges. However, improper forging processes can lead to coarse or uneven grain structures, hardening, and cracking; furthermore, the cost of forging is higher than that of casting. Castings can withstand higher shear and tensile loads than forged parts. The advantage of castings is their capability to produce complex geometries at relatively low costs, whereas the advantage of forged parts lies in their uniform internal microstructure and the absence of detrimental defects such as porosity and inclusions. Examples of differences between casting and forging processes include the use of centrifugal casting for certain flange types.

Centrifugal flanges are manufactured using a precision casting process. Compared to conventional sand casting, this casting method yields a significantly finer microstructure, resulting in markedly improved quality and reduced susceptibility to defects such as porosity, gas pores, and sand inclusions. To understand this process, it is essential to first comprehend how centrifugal flanges are produced—specifically, the manufacturing methodology and resulting products for flat-weld flanges via centrifugal casting.

The manufacturing process consists of the following steps:

① Melting the selected raw steel material in a medium-frequency electric furnace until the steel temperature reaches 1600–1700 °C;

② Preheating the metal mold to 800–900 °C and maintaining this constant temperature;

③ Activating the centrifuge to inject the molten steel from step into the preheated metal mold from step ②;

④ Allowing the casting to cool naturally to 800–900 °C and holding it for 1–10 min;

⑤ Cooling the casting with water until it approaches room temperature, then removing the casting from the mold.

Let us now examine the production process flow for forged flanges:

the forging process typically consists of the following stages—selection of high-quality steel billets, cutting, heating, forming, and post-forging cooling. The primary forging methods include free forging, die forging, and pattern forging. During production, the appropriate forging method is selected based on the required quality of the forged part and the production batch size. Free forging offers low production rates but allows for larger machining allowances; however, it utilizes simple tools and possesses high versatility, making it widely adopted for forging parts with simple geometries in single-piece or small-batch production scenarios. Equipment for free forging includes air hammers, steam-air hammers, and hydraulic presses, each suited for the production of small, medium, and large forged parts, respectively. Die forging, on the other hand, delivers high production rates, features simple operation, and facilitates easy mechanization and automation. Die-forged parts exhibit high dimensional precision, require smaller machining allowances, and exhibit a more optimized grain structure distribution, thereby further enhancing the service life of the components.

Basic operations in free forging:

In free forging, the shape of the workpiece is progressively formed from the blank through a series of fundamental deformation operations. The basic operations in free forging include upsetting, drawing, punching, bending, and cutting.

1. Upsetting: Upsetting is an operation in which the original blank is forged along the axial direction to reduce its height and increase its cross-sectional area. This operation is commonly used in the forging of gear blanks and other disc-shaped workpieces. Upsetting can be classified as full upsetting or partial upsetting.

2. Drawing: Drawing is a forging operation that increases the length of the blank while reducing its cross-sectional area; it is typically employed to produce shaft blanks, such as lathe spindles and connecting rods.

3. Punching: Punching is a forging operation in which a punch is used to create through holes or blind holes in the blank.

4. Bending: Bending is a forging operation that bends the blank to a specific angle or shape.

5. Torsion: Torsion is a forging operation in which a portion of the blank is rotated relative to another portion by a certain angle.

6. Cutting: Cutting is a forging operation used to segment the blank or remove the end piece.

(1)Die forging:

formally known as model forging, involves placing a heated blank into a forging die fixed to a die forging machine to shape it.

1. Basic Processes of Die Forging The die forging process consists of: blanking, heating, pre-forging, final forging, blank punching, edge trimming, tempering, and shot peening. Common process operations include rough upsetting, elongation, bending, punching, and forming.

2. Common Die Forging Equipment Commonly used die forging equipment includes die hammers, hot die forging presses, flat forging machines, and friction presses. In simple terms, forged flanges offer superior quality; they are typically produced via die forging, resulting in a fine-grained crystal structure, high strength, and, of course, a higher manufacturing cost. Both cast and forged flanges are common manufacturing methods for flanges; the choice depends on the strength requirements of the component. If the strength requirements are not stringent, machine-cut flanges may also be selected.

(3) Cut-flange Production In this method, a disk—containing the inner and outer diameters and the required thickness for further machining—is directly cut from a center plate; subsequent machining then includes the creation of bolt holes and water lines. Flanges produced in this manner are termed "cut-flanges," and their maximum diameter is limited by the width of the center plate.

(4) Rolled-flange Production The process of cutting strips from a center plate and rolling them into a circular shape is called "rolling," which is predominantly used in the production of large flanges. After rolling, the flanges are welded, flattened, and then subjected to the machining of water lines and bolt holes. Application Scope: Due to their excellent overall performance, flanges are widely utilized in various fundamental engineering applications, including chemical processing, construction, water supply and drainage systems, petroleum industry, light and heavy industries, refrigeration, sanitary facilities, plumbing, fire protection, electric power, aerospace, and shipbuilding.

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Introduction to the Manufacturing of Various Flanges