A New Forging Process for Large Hollow Flange

The use of core rod elongation to forge large hollow flanges has successfully solved the problem of unqualified ultrasonic testing of flange forgings, effectively ensuring the internal quality of the forgings.

The size of flange forgings for a large hydroelectric unit is shown in Figure 1, with a forging weight of 64t. This flange has a larger size and the ultrasonic testing standard for forgings is equivalent to EN10228-3 quality level 3, far exceeding the requirements of the standard JB/T1270-2002 for conventional hydropower. The conventional forging process involves upsetting the flange part I inside the mold. Still, it is prone to forming flaky or dense defects inside the forging, resulting in ultrasonic testing exceeding the standard. The excessive defects are mainly concentrated in the middle of the flange height in Part I and the 1/3 wall thickness in the direction of the inner wall diameter, as shown in Figure 1.

Figure.1 Schematic diagram of flange forging dimensions and excessive defects

The new process of forging large hollow flanges using core rod elongation has successfully solved the problem of ultrasonic testing exceeding the standard for large hollow flange forgings.

1. Problems with traditional forging processes for large hollow flanges

The traditional forging process is shown in Figure 2. During the forging process, the third heat is mainly formed by upsetting the mold to form the flange part I. This process is prone to producing similar layered defects, resulting in unqualified ultrasonic testing.

Fire frequency	Working Procedure	Schematic diagram of deformation process	Using tools
I	Press The Jaw		Upper flat and lower V-shaped anvil
II	1. Upsetting		Upsetting plate
	2. Elongation		Upper flat and lower V-shaped anvil
	3. Blanking		Gas cutting machine
III	1. Pre upsetting		Upset plate
	2. Mold forming		Mould
	3. Expanding holes		Hollow punch
IV	1. Enlarge the hole		Enlarged hole horse rack
	2. Repair		Expanding core rod

Figure.2 Schematic diagram of the traditional forging process for forging hollow flanges

Fire frequency	Working Procedure	Schematic diagram of deformation process	Using tools
I	1． Press The Jaw		Upper flat and lower V-shaped anvil
II	1. Upsetting		Upsetting plate
	2. Elongation		Upper flat and lower V-shaped anvil
	3. Blanking		Gas cutting machine
III	1. Upsetting		Upper and lower spherical upsetting plates
	2. Punching		Hollow punch
IV	1. Elongation		Upper flat and lower V-shaped anvil
	2. Material distribution		Expanded core rod
	3. Extract Part II		Chopping machine
	4. Trimming		Gas cutting machine
	5. Gas cut into 2 pieces

Figure.3 Schematic diagram of the new process

2. Forging Process for Large Hollow Flange

To solve the problem of difficulty in passing ultrasonic testing of large flange forgings, we have adopted a new process of drawing and forging hollow flanges with core rods, as shown in Figure 3. The key to the new process is to use a core rod to elongate the formed flange, avoiding the stress state that conventional forging methods mainly use upsetting to deform the formed flange and effectively avoiding the generation of layered defects. Practice and theory have proven that when the height to diameter ratio of forgings is less than 1, there exists a hydrostatic pressure zone and a shear stress zone during upsetting. According to theoretical analysis, transverse cracks are prone to initiate in the shear stress zone, resulting in layered defects and a low qualification rate for non-destructive testing of cake forgings.

3. Discussion

When forging such flanges using traditional techniques, the first part is mainly formed by upsetting in the mold, which has a shear stress zone and is prone to producing layered defects, leading to unqualified ultrasonic testing. The improved new process uses the method of core rod elongation to forge hollow flanges, which avoids this problem.

Due to the short length of flange II, if the II parts are directly divided, the length of the material will be too short, and serious concave centers will appear on the end face when drawing the II parts, making it difficult to ensure the size of the II-part forging. In order to ensure the forging conditions of Part II or meet the material splitting length of Part II, the new process generally adopts the process mode of forging two flanges from one steel ingot. By connecting two II parts, the material separation length of Part II is met. If there is only a single flange in production, Part II can also be connected to a cylinder with the same inner and outer diameter to meet the material separation length of Part II.

4. Conclusion

• (1) The new process uses the method of core rod elongation to forge hollow flanges, successfully solving the problem of difficult ultrasonic testing for large hollow flange forgings and effectively ensuring the internal quality of the forgings.
• (2) The new process does not require specialized molds for forging flange forgings, saving the cost of raw materials.

Author: Meng Xiangli, Zhao Xin

Source: China Forged Flanges Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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