Differences between forged flange and cast flange

The difference between forged flange and cast flange

Casting flange is characterized by easy access to other methods not easy to obtain the complex shape of the workpiece; casting flange low cost; can use special technology to obtain precision castings, the surface without processing that has the ideal finish; casting forming simple, cheaper than forging flange; but casting flange defects and non-dense areas easily, in strong corrosion and high pressure occasions domestic technology generally can not guarantee the quality of forgings.

Forged flanges are forged using forging equipment to forge and shape the bar material, generally unable to forge a more complex workpiece, requiring a larger amount of processing, but forged flanges are more dense in structure, not prone to internal defects, so they are widely used in demanding parts processing, such as valve seats, spools, valve stems, etc. In high-pressure and strong corrosion alloy valves, forged valve bodies are also used in large numbers.

Despite the tremendous development in casting technology and the use of computer technology to assist in optimizing the structural design and fluid geometry design of the casting process, it is still extremely difficult to meet the X-Ray/MT or PT quality requirements for Class 1 or 2 acceptance criteria, which are required by the harsh environments within nuclear power plants, thermal power plants or the petrochemical industry. Thus the need for welding improvements arises. However, the overall quality and reliability of the cast valve becomes difficult to guarantee after the weld is made. Sometimes all these problems are left in the cast welded metal frame. Test rods are usually specific to each temperature, but their analysis can be inconclusive. Even if a round test rod indicates that the chemical and physical properties are acceptable, there may still be internal defects within the casting itself that are difficult to detect and detract from its strength or corrosion resistance.
Some other drawbacks inside the cast valve or flange are clear cracks and hot tears that occur during solidification under the combined effects of stress concentrations caused by uneven shrinkage and the low strength of the metal at temperatures near the melting point. Lower casting temperatures can form cold scars, and the accumulation of sand or slag that occurs with molten metal can lead to staining. Low-level casting operations may also cause other defects.
The improvement of the casting to meet the X-ray quality requirements depends on grinding of the defective parts, welding and patching, heat treatment and repeated testing and inspection. Even in this case, the valve seat and gasket faces or butt weld ends may show fine line cracks that need to be re-welded and machined.
The casting process builds a delicate grain structure and improves the physical properties of the metal. In the real world use of the part, a proper design allows for particle flow in the direction of the main pressure.
The forged part needs to be consistent from piece to piece, free of any porosity, excess space, inclusions or other imperfections. This method produces components that have a high ratio of strength to weight. These components are commonly used in aircraft structures.
Advantages of forgings: The advantages of forgings are extendable length, contractable cross-section; contractable length, extendable cross-section; changeable length, changeable cross-section. The types of forgings are: free forging/hand forging, hot die forging/precision forging, top forging, roll forging and die forging.
Casting flange and forging flange are commonly used flange, these two flanges are different in price, casting out of the flange, the rough shape and size of accurate, small processing, low cost, but there are casting defects (porosity. Cracks. Inclusions); casting internal organization of poor streamline (if the cutting parts, streamline worse); forging flange generally lower carbon than casting flange is not easy to rust, forging streamline good, dense organization, mechanical properties better than casting flange; improper forging process will also appear grain size or uneven, hardening cracking phenomenon, forging costs higher than casting flange. Forgings than castings can withstand higher shear and tensile forces. The advantage of casting is that you can make a more complex shape, the cost is relatively low; forgings advantage is that the internal organization is uniform, there is no casting in the porosity, inclusions and other harmful defects; from the production process to distinguish between casting flange and forging flange is different, such as centrifugal flange is a kind of casting flange. Centrifugal flange belongs to the precision casting method of flange production, the casting than ordinary sand casting organization is much finer, the quality is improved a lot, not easy to appear tissue loosening, porosity, trachoma and other problems.
First of all, we need to understand how the centrifugal flange is produced, centrifugal casting to make flat welding flange process methods and products, which is characterized by the product after the following process steps processed from.

• ① The selected raw material steel into the medium frequency electric furnace melting, so that the temperature of the steel to 1600-1700 ℃.
• ② Pre-heating the metal mold to 800-900°C to maintain a constant temperature.
• ③ Start the centrifuge and inject the steel in step ① into the preheated metal mold in step ②.
• ④ Castings are naturally cooled to 800-900°C keeping 1-10 minutes.
• ⑤ Cool down to near room temperature with water, take off the mold and take out the casting.

Let’s understand the production process of forging flanges again: the forging process is generally composed of the following processes, namely, selecting high-quality billets for undercutting, heating, forming, and cooling after forging. The forging process methods are free forging, die forging and tire film forging. Production, according to the size of the forging quality, the number of production batch to choose different forging methods. Free forging productivity is low, processing allowance is large, but the tool is simple, versatility, so it is widely used to forge the shape of a simple single piece, small batch production of forgings. Free forging equipment includes air hammer, steam-air hammer and hydraulic press, which are suitable for the production of small, medium and large forgings respectively. Die forging productivity is high, simple operation, easy to achieve mechanization and automation. Die forging parts with high dimensional accuracy, small machining allowance, more reasonable fiber tissue distribution of forgings, can further improve the service life of the parts.
First, the basic process of free forging: free forging, the shape of the forgings is gradually forged into the billet through some basic deformation process. The basic processes of free forging are upsetting, drawing, punching, bending and cutting, etc.

• 1. Heading is the process of forging the original billet in the axial direction to reduce its height and increase its cross section. This process is often used to forge gear billets and other disc-shaped forgings. Upsetting is divided into two types: full upsetting and partial forging.
• 2. Drawing is a forging process that increases the length and decreases the cross-section of a billet, and is usually used to produce shaft blanks such as lathe spindles and connecting rods.
• 3. Punching: The forging process of using a punch to punch through holes or not through holes in a billet.
• 4. Bending: The forging process of bending a billet into a certain angle or shape.
• 5. Twisting: A forging process in which one part of a billet is rotated at an angle with respect to another part.
• 6. Cutting: The forging process of cutting a billet or removing the head.

Second, die forging; die forging is called model forging, where the heated billet is placed in the forging die fixed on the die forging equipment to forge the shape.

• 1. The basic process of die forging die forging process: under the material, heating, pre-forging, final forging, punching even skin, cutting edge, tempering, shot blasting. Commonly used processes are upsetting, drawing, bending, punching, forming.
• 2. Commonly used die forging equipment Commonly used die forging equipment are die forging hammer, hot die forging press, flat forging machine and friction press, etc.

Why choose forgings? Compared with castings, forged valve bodies have a more uniform structure, better density, better strength integrity, better dimensional characteristics, and smaller dimensional errors. Directional construction (piping) has higher performance than castings throughout in terms of strength and stress.
(1) High Strength
Hot forging promotes in-crystallization and grain refinement, allowing the material to achieve maximum possible strength and consistency with minimal piece-to-piece variation. Particle flow is precise along the contours of the valve body, and these continuous flow lines help to reduce the incidence of fatigue or common failures.
(2) Reliability
The ability to meet the structural requirements of the design forgings has always been one of the most important advantages of forgings, to some extent at the top of the above characteristics.
(3) Structural Integrity
Forging eliminates internal defects and produces a consistent metallographic organization, ensuring excellent performance. Where stress and intracrystalline corrosion are serious problems, forgings are able to guarantee long service life and trouble-free service.
(4) Consistency
The dimensional consistency of closed-die forging results in complete control of critical wall thicknesses, avoiding defects caused by core shifts in the casting process, and ensuring a consistent metallographic structure free of internal defects through high quality, non-separated ingots and the impact of 10,000 to 30,000 ton presses.

Quality Assurance of Forgings

For finished forgings, the entire requirement of the ASME standard is ultrasonic testing (U.T.), magnetic particle (M.T.) or liquid penetrant testing (P.T.). Scrap forgings found by U.T., M.T., or P.T. methods are very rare. Parts are procured with controlled lead times, so delivery of valves is more reliable. Comparison of the directional configuration of forged flanges and cast flanges have a creep fatigue resistance more than three times higher than castings in environments with large temperature variations.

Source: China Flange Forgings 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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