How to get high quality forged flanges?

What is a forged flange?

The mechanical properties of forged flange is a flange in the product the best products, its raw materials are generally billet, then after cutting and then continue to beat, to eliminate the ingot segregation, porosity and other defects. Both the price and the mechanical properties are one grade higher than the common cast flange. Flanges are parts that connect pipes to pipes and valves. They are connected to the ends of pipes. They are also used for flanges on the inlet and outlet of equipment. The connection between two devices is a part that connects the pipes to pipes and is connected to the ends of pipes. It is a subsidiary accessory product of the pipe. Forged flanges are mainly made of carbon steel, alloy steel, and stainless steel. The main standard of GB, American Standard, German standard, Japanese standard etc.. The main anticorrosive treatment is oiling and galvanizing. The forged steel flange has good pressure resistance, good temperature resistance, and is generally suitable for high pressure and high temperature working environment.

asme b16 5 a182 f316l wnrf flange 1 12 inch sch40s pn16 - How to get high quality forged flanges?

Production process

The production process is mainly divided into two kinds: forging and casting.

Production process of cast flanges

First of all we need to know how the production of centrifugal flange, centrifugal casting process for making flange and products, which is characterized in that the products through the following process steps and processing:
The selected raw material steel is melted in medium frequency electric furnace to make the temperature of molten steel reach 1600-1700.
The metal mold pre heated to 800-900 DEG C remain constant;
Starting the centrifuge, the step 1 of the steel water is injected into the step 2, the metal mold is preheated.
The casting of natural cooling to 800-900 DEG C for 1-10 minutes;
The water is cooled to near the normal temperature, and the casting is removed.

Production process of the forged flanges

The forging process is usually made up of the following procedures, that is, to select high quality billet blanking, heating, forming, and forging after cooling. The forging process includes free forging, die forging and fetal membrane forging. In production, different forging methods are selected according to the quality of the forgings and the number of production batches.
Free forging has many advantages such as low productivity, large machining allowance, but simple tool and versatility. So it is widely used for forging single piece and small batch forgings with simpler shape. Free forging equipment has air hammer, steam air hammer and hydraulic press and so on. It is suitable for small, large and large forgings. The die forging has high productivity, simple operation, and easy to realize mechanization and automation. The dimension precision of the die forgings is high, the machining allowance is small, and the distribution of the forgings is more reasonable, which can further improve the service life of the parts.

One. Free forging

Basic process: when free forging, the shape of the forgings is gradually forged by some basic deformation processes. The basic working procedures of free forging are upsetting, drawing long, punching, bending and cutting.

  • 1. upsetting and upsetting is the operation process that the original blank is forged along the axial direction, so that the height of the upsetting is reduced and the cross section increases. This process is often used for forging gear billets and other disc shaped forgings. The upsetting is divided into two kinds of upsetting and local forgings.
  • 2. drawing length is the forging process that makes the length of the blank increase and the cross section decreases. It is usually used to produce shaft parts, such as the spindle of the lathe and the connecting rod.
  • 3. punching punch forging processes out through holes or blind holes in the blank.
  • 4. a forging process that bending the blank to a certain angle or shape.
  • 5. a forging process that turns a part of the blank to a certain angle relative to the other.
  • 6. cutting head segmentation or the removal of blank forging process.

Two. Die forging

The die forging is called the model forging, and the heated blank is placed in the forging die fixed on the forging equipment.

  • 1. die forging: blanking, heating, preforging, finishing, flushing, cutting, tempering and shot peening. The common processes are upsetting, pulling, bending, punching and forming.
  • 2. common forging equipment commonly used equipment, forging die forging hot forging press, forging and friction press etc..

Generally speaking, the quality of forged flanges is better. Generally, it is produced by forging. The crystal structure is fine and the strength is high. Of course, the price is also expensive.
Whether casting flange or forged flange is a common manufacturing method of flange, see the strength requirement of components needed, if request is not high, you can also choose turning flange.

Three. Cut flanges

The plate is cut out of the flange directly on the medium plate with the internal and external diameter and thickness of the processing quantity, and then the bolt hole and the water line are processed. The flanges produced in this way are called cut flanges. The maximum diameter of such flanges is limited to the width of the medium plate.

Four. Coil flanges

The process of cutting a strip with a medium plate and then making a circle is called a roll, which is used for the production of some large flanges. After the success of the roll system, it is welded, then pressed, and then the process of water line and bolt hole.

Comparison of cast flanges and forged flanges

The shape and size of the casting blank flange accurately, small processing quantity and low cost, but the casting defects (pores. Cracks. Inclusion of casting structure); streamlined poor (if it is cut, streamlined worse) than the general casting flange forged flange; low carbon is not easy to rust, forging streamlined dense tissue. The mechanical properties, superior casting flange; forging process will also appear improper or uneven grain, grain hardening phenomenon, the cost is higher than the casting forged flange. The forgings can bear higher shear and tensile forces than the castings. The advantages of casting could have complicated shape, the cost is relatively low; forging has the advantages of uniform internal organization, there is no porosity in castings, inclusions and other harmful defects; from the production process of casting and forged flange flange between different, such as a centrifugal casting flange to flange. The centrifugal flange is a flange produced by precision casting. The casting is much thinner than the ordinary sand casting, and the quality is improved a lot. It is not easy to get loose porosity, trachoma and so on.

The characteristics of casting flange is easy to obtain the workpiece other methods is not easy to obtain complicated shape; casting flange low cost can be obtained; precision casting flange with special process, the surface without processing has ideal finish; casting steel flange forming is simple, the price is cheaper than the forged flange; but casting flange prone to defects and non dense area, ensure the quality of forged flange in strong corrosion and high pressure situations of domestic technology cannot in general.
Forged flanges are forged and shaped by forging equipment. They are generally unable to forge more complicated workpieces, requiring larger processing capacity. But the forged flange has dense structure and is not easy to appear internal defects.
Although the casting technology has made tremendous development, and the use of computer aided geometric design of fluid structure optimization design and casting process, but to achieve the 1 class or 2 class X ray /MT or PT quality acceptance standard is still extremely difficult, which are nuclear power plants, thermal power stations or in petrochemical industries the harsh environment of the required standard. Therefore, it is necessary to improve the welding. However, after welding, the overall quality and reliability of the cast flange becomes difficult to guarantee.
Some other defects in the casting flange are clear cracks and thermal tears during the solidification process due to the stress concentration caused by uneven shrinkage and the low strength of metals near melting point temperature. Low casting temperatures can cause cold scars, and the accumulation of sand grains or slag from molten metals will lead to stains. Low grade casting may also cause other defects.
The improvement of the cast flange to meet the requirements of X ray quality depends on the grinding, repair, heat treatment and repeated testing and testing of the defective parts. Even in this case, the flange seat and washer face or bump welding end may display fine line cracks that require heavy welding and machining.
The casting flange process built a fine particle structure and improved the physical properties of the metal. In the practical use of parts, a correct design can make the particle flow in the direction of the main pressure.

The flange produced by casting is accurate in shape and size, small in processing volume and low in cost, but with casting defects (pores, cracks, inclusions). The internal flow pattern of the casting is poor (if the cutting parts are of poor streamline type).
Forged steel flanges are generally less rust than cast steel flanges with low carbon content. Forging parts are streamlined, microstructure is more compact and mechanical properties are better than cast flanges.
If the forging process is unsuitable, there will be large or uneven grain, hardened cracks, and the cost of forging is higher than that of the cast flange.
The forgings can bear higher shear and tensile forces than the castings.
The advantage of the casting is that it can make a more complex shape, and the cost is low.
The advantages of the forgings are that the internal organization is uniform, and there are no harmful defects such as the pores and inclusions in the castings.
The difference between the casting flanges and the forged flanges is distinguished from the production process, such as the centrifugal flange is one of the cast flanges.
The centrifugal flange is a flange produced by precision casting. The casting is much thinner than the ordinary sand casting, and the quality is improved a lot. It is not easy to get loose porosity, trachoma and so on.

The advantages of forged flanges:

Forged flanges are less prone to rusting than the low carbon content of cast flanges. Forged flanges have a good streamline shape, a denser structure, and better mechanical properties than casting flanges. Improper forging processes can also result in large or uneven grain sizes and hard cracking. Forged flanges cost more than foundry flanges. Forged flanges can withstand higher shear and tensile forces than cast flanges. The advantage of the cast flange is that it can come up with a more complex shape, the cost is relatively low; the advantage of the forged flange is that the internal organization is uniform, there are no harmful defects such as pores, inclusions in the casting.

Why do you choose forged flanges? 

Compared with cast flange, forged flange has more uniform structure, better density, better strength integrity, better dimensional characteristics and smaller size error. The directional structure (pipeline) has a higher performance than the cast flange in the whole strength and stress.
(1) High strength
Hot forging promotes crystallization and grain refinement, allowing the material to achieve maximum possible strength and consistency, and the minimum variation between parts and parts. The flow of the particle flow is precisely along the body profile, and these continuous streamlines help to reduce the incidence of fatigue or common failures.
(2) Reliability
Forged flanges that meet the requirements of the design structure have always been one of the most important advantages of forged flanges, to some extent at the top of the above characteristics.
(3) Structural integrity
Forging eliminates internal defects and produces a coherent and consistent metallographic organization that ensures excellent performance. In places where stress and internal corrosion are serious, forged flanges can guarantee long service life and failure free service.
(4) Consistency
The dimensional consistency of closed die forging results in the complete control of the key wall thickness, avoiding the defects caused by the shifting of the core in the casting process. Through the impact of high quality, no separation steel ingot and 10 thousand to 30 thousand ton presses, it ensures the consistent metallographic structure without internal defects.

How to get high quality forged flanges?

When the temperature exceeds 300-400°C (blue brittle zone of steel) and reaches 700-800°C, the deformation shift will change sharply and the deformation energy will be greatly improved. According to the forging in different temperature regions, according to the different forged flange quality and forging process requirements, it can be divided into three forming temperature regions: cold forging, warm forging and hot forging. The original temperature range is divided into strict limits. Generally speaking, when forging at low temperature in the temperature region with recrystallization, the size of the forged flange changes little. Forging below 700°C, there is little oxide scale formation and no decarburization on the surface. Therefore, as long as the temperature and lubrication cooling are well controlled, the warm forging below 700°C can also have good accuracy. During hot forging, to obtain forged flanges with high dimensional accuracy, hot forging can be used in the temperature range of 900-1000°C. In addition, pay attention to improving the working environment of hot forging. Forging die life (hot forging 2-5 thousand, warm forging 10,000 to 20,000, cold forging 20,000 to 50,000) is replaced with forging labels in other temperature ranges, but it has a large degree of freedom and the blank is cold forged Deformation and work hardening are required to cause the forging die to withstand high deformation. Therefore, it is necessary to use a high-strength forging die and use a hard lubricating film treatment method for wear and use. In addition, in order to prevent cracks in the blank, intermediate steps are carried out when necessary to ensure the required deformability. In order to maintain a good lubrication state, the blank can be phosphated. In the continuous processing of bars and wire rods, the section can not be lubricated at present, and the possibility of using phosphating lubrication is being studied.
According to the moving mode of the blank, forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging, and closed upsetting. Closed die forging and closed upsetting have high material utilization because there is no flash. It is possible to complete the finishing of complex forged flanges with one process or several processes. Since there is no flash, the force-receiving area of the forged flange is reduced, and the required reduction is also reduced. However, it should be noted that the billet cannot be completely restricted. The restriction must strictly control the volume of the billet, control the relative position of the forging die and measure the forging flange, and strive to reduce the wear of the forging die. According to the movement mode of the forging die, forging can be divided into placement, placement swaging, roll forging, cross wedge rolling, drilling ring and cross rolling. Placement, swing swaging and drilling rings can also be processed by precision forging. Pre-process processing of materials. Rotary forging, which is the same as free forging, is also partially formed. Its advantage is that it can be formed even when the forging force is smaller than the size of the forged flange. In the forging method, the material expands from the vicinity of the die surface to the free surface during processing. Therefore, it is difficult to ensure accuracy. Therefore, the forging force can be used to obtain complex shapes and high precision by computer-controlled forging die movement direction and swaging processing. The product. For example, forged flanges such as steam turbine blades with many varieties and large sizes are produced.
The die movement and freedom of the forging equipment alternate. According to the characteristics of the bottom dead center deformation limitation, the forging equipment can be divided into some partial forms:
Limiting the forging force form: a hydraulic press that directly drives the slider by hydraulic pressure.
Quasi-preliminary restriction method: hydraulic press with hydraulic drive crank and connecting rod mechanism.
Initial restriction method: mechanical press with crank, connecting rod and wedge mechanism driving the slider.
In order to obtain high accuracy, attention should be paid to prevent the position deviation at the bottom dead center and control the speed and mold position. Because these will affect the forging flange tolerance, shape accuracy and forging die life. In addition, in order to maintain accuracy, attention should be paid to adjusting the gap of the slider guide rail, ensuring rigidity, adjusting the bottom dead center and using auxiliary transmission devices. In addition, there are vertical and horizontal movement of the slider according to the movement mode of the slider (used in the way, the compensation device can be used to increase the movement in other directions. The above methods are different, the required forging force, processing, material utilization, volume , Dimensional tolerances and lubrication cooling methods are different, these factors are also factors that affect the level of automation.

What are the characteristics of forged flanges and cast flanges?

Metal can improve its structure and mechanical properties after forging. After the casting structure is hot-worked and deformed by the forging method, due to the deformation and recrystallization of the metal, the original coarse dendrites and columnar crystal grains are small in diameter and the equiaxed recrystallized structure with uniform size, which causes the segregation and looseness of the internal deformation of the steel ingot. The pores and slag inclusions are compacted and welded, and the structure becomes tighter, which improves the plasticity and mechanical properties of the metal.
Generally speaking, the mechanical properties of cast flanges are lower than those of homogeneous forged flanges. Then, the forging process can ensure the continuity of the metal fiber structure, so that the fiber structure of the forged flange is consistent with the size of the forged flange, and the metal streamline is complete, which can ensure that the parts have good mechanical properties and long instead of using precision die forging. Forged flanges produced by cold extrusion, warm extrusion and other processes are unmatched by cast flanges.

Source: Network Arrangement – China Forged Flanges Manufacturer – Yaang Pipe Industry (www.metallicsteel.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.)

If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]

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References:

  • https://www.yaang.com/forged-flange-manufacturing-technology-and-requirements.html
  • https://www.yaang.com/comparison-of-forging-flange-and-casting-flange.html

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