Casting Picecs flange is characterized by easy access to other methods are not easy to obtain the shape of the complex parts; Casting Picecs flange low cost; can use a special process to obtain precision Casting Picecss, the surface without processing that is an ideal finish; Casting Picecs simple, Forged flange is cheap; but the Casting Picecss are prone to defects and non-dense areas, in the strong corrosion and high-pressure domestic technology generally can not guarantee the quality of forgings.
Forging flange is the use of forging equipment for the bar forging molding, generally can not forged more complex parts, the need for larger processing, but forging flange structure is relatively dense, not prone to internal defects, so Widely used in the requirements of high parts processing, such as valve seat, spool, stem, etc., in high pressure and strong corrosion alloy valve, forging valve body has also been widely used.
Although Casting Picecs technology has grown considerably and the use of computer technology to optimize the structural geometry of the structural design and Casting Picecs process, it is still extremely difficult to achieve Class 1 or Class 2 acceptance of standard X-ray / MT or PT quality requirements , And these are nuclear power plants, thermal power plants or petrochemical industry within the harsh environment required standards. So the need for welding improvement. However, after welding, the overall quality and reliability of the Casting Picecs valve becomes difficult to guarantee. Sometimes all these problems are left in the cast metal frame. The test rods are usually for each temperature, but their analysis may be uncertain. Even if the circular test rod indicates that the chemical and physical properties are acceptable, it is still possible that there is still an inherently difficult to detect damage to the inherent strength or corrosion resistance of the internal defects.
Other shortcomings in the Casting Picecs valve or flange are the clear cracks and hot tuffs that occur during the solidification process under the combined effect of stress concentration in the non-uniform shrinkage and the low strength of the metal near the melting point. Lower Casting Picecs temperatures can form cold scars, and the accumulation of sand or slag in molten metal can cause blemishes. Low-level Casting Picecs operations can also cause other defects.
Casting Picecs improvements to meet the requirements of X-ray quality depends on the defect parts of the grinding, welding, heat treatment and repeated testing and testing. Even in this case, the valve seat and washer face or the solder tip may show a thin wire crack that needs to be reworked and machined.
The Casting Picecs process builds fine particle structures and improves the physical properties of the metal. In the practical use of components, a correct design can make the particles flow in the direction of the main pressure.
Forging needs to be consistent with each piece, without any porosity, excess space, inclusions or other defects. This method produces a high ratio of components to strength to weight ratio. These elements are usually used in aircraft structures.
Advantages of Forging: The advantages of forgings are stretchable length, shrinkable cross section; shrinkable length, stretchable cross section; changeable length, changeable cross section. Forging the types are: free forging / hand forging, hot forging / precision forging, forging, rolling forging and forging.
Why choose forging? Compared with Casting Picecss, the valve body of the forging valve has a more uniform structure, better density, better strength integrity, better dimensional characteristics, and smaller dimensional error. The directional construction (piping) has a higher performance over the entire strength and stress.
(1) high strength
Hot forging facilitates crystallization and grain refinement, allowing the material to achieve maximum possible strength and consistency, and minimal variation between pieces and pieces. The stream of particles flows precisely along the contour of the valve body, and these continuous flow lines help to reduce the incidence of fatigue or common faults.
The forgiveness that meets the structural requirements of the design has been one of the most important advantages of forgings and, to some extent,
(3) structural integrity
Forging eliminates internal defects, resulting in coherent metallographic organization that ensures excellent performance. In the event of severe stress and corrosion problems within the crystal, forging can guarantee a longer service life and trouble-free service.
The uniformity of the size of the die forging results in complete control of the critical wall thickness, which avoids the defects caused by the displacement of the core in the Casting Picecs process. It ensures that there is no internal defect through the impact of high quality, non-separation ingot and 10,000 to 30,000 ton presses The consistent metallographic structure.
Forging quality assurance, through the use of forgings, as well as its consistency and high quality, the demand for X-ray for Category 1 cast parts is gone. The US Navy also used the same attitude when using forgings as nuclear components for nuclear submarines and aircraft carriers. For forgings, the full requirements of the ASME Code are Ultrasonic Testing (U.T.), Magnetic Powder (M.T.) or Liquid Permeation Test (P.T.). It is very rare to find out forged forgings by U.T., M.T., or P.T. Parts of the procurement, the delivery time can be controlled, so the delivery of the valve will be more reliable. Casting Picecs and Forging Body Oriented Directional Forgings In the environment where the temperature varies greatly, the creep resistance to fatigue is three times higher than that of the Casting Picecs.