24 Inch WCB 600LB Flat Gate Valve Body Casting
The castings of the valve body is an important part of the valve manufacturing process, and the quality of the valve casting determines the quality of the valve. The sand casting commonly used in the valve industry can be divided into wet sand, dry sand, water glass sand and furan resin self-setting sand according to different binders. Different molding methods have different advantages and disadvantages.In order to improve the product quality Quality, 24 inch WCB 600LB Flat Gate Valve Casting is usually produced with resin no-bake sand molding.
Resin no-bake sand molding is a casting process with resin as a binder. At room temperature, the binder undergoes a chemical reaction under the action of a curing agent to solidify the molding sand. Its characteristic is that the sand mold does not need to be dried, which shortens the production cycle and saves energy. Resin molding sand is easy to compact and has good collapsibility. The molding sand of castings is easy to clean. The castings have high dimensional accuracy and good surface finish, which can greatly improve the quality of Gate Valve Castings.
Its disadvantages are: high quality requirements for raw sand, slight pungent smell at the production site, and high cost of resin.
The mixing process of resin no-bake sand: resin no-bake sand is best to use a continuous sand mixer, adding raw sand, resin, curing agent, etc. in sequence, quickly mixed, mixed at any time, and used at any time.
The order of adding various raw materials when mixing resin sand is as follows:
Raw sand + curing agent (p-toluenesulfonic acid aqueous solution) - (120 ~ 180S) - resin + silane - (60 ~ 90S) - sand out
advanced equipment!
5T intermediate frequency furnace, 2.5T intermediate frequency furnace, 0.75T intermediate frequency furnace, resin sand box molding production line, nine-point temperature-controlled heat treatment kiln,，etc.
Perfect testing equipment!
complete molding sand laboratory, 45-channel direct-reading spectrometer, Co60-γ-ray flaw detector, X-ray flaw detector, fluorescent magnetic powder, ultrasonic, penetration flaw detection equipment, metallographic testing equipment and a full set of mechanical performance testing equipment.
Staff size!
160 employees, including 26 high and middle-level professional and technical personnel
Large factory area!
Covers an area of 32,000 square meters
Analysis of Gate Valve Casting Defects
Any gate valve casting will have internal defects, the existence of these defects will bring great hidden dangers to the internal quality of the gate valve casting, and the welding repair to eliminate these defects in the production process will also bring a great burden to the production. In particular, valves are thin-shell castings that withstand pressure and temperature, and the compactness of their internal structures is very important. Therefore, the internal defects of casting become the decisive factor affecting the quality of casting.
The internal defects of gate valve castings mainly include pores, slag inclusions, shrinkage porosity and cracks.
(1) Pores: Pores are produced by gas, the surface of the pores is smooth, and they are generated inside or near the surface of the gate valve casting, and their shapes are mostly round or oblong.
The main sources of gas that generate pores are:
① The nitrogen and hydrogen dissolved in the metal are contained in the metal during the solidification of the casting, forming closed circular or oval inner walls with metallic luster.
②Moisture or volatile substances in the molding material will turn into gas due to heating, forming pores with dark brown inner walls.
③ During the pouring process of the metal, due to the unstable flow, the air is involved to form pores.
Prevention method of stomatal defect:
① In smelting, rusty metal raw materials should be used as little as possible or not, and tools and ladles should be baked and dried.
②The pouring of molten steel should be done at high temperature and poured at low temperature, and the molten steel should be properly sedated to facilitate the floating of gas.
③ The process design of the pouring riser should increase the pressure head of molten steel to avoid gas entrapment, and set up an artificial gas path for reasonable exhaust.
④Moulding materials should control the water content and gas volume, increase the air permeability, and the sand mold and sand core should be baked and dried as much as possible.
24 inch WCB 600LB Flat Gate Valve Casting
Main production equipment:
(2) Shrinkage cavity: It is a coherent or incoherent circular or irregular cavity produced inside the gate valve casting (especially at the hot spot), with rough inner surface, darker color, thick metal grains, and many Dendritic crystals, gathered in one or more places, prone to leakage during hydrostatic test.
The reason for shrinkage cavity: when the metal is solidified from liquid to solid, the volume shrinks. If there is not enough molten steel supplement at this time, shrinkage cavity will inevitably occur. The shrinkage cavity of steel castings is basically caused by improper control of the sequential solidification process. The reasons may include incorrect riser settings, too high pouring temperature of molten steel, and large metal shrinkage.
Methods to prevent shrinkage cavities: ①Scientifically design the gating system of castings to achieve sequential solidification of molten steel, and the parts that solidify first should be supplemented with molten steel. ②Correctly and reasonably set riser, subsidy, internal and external cold iron to ensure sequential solidification. ③When the molten steel is poured, top injection from the riser is beneficial to ensure the temperature of the molten steel and feeding, and reduce the occurrence of shrinkage cavities. ④ In terms of pouring speed, low-speed pouring is more conducive to sequential solidification than high-speed pouring. ⑸The pouring temperature should not be too high. The molten steel is taken out of the furnace at high temperature and poured after sedation, which is beneficial to reduce shrinkage cavities.
(3) Sand inclusion (slag): Sand inclusion (slag) is commonly known as trachoma, which is an incoherent circular or irregular hole inside the casting. The hole is mixed with molding sand or steel slag, and the size is irregular. One or more places, often more on the upper part.
Causes of sand inclusions (slag): Slag inclusions are formed by the discrete steel slag entering the casting along with the molten steel during the smelting or pouring process of molten steel. The sand inclusion is due to the insufficient compactness of the cavity during molding. When the molten steel is poured into the cavity, the molding sand is washed up by the molten steel and enters the interior of the casting. In addition, improper operation when repairing the shape and closing the box, and the phenomenon of sand falling are also the reasons for the sand inclusion.
Methods to prevent sand (slag) from being produced:
① When molten steel is smelted, exhaust and slag should be exhausted as thoroughly as possible.
② The pouring ladle of molten steel should not be turned over as much as possible, but teapot ladle or bottom pouring ladle should be used to prevent the slag on the upper part of the molten steel from entering the casting cavity along the molten steel.
③ Castor slag measures should be taken when pouring molten steel to minimize the entry of steel slag into the cavity with molten steel.
④In order to reduce the possibility of sand inclusion, ensure the tightness of the sand mold during molding, be careful not to drop sand when repairing the mold, and blow the mold cavity clean before closing the box.
(4) Cracks: Most of the cracks in castings are hot cracks, with irregular shapes, penetrating or not penetrating, continuous or intermittent, and the metal at the cracks is dark or has surface oxidation.
The reasons for the cracks in Gate Valve Body Casting: There are two aspects, namely high temperature stress and liquid film deformation.
High-temperature stress is the stress formed by the shrinkage and deformation of molten steel at high temperatures. When the stress exceeds the strength or plastic deformation limit of the metal at this temperature, cracks will occur. Liquid film deformation is the formation of a liquid film between crystal grains during the solidification and crystallization process of molten steel. With the progress of solidification and crystallization, the liquid film is deformed. When the deformation amount and deformation speed exceed a certain limit, cracks are generated. The temperature range of thermal cracking is about 1200 ~ 1450 ℃.
24 inch WCB 600LB Flat Gate Valve Casting
Main production equipment:
Factors affecting cracks in Gate Valve Casting:
① S and P elements in steel are harmful factors for cracks, and their eutectics with iron reduce the strength and plasticity of cast steel at high temperatures, resulting in cracks.
② Slag inclusion and segregation in steel increase stress concentration, thus increasing hot cracking tendency.
③ The greater the linear shrinkage coefficient of the steel type, the greater the tendency of hot cracking.
④ The greater the thermal conductivity of the steel type, the greater the surface tension, the better the high-temperature mechanical properties, and the smaller the tendency of hot cracking.
⑤ The structural design of castings is poor in manufacturability, such as too small rounded corners, large wall thickness disparity, and severe stress concentration, which will cause cracks.
⑥The compactness of the sand mold is too high, and the poor yield of the core hinders the shrinkage of the gate valve casting and increases the tendency of cracks.
⑦Others, such as improper arrangement of the riser, too fast cooling of the gate valve casting, excessive stress caused by cutting the riser and heat treatment, etc. will also affect the generation of cracks.
According to the causes and influencing factors of the above cracks, corresponding measures can be taken to reduce and avoid the occurrence of crack defects.
Based on the above analysis of the causes of casting defects, finding out the existing problems and taking corresponding improvement measures, we can find a solution to casting defects, which is conducive to the improvement of casting quality.
Our company has complete testing tools, which can be tested according to requirements.
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