Steel Casting Design Flexibility
Cast steel valves are widely used due to their cost economy and design flexibility. As the basic structure of the valve casting is hollow structure, the shape is more complex, Steel Casting the casting process by the casting size, wall thickness, climate, raw materials and construction operations of the various constraints, therefore, cast steel often appear trachoma, pores, cracks, Steel Casting Shrinkage and inclusions and other casting defects, production control has a certain degree of difficulty, especially in the sand casting alloy steel castings for more. Because the steel alloy in the steel more liquid flow worse, casting defects are more likely to produce.
1, due to the poor fluidity of molten steel, in order to prevent the cast steel produced cold and pouring, cast steel wall thickness can not be less than 8mm; pouring system structure is simple; dry or hot cast; Temperature, generally 1520 ° ~ 1600 ° C, because the pouring temperature is high, the superheat of molten steel is large, the liquid is kept for a long time and the fluidity can be improved. Steel Casting But the pouring temperature is too high, will cause coarse grain, hot cracking, pores and sticky sand and other defects. So the general small, thin-walled and complex shape of the casting, the pouring temperature is about the melting point of steel temperature + 150 ℃; large, thick castings casting temperature than its melting point of about 100 ℃ or so.
2, due to the larger amount of cast steel shrinkage, in order to prevent castings shrinkage, shrinkage defects, in the casting process mostly use riser, Steel Casting cold iron and subsidies and other measures to achieve the order of solidification.
3, in order to prevent the cast steel parts shrinkage, shrinkage, pores and cracks, should make the wall thickness uniformity, to avoid sharp and right angle structure, in the molding sand with sawdust, in the core plus coke, and The use of hollow core and oil core, etc. to improve the sand or the core of the concession and permeability. 4, the melting point of cast steel is high, the corresponding pouring temperature is also high. High temperature molten steel and mold material interaction, easy to produce sticky sand defects. Therefore, Steel Casting the use of refractory high artificial quartz sand to do the mold, and in the casting surface brush by the quartz powder or zirconia powder made of paint. In order to reduce the gas source, improve the flow of molten steel and casting strength, most cast steel with dry or quick-drying type to cast, such as the use of CO2 hardened water glass quartz sand.
In the casting, the surface or near the surface, there are different sizes of smooth holes, the shape of a round, long and irregular, there are single, but also gathered into a piece. Steel Casting The color is white or with a layer of dark, sometimes covered with a layer of oxide. Due to the different sources and causes of gas formation, the manifestations of stomata are also different, with invasive porosity, precipitation porosity and reactive stomata. Invasive porosity larger, similar shape pear-shaped, often appear in the upper part of the casting near the core wall or pouring position, mainly due to the sand core gas generated in the metal can not escape, pear-shaped small holes The position indicates that the gas enters the cast member from there. Steel Casting Precipitation stomatal and scattered, generally located in the casting surface, often the same furnace casting almost all occur, mainly due to the metal in the melting process of the absorption of the gas before the solidification failed to all precipitation, in the casting to form many scattered small pores. Reactive stomata are due to the chemical reaction of the metal-to-metal interface, which is also known as subcutaneous stomata because of its uniform distribution and often occurring at 1-3è below the surface of the casting (sometimes under a layer of oxide). And because the pores are mostly elongated pinholes, Steel Casting the long axis and casting surface perpendicular, but also can be called pinholes.