Leakage reasons and prevention measures of cast steel valve

Abstract: Valves are widely used in chemical, food, pharmaceutical, power and other industries. According to the use of conditions, conveying system technology requirements and the different transmission medium, the valve material and specifications are not the same model, the type is very diverse. With the continuous improvement of modern production technology, the quality of the valve is also getting higher and higher. Due to the special structure of the valve, the casting process will produce a variety of casting defects, such as porosity, shrinkage, shrinkage and other quality defects, eventually leading to valve leakage. According to statistics, the valve leakage causes, mostly caused by the casting process shrinkage, shrinkage caused by two kinds of casting defects. In this paper, valve defects in the casting process of shrinkage, shrinkage and other quality defects, analyze the formation of reasons and to explore its preventive measures to improve the inherent quality of valve casting products.
Keywords: Valve Casting; Leakage; Reasons; Prevention and Control Measures Defective cavities, shrinkage and other defects are the main causes of valve leakage. Casting in the production process, the formation of some casting defects, resulting in the valve leakage during use, affecting its normal use. Research valve in the casting process quality defects caused by the reasons and to explore its preventive measures to improve the quality of its casting, to meet the needs of the industry's production process.
1 produce shrinkage, shrinkage and porosity reasons we all know, after the castings casting molten steel in the cooling process, to go through three stages of contraction: the first stage is the liquid contraction, with the mold of molten steel The second stage is the shrinkage of solidification, the shrinkage produced after the nucleation of the molten steel to complete solidification; the third stage is the solid state shrinkage, the molten steel is completely solidified, with the casting temperature Reduce the formation of body contraction. After research and analysis, casting shrinkage, shrinkage defects are mainly formed in the casting solidification shrinkage process. When the casting process, casting system and feeding riser set unreasonable, can not be timely hot section of the casting shrink, it will form a shrinkage in the hot section of the casting shrinkage or shrinkage For the valve, because of its complex structure , More heat nodes, while the heat node is not conducive to the riser set, so shrinkage, shrinkage is the valve casting defects most likely to occur.
In the casting solidification process, the degree of liquid shrinkage and pouring temperature has a relationship, the higher the pouring temperature, the greater the volume of molten steel expansion, whereas the larger the contraction. Under normal circumstances, to ensure filling the premise, to minimize pouring temperature. The coagulation shrinkage is mainly affected by the composition of the alloy. For example, if the remaining components are the same, if the content of carbon and silicon is larger, shrinkage will be smaller, and when the content of manganese and sulfur is relatively large, the shrinkage will be relatively large. Solid-state shrinkage is the complete solidification of the casting, with the reduction of temperature resulting shrinkage, for shrinkage, shrinkage casting defects have no effect. After the study, the shrinkage of castings, shrinkage casting defects mainly formed in the solidification and contraction phase.
2 shrinkage cavity, easy to produce parts of shrinkage defects Casting parts of the final cooling, usually casting the hot node is the most prone to shrinkage, shrinkage defects. For valves, the hot junction located at the bosses of the castings of the valve body and at the juncture of the cast flange and the body of the castings, have poor heat dissipation conditions at these locations and present defects when they are finally solidified. Need to prevent 3 To completely solve the valve in the casting process shrinkage, shrinkage and other quality defects, first of all need to start from the casting process design, selection of casting process, optimization of casting process design. Specific solutions include the following methods:
3.1 Optimization of riser design The original casting process: the riser design is the use of riser, after pouring plus efficient heat insulation cover agent. As the root of the riser Bo, leading to molten steel channel does not complement, affecting the normal feeding, leading to the casting valve casting still shrinkage, shrinkage defects. Riser optimization design, still setting the riser in the valve flange, and the preferred use of efficient heat insulation riser. After pouring, the riser burns and emits a lot of heat, reheating the molten steel in the riser for the second time to promote the order solidification and increase the feeding capacity of the riser to the castings. The existence of the flange shrinkage, shrinkage defects introduced riser, the valve to solve the quality problems exist.
3.2 Selection of cast cold iron mold under the type, the valve flange, the boss and the central valve body set outside the cold iron, shorten the riser effective supplement distance to avoid shrinkage in the central body area, Affect the valve quality.
3.3 welt design Casting on the type, set in the insulation under the riser flange attached to strengthen the order of the solidification of castings, and to ensure that the riser within the steel channel with a supplementary supply of hot section of the valve effectively refueling .
3.4 The optimal position of the gate The gate position for casting defects have a very big impact. For the valve, should be in the flange and the boss are provided with runners, and runners should be opened in the next type, casting process to ensure smooth casting filling, to avoid sand and slag production defects.
3.5 Pouring process optimization Pouring process parameters involved are pouring temperature, pouring time, pouring speed and slag removal, air entrainment operation requirements. Casting low temperature, the formation of pouring dissatisfaction, cold insulation defects, casting temperature is too high will have sticky sand defects, so casting process must be strictly in accordance with the requirements of the process control pouring temperature and pouring speed and degassing operation requirements to avoid other casting defect.
By taking these measures, the basic solution to the valve casting shrinkage, shrinkage problems, valve product quality has been significantly improved.
4 Conclusion To sum up, the cast steel body has two parts more prone to shrinkage, shrinkage defects: flange and valve body at the junction of the body boss. And for these defects to take the appropriate preventive measures, including: optimizing the casting Riser Design, selection of cold iron, pouring process of standardization. In addition, in order to prevent shrinkage, shrinkage and other casting defects, the production process must be strictly enforced, so as to improve the overall quality of valve casting products.
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