Prevention and control methods for shrinkage in mechanical valve castings
In the production process of mechanical valve castings, shrinkage has always been a key factor affecting the quality of castings. Shrinkage refers to the voids formed during the cooling process of castings due to the volume shrinkage of the alloy during solidification, which usually appears in the pouring part of castings, especially at the connection between the mold core and the casting. The formation of shrinkage not only affects the appearance of castings but also reduces the mechanical properties of castings. In severe cases, it may even cause the casting to break, affecting the service life of mechanical valve castings. Therefore, taking effective preventive control measures is crucial for reducing and preventing shrinkage.
I. Optimization of Casting Design
In the design of castings, it should be as possible as to reduce the uneven distribution of casting wall thickness, avoid stress concentration at the pouring gate, exhaust hole, core hole, and other parts. At the same time, for castings with complex shapes and unreasonable structures, it is recommended to use casting processes instead of forging or welding, etc., to reduce the occurrence of shrinkage. In addition, reasonable design of the casting system and riser design can also effectively reduce the occurrence of shrinkage.
II. Selection and Processing of Raw Materials
In the selection of raw materials, chemical composition uniformity and high purity should be chosen to reduce the occurrence of shrinkage. In the processing of raw materials, appropriate heat treatment processes should be adopted to eliminate residual stress in raw materials, improve the plasticity of raw materials, and thereby reduce the occurrence of shrinkage. In addition, measures should be taken to reduce the content of harmful elements in raw materials, such as sulfur and phosphorus, to reduce the occurrence of shrinkage.
III. Optimization of Casting Process
In the casting process, it should be avoided to have problems such as too high or too low casting temperature, too fast or too slow casting speed, and too high or too low casting pressure to reduce the occurrence of shrinkage. In addition, reasonable casting sequence and casting methods can also effectively reduce the occurrence of shrinkage. For example, using segmented casting methods can reduce the cooling speed of castings, thereby reducing the occurrence of shrinkage; using directional casting methods can avoid stress concentration in castings, thereby reducing the occurrence of shrinkage.
IV. Optimization of Cooling Process
In the cooling process, it should be avoided to have problems such as too fast or too slow cooling speed, and improper cooling methods to reduce the occurrence of shrinkage. For example, using slow cooling methods can reduce the cooling speed of castings, thereby reducing the occurrence of shrinkage; using uniform cooling methods can avoid stress concentration in castings, thereby reducing the occurrence of shrinkage.
V. Defect Detection and Treatment
During the casting production process, defects in castings should be detected regularly to discover and deal with shrinkage and other issues in time. For detected shrinkage, appropriate treatment measures should be taken, such as welding and grinding, to ensure the quality of castings.
In summary, for the prevention and control of shrinkage in mechanical valve casting parts, we should start from aspects such as design optimization, raw material processing, casting process optimization, cooling process optimization, and defect detection and treatment to reduce and prevent shrinkage, and improve the quality and service life of castings.