The grain size distribution of molding sand directly affects permeability, strength, surface roughness, and casting quality.
A reasonable grain size distribution can significantly improve the stability of the casting process and the quality of the castings.
Impact on Permeability:If the raw sand grains are too coarse, the molding sand will have insufficient permeability, making it difficult for gas to escape during pouring and easily leading to porosity defects. If the grains are too fine, the permeability may be too high, leading to increased molten metal penetration and reduced surface roughness. Optimizing the grain size distribution can control the permeability within a reasonable range (90-160), balancing the contradiction between gas escape and molten metal penetration.
Strength and Compactness: Uneven grain size distribution will cause fluctuations in the compactness of the molding sand (normal range 33%-42%), affecting the stability of the sand mold. For example, an excessively high proportion of 100-mesh sieve particles can reduce the fluidity of molding sand, leading to defects such as mold collapse and sand erosion. Optimized gradation can improve the surface roughness of cast steel parts from Ra 50-100μm to Ra 25-50μm.
Surface Roughness Optimization: Using graded sand processes (such as sieving the original sand into different particle sizes and then mixing them in proportion) can improve surface quality. Experiments show that the optimized surface roughness of castings can be improved by one grade (e.g., Ra value reduced from 100μm to 50μm), which is directly related to the uniformity of particle size distribution.
Refractory Resistance and High-Temperature Stability: Excessively coarse or unevenly distributed particles can cause sand adhesion in the molding sand under the action of high-temperature molten metal, affecting casting cleaning. A reasonable particle size distribution combined with refractory materials (e.g., SiO₂ content ≥85%) can improve refractoriness and reduce surface adhesion problems in castings. Of course, professional foundry companies can properly handle molding sand issues, which is a basic skill for foundries. If you have a large demand for custom castings, you can choose to cooperate with Mulan Metal. Mulan Metal has 12 years of experience in custom casting production and processing, and has helped customers in more than 30 countries complete the commissioned production of various custom castings, and has received consistent recognition. We look forward to your cooperation inquiries.
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