Judging the quality of casting sand is a comprehensive evaluation process that requires consideration of multiple factors. Here are some key indicators and methods used to evaluate the quality of casting sand.
1、 Chemical Composition of Casting Sand
Purity and Cleanliness: High quality casting sand should have high purity and cleanliness. Taking silicon sand as an example, the sand used for cast iron requires a SiO ₂ content of over 90%, while larger steel castings require a SiO ₂ content of over 97%. The content of other impurities such as soil and organic matter should be kept as low as possible to reduce their impact on the quality of castings.
Special components: According to specific usage requirements, the content of specific components such as MgO in special types of casting sands such as magnesia sand should meet the prescribed standards.
2、 Physical Properties of Casting Sand
Particle size and distribution: The particle size distribution of casting sand should be uniform, and the particle size range is usually between 0.1mm and 3.0mm. Casting sand with different particle size requirements is suitable for castings of different shapes and sizes. Excessive particle size can cause sand core detachment and shrinkage, while insufficient particle size can affect filling performance. Screening analysis is an effective method for understanding the particle size distribution of sand samples.
Shape and surface quality: The particle shape of casting sand is generally divided into circular sand, polygonal sand, and pointed sand. Circular sand has good fluidity, but poor breathability; Sharp edged sand has good breathability, but poor fluidity. High quality casting sand should have suitable particle shape and surface quality, such as smooth surface and no protruding edges and corners.
Loose density and flowability: Loose density reflects the density state of casting sand before vibration treatment. Liquidity refers to the ability of casting sand to flow freely in the mold. Both are important factors affecting the quality of castings. The direct weighing method and sampler method can be used to test loose density, while flowability can be evaluated by observing the flow of sand samples on inclined surfaces.
Hardness and toughness: Hardness refers to the compressive strength of casting sand, while toughness reflects its ability to resist destructive forces. Hardness testing can be conducted using a universal hardness testing machine, while toughness is usually evaluated by observing the deformation of the sand sample after being subjected to stress. High quality casting sand should have sufficient hardness and toughness to withstand various stresses during the casting process.
Fire resistance and thermal stability: Fire resistance refers to the stability of casting sand under high temperature conditions, while thermal stability refers to its ability to maintain stable performance during temperature changes. Insufficient fire resistance can lead to problems such as sand core collapse or sand mold cracking. High temperature testing and differential thermal analysis can be used to evaluate the fire resistance and thermal stability of casting sand.
3、 Other Indicators of Casting Sand
Moisture absorption: The moisture absorption of casting sand can affect its performance during storage and use. Excessive moisture absorption may lead to a decrease in mold forming accuracy and stability; If the moisture absorption is too low, it may lead to easy sand loss and erosion. Humidity testing can be used to evaluate the moisture absorption of casting sand.
Bonding and permeability: Bonding refers to the ability of casting sand to bond with binders, while permeability refers to the ability of sand molds to release internal gases. Both are important factors affecting the quality of castings. The adhesion and permeability of casting sand can be evaluated by observing the gas emission during the casting process and the porosity on the surface of the casting.
In summary, judging the quality of casting sand requires comprehensive consideration of its chemical composition, physical properties, and other relevant indicators. In practical applications, appropriate testing methods and evaluation standards should be selected based on specific usage requirements and process conditions.
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Post time:Sep . 05, 2024 15:59Next：Characteristics and Main Application Areas of Golden Sand