Knowledge

Section 1: Application of Baozhu Sand in Lost Foam Casting

The shape of the zircon sand grains is close to spherical, with good fluidity and high permeability. It can fill the slender holes, the inner angle parts of the castings and the complex inner cavity parts, and is also relatively easy to be compacted. It has high strength, does not break or powder, and has good reusability. It can also reduce the production cost of castings and improve the working environment in the workshop. It has been widely used in lost foam casting.

 

I. Performance Characteristics of Baozhu Sand

1. High Refractoriness: Baozhu sand is made from high-quality bauxite through high-temperature electric furnace melting. Its main component is aluminum oxide (Al2O3), with a refractoriness of over 1800°C, far exceeding that of ordinary silica sand. It can withstand the impact of molten steel during the lost foam casting process.

2. Excellent Fluidity: The particle shape of Baozhu sand is close to spherical, with a smooth surface and dense structure, providing excellent fluidity. It can easily fill the complex inner cavities and fine pores of lost foam molds, reducing the occurrence of sand inclusion defects.

3. Strong Permeability: Baozhu sand has good permeability, facilitating the discharge of gases and liquid pyrolysis products generated during the lost foam casting process, preventing fireback and casting defects.

4. Low Thermal Expansion Rate: Baozhu sand has an extremely low thermal expansion coefficient, with almost no expansion during the pouring process. This helps maintain the dimensional accuracy of the castings and prevents expansion defects.

5. Good Regenerability: Baozhu sand has high strength, is not prone to fragmentation, and has good reusability. It can be recycled repeatedly, reducing production costs and minimizing waste sand emissions.

 

II. Application Advantages of Baozhu Sand in Lost Foam Casting

1. Improved Casting Quality: Baozhu sand has high refractoriness, good fluidity and strong permeability, which can effectively prevent defects such as sand inclusion, porosity and scabbing in castings, and improve the surface quality and dimensional accuracy of castings.

2. Reduced Production Costs: The spherical particle shape and good filling property of Baozhu sand significantly reduce the amount of molding sand consumed per ton of casting, lowering production costs. Additionally, Baozhu sand has good reusability, reducing waste sand discharge and material consumption.

3. Improved Production Environment: As a green and environmentally friendly casting sand, Baozhu sand generates little or no dust and has a low content of silicon dust, reducing pollution to the production environment and minimizing health risks to workers.

 

III. Specific Applications of Baozhu Sand in Lost Foam Casting

1. Sand filling molding: In the lost foam casting process, baozhu sand is mainly used for filling the sand box. Through vibration compaction and other methods, it fills the complex inner cavities and fine pores in the mold to form a complete casting mold.

2. Use in combination with binders: Baozhu sand can be used in combination with binders such as resin to form high-strength and well-permeable molding sand, meeting the requirements for molding sand performance in lost foam casting.

3. Optimization of casting process: Using baozhu sand as the molding sand material in lost foam casting can optimize casting process parameters such as pouring temperature and pouring speed, improving casting efficiency and casting quality.

 

Section Two: Practical Cases

 

After using zircon sand for lost foam casting in the production of high manganese wear-resistant steel castings, due to the poor air permeability of the originally used quartz sand and magnesia olivine sand, a large number of defects such as scabs and pores appeared on the surface of the castings. After switching to zircon sand, the yield of finished castings increased by 7%.

 

Case One: Production of High Manganese Steel Castings

Problem: Before using Baozhu sand, high manganese steel castings suffered from severe sand sticking and sand inclusion issues. Each time, the cleaning and grinding of the castings required a significant amount of manpower and resources, increasing the production cost of the castings and causing surface quality defects.

Solution: Baozhu sand was adopted as the molding sand material for lost foam casting.

Effect: All casting defects such as sand sticking and sand inclusion were completely eliminated, and the production cost was reduced by nearly 6%.

 

Case Two: Production of Engine Cylinder Block

Problem: The original magnesia olivine sand was used as the filling sand. Due to the poor fluidity of the polygonal sand, defects such as rat tails and scabs occurred frequently.

Solution: Switch to using zircon sand for lost foam casting.

Result: The quality of the castings has been significantly improved, and the yield has increased by 5%.

 

Case Three: Lost Foam Cast Iron

Application: All use of zircon sand, with 3.2% sodium silicate added, and no coating applied to all cores and outer shapes.

Effect: The castings have a smooth surface, no sand sticking, and low energy consumption. The sand regeneration equipment is also relatively simple.

 

Case Four: Diesel Engine Water Jacket

Problem: The original sand had a large expansion coefficient, a large amount of binder was added, and the gas generation was high, resulting in unstable casting quality.

Solution: Lost foam casting was carried out using zircon sand.

Effect: The shortcomings of the original sand were overcome, the amount of resin added was reduced, and the product yield was improved.

 

Case Five: High Manganese and High Chromium Wear-resistant Cast Steel Parts

Problem: Quartz sand and magnesia olivine sand were used successively. Due to the poor permeability of these two sands, a large number of defects such as scabs and pores appeared on the surface of the castings.

Solution: Baotu sand was selected for dry sand molding.

Effect: Defects such as pores, scabs, and underburning were solved, and the yield rate increased by 7%.

 

Case 6: Lost Foam Casting of Large-Diameter Ductile Iron Water Meter Shell

Application: The white mold of the casting was buried with 70-140 mesh zircon sand, then covered with a film and sealed, followed by negative pressure vibration compaction.

 

Effect: Through actual pouring experiments, the quality of the castings before and after optimization was compared. It was found that after using the pearl zircon sand, the common casting defects in the water meter shell casting, such as the shell wall, bottom, end port, and flange plate, were effectively improved.

 

 

Section 3: Comparison of Several Commonly Used Sands

 

Pearl sand:

Advantages: The particle shape is close to true round, with good fluidity, strong permeability, small thermal expansion coefficient, high refractoriness, good reusability and strong environmental friendliness. These performance advantages enable pearl sand to significantly improve the quality of castings in lost foam casting, reduce the scrap rate and lower production costs.

Disadvantages: Large one-time investment.

Applications: Suitable for occasions with high requirements for casting quality, such as high-precision castings and complex-structured castings.

 

Silica sand (quartz sand):

Advantages: Widely distributed and low cost, with relatively high refractoriness.

Disadvantages: Diverse particle shapes, poor fluidity, large thermal expansion coefficient, which can easily lead to casting expansion defects and sand sticking and other quality problems. The reusability is average, and it is prone to generating dust, causing pollution to the production environment.

Applications: Suitable for occasions with low requirements for casting quality, or as an alternative to pearl sand when cost is a sensitive factor.

 

Mechanical sand:

Advantages: Wide sources, abundant resources, relatively low price.

Disadvantages: Prominent edges and corners, rough surface, average fluidity, and air permeability is affected by particle shape and gradation. The coefficient of thermal expansion and refractoriness vary depending on raw materials and processing techniques, generally lower than that of zircon sand. Regeneration is affected by particle shape and gradation, and it is prone to generating impurities such as stone powder.

Application: It can be used in some specific situations, but in lost foam casting, its performance is generally inferior to that of zircon sand and silica sand (quartz sand).

 

Silica sand:

Silica sandis still the main raw sand for casting. It is abundant in resources and low in price. Its performance usually meets the requirements of most castings and is easy to obtain locally. Therefore, it has long been the mainstream molding material in the casting industry. Silica sand has a relatively large thermal expansion coefficient and may cause sudden expansion due to phase change (573℃), resulting in sand inclusion in castings. Its thermal diffusivity and heat storage coefficient are relatively low, which can easily react with iron oxides to cause chemical sticking sand. Especially when producing high alloy steel castings or large cast steel parts, the probability of sticking sand in castings is greater, making the cleaning of castings extremely difficult. When the SiO2 content is low, the refractoriness of the raw sand is greatly reduced, causing thermal sticking sand. Moreover, it is prone to powdering.

For lost foam casting, the preferred sand is the shape. It must be round sand grains because round sand grains have good fluidity and good lateral sand feeding performance. For example, in the production test process, the lateral sand feeding distance of pearl sand can reach nearly 200mm, while that of fine quartz sand is less than 50mm, and the angle of repose can reach 60°. The amount of round sand grains sinking in a compacted state is very small. The amount of sinking of pearl sand per meter is about 30mm, while that of artificial quartz sand can be as much as 80mm. Therefore, when using angular sand, it is easy for the casting to grow tumors at the corners. The second is uniform particle size: uniform particle size molding sand has good air permeability and a low compacted sinking coefficient. Sand with uneven particle size has a large amount of sinking in a compacted state. Then other factors such as refractoriness should be considered.

After pouring, a large number of water droplets can be found under the plastic film in the quartz sand. The sand layer about 100 - 150mm away from the casting is wet as if it had been rained on. This is because the moisture in the quartz sand near the casting volatilizes and then condenses again when it cools. At this time, there will be a large number of pores on the surface of the casting, like being scorched by fire. At the same time, there will be carbon deposits under the coating layer, as if it had not been burned clean; or it may seem like the negative pressure is not enough. All these are due to the crystalline water in the quartz sand. However, the Baozhu sand is an artificial fused sand and does not contain crystalline water, which can reduce the formation of surface defects on the casting.

To ensure that the original sand for lost foam casting has sufficient fluidity to fill the complex deep cavity parts of the foam pattern, and considering that the relatively thick coating layer has certain mechanical strength to prevent the collapse of the box, the original sand for lost foam casting requires good roundness. Additionally, during the pouring process of lost foam casting, the foam pattern will undergo pyrolysis and combustion, generating a large amount of gas or liquid pyrolysis products. Therefore, the sand must have sufficient permeability to prevent the obstruction of the overflow of residues. The sand grains of Baozhu sand are nearly spherical in shape, have good fluidity and high permeability, can fill fine long holes, the inner angle parts of the casting and complex inner cavity parts, and are also relatively easy to compact. Moreover, the neutral material of Baozhu sand ensures its wide application in cast iron and cast steel (including high manganese steel, etc.).​​​​​​​

 

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