Sand casting is one of the most widely used processes in the manufacturing of automobile parts (engine blocks, cylinder heads), machinery parts (gears, valves), and pipe fittings, accounting for more than 70% of the total casting output. The quality of the sand mold directly affects the surface finish, dimensional accuracy, and internal quality of casting parts. Foundry grade bentonite powder, especially sodium montmorillonite-based bentonite, is the core binder in green sand molds, as it can bond sand particles together to form a sand mold with sufficient strength, while ensuring good collapsibility after casting (easy to clean the sand from the casting surface). The sodium montmorillonite in bentonite powder has strong water absorption and swelling capacity, and when mixed with silica sand and water, it forms a viscous film on the surface of sand particles, creating a strong bond between particles.
In green sand casting, the key performance indicators of the sand mold are green compression strength, dry compression strength, and collapsibility. Green compression strength (the strength of the sand mold before heating) needs to be 0.15 - 0.3 MPa to resist the pressure of molten metal; dry compression strength (the strength after drying) needs to be 0.8 - 1.5 MPa to prevent the sand mold from cracking during casting; collapsibility (the ability of the sand mold to break after casting) needs to be good to avoid sand sticking to the casting surface. When foundry grade bentonite powder is added to silica sand at a dosage of 3%-5%, the green compression strength of the sand mold can reach 0.2 - 0.25 MPa, and the dry compression strength can reach 1.0 - 1.2 MPa, fully meeting the requirements of medium and large casting parts.
An in-depth look at the Hubei automobile casting factory case reveals more details. Prior to using our foundry grade bentonite powder, the factory faced significant production inefficiencies due to subpar sand molds. The high rejection rate of 8% was not only costly but also disrupted the production schedule. After adopting our product, not only did the rejection rate plummet to 2%, but the factory also experienced a cascade of positive impacts. The reduced cleaning time from 40 minutes to 28 minutes per piece translated into substantial labor cost savings and increased production throughput. This transformation is largely attributed to the unique molecular structure of our bentonite powder. The sodium montmorillonite within has an expansive lattice structure that allows for superior water absorption. When subjected to the high temperatures of molten metal (1300 - 1500°C), this structure undergoes a controlled decomposition process. The sodium montmorillonite gradually breaks down into porous silica, which forms a non-adhesive layer between the sand mold and the casting. This physical separation mechanism ensures that the sand can be easily removed without leaving residues or causing damage to the casting surface.
For large-scale casting parts (such as marine engine cylinders with a weight of more than 10 tons), the sand mold requires higher strength and dimensional stability. We provide high-purity foundry grade bentonite powder (montmorillonite content ≥90%) for such scenarios. When the dosage is increased to 5%-7%, the dry compression strength of the sand mold can reach 1.5 - 1.8 MPa, and the dimensional accuracy of the casting part can be controlled within ±0.5 mm/m, meeting the strict tolerance requirements of large machinery parts.
To better understand the impact on casting quality, consider the role of impurities. Our bentonite powder has low ash content (≤3%) and low sand content (≤1%), which can reduce the formation of inclusions in the casting (impurities caused by sand mold erosion), improving the mechanical properties of the casting—for example, the tensile strength of gray cast iron castings can be increased by 10%-15%, reaching 250 - 300 MPa. In the case of marine engine cylinders, these enhanced mechanical properties are crucial for withstanding high-pressure and high-temperature operating conditions. The reduced inclusion formation also improves the fatigue resistance of the castings, extending their service life significantly.
Our foundry grade bentonite powder has two specifications: ordinary grade and high-purity grade. The ordinary grade has a montmorillonite content of 80%-85%, a moisture content of ≤10%, and a 200-mesh sieve residue of ≤0.5%, suitable for small and medium casting parts; the high-purity grade has a montmorillonite content of ≥90%, a moisture content of ≤8%, and a 200-mesh sieve residue of ≤0.2%, suitable for large and high-precision casting parts. Both grades meet the requirements of the national standard GB/T 25135-2010 《Foundry Bentonite》, and are tested for green compression strength, dry compression strength, and collapsibility in our laboratory.
For the surface modification service for special sand types, we employ advanced chemical and physical treatment methods. When dealing with chromite sand, we use a cationic surfactant treatment to enhance the electrostatic interaction between the bentonite powder and the sand particles. For zircon sand, which has a different surface chemistry, we apply a silane coupling agent treatment. These modification techniques are not only scientifically proven but also validated through rigorous in-house testing. Our R&D team continuously monitors and improves these processes to adapt to the evolving needs of the casting industry.
In terms of supply, we have a large-scale production base with an annual output of 50,000 tons of foundry grade bentonite powder, ensuring stable supply even during peak casting seasons. Our production base is equipped with state-of-the-art manufacturing facilities. We use automated production lines that can precisely control the production process, from raw material mixing to packaging. This not only ensures product consistency but also improves production efficiency. We use bulk packaging (20 - 50 tons/bulk bag) for large customers, which can reduce packaging costs by 20% compared to small bags. The products are transported by rail or sea, and the delivery cycle to domestic customers is 3 - 5 days, and to international customers (such as Southeast Asia, Europe) is 15 - 25 days. For international shipments, we work closely with reliable logistics partners to ensure the safe and timely delivery of our products. We also provide comprehensive logistics tracking services, allowing customers to monitor the status of their orders in real-time.
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