Jul 29, 2026Buying Guide
Application of Ceramic Bead Sand in Precoated Sand
Application of Ceramic Bead Sand in Precoated Sand
Application of Ceramic Bead Sand in Precoated Sand
1. Process Overview
Precoated sand is a precision core-making material coated with phenolic resin, curing agent and lubricant on raw sand surface, which forms shell molds and shell cores after heating and curing. It is widely used for complex thin-wall precision castings such as automobile engine blocks, cylinder heads, turbochargers, hydraulic valve bodies and axle housings.Traditional precoated sand adopts quartz silica sand as aggregate, while silica sand has angular particles, high thermal expansion coefficient and limited refractoriness. It easily causes four major defects: veining, metal penetration, blowholes and sand core cracking during production of high-temperature complex sand cores. In addition, silica sand features large specific surface area, high resin consumption, severe breakage during reclamation and massive waste sand discharge, leading to rising comprehensive production costs and environmental pressure.Ceramic bead sand is spherical artificial refractory sand made of high-alumina bauxite through high-temperature melting, jet granulation and multi-stage screening. It has angularity coefficient ≤1.1, refractoriness ≥1790℃ and thermal expansion rate of only 0.13% at 1000℃ with neutral chemical property. It serves as high-quality special raw sand for high-end precoated sand.Two technical routes are available for precoated sand production: 100% pure ceramic bead precoated sand, and mixed precoated sand with 20%-45% ceramic bead sand blended with quartz sand, adapting to different casting precision and cost demands, and fundamentally solving various casting defects of silica sand precoated sand.
2. Six Core Advantages of Ceramic Bead Sand for Precoated Sand
2.1 Spherical & Smooth Granules Reduce Resin Dosage and Gas Evolution
Ceramic bead sand features round, compact and smooth particles without sharp edges, with a far smaller specific surface area than silica sand. The dosage of phenolic resin can be reduced by 20%~35% under identical tensile strength of sand cores.Lower resin dosage directly cuts the total gas evolution of precoated sand (gas evolution controlled ≤12mL/g), fundamentally eliminating subsurface blowhole defects on thin-wall positions such as engine air passages and water jackets. Meanwhile, procurement costs of high-priced phenolic resin are drastically reduced, delivering remarkable cost reduction effects for mass core-making workshops.
2.2 Ultra-Low Thermal Expansion Eliminates Veining, Hot Tearing and Dimensional Deformation of Castings
Quartz sand undergoes crystal phase mutation at 573℃ with a thermal expansion rate as high as 1.5%. During high-temperature pouring, the surface layer of sand cores cracks due to thermal expansion, and molten metal penetrates cracks to form irreversible veining defects. Castings with thick hot spots are prone to hot tearing and dimensional out-of-tolerance.Ceramic bead sand generates no high-temperature crystal phase transformation, with a thermal expansion rate only 1/10 of silica sand, delivering outstanding dimensional stability of sand cores under high temperatures. The resin between spherical particles forms point contact, offering excellent high-temperature deformability to release solidification shrinkage stress of castings. The rejection rate of veining and hot tearing for complex steel, ductile iron and gray iron castings drops by over 60%, removing the need for expensive anti-veining additives.
2.3 High Refractoriness & Chemical Inertness Prevent Metal Penetration and Simplify Core-Making Procedures
Ceramic bead sand is mainly composed of corundum and mullite, with a refractoriness above 1800℃ and neutral property. It does not undergo oxidation interfacial reactions with molten steel or iron at high temperatures.For sand cores with thick hot spots and complex thin-wall inner cavities (turbocharger housings, cylinder head water jackets, hydraulic valve bodies), pure ceramic bead precoated sand delivers equivalent anti-metal penetration and chilling effects to chromite sand. Additional chromite facing sand is unnecessary, simplifying sand mixing and core-making processes and cutting expenditure on high-cost chromite sand.
2.4 Excellent Flowability & Filling Performance Enables Complete Forming of Complex Thin-Wall Sand Cores
The perfectly spherical structure endows ceramic bead sand with exceptional flowability, creating low resistance during sand shooting. It can fully fill narrow, multi-layer staggered thin-wall sand cores (engine water jackets, intake/exhaust manifolds, complex oil passage sand cores). Sand cores achieve uniform internal compactness without incomplete sand shooting or local looseness defects. The surface finish of casting inner cavities is significantly improved, with roughness up to Ra≤12.5μm, drastically reducing subsequent shot blasting and manual grinding & cleaning man-hours.
2.5 High Strength & Wear Resistance Ensures High Reclamation Rate of Used Sand for Waste Reduction & Environmental Compliance
Ceramic bead sand particles feature dense sintering and high Mohs hardness, resulting in extremely low particle breakage across the full workflow of precoating production, sand shooting, shakeout and thermal reclamation. In contrast, the sharp edges of silica sand wear and pulverize easily, and fine powder drastically reduces the strength of reclaimed sand.When the reclamation system for ceramic bead precoated sand is adopted, the reclamation rate of used sand remains stable above 96%. Supplementary new sand dosage is merely one-third of that in silica sand processes. The discharge of solid waste sand is greatly reduced without silicosis dust pollution, complying with industrial foundry environmental emission control policies and cutting solid waste disposal fees.
2.6 Good Shakeout Performance for Easy Casting Cleaning
After being heated at high temperature, the resin film on ceramic bead precoated sand decomposes easily. Sand cores automatically collapse after castings cool down, enabling smooth shakeout of deep cavity and slender oil passage sand cores without manual core chiseling. It drastically shortens casting cleaning man-hours, especially suitable for hydraulic and engine castings with complex internal structures.
3. Standard Process Parameters for Precoated Sand Production
3.1 Particle Size Selection of Ceramic Bead Sand
- Shell cores for ordinary gray iron & ductile iron small castings: 40/70 mesh;
- Complex thin-wall parts such as engine blocks, cylinder heads and turbochargers: wide-distribution 50/100 mesh;
- High-temperature steel castings of carbon steel & stainless steel: fine-grained 60/140 mesh multi-sieve wide grading to enhance refractory and anti-metal penetration performance.
3.2 Two Mainstream Mixing Ratio Schemes
Scheme 1: 100% Pure Ceramic Bead High-End Precoated Sand (High-Precision Steel & Turbo Parts)
100% ceramic bead sand, phenolic resin addition 1.6%~1.9%, hexamethylenetetramine curing agent accounts for 14%~17% of resin weight, stearate lubricant 0.05%~0.2%; tensile strength 6.5~8MPa, gas evolution ≤12mL/g.
Scheme 2: Mixed Precoated Sand of Ceramic Bead Sand & Quartz Sand (Cost-Effective Universal Scheme)
Ceramic bead sand accounts for 20%~45% of total raw sand, with the rest as scrubbed quartz sand; phenolic resin addition 1.2%~1.6%, balancing casting quality and raw material cost, suitable for mass production of ordinary ductile iron & gray iron castings.
3. Key Production Control Points
- Segregation prevention for mixed sand: The specific gravity of ceramic bead sand is higher than quartz sand, which easily causes stratification of light and heavy sand during sand mixing and sand shooting. It is necessary to optimize sand shooting pressure, adjust the blanking structure of sand hoppers, regularly detect the ceramic bead sand content in reclaimed sand, and supplement the mixing ratio of new sand.
- Matching of precoating raw materials: High-purity phenolic resin shall be selected for precoating production, and miscellaneous additives shall be minimized to ensure uniform coating of resin film on the smooth surface of ceramic bead sand and avoid local resin accumulation which increases gas evolution.
- Supporting reclamation system: Equipped with thermal + friction reclamation equipment to completely remove residual resin film on sand grains. Reclaimed sand can be recycled for 8~10 cycles with performance close to brand-new ceramic bead sand.
- Matching coating: Sand cores for steel and high-temperature resistant ductile iron castings can be thinly coated with special refractory shielding coating to further improve casting inner cavity finish and completely eliminate chemical metal penetration.
4. Summary of Comprehensive Benefits in Practical Production
- Quality Benefit: Resolves four major defects including veining, metal penetration, blowholes and sand core cracking in one go. Casting dimensional accuracy reaches CT6~CT7 grade, inner cavity surface finish is greatly optimized, and casting rejection rate drops by over 60%.
- Cost Benefit: Phenolic resin consumption is reduced by 20%~35%, eliminating procurement of chromite sand and anti-veining additives. The reclamation utilization rate of used sand exceeds 96%, cutting comprehensive molding material costs per ton of castings by 15%~30%.
- Production Benefit: Excellent flowability stabilizes forming of complex thin-wall sand cores and reduces rejects from poor sand shooting. Good sand core shakeout performance shortens grinding & cleaning man-hours by 40%, and mass production core-making capacity is significantly boosted.
- Environmental Benefit: Lower total resin addition reduces flue gas volatilization during pouring and improves workshop working environments. Waste sand discharge is drastically cut without silicosis dust hazard, meeting environmental control requirements for foundry industry.
5. Applicable Industries & Casting Range
- Automotive Foundry Industry: Engine blocks, cylinder heads, intake/exhaust manifolds, turbocharger housings, transmission housings, complex sand cores for water jackets and oil passages.
- Hydraulic Pump & Valve Industry: Carbon steel/stainless steel hydraulic valve bodies, water pump housings, multi-way valves and precision fluid castings.
- Construction Machinery & General Machinery: High-grade ductile iron axle housings, alloy gray iron, small-to-medium steel castings and rail transit precision castings.
