(Reprinted from: silicone)
Precision casting (also known as investment casting) is an advanced process that can produce high-precision and complex structural metal parts, and is widely used in aerospace, medical devices, automobile manufacturing and other fields. In the precision casting process, the preparation of the molded shell is a key link, which directly affects the surface quality, dimensional accuracy and yield of the casting. As an inorganic binder, silicon sol has become one of the core materials for the preparation of precision cast molded shells due to its excellent high temperature resistance, stability and environmental protection characteristics. This article systematically discusses the current application status, research progress and future development direction of silica sol in precision casting.
one
Characteristics of Silicon Sol and Its Function in Precision Casting
Silica Sol is a colloidal solution formed by dispersing nanoscale silica particles in water, with the following characteristics:
1High adhesion:The SiO₂ particles in the silicon sol form a three-dimensional network structure through dehydration and condensation, giving the shell a good room temperature and high temperature strength.
2low thermal expansion coefficient:The silicon sol shell has excellent dimensional stability at high temperatures, reducing the risk of casting deformation.
3. Environmental protection:Water is used as the dispersion medium, and it has no toxic volatiles, which is in line with the trend of green manufacturing.
4. Surface wetting:It is tightly combined with refractory materials (such as zircon sand and corundum powder) to improve the density of the shell.
In precision casting, silicon sol is mainly used for:
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Adhesives: Replace traditional ethyl silicate hydrolysate for preparation of multi-layer shells;
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Paint carrier: Mix it with refractory powder to make top coat to improve the surface finish of the casting;
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Enhancement agent: Improve thermal shock resistance and creep resistance of the shell through modification.
two
Preparation process and optimization of silicon sol shell
1. Typical shell making process
Silicone sol shells usually adopt the “impregnation-sand-drying” cycle process:
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Top coating: Silicone sol + fine-grained zircon powder (particle size
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Reinforcement layer: Silicone sol + bauxite or mullite sand (particle size 60-100 mesh), improving the overall strength of the shell;
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Drying conditions: Temperature is 25-30℃, humidity is 40-60%, drying time per layer is 4-8 hours.
2. Research on process optimization
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Drying process improvements: Use microwave drying or vacuum drying technology to shorten the drying time by more than 50%;
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Hierarchical structure design: Use nano-silicon sol (particle size 10-20nm) on the surface layer to reduce surface defects of the castings;
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Compound adhesive development: The silicone sol is combined with ethyl silicate or aluminum sol to improve the high temperature strength of the mold shell (the flexural strength reaches 3-5MPa at >1500℃).
three
Progress in the performance of silicon sol shell
1. High temperature performance improvement
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Nanomodification: Add nano Al₂O₃ or ZrO₂ particles (1-3wt%), and the high-temperature bending strength of the mold shell is increased by 30%-50%;
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Fiber reinforcement: Introduce ceramic fibers (such as aluminum silicate fibers) to reduce the tendency of cracking of the molded shell.
2. Environmentally friendly silicon sol system
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Water-based shell instead of alcohol-based shell: Reduce VOCs emissions and reduce drying energy consumption by 20%;
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Regenerated silicone sol technology: The waste silicon sol is recycled by centrifugation, with a utilization rate of more than 70%.
3. Exploration of intelligent applications
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Combined with 3D printing: Use silicon sol as a filler for photocuring resin to directly print complex shells;
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Sensor Embed: Integrate temperature/stress sensors in the molded shell to monitor the casting process in real time.
Four
Challenges and future development directions
1. Existing problems
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The shell is highly brittle and is prone to microcracks during dewaxing or roasting;
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The drying time is still longer than that of the organic binder system;
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Nanomotion costs are high and industrial applications are limited.
2. Future research focus
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Compound adhesive development: Study the hybrid system of silicon sol-organic polymers (such as polyvinyl alcohol), balance strength and toughness;
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Rapid curing technology: Develop ultraviolet curing or electric field-induced curing processes;
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Multifunctional shell design: Give intelligent characteristics such as self-healing and thermal conductivity regulation of the type shell.
five
Conclusion
With its unique physical and chemical properties, silicon sol has become one of the first choices for precision cast molded shell materials. Through nanomodification, composite adhesive design and process innovation, its high-temperature performance and environmental protection have been significantly improved. In the future, with the advancement of intelligent manufacturing and green manufacturing, silicon sol shell technology will continue to develop in the direction of high efficiency, intelligence and sustainability, providing better and more environmentally friendly solutions for the precision casting industry.