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Water Soluble Core Investment Casting is a casting process that uses water-soluble materials as cores, mainly used to manufacture castings with complex internal cavity structures. This technology combines the characteristics of traditional investment casting and water-soluble materials and is characterized by high efficiency, environmental protection and high precision.
Water soluble core investment casting usually uses water-soluble salts (such as sodium chloride, sodium sulfate, etc.) or wax as the core substrate. These materials have good mechanical strength at high temperatures and can quickly dissolve in water after cooling, thereby achieving rapid removal of the core.
Applications of Water Soluble Core Investment Casting
Water soluble core investment casting is particularly advantageous in applications that require complex internal structures, such as spring box castings,flange body castings, etc.
This technology can produce more complex cavity structures, precise holes, and complex geometries than traditional tool designs. At the same time, by controlling and monitoring its performance, injection, processing and dissolution times can be optimized. In addition, the dissolution process of water-soluble core materials is simple and environmentally friendly. It can be quickly dissolved by soaking the casting in water and adding a small amount of acid, thereby reducing subsequent processing.
flange body casting
spring box casting
The advantages of investment casting technology using water-soluble core materials are not limited to spring boxes and flange body castings, but are also widely used in the fields of automobiles, medical equipment, precision electronics, etc. For example, in the automotive industry, it is also used to produce exhaust system components (such as catalytic converter housings), cooling system components (such as water pump housings), and electrical system components (such as starter parts). These applications all rely on the high precision and complex internal structure capabilities brought by water-soluble core materials.
Water Soluble Core Investment Casting Parameters
| Parameter Category | Typical Scope/Requirements | Optimization Direction And Description |
| Core Parameters | ||
| Core Material Composition | Magnesium sulfate-based (MgSO₄), sodium chloride-based (NaCl) or complex salts (with binder) | Need to have high strength (compression ≥ 10MPa) and fast dissolution; compound salt can be added starch / PVA to improve dispersibility |
| Core Pressing Pressure | 80–120 MPa | Too low pressure leads to uneven density, too high easy to crack; need to control the powder moisture (1-3%) to improve molding properties |
| Core Sintering Temperature | 200-300°C (hold for 1-2 hours) | Sintering temperature too low leads to insufficient strength, too high affects the dissolution rate; composite salt needs to be heated up in stages to prevent thermal cracking |
| Mold and Shell Parameters | ||
| Molded Case Breathable Design | Topcoat viscosity: 25-30 s (flow cup #4) | High air permeability avoids gas retention during pouring; Alumina fiber (0.5-1%) is added to the top layer to enhance air permeability. |
| Number Of Layers Of Mold Shell | 5-7 layers (additional reinforcement in core support area) | Need to add 1-2 layers of paint around the core to prevent casting displacement; complex inner cavity using zircon sand + silica sol surface layer to enhance the finish |
| Pouring Parameters | ||
| Casting Temperature | “Aluminum alloy: 700-720°C (10-20°C lower than conventional) Stainless steel: 1550-1580°C” | Reduce the temperature to reduce the core thermal shock deformation; with the vacuum suction casting (vacuum degree ≤ 0.05MPa) to prevent air holes |
| Filling Speed | Aluminum alloy: 3-5 s (thin-walled parts) Stainless steel: High-pressure injection (filling pressure ≥ 0.8MPa) | Fast mold filling to avoid softening of the core; use of underfill + slit sprue to reduce turbulence |
| Dissolution Process | ||
| Dissolving Solution Temperature | 60-80°C (MgSO₄-based) 40-60°C (NaCl-based) | Too high a temperature accelerates mold shell corrosion, too low extends the dissolution time; adding 0.1% citric acid can improve the dissolution efficiency |
| Dissolution Time | 1-3 hours (depending on core volume) | Circulating water flow (flow rate ≥ 1.5m/s) or ultrasonic assistance (frequency 28kHz) is required for core wall thickness > 5mm. |
| Post-Processing Parameter | ||
| Residual Core Cleaning | High-pressure water gun (pressure ≥ 5MPa) + vibration screening | Complex internal cavity with backflush system; residual salts need conductivity detection (≤50μS/cm) |
| Green Processing | Neutralization of waste liquids (pH 6-8) + Metal ion recovery | Magnesium sulfate-based waste liquid can be crystallized and recycled; sodium chloride-based needs to be evaporated and concentrated for reuse |
Water Soluble Core Investment Casting Advantages
Solve the Problem of Core Pulling in Complex Cavities: This is one of the biggest advantages of water soluble core investment casting. As a new material to replace traditional wax cores, water-soluble cores have high strength and good demolding performance during the curing process, which is particularly suitable for the production of castings with complex inner cavity structures.
High Efficiency: The rapid dissolution characteristics of water-soluble cores make the casting cleaning process easier, reduce subsequent processing steps, and improve production efficiency.
High Precision: Due to the uniformity and stability of water-soluble core materials, the surface quality of castings is higher and the dimensional accuracy is also better.
Environmental Benefits: Water-soluble cores are environmentally friendly due to their recyclability. The salts and water used in the core removal process can be recycled, reducing waste and environmental impact.
Water Soluble Core Investment Casting Process
Step 1: Selection and Preparation of Core Materials
Water soluble core investment casting usually uses water-soluble salts (such as sodium chloride, sodium sulfate, etc.) or wax as core substrates. These materials have good mechanical strength at high temperatures and can be quickly dissolved in water after cooling, thereby achieving rapid removal of the core. For example, high-strength and water-soluble salt-based cores can be prepared by gel injection molding or lamination extrusion molding.
Step 2: Core Molding
Common molding methods include:
Gel injection molding: by mixing water-soluble materials with polymers to form a gel solution, injecting it into a mold for curing and molding, and then demolding to obtain a core.
Lamination extrusion molding: using an extruder to mix water-soluble powders with reinforcing materials (such as bauxite powder), a high-strength core is prepared by lamination extrusion.
3D printing technology: In recent years, 3D printing technology has been widely used in the rapid prototyping of water-soluble cores, especially for the manufacture of cores with complex shapes.
Step 3: Core Reinforcement and Optimization
In order to improve the strength and moisture resistance of the core, researchers added reinforcing materials such as kaolin and ceramic particles to the water-soluble core. For example, the tensile strength and moisture tolerance of the water-soluble potassium carbonate sand core can be significantly improved by adding kaolin. In addition, the water absorption and mechanical properties of the core can be improved by optimizing the sintering process.
Step 4: Casting and Cooling of the Casting
The prepared core is placed in the mold and the molten metal is poured for casting. After the casting is completed, the casting shrinks during the cooling process, and the core dissolves due to the characteristics of the water-soluble material, thereby forming an internal cavity structure.
Step 5: Post-treatment and Cleaning
After the casting is cooled, the residual core material can be quickly removed by simple water washing, thereby avoiding the chemical corrosion and environmental pollution problems in the traditional ceramic core cleaning process.
Step 6: Surface Quality Improvement
To improve the surface quality of the casting, a waterproof film can be set on the surface of the water-soluble core to prevent water vapor from eroding the core during demolding.