Silica sol investment casting delivers tight dimensional tolerances (+/-0.1 mm per 25 mm per ISO 8062-3 CT4-CT6) and superior surface finishes Ra 1.6 to 3.2 um (63-125 uin) without extensive primary machining. Unlike water glass (sodium silicate) casting, the silica sol binder system eliminates surface decarburization, reduces inclusion defects, and maintains precise geometry on complex internal passages, thin walls down to 1.5 mm, and sharp edges.
Our facility produces custom stainless steel components ranging from 0.01 kg to 50 kg for critical fluid handling, marine hardware, food processing equipment, and chemical processing components. Every heat is verified via optical emission spectrometry (OES) to guarantee material chemistry compliance before pouring.
Manufacturing Process
The silica sol investment casting process utilizes a ceramic shell build-up system to achieve fine surface fidelity and high dimensional repeatability across production runs.
Wax Injection & Pattern Assembly: Precision aluminum tooling injects modified wax patterns. Patterns are tree-assembled onto central runners with engineered gating to minimize turbulence and shrinkage porosity.
Ceramic Shell Building: Assembly trees undergo multi-coat dipping in controlled silica sol slurry and zircosil/mullite stucco dipping. Multi-stage humidity-controlled drying chambers (22°C +/- 2°C, relative humidity 55% +/- 5%) ensure shell strength without micro-cracking.
Steam Autoclave Dewaxing: Rapid steam dewaxing at 8 to 10 bar pressure clears pattern wax instantly without shell thermal expansion damage. Wax is recovered and filtered for non-critical gating re-use.
High-Temperature Shell Sintering: Shells burn out at 1,000°C to 1,150°C to burn residual organic matter and sinter ceramic grains into a rigid, non-reactive mold.
Induction Melting & Pouring: Stainless steel heats melt in medium-frequency induction furnaces. Molds pour while hot (950°C to 1,050°C) to prevent cold shuts and incomplete filling in thin sections.
Shakeout & Finishing: Post-cooling ceramic shells are removed via pneumatic knock-out and high-pressure water blasting. Castings undergo riser cutoff, grinding, shot blasting, heat treatment, and passivation.
Materials and Technical Specifications
Chemical Composition & Mechanical Performance
|
Alloy Grade |
Standard |
C (%) |
Cr (%) |
Ni (%) |
Mo (%) |
Tensile Strength (MPa) |
Yield Strength (MPa) |
Elongation (%) |
Hardness (HB) |
|
CF8 (304) |
ASTM A743 |
<= 0.08 |
18.0-21.0 |
8.0-11.0 |
- |
>= 485 |
>= 205 |
>= 35 |
140-180 |
|
CF3 (304L) |
ASTM A743 |
<= 0.03 |
18.0-21.0 |
8.0-12.0 |
- |
>= 485 |
>= 175 |
>= 35 |
130-170 |
|
CF8M (316) |
ASTM A743 |
<= 0.08 |
18.0-21.0 |
9.0-12.0 |
2.0-3.0 |
>= 485 |
>= 205 |
>= 30 |
140-190 |
|
CF3M (316L) |
ASTM A743 |
<= 0.03 |
17.0-21.0 |
9.0-13.0 |
2.0-3.0 |
>= 485 |
>= 175 |
>= 30 |
135-175 |
|
1.4408 |
EN 10213 |
<= 0.07 |
18.0-20.0 |
9.0-12.0 |
2.0-2.5 |
440-640 |
>= 185 |
>= 30 |
140-200 |
|
1.4581 |
EN 10213 |
<= 0.07 |
18.0-20.0 |
9.0-12.0 |
2.0-2.5 |
500-700 |
>= 210 |
>= 25 |
150-210 |
|
17-4PH (CB7Cu-1) |
ASTM A747 |
<= 0.07 |
15.5-17.5 |
3.6-4.6 |
Cu 2.8-5.0 |
>= 930 (H1075) |
>= 790 (H1075) |
>= 10 |
310-380 |
|
2205 (Duplex) |
ASTM A890 4A |
<= 0.03 |
21.0-23.0 |
4.5-6.5 |
2.5-3.5 |
>= 620 |
>= 450 |
>= 25 |
220-290 |
Technical Capabilities Matrix
|
Parameter |
Specification / Capability |
|
Linear Tolerances |
ISO 8062-3 CT4-CT6 (VDG P690 D1/D2) |
|
Surface Roughness |
Ra 1.6 um to 3.2 um as-cast (Ra 0.4 um post-polishing) |
|
Minimum Wall Thickness |
1.5 mm (localized features down to 1.0 mm based on geometry) |
|
Weight Range |
0.01 kg to 50.0 kg |
|
Maximum Envelope Size |
600 mm x 500 mm x 400 mm |
|
Angle Tolerance |
+/-0.5° |
Key Product Features
Near-Net Shape Accuracy:
Reduces secondary machining stock to 0.5 mm - 1.0 mm on critical faces, eliminating draft angles required by sand or forging processes.
Corrosion Resistance:
Pure silica sol shells eliminate carbon pickup during pouring, protecting intergranular corrosion resistance in 304L, 316L, and Duplex grades.
Complex Geometry Integration:
Internal fluid passages, undercuts, blind holes, and thin-walled structural webs are cast directly without multi-piece welding.
Fine Surface Quality:
Eliminates surface pitting and sand inclusions typical of sodium silicate or green sand castings, reducing polishing cycles for sanitary fittings.
Typical Applications
Fluid Handling & Valve Hardware: Valve bodies, ball valve spheres, butterfly valve discs, impeller blades, pump casings, and sanitary pipe unions.
Marine Components: Cleats, hinges, bow chocks, thru-hull fittings, deck hardware, and rudders exposed to saltwater environments.
Food & Pharmaceutical Processing: Homogenizer components, filling nozzles, pump housing manifolds, and sensor brackets requiring Ra < 0.8 um electropolished surfaces.
Industrial & Heavy Equipment: Lock components, conveyor chain links, structural brackets, burner nozzles, and pressure vessel nozzles.
Machining and Secondary Operations
Our in-house CNC machine shop handles tight-tolerance features directly on finished castings to supply drop-in assemblies:
CNC Milling & Turning:
3-axis, 4-axis, and 5-axis CNC machining centers achieve feature tolerances down to +/-0.008 mm.
Thread Cutting & Tapping:
Metric (M), NPT, BSPP, and BSPT precision internal and external threads.
Heat Treatments:
Solution annealing (1,040°C to 1,120°C followed by rapid water quench), precipitation hardening (H900, H1075, H1150 for 17-4PH), and stress relieving.
Surface Finishing:
Glass bead blasting, electro-polishing, mechanical mirror polishing (800 grit), chemical passivation per ASTM A967, and acid pickling.
Quality Control and Inspection
Every production lot undergoes verification against customer specifications and international standards using dedicated inspection tooling.
Chemical Verification: Spectrochemical analysis per heat with real-time melt adjustments via Oxford/Thermo Fisher Spectrometers.
Dimensional Inspection: Hexagon Coordinate Measuring Machine (CMM), 3D blue-light optical scanners, plug/thread gauges, and customized height gauges.
Non-Destructive Testing (NDT): Liquid Penetrant Inspection (LPI/PT) per ASTM E1417, Radiographic Testing (RT) per ASTM E1928, and Hydrostatic Pressure Testing up to 300 bar.
Destructive Testing: Tensile testing (Room & Elevated Temperature), Charpy V-Notch Impact Testing down to -196°C, Metallographic grain size/ferrite content analysis, and Brinell/Rockwell hardness testing.
Documentation: EN 10204 3.1 Material Test Reports (MTR), Dimensional Inspection Reports, Heat Treatment Charts, and NDT Certifications supplied with every shipment.
OEM and Custom Manufacturing
We process custom OEM projects from preliminary design evaluation through mass production. Our engineering team assists with casting design optimization to lower production costs and prevent defects before mold production.
DFM Engineering Analysis:
Solidification modeling via MAGMASOFT/ProCAST to detect shrinkage cavities, hot tears, and air entrapment prior to tooling cut.
Tooling Production:
Aluminum pattern dies machined via high-speed CNC centers in-house, ensuring short lead times (15 to 20 days for tooling and initial sample approval).
Reverse Engineering:
3D optical scanning of physical samples to recreate parametric CAD models for obsolete or undocumented replacement parts.
What Buyers Should Provide for an RFQ
To receive a detailed commercial quotation and DFM assessment within 24-48 hours, please submit the following specifications:
2D Engineering Drawings: PDF/DWG format specifying critical dimensions, linear/geometric tolerances, surface finishes, and inspection points.
3D CAD Models: STEP, IGES, or X_T files for volume, wall-thickness, and gating feasibility evaluations.
Material Grade: Specific international standard (e.g., ASTM A743 CF8M, EN 10213 1.4408) or required mechanical properties.
Order Volume: Estimated Initial Order Quantity (EOR) and Annual Usage Quantity (EAU) to optimize tooling cavitation.
Secondary Processing Requirements: Heat treatment specifications, CNC machining requirements, surface treatment (bead blast, electropolish), and special packaging.
Testing & Certification Needs: Requirement for 3.1 MTR, NDT (PT/RT), Pressure testing, or 3rd-party inspections (SGS, TUV, BV).
Frequently Asked Questions
Q: What is the primary difference in surface quality between silica sol and sodium silicate (water glass) casting?
A: Silica sol casting uses a pure zircon powder/silica sol binder system that achieves a surface roughness of Ra 1.6 - 3.2 um. Water glass casting produces a rougher surface (Ra 6.3 - 12.5 um) and suffers from surface decarburization, requiring significantly more secondary machining and grinding.
Q: What standard linear tolerances can your casting process achieve without machining?
A: Standard production achieves ISO 8062-3 CT5-CT6 tolerances. Critical dimensions can be held to CT4 (+/-0.1 mm for dimensions under 25 mm) through controlled shell drying and precision wax injection tooling.
Q: How do you prevent intergranular corrosion in 316L castings?
A: Carbon content is controlled below 0.03% during induction melting. All stainless steel castings undergo full solution annealing (1,080°C to 1,120°C followed by rapid water quenching) to re-dissolve chromium carbides into the austenite matrix.
Q: What are your standard lead times for tooling, samples, and mass production?
A: Tooling & First Article Samples (FAIR): 15 to 25 calendar days.
Mass Production Delivery: 30 to 40 calendar days following sample sign-off.
