Custom Industrial Flywheels
in Cast Iron & Ductile Iron
Kurt Foundry engineers and manufactures heavy-duty custom cast iron flywheels — from 50 lbs to 5,000 lbs per piece — for industrial machinery, diesel power plants, stamping presses, and large compressors. We deliver fully CNC-machined, porosity-verified components directly to your facility worldwide.
When Rotational Mass Cannot Fail
A flywheel failure is not a maintenance event — it is a production catastrophe. Internal casting defects invisible to the naked eye can trigger a full burst at operating speed, taking out the machine and the line with it.
Kurt Foundry pours custom cast iron flywheels from 50 lbs to 5,000 lbs, with every casting verified by 3D solidification simulation, ultrasonic testing, and CMM inspection before it leaves our facility.
We handle everything in-house — casting, CNC machining, and quality documentation — then ship directly to your facility anywhere in the world. No brokers, no middlemen, no surprises on landed cost.
Whether your application needs the vibration-damping of custom gray iron castings or the burst resistance of custom ductile iron castings, our engineering team works directly from your 2D drawings and 3D CAD files.
Choosing the Right Iron Grade for Your Custom Flywheel
Material selection is the most critical engineering decision in any custom flywheel project. The wrong grade can mean a part that cracks under cyclic stress, warps during machining, or bursts at operating speed. Below is how our engineering team evaluates material fit for every heavy-duty application.
Gray Iron Flywheels (ASTM A48)
Gray iron is the most widely specified material for heavy industrial flywheels. Its flake graphite microstructure absorbs and dissipates torsional shock loads — protecting drivetrain bearings and gearboxes from vibrational damage.
We cast gray iron flywheels to ASTM A48 Class 30 and Class 40, covering standard industrial presses, jaw crushers, and large compressor drives.
Gray iron machines exceptionally well, allowing our CNC team to hold tight bore concentricity on pieces that other materials would resist — at a lower cost per kilogram than ductile iron.
Ductile Iron Flywheels (ASTM A536)
When a flywheel operates at high RPM or faces sustained impact loading, ductile iron is the correct choice. Its spheroidal graphite nodules allow the material to deform plastically before fracturing — preventing catastrophic burst failure.
We cast ductile iron flywheels to ASTM A536 Grade 65-45-12 and 80-55-06, specified for high-RPM diesel generator sets, heavy marine propulsion systems, and severe-duty industrial equipment.
Where burst containment is a hard engineering requirement — not a preference — ductile iron delivers the tensile strength and ductility that gray iron cannot.
Custom Flywheel Material Grades & Mechanical Properties
| Standard / Grade | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Typical Flywheel Applications |
|---|---|---|---|---|
| ASTM A48 Class 30 (Gray Iron) | ≥ 207 | N/A (Brittle) | N/A | Standard industrial press flywheels, machine tools, vibration-damping drives. |
| ASTM A48 Class 40 (Gray Iron) | ≥ 276 | N/A (Brittle) | N/A | Heavy-duty jaw crushers, large compressor flywheels requiring higher tensile strength. |
| ASTM A536 65-45-12 (Ductile Iron) | ≥ 448 | ≥ 310 | ≥ 12 | High-RPM diesel engine flywheels, generator drive flywheels, high-stress rotational assemblies. |
| ASTM A536 80-55-06 (Ductile Iron) | ≥ 552 | ≥ 379 | ≥ 6 | Severe-duty industrial flywheels requiring maximum burst resistance and impact tolerance. |
Single-Source CNC Machining & Guaranteed Concentricity
Casting and machining are handled in the same facility. Our 5-axis CNC centers turn the OD, bore the center hole, and cut the keyway — all held to strict runout tolerances verified by CMM.
Single-source control eliminates the tolerance stack-up that occurs when casting and machining are split between two suppliers.
Every flywheel ships with a full CMM inspection report — statically balanced and ready for your drive assembly.
How We Manufacture Your Custom Industrial Flywheel
1. DFM Review & 3D Solidification Simulation
Before any tooling is cut, our engineers import your CAD file into Magmasoft 3D simulation software. We model the complete solidification behavior of the flywheel casting — paying particular attention to the thick central hub, where the last metal to solidify is most vulnerable to internal shrinkage porosity. We engineer optimized gating and riser placements to feed molten iron into the hub directly, ensuring the finished casting is fully dense and porosity-free. No tooling order is placed until the simulation confirms a sound casting.
2. Furan Resin Sand Molding
Our automated lines use furan resin sand to create rigid, dimensionally stable molds. Understanding the types of sand used in sand casting is essential when producing heavy flywheels — the mold must resist the enormous metallostatic pressure of several thousand pounds of molten iron without wall movement. Furan resin binders provide the strength to hold exact tolerances during pouring.
3. Spectrometer-Verified Pouring
Immediately before each pour, we conduct spectrometric chemical analysis of the molten iron. For gray iron flywheels, we verify the Carbon Equivalent (CE) to confirm the correct graphite flake morphology for maximum vibration damping. For ductile iron flywheels, we verify the nodularity rate to guarantee the spheroidal graphite structure that delivers burst resistance. Chemistry is documented and included in the Material Test Report (MTR) for your records.
4. Controlled Thermal Stress Relief
Heavy flywheels present a thermal engineering challenge during solidification: the thick hub and the thinner outer web cool at significantly different rates. This differential cooling generates internal residual stresses locked into the casting. If not eliminated, these stresses relieve themselves during CNC machining — causing the part to warp and go out of tolerance. We perform controlled thermal stress relief heat treatment on all heavy flywheel castings before any machining begins, ensuring the part is dimensionally stable throughout the entire cutting process.
5. CNC Machining, UT/MPI Inspection & CMM Verification
After shot-blasting, the stress-relieved casting transfers to our 5-axis CNC machining centers for turning, boring, and keyway cutting. Critical hub sections are then scanned by ultrasonic testing (UT) to confirm zero internal voids. High-stress transition zones undergo magnetic particle inspection (MPI) for surface crack detection. Finally, a Coordinate Measuring Machine (CMM) verifies all critical dimensions — bore diameter, OD concentricity, and runout tolerances — before the part is approved for packaging.
Quality Control Built for Global OEM Standards
Industrial flywheels are safety-critical rotating components. A quality escape that reaches your assembly floor can trigger a full line shutdown, a costly recall, or — in the worst case — an uncontained burst. Our quality system is designed so that every defect is caught in our facility before shipment. Lead engineers at our OEM customers worldwide receive a complete quality documentation package with every order.
- Ultrasonic Testing (UT) — Hub Integrity: We scan every heavy hub section with calibrated UT equipment to guarantee zero internal shrinkage cavities or gas voids. A clean UT scan is a prerequisite for machining approval.
- Spectrometry & Full Material Test Reports (MTRs): We provide fully traceable MTRs documenting the exact chemical composition of your specific casting batch — Carbon Equivalent for gray iron, nodularity rate for ductile iron — for your QA file.
- CMM Dimensional Verification: Our Coordinate Measuring Machine verifies the machined bore diameter, outer diameter concentricity, and runout tolerances on every flywheel before packaging. CMM reports ship with the part.
- Magnetic Particle Inspection (MPI) — Surface Integrity: We apply MPI to all high-stress transition areas — hub-to-web fillets and spoke roots — to detect microscopic surface cracks before the flywheel is approved for export.
Worldwide Export Shipping — Direct from Foundry
Kurt Foundry exports to customers across North America, Europe, Southeast Asia, the Middle East, and Australia. We have refined the international logistics process over thousands of shipments and manage the entire chain from our foundry floor to your receiving dock.
We offer flexible shipping terms including FOB, CIF, and DDP depending on your destination and preference. Your procurement team receives a single direct-factory price with full freight transparency — no hidden costs.
All heavy flywheels are packaged in ISPM-15 certified fumigated wooden crates with rust-preventative oil coating and internal blocking to prevent movement under ocean transit vibration.
Ocean Freight
We arrange full-container or LCL ocean freight from Qingdao to ports worldwide — USA, Canada, Europe, Southeast Asia, Middle East, and Australia.
Flexible Trade Terms
We support FOB, CIF, and DDP shipping terms. Choose the arrangement that fits your procurement process and import requirements.
Last-Mile Delivery
Under DDP terms, we arrange customs clearance and inland trucking directly to your facility — available for USA, Canada, and select European destinations.
ISPM-15 Crating
All flywheels ship in certified fumigated wooden crates with rust-preventative coating and full export documentation.
Frequently Asked Questions
The correct material depends on your operating speed, impact loading, and failure mode requirements. Gray iron (ASTM A48 Class 30 or 40) is the standard choice for heavy stamping presses, large compressors, and crusher drives because its flake graphite microstructure provides outstanding vibration and torsional shock damping. Ductile iron (ASTM A536 Grade 65-45-12 or 80-55-06) is specified when the flywheel operates at high RPMs or when a burst failure — rather than a crack — is an absolute engineering requirement. Our engineering team reviews your application parameters and recommends the grade before any tooling is ordered.
The thick central hub of a heavy industrial flywheel is the highest-risk area for internal shrinkage porosity because it is the last section to solidify. We address this directly during the DFM stage using Magmasoft 3D solidification simulation. Before we cut a single pattern, our engineers model the complete thermal solidification sequence and design the gating and riser system to feed a continuous supply of molten iron into the hub until it is fully solid. To understand our approach in more detail, read how sand casting works and how proper riser engineering prevents internal voids.
Our heavy resin sand molding lines and floor molding pits allow us to pour custom cast iron flywheels ranging from 50 lbs up to 5,000 lbs (approximately 2.5 tons) as a single casting. For flywheels above 500 lbs, we use floor molding with custom-fabricated patterns to accommodate the dimensional scale. Contact our team with your weight and diameter requirements to confirm feasibility.
We supply fully CNC-machined flywheels held to tight concentricity and runout tolerances verified by CMM inspection. This precision machining ensures the flywheel is statically balanced and very close to dynamic balance. The majority of our OEM customers perform the final precision dynamic balancing step after mounting the flywheel onto their specific motor shaft or drive assembly — at which point the complete rotating assembly can be balanced as a system. If your application requires us to perform in-house dynamic balancing before export, please specify this requirement in your RFQ.
Yes. We export to customers across North America, Europe, Southeast Asia, the Middle East, and Australia. We offer FOB, CIF, and DDP shipping terms depending on your destination and preference. All heavy flywheels are packaged in ISPM-15 certified fumigated wooden crates with rust-preventative coating for ocean transit. Contact us with your destination port and we will provide a full landed-cost breakdown.
Each custom flywheel shipment includes a full quality documentation package: a Material Test Report (MTR) with certified chemical composition and mechanical properties of the specific casting batch, UT inspection records for hub sections, MPI inspection records for high-stress surface areas, and a CMM dimensional inspection report verifying bore concentricity, outer diameter, and runout tolerances. Export documents include a commercial invoice, packing list, Bill of Lading, and ISPM-15 phytosanitary certificate for the wooden crating.
Ready to Quote Your Custom Industrial Flywheel?
Send us your 2D engineering drawings and 3D CAD files (STEP, IGES, or SolidWorks formats). Our foundry engineering team will conduct a complimentary Design for Manufacturability (DFM) review and return a competitive direct-factory quote within 48 business hours.
Submit Your Drawings & Get a QuoteNo CAD files? No problem. Contact us first — our team will explain the reverse engineering process and guide your submission step by step.