Cast Iron Vibration Damping
Who this helps: Design Engineers / Buyers targeting low-noise, low-vibration (NVH) housings, bases, pump/gearbox frames, and brackets.
What you’ll get: clear physics for damping, when gray/grey iron beats ductile iron or steel, grade & microstructure tips, DFM rules that kill ringing, copy-paste drawing notes, and an acceptance test plan you can run on pilots.
Prepared by YB Metal Solution. Share your drawing via /rfq—YB Metal will return a part-specific material pick, rib/wall update, and NVH test plan.
Author: YB Metal Solution Engineering Team (hereafter YB Metal)
Table of contents
- Why gray iron damps better
- Where gray vs ductile/steel makes a real difference
- Grades & microstructure (A48 ⇆ EN-GJL) for NVH
- DFM for damping: ribs, walls, mounts, and joints
- Process & finish effects on NVH
- How to measure and accept: quick NVH plan
- What to put on the drawing (copy–paste)
- What YB Metal delivers
- Related internal resources
- FAQs
Why gray iron damps better
- The short physics: flake graphite in gray/grey iron creates lots of graphite–matrix interfaces. Under vibration, micro-slip and micro-plasticity at these interfaces convert mechanical energy into heat (internal friction / loss factor).
- By contrast, ductile (SG) iron has graphite nodules with far fewer interfaces per unit volume → higher stiffness & fatigue, lower damping. Steel sits even lower on damping.
- Implication for design: if noise and “ringing” dominate, gray iron first; if ultimate strength/impact rules, consider ductile iron (or ADI) and add damping via geometry/mounts.
Reference comparisons on your site:
Where gray vs ductile/steel makes a real difference
| Part family | Typical duty | Why gray iron still wins |
|---|---|---|
| Pump/gearbox housings & bases | Broadband excitation from gears/impellers | Gray iron knocks down structure-borne noise and ringing; keeps cost low |
| Motor/drive end shields & pedestals | Harmonic orders from motors, belts | Higher damping + cast-in ribbing reduces tonal whine |
| Compressor/AG equipment frames | Impacts, pulsation, road-salt environments (coat outside) | Gray iron + coating system delivers NVH + cost balance |
| Machine tool sub-bases, brackets | Large panels, modal issues | Better loss factor lowers amplification at modes |
When to not choose gray iron: thin, highly loaded structures needing high yield/impact → ductile iron / ADI with NVH handled by mounts, ribs, mass loading.
Grades & microstructure (A48 ⇆ EN-GJL) for NVH
Rule of thumb: within gray iron, more pearlite / higher grade → higher stiffness, usually slightly lower damping; more ferrite / lower grade → more damping but lower stiffness. Pick a middle grade that meets stiffness while preserving damping.
| Use case | Gray iron grade (US ⇆ EU) | NVH intent |
|---|---|---|
| General housings/bases | ASTM A48 Class 35–40 ⇆ EN-GJL-250–300 | Balanced stiffness & damping |
| Stiff panels with moderate loads | A48 Class 40–50 ⇆ EN-GJL-300–350 | More stiffness; still better damping than DI/steel |
| Lightly loaded, maximum damping | A48 Class 30 ⇆ EN-GJL-200 | Highest damping; check stiffness/deflection |
If you must step up to ductile iron for strength, make it intentional and manage NVH via DFM (next section). Ductile/ADI grade comparisons:
DFM for damping: ribs, walls, mounts, and joints
Wall & rib strategy
- Favor uniform walls with ribbing instead of slabs: ribs move modes and add path damping.
- Use fillets/radii to avoid stress risers that excite ringing: see Fillet & Radius Rules
- Start from wall guidelines: Wall Thickness Rules
Mounting & isolation
- Design mount pads to accept elastomer or visco shims; add through-thickness ribs that lead vibration into damped supports.
- Avoid long, unsupported panels; break with stiffener grids.
Joints & covers
- Use gasketed joints (visco layer) over metal-to-metal where possible.
- For covers/guards, bias to gray iron over steel sheet when NVH is critical.
Machining & surfaces
- Unnecessary full-face machining removes textured as-cast skin that helps damping; machine only where needed.
- Surface finish targets and process comparisons:
Tolerances & datums
Keep CT grades realistic to avoid over-machining mass away:
Process & finish effects on NVH
- Green sand often yields fine as-cast skins and practical damping for housings; resin sand is ideal for heavy sections. Compare capabilities:
- Green Sand Casting
- Resin vs Green Sand
- Shell molding helps thin, uniform walls that shift modes upward (may reduce mass-based damping—add ribs/visco pads):
- Shell Molding for Thin-Wall
- Coatings won’t replace material damping, but powder + elastomer interfaces can trim tonal peaks on covers.
How to measure and accept: quick NVH plan
Pilot acceptance (practical, shop-floor friendly):
- Material decision: gray iron grade pick with A48 ⇆ EN-GJL mapping to hit stiffness & damping.
- Rib/wall optimization: quick FE-guided rib layout, fillet sizes, and wall uniformity recommendations.
- Process choice: green/resin/shell with CT & Ra expectations and machining stock.
- Pilot evidence pack: ring-down & FRF plots, installed sound power ΔdB, and CMM on mounting features.
Need an NVH-specific design review? Upload your drawing at /rfq—we’ll return recommendations and a quote.
What YB Metal delivers
YB Metal quotes with a machining plan attached:
- Cutting data by operation (vc, f, ap), tool list and expected tool life by HBW.
- Coolant/filtration setup, burr and finish plan (Ra by zone).
- Cycle-time and cost impact of gray vs ductile options; suggestions to tweak casting (boss/rib) for shorter cycles.
Upload your drawing via —we’ll return a part-specific plan and quotation.
FAQs
CTA — specify with proof, not guesses
Choose gray iron on purpose for NVH—then prove it with a simple ring-down + FRF plan. Upload your drawing to /rfq and YB Metal will send back a grade pick, rib plan, and test sheet.