Guided by YB Metal (Suzhou, China) — resin sand vs green sand & shell molding under one roof, with machining, simulation, and traceable QA.
If you’re choosing between resin sand casting and green sand, start with accuracy, surface finish, core complexity, and batch economics. This guide gives practical ranges (ISO 8062 CT & Ra), wall rules, decision tables, and drawing notes you can put on your RFQ today.
Table of contents
- Quick definitions & when each shines
- Capability compare: CT grades & surface finish
- Wall thickness, weight & batch ranges
- Cores, yield & cost levers
- Drawing & RFQ notes (what to specify)
- Decision matrix (copy-paste)
- FAQs
Quick definitions & when each shines
- Resin sand / No-bake（self-hardening）: Sand mixed with a liquid binder (phenolic/furan/alkaline phenolic, etc.) cures in the mold. Pros: better dimensional consistency than green sand, great for cores and medium-to-large housings; good surface finish; flexible for low-to-mid volumes.
- Green sand: Clay-bonded sand compacted around the pattern and poured “green” (moist). Pros: lowest cost per mold, fast cycles, excellent for high-volume simple shapes; modern lines still achieve solid consistency with SPC.
Capability compare: CT grades & surface finish
Indicative ranges. Your drawing/spec and foundry capability prevail.
| Process | ISO 8062-3 CT grade (typical) | 100 mm linear tol (indicative) | Surface finish Ra (as-cast) | Notes |
|---|---|---|---|---|
| Green sand | CT9–CT10 | ±1.6–2.4 mm (±0.063–0.094 in) | 6.3–12.5 μm (250–500 μin) | Lowest cost; great for volume |
| Resin / no-bake | CT8–CT9 | ±1.2–1.8 mm (±0.047–0.071 in) | 3.2–6.3 μm (125–250 μin) | Better accuracy & finish; strong on cores |
| Shell (context) | CT6–CT7 | ±0.6–1.0 mm (±0.024–0.039 in) | 1.6–3.2 μm (63–125 μin) | Best among sand molds; higher tooling cost |
Wall thickness, weight & batch ranges
Table B — Practical minimum walls & part scope
| Material / Process | Min wall – Green sand | Min wall – Resin | Typical part weight | Best batch window |
|---|---|---|---|---|
| Gray iron | 3–5 mm (0.12–0.20 in) | 3.5–6 mm (0.14–0.24 in) | 2–120 kg (4–265 lb) | 80–5,000 pcs |
| Ductile iron | 4–6 mm (0.16–0.24 in) | 5–7 mm (0.20–0.28 in) | 3–300 kg (7–661 lb) | 50–2,000 pcs |
| Large housings | — | Resin preferred | 30–800 kg (66–1,764 lb) | 20–500 pcs |
Resin molds are mechanically stronger and handle larger cores; shell wins for very thin walls.
Cores, yield & cost levers
- Cores & geometry: Resin/no-bake supports large, multi-piece cores and deep pockets with better stability; green sand excels when cores are few/simple.
- Yield: Resin allows optimized risers/chills and stable core prints, often improving yield 5–10% vs a comparable green-sand layout on complex housings.
- Tooling & setup: Green-sand patterns usually cheaper; resin relies more on coreboxes and coatings.
- Surface & machining: Resin’s smoother as-cast surface can reduce machining stock (see Table C) and shot-blast time.
Table C — Typical machining allowance (iron castings)
| Mass range | Green sand stock | Resin/no-bake stock |
|---|---|---|
| 5–10 kg (11–22 lb) | 1.5–2.5 mm (0.06–0.10 in) | 1.2–2.0 mm (0.05–0.08 in) |
| 10–50 kg (22–110 lb) | 2.5–3.5 mm (0.10–0.14 in) | 2.0–3.0 mm (0.08–0.12 in) |
| 50–200 kg (110–441 lb) | 3.5–5.0 mm (0.14–0.20 in) | 3.0–4.0 mm (0.12–0.16 in) |
Drawing & RFQ notes (what to specify)
- Process & CT: e.g., Resin sand (no-bake), ISO 8062-3 CT8（green sand drawings use CT9–CT10）
- Surface finish: machined faces Ra 3.2–6.3 μm (125–250 μin)；call out as-cast finish only where truly needed.
- Leak/NDT (housings): method（air under water / dry air mass flow）、0.8–1.5 bar for 30–60 s + allowable leak rate；RT/UT zones as required.
- Machining stock: use Table C by mass range；avoid blanket high stock.
- Units: include mm/in and kg/lb；spell gray/grey once for clarity.
Decision matrix（copy-paste）
Table D — When to use resin vs green sand
| Requirement / Scenario | Choose Resin / No-bake | Choose Green Sand |
|---|---|---|
| Tight CT & better as-cast surface | ✅ CT8–CT9, Ra 3.2–6.3 μm | |
| Large cores / deep pockets / complex housings | ✅ Core stability & layout flexibility | |
| Medium batches with frequent changeovers | ✅ Good economics, flexible | |
| High-volume simple shapes | ✅ Lowest mold cost & fastest cycles | |
| Min wall very thin | Consider shell | ✅ Green sand for 3–5 mm gray iron |
| Lowest pattern cost, fast tooling | ✅ Often cheaper & faster | |
| Need to reduce machining stock | ✅ Smoother as-cast → lower stock |
FAQs
CTA — get a process recommendation you can defend
YBmetal runs green sand, resin/no-bake, and shell with machining. We simulate gating/risers, quote with CT & Ra assumptions, and provide leak/NDT evidence during pilot runs.