Specifying an automatic molding line starts with four binding numbers: flask size (mm), compacted shot weight (kg), mold closure force (kN) and rated molds-per-hour under continuous duty; the wrong answer on any one of these collapses the line's effective OEE [S1].
The four numbers are not independent — flask envelope sets shot-weight ceiling, shot weight sets closure-force demand, and closure force together with cycle geometry sets throughput; treat them as a coupled envelope, not a checklist [S1].
Flask Size and Shot Weight as the Hard Envelope
Flask dimensions define the largest part envelope a line can pour; common standard flask sizes for automatic green-sand lines cluster around 600×500 mm (job-shop), 750×650 mm (mid-duty automotive) and 1000×800 mm or 1200×900 mm (heavy castings), with each step roughly doubling sand demand per cycle [S1].
Compacted shot weight follows the flask volume at a typical green-sand bulk density near 1.55–1.70 g/cm³; a 750×650×250 mm flask at 1.6 g/cm³ takes roughly 195 kg of sand per mold, so a 120 molds/hr target implies a continuous sand throughput above 23 t/hr into the molding station alone, excluding sand returned through the molding line loop [S1].
Closure Force and Compaction Method Drive Cycle Time
Closure force on high-pressure horizontal-flask lines typically sits in the 600–1500 kN band for mid-size flasks and 2000–4000 kN for the 1000×800 class, with jolt-squeeze at the low end and shoot-squeeze or air-impact at the high end producing harder ramming (green hardness 85–95 vs 70–80) and faster draw [S1].
A shoot-squeeze station can finish a 200 kg shot in 18–22 s, versus 30–40 s on a jolt-squeeze rig of comparable flask; this 10–20 s delta is the single largest contributor to whether a 120 molds/hr rating is actually achievable on a real part mix [S1].
Throughput Bands and What Each Line Class Is For
Three practical bands cover most spec work: (a) compact flask (≤600×500) automatic lines at 30–60 molds/hr suit job shops and small foundry cells with frequent changeovers; (b) mid-size (750×650) DISA-style or flask-less vertical lines at 80–160 molds/hr are the workhorse of ductile-iron automotive and pump-valve casters; (c) heavy flask (≥1000×800) horizontal lines at 40–90 molds/hr with high-pressure compaction are built for heavy machinery, valve bodies and large pump housings where part weight—not speed—is the constraint [S1].
For comparison on three decision criteria (flask size mm, closure force kN, typical molds/hr): job-shop compact lines 600×500 / 600–800 / 30–60; mid-duty DISA-index 750×650 / 1000–1500 / 80–160; heavy-flask horizontal 1000×800 / 2000–4000 / 40–90; selecting outside these bands usually means a custom engineered line with 6–9 month delivery [S1].
Sand System, Cores and the Hidden Capacity Levers
An automatic molding line is only as fast as its sand plant: a typical green-sand loop needs a mix rate of 2.0–2.5× the net sand consumption (to cover moisture make-up, bentonite addition and return-sand conditioning), so a 120 molds/hr line at 195 kg/mold needs a 50–60 t/hr mixer [S1].
Core supply is the other silent bottleneck. Core making machine sizing must match the average cores-per-mold of the part mix; sand cores from a cold-box or shell core making machine typically cure in 20–60 s, so 1–2 cores per mold at 120 molds/hr pushes the core shooter into the 100–150 cores/hr band, with the buffer of a 200-core magazine as the minimum practical buffer [S1].
For part mixes with thin walls, complex internal passages, or tight dimensional tolerances, shell molding machine cores deliver surface finish of Ra 3.2–6.3 µm versus 6.3–12.5 µm for green-sand cores, but cycle time per core runs 90–180 s — so specifying shell cores on a 120+ molds/hr line is the wrong default unless the part justifies it [S1].
What the Line Is NOT For — and Common Sizing Traps
Specifying a high-pressure horizontal-flask line for low-volume, high-mix work is a classic over-spec: changeover on a 1200×800 mm flask rig takes 15–40 minutes versus 5–10 minutes on a compact flask-less unit, and the throughput rating of 60–90 molds/hr is unreachable when changeover dominates the day [S1].
Conversely, putting a 100 kg casting on a 600×500 mm compact line forces flask-oversize patterns and sand waste above 12–15%; a single flask-size miscalculation typically adds 8–12% to per-ton sand cost over the line's life, and is the most expensive spec error in the first 12 months of operation [S1].
Standards, Sourcing and Decision Signals to Track
Line acceptance is normally tied to OEM performance tests at the factory (continuous-run at rated molds/hr, hardness uniformity, mold weight repeatability within ±2%) and on-site SAT over 8 hours at 100% rated throughput; foundry side, ISO 9001 + IATF 16949 for automotive supply, plus any customer-specific casting standards (EN 1563 for ductile iron, ASTM A536 equivalent) — the line must demonstrably hold the casting-spec tolerances, not just the cycle count [S1].
Trackable signals over the next procurement cycle: (a) whether the supplier's quoted molds/hr is based on a 5 mm flask thickness or 10 mm, since the thinner flask can lift rated throughput 15–25% on the same closure force; (b) sand-to-metal ratio quoted in the binder, with a target 6–9:1 for ductile iron on green-sand lines — values above 10:1 flag an under-sized sand plant for the rated throughput [S1].
Spare-parts depth and local service coverage should be treated as a primary spec line, not a footnote: a 6–9 month custom line is non-productive for 4–8 weeks waiting on a single wear plate on a critical-path conveyor, which is why a supplier with regional wear-parts stock typically wins on lifecycle cost even at a 5–8% premium on purchase price [S1].