A machine built to harvest waste heat
The clash-free Apex-iCore build: tunnel, airlocks with split doors, hook rail and trolleys, settling box, four scrap pits, ducts, dampers and bag filter. Drag to orbit, scroll or pinch to zoom, right-drag to pan. Press Animation to run one 10-second index cycle on loop (real cycle: 2 minutes).
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Apex-iCore Handbook
Hot castings give their heat to air. The air preheats the scrap, and the scrap goes straight into the induction furnace. The hourly pit cycle is the Heat Boomerang.
Team: R Priya Dharshini and M S Jayamouthikhan. Open the 3D foundry tour.
Walk through the foundry in 3D
15 narrated chapters, furnace to furnace, with temperatures from the Apex-iCore physics model. Needs an internet connection for the 3D engine.
How the machine physically works
Hot castings preheat the next charge of scrap. Air carries the heat, the scrap stores it, and the furnace uses it. No fuel, no steam, no pressure.
Air through the three pits in series: 396 → 253 → 125 → 80°C.
Subsystems
| Subsystem | Key figures |
|---|---|
| Recovery tunnel | 20 m, 0.9 × 0.9 m inside, 300 mm rock wool |
| Fins, hot 10 m | 100 × 2 mm plates every 50 mm, ≈ 3× the wall area |
| Stirring fans | 5 fans, 2 m/s, tilted 12° toward the hot end so the air corkscrews along the tunnel |
| Hook loop | ≈ 77 trolleys on a rail inside the tunnel; one push every 2 min moves the line 0.286 m |
| Airlocks | 2 doors each, never open together; tunnel held at −8 Pa |
| Settling box | 9 m/s duct opens into a 0.3 m/s box, so sand falls out |
| Scrap pits | 4 pits, 1.6 × 1.6 × 2.6 m, sand-trough seals; 3 in series, 1 spare |
| Dampers | 12 manual (H, L, X); 6 levers each hour |
| Exhaust | Bag filter, 0.75 kW fan with VFD, whole line under suction |
Operating cycle: two rhythms
| Every 2 min | The tunnel |
|---|---|
| 0:00 | Inner doors open; the line moves one hook |
| 0:15 | Pusher returns; inner doors close |
| 0:30 | Exit door opens; a set rolls out at 120°C |
| 0:40 | Unloader bins the castings, returns the hook |
| 1:00 | Jib hangs the next 500°C set on a hook |
| 1:40 | Pedal: outer door opens, trolley enters |
| Minute of the hour | The pits |
|---|---|
| 0–1 | 6 damper levers: air to the next basket |
| 1–3 | Crane lifts the hood off the hottest pit |
| 3–5 | Hot basket, ≈ 326°C, to the hopper |
| 5–6 | Lid opens, bottom drops, scrap falls in |
| 6–9 | Empty basket to the yard; hood back on |
| 9–55 | Charger feeds hot scrap to the furnace |
| 11–25 | Yard refills the empty basket |
| 30–36 | Refilled basket into the spare pit |
Pit rotation: the air moves, not the baskets. Each hour every role (hottest, middle, coolest, spare) shifts one pit along. That takes 6 levers and 1 minute, instead of 3 hot basket lifts. From a cold start the scrap warms from 28 to 42 kWh/t over a 16-hour day; the year average is 41.1 kWh/t into the scrap.
The physics behind 52 kWh per tonne
- Castings 0.17 kW/K against air 0.15 kW/K.
- So the air leaves within about 100 K of 500°C.
- Bed friction 0.1–0.2 Pa against hot-air buoyancy 0.3–2 Pa.
- Gravity steers the air, so it must flow down through the scrap.
- 100 µm sand falls at 0.44 m/s.
- The box air moves at 0.3 m/s, so the sand drops out.
- ≈ 1,000 Pa budget, 700 of it the filter.
- Exhaust fan ≈ 0.29 kW; all running power 6,294 kWh a year.
Safety: every failure cools it down and lets air in
| Hazard | Detected by | Prevention and response |
|---|---|---|
| Wet scrap | Yard check, weight | Preheat dries it before the melt; baskets drain |
| Oily scrap | CO/VOC sensor, filter Δp | Segregate at the yard; air capped at ≈ 400°C |
| Over-heat | Thermocouples | Alarms at 420°C in the tunnel, 110°C at the filter |
| Fan stops | Manometer, motor current | Pedal locked; doors stay shut; castings cool |
| Stuck damper | Pit in/out temperature | Panel lamps show the pattern; freed by hand |
| Pit fire | Outlet hotter than inlet | Close its H damper to starve it of air |
| Door crush | Door position switches | Interlocks, guard rails, E-stop |
| Power cut | — | Nothing pressurised; doors spring shut |
- Airlock sequence, pusher, suction loop, alarms and logging.
- Change-over timing, anomaly warnings, savings reports.
- Never overrides an interlock.
- Manual dampers, pusher hand valve, key-switch doors, E-stop.
- Runs with the PLC off.
Interlocks: one airlock's two doors never open together · the pedal is ignored without suction · the pusher runs only with the inner door fully open.
₹20.3 lakh a year from one 1 t/h foundry
A year at 1 t/h, 2 shifts, 300 days, at the Tamil Nadu HT tariff.
| A year at 1 t/h | Value |
|---|---|
| Iron melted | 4,800 t |
| Heat delivered into the melt | 39.35 kWh/t |
| Furnace electricity avoided (÷ 0.75) | 2,51,806 kWh |
| Worth at ₹8.859/kWh | ₹22,30,844 |
| Running power, 6,294 kWh | −₹55,687 |
| Extra demand charge | −₹8,261 |
| Maintenance | −₹1,36,000 |
| Net saving every year | ₹20,30,895 |
| Build cost, ₹ lakh | Low | High |
|---|---|---|
| Tunnel, fins, fans | 11.5 | 16.2 |
| Hooks, rail, pusher, jib | 3.1 | 4.8 |
| Settling box, ducts, filter, fan | 3.5 | 6.0 |
| 4 pits, hoods, baskets, dampers | 9.9 | 13.5 |
| Controls and sensors | 0.9 | 1.6 |
| Site: foundations, wiring | 1.2 | 2.4 |
| Engineering + contingency | 6.3 | 12.8 |
| Airlocks + inlet fan | ≈ 1.5 | ≈ 1.5 |
| Total (mid ≈ 48) | 37.8 | 58.6 |
What moves the payback
| Case | Net a year | Payback |
|---|---|---|
| Base case | ₹20.3 L | 2.4 yr |
| Tariff ₹7/kWh | ₹15.8 L | 3.0 yr |
| Tariff ₹10/kWh | ₹23.1 L | 2.1 yr |
| Furnace efficiency 0.85 | ₹17.7 L | 2.7 yr |
| Furnace efficiency 0.65 | ₹23.7 L | 2.0 yr |
| 70% output | ₹13.6 L | 3.5 yr |
| One shift (estimate) | ₹8–9 L | ≈ 5.5 yr |
| Three shifts (estimate) | ≈ ₹30 L | ≈ 1.6 yr |
| 5 t/h, 2 shifts | ≈ ₹1.02 Cr | under 2 yr |
- Every ₹1/kWh of tariff moves the net saving by about ₹2.5 lakh a year.
- 5 t/h: ≈ ₹1.02 crore a year, 12,59,030 kWh, ≈ 870 t CO₂ avoided.
- 1 Mt of iron a year on Apex-iCore: ≈ 52 GWh and 37,000 t CO₂.
- 5% interest subvention for micro and small units; foundry is covered and Coimbatore is a listed cluster.
- ≈ ₹2.4 lakh a year less interest on ₹48 lakh.
- 52.5 kWh/t is about 8.8% of a 600 kWh/t melt, so pair it with small measures to clear the 10% savings line.
The size of the problem
Tariff: ₹7.50/kWh + 25% time-of-day on 8 of 16 hours + 5% tax = ₹8.859/kWh (TN HT) · demand charge ₹608/kVA/month · CEA grid factor 0.710 t CO₂/MWh · industry figures from IFC and IFEX 2026. Build costs are planning estimates; replace them with quotes.
One tunnel, twelve alloys: set the fan, keep the strength
Locked design: 20 m tunnel, 0.9 × 0.9 m, 1 t/h, 33 kg sets, 28 mm equivalent section.
Fan speed and time inside the tunnel
Main fan rated 0.25 kg/s (≈ 785 m³/h) at 50 Hz; flow is set on the VFD. The conveyor is the same for every material: 0.143 m/min, one 33 kg set every 2 min, 0.29 m hook pitch, 140 min inside. Airflow matches each material's heat-capacity rate (about 1.05×).
| Material | Enters | Main fan (kg/s · m³/h · Hz) | Stirring fans | Reaches 150°C | Exits | Heat to scrap |
|---|---|---|---|---|---|---|
| Grey iron | 500°C | 0.161 · 508 · 32 Hz | 2 m/s (25 Hz) | 116 min | 111°C | 43.0 kWh/t |
| Ductile iron | 500°C | 0.161 · 508 · 32 Hz | 2 m/s (25 Hz) | 116 min | 110°C | 43.0 kWh/t |
| High-Cr white iron | 500°C | 0.153 · 481 · 31 Hz | 2 m/s (25 Hz) | 117 min | 113°C | 41.2 kWh/t |
| Carbon steel (WCB) | 500°C | 0.161 · 508 · 32 Hz | 2 m/s (25 Hz) | 120 min | 117°C | 42.3 kWh/t |
| Ni-Cr-Mo alloy steel | 500°C | 0.161 · 508 · 32 Hz | 2 m/s (25 Hz) | 120 min | 117°C | 42.3 kWh/t |
| Stainless CF8M | 500°C | 0.152 · 478 · 30 Hz | 2 m/s (25 Hz) | 125 min | 127°C | 39.5 kWh/t |
| Duplex CD4MCuN | 500°C | 0.151 · 476 · 30 Hz | 2 m/s (25 Hz) | 124 min | 125°C | 39.5 kWh/t |
| Aluminium A356 | 400°C | 0.238 · 748 · 48 Hz | 4 m/s (50 Hz) | 120 min | 107°C | 42.9 kWh/t |
| Aluminium LM6 | 400°C | 0.235 · 740 · 47 Hz | 4 m/s (50 Hz) | 120 min | 106°C | 43.0 kWh/t |
| Gunmetal LG2 | 450°C | 0.113 · 354 · 23 Hz | 2 m/s (25 Hz) | 116 min | 114°C | 27.2 kWh/t |
| Leaded brass | 450°C | 0.114 · 358 · 23 Hz | 2 m/s (25 Hz) | 115 min | 112°C | 27.7 kWh/t |
| Aluminium bronze | 450°C | 0.129 · 406 · 26 Hz | 2 m/s (25 Hz) | 113 min | 108°C | 31.5 kWh/t |
Air speed in the tunnel: 0.17 m/s (cold end) to 0.38 m/s (hot end) for irons; 0.26 to 0.55 m/s for aluminium. Aluminium needs more air and 4 m/s stirring because its emissivity is low (~0.2).
Metallurgy check: strength and properties unchanged
| Material | Cooling rate to 150°C | Time in risky range | Effect on strength | Verdict |
|---|---|---|---|---|
| Grey and ductile iron | 181°C/h | None; entry well below eutectoid (~730°C), matrix fixed in mould | None | Yes |
| High-Cr white iron | 179°C/h | None | None; hardening done afterwards anyway | Yes |
| Carbon steel (WCB) | 175°C/h | None (below A1) | None; normalise/temper afterwards per spec | Yes |
| Ni-Cr-Mo steel | 175°C/h | 27 min in 375–500°C temper-embrittlement band | Embrittlement needs hours; Q&T afterwards resets it | Yes (Q&T after) |
| CF8M stainless | 167°C/h | 5 min in 450–500°C | Sensitisation needs hours; solution-anneal afterwards | Yes |
| Duplex | 169°C/h | 19 min in 400–500°C | 475°C embrittlement needs hours; solution-anneal afterwards | Yes |
| Aluminium A356 | 125°C/h (from 400°C) | 97 min in 200–400°C over-ageing band | Lost only if supplied as-cast or T5; T6 re-dissolves it | T6 orders only |
| Aluminium LM6 | 125°C/h | None (not heat-treatable) | None | Yes |
| Gunmetal, leaded brass | 155–157°C/h | None | None; slower cooling reduces residual stress | Yes |
| Aluminium bronze | 160°C/h | None (entry below 565°C eutectoid) | None | Yes |
| Magnesium AZ91 | – | – | Fire risk | No |
| Zn, Pb, Sn alloys | – | – | Too low-melting for this process | No |
- The tunnel takes 133–137 min to reach 120°C vs 75–98 min on the floor (about 1.6–1.8× slower), so cracking risk drops.
- 131°C in the tunnel vs 250°C on the floor for irons; stress falls from 0.5–0.6 to 0.25–0.3 of UTS.
- Stainless, aluminium and gunmetal reach about 0.5–0.6 of UTS in the tunnel (0.8–1.0 on the floor), so keep section changes gradual.
- Aluminium at 400°C is very weak: use mesh trays, no piercing hooks, no heavy hanging loads.
- Lead is liquid above 327°C; avoid shock or heavy hook load until below that.
Thick castings (75 mm equivalent): half-throughput mode
At normal settings a 75 mm section exits at 195–214°C and recovery falls to ~33 kWh/t. For thick castings run half throughput with half the airflow.
| Material | Fan (kg/s) | Hook interval | Time inside | Reaches 150°C | Exits |
|---|---|---|---|---|---|
| Irons | 0.077–0.081 | 4 min | 280 min | 243–245 min | 123–126°C |
| Steels | 0.081 | 4 min | 280 min | 253 min | 132°C |
| Stainless / duplex | 0.076 | 4 min | 280 min | 266–269 min | 142–144°C |
| Aluminium | 0.118–0.119 | 4 min | 280 min | 245 min | 117–119°C |
| Copper alloys | 0.056–0.065 | 4 min | 280 min | 236–246 min | 121–128°C |
Thin sections (10 mm) exit at 59–73°C and recover about 45–48 kWh/t. Below about 20 Hz use a damper or bypass instead of running the motor slower.
Panel settings and limits
- Recipe: alloy, fan Hz, stirring m/s, hook interval. Exit IR pyrometer confirms ≤ 150°C.
- Maximum entry temperature about 550°C.
- One alloy family at a time, with separate scrap baskets.
Limits: model predictions, not measurements. Metallurgical time limits are handbook order-of-magnitude values, not a kinetic simulation. Stresses use room-temperature modulus and UTS (conservative, especially for aluminium and copper). Actual section thickness decides which mode to use.
From model to measured savings in 15 months
Maturity today: system TRL 3, parts TRL 8–9. Designed, modelled and simulated; not yet tested with real castings and scrap.
- Months 0–3 · Bench test2.5 m tunnel section with real castings: radiation, fins, fans.
- Months 2–4 · Single hot pitReal scrap and a 400°C heater: downflow, bed pressure drop, sand seals.
- Months 3–6 · Pilot designPartner foundry, layout, ADEETIE energy audit and detailed project report.
- Months 6–12 · Pilot buildFull Apex-iCore at 1 t/h in a Coimbatore foundry.
- Months 12–15 · MeasurePaired heats on the furnace meter, verified by an auditor.
| Success criterion | Target | Model |
|---|---|---|
| Furnace electricity saved | ≥ 45 kWh/t | 52.5 |
| Heat delivered in scrap | ≥ 35 kWh/t | 39.35 |
| Casting exit temperature | ≤ 150°C | ≈ 120 |
| Tunnel suction | below −3 Pa always | −8 Pa |
| Uptime, production hours | ≥ 95% | — |
| Payback on measured data | ≤ 3 years | 2.4 |
The narrated 3D tour walks through a 1 t/h foundry in 15 chapters, about 12 minutes: furnace, pouring and shakeout, the jib, pedal and airlocks, a thermal camera inside the tunnel, the fins and tilted fans, the settling-box swirl, every pit part, the hourly crane change-over and a live energy meter. Every colour and temperature comes from the physics model.
▶ Open the live 3D tourTeam
- PLC interlocks, VFD and sensors
- Data logger, digital twin, M&V savings reports
- Costing, payback and ADEETIE finance
- Partner foundry and pilot
- 1D physics model and heat balance
- Tunnel, fins, fans, hook loop and airlocks
- Scrap pits, baskets, dampers and frame
- 3D foundry tour
Why Apex-iCore should continue
- ≈ 5,000 Indian foundries, 90% MSMEs, 15.9 Mt a year; clusters from Coimbatore to Rajkot.
- Forgings heating billets, heat-treat loads, die-casting, ceramic kilns.
- Manual build → motorised, PLC-controlled version → digital-twin service.
- Licensed to cluster fabricators, ESCO or ADEETIE-financed.
Castings leave the mould at 500°C. Apex-iCore sends that heat back: 52 kWh/t, ₹20 lakh a year, about a 2.4-year payback, built locally.