1. Why foundry HVAC is its own engineering discipline
A foundry is not a steel mill in miniature. A steel mill is primary metal production at continuous tonnage with HVAC dominated by sheer flue volume and continuous cooling-water tower load. A foundry is secondary metal processing: discrete heats, discrete pours, discrete moulds, an exhaust schedule that swings from idle to peak every few minutes. Foundry exhaust must handle thermal cycling, abrasive shake-out dust, chemically-bonded sand binders, wax burn-off vapour and combustible-metal-dust deflagration risk inside the same building.
Foundry ductwork lives or dies on five demands at once: heat resistance (1200–1600 degC ferrous pour, 600–1000 degC heat treatment, 700–850 degC reverberatory aluminium); abrasion resistance (silica sand at shake-out and shot blast strips zinc and paint in months); corrosion resistance (sulfur from furan and phenolic urethane binders, alkaline halide fume from aluminium fluxes); deflagration resistance (NFPA 484 for combustible aluminium and magnesium dust); and acoustic performance (NC-65 industrial environments). Each is manageable alone. Together they explain why a generic data-centre fabricator who treats a foundry as just another industrial job loses money on the first project.
This guide walks every major foundry process and explains what changes about the ductwork. We start with the regulatory backbone, then map the foundry floor section-by-section, then close with the SBKJ machine configuration that gives a fabricator the production envelope to serve this market.
2. The Australian regulatory stack — AS 1668.2, AS 1885, AS 4024, AS/NZS 60079, NFPA 484, NFPA 86
Foundry HVAC in Australia sits at the intersection of half a dozen standards, and ignoring any one of them is a notice-of-non-compliance from SafeWork Australia or the state EPA waiting to happen.
2.1 AS 1668.2 — mechanical ventilation for buildings
AS 1668.2 is the umbrella standard for mechanical ventilation of all building classifications. Foundries fall under industrial occupancy; Table 4 sets minimum extract rates for metal melting, pouring, casting, machining, grinding, welding and painting. In practice a foundry seldom gets close to the minimum — LEV at each individual source drives total exhaust well above the building-volume figure. Where AS 1668.2 matters most is the make-up air requirement: every cubic metre extracted must be replaced by tempered, filtered air, keeping the pouring floor at neutral or slightly positive pressure relative to office and laboratory zones.
Read together with our AS 1668.2 reference, the practical sizing rule is: design the LEV first, size each branch for capture and transport velocity, sum total exhaust, then provide make-up air to match.
2.2 AS 1885 — safety in metal casting workplaces
AS 1885 is the foundry-specific occupational safety standard. It addresses fume control at melting and pouring, dust control at moulding and reclamation, silica exposure at shake-out and fettling, noise control at shot-blast and grinding, and the layout of the pouring floor itself. AS 1885 makes LEV mandatory at every fume and dust source — not optional — and it sets the procedural backbone for the SafeWork Australia exposure standards for respirable crystalline silica (0.05 mg/m3 over 8 hours) and respirable iron oxide (5 mg/m3). Where AS 1885 is silent on duct construction, the practitioner falls back on AS/NZS 4254 and AS 1668.2.
2.3 AS/NZS 60079 — explosive atmospheres
Aluminium, magnesium, titanium and zirconium dust are combustible. Once you have a foundry that produces fine particles of any of those four metals — magnesium die-casting, aluminium grinding and fettling, titanium investment casting — AS/NZS 60079.10.2 requires a hazardous-area classification of any zone where airborne dust can reach explosible concentration. The classification (Zone 20, 21, 22) drives Ex-rated electrical equipment requirements for fans, motors, instrumentation and lighting on the ductwork system, and it drives bonding and grounding of every duct segment to prevent static discharge ignition.
2.4 NFPA 484 — combustible metals
NFPA 484 is not an Australian standard but is referenced extensively by Australian foundry insurance underwriters and is the de-facto engineering reference for combustible metal dust handling. NFPA 484 mandates wet-collection extraction for fine aluminium, magnesium and titanium dust, prohibits dry baghouses without engineered deflagration venting, and sets the bonding, grounding and isolation-damper requirements that prevent a baghouse fire from propagating back into the ductwork main. Magnesium dust in particular is harder to extinguish than aluminium — water reacts violently with hot magnesium — and the recommended extraction is a sealed wet-bath collector with inert-atmosphere cover gas at the top of the water.
2.5 NFPA 86 — industrial ovens and furnaces
Foundry heat treatment — annealing, normalising, stress relief, tempering, age hardening for aluminium — happens in gas-fired or electric ovens running 600–1000 degC. NFPA 86 applies to every such oven and dictates the exhaust topology: lower explosive limit (LEL) monitoring, purge cycles before lighting, explosion venting and dedicated exhaust risers that do not share trunk capacity with general foundry exhaust. The combustion of any volatile from off-gassed castings — residual binder, mould-release oil, machining cutting fluid — can produce flammable concentrations in the oven volume, and NFPA 86 is the procedural backbone that prevents the oven from being the next foundry headline.
2.6 AS 4024 — machinery safety
AS 4024 is the machinery safety standard. It applies to every piece of equipment with moving parts, which in a foundry includes shake-out conveyors, sand reclamation hoods, fettling cabinets, shot-blast booths, grinding stations, polishing wheels, die-casting machines and core-shooting machines. AS 4024 requires interlocked guards, emergency stops, dust-mains isolation dampers on every machine that can produce dust at concentration, and inspection access ports at intervals through the ductwork. The compliance interaction with the duct design is that every machine connected to extract has a guarded interface to the duct, and every duct branch has a damper that can be closed for machine isolation during maintenance.
3. The foundry floor, section by section
The most reliable way to specify foundry HVAC is to walk the process flow. Every Australian foundry maps to a variant of the same eight-station sequence: pattern shop, mould making, core making, melting and pouring, shake-out, knock-out and fettling, heat treatment, and finishing (shot blast, paint). Each station has its own characteristic dust load, fume chemistry, temperature, capture velocity and material requirement.
3.1 Pattern shop — ambient comfort and woodworking dust
The pattern shop is the foundry's quietest zone. Patterns are made of wood, plastic or aluminium, and the dominant LEV demand is woodworking dust extraction at saws, routers and sanders. Capture velocity at the tool is typically 1.0–1.5 m/s; transport velocity in dust mains is 18–22 m/s. The duct work here is conventional galvanised spiral, sized to AS/NZS 4254 medium-pressure, with branches sized for the largest tool running. The pattern shop is also where the foundry's design office lives — NC-50 acoustic target, supply-air with HEPA pre-filters, and a small overpressure relative to the rest of the building to keep sand and metal dust out.
3.2 Sand-casting moulding floor — green sand, no-bake, shell mould, V-process
Sand-casting is the highest-volume process in most Australian foundries. Four sand systems dominate:
Green sand uses moist clay-bonded silica sand. The mould is rammed around the pattern, the metal poured, and the sand reclaimed at shake-out. The dominant dust load comes from sand reclamation — primary cooler, magnetic separator, screen deck and pneumatic conveyor. Each is an LEV source needing 18–22 m/s transport velocity. The chemistry is benign — moist silica — but the dust loading is high enough that abrasion governs material selection. Painted carbon steel or aluminised steel works for cool-side mains; the wet-bath side of the scrubber gets 316L.
No-bake systems use silica sand bonded with chemical binders that cure at ambient temperature — furan, phenolic urethane (PUNB), sodium silicate (CO2 hardened) and alkaline phenolic. The chemical binders produce fume during mixing, ramming and pouring. Furan releases formaldehyde and SO2; PUNB releases isocyanates and aromatic hydrocarbons; sodium silicate is relatively benign but produces alkaline dust during reclamation. LEV is mandatory at the mixer, the ramming station and the pouring rail. Material selection downstream of the mixer is 316L stainless for sulfur-bearing furan systems and aluminised steel for PUNB.
Shell mould (Croning process) coats silica sand with phenolic resin and cures the shell against a heated pattern plate. The dust is fine, the resin fume is significant during the heat cure, and the exhaust must capture both. LEV at the shell box exhausts to a thermal oxidiser or activated-carbon adsorber to deal with phenolic VOC before discharge.
V-process (vacuum-process moulding) uses dry, unbonded silica sand held in shape by vacuum applied through a polyethylene film. The process is clean — no binders, no chemical fume — but vacuum-line dust extraction is essential to keep the vacuum pumps clean. The vacuum side of a V-process system runs at much higher static pressure than conventional exhaust, and the ductwork must be reinforced beyond medium-pressure to AS/NZS 4254 high-pressure or rolled-and-welded heavy-gauge for vacuum loads above 8 kPa.
3.3 Core making
Cores form the internal cavities of castings — water jackets in engine blocks, port shapes in valve bodies, internal channels in pump casings. The four common core chemistries are cold-box (amine-cured phenolic urethane), warm-box (acid-catalysed furan), hot-box (heat-cured phenolic and furan) and inorganic (silicate or aluminate). Amine-cured cold-box releases triethylamine or dimethylethylamine during cure — a strong-smelling, toxic gas that requires dedicated catalytic scrubbing before discharge. Hot-box cores release significant formaldehyde and sulfur compounds during cure. The core-shop exhaust is one of the most chemically demanding extracts in a foundry: 316L stainless mains, scrubber treatment before discharge, and LEV capture velocity of 0.5–1.0 m/s at every machine.
3.4 Investment casting — lost-wax
Investment casting (lost-wax, precision casting) is its own discipline. The process: a wax pattern is built, dipped repeatedly into a ceramic slurry to build a shell, the shell is dried, the wax is melted out, the shell is fired, and metal is poured. Each step has its own ventilation demand.
Wax pattern injection happens in temperature-controlled rooms — typically 20–22 degC, low humidity — to maintain wax dimensional stability. The LEV demand here is modest, but room conditioning is precise. Shell building happens in dipping rooms with controlled relative humidity (40–60% RH typical) — too dry and the shell cracks during drying, too humid and the binder doesn't set. Shell drying ovens run 30–50 degC with controlled airflow over the parts. De-waxing autoclaves or flash-fire ovens produce wax vapour that must be condensed and recovered — wax is expensive enough that nearly every investment caster runs a wax-recovery condenser on the de-wax exhaust. The shell-firing kiln runs 900–1100 degC and falls under NFPA 86.
Investment casting pour temperatures match the metal: 1500–1700 degC for steel, 1450–1500 degC for nickel alloys, 1450 degC for iron, 1200–1400 degC for cobalt alloys. Pour-off LEV at the kiln-side pouring station is a refractory-lined hood with stack discharge after a particulate scrubber. Post-cast shell knockout — usually by vibratory hammer or media blast — produces fine ceramic dust requiring 18–22 m/s transport velocity in a dedicated dust main.
3.5 Die casting — high-pressure aluminium, magnesium and zinc
High-pressure die casting (HPDC) is the most automated foundry process. Molten metal is injected into a steel die at 30–150 MPa shot pressure; the casting solidifies in seconds and the die opens to eject the part. Aluminium HPDC dominates the Australian die-cast volume (engine blocks, gearbox housings, structural body parts), with magnesium HPDC growing for weight-critical automotive and aerospace applications, and zinc HPDC serving precision fittings and decorative parts.
Aluminium HPDC ventilation has three demands. Die spray — water-based mould release sprayed onto the die between shots — generates aerosol mist that must be captured at the die area. Metallic vapour from the molten aluminium passing through the shot sleeve produces fine aluminium oxide fume. Combustion products from gas-fired holding furnaces serve a continuous low-volume CO and NOx load. The standard capture geometry is a push-pull slot hood across the die opening or an overhead canopy with sufficient face velocity to entrain die-spray mist (1.0–1.5 m/s capture velocity at the operator's working face).
Magnesium HPDC is more demanding. Magnesium ignites at much lower temperatures than aluminium and any fine magnesium dust is a Class D combustible-metal hazard. NFPA 484 applies in full: wet-bath collection only, no dry baghouses, bonded and grounded ductwork, and SF6 or sulfur dioxide cover gas above the molten magnesium to suppress ignition. The cover-gas stack stream is its own LEV branch with stainless steel mains and dedicated scrubber treatment before discharge — SF6 is a potent greenhouse gas with strict emission limits, and modern magnesium foundries are transitioning to fluorinated ketone cover gases that need different scrubber chemistry.
Zinc HPDC is the gentlest of the three. Zinc melts at 419 degC, pour temperature is typically 420–450 degC, and the fume load is light. Standard galvanised duct with painted-steel reinforcement is acceptable for zinc die-casting exhaust, with normal capture velocity at the die area.
Low-pressure die casting (LPDC) — used for higher-quality aluminium parts like wheels and structural castings — operates at much lower fill pressure and slower fill velocity. The ventilation demand is similar to HPDC but lower in spike load.
3.6 Melting and pouring — the heat-load heart of the foundry
The melting floor is where foundry HVAC stops being routine industrial ventilation and starts being a refractory engineering problem.
Cupola furnaces are the traditional iron-melting workhorse — a vertical shaft charged from the top with iron, coke and flux, with air blown in through tuyeres near the base. Melting at 1450–1650 degC. Exhaust is continuous, hot and chemically aggressive: CO, SO2 from coke sulfur, NOx, metallic fume (manganese, silicon, iron oxide), and charge particulate. Cupola exhaust requires refractory-lined steel duct for the first 5–10 m above the charge door — castable refractory or ceramic blanket inside a 6 mm mild steel shell, 1200 degC service. Downstream, the stream is cooled in a quench tower before a wet scrubber or deflagration-protected baghouse.
Coreless induction furnaces are the modern workhorse for iron, steel and some non-ferrous melting. AC current in a copper coil induces eddy currents in the metal charge, which melts from within. Pour temperatures 1500–1700 degC steel, 1450–1550 degC iron. Capture is localised side-draft canopy hoods over the pour zone. Fume chemistry is cleaner than cupola but spike load during melt-down is high. Refractory-lined exhaust for the first 3–5 m, then carbon steel through baghouse or scrubber.
Reverberatory furnaces are bath furnaces used for aluminium melting in volume foundries. Pour temperature 700–850 degC. The fume chemistry is alkaline halide (chlorides and fluorides from melt-treatment fluxes), aluminium oxide particulate, and burner combustion products. Halide fume is corrosive to carbon steel and zinc — 316L stainless or hot-dip aluminised steel is mandatory.
Electric arc furnaces (EAF) in foundries are used for steel castings and high-alloy work. Pour temperature 1600–1800 degC. Capture typically combines a fourth-hole port in the furnace roof (drawing fume during melting) with a canopy hood for fugitive emissions during charging and tapping. Both feed a refractory-lined main. Spike loads are 3–4 times steady-state; duct must be sized for spike.
Gas-fired crucible furnaces are common in small-to-mid non-ferrous foundries (aluminium, brass, bronze, copper). Pour 700 degC aluminium to 1100 degC bronze. Low-volume continuous fume, common canopy main serving multiple crucibles. Aluminised steel or 316L depending on alloy mix.
Pouring-floor make-up air is the most often-neglected design issue. Every cubic metre extracted must be replaced with tempered, clean make-up air. The pouring floor must remain at neutral or slightly positive pressure to prevent furnace-stack backdraft. Mechanical make-up air is universal in modern Australian foundries — naturally aspirated buildings are inadequate above small-scale jobbing.
3.7 Shake-out and sand reclamation
Shake-out is where the cooled casting is separated from its sand mould. The casting is typically still 200–500 degC when it arrives at shake-out, and the impact of the casting on the shake-out grid generates significant dust as the sand breaks free. The dust is largely silica with iron oxide contamination from the casting surface and is the single highest particulate source in a sand-casting foundry.
Shake-out LEV is a side-draft or overhead canopy hood capturing both fugitive dust and the residual fume from the still-hot casting. Capture velocity 1.0–1.5 m/s at the grid edge; transport velocity 18–22 m/s in the dust main. Material selection is painted carbon steel for the downstream of cooling, with 316L for the wet-bath side of the scrubber.
Sand reclamation downstream of shake-out — primary cooler, classifier, magnetic separator, screen deck — is a continuous-duty dust source. Each reclamation machine is an LEV point with its own branch, and the system designer must size each branch independently to capture velocity and transport velocity rather than treating them as one zone.
3.8 Knock-out and fettling — silica dust ground zero
Fettling is the cleanup of the raw casting: removal of gates, risers and flash; surface grinding of parting lines; chipping of residual sand from internal passages. It is the highest silica-exposure activity in a foundry, and SafeWork Australia's 0.05 mg/m3 respirable crystalline silica exposure limit drives the LEV design at every fettling station.
Standard fettling capture is a downdraft table or backdraft bench, with a slot hood drawing dust away from the operator's breathing zone. Face velocity 0.5–0.7 m/s across the working aperture; transport velocity 18–22 m/s in the branch. The capture works only if the operator is upstream of the air movement — operator positioning is a procedural control as well as an engineering control, and an effective fettling station includes operator-position marking on the floor.
Knock-out cabinets — automated chipping and rumbling stations for breaking residual sand off complex internal passages — are fully enclosed with LEV. They are AS 4024 machinery-safety items: interlocked doors, dust-mains isolation dampers, sound enclosure for noise control. Knock-out cabinet dust mains feed a high-efficiency dust collector and the discharge stack monitors particulate emissions per state EPA licence conditions.
3.9 Heat treatment — annealing, normalising, tempering, stress relief
Heat treatment ovens at 600–1000 degC fall under NFPA 86. The exhaust includes combustion products from gas-fired burners, residual binder vapour from the cast surface, residual mould-release or core-binder breakdown products, and any solvent residue from prior machining. LEL monitoring at the exhaust stack, purge cycles before lighting, explosion venting on the oven shell, and dedicated stack risers separate from general foundry exhaust are all NFPA 86 requirements.
Aluminium heat treatment is different from ferrous heat treatment. T6 age hardening of aluminium runs 150–200 degC, well below NFPA 86 thresholds. T4 solution heat treatment runs 470–540 degC and falls under NFPA 86. The fume load is light but the volume is significant — solution-heat-treatment ovens for aluminium are often the largest single oven in a die-cast foundry, with corresponding exhaust capacity.
3.10 Shot blast — silica plus iron oxide
Shot blast cleaning of castings uses steel shot, grit or cut wire propelled against the casting at 60–80 m/s. The booth interior is dense with shot, dust and the abraded surface contamination of the casting (residual silica sand, scale from heat treatment, iron oxide from the steel surface). The dust load on the LEV is heavy — shot-blast cabinets typically need 0.5 m/s face velocity at the work aperture and 18–22 m/s in the dust main, with cyclone pre-separation to drop out shot and coarse particle before the baghouse.
Shot-blast cabinets are AS 4024 machinery-safety enclosures: interlocked doors, dust-mains isolation dampers, light-curtain protection at the work aperture, sound enclosure for noise control (shot-blast noise can exceed 100 dBA inside the booth). LEV makes the difference between a shot-blast booth that complies with worker exposure limits and one that doesn't.
3.11 Painting and coating — NFPA 33 spray booths
Castings that are sold painted or coated finish in spray booths governed by NFPA 33 — Standard for Spray Application Using Flammable or Combustible Materials. A spray booth has its own LEV chemistry: solvent vapour from the paint, paint overspray particulate, and combustion-product loading from any flash-off oven downstream. The booth is a hazardous area under AS/NZS 60079 and requires Ex-rated electrical equipment, bonded and grounded ductwork, and LEL monitoring at the exhaust stack.
Booth construction is typically a downdraft topology — air supplied from above the operator, extracted through a floor or low-side grille, paint overspray captured in dry filters or a wet wash, and exhaust discharged through a stack with explosion-protected dampers. The supply air must be tempered and HEPA-filtered to keep paint quality consistent. The exhaust main feeds an after-filter or thermal oxidiser before discharge per state EPA licence.
4. Exhaust chemistry — what the air actually contains
The chemistry of foundry exhaust drives material selection, scrubber design and discharge-stack monitoring. Five contaminant classes dominate.
4.1 Carbon monoxide
CO is produced anywhere there is incomplete combustion: cupola coke beds, gas-fired holding furnaces, gas-fired heat-treatment ovens, gas-fired ladle pre-heaters. SafeWork Australia exposure standard for CO is 30 ppm over 8 hours. CO is colourless, odourless and toxic; the LEV design must capture it at source, and the ventilation design must prevent re-entrainment into the workplace breathing zone. CO monitoring at the workplace level — fixed CO sensors at strategic floor locations — is standard practice in modern Australian iron and steel foundries.
4.2 Sulfur dioxide and sulfur trioxide
SO2 and SO3 come from sulfur in coke (cupola), sulfur in chemically-bonded sand binders (furan systems), and sulfur in some core gases. SO2 is corrosive to carbon steel and to galvanising; SO3 with moisture forms sulfuric acid mist, which is corrosive to almost everything except 316L stainless, FRP and acid-resistant coatings. SO2 exposure standard is 1 ppm over 8 hours. Wet-scrubber neutralisation with sodium hydroxide or lime is the standard control before stack discharge.
4.3 Oxides of nitrogen
NOx is produced at any combustion process above 1500 degC and is unavoidable in cupola, electric arc and gas-fired reverberatory furnaces. Selective catalytic reduction (SCR) on the exhaust after particulate removal is the typical control on larger foundries; smaller operations rely on combustion tuning to reduce NOx formation in-situ. State EPA stack-monitoring licences typically include NOx limits, and continuous-emissions monitoring is standard at major Australian foundries.
4.4 Volatile organic compounds (VOC)
VOC comes from chemical sand binders (furan, phenolic urethane), core chemistries (cold-box amines, hot-box phenolic), wax (investment casting), die-cast mould release (oil-based release), heat-treatment oven residues and paint solvents. The control is process-specific — activated carbon adsorption for organic vapour, thermal or catalytic oxidation for high-load streams, condensation for recoverable wax — and discharge stacks are monitored against state EPA VOC limits.
4.5 Particulate
Particulate covers silica dust (shake-out, fettling, sand reclamation), iron oxide (shot blast, grinding), aluminium oxide (aluminium melting, die-cast), zinc oxide (zinc die-cast and galvanised-steel handling), refractory dust (kiln and furnace maintenance) and ceramic shell dust (investment casting knockout). Total airborne particulate at the workplace must remain below the AS 1885 threshold; respirable crystalline silica must remain below 0.05 mg/m3 (0.025 mg/m3 in some jurisdictions); respirable iron oxide must remain below 5 mg/m3. Particulate stack emissions are monitored against state EPA limits and require continuous-emissions monitoring at most major foundries.
5. Material selection — why galvanised fails and what replaces it
Galvanised duct is the workhorse of HVAC fabrication. Across data centres, commercial towers, hospitals and schools, hot-dip-galvanised carbon steel sheet to AS/NZS 4254 is the right answer for 95% of the duct work. In a foundry, it is the wrong answer for almost every duct.
5.1 Why galvanised fails in a foundry
Galvanised carbon steel fails in foundry exhaust for three reasons:
First, temperature. Zinc coating volatilises above 419 degC and fumes above 250 degC service temperature. Cupola exhaust at 600–1200 degC, induction furnace fume at 400–600 degC, reverberatory aluminium exhaust at 200–400 degC, and heat-treatment oven exhaust at 200–800 degC all exceed the safe service temperature of galvanising. Beyond just losing the coating, volatilised zinc itself adds to the contaminant load.
Second, abrasion. Silica sand at shake-out, knock-out and shot blast strips zinc coating mechanically. A typical sand-casting foundry's shake-out exhaust strips zinc inside 6–12 months of service, exposing bare carbon steel to the corrosive moist exhaust stream, which then perforates inside 12–24 months. Painted carbon steel performs only marginally better; aluminised steel and stainless steel are the practical alternatives.
Third, sulfur attack. Sulfur from coke (cupola) and from chemical sand binders (furan) reacts with zinc to form zinc sulfate, which is hygroscopic, flakes off in service, and contaminates the air stream. Even at temperatures below the volatilisation point, sulfur attack converts a galvanised duct into a high-maintenance liability.
5.2 Refractory-lined mild steel for furnace exhaust
The standard material for furnace exhaust within 3–10 m of the furnace is refractory-lined mild steel. The construction is a 6–10 mm mild steel shell with 50–100 mm of castable refractory or insulating ceramic blanket lining the interior. The refractory is castable monolithic for round mains (cast in place against a mandrel) or modular pre-cast tiles for rectangular mains. Service temperature inside the refractory face can run 1200 degC; the outer shell remains below 200 degC and is paintable carbon steel.
Refractory-lined duct must be inspected on a maintenance schedule — typically annual visual inspection of access ports, with refractory replacement of any section showing crack propagation or spalling. The refractory ages from thermal cycling: continuous-duty cupola mains last 5–8 years; intermittent-duty induction-furnace mains last 8–12 years. The replacement cost is significant but predictable.
5.3 Hot-dip aluminised steel for medium-temperature mains
Aluminised steel — carbon steel coated with an aluminium-silicon alloy by hot-dip process — is the material of choice for medium-temperature foundry exhaust between the refractory section and the scrubber inlet. Service temperature 400–600 degC, good corrosion resistance to mildly acidic exhaust, good abrasion resistance against fine dust. Aluminised steel is significantly cheaper than 316L stainless and is the practical choice for the longest section of any foundry exhaust main.
5.4 316L stainless for corrosive and cooling-water streams
316L stainless is reserved for the most corrosive streams: reverberatory aluminium halide fume, sulfur-bearing furan reclamation exhaust, sulfur-acid mist downstream of cupola wet scrubbers, and any duct in contact with cooling water (induction-furnace cooling circuits, scrubber recirculation). 316L is also the standard for supply-air mains in clean make-up zones — the laboratory air, the pattern-shop air, and the office-and-cafeteria air — where corrosion-free service for 30 years is the goal.
5.5 FRP and acid-resistant coatings for scrubber outlets
The clean side of a wet scrubber — between the demister and the discharge stack — carries saturated air at near-ambient temperature with potential acid carryover. Fibre-reinforced plastic (FRP) ducting or epoxy-coated carbon steel is the standard solution. FRP is corrosion-immune and lightweight, but it is non-conducting and requires bonding and grounding for any duct in a combustible-metals zone.
6. Sizing and design — capture velocity, transport velocity, and acoustic targets
6.1 Capture velocity at the source
Capture velocity is the air-flow speed required at the dust or fume source to entrain contaminant into the hood. ACGIH Industrial Ventilation Manual values are the practical reference:
- Low-velocity dust release (welding fume, ambient pattern-shop dust): 0.25–0.5 m/s
- Active dust release in moving air (shake-out, fettling, sanding): 0.5–1.0 m/s
- High-velocity dust release (shot blast, grinding wheels, knock-out): 1.0–2.5 m/s
- Pour-off fume capture at canopy hood: 1.0–1.5 m/s face velocity at the canopy
6.2 Transport velocity in the duct
Transport velocity is the in-duct air speed required to keep the captured dust in suspension. Below transport velocity, dust drops out and accumulates in horizontal runs; above transport velocity, abrasive wear on duct walls and elbows accelerates and noise rises.
- Vapour, fume and very fine dust (welding fume, paint mist): 10–13 m/s
- Fine dust (cotton lint, pattern-shop dust, light woodworking): 13–18 m/s
- Medium dust (general foundry shake-out, sand reclamation): 18–20 m/s
- Heavy or sticky dust (foundry fettling, knock-out, shot blast): 20–22 m/s
- Very heavy abrasive material (metal turnings, refractory dust): 22–25 m/s
6.3 Hood geometry — push-pull, slot, canopy, downdraft, backdraft
Hood selection is process-driven. Push-pull slot hoods across die-casting machines combine a push jet to direct fume across the work area with an extract slot on the opposite side. Slot hoods along benches give a draw-off across the operator's work zone. Canopy hoods over melting furnaces and pouring stations capture rising hot fume by buoyancy assisted by extract. Downdraft tables at fettling and grinding capture dust below the operator. Backdraft benches behind chipping and de-coring stations draw dust away from the breathing zone.
6.4 Acoustic targets — NC-65 industrial, NC-50 office
Foundry general industrial areas are NC-65 environments — accepted as a heavy-industrial standard with mandatory hearing protection in the active production zones (shake-out, fettling, shot blast). Office, laboratory and operator-cabin zones design to NC-50. Acoustic lagging on exhaust mains passing near manned workstations, NC-rated supply-air attenuators in laboratory and office branches, and sound-rated wall penetrations between production and office zones are standard practice. The acoustic budget is set at design stage and reviewed at commissioning; foundries that try to fix acoustics retroactively spend two to three times the cost of building it in.
7. Australian foundry operators — a market snapshot
The Australian foundry industry is concentrated in a smaller number of larger operators than it was twenty years ago, with specialisation by metal type, casting method and end-market. The seven operators below cover the bulk of mainland Australian foundry production and give a flavour of the diversity of HVAC requirements:
7.1 Bradken — large castings for mining and rail
Bradken is the largest manganese-steel casting house in the southern hemisphere, with foundries in NSW, Queensland (Wacol, Ipswich) and WA (Henderson). The mix is mining-truck buckets and ground-engaging tools, rail wheels and bogies, and large-tonnage industrial castings — driving electric-arc furnaces at 1700–1800 degC pour, heavy shake-out and shot-blast halls, and dedicated quench and heat-treatment lines. Bradken is the archetype for refractory-lined exhaust, multi-stage particulate control and major LEV at fettling.
7.2 Castech — Brisbane investment casting
Castech is a Brisbane-based investment-casting specialist serving resources, defence and pump-and-valve markets. The lost-wax process drives a different HVAC mix from sand casting: wax-recovery condensers, shell-drying climate control (40–60% RH), shell-firing kilns under NFPA 86, and pour-off canopies for alloys up to 1700 degC. The dipping-room and wax-room climate-conditioning load is a significant fraction of total HVAC capacity.
7.3 OneSteel (Liberty) Wagga Wagga — rail wheels and crossings
The OneSteel facility at Wagga Wagga — part of the Liberty Steel group — operates rail-wheel and rail-crossing casting in central NSW. Heavy steel castings poured at 1600–1700 degC, with downstream quench, temper and machining. The HVAC footprint is dominated by electric-arc furnace fume capture, quench-tank vapour management, and heat-treatment oven exhaust per NFPA 86 — a textbook secondary-steel-casting site distinct from primary mill operations.
7.4 Furphy Engineering — Shepparton heavy castings
Furphy Engineering in Shepparton, Victoria, operates a heavy-casting foundry and engineering works with deep history in pressure-vessel, agricultural and process castings. The cast-iron and steel mix drives cupola and induction-furnace mains, sand-reclamation systems, fettling and shot-blast lines, plus a parallel pressure-vessel shop with its own welding-fume LEV. Shepparton's regional location adds a cold-winter make-up-air heating load not seen in coastal foundries.
7.5 ACL Bearings — Wagga Wagga and Launceston
ACL Bearings, with plants in Wagga Wagga and Launceston, casts and machines bearing inserts and engine bearings in high-precision non-ferrous alloys (lead-tin-copper, aluminium-tin, copper-lead). Lead-bearing alloys add a regulated heavy-metal fume load that requires HEPA-grade after-filtration before discharge.
7.6 Castalloy — Adelaide aluminium die casting
Castalloy in Adelaide is a high-pressure aluminium die-casting house serving automotive and structural-aluminium markets. The HVAC mix is dominated by die-spray-mist capture, gas-fired holding-furnace exhaust, T4 and T6 heat-treatment ovens per NFPA 86, and shot-blast and trim cleaning. HPDC operations run at the highest production tempo of any Australian foundry segment and the HVAC system must keep pace without contaminant carryover.
7.7 Comsteel — Moly-Cop grinding media
Comsteel, part of the Moly-Cop group, manufactures grinding media (steel balls and rods) for mining at Newcastle NSW. Forged-and-cast steel media, with heavy heat-treatment exhaust, shot-blast finishing and large electric-arc furnace fume capture — secondary steel casting at scale serving a single dominant end-customer.
7.8 What the operator mix means for fabricators
The Australian foundry market is not a single homogeneous segment. Bradken needs refractory-lined exhaust and large-bore baghouse mains. Castech needs precision climate control and wax-recovery condensers. Castalloy needs die-spray-mist capture and NFPA 484 combustible-metals handling. Each operator type drives a different mix of duct material, duct geometry and capture-hood design.
8. The wet-scrubber and baghouse interface
Almost every foundry exhaust stream terminates at either a wet scrubber or a baghouse. The choice between them is process- and chemistry-driven.
8.1 Wet scrubbers
Wet scrubbers — venturi, spray-tower or packed-bed — pass the exhaust through water spray that captures particulate and absorbs water-soluble gas. They are mandatory for combustible-metal dust (aluminium, magnesium), preferred for high-sulfur streams (cupola, furan reclamation), and common for any stream with sticky or hygroscopic particulate that would blind a baghouse filter. The disadvantages are water consumption (closed-loop with bleed-off treatment is standard), the need for sludge handling, and the saturated stack discharge that requires a tall stack to clear the building plume.
Duct-side considerations at the scrubber inlet are vacuum loading — the scrubber generates significant static pressure drop, and the inlet duct sees up to 6–10 kPa vacuum. Standard medium-pressure AS/NZS 4254 duct is inadequate for sustained vacuum at this level; reinforced spiral or heavy-gauge welded construction is the typical solution. 316L stainless is standard for the wet-side inlet ducting because of acid-mist carryover.
8.2 Baghouses
Baghouses use fabric filter elements (typically polyester, aramid or PTFE membrane) to capture dust mechanically. They are the preferred choice for dry non-combustible dust streams (fettling, shake-out, shot-blast, sand-reclamation in ferrous foundries) and offer high collection efficiency (99.5%+ on particulate) with no water consumption. The disadvantages are filter-bag life (12–36 months depending on dust load), the temperature limit (typical bags fail above 250 degC), and explosion-protection requirements for any combustible-dust application.
Duct-side considerations at the baghouse inlet are temperature — the duct must cool the exhaust to below the bag's service temperature, typically by passing through a quench tower or evaporative cooler upstream of the baghouse. Standard mild steel ducting works upstream of cooling; downstream of cooling the duct sees a saturated stream and 316L is preferred. The clean-side of the baghouse, between the bag plenum and the discharge stack, is sized for low velocity (10–15 m/s) because all particulate has been removed.
8.3 Combination systems
Many modern Australian foundries run combination systems — cyclone pre-separator for coarse particulate drop-out, evaporative cooler for temperature reduction, baghouse for fine-particulate capture, and wet scrubber or polishing scrubber for any residual acid-gas removal before stack discharge. The duct system is correspondingly complex, with material transitions at each stage and damper isolation at each module. The duct designer's task is to lay out the system so each module can be isolated for maintenance without taking the entire foundry off-line.
9. Local exhaust ventilation (LEV) — the workhorse of foundry compliance
Every dust and fume source in a foundry gets its own LEV branch. Total LEV exhaust in a mid-sized Australian foundry is typically 50,000–200,000 m3/h, distributed across 20–80 individual branches. Each branch is sized for its source capture and transport velocity, with isolation dampers for maintenance.
9.1 Branch sizing
Branch sizing starts from capture velocity at the source, converts to volumetric flow at the hood face, then sizes the branch to maintain transport velocity. A typical fettling-bench branch is 800–1200 m3/h, 250–300 mm diameter at 18–20 m/s transport velocity. A typical pouring-floor canopy branch is 8,000–15,000 m3/h, 500–600 mm at 18 m/s. A cupola main is 50,000+ m3/h, 1200–1500 mm diameter at 15–18 m/s in refractory-lined mild steel.
9.2 Balancing
LEV systems are pressure-balanced — each branch is sized so the static pressure drop from hood face to main collection point is equal across all simultaneously-operating branches. Without balancing, the branches closest to the fan starve the more distant branches of capture velocity. Balancing dampers at each branch are used for commissioning trim; the fundamentals must be right at design stage.
9.3 Make-up air
Every cubic metre of LEV exhaust must be matched by clean make-up air. In a 100,000 m3/h foundry LEV system, that means 100,000 m3/h of supply air at the design condition. Make-up air is delivered through 316L stainless or hot-dip galvanised supply-air mains, with HEPA pre-filters at clean make-up points (laboratory, office, operator cabin), and direct-gas-fired tempering for winter heating in temperate-climate foundries.
10. Typical project sizes — Australian foundry HVAC
A new Australian foundry HVAC project runs a predictable size range. Five reference points:
- Small jobbing iron foundry (1–5 t/day): Total LEV 25,000–50,000 m3/h, 6–12 hoods. Duct footprint AUD 150,000–350,000.
- Mid-size investment caster (10–25 t/month): Total LEV 30,000–80,000 m3/h, 15–25 hoods across wax, dipping, drying, de-wax, kiln, pour, knock-out. Heavy 316L stainless content. Duct footprint AUD 400,000–900,000.
- Mid-size aluminium die caster (200–500 t/month): Total LEV 80,000–150,000 m3/h, 20–35 hoods. NFPA 484 combustible-metals zoning. Duct footprint AUD 800,000–1.5 m.
- Large heavy-casting iron foundry (mining buckets, rail wheels): Total LEV 150,000–300,000 m3/h, 40–80 hoods, refractory-lined exhaust dominant. Duct footprint AUD 1.5 m–3.0 m.
- Large precision steel-casting foundry (manganese, alloy steel): Total LEV 150,000–250,000 m3/h, 30–60 hoods, EAF capture, NFPA 86 heat-treatment compliance. Duct footprint AUD 1.2 m–2.5 m.
11. The SBKJ machine configuration for foundry fabrication
Foundry duct work is the most demanding production envelope a sheet-metal fabricator can take on. The right SBKJ machine configuration gives the fabricator the capability to serve every duct-material requirement in this guide without subcontracting any major operation.
11.1 SBAL-V stainless option auto duct line
The SBAL-V auto duct production line is SBKJ's flagship rectangular duct line. With the stainless-steel processing option, the SBAL-V handles 304 and 316L stainless sheet in addition to standard galvanised and aluminised steel, with appropriate tooling for stainless thickness range and surface protection during forming. The SBAL-V is the right answer for a foundry-segment fabricator who needs to produce 316L mains for cooling-water and chemistry-control runs alongside conventional duct for plant air handling. See our machine catalogue and the SBAL-V vs SBAL-III comparison for detail.
11.2 SBTF-2020 spiral tubeformer for dust mains
Foundry dust mains — shake-out, fettling, knock-out, sand-reclamation, shot-blast — are best fabricated as spiral round duct. Round duct gives the best aerodynamic profile for high transport velocity (18–22 m/s) and the lowest abrasive-wear surface for dust-laden streams. The SBTF-2020 spiral tubeformer produces round duct from 80 mm to 1500 mm diameter in galvanised, aluminised or stainless steel sheet. For high-volume foundry dust-main work, the SBTF-2020 is the practical fabrication envelope. Cross-reference our spiral duct forming guide for production technique.
11.3 TIG seam welder for hot-side mains
Hot-side foundry exhaust mains downstream of the refractory section run too hot for sealants and gasketed flanges. The duct seam must be continuously welded — TIG welding for 316L stainless, MIG or stick for carbon steel — to maintain integrity under thermal cycling and to avoid sulfur attack at any unsealed lap. SBKJ's TIG seam welder option for the SBTF spiral line gives an in-line continuous TIG weld on stainless spiral duct, eliminating subcontracted weld work. See our welding methods reference for technique selection.
11.4 Refractory-lined option for furnace exhaust mains
The deep-furnace section of every foundry exhaust is refractory-lined mild steel. SBKJ supplies the carbon-steel outer shell with prepared flanges and refractory-anchor studs welded to the interior at the appropriate density. The refractory cast or blanket installation is typically performed by a specialist refractory contractor at the foundry site, but the outer-shell fabrication — flanged, anchor-studded, internally-prepared — is fully achievable on the SBAL-V production line with the heavy-gauge option.
11.5 Reinforced spiral for vacuum loads
Wet-scrubber inlet ducts and V-process vacuum mains see vacuum loading well above AS/NZS 4254 medium-pressure ratings. The SBTF spiral line produces reinforced spiral with thicker gauge and rolled-on external ribs, giving a vacuum-rated round duct without the cost of full welded construction. For static pressure differentials above 8 kPa, the reinforced spiral is the cost-competitive answer.
12. Practical fabrication and installation considerations
12.1 Refractory anchoring
Refractory-lined ducts use stud anchors welded to the inside of the carbon-steel shell at a density of typically 1 anchor per 0.1–0.25 m2, depending on refractory thickness and service temperature. Anchor pattern is laid out at fabrication time, not at installation. The duct fabricator who omits anchor studs at production time forces a site-weld retrofit that is slow, expensive and rarely as good as the factory weld.
12.2 Thermal expansion
A 30 m run of carbon-steel duct expands approximately 90 mm between ambient and 300 degC service. Foundry exhaust mains must include expansion joints — bellows expansion joints in lower-temperature sections, brick-and-fibre expansion joints in refractory-lined sections — sized for the design temperature range. Rigid mounting of long exhaust runs is a common cause of premature failure as thermal stress tears welded joints.
12.3 Inspection access
AS 4024 and AS 1885 both require regular inspection of foundry ductwork. Access ports are sized for camera inspection (200 mm minimum) or for personnel entry (600 mm) on confined-space-compliant work. Inspection-port positioning is process-driven: every 5–10 m on horizontal runs, at every elbow, at every branch take-off, and on either side of every damper.
12.4 Insulation and acoustic lagging
Foundry exhaust mains over manned work zones are insulated externally for personnel protection — exterior shell temperatures of 60 degC or higher are an AS 4024 burn hazard. Acoustic lagging on top of the thermal insulation gives NC-65 acoustic compliance in production areas and NC-50 in adjacent office and laboratory zones. The combined insulation-and-lagging package is bulky and must be coordinated with structural-clearance budgets at design time.
12.5 Dampers and isolation
Every machine on a shared dust or fume main needs an isolation damper for safe maintenance. Dampers in foundry service are heavy-duty butterfly or guillotine designs with high-temperature seals, refractory packing where service temperature warrants, and position indicators on the AS 4024 lock-out chain. Fire dampers per AS 1668.1 are required at zone boundaries; smoke dampers are typically not required in foundry occupancy but are sometimes specified at office/production boundaries.
13. Where this connects to the rest of the SBKJ insight library
Foundry HVAC sits in the heavy-industry corner of the SBKJ insight library. Five companion guides are worth reading alongside:
14. Twelve-point checklist for a foundry HVAC specification
The condensed version of this entire guide is a twelve-point checklist that an engineer can run against any foundry HVAC specification before sign-off:
- Every dust and fume source mapped, classified by temperature and chemistry, and assigned to a dedicated LEV branch with documented capture velocity.
- Cupola, induction, electric-arc and reverberatory exhaust mains within 5 m of the furnace specified as refractory-lined mild steel with internal anchor studs at appropriate density.
- Medium-temperature exhaust mains specified as hot-dip aluminised steel; corrosive and cooling-water mains specified as 316L stainless.
- Dust mains sized at 18–22 m/s transport velocity; vapour and fume mains at 10–13 m/s.
- Combustible-metal-dust zones identified per NFPA 484 and AS/NZS 60079; wet-bath collection specified; bonding and grounding documented.
- Heat-treatment ovens specified per NFPA 86 with LEL monitoring, purge-and-light sequence and dedicated stack risers.
- Make-up air system sized for total exhaust with neutral or slightly positive pressure on the pouring floor relative to office and laboratory zones.
- Acoustic targets specified: NC-65 in production, NC-50 in office, with lagging budget coordinated at duct-routing stage.
- AS 4024 machinery-safety interface confirmed on every dust-extraction connection — interlocked guards, isolation dampers, inspection-port positioning.
- Thermal expansion provided for on every hot-side run; bellows or brick-and-fibre expansion joints specified at design stage.
- Wet-scrubber and baghouse inlet duct vacuum loads specified above AS/NZS 4254 medium-pressure where required; reinforced spiral or heavy-gauge welded construction substituted.
- SafeWork Australia and state EPA compliance evidence — silica dust sampling plan, stack-emissions monitoring plan and inspection-and-maintenance schedule — drafted before commissioning.
Get an itemised SBKJ quote for foundry duct production →
FAQ
Why does galvanized ductwork fail in foundries?
Zinc volatilises above 419 degC and fumes above 250 degC service, so any cupola, induction, reverberatory or heat-treatment exhaust strips the zinc coating quickly. Silica sand abrasion at shake-out and shot blast strips zinc mechanically inside a year, and sulfur compounds from chemical binders (furan, phenolic urethane) react with zinc to form zinc sulfate. Refractory-lined mild steel for furnace exhaust, hot-dip aluminised steel for medium-temperature mains, and 316L stainless for corrosive streams and cooling-water mains are the standard substitutes.
What Australian standards apply to foundry HVAC ductwork?
AS 1668.2 (mechanical ventilation), AS 1885 (metal-casting workplace safety), AS/NZS 60079 (hazardous-area classification for combustible metal dust), AS 4024 (machinery safety), AS/NZS 4254 (duct construction). NFPA 484 (combustible metals) and NFPA 86 (industrial ovens) are referenced by Australian insurance underwriters. SafeWork Australia exposure standards (0.05 mg/m3 respirable crystalline silica, 5 mg/m3 respirable iron oxide, 30 ppm CO) drive LEV sizing at every dust and fume source.
What furnace types need different exhaust strategies?
Cupola furnaces (iron, 1450–1650 degC) need refractory-lined exhaust to a wet scrubber. Coreless induction furnaces (iron and steel, 1500–1700 degC) need localised side-draft canopy capture. Reverberatory furnaces (aluminium, 700–850 degC) need acid-resistant ducting for halide fume. Electric arc furnaces handle spike loads during melting and need fourth-hole plus canopy capture. Gas-fired crucible furnaces (non-ferrous) need low-volume continuous canopy capture.
Why is NFPA 484 critical for aluminium and magnesium foundries?
Aluminium dust is explosible above 30 g/m3 and magnesium dust ignites at lower concentrations and is harder to extinguish. NFPA 484 mandates wet-bath collection, prohibits dry baghouses without deflagration protection, and requires bonding and grounding of ductwork to prevent static ignition. Magnesium die-casting houses and aluminium grinding/fettling are the highest-risk zones.
How do sand casting, investment casting and die casting ventilation differ?
Sand casting (green sand, no-bake, shell mould) generates the largest dust load and needs 18–22 m/s dust mains with cyclone pre-separation. Investment casting (lost-wax) generates fine ceramic dust at knockout plus wax vapour and ammonia from binders, with separate exhaust streams. High-pressure die casting (HPDC) generates die-spray mist, metallic vapour at the shot sleeve and combustion products, with capture concentrated at the die area.
