How powder coating curing ovens work
Powder coated parts, hung on an overhead conveyor or loaded in batches, pass through a curing oven where the powder melts, flows and cross-links. A typical cure is 10 to 20 minutes at a metal temperature of 160 to 200°C, so oven air is held at about 180 to 220°C. Most ovens are convection ovens: a recirculation fan draws air from the oven, passes it over a heat exchanger or a burner, and blows it back through supply ducts. Heating is by a gas or diesel burner, firing directly into the air or indirectly through a heat exchanger, or by electric heaters. Powders release little volatile matter, but some cure by-products and, on direct-fired ovens, burner gases must be removed. An exhaust fan does this, and a combustion air fan feeds the burner.
Where the FD fan sits
- Air intake
- FD (combustion air) fan
- Burner
- Heat exchanger or recirculation duct
- Oven chamber
Most powder oven burners are packaged units with the combustion air fan built in, mounted on the burner housing beside the oven. Larger ovens, or line burners placed in the recirculation duct, use a separate fan. Either way the fan draws air from the plant or from outside and delivers it to the burner at the pressure the burner needs, typically 100 to 300 mmWC at full fire.
Air at the FD fan
| Air temperature at the fan | Plant air, 30 to 50°C beside the oven |
| Dust | Overspray powder in the plant air; inlet filter needed |
| Pressure at the fan outlet | Typically 100 to 300 mmWC at the burner |
| Turndown | Burner modulates with oven load and temperature |
| Density at the design temperature | About 1.11 kg/m³ at 45°C, 93% of standard air. Pressure developed and power drawn scale with density, so the fan is selected at this condition and the motor is checked at the coldest operating or start-up condition. |
FD Fan selection for powder coating curing ovens
| Blade form | Backward curved, quiet on clean air |
| Material of construction | Mild steel, painted |
| Drive and arrangement | Direct mounted on the motor shaft |
| Bearings and cooling | Motor bearings; no cooling needed |
| Flow control | Damper linked to the fuel valve, or variable speed drive |
| Also specified | Inlet filter and air pressure switch |
What this FD fan has to cope with
Powder drawn into the burner
Powder coating shops have fine powder in the air near the spray booths and recovery units. If the burner fan draws it in, the powder melts in the burner head and fouls it. Placing the intake away from the booths, ducting air from outside, and fitting an inlet filter prevent this.
Air-fuel ratio drift
As damper linkages wear or the fan impeller collects dust, the air-fuel ratio drifts and the burner runs rich or lean. Rich firing on a direct-fired oven can discolour light shades of powder. Periodic combustion checks and a fan with stable delivery across the modulation range keep the burner right.
Warm air reducing capacity
Air beside the oven is warm, which lowers its density and the oxygen the fan delivers. A fan sized on the actual intake temperature at full fire, or an intake ducted from outside the building, avoids the burner running short of air on hot afternoons.
Energy and control
The burner fan is small, but any excess air it supplies is heated to oven temperature and then lost through the exhaust. Setting the air-fuel ratio correctly across the firing range saves far more gas than the fan's own power. A burner with good turndown, and a fan that follows it, avoids running surplus air during idle periods between loads.
ID fan and FD fan in powder coating curing ovens
| ID fan | FD fan | |
|---|---|---|
| Position | Oven roof, on the exhaust duct | On the burner housing |
| What it handles | Hot oven air with cure fumes | Ambient air |
| Temperature at the fan | 180 to 220°C | 30 to 50°C |
| Main design concern | Heat and fume condensation | Air-fuel ratio |
| Control | Oven pressure | Burner firing |
See also the Induced Draft (ID) Fan for powder coating curing ovens.
Questions buyers ask
What does the FD fan do on a powder coating oven?
It supplies combustion air to the burner that heats the powder coating oven. On packaged burners it is built into the burner; on larger ovens it may be a separate fan. It handles ambient air and must keep a steady air-fuel ratio as the burner modulates to hold the oven temperature.
Why is my powder oven burner fouling?
Powder from the spray area drawn in with the combustion air melts inside the burner and builds up on the head and the ignition electrodes. Moving the forced draft fan intake away from the booths, ducting air from outside, or fitting an inlet filter stops it. Cleaning the burner then restores normal firing.
Does an electric powder coating oven need an FD fan?
No. An electrically heated oven has no burner and so no combustion air fan. It still has recirculation fans to move air over the heaters and the parts, and usually an exhaust fan to remove cure fumes and hold the oven slightly negative at the openings.
Information needed to quote an FD fan for powder coating curing ovens
- Duty point. Combustion air quantity in m³/h or kg/h and the static pressure at the fan outlet, with the margins you want.
- Air condition. Site ambient temperature range and altitude, and whether the fan takes ambient air or air already heated.
- System. Boiler or furnace capacity and fuel, resistance of the air heater, windbox, grate or burner, and the existing fan curve or nameplate if this is a replacement.
- Mechanical. Drive arrangement, flow control (damper, inlet vanes or variable speed drive), noise limit, rotation and discharge orientation.
- Burner. Burner make, rating and the air pressure it needs at full fire.
- Air source. Location of the fan intake relative to the spray booths, and the air temperature there.
Built and tested in Chennai
Adroit Fantech Engineers has designed and manufactured industrial fans at Ayanambakkam, Chennai since 2004. Each impeller, casing and shaft is built for the gas and temperature it will see, performance tested as per IS 4894 or BS 848 Part I, and balanced to grade G 6.3 or G 2.5 as per ISO 21940-11, with the records supplied with the fan. We also replace rotors and retrofit existing fans of any make.