The process
Annealing, normalising and tempering furnaces need recirculation fans inside the chamber for temperature uniformity, combustion air for the burners, and a flue fan where the furnace is under draft. The recirculation fan is a plug fan running inside the hot zone.
The gas at the fan
Clean air at elevated temperature from a dryer, oven or cooling duty. The selection is made at the hot density, with the shaft and bearings arranged for continuous hot running.
Selection for this duty
| Blade form | Backward curved or aerofoil for the best efficiency on clean gas |
| Material of construction | Mild steel |
| Drive and bearings | Direct coupled, shaft cooling disc, bearings in a pedestal outside the gas stream, allowance for thermal growth |
| Density at the fan | At about 250°C the gas density is close to 0.67 kg/m³, 56% of standard air. Pressure developed and power drawn fall in the same ratio, so the selection is made at this density and the motor is checked at cold start. |
A centrifugal impeller without a scroll, plugged through the wall of an oven, dryer or air handling unit so it recirculates the air inside the chamber. Belt driven or direct driven from outside the hot zone. Client-stated blade types for the Plug Fan in general: Backward curved.
Industries
Other fans in heat treatment furnaces
Plug Fan in other processes
Glass Forming and Annealing LehrsCeramic Tunnel and Roller KilnsBelt and Tray DryersFood Ovens and FryersTextile Stenters and DryersAutomotive Paint ShopsPowder Coating Lines
Information needed to select or quote
- Duty point. Volume flow and static pressure at the fan inlet, with the gas density and temperature or the conditions to derive it.
- Operating conditions. Site altitude, normal operating temperature and continuous or intermittent duty.
- Gas stream. Dust loading and particle size, corrosive species, moisture, upset temperature and any tendency of the material to deposit on the impeller.
- Mechanical. Rotation viewed from the drive end, discharge orientation and motor power.