Centrifugal Fan Materials And Construction

Most fan casings tend to be cast from aluminium – regardless of which type the fan may be. LM6 is a popular grade of aluminium for fans for the following reasons:

• Its excellent thermal conductivity helps in dissipating the heat generated during the operation of the fan. This helps to keep the fan cool and prevents any damage to internal components due to excessive heat.
• LM6’s high strength-to-weight ratio makes it a lightweight yet sturdy material for the casing. This helps to reduce the overall weight of the fan, making it easier to install and transport.
• High resistance to corrosion – making it suitable for use in harsh environments such as chemical plants. This property helps to extend the life of the fan and reduces maintenance costs.
• LM6 is easy to cast and machine – reducing the time and cost of manufacturing the fan.

Fan motors also tend to be constructed from diecast aluminium. Most housings are of the ‘squirrel cage’ type with fins to aid cooling.

Aluminium is usually the material of choice for motor housings for all the reasons outlined above. But cast iron is recommended for applications where robustness is key – especially in environments where there is a risk of explosions.

Cast iron is strong and durable. It has good mechanical strength and is resistant to wear and tear. However, it is much heavier than aluminium – and it is also vulnerable to corrosion. Applying a protective coating, such as paint or enamel, can prevent exposure of the cast iron to moisture and oxygen.

Impellers comprise a back plate, shroud (front) plate and blades.

Forward-curved centrifugal fan impellers are manufactured from mild steel that is protected with a layer of zinc to help prevent corrosion. That zinc layer can be applied by galvanisation (dipping in molten zinc) or by plating (using electrolysis).

 Backward-curved and radial centrifugal fans have larger, weightier impellers than their forward-curved counterparts. The impeller blades of backward-curved and radial fans are bigger (and spaced further apart) than those in the ‘hamster wheel’ impellers of forward-curved fans.

This means that backward-curved and radial impellers are usually manufactured from thicker, heavier steel that can be wet painted if required. (Blade size and spacing is not the issue it can be with forward-curved impellers).

These heavier impellers are almost always handmade, whereas the forward-curved variety are usually machine manufactured because the steel is thinner and more workable. However, forward-curved impellers can be custom-made by hand if required.