Why Fan Materials And Construction Matter So Much
The materials used in the construction of your specified centrifugal fan are of major importance. They will often be determined by the working environment – or the quality of the air passing through the fan.
Centrifugal fan materials and construction methods can differ, depending on which type of unit is specified: forward curved, backward curved or radial. It is important to consider the fan’s casing, motor and impeller – especially the latter because it plays such a crucial role in moving the air.
Fan Casings – Diecast Aluminium vs Stainless Steel
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.
A typical example is the VBL6 – a highly popular forward-curved centrifugal fan. This compact but powerful fan is produced in large volumes for applications including fume cupboards and clean rooms. The VBL6’s LM6 casing is finished in black powder coating for added protection.
However, aluminium has a low melting point, so stainless steel is recommended for more challenging industrial environments. In this instance, the casing must be fabricated (welded) rather than cast.
This is a more labour-intensive process than sand casting or gravity casting an aluminium casing. But opting for fabrication rather than casting makes it quicker and easier to add in custom features.
Grade 304 stainless steel is recommended for general applications where diecast aluminium is not suitable. (Grade 304 is the world’s most popular type of stainless steel, not least because it’s the one used for cutlery.) However, grade 316 would be needed for food processing, pharmaceutical or petrochemical applications. And grade 316L offers superior corrosion resistance because it has a lower carbon content.
Fan Motors’ Construction
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 – Materials And Construction By Fan Type
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.
Get Expert Technical Advice On Fan Construction And Materials
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