Fläkt Woods has melted away conventional fan technology, by creating a range of larger diameter aluminium impellers that can operate at higher speeds in emergency situations for two hours at 400°C.
Pure aluminium has a melting temperature of 660°C, aluminium alloys liquefy as low as 577°C, so the Company has stretched the range to the very limits of the material. This has been achieved in part by using some of the latest finite element analysis and also because in-house experts understand exactly what can be achieved with the proposed solution in practice.
Aluminium is used by Fläkt Woods because it remains the most efficient solution for fan hubs and impellers, allowing complex aerodynamic shapes to be cast compared with steel flat blades that require higher energy for similar performances. Eight years ago the Company was the first to create a range of aluminium impellers that would work at temperatures of 400°C for two hours at up to 2 pole speed.
These fans have traditionally been used for tunnel and metro venting, the new fans have already proven themselves in HVAC applications, such as retail and office buildings as well as their established markets.
Research and development
As a result of previous research, engineers already knew that aluminium dramatically loses strength at elevated temperatures, and fatigue fractures become aggravated as low as 160 degrees Celsius. Further physical tests were needed for the increased temperatures, and these were carried out on various aluminium alloys at Fläkt Wood’s Colchester laboratories.
Once these results were known, finite element analysis (FEA) was used to refine the design to increase strength in the zones where stresses are highest. Stress analysis of the impeller by experimental and FEA, has shown that the stress pattern in impeller components is highly complex. As a result, getting the exact forces applied is critical, only then can component stresses be reduced.
Issues included having to prove the design operating stresses as at higher temperatures when the hub deforms, and the blades slowly grow in length as the metal stretches.
A conventional hub design was used and redefined with FEA, Stresses were studied and the design refined to keep them within calculated limits. Once engineers were happy with the results, a prototype was manufactured using real castings. The final piece of the jigsaw came when CE testing was successfully carried out by BSRIA on a 4 pole fan with a diameter of 1250mm.
A completely new range
Fläkt Woods is excited about the possibilities. The breakthrough means that a range of new fans are available for emergency smoke extraction at 400°C, a critical extension of their already world beating range for emergency smoke ventilation and control.
The variety of fans is impressive, with faster speeds in the medium range and much larger diameters at 4 pole speeds. These range from small 315 mm diameter fans, through to 710 mm diameter 2 pole fans that can work at higher speeds for tunnel jet thrust fans, and much larger 1250 mm diameter fans. The Company is currently testing a 1400 mm diameter 4 pole fan using the same technology, which will be a ground breaking achievement for the fan industry once proven.
Fläkt Woods has melted away conventional fan technology, by creating a range of larger diameter aluminium impellers that can operate at higher speeds in emergency situations for two hours at 400°C.
Pure aluminium has a melting temperature of 660°C, aluminium alloys liquefy as low as 577°C, so the Company has stretched the range to the very limits of the material. This has been achieved in part by using some of the latest finite element analysis and also because in-house experts understand exactly what can be achieved with the proposed solution in practice.
Aluminium is used by Fläkt Woods because it remains the most efficient solution for fan hubs and impellers, allowing complex aerodynamic shapes to be cast compared with steel flat blades that require higher energy for similar performances. Eight years ago the Company was the first to create a range of aluminium impellers that would work at temperatures of 400°C for two hours at up to 2 pole speed.
These fans have traditionally been used for tunnel and metro venting, the new fans have already proven themselves in HVAC applications, such as retail and office buildings as well as their established markets.
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