Ventilation Fan

[lh.ahn84]

Dears,
Could you pls kindly help me to find out the root of cause of one problem.We are installing the 100000 CMH,axial fan for engine room in one of the ship.The spec of the fan is as follow,
Capacity 100000 CMH
SP 400 pa
Elec 440V/3ph/60 HZ
Power 45 KW
Cavity 16
Blades 12
Material Aluminium alloy
RPM 1750

There is a problem that we have to change the impeller more thn a dozen of times since the impeller is keep on breaking like once a month.The bottom of the fan ,there is a foundation and after that there is a structural chamber,all together total 1600 mm.The fan dia is 1120.
Thanks for ur interest in this thread and looking for ur advise and comments.

[desA]

I suggest you take some pictures of the fan failures & post them up for comment.

Aluminium alloys will suffer in a fatigue environment, especially if geometric stress-raisers exist, or excessive porosity.

[mad fridgie]

Thats moving at a fair few "Knots"
Are you building the fan up yourselves.
Fitting the 12 blades to the hub? If so you are likely making with an inbalance. (causing a lot of stress)
I would suggest you have these built by a specialist and have it balanced.
Similar to what is done on a car wheel!

[chemi-cool]

you should use a belt driven fan or centrifugal fan, much less stress on the motor and blades

[lowcool]

increase the number of blades and reduce the pitch or as above

[Brian_UK]

Check that there is a good screen in front of the fan, there may be foreign matter getting sucked through and hitting the blades.

[Magoo]

If I read it correctly you have a case diameter of 1600mm and a fan diameter of 1120mm, at the high volume rate and static pressure of 400pa, you will get very high slippage, off the end of blades creating buffeting/ pulsing. This will flex the blades and create metal fatigue and broken blades.

[Tesla]

Yes as mad fridgie suggests check for imballance. Also check for harmonic resonance or cavitation. you could take basic measurement with a scope and sensitive mic but probably an engineer would need to analyse. But on a quick calculation from your specs it does'nt add up - can you provide some fan curves or possiby contact the manufacturer for more data? and measure pressure differential across the fan

[ref717]

This fan blade falure is a complicated issue. You need to first investigate where is the fracture surface and analyze if it was fatigue failure or material failure?. Anyway, above comments are correct.,you may have an inbalanced fan blade or
aerodynamic disturbance that resulted in resonant vibration.

[lh.ahn84]

Dears,
Thanks for ur valuable comments,we checked the balancing and found that is out 0.05 mm only.And for the material,the casting seems is not so bad that mean we cant find the air sac in the section of the impeller.And we cover the fan with the 12x12 x GA 16 wiremesh with reinforcement.So probably the is nothing to come and touch the impeller.We now suspect that because of the back pressure.Since the discharge side is only 1D of the fan and suction side is too.Now we install the guidevane at the discharge side and have to see the result.
Regards
Aung