Bent fan blades

[corrosionman]

We refurbish a 5 foot dia fan every 18 months - - Its what we call a paddle fan - -6 blades that are like the paddle on a paddle ship - -the blades are 3/8 thick and they push a heavily loaded mineral dust up the exit stack. - - the tips of the blades are always greatly bentbut we know there is nothing heavy or solid goes into the fan system.
I have two queries
1)If a thick steel blade constantly hits heavy mineral dust will it eventually bend even though the blade itself is still in very good paint condition after 18 months.
2)Are we correct in just making the fan blade tips red hot and straightening them with a hammer and is there a limit to how often we can do this - - are there any metallurgical things we should be avoiding - - it would be very undesirable for one of our "straightened area" to break free because it would send the fan massively out of balance
and also there would be a risk the piece of blade going like a missile.
Any comments much appreciated
Corrosionman.

 

[berkshire]

One of the ways of forming metal is shot peening.
What is the largest particle size?
B.E.

 

[Compositepro]

It is more likely that there is dust accumulating somewhere before the fan that periodically breaks loose in clumps that hit the fan blades.

 

[btrueblood]

What CompositePro said, but I was thinking of clumps from 'way up in the stack breaking loose and falling back to hit the blades.

 

[arunmrao]

Is the fan continuously run ? Perhaps during the stoppages there is some agglomeration taking place or there are lumps which have missed being sieved/crushed hitting the fan.

Learn the rules,so you know how to break them properly.
Dalai Lama

_____________________________________

 

[unclesyd]

Are all the blades bent close to the same amount? It will vary a little if you have straightened it.

I would try to locate someone in your area well versed in the art of flame straightening metal to give you a short course in how to straighten your blade without the hammer and high heat.

As you state you are inviting a chunk to come flying off.

 

[berkshire]

If the blades are bending evenly, you are most likely creating a somewhat crude backwards inclined fan.
If that is the case it should not make any difference to the efficiency of the fan. I would just leave them bent.
Now if only one blade is bent , that is a different problem.
B.E.

 

[EngAddict]

Are you sure the paddle blades were not bent to start with? A backward curved fan is much more efficient than a radial. It seems strange for a paddle impeller with a high particle load to still have it's paint in good nick, I doubt it was the mineral dust that caused it.
Do you have the fan designation, this will tell you the types of blades. Do you have any design calcs or drawings of the as built model?

 

[kellnerp]

Why not rubber line the blades?

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