balancing a fan.... question mainly for mechanicals guys 1

[uhpo]

I try to balance a fan with 3000 mm diameter, like a propeller, and I ask on my supposed ignorance for a dinamical balancing, and the guys on the office laugh with me, cause they tell me that this kind of stuff is not possible to balance on dinamical way, i´m not interested too much on machematical conclusion, i would like to know if they are cheating with me and if it´s like this some information about standard or papers that explain me when in a fan i have to balance on dinamical or static.....

 

[tygerdawg]

Is done all the time. Large diameter rotating bodies & high rotational speeds will ruin your day if not balanced. There are methods, instruments, & equipment out there to sense the location & magnitude of a mass imbalance at a particular rotational speed, and to recommend corrective actions in the form of adding/subtracting masses to/from locations on the moving body. Think: automotive wheel.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[rmw]

If I understand your situation, your fan is an aerofoil shaped propeller bladed type fan, right?

While Tygerdog correctly describes the methodolgy of fan balancing, it is a little more difficult with a specifically shaped blade.

You can't add much material to the light side without disturbing the shape and contour of the blade, but you can remove material on the heavy side by shaving off material in a manner that the shape and contour is maintained. Especially in the tip area.

Depending on the shape of the blade, there might be areas where airflow across the blade is low where you could drill a series of shallow holes.

If the fan is so out of balance that you can't balance it without destroying the aerofoil contours, then you are sunk.

In all of the above, you have to be careful not to weaken the blade or disturb or disrupt the airflow patterns in critical areas. Tygerdog makes a good point. An automotive wheel isn't balanced on the rubber parts, it is balanced on the metal parts where adding weight is possible with weights designed to be placed there.


I'd contact the manufacturer of the fan to see what they recommend regarding balancing of their fans.
There is not a fan out there that doesn't require some kind of balance - before you get it or after - so they should know how they planned to do that.

 

[desertfox]

hi uhpo

Balancing is the previous poster said is done all the time have a look at these sites:-

http://www.argusfanstechnologies.com/Fan_Balancing_Vibration_Analysis.html

http://shjpbalancer.en.made-in-chin...Fan-Impeller-Balancing-Machine-PHW-3000-.html

desertfox

 

[electricpete]

I believe the correct definition of dynamic balancing is as everyone assumes above - simply that the rotor spins during balancing.

There is however some quirky terminology of "static unbalance", "couple unbalance", and "dynamic unbalance" with distinctly different meanings that may lead some people to use the term "static balancing" to indicate single-plane balancing and "dynamic balancing" to indicate 2-plane balancing.

See here:

http://www.bksv.com/doc/bo0276.pdf

Static Balancing involves resolving primary forces into one plane and adding a mass in that plane only.
[implies one-plane balancing = static balancing for this author]

Example Two:
Performing two-plane (dynamic) balancing on a machine that has a rigid rotor supported in two bearings.
[implies two-plane balancing = dynamic balancing for this author]

[/quote]

Note that figures 1, 2, 3, 4 do correctly convey the concepts of "static unbalance", "couple unbalance", "dynamic unbalance". But these "unbalance" terms should not imo be mixed up with "balancing" in the way the author did above.

Nevertheless, some people interpet the terminology the same way as used in the paper. In which case the guys in your office would be saying that you can't/shouldn't 2-plane balance the fan, which is probably correct conclusion (not terminology) since it is undoubtedly a small L/D rotor.

I would suggest there is a simple resolution to your question: ask the people who said the fan cannot be dynamically balanced why they think it cannot be dynamically balanced. This may lead to discussion of terminology or completely different reasons....

=====================================
(2B)+(2B)' ?

 

[uhpo]

thanks for all this information specially electricpete, but really what is numbers for saying.. this L/D is to small and we must do just one plane...

 

[electricpete]

If fan Length / Diameter < 1/3, fan can be single-plane balanced (vs 2-plane) per ARI GUIDELINE G-2002, “MECHANICAL BALANCE OF FANS AND BLOWERS”

I have seen numbers from 1/2 to 1/6 in other sources.

=====================================
(2B)+(2B)' ?

 

[electricpete]

The reason is that for small L/D, the rotor basically acts like a disk. There is not likely any couple unbalance present, and there is not much separation between balance planes (relative to diameter) available for couple correction.

=====================================
(2B)+(2B)' ?

 

[rhatcher]

The attached picture may help the explanation. This shows an induction motor rotor with the driven fan attached. The complete rotating assembly is sitting on a dynamic balance machine.

The rotor is two plane balanced. The fan is single plane balanced. Regardless of size, a fan will be always be single plane balanced.

For a fan that is 3 meters in diameter, there are few balance machines that can handle that size. We do have one here that could do it but that is not the best solution for the OP.

In most cases a fan of this size would be dynamically balanced in place. This type of service is commonly offered and relatively inexpensive.

I will finish by saying that many balance problems on large fans are due to dirt or other material building up on the blades. I would recommend cleaning the fan first to see if the vibration goes away before hiring a balance technician.