Motor fan change material from plastic to stainless steel

[jonos]

Dear everybody,

My motor get a problem. Motor fan's was broken, original material from plastic, then I change material to stainless steel. Data of motor are rated output 75 kW, rated voltage 380 volt, No. of poles 2, IP 55, manufacture ABB Finlandia, effisiency 100%load is 94.9%
75%load is 94.9%
50%load is 93.9%
Current 100%load is 0.89%
75%load is 0.87%
50%load is 0.81%
Motor torque rated ~25 kgf-m
motor torque starting 230%
motor torque breakdown 330%
Starting current 750%

My questions are:
1. Is there any effect if I change material of fan?(weight new fan is 2.2kg, the old fan less than 0.3kg)
2. Is there dynamic balancing for rotor?
Thank you for your attention and cooperation.
Rgs,
Jonos

 

[jOmega]

The important consideration is that the new fan (SS) moves the same volume of air per unit rpm. This is to ensure that the designed cooling of the motor is attained.

Rotors are balanced before being installed in the motor housing. The fan is usually attached after the end bells are installed and before the fan-cover (guard) is installed. I don't know of any balancing that occurs AFTER the rotor is installed in the housing.

The weight of the new fan being much higher will have an inertial effect on acceleration of the motor... it adds to the inertia of the motor... so that the motor might take a bit more time to accelerate to full speed. However, compared to the inertia of the rotor, the inertia of the fan is a fraction and will have very little noticible impact, if any.

The original fan was most likely made of Polyproplyne because it is much less costly than S.S. fan and there is a slight efficiency benefit over the S.S. fan.

 

[jonos]

jOmega,

Thank you for your explanation, how about the ball bearings (6316C4)? Is there any effect like lifetime, work function and so on?

Thank you,
Rgs,
jonos

 

[jbartos]

Suggestion: Chances are that the SS fan will have bigger vibrations since it is heavier with the stronger impact of its imperfections on the bearings. It may be prudent to contact the motor manufacturer tech support for all options left to this motor fan. Also, if the cooling of the motor is not designed bidirectional, the fan propeller must produce the air flow in the same direction as the old one.

 

[edison123]

jonos,

did you see any big increase in motor vibration after the fan change ? if you did, then balance the rotor with the new fan ?

as regards the bearing load, the fan effect on the bearings will be not so significant as compared to the rotor .

 

[jonos]

Dear edison123,

Vibration not so higher than original fan, so if vibration more higher than normally, should I balancing the rotor?
just inform you the DE and NDE bearings are 6316 C4

Rgs,
jonos

 

[edison123]

jonos,

Did you take motor vibration readings before and after the change of fan and is so, could you post them here ?

If you took the vibration readings only after the change of fan, you could post them also so that we can decide whether your motor needs balancing.

 

[jbartos]

Suggestion: Fine-tuned SS fan propeller will probably be more expensive.

 

[jOmega]

Hello Jonos

I wanted to be sure that the advice I give you is correct, and so, on your behalf, I contacted an associate at Leeson Electric Motors.... who in-turn, passed the questions on to their engineering department.

Here are the answers and comments:


"The motor rotor-shaft is balanced without a fan. It will not be affected by the change to a stainless fan.

The fan should be balanced before using it. If it is balanced, the assembly will be balanced.

Bearing life should not be affected by the fan unless it is very heavy. If we are talking a cooling fan that weighs a few pounds, we are fine. ...If we are talking a fan that weighs 100 lbs we should look at the bearing life.

It is implied that the motor cooling fan (which is Polyproplyne) is being replaced. If this is true then motor cooling is a concern.

The new fan must have the same cfm or more of air over the motor as the old one. If not there may be problems with bearing life and motor life because of heat.

The customer can probably do this by feel. If the new fan pushes more air than the old one "by feel" it is probably OK, (checked close to the motor housing not far away). Also could compare surface temperature on the application as a check also.

Jonos, I hope this puts your mind at ease.... you may want to pull the S.S. fan and have its balance checked before putting it back in service.

Kind regards,
jOmega

 

[pennpoint]

jOmega (Electrical)
WoW! that was really good!
Where did you get that info? in red even.

 

[jonos]

Dear jOmega,

Thank you very much for your attention. It is important for me.


Best regards,
jonos

 

[jOmega]

Pennpoint

The information came from the engineering department of Leeson Electric Motors Co.; a Division of Regal-Beloit Corp.

 

[jbartos]

Suggestion: More fan cfm will consume "would be motor shaft output power" that would then have to be somewhat reduced. However, the fan power consumption is relatively small with respect to the motor shaft output HP power.

 

[jOmega]

JB:

It's a 75 kW motor...

Just what percentage of that 75 kW do you think the Stainless Steel shaft fan will suck-up as compared to the original Polypropylene fan ??????

Care to offer a number ?

 

[RAMConsult]

Gentlemen, All other things being equal the design of the fan, not its material, determines how much shaft power it will take to move a given CFM at rated speed. The mass of the fan is less important than its placement, it is the polar moment of inertia that will affect the torque required to accelerate the shaft. It is even possible to design a lighter fan that takes longer to accelerate than a heavier one by placing more of the material at the outer tip of the blade, as in using a fan ring. None of this will affect its steady-state operation if it is properly balanced.

 

[jbartos]

Eng-tip to jOmega (Electrical) Aug 29, 2003 marked ///\\JB:
It's a 75 kW motor...
Just what percentage of that 75 kW do you think the Stainless Steel shaft fan will suck-up as compared to the original Polypropylene fan ??????
Care to offer a number ?
///Probably less than 2kW. However, I mentioned in my posting that it would be relatively small power consumption. However, I have worked on fans for tunnels rated 350HP, each.\\

 

[jOmega]

JB... You do understand that this is a shaft fan on the back end of the motor, used for cooling the motor....

Now let's look at that 2 kW number you guessed.... that's about 2-2/3% ... which seems a tad high... (yes, you offered that number as a MAX..)

Please do consider that if the new S.S. fan moves the same volume of air as the original Polyproplyne fan.... then the motor sees no real or noticable decrease in efficiency. Ergo, consideration is of no real consequence to JONOS ... or anyone else who would make such a replacement. You would agree ? ? ?


JB, you also said : "However, I have worked on fans for tunnels rated 350HP, each"

How does this statement relate to the foregoing discussion ? ?
You lost me on this one ..

 

[jbartos]

Suggestion to the previous posting jOmega (Electrical) Aug 31, 2003 marked ///\\JB... You do understand that this is a shaft fan on the back end of the motor, used for cooling the motor....
///If I did not understand this primitive motor fact, I would not be here. Do you use your common sense in your posting?\\Now let's look at that 2 kW number you guessed.... that's about 2-2/3% ... which seems a tad high... (yes, you offered that number as a MAX..)
///The high efficiency motors are reaching about 95% efficiency. The 5% losses are substantially shared by the motor cooling.\\Please do consider that if the new S.S. fan moves the same volume of air
///It may or may not. The CFM of the fan is a variable when it comes to fan propeller replacement.\\ as the original Polyproplyne fan.... then the motor sees no real or noticable decrease in efficiency. Ergo, consideration is of no real consequence to JONOS ... or anyone else who would make such a replacement. You would agree ? ? ?
///I see just your noticeable rhetorics in this paragraph.\
JB, you also said : "However, I have worked on fans for tunnels rated 350HP, each"

How does this statement relate to the foregoing discussion ? ?
You lost me on this one ..
///This is meant to avoid ridiculing such as your statement "JB... You do understand that this is a shaft fan on the back end of the motor, used for cooling the motor...."\\\

 

[jOmega]

JB:

You said:
"///If I did not understand this primitive motor fact, I would not be here. Do you use your common sense in your posting?\\\"

Reply:
JB: for the sake of clarity when responding to your comments, I find it necessary to "state the obvious", just to be sure that you understand what is being said, and why. As an example, in this thread, the subject is the replacement of a shaft fan on a 75 kW motor. But in a previous post, you said "However, I have worked on fans for tunnels rated 350HP, each" which has absolutely no relevance to the topic of this thread!, ergo, I restated the obvious, that the discussion is about a shaft fan.

Relevance, JB, relevance.

You said:

///It may or may not. The CFM of the fan is a variable when it comes to fan propeller replacement.\\


Reply:


JB, read my statement again.
It is predicated upon the new SS fan moving the same volume of air as the original fan, and consequent thereto, no loss of efficiency would occur.

To which you replied.... ..."it may or may not.The CFM of the fan is a variable when it comes to fan propeller replacement."

From your reply, JB, it would appear you either:
a) didn't read my statement, or
b) didn't understand my statement.


JB, as an intelligent individual, is it not reasonable to expect that if YOU were the one replacing the shaft fan on a motor with something other than the OEM part, that you'd contact the motor manufacturer and inquire:
- How many CFM (CMM) are required for design cooling ?
- Do you have a Stainless Steel replacement available for my motor ?

And as an intelligent individual, if the mfgr. doesn't have an S.S. replacement fan, is it not reasonable to expect that you would select one from a third party supplier that meets or exceeds the design air flow spec as told to you by the motor manufacturer ?

I certainly have no problem crediting jonos[/] with such intelligence; do you ?


You said:
"///I see just your noticeable rhetorics in this paragraph.\\\"

Reply:
.....I'm sorry you didn't understand it. Perhaps reading it again will bring clarity and meaning to the words and thoughts offered therin.