PUMP MOTOR 9

[macfa1]

Hello,

this question is in relation to grinding material from the feet of a Thyseen Type 6X13SVC-L Pump.

We recently ground 6mm from the 50mm thick feet of the motor for our pump.However, we wer later told that this would make the motor unstable etc and this was not good practice. Can anyone give me any insight into why this might be the case?

Thanks in advance,

Alan

 

[DougMSOE]

macfa1,
If I understand your question correctly...
You ground 6mm from the feet of a motor, then someone said that this would make the motor unsuitable for the intended use.
The only reasons that I can think of is that there might be a problem with the strength of the mounting foot.
OR
The possibility of creating a "soft foot" on the motor. The "soft foot" is the case of the old milk stool with 3 legs is always stable but add a 4th and the stool will rock.
Hope this helps.

 

[TomG33]

The only thing that I can Think of that could be a problem is that the original footings of the machine would have been Machined to be flat.

Your use of the word "Grind" tends to suggest a less then perfect machineing process was used. This may or may not be the case.

however a very flat surface shold be used for the mounting, so the the forces are spread out evenly over the surface of the footing.

During your normal motor allignment process It should be standard practice to use Shim Material that at least equals the area of the foot pad.

If a High Spot is created by the Grinding process then the forces of the motor torque, (or even just the weight of the motor,) could cause this high spot to be flattened over time, resulting the footing becoming loose.

Perhaps this is the instability they refer to.

Good Luck
Tom

 

[electricpete]

I agree with Doug on the subject of soft foot. If it is a 2-pole motor (~3600rpm in US or ~3000rpm overseas), then the foot and base flatness and planarity need to be absolutely pristine or you will get twice line frequency vibration.

Why was 6mm ground off?

I don't recognize the machine description. Is it horizontal or vertical? Flange or face mounted? Pump mounted separate from motor? If so was alignment adjusted after shimming feet?

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[pennpoint]

Define your use of the term "grind"
Regards
pennpoint

 

[pablo02]

I think Doug and TomG -- the motor's feet are either "ground" or machined to form a flat plane -- if you hand grind one foot, you can not maintain that same plane and shimming will not provide an even distribution on the foot and alignment will not be consistant...

("grinding" covers a number of areas -- most of you are probably thinking of a hand grinder which is far from precise -- however, there is also machine grinding which can produce a very fine surface and is used in place of what we usually refer to as machining in certain applications) i.e. it is preferable to "stone" (or grind) a commutator... many motor commutators are machined, but generator excitors are usually "stoned"...

 

[enginesrus]

If I understand correctly. The "feet" ie mounting points.
Are approx 2.0 inches thick, and you removed approx 1/4 inch off them. I would have instead, removed material from what ever the motor is intended to be mounted on. Or shimmed up what ever the motor was to be connected to, if that was done for an alinement issue. If they "were" approx 2 inches thick. That is a pretty good size motor. And if the manufacture made them like that, then they did it for a good reason. What kind of material is it? If it is something other than steel, you may have weakened them.

 

[macfa1]

Hi all,

thanks for the replies.
Just to make it clearer: The feet are made of Cast Iron, and we are worried that the structural integrity of the motor might be damaged du to the grinding. When I say grinding I mean that material was machined fromthe feet, exactly like "Pablo02" said. I don´t, however, understand how the internal structure of the motor could be damaged. One of the guys here says that due to vibrations there could be some damage done, but can´t explain what type of damaged - any of you ever heardof anything like this?

The reason we didn´t shorten the foundations on which the motor stands, is beacuse it would take too long and we need the pump to be operational as soon as possible.

We would have put some shims under the pump, but if we did that then we would have to work on both the suction and discharge lines and that would also take an age, which is why we opted for the easy option of machining the feet!

...anyways, 3 hours after I posted this thread the motor bearing failed, wnd we don´t know why! Any ideas? Of course they´re blaming us because we machined the feet, but they can´t prove it!

Hope you guys can give some insight. thanks.

A

 

[jbartos]

Question: Has the motor-pump set come on a skid or have you been integrating motor and pump?

 

[jbartos]

Suggestion: The original posting might also be posted in the Mechanical Engineering section of this Forum since it is much tooooo much on the mechanical engineering and design side.

 

[electricpete]

More often than not if a bearing fails shortly after startup it is lub problem.

But there are certainly other possibilities. Did the alignment change?

Regarding your feet as I said if this is a 2-pole motor you had pretty high vibs (did you measure them?). Vibration can certainly damage bearings but usually it doesn't occur that rapidly.

Best way to answer your question is a thorough inspection of the machine and failed bearing.

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[edison123]

Were your motor bearings protected from the flying metal when you ground the feet ? 6 mm from all four feet is lot of very fine material removal by grinding. If the ground cast iron powder entered in to your bearing houses, it could account for your early bearing failure.

I do not think 6 mm removal from a 50 mm base will affect its structural integrity greatly.

 

[enginesrus]

If the mounts weren't machined very close, it could have put a warp in the housing. That would cause the bearings to fail. It could have been a junk motor to begin with too. But now your stuck with it because you altered it. Big no no. See with the down time now, you would been better off doing something else than cut material off the feet. Like I said the manufacture made them that large for a reason. I would NOT have cut off them especially if they where CAST IRON. Cast iron has a low tensil strength compaired to steel. And would easily crack if bolted down unevenly, especially if they where weakened.

 

[jet1749]

Machining of the motor feet if not done in a completely controlled manner will produce the phenomenae of "soft foot" Presumabaly when this was undertaken the motor feet were checked for surface contact area (footprint) across all of the individual feet? Attempting to fit the motor to its bed and carrying out a "soft foot check" with laser alignment equipement is definately required. The usual rule of thumb allowance for error is about 0.002" if you cannot achieve this it is very likely that you have introduced significant stress and loading into the motor structure and a reliability problem would likely occur in the bearings. It is unfortunate that the motor bearings have subsequently failed in short order, but given the mods carried out I personally would be very suspicious of those feet and would certainly want to prove that they were not the cause of failure.

 

[macfa1]

Hi all,

thanks again. Still not confirmed the cause for the bearing failure!

When the motor was put back we used "Optalign"(lasers alignment equipment) to align the couplings, without any difficulties!

I appreciate the point about the tensile strenght of cast iron, but there are no visible cracks, and we´re not in a position to test internal cracks, and I´m not sure if that would affect the bearings anyways?

The Lubrication used was correct, unfortunately, because that would have been an answer to the problem!

We didn´t measure the vibrations, but I like that theory - don´t know if the other engineers will buy it and I don´t know how to prove it? Any ideas?

Cheers,

A

 

[enginesrus]

More than likely it is warpage problem. Like Jet1749 mentioned the flatness of the feet and the mounting point would have to be close to keep out any clamping stresses.
What happened to the original motor that was removed? What failed on it? Is there a chance that an integral pump motor combination is available to do that job? You may have mounting plate, alinement and drive coupling issues. Is the mounting plate thick and strong enough? What kind of coupling is used?