Motor bed construction 3

[edison123]

I recently saw a motor bed of a 3.3 KV, 2000 HP, 1500 RPM motor made up of 8" x 3" boxed up channels welded intermittently at the 3" sides. (The 8" sides were vertical).

What struck me was that the motor was sitting on the welded edges of the channels (3" sides). (There were no welds where the motor was seating.)

The bed was vibrating whenever the motor was loaded (it was a rubber mixing mill called banbury with multi-stage gearing). I could feel the vibrations standing on the bed.

Is this type of motor beds with boxed up channels good / acceptable ? (I prefer 'I' beams instead of channels)

*Nothing exists except atoms and empty space; everything else is just an opinion*

 

[wrsharper]

On the surface this seems a bad idea but maybe the installer, from past experience, needed the motor to have movement during operation.

 

[edison123]

Thanks wrsharper. The motor is driving a gear train and is rigidly coupled to the pinion gear.

Could you pls clarify your post about the movement of the motor ?

Thanks again.

*Nothing exists except atoms and empty space; everything else is just an opinion*

 

[edison123]

The motor bed is like this []====[] with intermittent welding of the channels at the top and bottom.

*Nothing exists except atoms and empty space; everything else is just an opinion*

 

[wrsharper]

This size of motor is out of my range of experience. The idea seems foolish to me but I thought there must be some justification. If there is a rigid coupling then it does not make any sense to me but someone made the decision for the unorthodox installation and must have had a reason. I am sure someone with more experience will respond to this thread. Regards

 

[electricpete]

Here are some thumbrules often applied for industrial machinery:
1 - should be mounted on cement foundation with mass 5x the mass of the rotating machine
2 - The triangle from the bottom outer corners of the cement to the shaft centerline should be an equilateral triangle or shorter.
3 - foundation should be 6" larger than baseplate for large machines.

The reason for the weight I believe is to minimize vibration of the rotating equipment.

The reason for a stiff base I believe is to prevent distortion under the various loads include weight, torque loads from motor, in your case radial loads from the gears. There are devices such as permalign which can measure actual movement from off-line to running which presumably would detect movement associated with base flexing.

I don't have any standards or references handy. I know API has some standards which are very specific on base construction


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[edison123]

Thx pete. That was new information especially the equilateral triangle seems to make in terms of stability.

(T tried to give a LPS for some reason I am not able to. Must be due my accessing the net throught my mobile.)



*Nothing exists except atoms and empty space; everything else is just an opinion*

 

[waross]

Thanks for the information electricpete. Another lps.
edison123; I would be looking into the possibility of filling the boxes with grout or concrete. With a Hi-Early (28 Hours to cure) strength cement you may possibly complete the work during a weekend shutdown.
respectfully

 

[wrsharper]

The motor should sit on a concrete pad. It should be prevented from any movement and provided a stable base for the machine, in most applications. If this is infesable then a steel frame of one inch steel that is solidly mounted to the floor. From the original description I thought that maybe the motor had to twist a little bit so it did not hurt the drive train. IMHO, Grout?

 

[macmil]

Is the steel base frame solidly anchored to the foundation ? Is the foundation sufficiently massive ? If not, and the foundation is moving, nothing you do with the steel frame will help. Is the base frame distorting ? Would more weld where the channels butt help ? Concrete or grout may help by altering the mass of the frame if there's a rogue harmonic in the set up.