Good morning,

I've just returned from taking a set of phase readings on a Hoffman 6-stage blower. The 350 hp motor was just overhauled & re-installed.

Did a laser alignment and put everything within .002-3, did the hot alignment using the "temp differential X CL distance from shaft to feet X .000006" which equals the shim value to add to the feet...This formula was given to me from the Hoffman Rep.

On my first set of readings I noticed both motor bearings with an elevated HVEL value of .27 ips to .32 ips. Not very good. HACC are running a bit high to but not in alarm.

My phase readings were solid across the coupling at the radial positions, but axially they all are erratic. All are reading from 65 degrees to over 300 degrees, and jumping around. Did not have this problem radially.

Amplitude on the blower side is very good, but the motor is running .8 to 1.1 ips in the axial positions, not good on the motor side. We have Thomas couplings with shim packs on all our blowers. I didn't change it out because it still looked good, no bad or damaged shims in that, as far as being cracked or separated so I reused it. Nice flat and even not wavy...

I use a Monarch vibration strobe for these readings along with my SKF Microlog CMVA 65...I don't know alot about motors but I noticed a steady humming, up and down in intensity, at the same time the shaft was moving around back and forth with the strobe on it, and locked on for the readings. The axial position is when the shaft moved. It did not do this in the radial position. Is that a signal?

I've considered the possibility of misalignment or a coupling problem but am not sure. I have to trust my laser alignment, because thats all I have. This machine has always been in the green before the motor bearing starting to crash, now the #2 bearing is in yellow alarm on the HVEL point.It's aggravating to do all this work and come back up with this problem.

Any suggestions would be appreciated...

Thanks Guys!

Geaux LSU

Fourthings to consider:
One, instead of calculating center height x temp. rise, average the temp. rise across every couple of inches of the machine. It may run 100 degrees hotter, but not all the way down to the feet. Measure the temperature of the things that can grow.

Second, did you loosen the shim pack coupling while making the moves? Or, did you loosen it after the moves, to reduce stresses you might put in the shim pack during moving?

Third, is this a sleeve bearing motor? If so, did you scribe to find the magnetic center? Sometimes the shafts can move back and forth axially.

Fourth, have you checked the motor uncoupled? Does it have problems when it's not conneceted?

quote:

at the same time the shaft was moving around back and forth with the strobe on it, and locked on for the readings. The axial position is when the shaft moved.

Was this movement extremely slow or in tune with the "steady humming, up and down in intensity" you hear or about what frequency is it moving?

Hello Stan,

Well I can answer some of those. The bearings are ball, NTN 6219 so magnetic center is not a factor.

I did measure the distance between the hubs before removing the motor. Most always they are excactly 7". Put it back the same way. 7-inches

It has always been standard procedure here to install the couplng before the alignment, Shim packs are already mounted and torqued to the coupling when we put all that back in.

As far as taking the temp measurements. I've always done this directly on the outlets of the blower. Never tried using measurements at the feet or anywhere else.

Here are the numbers I used on the shim calculations:

Temp Differential = 120 degrees X
CL Distance = 22.50 in X
Constant Value =.000006....= .016
______________________________

Shims = .016 Added to all 4 motor feet and blower inlet.

We normally do not check the motor uncoupled. We assume a new motor would be okay.

Hello Ralph,

The shaft movement was in tune with the humming. Back and forth as it cycled. Sometimes the shaft would even turn a complete revolution. I've been told rotor bars would cause this noise, but in this case you wouldn't think so.

quote:

Originally posted by Ralph Stewart:

quote:

at the same time the shaft was moving around back and forth with the strobe on it, and locked on for the readings. The axial position is when the shaft moved.

Was this movement extremely slow or in tune with the "steady humming, up and down in intensity" you hear or about what frequency is it moving?

If you want to check the alignment, do a real hot alignment. Shut the machine off, LOTO, then jump on it as quick as you can and take 1 reading. Look at the vertical corrections. If they are very far off, make that correction. Move it horizontally to bring it in, and then bolt it back down.

Dtan has some good suggestions. If that is a Thomas coupling, you definately need to loosen it up to relieve the stress in it. If you put any waves in it when you moved the motor, then they are still there, and will cause high axial.

The mag center on the motor is another good one, if it is sleeve bearing.

Dave

Dave,

That is something that does make sense. Loosening the coupling from the hubs a bit I mean. We've never tried that...I do know that over the years when taking these couplings loose, sometimes it jumps a bit when it comes off the hub. That tells me there is a misalignment. This is when it's still hot. But you would think the shim pack would forgive that tiny bit...

That is one thing I do, and that is hurry up after a shut-down for hot-alignment. Judging from what I've heard you don't have much time to get that one reading, and one reading is all there is time for. After 15 minutes or so, I would think it's too late to be accurate.

Is that a fair statement? There are many things to consider, which I don't think we have done here at this plant yet, and I still have a lot to learn being only a level 1 analyst.

Thanks,

Generally the Hoffman blowers have the thermals marked on the I/B feet and I think they have an unequal growth from end to end.

A Hot check would be nice with Acculign if possible. This will enable you to monitor it while running.

For the City of Atlanta I changed to gear type coupling and problems (several) went away (1000 HP). They were going through too many starts and stops with the Thomas coupling outside the tolerance box (0.003" & 45 seconds). They were experiencing coupling failure with disc flying apart and high vibrations.

The "hot" alignment is a "have to" situation.

Here is something else I noticed when I started doing alignments. Some techs attach the laser alignment heads on the hubs, instead of on the machine shafts themselves. Sometimes there is not enough shaft to attach them to.

I would assume the shaft is correct, since we are doing shaft alignments.

Thats what I need Sam, a way to do alignments while the maching is running. Will Acculign allow this?

I suggested the gear and grease couplings but they don't want to have to keep shutting blowers down for lubrication.

quote:

Originally posted by Sam Pickens:
Generally the Hoffman blowers have the thermals marked on the I/B feet and I think they have an unequal growth from end to end.

A Hot check would be nice with Acculign if possible. This will enable you to monitor it while running.

For the City of Atlanta I changed to gear type coupling and problems (several) went away (1000 HP). They were going through too many starts and stops with the Thomas coupling outside the tolerance box (0.003" & 45 seconds). They were experiencing coupling failure with disc flying apart and high vibrations.

The "hot" alignment is a "have to" situation.

1st member = shaft
2nd member = hub (solid fit)
3rd member = discs (flexible)

You may use the hub if solid. Never the third member. And this rule applies to dynamic rotation - where both shafts are rotated together.

quote:

The shaft movement was in tune with the humming. Back and forth as it cycled. Sometimes the shaft would even turn a complete revolution. I've been told rotor bars would cause this noise, but in this case you wouldn't think so.

SOrt of sounds like, from the description, that the load is changing, causing the motor to increase and decrease in speed slightly, for the shaft to make a complete revolution from the "frozen" strobe position. You are correct, rotor bars do give this type scenario. But like you said, why a rebuilt motor having rotor bar troubles?

But why does a 6219 bearing have so much axial movement. "SO MUCH", is an unknown number. How much does the shaft move axially? Is it moving as much as 4 mils (.8 in/sec at 3600 rpm)?

Guess this is a 3600 rpm motor huh?

I would look at the coupling first, like the other guys said, the coupling may be in a bind after moving the motor during alignment.

Yes, we have done both here, but never the 3rd member, a no-no

quote:

Originally posted by Sam Pickens:
1st member = shaft
2nd member = hub (solid fit)
3rd member = discs (flexible)

You may use the hub if solid. Never the third member. And this rule applies to dynamic rotation - where both shafts are rotated together.

Here's whats bugging me Ralph. The amplitude axially on the motor is .9 to 1.1 ips, but the blower itself is only .09 to .11. The movement is not transferring across the coupling. Duhh. The phase angles however are all very erratic anywhere from 55 to 310 degrees.

Yes this blower is running at 3570 rpm

I would say in a 5 year period I have aligned a total of 8 blowers. I've never seen one with these reading yet, and in alarm mode.

quote:

Originally posted by Ralph Stewart:

quote:

The shaft movement was in tune with the humming. Back and forth as it cycled. Sometimes the shaft would even turn a complete revolution. I've been told rotor bars would cause this noise, but in this case you wouldn't think so.

SOrt of sounds like, from the description, that the load is changing, causing the motor to increase and decrease in speed slightly, for the shaft to make a complete revolution from the "frozen" strobe position. You are correct, rotor bars do give this type scenario. But like you said, why a rebuilt motor having rotor bar troubles?

But why does a 6219 bearing have so much axial movement. "SO MUCH", is an unknown number. How much does the shaft move axially? Is it moving as much as 4 mils (.8 in/sec at 3600 rpm)?

Guess this is a 3600 rpm motor huh?

I would look at the coupling first, like the other guys said, the coupling may be in a bind after moving the motor during alignment.

One thing I did want to mention is that I cannot loosen this coupling too much during the alignment or I may lose my signal to the laser head. We use the Vibralign V180 System dual lasers...

quote:

Originally posted by RRS_Dave:
If you want to check the alignment, do a real hot alignment. Shut the machine off, LOTO, then jump on it as quick as you can and take 1 reading. Look at the vertical corrections. If they are very far off, make that correction. Move it horizontally to bring it in, and then bolt it back down.

Dtan has some good suggestions. If that is a Thomas coupling, you definately need to loosen it up to relieve the stress in it. If you put any waves in it when you moved the motor, then they are still there, and will cause high axial.

The mag center on the motor is another good one, if it is sleeve bearing.

Dave

When you say loosen, do you mean loosen one side of it. There are 6 bolts holding each side to the hub. Loosen just enough to put a tiny space between the bolt head and the hub?

RRod,

Yes, 1 reading within 10 to 15 minutes is the best you hope for. I have watched machines cool down (heat up in the case of refrig compressors) with the laser attached (Rotolign).
Once you get one reading, just make that correction and call it good.

As far as loosening up the coupling, Loosen the bolts that connect the discs to the solid hub. Loosen them all, wiggle it a bit, and then retighten them. If they are in much of a bind, you'll see them move (as you said).

Good luck, those Thomas couplings won't take a lot of axial movement before they start cracking. However, I have found they do act as a good absorber or dampner of that movement. It doesn't seem to transfer across very readily.

Dave

The Acculign system is great and very affordable. Do a search: Jack Essinger is now deceased but his son carries on the business. Jack was one of the best in the industry and developed a super good system.

I did a 700 HP ID fan and greased w/EP 1 - eight years later it was 'as new' condition. Typically did annual greasing. A good structural grease is needed on gear couplings especially with great alignment. They are not bearings.

Your referring to the ones I marked in the attached photo right Dave? Or the shim pack itself? It would be tough to get to those.

quote:

The amplitude axially on the motor is .9 to 1.1 ips, but the blower itself is only .09 to .11. The movement is not transferring across the coupling. Duhh. The phase angles however are all very erratic anywhere from 55 to 310 degrees.

Vibration movement travels the path of least resistance, just like electricity.

Something must be wrong in the motor if the alignment or coupling is not causing the problem amplitude. Where are you taking the axial reading at? 1 in/sec is too high regardless of where the reading is, but is this reading at the top of the motor over the center of the coupling or on the side or close to the shaft?