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Thread: York Ram motor
03-03-2012, 10:19 PM #1
York Ram motor
Back again still sulking over a Ram motor gone bad during my watch. Long story short ended up with a brand new Ram motor from Johnson/York baltimore parts. 800 Hp on a york YK with a VFD. Old motor had a history of vibration coming from the ODE of the motor and after a recent bearing change from yours truely a grease fire erupted, a catristraufic rear bearing failure occured and the motor was sent out for extensive repair. In the interem the new motor was set and started uncoupled. A noticable vibration was coming from the ODE of the motor. I could not F+++++ beleive it. Vibration anaylsis showed 4 times the the Horizontal magnitude from the ODE bearing of that from the test certificate from Ram. Brought local Johnson in to test with there equipment, same thing, readings unaceptable. 11 to 12 tests later, coupling on, coupling off, 30 HZ, 60HZ, ect,we found that when the rear bolts were loose the vibration plumited. The motor was set on the original shim stacks and no noticable soft foot was suspected but I was obviously wrong on that. Ended up lifting the motor over 1.20 thousands at the left foot and 70 thousands on the right foot until the vibration was acceptable when the bolts were tightened.The motor had been in a serious bind causing the problem. Now I worked for york a lot of years and must of had my head in the sand on this one. How on earth are you to tell if the motor is in a binde or not. The coupling total indicator readings only changed .001 from the original setting to that of when the motor was lifted darn near 1/8 of an inch in the rear. I asked a couple of old York guys I still know and no real insight was gained. I would love some input on this, if any one has had a simular situation. Thanks
03-04-2012, 12:01 AM #2Professional Member*
- Join Date
- Dec 2008
- Dixiana, AL
.120" is almost 1/8th of an inch. With the bolts loose or out of the feet, you should have been able to slide the loose shims around by hand. Same with the other foot if it took .070" (1/16th" +) to bring it to a no strain position. The foot may have been touching the shims, but the shims would have been loose at best. We won't discuss the intricacies of setting a motor on an open forum. Was this chiller shipped broken down to be field assembled or as a package?
03-04-2012, 12:02 AM #3
do you have a copy of the report? it sounds more like 'eccentricity' problems rather than misalignment problems (but you could have had misalignment as well). misalignment usually causes 1x and 2x vibration signatures. looseness causes lots of harmonics. eccentricity of the frame can ruin bearings as well as cause what looks like a 2x spike but it is really 2x the electrical frequency. you need to have high resolution to tell the difference.
vibration analysis is a wonderful tool. it proves what is what.
also keep in mind your power. a 1 mil of vibration on a 1 HP motor has a lot less power (and damage) than a 1 mil vibration on an 800 HP motor.
todays motors have a lot less iron in them. that allows them to flex much more easily. this can really mess with detecting soft foot conditions.Time to get my nerd on!
03-04-2012, 04:34 AM #4
I think you are correct on the motor flexing due to less iron as the shims were not loose at all, I watched the motor as it set down on them and they were tight. My misalinement was .008 high and .006 to the right befour the motor was lifted and .007 high and .006 right after it was shimed up. Good point about the possible break down when installed, I will check into that. the base is either not level or the motor is twisted at the D flange, my guess is the base is not flat. Every York I see seems to have the same shim stack, it is like they just go by a math calculation or something. The repaired motor coming back is going on the next chiller over and i am going to be more methodical on the approach of removal and install, I would like to get to the root of this. It is just really hard to measure as there is no good referance points and the motor is so heavy it bends the whole damm machine.I am curious if some of the cronic bearing problems on York machines could be caused by bent motors. A side note is the that the shaft dynamic variable off set or axial mis alignment of the rotor to the stator is measured in minutes of arch, and if you do the math for a 48 inch circle at the tolerance of 2 minutes of arch it is .003 thousands of shaft mis alinement from the drive end bearing to the oppicit end bearing. Trippy uhh.
03-04-2012, 10:38 AM #5
Sounds like possible angular soft foot, once you torque the motor feet it shows it's ugly self. Binding your rotor like a bent shaft, and or causing a unequal air gap between the stator and rotor in which will also induce a vibration.
03-04-2012, 11:02 AM #6
A little hard to see and explain, but motor mounts may not be square( spool piece to rear motor mount) not on a 90 degree plain. Causing your distorted frame when bolts get torqued.
03-04-2012, 02:31 PM #7
this is a great reason to stick with the job even though it looks (at first) like it was your fault (which the last set of bearings could have been), however, the continued issues show that it may have been related to manufacturing (or installation...check that pad for level!).
sometimes you have to wait a while to get justification.Time to get my nerd on!
03-04-2012, 06:40 PM #8
Same thing only different !
I had a similar problem in downtown Houston. YK's that were eating seals at the rate of one per year. When I checked alignment it was way out, pulling up .060" and left .095" facing the compressor input shaft. Found out from the customer that these chillers had to be knocked down completely when they were installed. The D-ring was the problem as it was never doweled or match marked prior to teardown and the mismatched paint lines were quite obvious. So I got everything loose and broke out the hydraulics. As far as I know this customer hasn't had to replace a seal on either unit since. -GEOOf all the things I have lost in my life, I miss my mind the most-GEO
03-04-2012, 10:01 PM #9
Great comments and I do appreaciate the experiances of simular circumstances. Geo it is remakable as I was wondering if there was enough play in the D flage bolt pattern to allow for the motor to twist. If I may I have a final question befour I can possibly repay in kind with some insight gained after installing this next motor. The motor base plane compared to the D flange bolt pattern seems to be very hard to measure as there is no real flat referance point. The 18 inch span of the D flange lip of the motor as it goes into the D flange housing also seems very hard to measure. As well once it is snugged up into the housing I would think it would be very hard to test if it will twist in the slop of the bolt patter and really not knowing if the base is truely flat what does it matter. There is time in this job and I will check everything possible going in and going out and I am sure I am over thinking this thing but any creative ideas you would like tested to prove the motor is flat and level with out being in a binde, I will do it. Two things are hanging me up, 1. The alignment changed basicly nothing when satisfying the vibration by lifting the motor almost an 1/8 of an inch in the rear. 2. The ability of a 2 ton mass to droop an 1/8 of an inch and not show a gap discrepancy while snugging up the bolts is hard to fathom. Which I forgot to mention I tested with fealer gauges at the top and bottom while loosing the bolts oppicite of each other with the weight off. Any way too long winded the job is scheduled for 3/12 perhaps an appifany will strike in the mean time. Thanks again.
03-05-2012, 01:19 AM #10
the gaps and tolerances are small and the HP is big. not enough iron in the motors anymore to make it 'bullet-proof'. i don't know if you could measure it accurately enough. even if you could, sag in the motor (due to weight) could be causing the issue, not 'true-ness'.
my US Motors catalog shows a 1 hp, 1800 rpm motor weighing in at 27 lbs...27 lbs/hp. a 50 hp motor is weighing in at 415 lbs...8.3 lbs/hp. a 100 hp is coming in at 750 hp...7.5 lbs/hp
a York DJ motor (2000 hp) weighs 9500 lbs...that is 4.75 lbs per hp....where's the iron? it is the iron that helps to keep the motors shape especially under extreme stress. the bearings take a lot of stress...that stress is transfered to the casing. if the casing can not handle it, then the bearing housings can deform. instead of iron, we get aluminum or other 'alloys'. sure, there are some weight savings due to energy efficient designs and such but there isn't any substitute for iron and steel.
as an industry, we asked for cheaper motors....and we got 'em.Time to get my nerd on!
03-05-2012, 07:11 PM #11Professional Member
- Join Date
- Aug 2000
- Austell, Ga.
There are two OM's with 2000hp motors at a paper mill in So. Jawja that are 35 years old that have both been refurbished with extra motor winding sensors and have been upgraded to the absolute top end of thier service factor to get the extra tonnage. Each motor wieghs in at 12,000# and have had thier bearings replaced only during during the refurbishing.
Thier are 3 Big YK's (2250hp each)at the airport that have gone thru 7 or 8 motor changeouts and these behemoths wiegh in at a paltry 8800#. Severe vibration, bearing failure etc.
With a motor cost of around $120k each, you can see what kind of warranty money we are speaking of.
Whilst the amount of iron in the stator & rotor is pretty well fixed at so many cubic-inches per kw input the wieght reduction in the frame is a lose-lose situation and made worse even with anything but a very....VERY secure mounting platform. Methinks that the vessel mounted lil' feet on the YK's are anything but secure on a motor of this size..
But hey thats JMHO.....Ain't "None" of us as smart as "All" of us..
03-05-2012, 07:40 PM #12
Excellent analogy man I love math reasoning. I am beginning to see the writing on the wall. Perhaps finding precision measurements may be a futile endeavor when dealing with parts that bend. I recall a vibration guy mentioning in the past that Ram motors just did not have enough iron. Never experiencing an issue first hand it did not completely register, but when you put math to the problem it becomes real and understandable. So from here on the procedure will be, get it as close as possible, and then do a vibration analysis as a matter course. One final note though: after doing some digging I found that this machine was indeed disassembled and reassembled for installation by York in 2001. That was a mere 4 sets of bearings, two shaft seals, four condenser tube leaks and the system flat several times due to cracked fittings ago. Had I know all that, perhaps my approach would have been different. Who knows but it could very well be that doing my detective work, be four I caught the motor on fire, would have been a little better order of events. I can however tell you for certain,from first hand experience, that a man comes to terms very slowly when you fill the Hospital full of smoke from a raging grease fire. Three fire squads, a partial evacuation and every building engineer for two city blocks showing up on your behalf, makes for one lousy day. One final request, I still would love to get the Mighty Dave Sailors opinion at York engineering on the factory proceedure for squaring up a motor. I am no longer in the click but maybe some one out there is and could ask the wise master, the secret could then be revealed for all to see.
11-27-2012, 11:31 AM #13Professional Member
- Join Date
- Apr 2011
This has been a very interesting thread. I am experiencing problems with a 440 tons YK motor. The bearings are loosing the grease trough the shaft when the motor is turned on. I want to replace the bearings but the local York guy told me that they usually takes out the motor and send it to a local shop for them to replace bearings and make necessary corrections. I will be un Houston next month taking the overhoul course but I would like to know if this bearing replacement could be done on field or if in fact they are alway sent to a shop. Also does any one have a guess of how much could e charged for a job like that??