Sign up Calendar Latest Topics Donate
 
 
 


Reply
  Author   Comment   Page 2 of 2      Prev   1   2
ivibr8

Sr. Member
Registered:
Posts: 163
Reply with quote  #16 
EPete

I didn't realize Sof' Shoe product takes a while to get a permanent set. I wonder what that implies with vibration response?

From the website"

 Sof’ Shoe® shims permanently set over a 10 to 14 day period and beca"use of their unique formulation always provide continuous support.
electricpete

Sr. Member
Registered:
Posts: 651
Reply with quote  #17 
Quote:
I didn't realize Sof' Shoe product takes a while to get a permanent set.

Bingo!   That is the key to the quiz.  As Currant previously alluded, it takes up to 14 days for the product to "take a set" (he also gets credit for solving the puzzle... I pm'd him after his post because I wanted to drag out the quiz rather than letting the cat ouf of the bag so easily).

So the plastic shim was a solution to the problem and I just didn't give it enough time.
The answer to original quiz question: what should we do next (after the June 2017 installation/vib readings) was: just to wait a few weeks!
(and that's why I said it was waaay easier than what I thought). 

It's a tricky question for you guys because you probably don't work with soft shims (although I did link to relevant page as a clue).  I actually didn't have any excuse because I knew full well that it takes time for the shims to set.  In my defense,  in the past we had always seen SOME initial reduction in vib, and it reduced further over time. This one didn't fit the previous pattern, we had an immediate increase rather than immediate decrease, so for some reason I jumped right to the conclusion that the plastic shims didn't work (without allowing them any waiting period). I had a story in my mind that the 0.014" gap deviation across the foot was too much  to make up with the plastic shims based on what I read in their literature (each plastic shim has a limit for how much it can accommodate). 

===============================================
 
Putting aside all the drama / mystery that I tried to create with a "quiz", what useful do we learn from all of this:
I guess it's just a case study that soft shims can be used to reduce vibration associated with angle soft foot condition up to 0.014" across the foot. 
Most of the cases we come across are foot-sensitive 2*LF  and are resolved (*) with the plastic shim. 
This particular one was foot-sensitive 1X and was also resolved (*) with the plastic shim. 

* "Resolved" in the sense that it makes the vibration go away and it has no adverse consequences that I know of.  It does require more attention every time you go back to maintain the machine (once you torque those bolts on initial installation of plastic shims,  any activity that involves loosening the bolts will require you to replace the plastic shims).  Other possible solutions would have been step shimming (we never have much luck with that) or attempting to remove the angle  from the motor feet and/or base (that's probably the best permanent solution, but of course requires a bigger initial investment of time/effort)



ivibr8

Sr. Member
Registered:
Posts: 163
Reply with quote  #18 
Pete....a very interesting case history, but I have to admit I'm still somewhat confused.

I would assume that as the sof shim "aged", its stiffness changes (perhaps its damping property as well) and hardens.  Yes?

If that's true, why would I not expect that the vibration would go down if it was replaced with solid shims?  In one of your responses, you stated "No we did not replace soft shims with solid. But if we did that, i am confident vib would remain high when all bolts tightened, similar to the initial reading from 2015."

I occasionally come across angular soft foot issues in the field. I may contact the company to see if I can get a sample and try it out.

Thanks for the lesson
Jim P
electricpete

Sr. Member
Registered:
Posts: 651
Reply with quote  #19 
Here's what the link says
  • Shoe® with its unique properties, cold flows into angular gaps allowing for complete surface contact between a motor’s foot and base. Sof’ Shoe® shims permanently set over a 10 to 14 day period and because of their unique formulation always provide continuous support.


Here's my thoughts. 

The shim does not completely conform to the irregular gap immediately when you torque the bolt initially.  It flows over time to conform to that shape (similar to how a metal might creep over time under load). 

So initially when torqued, the shim more resembles a uniform steel shim and the motor feet/base must flex as the holddown bolt is tightened.

Upon that initial torquing, there is a particular stress  built into the steel parts (motor feet and base) which creates uneven pressure on the plastic shim.... the highest pressure is at the narrowest point of the original gap and the lowest pressure is at the widest point of the original gap. Over time, the shim flows to releive the uneven pressure and accommodate the original gap shape. 
Dan Timberlake

Sr. Member
Registered:
Posts: 116
Reply with quote  #20 
Hi EPete,

I did not look at any newer info since EP's pdf showing a what I judge to be a cruel joke of a pump base plate.  I see the pump manufacturer's name is blacked out.  I'd like to know it, as we have occasion to buy pumps, and if this pump base is typical of their construction I'd want them off our list of approved suppliers. Seriously.
  • Do you have more of these exact pumps, or more pumps from brand X ?  Do they bases of similar design? How do they run?
  • What are the values of the three thicknesses  ( t1, t2, and t3) in the attached image?  Are the pump supports really only as thick as the coupling guard ?
  • Was the motor foot angularity/wedge assessment based on measuring the gap between the burly motor foot and the kitchen table, I mean sheet steel pump base? Or, was the motor removed and and placed on a known flat base or checked with a straight edge? I think the motor foot angularity is in fact motor-base-formed-from-folded-steel-sheet angularity.  (Definitions of "sheet" based on thickness vary.  The dividing line usually ranges between .1875 and .25" . https://www.onlinemetals.com/merchant.cfm?id=839&step=2  "
  • Have you still only run the motor solo ? I would fully expect that those bizarre croquet wickets propping up the pump will single-handedly bring on a rash of new "vibration" issues starting the day the motor and pump are run coupled.
  • Depending on what the OEM has to say, and will do for free, I'd immediately cut out the thin bent shield the motor bolts to and replace it with a properly thick ground flat steel base plate spanning the 100% welded enclosed section of unknown and suspicious by association stoutness.  I'd run that same plate all the way under the pump and replace the sticky wickets with steel blocks as well.  




Attached Images
jpeg non base base.jpg (270.57 KB, 19 views)

RustyCas

Avatar / Picture

Admin
Registered:
Posts: 1,810
Reply with quote  #21 
I've seen a lot worse than that motor base, but it's still crappy.  The only worse pump base was the one I posted that had the pump supported on pieces of all-thread about 18" in the air.  I am constantly amazed at how horrible many (most?) pump/motor bases are.  It's like they have no clue about what makes something stiff.  What is really sad is when they have a thick baseplate that "looks" like it will be plenty stiff enough, but it's spanning 18-24" so it's not really stiff at all.  The only thing that matters is depth (height), and carrying the load to ground as close to the feet as possible.  You could usually build a base 10X stiffer using 1/2 the material they use, if they just had a clue.
__________________
"The trend is your friend"
Curran919

Avatar / Picture

Sr. Member / Supporter
Registered:
Posts: 599
Reply with quote  #22 
Quote:
Originally Posted by Dan Timberlake
I did not look at any newer info since EP's pdf showing a what I judge to be a cruel joke of a pump base plate.  I see the pump manufacturer's name is blacked out.  I'd like to know it, as we have occasion to buy pumps, and if this pump base is typical of their construction I'd want them off our list of approved suppliers. Seriously.


Wow! This is definitely not one of our pumps, but you can't always blame the packager for crap baseplates. We make a lot of crap baseplates. 1/3 of the time, its all our fault, but 2/3  of the time, its because the buyer expects the baseplate to be less than 5% the cost of the pump. That'll get you a bent piece of plate, despite out efforts to persuade otherwise. Of course, a bent piece of plate can perform just fine and this should be a testament to that. E-Pete gave no mention of pump vibes (assumed low) and motor vibes were also low with the correct shimming. Don't fix what ain't broke!

Quote:
As Currant previously alluded, it takes up to 14 days for the product to "take a set"


I'm... surprised to hear that? [cool] I am still not quite sure how they work though. I thought they would be a soft elastomer, but it sounds more like they are a hard plastic that don't initially deform during torque. Does the compression of the sofshoe occur slowly over the first few days of torque and then continue to set over the next few days?
electricpete

Sr. Member
Registered:
Posts: 651
Reply with quote  #23 

I had noticed the flimsy motor base with no support under center from two viewpoints:

  1. It is made as a single piece with a large-radius bend at each corner.  The motor foot sits close to that large radius bend. That bent piece of metal may be the source of the severe angle foot (rather than the motor itself).
  2. It will tend to have a low first natural frequency and of course many higher natural frequencies above the first, so more likely to hit a natural frequency. That’s one of the reasons I was suspected that putting wedges under the center at each end would detune it (but I never got a chance to try).

I honestly didn’t notice the pump base was far flimsier than the motor base, but now that you mention it, wow. The nameplate on the pump is “Garbarino”.  I'm not familiar with all the details of what constraints they were under, so as Currant says it may not be their fault. 

We have three other similar units. This is the only one with elevated motor uncoupled vibration upon installation. None of them has been run coupled (the fluid system associated with the pump is not available).

Quote:
Does the compression of the sofshoe occur slowly over the first few days of torque and then continue to set over the next few days?

I don't know much more than what it says on the website and the fact that we have seen vibration decrease over time after installation on several occasions (usually we see initial decrease followed by further decrease, this one was different with initial increase followed by decrease....I can't quite explain that initial increase other than an unlucky tuning of the resonant base).  I picture the material has both elastic properties (conform immediately upon torquing) and cold-flow properties over time (similar to how some metals creep slowly under stress). 


RustyCas

Avatar / Picture

Admin
Registered:
Posts: 1,810
Reply with quote  #24 
Quote:
you can't always blame the packager for crap baseplates. We make a lot of crap baseplates. 1/3 of the time, its all our fault, but 2/3  of the time, its because the buyer expects the baseplate to be less than 5% the cost of the pump. That'll get you a bent piece of plate


Not buying this argument. Cost is not the problem -- knowledge is the problem. (Not talking about you, Curran)  For example, that motor baseplate looks to be tapped (not seeing any nuts on the bottom side), and the height seems to be arbitrary since the pump sits up so high.  So instead of using a bent plate, why not just a piece of flat stock on either side, running front to back,  1" x 4" would be fine. Would cost the same (or less) and be easier to fabricate (weld), and give the more bolts more purchase in the holes.  As for the pump, even sitting up that high, all they need to do is add a piece of 1/2" x 4" plate to each pedestal (for lack of a better word), standing on edge, flush to one end.  This stiffens the baseplate sufficiently, and stops the lateral motion (rock or sway).

__________________
"The trend is your friend"
Curran919

Avatar / Picture

Sr. Member / Supporter
Registered:
Posts: 599
Reply with quote  #25 
Quote:
Originally Posted by RustyCas


Not buying this argument. Cost is not the problem -- knowledge is the problem. (Not talking about you, Curran)  For example, that motor baseplate looks to be tapped (not seeing any nuts on the bottom side), and the height seems to be arbitrary since the pump sits up so high.  So instead of using a bent plate, why not just a piece of flat stock on either side, running front to back,  1" x 4" would be fine. Would cost the same (or less) and be easier to fabricate (weld), and give the more bolts more purchase in the holes.  As for the pump, even sitting up that high, all they need to do is add a piece of 1/2" x 4" plate to each pedestal (for lack of a better word), standing on edge, flush to one end.  This stiffens the baseplate sufficiently, and stops the lateral motion (rock or sway).


If their goal is to make the stiffest baseplate for as little money as possible, then your solution would probably be an advantage. However, given the size of the pump, I would guess that this is a high-volume, non-engineered pump. The baseplate is not going to need API or whatever standard. Once you get a baseplate that works (and from the sounds of it, it usually 'works'), then you will continue to produce baseplates in that cheap manner, not bothering to change the stiffness and maybe hitting a resonance. It looked like a screw pump. That bugger may be running between the first and second bending mode of that foundation. Like I said, if it works, don't fix it. I would never do this for an engineered pump. I would try to make it as stiff as possible, because you don't know whats gonna happen with those eignedynamics, but once you have a priori knowledge of the eigendynamics, you have no resonance, and your op vibe is low, just keep it there.
spciesla

Sr. Member
Registered:
Posts: 107
Reply with quote  #26 
Late to the game here (was on the road last week).  

Pete - What is the application for this train, that you leave the pump uncoupled?
RustyCas

Avatar / Picture

Admin
Registered:
Posts: 1,810
Reply with quote  #27 
That shallow bent baseplate looks to be about 24” square and about an 1” tall, made of 3/8” plate. If so, it weighs 64 lbs. To fab that you have to form it, and then it is continuously welded along the outer edges, and as far as they can reach inside (but maybe only an inch or so). So even the connection to the base is less than ideal. Combined weight of 2 pieces of 1” x 4” x 24” long is 53 lbs, so less steel. A lot faster to make 2 cuts on a band saw than to roll form or press that base. And you can then stitch weld (so cracks don’t “run”) on all 4 sides, so the same (or less) weld, a lot better connection, and 2x as many threads in the base (3/4” vs 3/8”).

As I said, cheaper, faster, and several orders of magnitude stiffer.

__________________
"The trend is your friend"
Danny Harvey

Sr. Member / Moderator / Supporter
Registered:
Posts: 1,403
Reply with quote  #28 
Here's another solution that doesn't take any time to set:

http://www.skf.com/group/products/maintenance-products/alignment-tools/shims/spherical-shims/index.html

I've never used them but I hope to on two big motors soon.
electricpete

Sr. Member
Registered:
Posts: 651
Reply with quote  #29 
Quote:
Pete - What is the application for this train, that you leave the pump uncoupled?

It's a natural question. I pm'd you some info. 

I'm not interested in discussing details of the application on a public forum.  Whenever possible, I try not to reveal my  indentity / industry / plant / application (that was the reason for the blacked out area on the pump... not to protect the pump vendor).  It enables me to share info more freely than I could otherwise.   I'm sure most plant people can relate to this. 
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.