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Bronze Bushing "extruding" under wear

Bronze Bushing "extruding" under wear

Bronze Bushing "extruding" under wear

(OP)
We've been manufacturing a pivot eye for one of our systems for about 10 years now.

Recently one has come back with the bronze bushing extruded out beyond the edges of the steel eye.

We've never seen this type of damage before, though in fairness, we very seldom get old parts back from the field, and we may be ignorant of some events.

The customer is asserting that the part was not overloaded, and that the bronze bushing extruded out of it's bore due to wear on the pivot pin. Has anyone seen 660 bronze flow like this?

Other indications of high load include crushed rolling elements in the crane bearing the eye pivots on, so it's certainly something we're thinking of as likely, though again there may be other explanations for that damage as well.
 
Thanks for any comments

RE: Bronze Bushing "extruding" under wear

Where lubrication guidelines followed?

Are there any provisions to accomodate twisting loads?  Misalignment?

Impact loading likely?

What are the design loads that the customer asserts to have not exceeded?

Was a material substitution made of which you are not aware?

Ted

RE: Bronze Bushing "extruding" under wear

from which country and how many years back in time did you get the 660 bronze from?

RE: Bronze Bushing "extruding" under wear

"Has anyone seen 660 bronze flow like this?"

Yes . . . from overloading and from too high of a cycle speed, i.e., overheating.

RE: Bronze Bushing "extruding" under wear

(OP)
Thanks for the interest all, here's some more information, hopefully it'll help out.

It's likely that the part was not greased as regularly as we'd like. We probably won't ever be sure, but that's the way we'd bet. The customer has assured us that regular lubrication has been applied. While it's probably possible to question this, we do know that similar units in similar settings and with similar use have not failed in this way. I don't think there's any reason to expect that the bushing saw WORSE maintenance than parts that have worked without complaint for years.

The part is a pivot eye bushing that sees either no motion or slow oscillation for almost all of it's service life.
The original 660 bronze would have been sourced about 9 years ago. We can try and locate records as to where it came from.

The customer is quite firm that no overload occurred, and suggests that the extrusion is a result of wear... but wear under slow speeds and not at elevated temperatures... We've just never seen anything like that happen.

If no-one else has personal experience with wear extruding a bronze bushing like this, are there any good references I could look into?  

RE: Bronze Bushing "extruding" under wear

Is there any possibility that this particular installation is subject to wind flutter, building or equipment vibration, or some other sort of low-level but nonetheless long-term induced vibration?  It would seem like an unusual vibration preculiar to that site might slowly hammer out the bushing even if well-lubed and safely loaded.  Any new construction on the site?  Vibratory earth compactors can cause surprising occurances some distance away...

RE: Bronze Bushing "extruding" under wear

Customers lie, or at least don't always tell the whole truth, sometimes because they don't know the whole truth, not necessarily because of mal intent.

If Jim Bob on the night shift overloads it but no one else knows, then they'll assume it's never been over loaded.

We get stuff back all the time damaged through obvious abuse that customers claim they know nothing about.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Bronze Bushing "extruding" under wear

Material suppliers also lie.

We got some 'leaded brass' (nominally 1 pct lead) from a Mexican supplier at a very attractive price.  It machined like butter, but turned gray in the brazing furnace.  It was analyzed at 19..25 pct lead.

 

Mike Halloran
Pembroke Pines, FL, USA

RE: Bronze Bushing "extruding" under wear

Ibreak...:
Sizes, orientations and magnitudes of parts and loads would be most helpful; you know these and we don't, so we're guessing as we try to comment.  I suspect the pivot pin is harder and stronger than the bronze bushing, right?  It isn't going to wear much w.r.t. the bushing.  Wear, crushing and other damage to roller elements at a radius significantly larger than the bushing would indicate high loading to me, based on your equip. history records, etc.  Maybe this crane sits in one position, and only rotates over a relatively short arc, and then only in one direction when loaded and under light weight, back again, in the other direction.  This might show wear and crushing on the rolling elements only on the loaded quadrant of the bearing circle.  Then you might get wear and extrusion on the bushing on its top edge on the loaded quadrant and on its bottom edge on the back side.  You have a sample, right in your hands, for testing the bronze, assuming it won't be reinstalled.  With out some serious looking, I don't know 660 bronze from any other bronze, but I'm sure it will extrude or flow from the bearing pressure exerted on it by a steel center (pivot) pin.  The bearing stress, likely quite high, and probably well above Fy, btwn. the center pin and the bushing is a Hertz bearing stress problem.  Any significant dia. difference btwn. the pin and the bushing, and/or any vertical axis angular misalignment btwn. them will lead to very high bearing stresses at the upper edge of the bushing on the loaded side; these would be extruding forces and stresses on the bronze, poison's ratio and all that good stuff, even if there were no high temps.

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