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Crane Boom Hinge Pins/Bushings - Max Allowable WearHelpful Member! 

CGWorkBoater (Mechanical) (OP)
8 Aug 03 17:09
I am trying to specify when to renew a pin or bushing (installed in crane booms), based on wear/loss of material (slopy fit), either in the pin or bushing, relate those dimensions to the remaining factor of safety still in the pin.  I didn't design the crane, so I am reverse engineering all of this.  I have found simple shear formulas, but I'm looking for something more detailed, like what the guy used to design the crane (like a spec for designing a pined connection).  Have found system design std specs, and "theoretical" type formulas for shear/etc., but nothing "practical" for simple component design. Any advice whould be greatly appreciated.
Helpful Member!  EdDanzer (Mechanical)
11 Aug 03 10:48
Most operators will complain when the boom gets to sloppy. The spec will depend on the pin and bushing material and hardness, also the type of grease. Hardened steel pins running against hardened steel bushings usually have galling, or bushing breaking failure, so it is hard to tell when to replace before it’s too late. Most people will not put an indicator on a pin joint to measure clearance, but 4 time the new would be a lot.
CGWorkBoater (Mechanical) (OP)
11 Aug 03 17:28
EdDanzer, thanks for the response.  Let me explain further.  Agree, typically, the operator will define the maintenance schedule, but not in my org.  I am trying to dismantle some wacky cultural practices (schedule-based over-maintenance) and move more toward a CBM approach. I'm not really trying to determine when to disassemble, I trying to justify no automatic disassembly (build a case for).

I am trying to make claims like "until you loose 5% of the pin you still have a factor of safety of 5:1, so taking the boom off is not warrented unless you have a problem".  I plan to gather all material and as-built dimensional data for each pined joint. I am just looking for some canned analysis, or a "go-by"'s, for sizing a pinned joint to help build my case. I know about the "theoretical" simple solutions, the ones you see in academic texts, but I was looking for one that takes fits, gaps between clevis/eyes, etc. into consideration.  Any more advice, or pointing me to a good "design handbook" of sorts would be a great help.

thanks again
EdDanzer (Mechanical)
11 Aug 03 20:42
I have never heard of a canned solution. Having tried doing FEA on pin joints with different clearances, you probably won’t believe the results or be able to justify the cost. The Machinery’s Handbook has information about bushing fits. In most cases when the clearance becomes greater than the maximum for a pin/bushing assembly that would be a good time to replace it. The problem you may run into is that this maybe either too much wear for the operator, or so little that replacement is too frequent.
9388 (Mechanical)
11 Aug 03 21:47
I personnelly think the most direct & effective way is to carry out a load test to 2x the SWL at frequency of twice/year.
boo1 (Mechanical)
12 Aug 03 1:53
Bushing wear is a seperate issue than load testing.  Wear is magnified in the boom movement.  

Check the owners manual or the manufactures field overhaul tolerance.
CGWorkBoater (Mechanical) (OP)
12 Aug 03 8:26
EdDanzer, Thanks, good advice, I'm going to go down the path of classifying the fits of the various pined joint we have per Machinery's Handbook and ANSI B4.1, and then come up with a scheme for bushing/pin renewal when a fit widens out of it's class.  I'll post my plan when it is done, invite you (and everyone) to review/critique.  I work for govt, so you may have just relieved a tiny fraction of your tax burden (but you may also have eliminated a tiny bit of commercial subsidization, but your company probably isn't affected).

Thanks again
boo1 (Mechanical)
12 Aug 03 12:29
For ur Gov check out the Navy NAVFAC-307 crane standard.

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