Pin wear from period loading needs a permanent solution 1

[Imposter666]

There is a maintenance inspection at this pin once a month. it is usually changed out right away as failure would be catastrophic for the production. I have summarized all the details in the picture below. Increasing pin diameter would definitely help as the contact area would increase. However, I don't think this would solve the problem completely on its own. I didn't want to make radical changes to the design. But I am willing to if it will get rid of the problem completely. What countermeasures do you think can be done here.

 

[TugboatEng]

I don't mean to repeat myself but everybody is ignoring the elephant in the room. Every single link in the chain is subject to the same wear. Chain is a terrible choice for this type of high cycle loading. I don't know why chain is required here but there is a reason fittings aren't available off the shelf to handle this type of cycling. Wire rope, on the other hand, has many options for fittings to fit on a pin.

I suspect OP is having a short life because they're not using the same pin that is listed in their spec. If the chain isn't wearing, a pin of similar material should last as long as the chain. With that said, chains used for lifting REQUIRE regular length measurements to determine wear so whatever you do to fix the pin isn't going to fix the rest of the system.

If you must use chain, I suggest using a roller chain as the bushings are built in.

 

[saplanti]

Inposter666,

I would condider changing the design completely unless there is a need for intermediate machined plate with pins.

Instead I would replace the inner machined plate with shackle with pin for connection to upper linkage and bow side to chain using a bit large safety factor. But on the shackle pin side connection you need to keep the Herzian stresses less than 1.8 x yield strength (even I would use lover than that, perhaps 1.2 x yield strength or just yield strength) since the pin is under small rotations.

 

[BrianE22]

They have actually tried that one, but it didn't show any improvement over the pin I listed up here. The plating is very thin and once it is pierced through it is basically same pin as this one here.

The plating they use is very thin. I would try .005" of hard chrome (assuming that will fit in your holes).

The replies seem to be split between using a softer material and letting it wear in and conform or using a harder material. As someone pointed out, the chain links themselves aren't wearing (or are they?). Does anyone know what they are made of? I don't think they have plating - just a strong, heat treated (for strength and hardness) steel I'd guess. I believe the contact pattern for the links would be a point which should have quite a bit for contact stress.

 

[goutam_freelance]

It appears that sliding at the contact surface is creating wear problem.If budget permits you can design a special attachment connected to end chain link which will have a ball or roller bearing fixed by pin and bushings etc. This will prevent wear due to sliding.

Engineers, think what we have done to the environment !

https://www.linkedin.com/in/goutam-das-59743b30/

 

[Compositepro]

"I believe the contact pattern for the links would be a point which should have quite a bit for contact stress."

In high strength lifting chains the ID of the links is very close to the diameter of the steel rod that the links are made from. With deflection under load there will be two lines of contact between each link rather than a point contact.

 

[IRstuff]

One of the memorable posts I've read on ET had to do with a cotton thread manufacturing engineer that was having issues with stainless steel guides getting cut by cotton thread. So, doesn't much matter what the relative difference in hardness is, enough abrasion will allow the softest materials to cut much harder materials, much like the water cutting river beds through granite canyons.

TTFN (ta ta for now)
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[Imposter666]

dhengr, it was my account. I new to this platform, didn't know where I am supposed to receive the notifications at. Anyways, I decided to create a new account with my personal email and provide what was asked of me under this new thread.

 

[Imposter666]

Guys, the design was done much before my time in the plant. I am trying to come up with something cheap that will solve the problem permanently at best or will require maybe yearly inspections at the pin instead of yearly inspections. Anyways, I looked at case I suggested: simply upgrading the pin to 12mm of same kind from Misumi. For my analysis, I choose a contact width of 1mm for both current and new model.

 

[Imposter666]

goutam_freelance:
Thanks for pointing out the sliding wear. The old pin used to be able to spin in the clevis freely. It also made minimal contact with chain. I am going to suggest to machine the bore diameter of the clevis to something tighter. So I am hoping that chain would only pull from one side of the pin. I am thinking that there will be certain plastic deformation as the chain makes a very little groove for itself. But it will stop at one point.

 

[rb1957]

a bigger pin will definitely help. whether it fixes the problem is open for debate ... wear is a difficult thing to solve with FEA.

It'd also help to have something to distribute the load over the pin ... like a machined piece that fits inside the chain link and makes a neat fit on the pin.

Is there no option for the chain ?

another day in paradise, or is paradise one day closer ?

 

[3DDave]

I think the usual approach must be for the chain maker welding a fitting onto the chain prior to heat treatment. However the wear between the links is still going to happen so simply meeting the same diameter and material should match the rest of the chain.

I spent a bit of time looking and I expected catalogs from chain makers would have some, but the most frequent was just a shackle with a straight pin or a split part that captures the outer shoulder of a link.

 

[Imposter666]

rb1957 and 3DDave:
As I mentioned, I will make the bore diameters with little tighter fit so the pin doesn't spin. I actually want the pin to deform a bit and increase its contact area. Also the pin and the chains are purchased parts. We usually refrain from modifying purchased parts. I could design something, but I am trying to get away with a simpler and cheaper option. Our maintenance crew is inspecting this pin monthly. If I could reduce the inspection cycle to let's say yearly, it would be a big improvement.

 

[rb1957]

cheap solutions generally yield the minimum results. if you're happy with that then "fill y'r boots".

I don't know how you'll inspect a tight fitting (possibly deformed, and I understand what you mean ... interference fit) bolt.

another day in paradise, or is paradise one day closer ?

 

[SwinnyGG]

There's also a factor which just occured to me which didn't before...

If you get enough deformation in the pin contact area, the displaced material may make it very difficult/impossible to remove the pin. Might want to think about that.

 

[DAVIDSTECKER]

Look into

https://www.stulzsicklessteel.com/creusabro/creusabro-8000.html

Better known as Hadfield Manganese or AR plate.
It is machinable as long as you do right, it work hardens but I believe you can anneal it if you need.
It gets harder than probably anything you've ever dealt with but it is also tough.
Used for rail road switch gear, crushers and mills.

 

[3DDave]

Imposter - rather than you modifying it, it's having the chain maker who has the facility to both make the modification and proof-load the finished product.

 

[IRstuff]

Are you always using the same chain and the same pin, or is it a set of different chains?

It seems to me that the pin in the photo has the profile that you probably want in your pin to begin with

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[TugboatEng]

That's why I find this post odd. This arrangement is very standard for lifting equipment. OP's pin does not match the part number provided so I believe the wrong pin is being used and that is the source of the problem.

 

[FacEngrPE]

Frequent inspection is necessary,
If this is part of a hoist sling,

29CFR1910.184(d) (OSHA General Industry) Slings - Inspections.
Each day before being used, the sling and all fastenings and attachments shall be inspected for damage or defects by a competent person designated by the employer. Additional inspections shall be performed during sling use, where service conditions warrant. Damaged or defective slings shall be immediately removed from service.

You can reduce - but not eliminate the wear by using case hardened alloy chains and fittings.
Lubrication will help, but needs to be applied daily, and does can be counterproductive if conditions are dusty. (Dust + Grease = lapping compound).
This recommendation is based on experience with scrap handling electromagnets.

Fred

 

[mfgenggear]

if the pins are centers less ground then thick engineering plate be applied then regrind. soft internal parent material, with hard chrome will last many cycles.
minimum thickness of plate needs to be .005 inch minimum. chrome is harder than carburized surface and is use for shaft bearing diameters as a repair,