Is more hardness necessary in this application?

[mod231]

Hello,
I am designing a rotary yoke device that is used as a spanner wrench to unthread 2 components. Actuation will be steady hydraulic, impact will not be used. I would like to make the yoke out of 3" plate. I am considering using 4140 moderately hardened, or possibly A514 as-is. It appears that the spanner pin holes in the yoke will have enough compressive strength based on my calcs, but I have concerns about the holes becoming egg shaped long term due to cold flow. Would it be prudent to specify the 4140 with extra hardness (& reserve tensile strength as a side benefit) to prevent the holes egging-out, or do think A514 in its as-received state would suffice?

Best Regards.

 

[redpicker]

Do your calc's take into account that you will not have perfect alignment? That is, there must be a tolerance to the dimensions between the mating surfaces, do your calculaitons take that tolerance into account?

Without being much more specific, I don't believe you will get a definative answer. If the difference in cost of the material is not an issue, I think I'd look at using the 4140 and if yielding or wear resulted in a short service life, you could get the contacting surfaces flame or induction hardened. A514 material does not seem to be suitable for surface hardening. You have mentioned that the general stress levels should be low enough not to cause a problem, but the contact stress levels may be. The surface hardening would take care of the high contact stresses.

rp

 

[mod231]

I took the tolerance issue into account by factor of safety.
I should clarify: I don't necessarily need a definitive answer, I would just like to hear people's opinions/experiences- like you shared.
I like the idea of localized hardening, thank you for the information.

Regards.

 

[Guest102023]

Consider plain steel with an removable insert of some harder steel for the contact surfaces. Wear and replacement time are minimized.

 

[EdStainless]

Can you make the pins larger diameter in the yolk and then tapper them to the working tips?
This would spread out the stress on the yolk and reduce the risk for distortion.

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Plymouth Tube

 

[mod231]

Brimstoner - this is the parallel conclusion I arrived at today. I'm likely going to use drill bushings.

EdStainless - Great idea. I think I can achieve this partly with the drill bushing idea, and I may be able to upsize the base of the pins.

Thanks to all.