Grey Iron? Alum Bronze? 4140? 1144? What Metal/Steel Alloy Grade to select/use???

[KJPecho]

Take a look at the image. I have 3 components making up an "EYEBALL" assembly. The 2 most important are depicted. We are just about ready to cut/machine parts but we need to make a call on what alloy/grade of metal we will be selecting to machine these components from. These components are machined SPHERICAL and rotate and clamp within one another. Their movement can be likened to the eyeball in your head. We have sliding/mating surfaces in a semi corrosive environment exposed to water/coolant. The "eyeball" depicted in GOLD/BROWN turns in all directions within the "Slew Ring", like your eyeball does. The "Slew Ring" is split so that it can contain/house the spherically machined "Eyeball" Component. The "Slew Ring" is also machined Spherically at the ID of the ring, but cylindrically at the OD of the ring. As these parts are sliding/rotating inside of one another machining tolerances are critical...so built in stresses from machining and any spring to the components would be detrimental. All mating/sliding surfaces will be greased sufficiently. I am told these components will experience pressures while in operation of around 200psi...so strength is not critical but is preferred.

So now down to the question at hand....when considering the "Slew Ring", what is the best material to choose? I am familiar with A36, A572-50 (all structural), A516-70 (PVQ) and 4140 (We make all of our case hardened tooling out of this)....but seeing as this component is much different in nature and in function I really have no clue what the best way to go about selecting a steel/metal alloy for this.

Initially Grey Cast Iron was recommended/suggested for the "Slew Ring" and that is due to the graphite in the iron and its lubricity. But the Slew ring is clamped down onto the Eyeball to stop its movement and freeze it in position and i am afraid that due to cast irons brittleness we could be in danger of cracking the slew ring during clamping and unclamping.

Another material that was suggested to look into was Aluminum Bronze. I am wondering if anyone has any insight on this and or any recommendations?

 

[TugboatEng]

Just spitballing, I know it opens up a lot of new failure modes, but your contact stress is very low. Maybe consider fabricating the section using a weldable 300 series stainless and plugging it with a wear resistant material?

 

[EdStainless]

As much as I like SS, I don't really see a 300 series alloy as being a good fit here. Maybe if you went with Nitronic 40 or 50 it would be durable enough. But a casting makes sense for this, easy shape and no thin sections.
This isn't a huge ring, rough size 36" OD x 4" wall x 18" long.
People do weld and roll rings that size, they also hot forge them (think Wyman and Ladish).

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P.E. Metallurgy, consulting work welcomed

 

[KJPecho]

After much thought research and consideration, my team did agree that the Ni-Resist suggestion was an ideal alloy for our parts....The problem now is who can we get this casting from....The only foundry i found that poured Ni-Resist in the size we need and was willing to do just a single part was Thompson Foundry out of Vancouver, CA. They said a large solid billet style casting weighed too much for their pour but if we made a "tool/pattern" for near net shape they might be able to assist...still not 100% sure that they will be able to do this for us but at least they didn't say no immediately.

The forging company we are familiar with and use is Scot Forge. But Ni-Resist Cast iron cannot be forged, correct? And it seems we are at the upper limit of most US & CANADA foundries with respect to size capabilities. I still have a few more companies to reach out to...if someone has a contact or a company they suggest to reach out to im all ears!

In talking to a few of these companies some have recommended a stainless forging if we cannot obtain this is Ni-Resist due to size/qty limitations...So a SS410 or SS420...I will look into those, thank you!

One further question....how would a SS410/420 interact with AluminumBronze Alloy? Would these two alloys still be a good fit together such as cast iron was?

 

[mfgenggear]

may be a lead

https://www.youtube.com/watch?v=EMFFyTpnqqE

 

[arunmrao]

What is the weight of the casting? Also the size,if you may share.

 

[mfgenggear]

an other lead

https://www.youtube.com/watch?v=Icu5LbcjDrc

 

[KJPecho]

I am not 100% sure of the weight...the rough size is 10" thick x 31" Diam

 

[KJPecho]

thank you for the leads there! they look promising i will reach out to them for sure...much much appreciated!

 

[EdStainless]

I don't see why 410/420 wouldn't work with AlBrz. Like I said they don't have great corrosion resistance but hosing them off with clean water will be about all that they need. If you wanted more corrosion resistance you could look at 431 or 440A.
If your part finished 34" OD x 30" ID then the blank will need to be about 36" x 28", give or take. I figure that 36"x 4"wallx 16"long will be 1800-2000lb, depending on exact size and alloy.
Casting this as a cylinder should not be a big deal, and the tooling can be dead simple. For one part I would cast a smooth walled blank and then put a ton of machine time into it. No reason to sink more cost into the casting tooling.

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P.E. Metallurgy, consulting work welcomed

 

[KJPecho]

@EdStainless

looking further into these alloys 410/420 are Martensitic and Nitronic's are in the austenitic family? Ni-Resist is an Austenitic Ductile Iron...The difference between the two martensitic and austenitic is the corrosion resistance? And isnt martensitic stainless very hard and less ductile than austenitic? Also how is the lubricity of these materials compare to that of cast iron?

 

[EdStainless]

With a martensitic you can pick the carbon level and the HT (temper temperature) to dial in the strength/hardness level that you desire.
In my experience the mating with Ni-Resist will be better, but I don't see the others posing a major problem. You will need to supply some degree of lubrication mostly to keep debris out of the joint and minimize metal contact.

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P.E. Metallurgy, consulting work welcomed

 

[KJPecho]

@EdStainless

Ed,

Why isn't SS316L a good choice in this application over say SS410/420?

Thanks!

 

[EdStainless]

It is soft and galls easily.
If you want that level of corrosion resistance then look at a duplex stainless like 2101 or 2202. For higher corrosion resistance there is 2205.
If you want an austenitic SS then look at Nitronic 50.
I still think that for a part that size you are better off with a casting. And that takes me back to Ni-Resist.

https://nickelinstitute.org/media/1...ni_resistandductileni_resistalloys_11018_.pdf

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P.E. Metallurgy, consulting work welcomed

 

[KJPecho]

Perfect thank you for your input on this Ed!