Silicone Bronze vs 304 Stainless 3

[mecheng2000]

I have a pin that rope winch (composite drum) spins on in a marine environment and gets a salt water splash from time to time. it has a threaded area with a nut that locks the drum in place. Loads are varying and never over a couple hundred pounds max. Im not happy with the 304 ss . how does silicon bronze compare to the 302 in terms of wear, strength, corrosion in an application like this? which grade would be most appropriate? the pin is fixed to the composite drum and spins in a fiberglass case. thanks in advance for any advice.

 

[TugboatEng]

How is the pin failing? Is it wearing or corroding? Does the drum have a bushing or does it ride directly on the pin? If it's spinning in the fiberglass, that material is quite abrasive and you may want to consider a bushing. 17-4PH would be an improvement over 304ss for wear resistance and tolerates salt spray provided you keep it greased. If you are going to run the fiberglass directly on the pin and don't want to use lube then maybe zirconia ceramic would be a option.

 

[mecheng2000]

thanks for the reply! its directly on fiberglass but only spins two turns for full range of the winch. it lasts years, but it is big deal when it fails. I'm looking for something I dont have to worry about for the next 20 years.
an added complication is that an off the shelf socket is welded on the end of the shaft to accept the winch handle. And there is an off the shelf nut to clutch the winch. I suppose I could machine fit the shaft to the socket and put a roll pin in to secure it.
I should add that this is a dry pin with no way to get to it to lubricate it.
I'll look into the 17-4PH . . . thanks for the tip. Here is a picture of a failure of this item. this is 3/4 inch od by the way. i think it is stress cracking + corrosion over time. the range of motion of this pin is only 2 revolutions in both directions.

 

[EdStainless]

If you want to do this once then look at Nickel Aluminum Bronze or better yet Monel.
There are some other high performance alloys that would work, but they would be harder to find.
The 304 could have SCC, or it could be fatigue originating from a corrosion pit.
It sounds like you need to step back and re-deign this system a bit.

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

Tests using smooth bent beam specimens stressed up to the 0.2%
yield strength of the material and exposed to marine atmosphere on
the 80 ft. (24.4 m) lot, 82 ft. (25 m) from the waterline, show that 17-4 PH
Stainless Steel is quite susceptible to stress corrosion cracking when
in Condition H 900. In Condition A, and when hardened at temperatures
of 1025 °F (552 °C) and higher; the alloy is highly resistant to stress
corrosion cracking. In addition, many years of service experience in
marine atmospheres and in high-purity water at high temperatures
demonstrate the resistance of the alloy to this type of failure.

Credit to the source of course:

https://www.aksteel.com/sites/default/files/2018-01/174ph201706.pdf

Seeing as wear doesn't seem to be related to the failure here, I agree with Ed that a bronze alloy will be an upgrade without the complexities of stainless steel.

 

[mecheng2000]

Thanks for the great advice. Im going to look at monel and see how affordable that would be.

 

Aluminium bronze or Monel.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[WKTaylor]

Check out specs, thus... the marine environment is NO ONE's Friend!

SAE
J1776 Marine Vehicles - Hydraulic System Pumps and Motors - Design and Specification Guide
J1777 General Environmental Considerations for Marine Vehicles, Information Report
J1781 Ship Systems and Equipment – Materials for Fluid Systems
J2270 Ship Systems and Equipment - Threaded Fasteners - Inspection, Test, and Installation Guidance
j2271 Ship Systems and Equipment—Part Standard for Studs— Continuous and Double End (Inch Series)
J2280 Ship Systems and Equipment - Fasteners - Selection and Identification Requirements, Standard
J2295 Fastener Part Standard - Cap Screws, Hex, Heavy Hex and Heavy Hex Structural Bolts, and Hex Nuts (Inch Dimensioned)
J2485 Fastener Part Standard - Machine Screw Nuts (Metric and Inch)

also...

MIL-HDBK-735 MATERIAL DETERIORATION PREVENTION AND CONTROL GUIDE FOR ARMY MATERIEL, PART ONE, METALS
MIL-HDBK-843 SHIP METALLIC MATERIAL COMPARISON
MIL-STD-1365 GENERAL DESIGN CRITERIA FOR HANDLING EQUIPMENT - ASSOCIATED WITH WEAPONS AND RELATED ITEMS [ships]

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[blacksmith37]

Nickel aluminum is good for sea water ; there are a few grades with different strength levels.

 

[gringor]

thanks again for the advice. i can get some silicon bronze for a relatively good price I think. would that be every bit as strong as 304 stainless steel?

 

[EdStainless]

Most Si Bronze is used for electrical connections and do not have great corrosion resistance (they have good strength and are OK at elevated temps). There are some Al-Si grades that aren't bad, but in general noting like a Ni-Al Bronze would be.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[gringor]

thanks! heres what I am looking at right now

https://www.avivametals.com/products/c65500-high-silicon-bronze-a