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Old 04-07-2013
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Aluminum screws instead of stainless

Considering that stainless screws into aluminum will corrode in spite of using Tefzel gel (the gel will eventually wash out). Why not use aluminum screws?
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Old 04-07-2013
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Re: Aluminum screws instead of stainless

Aluminum screws are not very strong. They may be alright for fastening trim but for anything else the are likely to fail.
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Re: Aluminum screws instead of stainless

Aluminum screws should actually work fine. 6061-T6 has a min yield of 35ksi compared to 316 stainless steel with a yield of 45ksi. That means that a 3/8" machine screw of 6061-T6 will handle 3864 pounds before deforming permanently where the stainless can go to 4968 pounds. Yes, there is a difference, but is the aluminum screw already overkill? That's something that you'd have to decide. Is the decrease in strength worth the decrease corrosion? But . . . have you pulled any two aluminum components apart lately? I pulled my gooseneck out of the boom and found gobs of corrosion inside. Quite frankly, regardless of the numbers, stainless is still probably the best answer. New technologies aside, sometimes the old ways are the best ways, tried and true.
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Re: Aluminum screws instead of stainless

You are correct that the yield strengths are in the same ballpark, but the tensile strength of 316 is 90kpsi, compared to 42kpsi for 6061-t6.
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Re: Aluminum screws instead of stainless

Looking over the galvanic series, Aluminum bronze looks good.........until you try to find any fasteners made from it. There are a couple of companies in India selling them. There must be something better than SS.
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Old 04-08-2013
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Re: Aluminum screws instead of stainless

Quote:
Originally Posted by Frogwatch View Post
Considering that stainless screws into aluminum will corrode in spite of using Tefzel gel (the gel will eventually wash out). Why not use aluminum screws?
Screws function in either tension or shear--i.e. "pull" along the center axis of the screw or, in shear, pull-push across with width of the screw. On a mast, almost all fasteners are loaded primarily in shear although mast mounted winches subject their lower fasteners to both shear and tension. Aluminum is relatively poor in tension, compared with a similar sized ss screw, and much poorer in shear. That said, one can certainly size aluminum screws for the loads they are likely to be subjected to although the fasteners will be proportionally larger and, being used less frequently, more difficult to find and costly. Being treated with TefGel, or Lanacote for that matter, and properly bedded to prevent water infiltration into the threads will prevent or limit the corrosion problem.
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Re: Aluminum screws instead of stainless

An aside...thought I had an inside track on some very light, very strong screws when
my son was home sorting out some Titanium screws used in spine surgery...until he
explained each screw sold for many hundreds of dollars!
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Re: Aluminum screws instead of stainless

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Originally Posted by HUGOSALT View Post
An aside...thought I had an inside track on some very light, very strong screws when
my son was home sorting out some Titanium screws used in spine surgery...until he
explained each screw sold for many hundreds of dollars!
Well, you can get non-surgical titanium bolts, screws and nuts for much less - (track) motorcycle tweakers use them a lot.

Hell, you can even get carbon fiber bolts and nuts (yes, really).
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Re: Aluminum screws instead of stainless

except that titanium is worst then stainless on the galvanic series
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Re: Aluminum screws instead of stainless

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Originally Posted by overbored View Post
except that titanium is worst then stainless on the galvanic series
Yes, depending on which ti alloy is used. However, it is easier to isolate electrically than stainless, and it doesn't suffer from crevice corrosion.

Last edited by One; 04-08-2013 at 11:41 AM.
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