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05-19-2015, 08:43 AM
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#1
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4 Rivet Member
1964 24' Tradewind
2006 39' Land Yacht 396 XL
Lawrence
, Kansas
Join Date: Oct 2012
Posts: 292
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Screws and Aluminum and Rust
If one is forced to use a screw that will come in contract with the aluminum what is the best metal make up of the screw? Should the screw be coated? Thanks in advance.
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05-19-2015, 09:13 AM
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#2
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Rivet Master
1973 27' Overlander
Portsmouth
, Virginia
Join Date: Jun 2012
Posts: 776
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Always use stainless, especially if it is exposed to weather.
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05-19-2015, 09:21 AM
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#3
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Rivet Master
1972 31' Sovereign
Lexington
, Minnesota
Join Date: Feb 2009
Posts: 3,991
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I second that recommendation.
Chris
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05-19-2015, 09:21 AM
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#4
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Rivet Master
1966 22' Safari
Hilltop Lakes
, Texas
Join Date: Jun 2008
Posts: 1,767
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Cadmium plated aircraft screws work well, should you choose to go that route.
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05-19-2015, 09:26 AM
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#5
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Rivet Master
2007 30' Classic
Oswego
, Illinois
Join Date: Jul 2010
Posts: 13,669
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I replace with stainless on each project and where corrosion becomes an issue.
Depending upon application I sometimes use a nylon washer/insulator and/or corrosion-Ex to retard the galvanic reaction.
__________________
-Rich-
"If the women don't find you handsome, they should at least find you handy." - Red Green
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05-19-2015, 09:27 AM
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#6
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4 Rivet Member
2015 30' Classic
Sherwood
, Oregon
Join Date: Mar 2015
Posts: 479
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The 18-8 stainless screw grade should be type 304 or 305 as they have a higher corrosion resistance due to a lower carbon content (.08).
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05-19-2015, 10:31 AM
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#7
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New Member
Charleston
, South Carolina
Join Date: Dec 2014
Posts: 4
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Galvanic Corrosion
Stainless steel fasteners have been covered and are the best option but one more is Loctite 222 for small fasteners. It prevents galvanic corrosion between the threads of dissimilar metals and prevents them from vibrating loose. Because it is low strength you will be able to back the screws out using a screwdriver. Do not use Loctite 262 unless you never want to remove the screw. 222 is pink in color and 262 is red. Hope you find something that works for you.
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05-19-2015, 10:35 AM
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#8
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Rivet Master
2012 30' Flying Cloud
San Antonio
, Texas
Join Date: Jul 2012
Posts: 682
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Stainless and here is what you coat the threads with prior to use.
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05-19-2015, 11:47 AM
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#9
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4 Rivet Member
1967 26' Overlander
Spartanburg
, South Carolina
Join Date: Jan 2011
Posts: 437
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As an old retired plant engineer, I agree with most of the comments esp using Loctite to prevent galvanic corrosion. There are other products available for that but my experience with Loctite in general is they know their business. They also have a very good customer service department who will talk with you on the phone.
Don't know about the Permatex with aluminum and suggest you read the label and/or go to their web site for more info before using. I would also suggest using aluminum screws where the application will allow the lower tensile strength. That will generally eliminate galvanic corrosion or at least minimize it depending on the alloy.
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05-19-2015, 11:56 AM
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#10
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Rivet Master
2012 23' FB International
Woodstock
, Ontario
Join Date: Aug 2014
Posts: 1,428
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I noted in a previous thread on this topic that I used SS on the stainless fittings on my sailboat Aluminum mast. Never had a problem. Some one noted that they were an Aerospace engineer and they use SS on airplane aluminum all the time.
JCW
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05-19-2015, 12:12 PM
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#11
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Moderator
Vintage Kin Owner
...
, ...
Join Date: Jul 2007
Posts: 11,696
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Screws and Aluminum and Rust
Ditto on the stainless steel recommendations. Galvanic corrosion is the big concern joining dissimilar metals. Rust is a by-product of ferrous metal corrosion, but using stainless will ease your concerns over discoloration.
__________________
"One of the best lessons I've learned is that you don't worry about criticism from people you wouldn't seek advice from."
William C. Swinney
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05-19-2015, 01:10 PM
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#12
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Rivet Master
1981 31' Excella II
New Market
, Alabama
Join Date: Sep 2011
Posts: 6,145
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Aluminum and Stainless steel are pretty good at self insulating each other and should not have a huge problem with galvanic corrosion with each other. A hot dip galvanized washer as an anode is not a bad idea. Thin electroplated washers won't last long because the coating is not thick enough to last long. Belly skins have the most corrosion issues because of road salt and water leaks from above and soaked insulation.
Perry
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05-19-2015, 08:52 PM
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#13
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4 Rivet Member
1964 24' Tradewind
2006 39' Land Yacht 396 XL
Lawrence
, Kansas
Join Date: Oct 2012
Posts: 292
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Good info. Thanks everyone.
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05-20-2015, 09:15 AM
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#14
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Rivet Master
2012 30' Flying Cloud
San Antonio
, Texas
Join Date: Jul 2012
Posts: 682
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Quote:
Originally Posted by Jacob D
As an old retired plant engineer, I agree with most of the comments esp using Loctite to prevent galvanic corrosion. There are other products available for that but my experience with Loctite in general is they know their business. They also have a very good customer service department who will talk with you on the phone.
Don't know about the Permatex with aluminum and suggest you read the label and/or go to their web site for more info before using. I would also suggest using aluminum screws where the application will allow the lower tensile strength. That will generally eliminate galvanic corrosion or at least minimize it depending on the alloy.
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A follow up on Jacob's note of caution: I've used Permatex for years in the salt water marine environment of stainless screws/bolts and aluminum. You have to try real hard to get much worse than that.
Product Description
Size: 8 Ounce
Permatex Anti-Seize Lubricant is a highly refined blend of aluminum, copper and graphite lubricants, for use during assembly to prevent galling, corrosion and seizing, and to assure easier disassembly. Featuring salt, corrosion and moisture resistance, this lubricant is ideal for marine use. With a temperature range from -60 degrees Fahrenheit to 1600 degrees Fahrenheit, it will not evaporate or harden in extreme temperatures.
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05-20-2015, 01:29 PM
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#15
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Rivet Master
1981 31' Excella II
New Market
, Alabama
Join Date: Sep 2011
Posts: 6,145
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Anti Seize is never a bad idea with heat and corrosion environments.
Perry
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05-21-2015, 09:40 AM
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#16
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4 Rivet Member
2015 30' Classic
Sherwood
, Oregon
Join Date: Mar 2015
Posts: 479
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If anti-seize is used it should be zinc based anti-seize with no copper content according to the builder of my aluminium jet boat. Loctite product number 39901 is zinc based and will minimize galvanic corrosion.
Also, I would not use zinc plated washers or any zinc plated fasteners because the zinc acts as a sacrificial anode and after a few years the underlying carbon steel will come into contact with the aluminium resulting in corrosion.
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05-21-2015, 12:08 PM
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#17
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Rivet Master
1981 31' Excella II
New Market
, Alabama
Join Date: Sep 2011
Posts: 6,145
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The double dip galvanized steel washers are made for corrosive environments and that is why the coating is so thick. Stainless steel is fine as well but it might tend to corrode the aluminum since it is cathodic to aluminum.
Perry
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05-23-2015, 07:21 PM
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#18
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Rivet Master
2012 30' Flying Cloud
San Antonio
, Texas
Join Date: Jul 2012
Posts: 682
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Quote:
Originally Posted by NWRVR
If anti-seize is used it should be zinc based anti-seize with no copper content according to the builder of my aluminium jet boat. Loctite product number 39901 is zinc based and will minimize galvanic corrosion.
Also, I would not use zinc plated washers or any zinc plated fasteners because the zinc acts as a sacrificial anode and after a few years the underlying carbon steel will come into contact with the aluminium resulting in corrosion.
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All these products minimize galvanic corrosion--that's what we're talking about here. I personally don't buy your jet boat builder's no copper story since original Permatex has been used on aluminum in the saltwater/aluminum boating industry, with no problems, long before Locktite ever produced an anti seize product. That said, if one is afraid of copper, use a copper free product. Heck, use the food safe stuff if you want, just use Stainless and some anti seize--done deal.
Howard
Sent from my iPad using Airstream Forums
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05-24-2015, 12:20 AM
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#19
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4 Rivet Member
2015 30' Classic
Sherwood
, Oregon
Join Date: Mar 2015
Posts: 479
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Quote:
Originally Posted by Howard L.
All these products minimize galvanic corrosion--that's what we're talking about here. I personally don't buy your jet boat builder's no copper story since original Permatex has been used on aluminum in the saltwater/aluminum boating industry, with no problems, long before Locktite ever produced an anti seize product. That said, if one is afraid of copper, use a copper free product. Heck, use the food safe stuff if you want, just use Stainless and some anti seize--done deal.
Howard
Sent from my iPad using Airstream Forums
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My North River Commander 21 is nine years old without any signs of corrosion so I'll go with what the builder recommends. In the late 80s I owned a marine repair business and we drilled out many corroded bolts from out drives and out boards. Preventative maintenance has come a long ways since then so I'll go with what the guys recommend that build the high dollar aluminium toys today. All we can do is post recommendations for the original poster and from that, he/she can make a decision or seek more competent advice.
__________________
2015 Classic 30A, Blue OX Sway Pro, 2016 F350 4x4 Ultimate Lariat crew cab SRW, LWB, 6.7 PSD, 20" wheels, Ingot Silver Metallic, DiamondBack tonneau cover, TrailFX wheel-to-wheel step bars.
Sold: 2014 25FB International Serenity
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05-25-2015, 07:38 PM
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#20
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Rivet Master
2012 30' Flying Cloud
San Antonio
, Texas
Join Date: Jul 2012
Posts: 682
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Absolutely, to each his own. Just use something
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