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Silicon bronze or stainless steel screws?

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Silicon bronze or stainless steel screws?

Postby FCE woodiesparts » Tue Aug 09, 2011 3:39 pm

Hi, if you read this topic you probably think about using stainless steel screws in your riva.
Well the answer is NO.
I have seen countless Rivas with these screws and all are bleeding .
Just 2 weeks ago a client came to me for wood and screws and he asked me why the chine ( connection from bottom with side) was bleeding with blisters.I told him" because someone did a bad restoration, remove the paint and you'll see!" :cry:
As soon as the screws are damaged, for example with your screwdriver or sanding paper they are just steel! It will repair itself but it needs to( let me say) corrode again.
I've seen it in my first restoration ( an Arcangeli) 2 years later I had to do it all over again.
And what is worse? Do a job with good screws at a higher price or remove a bottom and do it twice? :?:

Let me explain in the next chapter.
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Re: Silicon bronze or stainless steel screws?

Postby FCE woodiesparts » Tue Aug 09, 2011 3:42 pm

Here is the text from my website and Internet:
The inherent corrosion resistance of stainless steels is derived from alloying the base iron with chromium.
The corrosion resistance of stainless steel arises from a 'passive', chromium-rich, oxide film that forms naturally on the surface of the steel. Although extremely thin this protective film is strongly adherent, and chemically stable (i.e. passive) under conditions which provide sufficient oxygen to the surface. This 'normal' condition is the passive state.
The key to the durability of the corrosion resistance of stainless steels is that if the film is damaged it will normally self repair (provided there is sufficient oxygen available).
However, when screwed in, the passive state can be damaged, resulting in corrosive attack. The film will normally repair itself if sufficient oxygen is provided. If the film is destroyed the surface is said to be in the active state.
Active stainless is 5 stages worse than Silicon bronze and passive is 4 stages better tan Silicon bronze, so under normal oxygen circumstances and not damaged it is better to use Passive Stainless. However as soon as you use it underwater or under paint it goes 9 steps worse. Whatever you use 316 or 304. And your bit may never damage the screw! Nor is it impossible for the hard wood Not to remove the thin layer when you enter the screw at high speed.
We provide Chromed Silicon bronze screws, these are, when not damaged 1 step lower than Stainless passive, so almost as good but still 5 steps better then the damaged stainless screw.
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Re: Silicon bronze or stainless steel screws?

Postby FCE woodiesparts » Tue Aug 09, 2011 3:44 pm

So I hope you understand why not to use . In a next topic I will explain why you better do not use them in the chromed parts. :arrow:
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Re: Silicon bronze or stainless steel screws?

Postby Eric T. » Wed Aug 10, 2011 2:03 am

Excellent topic FCE!!

And a great description.

In addition to the oxygen deprivation the Galvanic junction of the two dissimilar metals plays a large role in corrosion resistance and "iron staining" , especially in underwater fittings... even more pronounced in sea water.
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