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Re: [Shop-talk] Welding a cracked fan Blade

To: nogera2@att.net
Subject: Re: [Shop-talk] Welding a cracked fan Blade
From: James F Juhas <james.f.juhas@snet.net>
Date: Mon, 01 Dec 2008 10:25:46 -0500
That is exactly what I would do, and indeed, what I was going to do when 
my MGA fan lost a blade through my left fender well at 6,000 rpm on the 
Lightening course at NJMP.  Notwithstanding the fact that I picked up 
considerable horsepower after I took the fan off, I doubted the wisdom 
of making the repair after taking a close look at it.  Besides the blade 
that broke off, another had a partial crack and would have been next to 
go.  And this was in September, after a close inspection of the fan in 
August revealed no likely defects.  The moral is to be wary of 
50-year-old steel.

But if you're not racing, and there is no replacement available, welding 
as you describe should fix it.  I would suggest a careful gas weld on a 
beveled seam so as to ensure full penetration and a softer heat temper.  
>From what I understand, mig or tig can result in a more pronounced 
boundary between the weld and the core metal, leaving it susceptible to 
further cracking along that join.  The arc weld could probably be 
annealed if arc welded by heating it and allowing it to cool slowly. 

My comments here are appropriate for a stamped sheet metal blade.  If 
you're talking about a cast piece, I'm sure a different set of rules 
apply, and I have no experience there.

nogera2@att.net wrote:
> I've got a metal ( very thick ) fan blade, which is no longer available,
> that has a crack in one of the blades. 
> I'm thinking of drilling a hole at the end of the crack and welding it up
> then grinding the weld flush. 
> Anyone see any problem with that or have other suggestions?
>
> Bob 
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