failed seat back - Brampton Rebel meeting

[Mnleber]

Found it thanks. Only file I didn't look in to.

Mike LeBer R683



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[steve whitenect]

Something you might was to think of is how these seat backs are welded.
This is a common problem with mig welding 4130 steel. 4130 requires preheat
before welding and lengthy cool down for proper retention of it's tensile
strength or most of it anyways. That's why oxy/act is still prefered for
maximum strength. You preheat while waiting for the puddle to form and
there is a greater spread of heat, thus a longer cool down. The guy who
designed the Bearhawk shows a great test of this fact. He welded two sets of
tubes together at 90 degrees, one by each method. He then inserted a rod in
the end of each tube and forced the ron up and down. The one welded with a
mig broke in two or three strokes while the other took quite a few more
before cracking. Just a thought....

Steve W.

From: klehman@albedo.net
Reply-To: <murphy-rebel@dcsol.com>
To: murphy-rebel@dcsol.com
Subject: Re: failed seat back - Brampton Rebel meeting
Date: Tue, 13 May 2003 09:35:13 -0400

The welds on your seat looked excellent to me Drew but no matter how
good the weld, I agree that there is probably still risk from the heat
affected zone (HAZ) there even though I think the 4130 is normally
supplied in an annealed state. Don't know about .035 wall tube but I've
seen the HAZ change the temper in both directions (softer and harder)
with thicker steel, depending on air cooling surface and heat conduction
into the part. With a quick look I thought the rivet hole was a bigger
factor on your seat but either way I'm still inclined to think it is a
trouble spot if cracks are propagating from a round rivet hole. And I
suspect a risk probably exists even without rivets. A tube cantilevered
past a welded joint is a potential failure point in my opinion unless
stress is kept very low. I hate seeing engine mounts where that is done.
Sounds like MAM has fixed this on the SR from what Wayne said. Bet they
upgrade the Rebel seat back eventually as well. I might add some more
re-inforcement on mine even though I did not rivet into the frame.
thanks for sharing this with us.
Ken


Drew Dalgleish wrote:

Thank's for putting that picture up Ken. To all. When the seat failed I

was

taxiing across the ramp at centralia I was not placing any extra stress

on

it other than maybe wriggling around a bit to get settled. The seat back
didn't snap in two it just quietly folded back. I may have overstressed

the

back a month or so ago when I was rearranging a new jacket I have that's
covered with bits of velcro. The rivet holes are close enough to the

weld

that the steel probably doesn't have any temper left in it. I talked to
Brian Godden today to report the failure and he said they'd look into it
but he didn't sound very concerned about it.

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