The texture you describe is called mill scale. It will come off with a sanding
block
& 180 grit or even a soft wheel on a 4" grinder but you need to be carefull
with that
and use as fine a grit as you can find with the grinder.
Then you can dress it down as shiny as you want with 240, 320, 400 etc.
I assume there is a bit of a divit which will require some sanding without the
block.
For heating metal with a torch you want to use a rose bud tip. A rose bud
isn't as
concentrated as a cutting tip. You should be able to reach inside the tube
with a
porting tool and conical emery cloth tips to get that as well.
Jim g
----- Original Message -----
From: "Robert M. Lang" <lang@isis.mit.edu>
To: fot@autox.team.net
Sent: Tuesday, May 17, 2011 9:23:51 AM
Subject: [Fot] metalurgy question
Hi,
I'm fettling a Falcon SS header for one of my TR6's. The installation
pretty much requires that you make some reliefs in the downpipe so that
you can install the hold-downs. No surprises there.
Now, although I've been using an oxy-acetylene torch for 15 years, I've
never actually trained on it's use, so I'm on new ground owing to the
material - 304 stainless.
I heated the tube area where it's to be relieved so that it's bright red.
I then hammered the tube with various types of hammers to get the general
shape I want. Again, no big deal.
The issue / question is: when the tube cools down, it has a fairly rough
texture to it. It's sort of grey-ish. I'm thinking that I may have
overheated the surface and / or had the flame a tad (or extremely) on the
"oxidizing" side if things. So, assuming that I was closer to "welding"
than just reshaping, is it possible to bring the surface back to something
that looks like tubing from the tube factory or should I just leave well
enough alone?
The eventual goal is to ceramic coat the header, if that has an bearing on
the topic.
regards,
rml
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rent
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