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Angle thingy....plate....

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bogstandard:
Bernd I think is perfectly correct on this one.

That looks like a piece of cold rolled steel, and the outer skin, once oxidised over (rusted), can become hard as glass. Once you can break thru the hard very thin skin, usually no further problems occur. You should treat it as you do with a cast iron casting. If you need to drill it in its rusty state, just knock the skin off with a grinder first, in the area you want to drill.

John

Darren:
Thanks guys,

I'll take the crust off with the shaper and see how it drills.....

Now off to find out what cold rolled is, (rolled to thickness cold rather than hot  I assume, but why?)

Edit:

Wiki says cold rolling is a method to not only change the thickness of metal but also to harden it and relieve stresses. It also makes it more brittle at the same time.
Three stages depending how squeesed it is,

"Cold rolled metal is given a rating based on the degree it was cold worked. "Skin-rolled" metal undergoes the least rolling, being compressed only 0.5-1% to harden the surface of the metal and make it more easily workable for later processes. Higher ratings are "quarter hard," "half hard" and "full hard"; in the last of these, the thickness of the metal is reduced by 50%"

bogstandard:
Cold rolled is 'usually' identified by a dark surface skin, with a slight radius on the edges of the material, ie, they are not square but have a slightly rounded profile. Most of your angle irons and  flat strip and such are cold rolled.

http://www.efunda.com/processes/metal_processing/cold_rolling.cfm

The problem with them is that if left to corrode the skin can get rather hard, and in certain cases delaminate from the parent metal leaving behind a very rough surface.

John

Darren:
Thanks John,

This troublesome piece deff has a pronounced curve to its edge. Also coming from the scrappy it's quite corroded so looks like it's been there a while, and of course it was somewhere else before that.

At least I have some idea how to deal with such pieces now, ta  :wave:

Learn a little every day  :)

Bernd:
Bogs,

You must have different angle than we do here. The angle I've used has all been hot rolled. It has a dark balckish-blue tint to it and a bit of scale. I've never seen cold rolded angle here unless it is of the smaller angles.

Bernd

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