Can anyone explain this? Making rings goes weird.

[chunkolini]

Im making a sculpture out of 8mm mild steel rings. All hot rolled/ black oxide finish. Internal diameter around 30mm.
Some bars roll perfectly Some don't; they won't go tight onto the roller just make a horrible mess.
There's possibly a tiny variation in thickness.
Drove me mad until I worked out which batch is behaving itself. Luckily they are stored separately. There is a thin bloom of rust on the good stuff.
Two pieces in the photo.
Both used the same roller.
Weird.

 

[addjunkie]

Are they supplied in a different state of heat treatment, not sure with bar, but tube certainly can be

 

[Pond frog]

With hot rolled black there seems to be very little quality control with the steel properties nowadays particularly with thinner stock, I’ve had 6m lengths that are stiff at one end and like soft liquorice the other end . I put it down to cheap Chinese steel . With thin steel if I really need it to be consistent I tend to buy bright stock .
It seems to have got much worse in the last 4 or 5 years

 

[Pond frog]

No idea why the font changed halfway through that reply

 

[Woody.v8]

I thought @chunkolini was describing Mexican food for a moment.

 

[BrokenBiker]

With hot rolled black there seems to be very little quality control with the steel properties nowadays particularly with thinner stock, I’ve had 6m lengths that are stiff at one end and like soft liquorice the other end . I put it down to cheap Chinese steel . With thin steel if I really need it to be consistent I tend to buy bright stock .
It seems to have got much worse in the last 4 or 5 years

I've noticed similar with flat bar as well, I've had some lengths of 30x3mm and some of it bends and cuts as you would expect, then other lengths have almost cast iron like sparks and doesn't like to be bent cold

 

[Hitch]

Probably just where its such low quality, imported from who knows where.

Merchant bar is pretty much the bottom of the pile quality wise.

 

[Erie Fred]

The tolerances for size on hot rolled are pretty loose.

 

[chunkolini]

As simple as that.
Poor tolerances
Drove me scatty as I had just rebuilt the roller and figured it had gone wrong