Coatings over hot rolled steel

[Kingspeedy2]

My crites sub fram connectors are hot rolled steel.
The mill scale is firmly affixed.And tough to remove.A flapper disk does take it off but is time consuming and difficul to remove evenly without gouging
Sandbalsting would work but is it necessary to remove the scale ?
I was planning on using 2 part epoxy

[lavron]

I can't say it would work but you might try Phosphoric acid like I used for rust clean up, it would be cheap to try.

viewtopic.php?f=23&t=15087

It does etch metal not just remove/convert rust because the spots I had bare were much cleaner after using it.

See Ya,
Mike

[A/FX]

My crites sub fram connectors are hot rolled steel.
The mill scale is firmly affixed.And tough to remove.A flapper disk does take it off but is time consuming and difficul to remove evenly without gouging
Sandbalsting would work but is it necessary to remove the scale ?
I was planning on using 2 part epoxy

Bite the bullet and blast them. You do not have to use sand, a media like iron oxide it will remove the scale and leave a decent finish that will have good “tooth”for your epoxy primer. If you do not want to blast them try a scotch brite type disc for your grinder. They orange color will cut the mill scale but also will remove material if you are not careful. A black disc will not remove material.
Hot roll material is normally less expensive than cold rolled so some places use it to cut costs. I normally fabricate using cold roll.
Jim

[Rocket989]

Huh...my Crites connectors looked OK. I wire brushed ‘em with an angle grinder (the smaller frame rail reinforcements by hand), wiped down with acetone, and primed/painted. You’ll have to Roloc the spots to weld anyway so I wanted something that’d come off easy enough!

[Kingspeedy2]

I had some muriatic acid and that worked like a charm, I rinsed to neutralize the muriatic so they bloomed up instantly.
I then hit them with Eastwoods after blast which is most likely just phosphoric acid and that fixed that.A thorough drying , scuff and a wipe with thinners. should be good to go. Obviously take all necessary precautions with any acid and ensure the area is well ventilated or your up wind, as the reaction off gases quite a bit