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Cold Roll vs Hot Rolled Finishes

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  • Bob the Welder
    replied
    Dave, I understand the need for down and dirty on some occasions. Been there and done that plenty of times. But there is a time and place for that and it seems too many get the idea that all that is needed is a cursory swipe with a wire brush and they are good to go. Then you get the pictures of welds that look like swiss cheese and a question about 'what happened?'.

    For the beginners and the more advanced alike, it's important to realize that good welds are made in part by preparation and not just by technique. One of those being a clean weld surface.

    Interestingly, I found out from a friend that trying to TIG plasma cut steel without grinding the edge results in lots of porosity.
    That should be a given, something that everyone should know and understand. The OP asked if anything besides normal cleaning and fitup was needed for welding. To me that means a clean weld joint (no rust, slag, paint, oil, etc.) and no gaps in an open root beyond 5/32". After that a backer bar is needed. Also, sufficient room is required to deposit weld without any slag entrapment in a multi-pass weld.

    I'm not pointing fingers or trying to put anyone down. Just trying to point out the importance of good work habits. Does it take longer? You bet. Is it worth it? You bet.

    And on a lighter note. MERRY CHRISTMAS to everyone!

    Bob.

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  • whateg0
    replied
    Bob,

    I don't think that not grinding every weld down to bare shiny steel is really a shortcut in all cases. The fact is that sometimes it's just not practical to do so. Take a baler in the middle of the field, for example. First, it isn't always possible to get a grinder into the spot that needs repair. Second, it isn't always necessary, especially with FC or stick. That's not to say that an effort shouldn't be made to remove loose scale and dirt or grease. IMHO, it's like taking the time to cut pieces to fit perfectly versus having a small, possibly inconsistent gap that can be easily filled with filler. A person could take the 20 minutes to make it fit perfectly, or they could cut to be close and git-r-done in 3 minutes and be on their way. There are absolutely situations that dictate that everything be done to the Nth degree, but most hobbiest aren't working on bridges, ships, or spacecraft.

    Dave

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  • Bob the Welder
    replied
    Every welder should have plenty of rocks and tiger paws to prep their weld joints. As metarinka says, in the professional world that's what is expected a, properly prepped joint. That's one of the requirements for making high quality welds on a consistent basis.

    I don't quite understand why people will make the commitment to spend large sums of money on nice setups and then take shortcuts that can lead to less than satisfactory results. My Dad always taught me to do it right the first time and to take pride in your work.

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  • Lou N
    replied
    Thanks everyone. I will do a better prep job from here on out; a flap wheel is in my future! Have a great Holiday all!

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  • metarinka
    replied
    In the professional world I make all my welders grind back 3" in all directions (code books say 2") to bright metal. Regardless of process. Although this is especially true for GTAW.

    for cold rolled, personally I tap them with a flap wheel disk, hit them with some sand paper, or degrease it if it's really oily.

    For hot rolled, at the bare minimum I tap them with a grinder to get the mill scale off or hit them with a wire wheel brush. stick and GMAW will take a little more contamination than gtaw, but why test it? mill scale will give you could roll and lack of fusion and affect penetration.

    It's like putting oil on a pan, things won't stick as well to the mill scale.

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  • whateg0
    replied
    I don't always grind mill scale off for GMAW. For GTAW, though, it is a must. Interestingly, I found out from a friend that trying to TIG plasma cut steel without grinding the edge results in lots of porosity.

    Dave

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  • fjk
    replied
    Originally posted by Lou N View Post
    Thanks for the replies gents. So would I be correct that no special preparation is necessary before welding other than normal cleaning and fit up when dealing with either cold or hot rolled steel?
    Depends on what you mean by special

    For HRS you really want to get as much of the gunk
    off as you can. In a perfect world, you get it down to nice
    bright and shiny bare metal. But the world isn't perfect.

    MIG gets an upset tummy on gunk.
    Stick eats up gunk and spits out the pieces.
    I am not a TIGster, so one of the other guys would have to chime in on that.

    Frank

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  • Bob the Welder
    replied
    In a nutshell, yes.

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  • Lou N
    replied
    Thanks for the replies gents. So would I be correct that no special preparation is necessary before welding other than normal cleaning and fit up when dealing with either cold or hot rolled steel?

    Lou

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  • Bob the Welder
    replied
    Check these out.

    http://en.wikipedia.org/wiki/Rolling_(metalworking)

    http://www.spaco.org/hrvscr.htm

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  • metarinka
    replied
    Cold rolled steel will have a a very uniform finish and uniform dimensions. It looks much more silvery and shiney as opposed to hot rolled steel.

    hot rolled steel will have a grey/black coating of powdery mill scale that will stain everything it touches. Also the dimensional tolerances will generally be much poorer.

    On top of that there's various standard finishes, brushed, polished, mirror polish etc that are called out usually for architectural applications. Sometimes materials is pickled or primed to prevent flash rust.

    Don't quote me on this, but it was my understanding that most structural sections were hot rolled, because you simply can't cold roll material to I beams and C channels and the likes. However material can be hot formed to near net shape, then cold rolled for the final pass to get good dimensions and surface finish without the price and hassle of repeated cold forming.

    Leave a comment:


  • Lou N
    started a topic Cold Roll vs Hot Rolled Finishes

    Cold Roll vs Hot Rolled Finishes

    All,

    Are structural shapes (square tubing for example) usually cold rolled or hot rolled?

    I have some 1" square tubing (16g) and it has a darkish grey finish on it (not galvanized) that appears to keep it from rusting. Is that the result of the pickling process and what should be done (if anything) to prepare it for welding?

    I also have some flat steel bar stock that is marked weldable steel, but it is lighter in color. Is that because it was cold rolled?

    Thanks,
    Lou
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