Welding ss topwork, how would you do it?

  1. BRODTuning Member

    Messages:
    128
    south wales
    Hi all, im 16 and basically an unofficial apprentice (been working for this company for three weeks now)...we make bespoke stainless products 99% of which are catering related , canopies, serverys, hot cuboards, sinks and shelves etc. Even though i havent been working there long, im welding such things as 1.2mm 30x30 box frames, panels onto frames, cappers, the end on topwork etc. near enough everything that we do day in day out to a decent standard, obviously a long way to go to get to the level id like! but im making good progress :) .....However, today i spoke to two of the fabricators that work there about how they weld topwork on hot cuboards and units etc. together on site. This basically involves preparing the joint and welding the two work surfaces together with as little distortion as possible. The one guy said his method was to weld roughly 50mm then cool it with the air off a grinder or an airline if theres one available on site. The other (whos the one that ends up with the job of welding the joint 90% of the time) said he places lots of small tacks right alone the joint then welds it all in one go then cools afterwards. I would have thought that would give massive distorion since you would be putting large amounts of heat into typically 1.5mm 304 stainless sheet (we often use 1.2mm and 2.0mm also) BUT this guys work has been said to have had the best results. He basically described it as the sheet all being heated (expanded) then cooled (contracted) in roughly the same sequence where as he described the other guys method as heating then cooling then heating then cooling which obviously expands and contracts the metal a larger amount of times as he only welds roughly 50/70mm each time. He said something like, the first time it expands and lifts, the second it sinks or becomes brittle then the third it looses alot of its properties or something like that (dont quote me, these long hours get to you! :whistle: ) It did make sense in the way he said it but id like to know your opinions! If this was your job and your name on the line, how would you go about doing it? dont forget that this joint is then ground back and polished to a dull finish so that will also put in a hell of alot of heat too! if someone would talk through how you would do the job, that would be great!
    Thanks for reading :)
    Brad.
     
  2. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,472
    Location:
    East Yorkshire
    Well for one the "other" guy MUST be tacking the two pieces up. If he didn't as soon as he started welding it would twist in all directions. Hopefully the two would mate-up perfectly, once tacked up every 20mm. If this is the case I would do it in one go, autogenously, done correctly you put very little heat into the piece therefore stopping the warp, with little if no sugaring on the back.

    It's not something you can do straight away, it took me a long time to master, and I'm still far from perfect.
     
  3. hotrodder Member

    Messages:
    4,587
    SE England
    What Shox said. Some of the explanation the guys gave you for why they do things the way they do are a bit meh. Stainless is a poor conductor of heat and has a high coefficient of expansion... unlike ally the heat stays pretty local to the weld, the heated area also expands and contracts a lot more than carbon steel does and the welds themselves will shrink more

    The guy that's stitching it together and quenching runs... as Shox said you'd still need lots of tacks to stop the edges moving around like -_ as the weld progesses. Backstepping the welds generally makes less of a mess than starting at one end and working across. Quenching won't stop distortion it'll just keep it more localised. As the weld progresses there's less and less 'places' for it to move without buckling... that description is a bit meh too... it's hard to describe but basically it can change the way it moves which is probably what the 'one shot' guy was getting at with his even heating and cooling explanation.
    Putting too much heat into it/dithering around when doing it in one shot can make a right mess though. It's one of the reasons i prefer metal shaping- you can place welds in areas with geometry that resists distortion and/or are easier to correct than large, flat expanses

    The lifting/sinking thing can and does definately happen. The brittleness/losing it's properties not so much although it depends on how hot you get things while welding. Lots of stop/starts and quenching austenitic stainless won't damage it, welding too hot/slow and allowing it to 'coke' up (sugar) will

    Oh, one last thing. Paragraphs :D (waits for someone to point out my various grammatical and spieling errors :laughing:)
     
  4. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,472
    Location:
    East Yorkshire
    As ever Hotrodder explains it far better than me.

    What I didn't say is I used to build Extraction canopies for commercial kitchens, we did no welding on site, everything was done in controlled workshop conditions, so that we could minimise such things as warpage to panels, but as HR rightly said design is all important. On the occasions I had to go on site for the most part I found worktops that required welding on site were poorly designed. Anyway that is by the by.

    What I was going to add is, if you are going to use the step back method, autogenously, you need to add some rod at the end of each stop, other wise the weld will sink and it will be very hard to restart without burning through the problem you then have is this can pull the sheet. Hence the reason why I prefer to weld in a oner


    Oh and I found this site a while back Free English Grammer Lessons
     
  5. BRODTuning Member

    Messages:
    128
    south wales
    I never was very good with paragraphs, anyhow. Im not planning on doing this for a long time obviously as im still green to this work (not that its my decision anyway). I was more interested in what is the more reccomended way that is more likely to give good results. We couldnt make the work surface in one go in the workshop anyway as it was over 12 meters long so obviously wouldnt have been able to transport it to site. So it had to be welded there rather than in the workshop. Whenever possible they are done in the workshop but obviously with something of this size it wasnt do-able. Sorry for missing out the first part but yes both of them tack up but the 'one shot' guy said he does alot more tacks. He described the other guys method to me as putting tension in the metal then when its cleaned off and polished, it can sometimes crack which is obviously the last thing you want to happen when you are a few hundred miles away from the shop. Where as with his method this hasnt happened (according to him).

    I guess its what works best for you. Thanks for the advice though, ill try and put it into practice :)
    Brad.
     
  6. Paul.

    Paul. Moderator Staff Member

    Messages:
    6,511
    Location:
    Northampton. UK
    Not a worktop but the same problem, a last minute change of design meant I had to butt weld the tongue on this sorting tray the other day, Its bigger than it looks, the outlet is 400mm wide and has to be pretty much invisible from both sides, used the lots of tacks, short runs and air quenching with a blowgun method, with it clamped to a lump of copper bar, first from one side then turned it over and welded the back.
     
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  7. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    15,472
    Location:
    East Yorkshire
    What's the thickness? Paul
     
  8. Hitch

    Hitch Moderator Staff Member

    Messages:
    12,278
    Somerset
    I had to weld a worktop in situ back along, sparkys and builders had removed it while the main building works were going on, then I had the job of rejoining it.
    Lots and lots of tacks, as with anything thin stainless. I normally go about 15-20mm apart.
    Then a bit here and there to minimalise heat as far as possible.

    Think i wedged a bit of alloy flat bar underneath it from memory.

    Bit of a gash job really, weld it up as neat as possible, then flap disc the weld back and grain up a line through it.
    Never going to be nice, it was cut out with a 9", and put back in and screwed inplace without cleaning the edges of straightening the cuts to get a good fit up.

    More of a how not, than a how too.
     
  9. gavuk

    gavuk artful-bodger

    Messages:
    2,951
    uk wiltshire
    I used to make a lot of guards and drawers etc for the food industry.

    Mostly 1.6mm and mirror polished,again tacked at 20mm intervals, then gaps tapped close then a fast autogenous run .
     
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  10. Paul.

    Paul. Moderator Staff Member

    Messages:
    6,511
    Location:
    Northampton. UK
    Its 1.5mm,
     
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