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  1. #1
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    Default Pic's of an old job, Considering doing another new job

    Hey guys me again more questions to ask, i done this live bait tank maybe 1 year ago and it was a real bummer with the outcome because i could not fine tune my tig alloy technique but of late i have been looking around online at aluminium products and a lot of people who manufacturer products out of aluminium have there welds ground down it doesn't look all that ascetically pleasing but it did put into my mind that my welds may be ok in cases like this that are not structural

    these pictures are a live bait tank i think i may have done a build on here but now knowing people grind down there welds i will actually show all my welds as i can grind them down ha

    can someone give me pointers on where i am going wrong? i ran one really nice bead on this whole piece and that bead were along a piece of alloy i never cut it was the side of the sheet so this leaves me to believe maybe i am the one contaminating my alloy sheet

    my welds came out with porosity sand looking welds, i am almost there as for tig welding aluminium i just need to break that boundary

    the next project i am looking at i have 1200x1200mm sheet of 4mm alloy I'm looking at building a fuel tank for my boat which will be 300x140x1200mm but being fuel i need to get my welding sorted and have no leaks

    if u guys can offer some pointers on where im going wrong would be great, this job pictured i had laid a wooden pallet on the grass than the sheet of alloy on the pallet than cut it with a circular saw with the stock steel blade which is now rusting
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  2. #2
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    Default

    Some of those look fine in areas.

    It's worth noting that with TIG, you can go back and re-melt a weld, so some of those with pinholes or porosity could probably be fixed by running the torch along them again.

  3. #3
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    Yeah its the pepper in the weld that is getting me Rusty do u think i was to high or low on AC frequency?

  4. #4
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    Aluminium has to be really clean to weld it well, otherwise the welds get contaminated and things go down hill. Get yourself a bottle of acetone and at the very least clean the sheet where you are going to weld it. Some of those welds look like you have run straight over dirt/ muck on the sheet. I would be guessing that is where some of the contamination is coming from. AC frequency will help with penetration/ spread of weld but does not really interact with contamination.

    Michael

  5. #5
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    Hey Michael do u think when i was cutting the aluminium sheet the dirt possibly kicked up from the saw because this was a brand new sheet from the factory when i weld6ed this bait tank, it has been sitting around for some time now so its dirty now

    The job i want to do next is a pretty large job for me anyway as it will be around 6.5 meters of tig weld/bead unless i build a 1.4m sheet metal bender

  6. #6
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    Contamination could be from anywhere, if it sat on an oily spot, a bit of mud, anything even metal filings will do it.
    Depending on the cause of the porosity, it may not come out with rewelding, you may need to grind it out, and start again.
    When you cut/grind aluminium keep the discs seperate from any other metal discs, as the metal dust in the discs WILL contaminate the aluminium, leading to porosity, and rust spots!!!
    Making a fuel tank is NOT a simple thing, I've seen proffesionaly made tanks give problems. If it were me, I'd get a place with a folder to bend them up rather than weld the edges.
    Distortion and stresses built into a tank leads to problems. Even baffles in the incorrect place will cause problems also.
    When you decide to make your tank, I suggest that you post a drawing/sketch on here for comment, your layout of the flat sheet, proposed bends, baffle placement, design of the baffle, pickup point, breather and filler points, it'll save you some headaches in the long term. I used to build fuel tanks for 4WD vehicles and have seen many a fault in the designs.
    If you don't want to discuss this openly PM me for my email address,
    Kryn
    To grow old is mandatory, growing up is optional.

  7. #7
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    Thanks KBs i wasnt really going with a baffle as the tank is only around 50 litres its going in a 18 foot boat if a baffle is needed that shouldnt be a big problem

    I'll try draw something up tomorrow

    The saw i use is a circular saw i have used it for wood before so that may be the contamination

  8. #8
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    Quote Originally Posted by gazza2009au View Post
    Hey Michael do u think when i was cutting the aluminium sheet the dirt possibly kicked up from the saw because this was a brand new sheet from the factory when i weld6ed this bait tank, it has been sitting around for some time now so its dirty now
    Looking at the picture
    004.jpg
    That Al is not clean enough to weld - it has to look like it is brand new & shiny. For critical jobs it is cleaned with a Stainless steel wire brush (must be non-ferrous) and then wiped over with solvent (like acetone) to remove dirt, grease and oil. If the solvent leaves a residue then it is not suitable.

    One of the best hints I ever got for welding Al was to heat it up until it is ready to melt then jam the filler in - but if it is not clean then the Al does not flow so all you get is a big blobby buildup of filler. That is what you can see by the dirty patch on the left edge. Towards the right the weld bead looks better.

    Other critical things are the amount of heat used - if you don't have things hot enough then they won't flow, and the fit up is also critical. TIG is brilliant at bridging gaps but again, tends to make blobby welds and puts extra heat in. The joint gap needs to be small and uniform.

    For cutting you are better off with mechanical cuts rather than grinder discs. They tend to smear the metal and are not as clean as a sheared cut. You may be better off getting a sheet metal place to cut your sheet for you rather than DIY.

    As for making a fuel tank, it is the last type of project I would think suitable for someone still learning the processes. Fuel will seep through pin holes and once it does, you have to industrially steam clean before you can reweld. Therefore your welds have to be good straight out of the box.

    Michael

  9. #9
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    That's a good point - while I mentioned you can re-weld a TIG joint, if a petrol tank ends up having a leak, fixing a bad weld becomes a much more challenging task due to the risk of explosion if the tank is not prepared correctly.

  10. #10
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    That tank was brand new alloy when i welded it it has been sitting around in all weather for a year or two i never asked about the welds on it untill now because i thought it were not good enough

    i was going to fill the tank with water and let it sit on the shed cement floor to look for leaks untill i am 100% sure its sealed before putting petrol in it

  11. #11
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    You would be better off sealing it, applying a little bit of air pressure to it (maybe 5 to 10psi?) and then watch for a pressure drop over several hours. You may also have to run around with some soapy water.

    I did notice that you said you started off with clean sheet but I used the dirt as place markers as the smudges just happened to sit near the areas of interest.

    Michael

  12. #12
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    Michael i never even thought about filling it with air that would be better than filling with water, i will draw up a sketch now i forgot about it earlier

  13. #13
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    Just watch the pressure. Water is good because being (mainly) in-compressible, if something bursts there is not much stored energy there. Air on the other hand compresses and so could go bang in a big way if over-pressurised. However, once the water is there, you then run into problems with it getting into pinholes etc and contaminating welds if they are not perfect.

    Michael

  14. #14
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    I was planning on just keeping it very basic 120cm wide, 14cm high, 30cm depth
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  15. #15
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    As you're making the tank 1200 long, I'd definetly put in 2 baffles. That is a fair amount of fuel to be sloshing around, either on the road or the sea.
    To make your baffles, put a fold on all 4 sides approx 25mm long, your corners will need to be trimmed, I'd look at 40X40 on all corners, after the corners are folded, this will allow fuel to quickly get in and out, yet enough to slow down the sloshing effect. Weld the baffles on the folded flat section not on the bent side, will only need about 3 X 25 mm long on the 30cm side and 1 X 14cm side, if you can't get to weld the top section on the baffles, drill 4 X 12mm diam holes close to the ends and evenly spaced for the other 2, and plug weld the baffle in place.
    You could also fold your ends the same way, so that your folds are inwards, and will have something to weld to, rather than a butt joint, this is a lap joint.
    Put your filling point at the highest point in the boat, and your outlet/pickup at the lowest point in the boat, so you don't get an airlock.
    For the outlet/pickup you don't really want it right at the bottom, that's where water/condensation will collect, and you won't want that 40NM out at sea???? Easiest way to do the outlet is to weld a piece of 12mm thick aluminium in the area, where you want it, then drill and tap to suit a 1/4" or 3/8" BSP to take a barbed nipple. Don't weld in a piece of tube for the outlet, as sometimes fatigue can cause problems.
    I'd also fit a water trap device, set up so that any fuel will NOT spill into the bilge area when draining it.
    Hope this helps,
    Kryn
    To grow old is mandatory, growing up is optional.

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