Welding or Brazing

Discussion in 'American RV's' started by American Dream, Aug 13, 2008.

  1. American Dream

    American Dream Read Only Funster

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    Hi

    Has anyone got experience of repairing Cast Iron?

    I seem to remember that it could be done...

    Can you weld cast iron with special flux/rods or is brazing better?
     
  2. dazzer

    dazzer Read Only Funster

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    Welding cast is possible but is very hard to do and you need to have a forge/kiln to get the piece you are repairing red hot for the actual welding to be done, the welded piece is then cooled down very slowly over a number of hours or even days :Eeek: to prevent cracking of the newly welded area.

    This really is a job for a specialist and is very expensive with no guarantee of success. In actual fact there is a much higher chance of the repair failing during the cooling process.:cry:

    If i were you id buy a new part and be sure it will work :Sad:
     
  3. reader

    reader Deleted User

    I will back up what Dazzer says, you can weld cast iron with with Manual arc or Gas Processes, but it does need preheating and possibly post heating to control the cooling rate. There is a technique which needs to be followed. If it is important ie engine block/gearbox casing etc please dont attempt yourself, long term its cheaper to take to a specialist, and make sure they can do cast iron
     
  4. American Dream

    American Dream Read Only Funster

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    iF only that were possible Dazzer.It is 29 years old!!!!

    Saying that, I MAY just have found one.....:Cool:
     
  5. dazzer

    dazzer Read Only Funster

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    Dont see what the problem is Steve :Eeek: im 39 and can walk into any hospital and buy a new knee/hip/elbow etc :Rofl1::Rofl1:
     
  6. Geo

    Geo Trader - Funster

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    And its broke already, check your Warranty:thumb:
     
  7. olley

    olley Funster

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    Hi we used to Braze cast iron quite successfully, but it depends what the item is being used for. Another method we used on presses was metal stitching but thats no good if it needs to be water tight.

    Olley
     
  8. andyman

    andyman Read Only Funster

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    Cast iron is welded with nickle welding rods, so be in for a shock at the cost of the rods.
     
  9. American Dream

    American Dream Read Only Funster

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    We brazed a cast piece some years ago and it proves to be a VERY good heatsink.:Doh:

    Exhaust gases.
     
  10. madbluemad

    madbluemad

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    The welding of cast iron has been notoriously called a "black art". Individual castings of equivalent types can vary in response to welding, and so the details of the procedure are considered critical by experienced practitioners.

    Most castings are produced to net shape, so welding is usualy for repair and maintenance rather than fabrication.

    The two commonest types of cast iron have around 3%C and 2%Si.

    Flake graphite grey iron varies in quality and impurity content, with relatively low strength and ductility.

    Spheroidal graphite(SG), Nodular or ductile iron is treated with magnesium, has fewer impurities, superior mechanichal properties, and more reliable weldability.

    Electrodes based on pure nickel and nickel-iron alloys are most widley used. Electrode flux coverings are of a basic type plus graphite to give a weld deposit deoxidised and saturated with carbon. This mimics some of the characteristics of cast iron but is non-hardenable and easily machined.

    Another group, high alloy austenitic irons (Ni-Resist types) are also produced in flake and SG grades. Electrodes of the Ni Fe type are used because matching weld metal is to hard. Preheat of around 300-350°C is required for the flake graphite grades, but for SG grades buttering at low temperature is preferred to avoid HAZ hot cracking.

    Martensitic cast iron (Ni-Hard Types) and the various white irons are generally considered too crack-sensitive or brittle to be welded satisfactorily.

    If you have an engine block that has to be repaired or replaced you could try the repair but you need to know what your doing.

    Excavate the area to be repaired, I assume its a crack, clean the excavated area and the area surrounding it taking care not to introduce any friction heat. Preheat to 150°C.

    Use a METRODE SOFT FLOW Ni, 2.5mm Manual Metal Arc Electrode on Elctrode DC +VE or AC with an Open Circut Voltage of 50V minimum 60 to 80amps.

    Butter the prepared area to be repared. This will give you a ductile and consumable friendly area. Complete the weld using light stringer beads. Do not deposit heavy beads of weld metal or weave the electrode from side to side.

    Once completed allow the casting to cool slowly under a thermal blanket. If the casting needs to be machined make sure that you examine the weld using a Magnetic Particle Inspection or Eddy Current Inspection Method.

    Its expensive, there's no guarantee but thats the way its done.


    Jim:Smile:
     
    Last edited: Aug 13, 2008
  11. American Dream

    American Dream Read Only Funster

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    Cheers Jim,

    I am concerned that the welding process MAY introduce distortion in the casting causing problems afterwards.

    Looking into possibly sourcing another part.:Eeek:
     
  12. madbluemad

    madbluemad

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    I doubt that distortion would be an issue however dependant upon what it is that your trying to repair, its size, its value and the nature of the repair a new or new to you part is the way that I would go.

    Jim :Smile:
     
  13. American Dream

    American Dream Read Only Funster

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    Cheers Jim.:thumb:
     
  14. Diabalo

    Diabalo Funster

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    As an ex welder some cast iron can be repaired successfully. I used to do a lot of it with either Gas or electric arc. It is extreemly dificult to do but done correctly it works , but the suuccess will depend on several factors, size of crack thickness of metal loading and stress points etc.
    The key thing is preperation, with a crack it would be veed out past the end of the crack to an angle depending on material thickness. Warm everything up then build up the vee trying not to get everything too hot. Once completed let it cool down slowly usually over night in an oven or sand pit. I also used to planish the weld to relieve any built up stress once cooled.

    Metal stitching does work for some repairs, I have seen it done on high pressure pumps and they have not leaked.

    As for brazing, I do not think it a good idea for anything that gets hot and cold as brass and cast iron will expand at different rates and could lead to another faliure
     
  15. olley

    olley Funster

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    Hi Diabalo, I stand corrected, my experience was only on joining presses and I just assumed it wouldn't be water tight, likewise with the brazing and it was just over 30 years ago when I was working as a maintenance fitter for "Manganese and Bronze" :Rofl1:

    Olley
     
  16. ruffingitsmoothly

    ruffingitsmoothly Read Only Funster

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    Hi Olley

    Years ago I had a Scania truck which had a cracked block behind the fuel pump it had been repaired after a fashion by welding but was still leaking!

    I contacted a company and removed the fuel pump for access, an old fellow came down and over the course of the day he removed a section of the water jacket and proceeded to stitch in a plate he made he just drilled tapped and screwed in threaded bar then went back over again overlapping until there was no crack to be seen!

    That lasted and never leaked atall for at least 4 years and I dare say alot longer for the new owner of the truck.

    Regards Pat
     
  17. olley

    olley Funster

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    Hi RIS I used to work on rollatrucks they had 6 cylinder scania engines, very reliable, they had centrifugal oil filters never understood why other manufacturer's didn't use them.

    Olley
     
  18. American Dream

    American Dream Read Only Funster

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    Thanks Dane.

    I have taken a closer look and it appears that someone has already had an attempt to repair this.:Doh:

    Looks like they have brazed and it's worked loose due to the different expansion /contraction rates you mention.

    I'll try Rock.They might just be able to get one.:thumb:

    Cheers to all for the advice.:BigGrin:
     
  19. American Dream

    American Dream Read Only Funster

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    Thanks Andyman. I think I'll try to source new (old stock) if possible now.:cry:
     
  20. American Dream

    American Dream Read Only Funster

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    So ....You're suggesting I take the old girl to a DODGEy Hospital then Dazzer.:Rofl1:
     

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