Welding 2mm to 10mm steel

[rosinante]

Hi All I have a job on at work where I will have to weld a fan nozzle to a plate in the back of a vacuum furnace[ the fan is 320HP] and the nozzle guides the gas into the impeller from the heat exchanger,the nozzle is 400mm dia spun from mid steel and when centralised will have to be welded to a 10mm thick backplane,I have an inverter type stick welder,Q what rod/current should I use?I should mention that 40%of the existing weld stiches have failed allowing the impeller to foul--- 4 man days labour to access the motor/nozzle so I want to get it right,next Q should I start the arc on the thick part and weave on and off of the thinner part or vice versa, as is pretty obvious I am not a pro welder just the only fitter they have got!!
The pressure is a little daunting as the consequences of it failing can be pretty catastrophic and expensive,thanks for reading

Heres hoping

Cheers
Chris

 

[busa]

Hi All I have a job on at work where I will have to weld a fan nozzle to a plate in the back of a vacuum furnace[ the fan is 320HP] and the nozzle guides the gas into the impeller from the heat exchanger,the nozzle is 400mm dia spun from mid steel and when centralised will have to be welded to a 10mm thick backplane,I have an inverter type stick welder,Q what rod/current should I use?I should mention that 40%of the existing weld stiches have failed allowing the impeller to foul--- 4 man days labour to access the motor/nozzle so I want to get it right,next Q should I start the arc on the thick part and weave on and off of the thinner part or vice versa, as is pretty obvious I am not a pro welder just the only fitter they have got!!
The pressure is a little daunting as the consequences of it failing can be pretty catastrophic and expensive,thanks for reading

Heres hoping

Cheers
Chris

Nobody should be subjected to pressure like that in this day and age. If you think that the job is too much for you or outwith your capabilities then you should tell your employer and advise him to hire professionals to do the work. Remember that in situations like these, if it all goes pearshaped and someone gets hurt, or worse, then the finger of blame will point directly at YOU.

 

[Welderpaul]

Sounds like they are trying to get the job done on the cheap using their own staff (you) rather than paying a welder to do it. If your concerned in any way, tell them you don't want to do it. If it fails, its you that will suffer the consequences.

 

[big ted]

i agree

 

[brightspark]

i agree

is that called when the sh ,,.,.t hits the fan

 

[Douglas]

If the thinner metal is sat on the 10 mm plate the tendency for the thin stuff to blow through will be exacerbated. Even if you set the nozzle in the 10mm plate (so that the exposed edge is the 10mm instead of the 2mm) you are still courting difficulties if your experience is limited.
You don't say whether the article is in position i.e in the downhand, vertical or overhead positions or what MS rods are available?
Your assumption to strike on the thicker material is correct but rather than weave onto the thinner stuff flick forwards and backwards favouring the thicker stuff. I imagine you're concern is that you will blow through - only experience can tell you at what point the temp is so critical that the thin stuff will collapse.
Amps - 50 - 75 depending on position. If downhand I'd probably do it in two. Put one down on the thick stuff in order to build the temp up in it so as to reduce the differentials in dissimilar thicknesses and don't worry if you leave slag holes against the thin stuff, it'll catch where it will. On completion of the first run clean all slag out manually with a sharp edge, not a grinder. Then flick a quick one over the top to seal it.
Not an easy one and I'd agree with previous posts also more info re position and available consumables would be good. If you're still unsure don't do it and ask a welder- I met one once...

Douglas

 

[chap]

Can't answer the questions, but with regards to the work pressure.. if it's not a problam that the furnace may have to come off-line again for the work to be repeated, it won't fail dangerously/expensively (though you elude that it might do) and your time isn't otherwise spoken for, then i don't see a problem with the 'have a go' kind of attitude.
But the flipside is, being a competant technician you are able to recognise when something is beyond your capabilities and so outsource that part of the job. Then the worry is knowing who will do a good job, and getting the boss to pay for it!

 

[cookie munsta]

Rivets? yeah that should do it

 

[brightspark]

im not a welder but using stick run a weld round the 2mm pipe that will build it up to 4mm .then weld to the 10mm plate at the higher amperage . not much chance of blowing through then thats what i normaly do

 

[mike os]

surely easier to mig? even if you have to hire a set the cost is easily offset by the risk of failure

Personally tho if you are not happy doing it get someone who is, the "cost of failure" argument should win the day & I guess it would not be that much to get a pro in.

 

[rosinante]

10mm t0 2mm

Hi Thanks for your replies,as indicated disretion is the better part etc so I have told the gaffer that the job will have to be done by a pro and advice sought from the german manufacturers,
i forgot to add in original post that the 10mm backplane is in 2 halves bolted and welded together and all the welds on the l/h side have cracked,we refitted the motor & impeller [1.2 tonnes] today and there is 3-4mm clearance but when it was accessed initialy there was contact when the motor was turned by hand and large burrs where contact had happend during the quench cycle so distortion is occurring at temp
thanks again guys

good forum this,will try and get some pics so you can se what im on about.
cheers
Chris