# Forum Home Renovation Metalwork & Welding  Trouble with welding certain engine/machinery parts

## PlatypusGardens

Have come across this a few times (most recently just earlier today) when welding (mostly) bearing casings and gears/sprockets.... 
The (mig) welds don't stick, they turn to popcorn and the steel starts "sweating" what I would assume is oil deposits and it smokes and catches fire. 
Eventually after pumping enough heat in to it, it's possible to get a good weld happening. 
Seems to be the case no matter how much you degrease and clean the steel.
It's as if the oil (or whatever) is soaked in to the steel...   :Confused:  
For the most part when this happens I chuck that piece in the bin, but at times I really need THAT part for whatever I'm making.    
So 
What's going on there?   :Unsure:

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## Oldsaltoz

I am no welder but I think any cast iron is stitched not welded? 
That's what they did to an old marine engine I had many years ago, worked well.  
Good luck and fair winds.   :Smilie:

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## PlatypusGardens

For the most part I have had no issues welding cast steel, like bearings etc.  
It's only old parts that present this problem.
Or ones that (presumably) have been submerged in oil and probably got hot....and soaked up some of the oil.....?

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## PlatypusGardens

I guess I'm more interested in whether the steel ACTUALLY soaks the oil up.... 
As it will start to sweat and leech even after thorough degreasing and flap discing back to clean and shiny   :Unsure:

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## Marc

It does near the surface, the space between grains can be big enough for oil molecules to soak in.
heat it up with the oxy and once all the oil comes to the surface you can weld it no problem.

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## PlatypusGardens

Mmm still don't have an oxy mate.....

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## Uncle Bob

Maybe the troublesome steel is oil quenched tempered steel?

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## Marc

Heat beads and a grill. That's hot enough 
PS
for heating you can use a 9k lpg bottle and compressed air. Need an llpg heating nozzle though, not the oxy acetylene nozzle.

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## Uncle Bob

> Heat beads and a grill. That's hot enough 
> PS
> for heating you can use a 9k lpg bottle and compressed air. Need an llpg heating nozzle though, not the oxy acetylene nozzle.

  Or this  :Smilie:

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## Marc

Model 89-3 | The Harris Products Group

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## PlatypusGardens

> It does near the surface, the space between grains can be big enough for oil molecules to soak in.
> heat it up with the oxy and once all the oil comes to the surface you can weld it no problem.

  
Great, so that would explain why it works after a while (and lots of smoke and fire)   :Smilie:

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## Marc

> Great, so that would explain why it works after a while (and lots of smoke and fire)

  Yes, yet most people would tell you that such is not the case and metal can not absorb oil with lots of yada yada

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## PlatypusGardens

> Yes, yet most people would tell you that such is not the case and metal can not absorb oil with lots of yada yada

  
Well I've heard people talk about "case hardening" by heating steel and dunking it in sump oil, so it makes sense.   :Smilie:

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## Marc

That's a different story. Tempering or hardening steel by heating it up and cooling it quickly is done in water or oil depending on the steel. If you want to make a blade, use spring steel and quench in oil and you get a good blade. Quench it in water and it will brake, cooling too fast. other steel with less carbon than 1095 can be tempered in water. The Japanese Katana is tempered in water  
Metal has a crystalline structure and on the surface the voids between crystals are big enough to allow some molecules of oil

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## ringtail

Yep seen it heaps PG. Heat it up and burn that crap out. Maybe get a map gas set up. Cheap and does the job and under $120 with the bigger torch. Fluxcore is not as badly effected by it  :Wink:   But still not good.

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## Random Username

With the gears and sprockets it may also be the case that they are made out of one of the higher alloy steels; I've watched a weld bead peel off a 'ground engaging tool' (dozer tooth) like it was slag from an arc run.  Heating the tooth up overcame the issue. 
However, some gears these days are make by sintering (metal dust plus heat plus pressure) and I can imagine them working a bit like an oil sponge...

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## Oldsaltoz

Cast iron is particularly porous, and cast iron keels on a boat are a nightmare to prevent them corroding. I have must have spent hundreds of hours working on them over the years. 
I had one with a pocket of sand in it, just a very thin layer of steel covering it, exposed when sand blasting to to a class 2.5, shiny grey and no shadows
.
It's also prone to flash rusting and will start turning brown after just a few minutes. 
Ask any sailor who ever a cast iron keel.   :Frown:  
Good luck and fair winds.  :Smilie:

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## PlatypusGardens

All interesting stuff, guys.   :2thumbsup:   
I had one bearing ring a while back that just would not weld at all.
There was no oil leeching or anything, and the welds, while they looked ok, just cracked off the surface immediately after. 
Might have been some alloy mixture then?   :Confused:

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## Marc

Some very hard steel is not weldable cold. Much less with soft MIG wire. 
You can get it red hot and anneal it or heat it up and weld it hot and bury it in dry sand to cool down slowly. Either way it will not be a structural weld or you need to use special steel rods and a stick welder.

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## lazydays

FYI. Case hardening is slightly different and has it advantages/disadvantages. Steel must have a carbon content of greater than .8% (or .08% carbon...I forget) to have the ability to be heat treated. i.e. heated up to about 780C and then quenched in water or oil depending on alloy composition and then annealed back to required hardness.
Case hardening is done on mild steel which cannot be normally hardened. Pack a carbon rich material such as charcoal around the object, heat to about 800C and the longer you leave it the greater the penetration of carbon. Let object cool naturally.
re-heat object to 780C and quench. It will have a rock hard wear proof surface but the attributes of some "flexibilty and torque" on the inside. Also a cheap way to harden steel using scarp material. It's main attributes are surface wearability and not much good for tools as after a few sharpenings you are back to mild steel.
Interesting when you break a sample piece open you can easily see the finer grain structure and penetration of carbon to measure depth. We always put a sample piece in and used that to measure pentration...I think a couple of hours gave about 2 or 3mm but that was in a life a long time ago.

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