Forge Weld: Setting on Wood Block?

[Andy98]

Hi, continuing my practice of vicarious blacksmithing, I came across,this video:

In the video, the blacksmith sets the initial weld with the workpeice resting on a wood block (happens in the first minute).

I assumed this was for stability, but thinking about it more (while watching Mark Aspery's scarf welding videos) it occured to me that the wood would also help insulate the work piece from the heat-stealing anvil. Further, since that wood is burning it might actually heat the metal  and reduce oxidization.

Is that a crazy thought? Has anyone ever seen this approach before who could explain it?

[Will W.]

I am no expert, but my assumption is that it may help with heat transfer. The wood is not as cold as the anvil, so less heat would be robbed, or it would steal it more slowly I guess I should say. The idea that the burning wood would heat the metal is a fallacy however, wood burns somewhere between 400-500 degrees F, iirc, and the steel has to be up to around 2000 degrees F to weld, again iirc (this also depends on alloy.) The wood, even when it's on fire, it still going to suck heat out of the metal. It's possible, I suppose, that it may also help reduce oxidation, since the oxygen in the ambient air may be drawn to the chemical reaction of the burning wood rather than to the steel, but that I do not know. 

[jlpservicesinc]

Hammering on the wood would help to hold the pieces more closely together while you set the weld vs on the flat of the anvil which will make each piece want to spread or move apart the rods not directly below one another.. ..  You could do the same thing in a swage block or a stump.. 

[Andy98]

12 hours ago, Will W. said:

The idea that the burning wood would heat the metal is a fallacy however, wood burns somewhere between 400-500 degrees F

I think that is the autoignition temperature, not the flame temperature.

Per this link the flame temperature in the "continuous" part of the flame is around 1500F and Wikipedia states it as ~1800F.

So not welding heats, but surely hot enough to significantly reduce the rate of cooling. Combined with the insulation effect of the wood, and the helpful pressure distribution the wood would give when you land the tacking blows, that seems useful... 

[David R.]

Interesting...., I could see the obvious advantage being reduction in distortion of the pieces as well as the additional advantage of the wood being an insulator. 

End grain stump works amazingly well as swedge for dishing etc. so I will have to give it a try.

Is this done with a wood block on anvil or a seperate block? What is the set up?

[Andy98]

30 minutes ago, David R. said:

Is this done with a wood block on anvil or a seperate block? What is the set up?

All I know is what's in the video. He uses a thick wood board placed on his anvil, and just for the initial setting blows. Second heat onward are directly on the anvil or powerhammer.

He was using it for welding an oddly shaped billet made up of many pieces of cable, hence my initial assumption it was for stability. But he also does it when setting the welds on more uniform billets as well.

Most of the comments on the video are in, I think, Russian - so I couldn't gleen anything there (admittedly I didn't try that hard). I might comment and see if he replies.