Thursday, May 24, 2012

Forging 'the custard'

 Edited from my ongoing on  Don Fogg's Bladesmithing Forum

Darrel so when you say 'weld in all the edges'... do you mean basically turning it on it's side and hammering down all the little bits at welding heat?   I'm assuming this is easier with lower carbon steel and iron.  On my very high carbon stuff.. those little bits just fall off.  

I would most certainly *not* hold my working methods up as the ideal!

That being said, I'm just coming off a two month research / learning project called 'Bloom to Bar'. So for while there all I was doing in the shop was working up some of my big pile of blooms (!)
So, that being said, take a look at :
'A Typical Work Session' (earlier on Bloom 2 Bar)

Jesus Hernandez also has a good visual tutorial over on his web site.

I have also seen on this forum some good advice given by Lee Sauder on this same topic.

Blooms have a structure that Lee describes as 'like a custard' - think of a lemon meringue, turned upside down.
The centre is a hard 'nut' of iron, often quite dense, with a spongy layer, often with a lot of air spaces and more slag included around the outside. As you might guess, a larger bloom might be cut apart, so more like a wedge of pie than the whole thing like you see on a small bloom.

(There is a variation in carbon content within a single bloom as well. Lets just leave that one. If anything, this carbon variation exaggerates the effects.)

Of course, the two different densities of metal move at different rates. That's one reason a press, squeezing in one direction does work more effectively than hand tools. The raw size of the mass also works against anyone attempting this process working alone. With excellent skill and co-ordination between a master hand and striker, of course the compaction process can be carried out by hand. (Watch Lee and Mike McCarthy work some time!)

So your first step is just pressing downwards at welding heat, collapsing the air spaces of the outside 'meringue' and forcing them on to the hard nut in the centre.
This does help on the edges however, which remain ragged. I have had some luck placing the then flat disk on its edge and pressing in / down. Its a tall thin shape, with soft edges, so the press tends to slide it sideways and I certainly find that process hard to control. Also the press works in a flat plane, and most often the bloom disk is round or oval.

Taken together, I had found it just as effective to hand hammer the edges in. I would place the disk flat on the anvil, then lean way over so I can fire blows almost dead horizontal from the far side of the anvil back towards the disk and my tong hand. This also allows you to both heat and forge on section of the bloom disk at a time.

Clear as mud?

Technically, the Bloom 2 Bar Project ended (at its most generous) May 15.
I will however, continue to cross post items from my regular blog (Hammered Out Bits) here, for topics directly related to the theme of bloom into bar - and beyond.

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February 15 - May 15, 2012 : Supported by a Crafts Projects - Creation and Development Grant

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