Hey everybody, what is going on?
I'm Roger in Technology and welcome to Thing of the Week for the twelfth of May 2015
Mankinds mastery of fire was once a turning point of civilisation. Controlling and maintaining fire led us from the stone age to the bronze age which gave us access to all manner of new tools, toys and technology. Thousands of years later, we are able to casually and recreationally create a foundry from household materials, standing on the shoulders of giants that have forged a path before us.
This week we'll be talking about my new foundry, started in a previous article here:
I took the time to test my foundry fire, using a piece of 3/8 inch roundbar as a thermometer and the results were as good as I could have hoped. And possibly better.
There are a few differences between this bucket foundry and the original build. I wasn't happy with the shallow depth of the first build so in the intervening week I poured a second layer to nearly fill the bucket with refractory concrete and get a good seven or eight inch depth to snugly fit my graphite crucible. For safety reasons this meant the foundry was out of action for a weekend while it cured, but it'll cleanly fit my 155mm crucible.
The mix was the same 50/50 sand and plaster of paris and poured in the top to fill out the height. The sand was less compact than the first batch so the colour is a fraction paler but it's the same colour once blackened with fire and colour coordination wasn't on the feature set.
Air Blast
The bucket forge here is powered by a cheap hairdrier from the supermarket it's on a low setting, and a good six inches from the air intake to keep it cool. There is no ducting - the picture was taken live with the setup. With some ducting I could blast the air right into the fuel and get a much better burn so I think the airflow could be improved.
The reliance on electricity isn't a huge problem but one I'm going to move away from. I'm estimating around 30-40 cubic feet per minute and fifty at the tops. For under ten English pounds I can buy an eighty cfm brushless 12v dc fan and power it from a peltier thermoelectric generator using the heat of the fire to fan its own flames. I'm also considering steam power, which would be a nice metalwork project.
Sparky
Astute observers will notice there are a lot of sparks in the picture. I chose this picture simply because sparks look cool and I'm embarrassed to admit it - but they are just from some kindling I added. Most of the fuel was clean, which overall is a requirement for a hot burn. The fuel here was cheap lump-wood charcoal from a supermarket and it's quite good enough for a home foundry. It was a clean, hot, almost smokeless burn.
Off camera, two fourteen litre buckets of water stood by quench any cinders that ignited the dry recently cut grass and woodchips left from the afternoons whittling. Safety first people.
Temperatures reached
This 3/8 inch round-bar reached a good yellow colour and in the region of 1100 to 1200 degrees C, that's something like 2000 to 2100 degrees F and well hot enough for working with. From its softness I've no doubt it was that hot.
My goal was to reach a steady nine-fifty degrees so that I could confidently melt bronze and frankly having exceeded that with a margin to spare this yellow steel signifies a reason to celebrate.
In fact I was amazed how quickly the fire beat the nine-fifty mark without the lid on or a proper air supply. It's already hot enough to melt bronze, and there are several improvements to be made.
Refractory lining
By the time this picture was taken, the exterior of the bucket was warming up but still cool enough to hold your hand against - maybe 50 Celsius rising to around 70 near the base compared to bringing steel round-bar up to a thousand degrees. The base is slightly thinner than the walls because I wanted as much crucible height as I could get and it's the weakpoint in the design.
The exterior wall eventually got hot - maybe even above a hundred - and and extended forging could be a problem. As a foundry for small bronze, brass or aluminium projects then the bucket wouldn't get overly hot but it will really heat up if I run it as a forge for a few hours. A sturdy base of commercial firebricks - then it'll be fine. I don't think the bucket has any risk of failing.
Closing thoughts
You can do an awful lot with very little. Plaster of paris, sand, and a steel bucket cost next to nothing in this day and age. I bought a value hairdryer from the supermarket and used some cheap lumpwood charcoal to get these results in my garden.
Armed with a modern understanding of metallurgy that outstrips my bronze age counterpart, I should be able to produce results worthy of a traditional redsmith. The first world information age has provided means and materials that would have astounded and amazed bronze age Europe.
I started this journey knowing very little about the technological landscape from three thousand years ago and I'm already impressed with what they achieved, and they did it without being able to drive to the retail park and buy sand or order buckets online.
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