Hey everybody what is going on?
This is Roger in Technology and welcome to thing of the week for the 27th of August 2015.
This week - Foundry tools!
The bucket foundry I built here is exactly what the doctor ordered, its a galvanised steel bucket and a refractory mix of about four parts plaster, four sand and three water. There are details on the construction on a previous post.
While I had to buy a steel bucket, those things are cheap enough and I knew it wouldn't break the bank. Likewise for the plaster of paris and sand and making a thrifty blast forge capable of any amount of metalwork is easier - and cheaper - than you can imagine. Here is the little fellow in action.
There are a few more materials here, a one inch steel tube and a value hair drier for an air blast. These were bought pretty cheaply. The pictured timber supports are actually my cope and drag frames for the casting flask, so I'm not counting those in the cost. The air blast does need a dedicated support, although a few blocks or timber is going to be more than sufficient for a long time yet. It also needs a regulator, because the direct blast from the blower provides too much heat.
As well as buying the materials to make the forge, next on the shopping list was a graphite crucible looking something like this.
The crucible is a precision tool, and it was important enough for me to spend the money rather than fabricating a steel cup. The thing is rated a lot hotter than steel too, by at least a thousand degrees, which is a pretty good safety margin. Melting Aluminium and brass isn't going to take more than a thousand degrees, and neither is hardening steel so I'm very happy to have a crucible that can withstand a lot more than I'm every going to need.
The lid is the same refractory concrete as the foundry walls, with galvanised steel hooks set into it. The two hooks were bought new from the hardware store - its a needless expense when they could be beat out of steel but the wide square bases will help it hold in the concrete and I didn't want to spend any time on such a trivial item.
Once the mix was poured in, it flowed around the hook bases and the plastic cup formed a circular hole and I just had to let the thing dry before popping it out the hold. The technique was about right but I want the next lid to be thicker.
With the lid off, the crucible can be seen here glowing a bright orange at its hottest point. You can see the ash line around the edge of the lid. While its clearly more the large enough to cover the foundry I might consider an inch or so larger diameter.
It's worth mentioning that the fire at this point is running too hot - which is why I had the lid off. Actually it's running at a tad over two thousand degrees by my best guess. If that steel stays in there too long it'll start dripping. As well as being too hot for steel, that temperature is far too hot to cook bacon. As far as I can tell, bacon vaporises at two thousands degrees (3600 Farenheit) and while I tried eating what was left of it after it had been extinguished it wasn't a pleasant experience.
Cooking bacon is reasonably easy in a fire up to two or three hundred degrees, where it will sizzle well and taste delicious, but I think that anything above about a thousand degrees centigrade (1800 F) is going to do more harm than good and the direct heat of a forge fire is unlikely to yield good results.
Using nine-hundred to a thousand degrees as a maximum cooking heat is probably a good rule of thumb. If its hot enough to liquidise copper then its too hot to cook with. Our domestic oven will reach 230 ish degrees which is just shy of the temperatures needed to temper the steel of its construction.
A discussion on cooking over the forge will have to wait for another time, while I consider some sort of heat shielding that can withstand the inferno.
Todays heat used up the last of the summer BBQ charcoal, so was the last free burn and I'll have to buy some real coal next time. The crucible was packed with sugar and sealed with my knife while it burned for a couple of hours to case harden the steel before a water quench. It was a lot of work to go through, and a better grade of steel would have skipped straight to the quench and temper.
Until next time, keep your projects moving. Finding time for recreational hard graft can be difficult but maintaining momentum is important.
No comments:
Post a Comment