Well the large furnace I've always wanted is finally finished, this furnace is primarily for melting cast iron. It has a capacity of up to a #40 crucible, being this size it will require some work to design a trolley to both lift, transport and pour.
This was not a one man design and build and could not have been completed without the input and drive from my good friend Ian Arstall.
For this beast to melt iron an oil/gas burner had to be designed and manufactured. The idea is to pre-heat the furnace on gas then bring on the oil. The reason behind this is to have enough initial heat within the furnace to prevent the oil from smoking when initially turned on.
On our first fire the furnace hit 1300 deg C within 15 minutes. On the second fire we decided to try melting some iron, old brake discs in an A12 clay graphite crucible from Vesuvious. As we had never melted iron in this way before a few lessons were learnt. I must admit melting iron is totally different to melting non ferrous metals, in fact you can throw away the rule book used for the lower melting metals. The heat required to melt and pour iron is around 1550 deg C, the radiant heat generated from both the furnace and crucible is incredible and certainly tests the nerves particularly when pouring. A trolley for handling the crucible will need to be made to increase the distance between me and the hot stuff. There is an enormous amount of surface crud produced, in fact half the crucible seemed to be crud, this made it hard to judge how much molten iron was actually in the pot. The scraping tools we use for the bronze weren't up to the job so some new stainless steel utensils will have to be made for the next melt.
We rammed up some simple molds to pour off what iron we melted. Being a new type of burner that we had never used in action before some basic rules of thumb for tuning will have to be developed over the next couple of melts. The initial firing is done with LPG. The blower is a high pressure vane type found at the local scrap dealer. The oil is used automatic transmission fluid forced through a Tweeco tip via air pressure. The oil is in an old compressor tank which is pressurized with air and forced through a Tweeco tip via a metering valve. The burner has a venturi machined into it, and the flare is actually cast using high temp castable the whole system works extremely well.
The furnace is a composite of high temp materials. The lower section is high temp castable. The mid section in made using Fiber Frax in the outer section and a cast kaowool tube around 350mm in diameter in the center. The lid is made using Fiber Frax wool with a fiber Frax board on the underside sandwiching it together. The whole show is coated in a high temp rigidiser called J Coat with an ITC 100 coating over the top. When the melt was finished the furnace held up fairly well except for the lid. The Fiber Frax wool melted out so we'll rebuild it with the high temp castable before the next melt.
Arrangement of the burner. Oil nozzle in the front with the metering valve,
gas burner at the rear with the isolating ball valve.
The furnace in the raised position with the small A12 crucible for the first test.
Note the oil tank and blower at the rear.
The furnace in full flight running on oil. Note the absolute lack of smoke.