I've been interested in melting metal before embarking on the plane project and somehow knew it would come to this. After reading The Metalcasters Bible by CW Ammen and doing some serious websurfing I found a fairly inexpensive way to make a low maintenance/cost furnace and burner. The 1" diameter burner is of a sliding choke type and took a few hours to make. (See Hybridburners website) Ron Reil has a website detailing a smaller, simpler burner and even some derivatives of his design. My crucible is made of steel and can hold enough to make a crankcase for the seven cylinder radial should I ever decide to make a second engine. The furnace was made with a stainless steel shell and 25 gallons of homemade refractory. The recipe was...
1.5 Parts Portland cement (Probably could have ommited)
2 Parts Sand
1.5 Parts Perlite
2 Parts Fireclay
Yes, the portland cement adds an element of danger as it can explode when heated. The refractory was hand mixed in small amounts and rammed thoroughly to avoid air pockets. I used as little water as possible in the mix and waited a week for the furnace to cure before firing it. A wood fire was burned in it for several hours before really putting some heat to it. Although I haven't had a problem it still doesn't stop me from wearing safety glasses and equipment when operating it. I plan on coating the inside with ITC100 after a few more firings.
The primary reason for making the furnace was for the production of cylinder head parts for my engine. The finned top half of the L-head and it's combustion chamber should be much easier to cast than machining from solid. My subhead (lower part of head containing valves and ports) will have some custom finning as well.
Although sandcasting would be easier I've decided to go the best route which is a gravity mold or permanent mold for anything going on the plane. There are so many reasons to go with this type of mold it just seemed foolish not to. (See this site) The main pain now is designing a mold which is able to feed sections where shrinkage occurs. My first perm mold attempt went OK but had a massive cavity missing from the middle due to shrinkage. I enlarged the feeders for the second attempt but it still wasn't enough. My third attempt was a great improvement due to merging the two small sprues resulting in a large feeder. There are just a few spots on this mold that need to be addressed and I'll be ready to make some real parts. After my third casting I'm much more comfortable with the process and have my controls in place so that I can make consistent results.
My first casting! You can't see it but there is a hollow section beteen the two valve spring bases. VW jug shown where it will eventually be when I can make better castings.
The permanent mold after it's third cast and modification.
My second casting. The shrinkage is less on this one than the first. You can see that I have two small sprues/feeders. These were not enough.
After pouring my third casting I decided to melt the first two while the furnace was hot. At least this way I can save fuel and have longer lasting equipment. I'm just starting to get the hang of this stuff.
The three pictures above are of my third casting. The single sprues were made into one for better feeding. There are still feeding/ shrinkage issues which need to be addressed but it's a great impovement over the first two.
