Furnace updates
Last update 3/3/07
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VERY IMPORTANT
I haven't just sold you a book and that's it! Please contact me if there is anything that is unclear! Since there are a number of options for materials etc. to construct your furnace from, you might want to check the suitability with me before hand, I can't promise I will know the answer, but if I can help I will.
This furnace performs exactly as I describe on this site, and in the book. If yours doesn't, CONTACT ME
it's probably something very simple to sort out, after all, it's a very simple furnace!
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Firstly I will put here any information that will help with either the building or using my waste oil furnace. This book is my first attempt at writing anything! So for some bits, a little supplementary information here and there might help.
So far only one thing has cropped up, and this is from my own "playing," something I feel could stand a little additional information.
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Secondly I have some ideas for additional uses for the furnace, sort of "add ons" to give it greater scope within your workshop, but until I have time to build them myself and try them out, I won't post them.
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First Update
Two things have become apparent to me, which can be covered in one update.
Once you've lit your furnace the first time to dry it out, if you followed my advise in the book, you would have had it burning wood for a long time to build the heat up slowly, then you've turned the oil on, this doesn't give you a true picture of how the furnace would normally be used burning oil from a cold start.
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Follow the instructions in the book, but don't put a crucible in it until you've had a good chance to "play around", see how "hard" you can get it running, get it really roaring away building up a very high heat, just how hot can you get it? Don't melt your lining though!
Play with the fuel/air mix to see what effect it has; while the furnace is empty you can get a good knowledge of using this waste oil system.
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This now brings me to the second part of this update which is directly related to the above.
Once a crucible is in the furnace, it "absorbs" a fair amount of the heat being generated. If you've understood exactly how this system works you'll know that the internal heat build up, and enough fuel being burnt are very important for this system to generate the vast amounts of heat it's capable of. As it heats up, more fuel/air can be added to generate more heat, then more fuel/air is added generating yet more heat etc.
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With a crucible in it , more time must be allowed for each of these increases to heat both the crucible and its contents before turning it up again.
Allow the furnace to "settle down" from its initial start up as described in the book, once you are ready to adjust the fuel "properly" it's a good time to put the crucible in.The perfect exhaust flame is "full yellow" with some orange in it, when the furnace has only just been lit, this might have more orange in it than it will have 5 mins. later. Once it gets good and hot, this will turn more white, now you're really cooking!
The larger the crucible, the longer you must leave it between these increases, you won't really notice too many problems with a small crucible, but when I went for the A20 I really noticed it!
You'll know when you are being a bit "swift" with the fuel increases, the first sign is smoke coming from the bottom of the furnace, this is unvaporised fuel soaking in to the bottom lining, no real harm here, but it will take a while to clear as the bottom will act as a wick, absorbing a fair amount of fuel. An even greater excess of fuel flow and you will get oil drops from the bottom, these make a mess, but a drip tray will collect them, a little experience will prevent this from happening though. Once the furnace reaches a certain temp. this will no longer happen, too much fuel will simply show itself in the exhaust flame.
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Remember though, we're not talking a great deal of time here, with an A4 crucible of cast iron in the furnace, I'm skimming the slag from the liquid metal ready for its first top up after around 25-30 mins. from placing the crucible in the furnace.
Bear in mind though, your furnace will behave slightly differently than mine, although it uses exactly the same principal as mine, it was built with different bits and pieces!
By adding this information to the "Using the furnace" section in the book, you should be fine, you'd probably be fine with just the book, but this might help.
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Second Update
Zircon Coating The lining
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My lining has suffered from the abuse I've subjected it to during the "testing stages" of the furnace. It was black and lumpy, and has suffered from a certain amount of melting. It still has plenty of life left in it, but I was wondering if the "blackness" was absorbing some of the heat that the white surface it started with, would have reflected back onto the crucible, therefore slowing down the heating up process.
A lot of this could have been avoided by not it running it quite so hard, but...............
Nebojsa (see The Guest Gallery) kindly contacted me and suggested Zircon as a protective coating.
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This is the state my 1700 degC. lining This shows a couple of 1700degC
was in plinths, it takes no prisoners this
furnace!
Click on the pictures for a larger view
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After a few hours with an angle grinder, and a couple of coats of zircon paint I had this;
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However, the next time I used the furnace, the zircon wasn't looking very good, and the performance was not encouraging at all.
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There is some iron slag that's been blow around in here, but the nice white finish is suffering!
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I also tried the zircon in a small furnace / kiln I have and run on natural gas. I intended it to be used as a small kiln, but fitted a side burner opening so it could double as a small furnace.
The lining is clay / sand with an extremely high pearlite content to help insulate and build up the heat from the small burner I use with it as a kiln.
Trying it as a furnace I found the pearlite was vaporising so I have really only used it as a kiln.
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The zircon is amazing as a protective coating, it really does help to keep the heat inside the furnace and away from the lining, I have used the small gas furnace / kiln a few times since as a furnace, and there has been no more damage to the pearlite in the lining, despite running it nice and hot.
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This is using one of my cast iron crucibles for alli. they really do work well!
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HOWEVER!!
The waste oil furnace doesn't like it at all. I haven't done enough experimentation with the zircon to come to a firm conclusion, but I would like to give you my first impressions for the benefit of anyone thinking of coating the lining of a furnace of my design with some kind of high temp. coating.
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The furnace needs the build up of heat in the lining to operate at its best, the insulation layer keeps most of this heat in the lining, so once the initial heating up is done, it preforms much better without the zirco than with it.
I believe that so much heat escapes through the exhaust, with the zircon stopping the lining from absorbing the heat as it passes through the furnace, it is simply going to waste!
Although I still could melt cast iron, it was not the in the "easy style" I've gotten used to with this furnace, and I couldn't believe how fast the furnace interior cooled down when I had the lid open to remove the crucible. There was simply not enough high temp. stored heat, this means should a second crucible of cast iron need to be melted, the furnace itself isn't helping you, the heat needed will need to be generated from fresh.
The way the waste oil system operates, it really does need this "stored heat" to "do its thing!" Anybody who has my book will understand why by lookin at how the system works.
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Also, with the gas kiln / furnace, although the lining is now suitable for the higher heat of using it as a furnace, it also seems slower to get up to a good heat, although due to damaging the lining I haven't used it as a furnace for so long, I couldn't swear to it.
But I think I have spoiled it as a kiln, I relied on a very small burner slowly building up the internal temp. over a longish period of time.
Then once the pot (or whatever was inside) had sat glowing with a red heat for a period of time, turning the burner off and closing the lid to allow it to cool very slowly.
Now, since the lining isn't absorbing the heat, it doesn't build up the temp. with the small burner, and even when the furnace burner is used, it cools down to quickly to be of use as a kiln.
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In conclusion
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While zircon, or I should imagine any other protective coating for that matter, has a use for reflecting the heat away from the surface it's painted on, there is a trade off to be considered.
I haven't done enough experimenting to be conclusive in my thinking for other uses of the zircon beyond suggesting that it isn't a good idea for a furnace using my waste oil design. The heat build up in the lining is too important to how the system works.
This is something that other people experimenting with waste oil might want to consider as well.
For that matter, providing your lining is rated high enough for the use you intend for it I think it might be detrimental for any small furnace whatever the fuel.
If your lining isn't of a high enough rating, perhaps re-lining with something more suitable would be a better long term solution than using zircon or a similar coating, they are not cheap!
Using the furnace lining as a "heat store" for the energy we're generating seems a better idea than allowing most of it to simply go out with the exhaust.
Insulation between the lining and the atmosphere to slow down the heat dissipating from the lining is the way to go.