Hi Everyone, I got a portable raku kiln a while back and I haven't been able to get good results. I was using a 17 pound propane tank which kept freezing up so I got a
100lb tank yesterday and it just seemed not to get hot enough. I'm wondering if the kiln is in- sufficent. It's a Bracker brand. It came as a kit with the flame coming from a 50,000btu grass burner, gloves, tongs, soft bricks, a shelf,etc. The kiln itself is a large trash can lid with hardware wire attatched lined with a stiff fiber blanket. Has anyone had experience with this kind of kit? Thanks, Sandi
If your tank is freezing, then put it in a large container of water. This will keep the pressure up. The 100 lb tank should have no pressure problems. It is not the size of the tank that determines the heat. It is the burner. What temp are you trying to get to. I fire a garbage can style raku kiln that I built and I have no problem getting up to temp. I can go easily to 1800 F in 20 to 25 minutes. I am using a 20 lb tank of propane as my fuel. My burner is rated at
100,000 btu, but 50,000 should still get you up to temp. Is there enough air getting into the kiln for full combustion? Too little air around the burner and it won't matter what size tank or burner you have, you just will not get enough heat.
I'm guessing the problem is the opposite of what you suspect. Not too little gas, but too much. And too little air. It's a common problem when firing raku kilns - especially when the system does not have a regulator to control the gas pressure which most grass burner systems don't. Flames shooting out the top of the kiln look impressive, but don't help heat the ware.
The best thing I can suggest is to have someone who has experience firing raku kilns assist you with the first couple of firings. Some things are easy to demonstrate but hard to explain. . .
If that's not possible, try firing slower with less gas pressure. Pull the burner back 1" from the burner port so that air is entrained in to the flow. For the first 2/3rds of the firing, there should be no visible flames coming out of the exhaust port. For the last part of the firing, there should be no more than about 4" of flame coming out of the burner port. When flames are shooting a foot or two out the top of a raku kiln, then combustion is occurring outside the kiln where the heat is wasted.
Also, since you likely don't have a pressure regulator, you'll need to listen to the sound your burn makes so you can manually adjust the gas flow as pressure drops off in the tank - though with a 100 gallon tank the pressure drop should be minimal.
It may well be that you are putting much too much heat into it: beg, borrow, or buy a thermocouple and pyrometer if you haven't got one, and starting with the smallest flame possible on the Burner, increase it only enough to get a steady rise in heat, for example about 150oC per hour. Stuffing too much heat into it uses up all the free air in the kiln, resulting in a heavy reduction which will prevent any increase in heat! The old kiln firer's saying: "More equals less" applies in full here. You will learn by experience how fast you can go
Thank you all for great information. I'm thinking now I shouldn't turn up the gas as far as it will go. Also there was a gentle breeze when I fired and flames were shooting out the hole where the weed burner goes in and looked like it could come back up the gas hose. Thank you again. Sandi
Yeah, that sounds like a bit too much gas to me! Flames should definitely NOT be coming out the burner hole. That's dangerous. I'm wondering if you have the weed burner adjusted properly. I've never used a weed burner, so don't know how adjustable the fuel / air mix is. Yellow / orange flames dancing around the burner head indicates a bad fuel / air mix. The flame coming out of it should be basically blue with very little yellow. Think of the tight blue cone of flame that comes off a properly adjusted Bunsen burner or the blue cone of flame that comes off a jet fighter engine at full throttle. A gentle breeze should not be able to push such a flame back out the burner port.
InspirePoint website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.