homebrew furnace questions

You might want to look at the recent/last copy of "model engineer" as there is an article about a home cast iron melting furnace running on gas. I am not looking at casting but glassblowing and have a 47kg Calor propane bottle, I know one can take at least 2.5 bar off these with appropriate regulators and so easily use non forced air burners although I am planning to use forced air for better mixture control. I do know a number of people that have used and are using either propane or LPG with non forced air systems using amal burners which are similar to some units such as Reil burners.
r>Hello All

Yes OK David 47Kg is a bit of a whopper the standard 15Kg I normally get from a local shop just round the corner ,I use these in the heater in the garage here and wanted to keep to this convienient size (its heavy enough for me ) :-) Yes of course 2.5 Bar is about 36 PSI and from what ive read you would need somewhere around 15 to 20 PSI for a non assisted burner So as you say with a high pressure regulator there should be no problem. The regulator on the 15Kg size is only 25 mBar (millibar) so I think I am gonna have to make up a blower to assist. I am not familiar with "model engineer" is that a UK publication ? I am not into model engineering myself. I got into wanting to cast metal by building a small homemade cnc milling machine on which i do engraving , which required some parts to be cast ,originally I did the melting in a small 1200 degree kiln however a couple of weeks ago the nichrome heating elements in the kiln burned out so I want to build myself a small furnace cheaply to take its place. I intend to use a 15Kg calor gas bottle as a skin ,I am sure you have seen the sort of thing I mean.I have allready cut the bottle down to size and wanted to make the burner next before i lash out on the castable refractory. Yesterday I made up a quick prototype burner something like from the photographs on It was then I realized that the gas pressure on the 15Kg calor was restricted to 25mbar and so this type of burner would not work and I would need a blower.
Regards Ron Priest
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David Bill> You might want to look at the recent/last copy of "model engineer" as

The 47kg is the largest portable I am aware of and the glassblowing gloryhole has a huge demand for gas, depending on temperature I may have to gang them to get the gas volume required at full chat but then it may be outputing 40kw+. See and . You should be able to get 2.5 bar from the smaller bottle but with reduced volume, its about heat input into the bottle and how much gas you can evaporate if your use is continuously. All the bottles as far as I am aware have the same fitting so the kg of gas you can draw per hour is limited by bottle size and temperature.
"Model Engineer" is a popular UK publication, I don't subscribe but a couple of neighbours do, see , should be easy to find at a good news agent in the UK.
Re your nichrome elements I hope 1200F was what you intended as 1200C would be above the recommended for nichrome, you should change to such as Kanthal A1 or equivalent, FeCrAl type element providing the refractory is upto it.
For refractory products I have dealt with Wright Refractories in Wordsley, Stourbridge. Prices seem good and Stuart Wright is knowledgable and friendly. Lots of glass people I know have recommended them to me. Depending on your location in the UK you may want to pick up the stuff yourself, I find as I am fairly close that for lower volumes as I use its cheaper to pop up and collect the stuff than have it shipped but it depends on the value of your time and how much you have.
r>Yes OK David

Go to your local gas supplier (Calor are not always the cheapest) and get an adjustable propane regulator. IIRC mine goes up to 45psi or so.
Mark Rand RTFM

I just went looking at the Calor.co.uk site, and they have these odd Blue and Green "Patio Gas" and "BBQ Gas" Butane bottles with an oddball Quick Connect regulator - Is this what you want to use?
I didn't realize they even used Butane for more than the old "Camping Gaz" disposable cylinders - Over here, all they sell it for is refilling cigarette lighters...
You really do need the larger 100-pound (47kg) Orange Propane bottle - or multiple small bottles on a common manifold - when using a high rate of LPG gas for a large furnace or kiln burner.
If you are taking the gas from a normal size Propane barbecue bottle, the liquefied gas has to boil to vapor inside the bottle, which requires a heat input, and the outside air can only supply that heat at a restricted rate through the steel. Draw off the gas too fast and the bottle gets cold from the effect of the vaporization, the pressure inside the bottle drops way off, and your burner goes out.
You can get around this by putting the Propane bottle in a bucket of hot water - but then you have to keep the water hot, and not too hot and overheat the cylinder to where the safety valve pops off...
They make higher pressure regulators - start scrounging.
If you still want to use the small Propane bottles you will need to make a manifold to get the necessary flow rate. Use a tee or cross fitting and two or three high-pressure flexible propane hoses with POL male fittings for the bottles, and the tee connects to the input of the 2.5 Bar regulator - the Calor dealer can set this up for you.
If you put check-valves on the bottle hoses, you can even change out an empty bottle while the burner keeps running on the others.
Or hire a larger permanent site tank, then you don't have to transport it anywhere for filling - they send the delivery truck out to you at about the same fuel price. (*)
(* - For fuel on their normal delivery route schedule - in the USA there is an extra charge for sending the truck out for "emergencies", and more for nights/weekends/holidays. In other words, get a big enough tank.)
The big tanks have a high enough draw rate that you can run a foundry burner all day. The 300-gallon / 1200L size would be plenty. -->--

Hello David
I am very impressed with your website and the "glory hole" furnace as you call it , your gallery of is most impressive I can see you are pretty much an expert It must be very satisfing to be able to create such fine works. Yes I can certainly see why you need the 47Kg fuel supply. The Kiln I used to use was salvaged from a Skip at the University where I work I am an electronics technician at Coventry University and the kiln used to be used for research into ceramic hybrid circuits a line of research that has now been discontinued it had a Cal digital controller with a max temperature of 1200 degrees Celcius. I used it about 2 dozen times to melt aluminium in an A4 salamander but it finally burned out I stripped the thing down and the element wire was complely brittle and literally fell apart in my hands I am only assuming the element was nichrome it may well have been made of something else but its years of use and rough treatment by me in melting aluminium killed it in the end. Thankyou for the information on Model Engineer and on Refractory Suppliers I cant find a web site for Wright Refractories so cant look up the prices but have had some quotes for refractory as much as £63 per 26Kg bag for 1800C Refractory you certainly have to shop around for this stuff. I am in Coventry so Birmingham is not that far to go ,perhaps you could give me some idea of their prices. Regards Ron Priest
David Bill> The 47kg is the largest portable I am aware of and the glassblowing

Hi Bruce Thanks for your reply In the UK lots of people use a small heater called a "Super Sir" these run on 15Kg Butane cylinders and are fitted with a low pressure 25mbar regulator as standard they are very popular here for use in the winter months I used mine hell of a lot this winter,which seemed to last forever. The 15Kg bottle of gas costs around =A313 ie 26 USD and this includes delivery if you get the gas from a local supplier ,if you buy direct from Calor it costs a lot more ie =A320 The Blue 15Kg Bottle is very,very common here in the UK most small hardware shops will stock only this size. I take your point about higher pressure regulators and multiple manifolds and I can see the physics involved .Using gas is just one idea of fueling a small furnace I am sure you have seen small furnaces that run on waste cooking oil as well and perhaps i should investigate this also,I am only in the planning stages of making a small furnace at the moment and trying to do as much research on this as I can. Since its only a hobby persuit I have to keep the costs down as much as possible.
Best Regards
Ron Priest

OK Mark I see ajustable regulators are sold on ebay and are very cheap I will investigate this
Cheers

Its Now pretty obvious to me that using calor gas is just not on as a fuel for a small furnace The gas pressure is just not hight enough and ajustable regulators are not available for calor. Propane is the answer but is more expensive than calor ajustable regulators are available for propane cheaply from ebay. I would like to thankyou all for your input on this
Best Regards
Ron Priest

Ron,
Thank you for the compliment about the glassblowing, been doing it about 6.5 years now as a hobby and getting better all the time. I must add some recent items to the gallery.
Regarding your kiln if it went to 1200C then I would expect Kanthal A1 FeCrAl elements or equivalent. They don't last forever and become brittle once fired so your use for melting Al may not have been responsible for the failure and handling them once used is likely to lead to breakage. I know you can damage exposed elements due to metal vapours/grease/carbon contaminating them but as Al is the main protective element in FeCrAl elements I not sure what effect it would have. I have contact details for a chap that sells element wire if you need it I can dig it out.
Wrights do have a website, well sort of, its under construction . Your best bet is to give them a ring on 01384 76493 and ask for a current price list, tell them what you want and they should be able to give you the details. I have the "potters and glass makers price list" which is a couple of pages. They sell a number of products from Thermal Ceramics such as VFB vacuum formed board, IFB insulating fire brick, Harbison-Walker Refractories such as castables.
Some fairly recent prices
Wrightcast 1600 BK castable £12.17 per 25kg bag. This is a Harbison-Walker product and comes under various name such as AP Green Mizzou. Good to 1650C.
1400 insulating castable £13.90 per 25kg. Good to 1400C.
Ceraboard 100 25 x 1000 x 1200 £35.31 per board.
Thermal Ceramics JM23 IFB 230 x 114 x 76 £1.05 each box 20.
Add VAT to those. Wright get a lot of things if you request it and keep stock of common stuff such as the 1600 BK, IFB, VFB but check stock with them first.
I can understand 1800C castable being expensive and over the top for a casting furnace I think. I do have some castable alumina and it was rather expensive.
Regarding one of your other threads I think you need to be careful what you refer to as Calor gas, I have Calor propane but they do do other gas mixes. I do now know of a cheaper source for propane so shall try them when the current bottle runs out.
Cheers
Dave
r>Hello David

Ron,
Forgot to mention in my other reply. When you get the castable ask the supplier for the recommended water mix ratio. This will be for vibratory casting and makes it hard work to mix. You can add a little more water but too much and you can easily get major seperation of the solids and cement binder leading to a poorer item. I recently made a small vabratory casting table and it transforms the castable from a thick stodge to a thick fluid which flows into the forms. I have also used a needle scaler on the back of a wood block to vibrate the mix locally to similar effect. I expect you can rent concrete vibrators from a hire shop if you were doing something big enough to warrant it.
r>Hello David

Small world.. I'm in Rugby :-) Lots of useful names and addresses from David. I suspect that I may be following some of them up as well.
Regards Mark Rand

Yes Mark As you say Small World David has been so very helpfull with local practical information and may I say that it has been a pleasure to chat with you all on this thread I will be off on holiday to greece shortly and will not be doing anything about starting this small furnace project untill I get back but I now have all the information I need to turn the Idea into reality thanks to this Group.
Best Regards
Ron Priest