# Furnace Project



## MozamPete (May 10, 2015)

I decided to put together a new thread of my furnace build.  I have been posting some summaries of the build on the POTD thread over the past couple of months so some of this may seem familiar/repetitive to those who have followed it there, but I thought it worth putting it all together in one place and to add a bit more detail as it has been by far the topic that has generated the most interest of my posts.

Building a small furnace, primarily with the intention of having a go at casting aluminium, had been on my todo list for a while but never made it to the top. A friend recent decided he wanted to build one too (to have a go at forging knives), so with a companion to help and bounce ideas off I finally got the motivation to build one.

After a bit of research we decided to build them around a 14kg LPG cylinders – these are the same diameter as the more popular 9kg cylinders but taller in height.  In the end a second hand 14kg cylinder was only marginally more expensive than a 9kg cylinder and gave the option of a greater internal volume if required.  The furnace I build was a vertical one for use with a crucible for melting aluminium, while my friend built a horizontal forge using the same base materials.


*The Burner*

The build started with turning up the components to build the burners from design plans my friend had found on the Internet through forging and blacksmithing forums.



The PRO V Burner is a venturi design (no forced air required) and supposed to be the bees knees according to his research of forums etc on the subject.

Credit for the burner design goes to a Daniel Gentile, and the plans can be downloaded from:

https://dg.box.net/shared/static/s3pjhjalji.pdf or

http://www.iforgeiron.com/topic/168...l=need+better+burner&fromsearch=1#entry170678

For materials I just used what I had at hand or was locally available and we managed to keep to his dimension within a couple of mm, slightly adjusting the diameter of the induction chambers to what tube we had available.

The body was mild steel and the flare I turned from a piece of unknown stainless steel I had lying around.  For the tube I had a length of suitable size galvanised pipe on hand but as I didn’t know how hot it would get during operation I decided to de-galvanise it before use. Soaking it for about 24 hours in vinegar, with a couple of wipe downs over that time to remove the oxide did a perfect job of removing all the zinc.









We used a 0.8mm MIG welding nozzle as the 'injector' (not sure what the right word is), but operated well with my regulator wound right down to the low end.  We have subsequently got a LPG regulator with a gauge and it operates well between 5 and 25 psi.






(The Mark 2 version under construction with some totally unnecessary knurling and grooving to add a bit of bling – still needs to have the air inlet slots milled in the body)

Also gave the burner a test fire in a micro forge I had quickly knocked up with a sand and fire clay refractory while waiting for the refractory products for the final furnace to arrive.  This has proven to be quite handy for heating of small parts (for quenching and oil blackening).





*The Furnace*

For the body of the furnace I used a 14kg LPG tank and cut into three sections so that the top and bottom sections can be used with or without the middle section as size requirements dictate. Normally I expect to just use the top and bottom section and will make a crucible that suits that size for casting aluminium - which was the primary purpose for building it – but as a wanted to make the furnace as versatile as possible and also use it for simple heat treating/annealing I occasionally may want the extra volume.

I managed to unscrew the valve from the empty LPG bottle by inserting a length of pipe into the bullnose outlet connection to give me sufficient leverage to break the thread seal. I may have just been lucky as I have read these can be very difficult to remove.  I then flushed the cylinder 3 or 4 times with water to ensure any residual gas was removed (and finally dropped a lite match in just to be 100% certain) before I started cutting

I bent up some handles from steel rod and welded them to the middle and bottom sections (the top section I kept the original LPG bottle handles), and cut and welded a burner holder tangentially to the proposed inner diameter of the furnace. Handles were actually hot bend using the micro forge above to heat them, and a simple jig in a vice to get them a consistent size.







The primary lining is two layers of 25mm thick ceramic fibre blanket (Aluminosilicate fibre) which keeps the weight down to a minimum as the furnace won’t have a permanent operating position in my workshop but will be put away and brought out as needed. We used the densest blanket we could get locally – 128 kg/m³.




On the bottom I cut five holes through the ceramic blanket to the steel body for ‘legs’ and poured a floor of castable refractory to provide a solid and stable surface for the crucible to sit on.




The entire internal surface was then coated with a two part refractory mix (Durrans RMS Module Coat - a water based zircon refractory coating) which is rated for 1700°C.  This is a very liquid product and was painted on.  It provided a thin, hard shell when fired but has tended to be quite brittle when applied over the flexible ceramic blanket and cracks if knocked.  This was especially a problem on the mating surfaces between two furnace sections where I had tried to taper the ceramic blanket edges to make the section fit together and self center. Any high points that took more than their share of weight would crack.

I have applied another couple more coats and it is becoming more hard wearing but I think a few further coats will still be added.







*Operation*

The first trial use of the forge ‘in anger’ was to try to anneal a 400mm long chunk of rail iron before I begin machining it. Took about 30 minutes to get the whole piece to red hot and I soaked it for a further 30 minutes to get a consistent color end to end. After heating I just sealed up the exhaust at the top of the furnace and left it overnight to cool down slowly.















In the photos I'm using an off cut of the ceramic blanket on top to reduce the exhaust hole size to limit heat loss (as the actual hole in the top of the furnace is large as it has been designed as a charge hole for feeding the crucible).  I will likely build a more permanent ‘cap’ to do this once I have some more experience of its operation and can optimise the minimum hole size.

Once it had got up to heat I just turned off the gas and put some more ceramic blanket off cuts on top with a brick to hold them down. I had a peak about 30 minutes into the cool down and the iron was still glowing red.

In subsequent uses I have stuck a thermocouple inside the furnace through the top/middle section joint (so should be out of the actual burner flame area) and I was getting a temperature above 1100degC without having done too much in the way of optimisation of the burner and exhaust hole size as yet.

During long operation I have measured the outside of the furnace getting to about 250degC


For my friend’s forge we used the same burner and refractory products, but configured the LPG cylinder differently to suit his application.  The LPG cylinder was cut in half, and once the ceramic blanket had been installed the two sections were welded back together.  The Module Coat was then painted on through the opening.


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## brino (May 10, 2015)

Hi Peter,

I really appreciate the long write up and lots of photos....Thanks!

I have done some aluminum casting (but was unsuccessful at melting copper) with propane burner like this one:
http://www.backyardmetalcasting.com/oliverburner1.html

It's been very useful for everything from heat treating to weed killing in my driveway.

.....and I'm thinking about trying cast iron. So far mostly a dream, but I have picked up the "Artful Bodger" book on a homemade waste oil burner:
http://artfulbodgermetalcasting.com/3.html

Please keep updating us on your progress.

So many fun projects, so few lifetimes to get thru them all!

-brino


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## MozamPete (May 11, 2015)

Brino,

I had my first go at casting brass over the weekend - melted down the two valves from the LPG tanks that were used for the furnace bodies.  Melted then down surprisingly quickly. Might have to dig up some copper and give it a go next weekend just to see it I'm getting hot enough or not.

I also find other used for the burner - gets the charcoal in the braai (BBQ) glowing pretty quickly.


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## kvt (May 11, 2015)

Brino,  That link looks similar to the one I use,   It melted my cast iron pot I was using as a crucible for AL, Made a real mess on the inside of the furnace to.   Have not gotten it cleaned out yet.  
but looking at Pete's I think it might get a little better output.   I still have to get a could of other projects out of the way and find me a bigger tank  (beer keg) to make my next one out of.  Have some larger pieces of Al that need melted down for some projects.


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## MozamPete (May 17, 2015)

Well I managed to melt some copper down over the weekend - just a couple of off cuts of copper pipe, about 80 grams in total. Took under twenty minutes from cold so I'm pretty happy with that and don't think it would be too much trouble to melt a larger quantity if I even had the need - it was just don't as an experiment to quantify the temperature I was getting.
Next to find some cast iron scrap and give that a go.


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## countryguy (May 17, 2015)

VERY Cool.  Wanted to ask what you used for the castable refractory mix?    My  son and I are rebuilding two old Thermolyme muffle furnaces.  I'm in Ohio on biz and it so happens they is a refractory outlet in Toledo.  I hope to pick up a few 50Lb bags of Mizzou and save the $100 bucks in shipping charges.  The plan is to use as a non insulating casting binder on the A1 coils into square element sheets that slide in/out.     Never ends does it!!! my oh my.  LOL.     

sunday night and time to take the shoes off and get ready to dream of hard steel, CNC and making stuff!   
Jeff.


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## MozamPete (May 18, 2015)

Hi Jeff,

The castable refractory was also a Durrans RMS product, Resicast 1700 N. Supposed to to good for 1700 degC.

I was looking at your furnace refurb - much more fun to keep the old controller going if you can keep in working, so much more character than a modern controller.

Peter


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## countryguy (May 18, 2015)

thanks Peter, 
   I agree.   It is a very pretty controller.  And I will repair it / tweak is when I get home and have a few hours.    At this point I have two bags of Mizzou sitting on the will-call of the Toledo refractories location.  And it's about an hour from home as I slip back up I-75 tomorrw.    We actually have two furnases.   A pre-Thermolyne 1730 made by TEMCO.   And the 1730 in the pic.   I've ordered some A1 coils. Pre-wound and spec'd for my 10Ohms per panel.    I get to make forms and then get the A1 routed w/ the castable then poured in.    We're having fun and so much learning going on my head's smoking. 

I need ramp and soak times.  And yes... We can run manually for a time.  One of the furnances for Annealing will get that controller hung back on it.  I just wish I did not have to fix every single thing I buy.  the Sweat equity has saved me at least $10G's or more... but man I just want to plug something in once of these days and work!  ;-)  all good though.  
Have a great day.


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## markknx (May 27, 2015)

Peter very nice burner. the .7mm is about what I put in mine .030" I run it about 7-10lbs to get up to heat then drop back to 4 1/2-5psi  for my forge. not the same burner but real close. I have also managed to hold 700 deg F pretty steady so tempering is a possible use
Speaking of other uses I can cook a hot dog faster than the microwave.
Mark


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## Ski (Apr 12, 2017)

MozamPete said:


> I decided to put together a new thread of my furnace build.  I have been posting some summaries of the build on the POTD thread over the past couple of months so some of this may seem familiar/repetitive to those who have followed it there, but I thought it worth putting it all together in one place and to add a bit more detail as it has been by far the topic that has generated the most interest of my posts.
> 
> Building a small furnace, primarily with the intention of having a go at casting aluminium, had been on my todo list for a while but never made it to the top. A friend recent decided he wanted to build one too (to have a go at forging knives), so with a companion to help and bounce ideas off I finally got the motivation to build one.
> 
> ...


Pete, Did the anneal succeed on the rail track?If so,how did it machine!  I have 3 mini anvils that I'd like to cut flat. Ski


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## MozamPete (Apr 12, 2017)

Ski said:


> Pete, Did the anneal succeed on the rail track?If so,how did it machine!  I have 3 mini anvils that I'd like to cut flat. Ski


Worked well
http://www.hobby-machinist.com/thre...in-your-shop-today.14637/page-262#post-413442


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## savarin (Apr 12, 2017)

Hi Pete, nice furnace. I like the way your burner slides into the side pipe.
Does air enter the furnace around the burner when in operation?


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## MozamPete (Apr 12, 2017)

savarin said:


> Hi Pete, nice furnace. I like the way your burner slides into the side pipe.
> Does air enter the furnace around the burner when in operation?


Thanks. The ID of the pipe is a pretty close fit to the OD of the flare so the only air getting in is air/fuel mix through the Venturi.
I actually get a lot more use out of it than initially expected so was well worth building. Gets used for casting, annealing, rough heat treatment, blackening parts (old oil quenching), hot bending bar stock and the occasional bit of forging. Plus the burner get used when we need to get the charcoal BBQ going in a hurry.


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