6 Attachment(s)
Building a natural gas forge - WIP
After making a few enquiries, discussions with the electrical furnace lads where I used to work, some calls to furnace suppliers, a few late nights on the internet and a few PMs with Corin I have decided to have a crack at building a natural gas fired forge.
The requirements are
- it has to be mobile as the only natural gas point we have outside the house is on the back veranda. SWMBO says I can use it there but when guests come it has to be removed at very short notice. Also a couple of other members have expressed interest in using it.
- Has to be able to anneal, harden and temper wood work tool blades up to ~10" long - it would be nice to be able to be able to go longer but that is not high on the priority at this stage
- Initially it has to be natural gas powered,
- has to be quick - can't afford to hand around waiting for heat up (OTOH that means it cannot be left unattended so lengthy heat treatments are unlikely)
So this is where I am currently at
https://www.woodworkforums.com/attach...d=260579&stc=1
Yes I agree it looks like something homeland security might be knocking on my door about soon.
The trolley is all ally jobbie I fished out of the skip where I used to work. It used to support a large 1960's Storage CRO that stopped working and was thrown out years ago.
The trolley has solid lockable wheels and a drawer a nice handle to move the whole thing around even when it is hot. The handle can also be used to hook forge tools over.
The forge body is supported on steel legs 110 mm away from the trolley to improve working height and also to protect the trolley.
The space underneath will be used to locate a small blower. Because natural gas does not have much energy and is also delivered at low pressure the high temperatures needed in forges can only be obtained using force/blown torches - more about that later.
Most of the 3/4" galv plumbing pieces and pipe come from my FILs bottomless box of plumbing pieces. The 1/2" stuff comes mainly from leftovers after installing the retic compressed air in the shed. So far I guess I have spent $40 on taps and bits and pieces.
The body of the forge is based on a small LPG bottle but what I have been focussing on mainly so far is the gas and air plumbing components.
There is still a fair bit of work to do on the body like cutting the ends off and cutting doorways at either end and adding small doors and then of course lining the interior etc
AFter lining and adding a refractory brick floor there will be ~8" of working diameter and an internal working length of ~14" which I am pretty happy about.
I am also making the entire ends of the bottle into large doors on hinges so that they can be opened up to view the torch tip positions more easily, and so the lining can be more easily replaced when required.
Because the interior of the forge after lining will be ~700 cu in the recommendation is to use two torches for that volume.
Here is one of the torches
https://www.woodworkforums.com/attach...d=260581&stc=1
The nozzle is 304L stainless to cope with the high temperature at the torch tip.
I can get a nice blue cone from this torch but for better flame stability the tip is supposed to be flared - something else to have a look at.
The T-piece with the wire coming away from it is a BBQ lighter point.
The chrome tap and all the flexy gas lines come from a skip outside a lab reno where I used to work and they are proper lab gas taps and hoses.
The big steel collar on the porch locks the torch to the tank and enables the height of the torch in the tank to be adjusted via a couple of grub screws
This is what the operator will see in front of them
https://www.woodworkforums.com/attach...d=260583&stc=1
The yellow handle lever tap is the master gas switch.
The two taps with the yellow tops are gas flow control to each torch
The red handles on the left (yes there are two - one is behind the topmost gas tap) are air flow control to each torch.
The blue handle and red handled taps on the right are part of an idle circuit - more about that later.
Here you can better see the master gas control (yellow lever) and the idler circuit (blue and red handled taps)
https://www.woodworkforums.com/attach...d=260586&stc=1
Here is a view from the other side showing the two air controls (red handled taps)
The large 25 mm brass adapters at the very top are forced air input lines - they don't have to be that big and I will probably scale then down when I sort the blower out.
https://www.woodworkforums.com/attach...d=260584&stc=1
Here is a view of the torch tips inside the tank,
Bear in mind 2" of insulation need to go around the inside of the tank - the torch tips should not be protruding below the lining..
https://www.woodworkforums.com/attach...d=260585&stc=1
You can also see how rusty the inside of the tank was.
The black gunk is the effect of phosphoric acid on the 1/2 mm thick layer of rust.
Nothing has been finally bolted or sealed in place. The bolts protruding into the tank will be turned around so that only their heads are inside the tank so they don; interfere with the lining.
In terms of a forced air supply I have been experimenting with a vacuum cleaner that has variable speed air flow control but even that seems to be way too much air so I had to add air flow control taps and spill most of the air during the testing with one torch - I don't expect much will change with two torches. I picked up a nice gentle blower out of a blower heater yesterday during kerbside pickup that might work - have to take a look at that more closely. Anyway -I have done enough experimentation to feel confident enough that it should work so I am working on the furnace body and plumbing first.
The build is a slow process (much slower than I thought it would be) but I am enjoying it and can't wait to make some heat.
3 Attachment(s)
Now with two torches running
After a bit of mucking about I managed to get the second torch to fire up. It turns out the easiest way to do this is just to open up the gas and air taps to the max with the vacuum cleaner on slowest speed, and then crank up the revs on the VC to about 1/3 of max.
The two bright spots at the top signify the two torches are alight.
Attachment 263442
After a couple of minutes the two hot spots from the two torches clearly show up on the floor of the forge
Attachment 263444
The two torches generate about 10" of working length on a piece of metal - i'm pretty happy with that.
Attachment 263443
Once the forge is fully warmed and running (about 10 minutes) it takes 2 minutes to heat up a 12 mm rod to working temp.
Running cost is about $2.80 an hour.