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forge burner pipework and fittings uk and other dumb questions

alan macdougall

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hello, im making a small propane bottle forge, and have a list of parts needed for this. 

I understand that galvanised pipework and reducers etc are not suitable, and am looking for black steel fittings, here in the uk. 

im also aware that the galv stuff is usable after a vinegar soak for a few days. 

Can I ask what these fittings, and pipework are original meant for, to help me track them down?  is it for industrial gas systems or?


im also looking at ceramic insulating wool blanket type stuff to line the bottle with.

ive come across a product called insulfrax, which looks good, it doesn't have any of the health issues of ceramic wool . I

t comes in a number of  densities, tho, these  being  64, 97, 128 and kg.m3 heres a link to the spec.

what density should I be looking for.? I thought either the 126 or 160?

Any opinions.

I think 50mm thickness should be ok? again, opinions? 


oh and while im here, im looking to put the burners into the bottle at around 3 o clock position, and  want a swirling pattern but should I aim them at the top part of the inside, the middle or the bottom? or does it not really matter that much? ive a tendency to over think stuff. 


Apologies for my lack of knowledge, but hopefully someone can keep me right. 



Edited by alan macdougall
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The rear door both reduces back pressure (something venturi burners do not care for) and lets you pass longer pieces through the forge.  It is not necessary, but it is occasionally handy, especially for doing heat treatment using a muffle pipe.

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thanks Alan.  Thanks for clearing that up. .

Do you have any opinions on the density of the insulfrax , the pipe fittings and the other stuff mentioned in my first post .?

thank you.

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Some conversion factors might prove helpful.

64 kg/m3 is 4 lb/cu ft

97 kg/m3 is 6 lb/cu ft

128 kg/m3 is 8 lb/cu ft

160 kg/m3 is 10 lb/cu ft

The 128 kg/m3, 8 lb/cu ft, density is usually recommended. 160 might be marginally better, but it's not usually easy to come by. 2 layers of 25mm, 1", are usually best in a round forge, as single layer of 50mm, 2", is more difficult to wrap smoothly.

In general, the material recommended for forges is high-temperature Ceramic Fibre Blanket. Usually rated to around 2600 degF or 1400 degC.

Insulfrax products are made by Unifrax and I think the Insulfrax range is a series of Low BioPersistence products made from Alkaline Earth Silicate fibres. The LBP fibres are soluble (I assume pretty slowly) in body fluids. The presumption seems to be that they are likely to be safer than insoluble Ceramic fibres over the long term. A ceramic fibre inhaled today will still be in the lung in 50 years. An LBP fibre inhaled today will not.

Different products have different temperature ratings, but the Low BioPersistence fibres generally tend to have significantly lower temperature ratings than the Ceramic fibre products. 

In the UK and much of Europe, it is becoming increasingly difficult to obtain non-LBP blanket.

The lower temperature rating of the LBP products means that the material used to provide a hot-face coating should ideally also provide insulative properties. This will help to limit the temperature at the interface of the hard refractory and fibre to less than the rated temperature of the fibre product. If using a 1400 degC-rated Ceramic fibre blanket, insulation is less of a consideration for the coating layer. 

The big names in refractories are Insulfrax and Morgan Thermal Ceramics. Insulfrax are best known for fibre products. Morgan Thermal Ceramics cover the full range of castables, Insulating Fire Bricks and fibre products. In my (admittedly fairly limited) experience, the Ceramic fibre blankets from other manufacturers seem to perform just as well as the big-name products of similar density and temperature rating. The best materials to use for the hot-face layer tend to be castables. A lot of folk use refractory mortar because it is cheap and readily available, but it does not last nearly as long as a well-chosen castable.

For burners, I would strongly suggest an Amal atmospheric injector from Burlen Fuel systems. You'll need gas fittings to connect to the injector, but the burner tube can be a straight section of pipe, threaded at one end to screw into the injector: I'd source a long stainless steel nipple from ebay or similar. This does away with any concerns over galv pipework, saves a lot of time and effort on your part and produces a burner that is extremely adjustable. Buy the burner factory-jetted for Butane, not for Propane, as it will give a higher maximum flame temperature on Propane than will the Propane-jetted injector. 

I'd only use a single burner, mainly to avoid the hassle of trying to balance two burners to the same mixture/temperature, and size it for your chamber. A 3/4" burner is good for about 350 cu in and a 1" burner is good for about 600 cu in, both to welding temperature.

A rear pass-through port is a good idea if there's any chance you'll want to do long stuff. You can block it off if you are only doing short stuff. I pack in an offcut of blanket personally, but I've seen others use IFB cut to fit.

With an Amal injector-based burner, the temperature control available with the screwed choke means that you are very unlikely to need a muffle tube for HT, though you MUST do your HT outdoors. Closing down the choke to get HT temperatures causes massive amounts of Carbon Monoxide and death is a very real possibility if you run the forge in an enclosed space. 


Edited by timgunn
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I'll chime in on the burner position.  If you're looking to get a swirl pattern in your forge, you will want the burner to come in at a tangent to the inside.  Picture the burner being horizontal, and coming into the forge at roughly the 2:00 position, give or take.  In other words, the top of your burner pipe, when It's sitting horizontally, should be roughly level with the top of the inside of your forge.

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I was hoping you'd chime in, Tim.  Good info as always.  The current castable refractory of choice seems to be cast-o-lite, a lightweight (comparatively) insulating castable.  A 15 - 20mm thick layer is good, more if you're going into production work.  I don't know if that brand name is readily available in the UK, but I feel sure there is something similar.  And Alex is correct on burner placement if you want a swirl.  If you prefer a hot spot as some do, horizontal at 3 o'clock is good if you plan on using the hot spot selectively.  I personally don't care for vertical burner placement because of the chimney effect after shutdown, but to each their own.

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