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I Forge Iron

Portable side blast forge


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The base devices a metal forger needs are blacksmith's iron, sledge and produce. The manufacture is maybe the most variable of the smiths devices. It can be powered by an extensive variety of powers and come in numerous designs. Its errand is straightforward, to deliver an adequately high temperature and in adequate ability to make metal plastic or even dissolve it. While the wellspring of air (the impact) is a need for all fuel smoldering manufactures. Air can be given by anything from blow pipes and cries to current air compressors and electric blowers. There are such a large number of approaches to create the impact that it is a different subject. The metal forger shop was altered with hand wrench drill squeezes, shears, punch presses and produces with proficient hand wrench or line shaft driven blowers. This was additionally the time of the steam hammer and mechanical force hammer and bringing us cast iron manufactures and fashion parts. Produce enhancements included cast "ducks home" tuyeres, fire pots and finish compact manufactures going from light weight bolt fashions and overwhelming obligation modern produces. Before the end of the 1800's gas and fuel oil produces wer being used and also enhanced coal and coke manufactures.





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4 hours ago, Broadus said:

I understood all of that, and I was calling the side screen a wind block. I've heard and seen that a big hood like that doesn't work outdoors, is it the side screen that makes yours work? Sorry if this sounds argumentative, I'm just making sure I get it right... That style of hood looks so much better and is much simpler to design around this style of forge.

Not argumentative at all, it's called research. It seems there is a lot of "I have heard" and "In theory" around, all I can say is that as you can see, that design works.

A few more things that may help, Chimney size works better above 10" diameter, The gentler the slope on the hood the better and make sure your line of sight to the fire when standing by is unblocked by the hood, 

The side screen is normally used if there is a substantial amount of wind present, if it is a relatively gentle breeze, it is not needed, 


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Clarification:  I design HVAC systems for a living, hoods are a small subset of this. I am not a professional industrial hood designer but have been responsible for designing hoods for anything from Type 1 commercial kitchen operations, BSL 3 capture, and welding operations in my career.

There are advantages and disadvantages to each type of hood.  I've used both, and correctly designed they both work well.  Everything in life is a compromise, you just need to decide what compromises you are willing to accept.

The side draft hood has a lot of advantages:

  1. It is smaller than a full sized overhead hood so more easily portable.
  2. It is typically located closer to the source of heat.  Since the temperature differential between the hot fumes rising off the fire and the surrounding air are what drives the exhaust, the closer the better.  For equal diameter and height stacks that temperature differential will move more air at higher velocity.
  3. It does not obscure the view from above or the sides

A couple of disadvantages:

  1. Side drafts are not always "self-starting" so to induce the exhaust flow you often will need to start the airflow up the stack by throwing in some burning paper or the like
  2. Careful attention to design is required to avoid having the bottom of the hood getting filled up with ash and/or coke pushed in while fire tending or dropping down the stack
  3. Optimal design should have a smooth transition to the stack, though it isn't as critical as with an overhead hood
  4. Stack support can be more problematic for a freestanding unit as the base of the hood is a lot smaller than a full hood.
  5. Because it handles hotter flue gases construction may need to be of thicker material and for a portable forge it may take longer too cool sufficiently to move when finished forging.

Overhead hoods have the reflection of those pros and cons, essentially, but there are a couple of caveats:

  1. Side skirts will help a lot, and can be designed with a 30-45 degree cut away if necessary.
  2. Hood should be kept as low as possible over the fire to avoid inducing more surrounding ambient air.  This can be a problem with both seeing your work and banging into the hood.  Any crosswinds may exacerbate this.  For outside forging attempt to orient your hood in a direction so the closed side is to the apparent wind if possible.
  3. Ideal capture velocity is around 100 FPM, ideal stack velocity is in the range of 1,500 - 3,000 FPM which should give an idea of relative cross sectional areas.  The heated plume from your forge will also spread out as it rises, so a good idea of how large a fire you are planning will help with your design.
  4. As mentioned the transition between the hood opening and stack is somewhat critical.  As there isn't the same heat differential driving the exhaust it is more important to have a gradual transition so you minimize your friction losses.
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The only time I have problems with smoke is when first lighting a coal fire, with charcoal you have to watch out for sparks/fleas being blown in to the audience.

I agree with Frosty about form and function, go with the KISS principle and find out what works then you can add the flash later - a good coat of heat proof paint makes a lot of difference to rust and welds for a small outlay.

Side blast or fire pot? to most of the people watching it does not matter, all they will see is a pile of coal/coke/charcoal and the fire. I find most folks are interested in seeing the bellows work than the hearth itself - it certainly gets the conversation going.

If you have the hood as in JohnB's pictures then unless you turn the hearth round they are not going to see any of the fittings at the rear so why the trouble, cost and weight?

The main things you will find the public want to know are often - is it a real fire? what are you cooking? do you shoe horses? my --------------- was a blacksmith etc

Some things I find at demo's is that it is hard work on your own, you will have folks round as soon as the fire is lit and you will have a devil of a time trying to catch a break. Also show the organisers you are serious - safety ropes, visible fire extinguishers, have documents to hand, insurance etc.. if you look and act professional it scores a lot of brownie points.

Sorry for the long missive


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On 5 May 2016 at 8:33 AM, turbo7 said:

It looks to me as if the bottom of the chimney is surrounded by the bosch? If that is the case wont this heat your cooling water? To a point where the water wont be doing any cooling at all. Why not just go with a sacrifical tuyere instead of a water-cooled one?

Not true. Water boils at 100 degrees as we all know right. You can't take water beyond that temperature as it will just boil off and become steam. Therefore your bosh never goes above 100 degrees, which is still pretty hot but it is so much cooler than the centre of your fire. So as it circulates around the tue, it will cool it to 100 degrees or so. So in effect the water is always cooling the tue. 


Have you considered making the design modular? I enjoy having a design that is easy to dismantle / reassemble. You could have a bolt together frame for your hood that you can strip down quickly and easily for example. 


All the best 


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9 minutes ago, Charles R. Stevens said:

Beg to differ, it's 212 degrees, what is this 100 degrees bunk?! ;-)

glad you jumped in Mac.


I'll start using centimetres if you're not careful. :P - That's a lie I only use millimetres when it's under an inch. Big stuff almost always gets measured in inches. 


Cheers Charles. Part of me wants to complete that side blast build when I get time. Ended up buying a proper side blast forge though. 



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We used centimetres mainly at school but I was lucky enough to use feet and inches when playing tabletop war-games so I'm quite happy to use both. 


Anyway we digress. 


Broads - I'm interested to know whether you will be fabricating a cone or just using thick walled pipe as it is? 


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I worked in the State materials lab a couple years and after about 3-4 months could convert from metric to SAE to engineering scales without thinking about it. I'd have a blue print scaled in decimal, changes in feet and inches and the lab does everything in metric.

It's been too many years though I have to stop and think, maybe even push a button or two in my Casio calculator watch. I sure wish those things had a light button. Sigh.

Frosty The Lucky.

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Mac I want to attempt to fabricate a cone from a  fan like pattern, but if that proves too difficult I'll try taking slices out of a thick pipe. 


I think I've finished my final design, if the weather is good tomorrow I'll start fabricating.

Thank you guys so much for the help!


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I'd still have a go at fabricating a cone if you can. I used the pipe / pie slice method which worked well enough though my maths were way off and the slices I made were too big. So my advice would be to cut very small slices to start off with. 


John, it just occurred to me that cast iron tue's are conical for a reason. I had always assumed this was because it helped to circulate the water better, but is it simply because that shape would have been easier to cast?


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6 hours ago, Everything Mac said:

John, it just occurred to me that cast iron tue's are conical for a reason. I had always assumed this was because it helped to circulate the water better, but is it simply because that shape would have been easier to cast?

Hi Andy, probably a bit of both, draft angles make for easier removal of patterns in the sand casting process used in making tuyeres, and the taper reduces the possibility of an air lock when the tuyere is being initially installed and filled with water, 

Some of the water cooled cast iron tuyeres had no bosh tank directly attached to them, but a reservoir tank was connected by pipes to them. This reservoir tank could also be used to provide hot water for other uses in the area.


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John B, could you elaborate on this comment? 

There is no necessity for the tue to be conical in shape, just tilt it forward at a slight angle so any air does not get trapped at the front when you are using it, 


When you say tilted forward, do you mean upward in relation to the bosh wall?

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