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Building a Forge

Advice and help appreciated :)

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ChrisB15/12/2019 09:17:52
448 forum posts
175 photos

In an earlier thread I had mentioned I needed to do some case hardening for some parts - this will not happen until I have the means to heat them up to the required temperature so I thought building a small forge (kiln or oven, not sure what I should call it!) would come handy both for this project and further future uses.

After reading both on this forum and watching videos on youtube I got a rough idea of what I need, but before I go ahead I thought I'd post here so if I'm going off track I'll get told off!

I have found a local fire brick supplier which has bricks capable for 1400'C - these should be ok for my use right? **LINK**

My next question is which way to lay the bricks and build the forge. The bricks measure 200x100x50mm. I would like to lay the bricks in a way such that I have a decent usable space inside the forge.

Most of the videos I seen using bricks lay the bricks as in the picture below right hand side without any mortar. That will give me a space 100mm square by 350mm deep. If I lay the bricks as on the left of the picture I would get a 150mm square by 350mm deep space - but I would be using mortar to hold everything in place. I also intend to surround and support the bricks with steel angle section all round the edges - which should help holding everything together.

Which way is the best practice to do the job, or are both acceptable?

forge.jpg

SillyOldDuffer15/12/2019 10:13:29
5018 forum posts
1062 photos

The bricks should be fine, though I see they are the heavy constructional type. It's possible to get lighter, much weaker bricks, that can be sawn to shape and are even better insulators. (The soft type are used to line kilns, whereas your Spanish blocks are strong enough to hold up an entire chimney.) I use soft bricks because my 'ovens' are all small temporary affairs, either for tiny indoor work, or larger objects outside. (Fire hazard.)

The construction on the right is much stronger than that on the left.

Two main problems with the left-hand build: the uprights are more likely to topple and there's no support for the right-hand end of the top bridging bricks. It's unstable. An oven that might fall over in the middle of a job due to an accidental bump isn't for me! Could be fixed by adding more support, but the bricks would have to be drilled and cut. Probably better to build a large brick kiln vertically, but an upright structure is more elaborate.

Depends on what the forge is for: the advantage of a small kiln for a bit of brazing is they don't need so much heat to get up to temperature. On the other hand small reduces working space and isn't smart if you need 10kg of molten cast-iron.

Dave

DMB15/12/2019 10:19:11
949 forum posts

Hi ChrisB,

Going on other's earlier postings, maybe better to use white insulation blocks from a building supplies co as they reflect and intensify the heat. Refractory bricks absorb and hold the heat, no so good for your proposed useage. Must emphasize that I have not tried this out, it's only what others have said. I plan to do this, next summer? maybe. See if you can track down prev. discussions on this subject.

John

JasonB15/12/2019 10:33:25
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16912 forum posts
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I'd go with the vermiculite bricks and boards, couple of layers of the board at the bottom, brick on end for the verticals and another couple of layers of board for the top would give 160 x 230 internal and no cement plus throw a lot more heat back into the work

3404615/12/2019 10:35:36
914 forum posts
6 photos

With DMB on this one.

Merchants gave me a dozen slightly damaged free.

No Mortar needed.

I can get a depth of 18 deep by 9 high by 10 wide without cutting ( inches )

Easily dismantled if not needed for a bit.

Bill

ChrisB15/12/2019 13:07:04
448 forum posts
175 photos

Thanks for the input gents, good thing I didn't go ahead with my plans!

I can't locate any vermiculite bricks locally, I had asked around and everyone directed me to the oven/fireplace type bricks I linked. I only results I'm getting for vermiculite is some potting compound at florists shops etc - not what I need!

I'm trying to locate an online supplier from abroad but delivery costs are quite high unfortunately. I'll keep on looking maybe I find something.

David George 115/12/2019 13:26:23
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1015 forum posts
320 photos

Try these for all sorts of material.

https://www.castreekilns.co.uk/refractory-44-c.asp

Not used them but they supplied a factory I worked at.

David

JasonB15/12/2019 13:29:06
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Why are you looking for an online supplier abroad, CuP that I linked to are in the UK?

Skamolex is the trade name made by Scamol if you want to search for that

Edited By JasonB on 15/12/2019 13:32:58

ChrisB15/12/2019 13:48:48
448 forum posts
175 photos

I'm getting confused, not sure if I'm looking at the same thing as prices vary quite a bit. The one you linked Jason **LINK** 230x115x25mm costs 12£ each. Are these the same? **LINK** These are the same size but cost 22£ for qty10. Am I looking at the same thing?

JasonB15/12/2019 15:13:19
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Certainly looks like the same stuff.

SillyOldDuffer15/12/2019 15:39:28
5018 forum posts
1062 photos
Posted by ChrisB on 15/12/2019 13:48:48:

I'm getting confused, not sure if I'm looking at the same thing as prices vary quite a bit. The one you linked Jason **LINK** 230x115x25mm costs 12£ each. Are these the same? **LINK** These are the same size but cost 22£ for qty10. Am I looking at the same thing?

It is confusing!

First off, there are two very different types of firebrick. One is designed to absorb heat and is used in night-storage heaters, reverberatory furnaces and maybe in chimneys. Useless for making forges because they soak up expensive heat like a sponge. Nearly as good as a bucket of water. The other is insulating bricks, but these come in a wide variety, depending on what they are for:

  1. From an ordinary building merchant, insulating bricks for keeping houses warm. Fairly strong and good insulators, but fire resistant rather than fire-proof. Not ideal for high-temperature work but cheap and available. People use them and seem happy.
  2. The Spanish items appear to be a strong constructional insulating brick intended for fireplaces and chimneys. They'd be good for building a serious furnace, something intended to take a lot of weight. However, the insulating properties of tough bricks isn't top-notch, and a proper furnace made from them would likely have an inner lining made from something more expensive, see below.
  3. Various bricks sold for furnace linings, pottery kilns etc. These tend to be soft and porous, good insulators, but constructionally weak. But even the weaker types should be plenty strong enough to to build a basic brazing hearth. Cost varies considerably with temperature resistance and strength: high temperature bricks (1500C) are distinctly more costly than 1000C bricks.

Just a guess, but maybe the Cup Alloys Vermaculite is high-temperature and wear-resistant for workshop use whereas the other type is more domestic. My pottery firebricks make a crumby white mess when moved, possibly Cup Alloys is sterner stuff.

My main problem with brazing isn't the hearth, it's the torch! With an ordinary tin-can torch, I find I need to build a junior igloo over and around the job, otherwise heat escapes so quickly it's hard hold the required temperature for long enough. Fumbling not tolerated! My feeling is a small torch needs all the help it can get from a well-insulated hearth, whilst a big torch will cope with a bigger hearth even if it's insulating bricks aren't top notch.

Beyond that I don't think the type of insulating brick is particularly mission critical unless very high-temperatures are needed. Just don't use ordinary bricks, especially if damp, or - far worse - heat-absorbing fire brick.

Dave

Tim Stevens15/12/2019 17:15:04
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1122 forum posts

On a different tack - it is not clear (or I missed it) how you will be heating the furnace. If you are using gas - perhaps with a big torch - You need to sort out the ventilation of the inner space. Get this wrong and the flame will not get enough air, and will go out. Supply too much air or allow too clear an exit and most of the heat will escape.

If you have an electric heat source, this problem does not arise, of course.

For the liner blocks, you might find it helpful to seek out suppliers of wood-burning stoves (which have linings, of course).

Regards, Tim

ChrisB15/12/2019 17:16:02
448 forum posts
175 photos

Thanks Dave for taking time to explain, much clearer now.

I sent the ebay seller a message asking for the temp rating of his bricks - seeing a similar listing on amazon **LINK** from the same seller I think they're rated to 1200'C, which would be plenty good for my use. £28 for 12 bricks and £15 delivery is a bargain!

ChrisB15/12/2019 17:27:31
448 forum posts
175 photos
Posted by Tim Stevens on 15/12/2019 17:15:04:

On a different tack - it is not clear (or I missed it) how you will be heating the furnace. If you are using gas - perhaps with a big torch - You need to sort out the ventilation of the inner space. Get this wrong and the flame will not get enough air, and will go out. Supply too much air or allow too clear an exit and most of the heat will escape.

Yes Tim, that is the next hurdle.

Most probably I will be using LPG gas not electricity for heating. I have seen builds of a venturi type burners on youtube - they look pretty simple and straight forward to build. **LINK**

ChrisB27/12/2019 16:25:35
448 forum posts
175 photos

The vermiculite bricks I linked from ebay are good for 1300'C according to the seller which should be good enough for me. He also has some other type of insulation brick with three levels of heat resistance which are also lightweight like this: **LINK**

Thinking about the burner, I have spent time on youtube and the internet and it seems the most fuel efficient and quick heating is the Ribbon burner. It seems to be able to operate at a lower gas pressure than a venturi burner, so I was thinking a domestic LPG cylinder and regulator might be able to keep up the gas flow for the flame...

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