Forges 101

[Square Nail]

I finally have a break with family and other responsibilities to get back to building my forge but have a question before starting with the Kaowool. Is it better to wrap the inside of a square forge with one piece and just fold it around the corners or cut 4 pieces and place them in one at a time? Or maybe one piece with miters cut at the corners? Thanks for the help!

[Frosty]

I cut it in pieces. I cut the roof to reach clear to the shell and the walls shorter to accommodate the roof's thickness for increased support and shorter bridging distance. Then I run sheet metal screws through the shell into the Kaowool every 4" or so to keep it where I put it.

Rigidizing and a hard refractory flame face might make enough of a difference but I'm a belt and suspenders kind of guy.

Frosty The Lucky.

[Square Nail]

Thanks Frosty! Thats about what I was figuring, I like the idea of the screws!

[(M)]

After considering my options and budget etc, I decided to go for a simple charcoal forge with some basic cement.  If I really enjoy it/ once I get some experience smithing I will probably build the muffler forge with the mods I learned using Frosty's research 101 

(M)

[Frosty]

4 hours ago, (M) said:

After considering my options and budget etc, I decided to go for a simple charcoal forge with some basic cement.  If I really enjoy it/ once I get some experience smithing I will probably build the muffler forge with the mods I learned using Frosty's research 101 

(M)

If you mean Portland Cement NO NO NO! It will not survive contact with a hot fire like found in a forge and will spall. POP throwing chips of HOT sharp concrete.

Take a look at the Just A Box Of Dirt JABOD forge. Charcoal works just fine in a compacted clay soil side blast forge. 

Frosty The Lucky.

[Mikey98118]

What is wrong with using Portland cement in refractory?

After all, if you look at some refractory's cement (binding agent), these two materials look very similar; that's because they are. However, what seperates cements used in concrete from the kind found in refractories, is that refractory cements can be forced dried, to expel the final water content that is chemically locked in its matrix. Concrete cements can never be completely dried, and so that water content will build steam pressure  within the concrete every time it's heated a few hundred degrees.

Some guys try to get around the problem by only using a little bit of Portland in their homemade refractory formulas; this is like trying to only jump off a little cliff, where they might just sprain an ankle, instead of breaking a neck. I am all for innovation, and all for saving money; that still doesn't help turn a pig's ear into a silk purse!

What is wrong with using sand and plaster as refractory?

 Plaster will not hold together anywhere near forge temperatures; but what if you used clay? That would still leave sand as your 'insulation.' Sand is basically silicon (glass). Have you ever tried to drink hot coffee or tea from a glass mug? there is a reason hot liquids are held in ceramic mugs; not in glass. Glass is a lousy excuse for an insulator. The whole point of a forge is to retain heat; not lose it into a heat sink.

[Mikey98118]

Forced drying and preheating refractory

Please note that no refractory is actually water proof. Only hard refractories with high silica content, which have been heated high enough and long enough to turn their silica content into glass, are even water resistant. Think of your refractory as being "bisque fired only" and you will have a good handle on its tendency to re-absorb some water content, from water vapor in the air. Ceramic products are finished glazed to seal them from water absorption; unfortunately, that isn't practical on refractory

All this is just to remind you to run you forge on low, and give it some time to drive any accumulated moisture out of its refractory, before bringing it to incandescent temperatures, if you want to avoid cracking and spalling. Even indoor forges, which haven't been run in a while, should be preheated before use.

Ceramic fiber products also absorb water; therefore, they should be flame dried before finish coats, which tend to seal in water content, are applied; steam pressure will cause rapid spalling of the finish coat. If you seal the burner port, it is wise to drill a small hole (1/8") in the bottom of your forge's shell, to allow steam to exit the forge. I've not only had steam, but even water drops drain from a forge after it has set idle for weeks in cold or rainy Seattle weather.

[Mikey98118]

On 7/21/2017 at 1:10 PM, Frosty said:

I cut it in pieces. I cut the roof to reach clear to the shell and the walls shorter to accommodate the roof's thickness for increased support and shorter bridging distance. Then I run sheet metal screws through the shell into the Kaowool every 4" or so to keep it where I put it.

rigidizing and a hard refractory flame face might make enough of a difference but I'm a belt and suspenders kind of guy.

Frosty The Lucky.

For me, half the point of rigidizing is to provide better support behind a thin hot-face layer; a belt and suspenders take on the deal is wise.

[Frosty]

It depends on how much span a flat roof has whether rigidizer is enough. Letting it dry completely before turning it over really prevents a humped floor like my present forge has. I got in a hurry and proved what I've been telling folk about getting in a hurry. AGAIN! Screws up through the shell didn't un-hump it either. No matter how much I screwed up on this forge it didn't correct the mistake. <sigh>

Frosty The Lucky.

[Mikey98118]

We all cycle through the same (irritating) lessons; I find that knowledge is great at building perspective, but any time we let our selves get sloppy, we make the same messes as the rawest newbie

[Frosty]

I just got in a hurry and fell prey to familiarity. Seriously, how many times have I given instructions on how to put this kind of liner together AND admonished the person to take their time and let it cure and dry properly? 

The current ribbon burner forge is also WAY too large, ANOTHER admonishment I ignored. Well, had I not screwed up the forge's floor I could've made partitions and only used half but with a humped floor it's a 2 burner forge with too small a porch to hold baffles securely. 

I think I'll make the replacement the way I made my first double lined forge. I'll cast the flame face and wrap it with Kaowool then wrap it with the shell. If I wanted to get silly complicated I could cast the burner blocks directly into the flame face but that's worse than silly, it's stupid on less than mass production or factory quantities. I can't help but think about it though.

I believe my next forge will be a vault and ribbon burner(s?) but haven't decided on size. 

Whatever I finally build I'm really REALLY going to try to avoid the mistakes. Time for a new batch. 

Frosty The Lucky.

[Mikey98118]

High temp ceramic fiber insulation for low cost

So now that we have a superb homemade refractory hot-face available (zirconium silicate & Veegum), we need a break in the price of higher temperature backing insulation. How about doing a little extra work in return for a whole lot of savings? Enter phase two: Bulk ceramic fiber

https://vod.ebay.com/vod/FetchOrderDetails?ViewPaymentStatus&purchaseOrderId=180000042145878

[Mikey98118]

2600 semi-hard & semi-insulating fire brick

"Thermal Ceramics, a division of the Morgan Crucible Co., England, has recently introduced a new product, K(R)-26 IFB. Historically, 2600F grade insulating firebrick have been relatively dense materials, generally produced by a pressing or wet compaction process. In 1998 Thermal Ceramics began extensive development efforts with the aim to produce a 2600F insulating firebrick using the company's unique casting process. The result of these efforts is the new K-26 IFB. Until now the advantages of the casting process -- more micro-porosity which improves thermal conductivity -- were not available in a 2600-degree brick. At a mean temperature of 2000F, the K-26 IFB performs equivalent to lower temperature IFB such as the K(R)-23 and the K(R)-25 on thermal conductivity value and substantially outperforms ceramic fiber blanket at temperatures higher than 2000F. And at a density of 40 lbs/ft(3), K-26 IFB is roughly equivalent to K-25 (2500) IFB."

The company's website is located at http://www.thermalceramics.com

Note: The only reason that this product will perform as well in ceramic fiber insulation at 2000 F is that most of the heat transfer at that temperature (and up) is by radiation; not by conduction. This means that only the portion of either product this can be applied to is the part that is at yellow incandescence.

eBay source of 2600 insulating fire bricks: https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1311.R1.TR6.TRC1.A0.H1.Xinsulating+f.TRS0&_nkw=insulating+fire+brick&_sacat=0

These bricks are semi-insulating, and be considered half-hard; they can stand up to thermal cycling without crumbling, and wont fracture from careful handling, but can be improved in mechanical strength, resistant to hot flux, and insulation value with a coating of zirconium silicate/Veegum homemade refractory

For all you people who buy half bricks to save money and trouble; here is a much better choice (even without the coating).

[Mikey98118]

The 1" thick version of these bricks make the perfect transition layer to place between a high alumina kiln shelf and a pillowing layer of ceramic fiber insulation, to protect it from being overheated by the shelf temperatures.

[MonkeyForge]

A short addition to the Veegum/Bentone + Zirconium silicate discussionwe have been having. On sintering a good rule of thumb:

 

• Time, which has a linear effect on the sintering. Doubling the sintering time doubles the amount of sintering that takes place.
• Particle size, which has an inverse power relationship on the amount of sintering. Reducing the average particle size will reduce the amount of sintering time required.
• Temperature, which affects sintering exponentially. A small change in the temperature will have a large effect on the sintering rate.

(Source: http://www.ceramicindustry.com/articles/86197-why-aren-t-you-firing-faster)

Sintering itself is a fairly complex process, especially if you consider the endless combination of raw materials you can combine to achieve different physical properties. I am by now means an expert but I have learnt a lot lately. Digitalfire has a comprehensive page on the process as well, and it has pictures

 

[Mikey98118]

Morgan Crucible company's 2600 F rated insulating fire bricks make a good balance of endurance and fuel efficiency. A heat reflection coating should bring them completely up to snuff for holding up to flame impingement, while increasing fuel efficiency even further. Do not use foamed clay fire brick as primary insulation; they have nearly zero mechanical strength, and crumble from thermal cycling. Semi-insulating alumina fire bricks have much more strength, but as is true of refractories, not all 2600 bricks are the same. Morgan claims their bricks to be much more insulating than other brands, because they have more micro-pores, which better block heating by conduction. A good indication of a material’s ability to slow heat conduction is its weight. The average 2600 aluminum based refractory is 85 lbs. to the cubic foot; bricks made out of it weigh the same. Morgan’s 2600 bricks are aerated during construction, and weigh only 45 pounds to the cubic foot.

I have been looking for a reasonably priced alternative to ceramic fiber board for years; This looks to be it. Alumina brick can be cut using ceramic rated cutoff disks in saws, and angle grinders, and drilled using carbide encrusted hole saws, and carbide tipped cement drilling bits.

[jcornell]

Veegum T is available from my go-to supplier, Axner.com.

http://www.axner.com/search.aspx?find=veegum

[Mikey98118]

 

thanks; every supplier we can come up with helps.

[Mikey98118]

Nothing is obvious to an anxious mind. Take flame paths; the longer the better is a given. But, take a careful  look at your forge:

(1) Is your back wall closed, accept for  a SMALL opening to occasionally pass long material through? Do you keep it closed when not in use? If not, you are shortening some of the flame's exit path, and wasting fuel.

(2) No two burners have identical flames; this goes double for homemade burners. If you have two or more burners, are they positioned so that the richest burner is at the back of the forge, and the leaner burning is forward of it? If you have three burners, and one burner is burning rich, one neutral, and one lean, they should be positioned as; back wall, than rich, than neutral, than lean, and than exhaust opening.

(3) A swirling flame path is a long flame path. But is isn't always possible to position your burner on a tangent. You may choose, for perfectly logical reasons to build a box forge; and their a lots of old box forges that you may decide to buy, and recondition. If you can't position the burner for a long flame path, try to produce a shorter flame. Multiple flame ceramic heads, such as found on ribbon burners, and Giberson style ceramic heads are the best choice for creating short hot flames. But many burners have a fast enough mixture flow to allow deliberate shortening the mixing tube, or mounting a radical flame nozzle, which will create a shorter brush flame. Nothing tried means nothing gained...

[Mikey98118]

Cerium oxide

Cerium oxide (CeO2) is an even more famous emissions agent than zirconia, is used as a stabilizing agent for zirconia oxide, and its flour (nanopowder) costs about one fifth that of zirconia oxide flour. Moreover cerium oxide nanoparticles disperse well into other mixtures. I think it might bump up performance levels of heat reflection in zirconium silicate refractories, and could partner with Veegum T as the ultimate homemade heat reflective coating.

Warning: Use a respirator; you DO NOT WANT this stuff entering your lungs!

 

[Frosty]

Can you post a link to it's properties as an IR re-emmiter? The MSDS says it's a potential skin and eye irritant, wear PPE. Don't eat it. No special handling instructions, pick up large spills with a shovel, No Reportable Quantity. No degradation hazards. Stable chemically. Reactive in acids, no hazard.  Non soluble in water, any temp. Etc. etc. Looks to be pretty benign though not as hard as zirconia if you're looking for abrasives. 

The stuff is commonly available as glass and lapidary polish, though I don't see anything about % of content in adds but I didn't dig. I'll look next time I'm in an auto parts store or Walmart, etc.

Interesting stuff Mike.

Frosty The Lucky. 

 

[Mikey98118]

Frosty,

You will have to dig hard to find any specific information on percentage of I.R. re-emission from cerium oxide; if I run across any such numbers, I will post them. What I found was mostly strewn through half a dozen inclusions of cerium oxide as a preferred emission agent, in lists of them in various patents for heat reflection coverings. I had already run across it is one of the substances used for stabilizing zirconia. And this, along with cerium oxide's vary small particles, (which is a natural outcome of its processing, rather than any need for grinding), decided me to include it with any future zirconia oxide of zirconium silicate based refractories and heat reflective coatings from now on.

One of the other ingredients I noted in heat reflection coatings was silica;  a preferred binding agent, because it passes radiant energy well. This makes me feel much better about using zirconium silicate in place of expensive stabilized zirconia flour in heat reflection formulas. 

[Mikey98118]

On 8/4/2017 at 0:24 PM, Frosty said:

Can you post a link to it's properties as an IR re-emmiter? The MSDS says it's a potential skin and eye irritant, wear PPE. Don't eat it. No special handling instructions, pick up large spills with a shovel, No Reportable Quantity. No degradation hazards. Stable chemically. Reactive in acids, no hazard.  Non soluble in water, any temp. Etc. etc. Looks to be pretty benign though not as hard as zirconia if you're looking for abrasives. 

Yes, and some even started out listing it, at a possible health product; for use as an antioxidant; apparently it is very reactive in human tissues; then they started finding it can enter cells, and now it is starting to be warned against. We don't want any brave souls achieving their Darwin awards, while officialdom is making up their minds, do we? The problem is that health issues have become just another political football.

[(M)]

On 7/21/2017 at 11:48 PM, Frosty said:

If you mean Portland Cement NO NO NO! It will not survive contact with a hot fire like found in a forge and will spall. POP throwing chips of HOT sharp concrete.

Take a look at the Just A Box Of Dirt JABOD forge. Charcoal works just fine in a compacted clay soil side blast forge. 

Frosty The Lucky.

No don't worry.  it is a firebrick refractory cement so it wont explode. it is good enough for now.  

[Frosty]

Refractory cement is a waste of money, it's intended to stick bricks together not act as a flame face. It'll have a limited lifespan in a forge bot shouldn't spall dangerously.

A real refractory intended for flame contact is a much better choice and often less expensive on the front end.

Frosty The Lucky.