Re: Refractory blanket how-to for welding forges.
- Greetings Michael,
Sorry for taking so long to respond.
I am reluctant to agree about iron forge welding at a red heat. My understanding is that a red heat is about 1300F to 1600F, the temperature that Borax melts, versus 2300F the temperature about which a person can perform a forge weld. See chart: http://www.blksmth.com/heat_colors.htm
While two pieces of iron/steel can be stuck together at a lower red heat, that is usually because those pieces of iron are "glued" together by the melted Borax. A true weld requires that the surfaces of both pieces of iron/steel are melted, and by tapping the two pieces of metal together, their liquid surfaces merge, thus causing the two to become one piece of iron/steel. The difference between two pieces that are glued together compared to a true weld is that the two pieces can be peeled apart when sufficient force is applied to separate them, while a true welded item can not be peeled apart.
During the over 40 years that I have been a hobby smith, I have even taken a course on forge welding where the instructor believed that glued pieces of steel were a valid forge weld, and that the test was to peel them back apart to see how clean the "forge weld" was. Fortunately, after taking a course some years ago with one of the founders of the American Bladesmith Society, a recognized Master Bladesmith, I feel that I have a better understanding of forge welding.
I am aware of perhaps the basics of both the reflective coatings, over castable coating, over two or more layers of rigidized refractory wool, as well as the (again) perhaps the basics of a cast shell of 2 or more inches of castable refractory... but I am definitely not an expert in building gas forges. I am more of a jack of all trades and a master of none. I believe that it is likely I have your book on my shelves somewhere, but since my wife is asleep, and many of my reference books are out of reach until building a new bathroom is complete, searching for it may not be possible.
I thank you for the referrals to the two suppliers you mentioned in your earlier missive, I will check but I believe I already have them in a table of available suppliers and their various brands of castables, rigidizer, ceramic wools, and three types of reflective coatings.
As for my name, it is David Einhorn... which translates in English into "Beloved Unicorn", Einhorn being the German word for Unicorn, and David being the Biblical version of the word Beloved. ;-)
I will message to you may email address. It would be my pleasure to gift a copy of my book to you if you provide a snail mail address for its delivery.
--- In firstname.lastname@example.org, michael.a.porter@... wrote:
> Dan recommended my book in the context of welding forge building; this brings up a subject I've been avoiding for years, but now it's time to "clear the air."
> The standard method of ceramic fiber placement shown in Gas Burners for Forges, Furnaces, & Kilns, was to position two layers of ceramic blanket material against the inside of the forge shell, wrapping them in position so that they would be trapped in place (like any other arch; through weak material compression at their ends) while stiffening into a permanent shape (the material is well known for "taking a set" as it loses springiness through repeated heating). This method has advantages for the builder of a typical gas fired hobby forge (easy and economical), BUT not for the construction of a blacksmith's dedicated welding forge. Experts agree that upset welding can be dependably done at red heat, but nearly everyone feels the urge to weld at far higher temps. It isn't a how-to author's job to shake an expert's finger in the face of readers, but to point out the best path, and then to try to accommodate preferences.
> An average would-be forge welder wants white heat. But, white-hot internal temperatures greatly accelerate shrinkage of ceramic fiber products. You're not going to find this problem touted in sales literature, but it's a hard fact of life; this leaves the builder of a general purpose gas fired forge fairly unmolested, until a fascination with forge welding develops; afterward, it usually leaves the victim switching to castable refractory and/or firebrick. But, there is a better way...
> Dudley F. Giberson, Jr. (a pioneer of the American hot-glass movement, and author of A Glassblower's Companion) perfected the technique of cutting his ceramic fiber blanket into folded squares, and highly compressing them against one another to form arch (and tube) shapes, thus making a complete end-run around the problem of shrinkage in his glass working equipment way back during the early days of ceramic fiber availability to the public (it was originally developed for NASA in the seventies). No one has found a better method since. Rigidizer, and toughening coats work best when the surface beneath them is itself highly stable. The reason for adopting this method in construction of casting furnaces should also be obvious.
> [Non-text portions of this message have been removed]
Recently someone on one of the casting groups commented that there was no such thing as a cement that can have all of the water baked out of it; I believe this was done in defense of the use of Portland cement in a homemade castable refractory. The official answer would be that the chemically locked portion of water in lime based cement cannot be baked out, but the chemically locked portion of water in refractory cements can be. I have always accepted this official version as the only reality...in the past. The limiting factors on "baking out all the water" are that the refractory must be taken to yellow heat in the first place, and that over time, water content can recollect in refractory if you're not careful to seal the refractory surfaces against water vapor in ambient air.
However, truth of any kind is seldom found effortlessly; including technical "truths". I suspect that a healthy debate, with both sides airing their views, might adjust what the majority of us accept as practical reality--to our mutual profit; this could be important for people wanting to make insulating refractories as secondary layers. Homemade refractory as an insulating secondary layer might be quite forgiving of official standards; standards useful for hot-face layers may constitute a waste of money in secondary refractory layers.
While casually dismissing the Portland cement idea, I have noted both resentment, and a strong hint of "I'll match your official facts with personal experience" in passing (heated) comments from the other side of this issue. Isn't it time they had a FAIR hearing; something open minded, maybe?