Jump to content
I Forge Iron

Greenpatch 421


Recommended Posts

Shrink checking is really common in a water based mud to use a generic term so developing cracks is probably the norm for the product if laid on thickly. If there is a next time you might try laying on really thin coats and letting it dry between.

Of course the problem might become spalling and that's a lot worse than patching cracks.

I'm really happy for you, there's nothing like designing and building a piece of equipment and having it perform as you wanted. Feels like sweet victory.

Frosty

Link to comment
Share on other sites

Frosty,
Thick, thin; the key word, I believe, is shrinkage. Some parts I did real thin, others not so thin. still cracks. I may try to "mortar" the cracks after the forge cools some time with, I don't know Greenpatch 421 MORTAR!?!? :D Do it when I know I won't use it again for a couple days. With the warmer weather coming, it should have time to dry thoroughly. But you are absolutely right about a successful DYI project!! ;)

James,
Will look forward to progress report :)

Scott

Link to comment
Share on other sites

  • 2 months later...

progress report

I lined the forge with a mix of kaolin, pyrax, and polyester fiber. The reasoning was the kaolin shrinks, the pyrax expands, and the polyester holds it together while it dries then burns out. I put a greased piece of 6" duct inside the ceramic wool insulation, and poured the mix in.

This didn't work worth a crap. With the forge on end, the wool compressed more at the bottom from the pressure head of the thin mix. The greased duct didn't let any air get to clay, so when I pulled it out there were chunks of wet clay attached. I smoothed it out by hand and dried it over about a week with light bulbs and a household space heater. It still cracked all over the place.

After ten plus hours of use, it isn't a total catastrophe. The insulation is stabilized. The lining is fairly durable. It is so thick that it holds heat really well for normalizing, but not so thick it takes too long to heat up.

Next time I'll leave out the polyester fiber - it really smells. I should have mixed the slip thicker and pressed it in by hand and smoothed it with a tool.

Link to comment
Share on other sites

James, I tried something similar to the duct inside to use as a mold and had similar results. I didn't grease it but it still didn't dry due to lack of air flow. In the end I just smeared the mortar and smoothed it by hand. I wore rubber gloves to protect my skin and it came out pretty good. The only draw back to the goves was that on second and additional coats the gloves shredded quickly due to the roughness of the first coat. I would use heavier kitchen gloves rather than the thin gloves my wife brings home from the hospital :D

Link to comment
Share on other sites

Use Sonotube, the cardboard cylinders used for concrete forms. Then ram it in as dry as will compact properly, the less water the less shrinkage.

Once it's rammed up and had a little time to set (actually SETTING is the best reason I know of to add about 1pt in 8-10 portland cement to home made refractory recipes) just peal the sonotube and let it dry completely.

Frosty

Link to comment
Share on other sites

  • 4 weeks later...

I welded a billet in the new forge and I found that Greenpatch 421, like most any other refractory, is not immune to the corrosiveness of molten borax. Seems to be more stable on the 3/4" slab that comprises the floor, however, but a small protrusion on the opening was easily breached while hot. No biggie; it will be easily repaired but can be used as is also. Mostly cosmetic. The sides maintained good rigidity even at a good yellow heat. Overall, it has surpassed my expectations and I am considering my testing stage complete.

Link to comment
Share on other sites

The only reasonably inexpensive alternative to zirconium ceramic I have seen recommended is Satinite. It is a dry motor from AP Green. It has a limited official shelf life. I belive if kept dry and double bagged it may last longer than that unmixed.
Boraxwill reduce hard fire brick to mush if it is heated long enough.

Link to comment
Share on other sites

A high phosphate or phosphate bonded refractory will be unaffected by hot borax or other fluxes. The refractory I used for my little pipe forge is no longer available but someone here uses another brand.

You might try searching refractory suppliers for the phosphate refractories. If it's important enough that is.

Frosty

Link to comment
Share on other sites

That I couldn't tell you. Perhaps a sales rep at a refractory outfit could. I know the guys at EJ Bartells in Anchorage LIKE talking about fire, the hotter the better and have always gone out of their way to get me the best available.

Just tell them what you're doing and that you need something resistant to caustics at high temps. If you say high phosphate right off that's what they'll look for or show you and there may be something better out there. That's why I like to describe what I need and see what they have before I tell them what will work.

Believe me, the guys at Bartells hold me in much higher regard than I deserve for building my own forges and burners. They regularly refer folks to me who want to build home made furnaces.

Frosty

Link to comment
Share on other sites


Just tell them what you're doing and that you need something resistant to caustics at high temps. If you say high phosphate right off that's what they'll look for or show you and there may be something better out there. That's why I like to describe what I need and see what they have before I tell them what will work.
Frosty


Sort of like, "It's better to ask forgiveness rather than ask permission!" LOL Thanks Fosty. I still have 40# or so of the green patch to make repairs ;), but I'll keep those guys in mind.
Link to comment
Share on other sites

No, it's more like not tainting testimony by telling the person what you want to hear first. I got my very best advice the first time I walked in the door and didn't know diddly about what was what. All I knew was I was making a propane fire in the 3,000f range and introducing borax to the mix. The sales rep was instantly intrigued and spent a good 45 minutes looking through product books and talking specs, performance, durability, longevity, application hassles, etc. etc. What we do is short or fast thermal cycling and that is really hard on refractories. This was something he really focused on.

Anyway, the industry is always coming up with new stuff and I like to find out what the dealer thinks before making up my mind. Unfortunately he asks MY opinion now instead. On the up side he often gives me samples to test.

Frosty

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...