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Hoffman's Forge
September 13, 2010
3:44 am
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Jymm Hoffman
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Forum Posts: 11
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September 10, 2010
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Starting with the manifold, it is made from 1 1/2 inch black pipe parts. The burner tips are 10 inch nipples cut in 1/2. I heat them up and flatten to a 1/8 inch sheet to act as a gauge. I no longer us elbows and street ells as it requires more adjusting or tuning of the burners tips. By only using T's, there is less need to adjust the burner tips (open one that is not burning as well as the other by using a long chisel while it is running.) The T's do not necessarily have to be welded together as I do, you can use short nipples to connect everything. I recomend one of this size burner tips for every 6 inches in length of shell. I used to recommend 1/8 inch hole for the gas, but the newer method of connecting a 1/4 nipple to a ball valve into the 1 1/2" to 1/1/2 inch T works fine.Or the 1/4" reducer can be plugged with 1/2' threaded rod, cut flush. Then drill a 5/32" hole in the center of the plug and counter sink (so the conter sink bevel is the outlet of the gas into the 1 1/2" pipe.)

VERY IMPORTANT: This system works on household gas pressure, here in the United States, that is 11 inches of water column, about 1/2 pound of pressure. A common regulator that is already set for this pressure is used on outdoor gas barbecue grills. Do not try this system on high pressure gas with this large of an orifice. I normally run 3/8 to 1/2 inch rubber propane hose from the regulator to the ball valve.

NEXT IMPORTANT PART: The blower must be a high speed blower that can produce not only enough CFM, but also enough pressure. I do not know what the minimums are, I use blowers readily available from Kayne & Son/Blacksmiths Depot: [COLOR=#384967]BLACKSMITHS DEPOT BLOWER[/COLOR][COLOR=#384967]. The small blower they sell works great, it is listed at 112 CFM at 36 ounces of pressure. I run my smaller 2 burner and large 3 burner systems with the same blower (not at the same time of course.)[/COLOR]

I also use 2 inches of ceramic fiber blanket to line the entire forge. I do occasionally replace the upper exposed layer from time to time. Normally as a result of me damaging the lining. I use a ram refractory called Ram Pack 85 to cover the bottom half of the system to protect the blanket from flux while forge welding. This also acts as a little bit of a heat sink that then in turn reflects the heat up and actually helps to make the system work better. I coat the entire interior with thinned down 3,000 mortar instead of ITC or a rigidizer. It is less expensive and serves the same purpose of containing the fibers from the blanket.

Some notes of recent changes to my forges that I finally pulled together and sent out to couple of friends:

Here's the Dixie Refractory contact is Ken Goedeker, email: [EMAIL=rss-ifs@att.net]rss-ifs@att.net[/EMAIL] Thermogen 60 STF is working very nicely, even with UPS shipping from Alabama to Pittsburgh, Pa area, the cost is less than 1/2 of local Harbison Walker dealer and Plasteck 85. Ken also gave me the best price on blanket, I use 1" 8 pound 2300 degree blanket. I don't remeber the cost of 3,000 degree mortar mix as am still using the sample he sent to me. He has been a great guy to work with and has visited my shop several times. First to see what I was doing prior to making recommendations, then to check up on things.

Some other notes on actual side by side comparison of forges, 4 forges 2 slightly different body styles, 1 set of old manifolds, one set of new:
Both were constructed the same in the bottom, at least 2 inches of blanket with at least 2 inches of plastic in center and about an inch thick coming up the side to completely cover blanket.

One version received 2 one inch layers of blanket in the top that were initially coated with a thinned down slurry of 3,000 degree mortar mix. The other version had one inch layer of blanket (in the top) with about an inch of Thermogen 60 STF.
Initial construction is faster with 2 inch blanket version.

The Thermogen version needs to set up over night and some sort of internal wire support. I followed the refractory salesman's recommendations in the following methods: First I welded a few stainless steel wires into the shell, then put a thin layer of 3,000 degree mortar on the shell, then put the blanket in, next step was to bend the wire to make hooks to help bite into plastic. The last version I did only a couple of these hooks and used some stainless steel wire mesh to hook into. Then the one inch of plastic is molded into place. It is still damp and very pliable after 12 plus hours of overnight air drying but more rigid. So I made certain everything in the forge was ready for final assembly and ready to fire up. First attempt at immediate assembly with out over night drying failed as the plastic dropped from the "ceiling." Once it is assembled I fire it up to cure and set the plastic. With the newer manifold method, both burner tips fired up right away. It took about an hour for the steam to stop coming out of the system and works fine.

Now the run time comparison. As I have been using a piece of 16 gauge sheet metal to form the burner tips, except on one forge I opened the burner tips up to about an 1/8th inch. The side by side version using the same opening of the burner tips takes longer for the hard liner to come up to temperature, but once it is there it is as good as the one without the hard liner. The one with the larger opened burner tips is just as fast as the "soft" shell, but I needed to add a gate valve to the air supply. Once this thing gets up to temperature, it needs both air and fuel to be cut down, unless you want to work at welding/burning temperatures. The latest hard-shell with the tighter burner tips also gave me some sound problems I encountered with a 3 burner. By opening the burner tips a little with a long chisel, the sound started to diminish. I recommend an 1/8th. opening on the hard-shell burner tips. Fuel consumption is only a guessing game for me and have not had anyone run the new version on small tanks, which is how I have previously determined consumption of about 1/2 gallon per hour on 2 burner systems and about 3/4 gallon per hour on 3 burners. The hard-shell versions are proving to last longer, protecting the blanket from me damaging it which is more of a problem than burnout.

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