BP0367 Forge Blower Duct

IForgeIron Blueprints
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BP0367 Forge Blower Duct
by Gerald Franklin

This re-cycled bathroom heater blower on my forge finally gave up the ghost and had to be replaced. I was in a hurry and didn’t want to get into a drawn out sheet metal exercise.







The squirrel cage blower was being replaced by this 4 ½” muffin fan. It came from Surplus Center (www.surpluscenter.com) and cost about $15. It is rated to move 108 CFM of air. I thought that it was a little stout for this application, but since it was to be rheostat controlled, I figured it would be worth a try.







The squirrel cage blower had its own shroud that couldn’t be easily adapted to my new fan, so I started looking for something quick to use for a duct. I found it in the form of a .50 caliber ammo box. It is about 11” long, which would allow me to mount the fan farther away from the tuyere than the old blower was. I suspect that a major reason for the demise of the old blower was excess heat getting to the fan motor from the fire pot.







The tuyere looks like this so I had to modify the ammo box to bolt to the side of it. This meant that hinges, latches, etc. needed to be removed from the box.







After the unneeded hardware was removed, my “duct” begins to take shape. The lid was saved to be the bottom of the duct. It will be re-attached later with a couple of sheet metal screws.







I drilled 3 each 5/16” holes through the side of the tuyere to mount the duct to. The tuyere is made from 3” angle welded into a box shape that was big enough to allow access from the inside to mark the hole position and air inlet size on the ammo box (duct).






After tracing the rectangular air inlet on one end of the box, I traced the outline of the inside of the fan onto the other end. Both cutouts were then cut with a metal cutting (24 tpi) jig saw blade.







I figured that I needed some sort of a gasket to seal the tuyere/duct attachment. I elected to use hi-temp rtv sealer. Whether it is going to be “hi-temp enough” will remain to be seen. All I need is a low-pressure seal, so if the stuff gets brittle from the heat later on, I think I’ll still have enough of a seal to work. If it burns out, I’ll punt.







The muffin fan mounted inside the ammo box. This is a trade off. If I put it outside, it would probably run cooler, but inside, it's out of the way.







The duct with fan mounted on the tuyere. The red stuff is the hi-temp rtv sealer. I also used the rtv sealer to build a grommet for the fan power cord pig-tail. I wanted to put a piece of screen wire over the fan opening to keep critters out but I couldn’t find it. Maybe it’ll turn up before the House Wrens start nesting in the spring.







The bottom of the duct (which used to be the top of the ammo box) is installed using a sheet metal screw through each side. These lids fit pretty tight on their own, so the sheet metal screws are just insurance. These lids have a water tight rubber seal on them. This was another reason that I elected to use the lid as the bottom since it puts the rubber seal farther away from the heat of the firepot.







The firepot, duct with fan, and ash dump are re-installed on the forge. Wiring will be re-routed after a test run of the fan. The red wire that goes under the duct is a ground wire that attaches to the duct housing via the sheet metal screw that anchors the bottom (ammo box lid) to the duct. The rheostat is the same one that controlled the old blower.







And, it looks like we get enough airflow to get a good fire going. Control with the rheostat is good, too.