blown forge

[jacob7]

Got some good ideas from the last thread and have come with a shell that's 10"x13" which will give me an inside measurement of 6"x11" an a volume of 311 cu. in. Does this sound feasible? If this size works what would be the blower size i would need in cfms? Also when you do feather damascus does it have to be stacked vertically or can it be attached to the end and put in the kiln horizontally?

[Ray Rogers]

The size seems good. As for cfm, it's pretty hard to have too much. My blower is 160 cfm and sometimes I use all of it. And, it's not all about cfm - it's just as important to have enough static pressure. You need 32 to 40 ounces of static pressure. Even 400 cfm won't do the job if there's no pressure behind it. Since few blowers actually carry their static pressure rating on them you pretty much just have to try what you have.

It doesn't matter what direction the billet faces/sits or whatever when it's in the forge as long as you know the orientation so that you can put it under the cutter correctly after it comes out of the forge. The entire billet is welded together long before you have to worry about cutting it so it isn't going to fall apart no matter how it lays.

If you haven't made any damascus yet you should probably get familiar with the process by making a few billets of something easier than feather pattern ...

[Crex]

Amen to that Ray!

[Doug Lester]

What Ray said about pressure. Like I said in the other thread, my 60 cfm blower had to be be run wide open or there was not enough pressure to keep the fire out of the burner tube. (I know that it sounds like there should be a fire inside but it's actually a fuel injection tube.) If the gas flow keeps blowing your match out, it probably will, use a propane torch to light your forge or rig some sort of an ignition system.

Doug

[jacob7]

thanks for the input guys

[jacob7]

Ray in your plans on your web site you have your nozzle in the back on mine would you put it in the back or in the middle and I reckon on the top at what angle? Can you put plistix 900f on the nozzle to keep it from burning up? Thanks

[Ray Rogers]

I do have my nozzles at the back of my forge but I also go to some lengths to explain that this is not something most people should copy. For normal use like on your forge I'd put the nozzle in the middle of the forge body. The numeric angle is not important - we spend too much time obsessing over exact angles in various parts of knife making and it is rarely necessary to know what angle is being used for much of anything. The angle will vary according to how thick the walls of your forge will be. By thickness, I mean the insulating wool or castable that fills the space between the outer forge shell and the interior of the forge. Your nozzle needs to enter the interior at and angle that will (more or less) direct the hot gasses onto the interior wall in front of the nozzle so that the gasses follow the rounded shape of the interior thus creating the desired 'swirl' effect. We DON'T want the nozzle to point directly at the billet or knife blade being heated - that would be bad. Aim the nozzle so that the gasses follow the curve of the interior wall and you'll be fine.

I'm not familiar with Plistix 900F but if the 900F is the temperature it can handle then it will be terribly inadequate. I doubt there is much of anything you can put on a nozzle that will guarantee that it won't erode. You probably saw where I used some castable for that purpose. If you read further, you'll see that worked for quite a while but eventually the castable broke down and fell off. The most effective thing I have found so far is to simply take advantage of the thick insulation on my forge. I have about 3" of insulation so I extend the nozzle 2" into the wall and let the remaining inch become the end of my nozzle. That's held up pretty well but, basically, nozzles are expendable so figure on replacing them every year or so.....

[Crex]

I have been "casting" my flares/nozzles in place when building the forge with satanite.
They seem to hold up very well...6 years on one forge. Last a lot longer than any metal, especially at welding heats. Wallow your insulation out wide enough at the port to accomodate the flare/nozzle plus a 1/4" coating of satanite. make your flare/nozzle form from light weight cardboard and masking tape. Coat the outside and wiggle in place with finger. Use a scrap piece of torch pipe with a few layers of tape (clearance) to help center the flare/nozzle. Once it sets up you can remove the pipe, it's ready and quite durable. Don't worry about the cardboard it is consumed on the first firing. Have been coating the inside of the flare with ITC100, but pretty sure it's not necessary.
This methodology will allow you to remove the torch easlily for touch-up/repair if it gets a crack or a corner breaks off. Pretty simple science.
That scrap piece of pipe can also be used to get your inside tangent alignment for the torch set the way you want it. Just slide it forward until you can see it on the inside for positioning of nozzle/flare.
Attached a drawing of torch positioning that may be helpful. The pic of the fired up forge is old and I have since been building the torch port coming in from the lower quadrant a little above the forge floor for better swirl effect-time.
(I understand that the flare is not necessary on a blown forge just a good durable port nozzle. I only use venturi style torches and need no electricity, preference thing for me.)

[jacob7]

Guys, since our last discussion I can't find a 10" pipe but found an 8" and will go with that for now (8 x 14). My question now Ray's forge used 2" pipe and a 2"x 1" reducer mine being smaller does it need to be as big and can the reducing elbow be smaller also? I also can get a blower which has a cfm of 273 @0.0in SP and @135cfm @.5in SP (what ever that means). Is that too big or just fine. Another what is the best way too cut very hard fire brick? Thanks

[Ray Rogers]

8" pipe wit 1" of wool in it should be fine. You probably could make the burner smaller but I used that same burner on a smaller forge and it worked fine. You can always turn it down but once you have it wide open that's all you're going to get.

That blower doesn't seem like it will have any static pressure. Put your hand in front of it, if it doesn't push you away pretty firmly it probably won't do.

Cut brick with a tile saw. Are you sure you have a hard fire brick? Most fire brick is soft. If you have a regular red building brick that's not a fire brick and it shouldn't go in a forge ...