There are a few things that you need to be concerned about when forge welding. They are:
- Keep it clean
- Use the right amount of flux (at the right time!)
- Reducing atmosphere
- Know when to weld
- Weld it, don't smash it
I'll address each one in turn.
Keep it clean:
Start with clean steal. The surfaces mst be free of any forge scale. Take an angle grinder and clean off ALL scale from the pieces to be welded.
Use the right amount of flux:
What flux will do for you is to keep oxygen out of your weld. Don't count on flux to "clean out" your weld. Keeping things clean is YOUR job. What you want to do is get the steel to a light red in color. This is hot enpough to melt the flux, but not so hot that you will be forming scale. Then you want to apply enough flux (20 mule team borax...from the laundry aisle) to create a light shiny coating. It will looks like wet glass. Too much flux will do two bad things. First, it can create inclusions in your weld. Second, it can splatter all over and burn the heck out of you and anything around you.
Reducing atmosphere:
You want a reducing atmosphere in your forge. This means that you have more fuel than oxygen in the forge. This will reduce the chances of your billet scaling and ruining your welds.
In a coal forge, you want to be burning only coke (no green coal) and you want to make sure that you have coke around all sides of your billet and that the fire is burning hot and clean. Forge welding in a coal forge can be quite a challenge as it can be very difficult to heat the entire billet evenly and at the same time it's very easy to burn steel in a coal forge. My suggestion if you're welding in a coal forge is to concentrate on a 2-3" section of your billet at a time. Heat, weld, wire brush and reflux immediately after welding, then concentrate on the next section.
In a gas forge (the way do my work) you can tune the atmosphere by watching the flame exiting the forge door. No flame exiting the forge is an oxidising atmosphere (all the fuel is being burnt inside the forge...there's more O2 left over), a little flame (1-3") coming out of the forge is a neutral atmosphere, and a 3-6" ORANGE flame exiting the forge door is a reducing atmosphere (some fuel still unburnt until it exits the forge and finds more oxygen to burn). If you've got BLUE flame exiting the forge, make sure you've got good ventilation as you're generating a lot of carbon monoxide.
Know when to weld:
Once your billet is fluxed, start to slowly bring it to a welding temperature. Slowly heating is more important in a coal forge than a gas forge. In a coal forge it's VERY easy to make extremely high temperatures in a localized area and burn your steel. A low to medium air blast to bring the billet to a high orange heat slowly will serve you best. A gas forge is a bit easier. Just get it to a high orange/low yellow heat and you'll be fine. There are a few way to know when it's the right time to weld. The first is by watching your flux and color. This will end up being probably all you use once you're used to welding. Watch for the flux to be "boiling" on the surface of the billet. The other thing you're looking for is a bright orange to yellow color. I've heard it likened to looking for boiling flux on a stick of butter. That's a prety accurate description.
Weld it, don't smash it:
When you're to this point you're ready to weld. It's very important to know exactly when you're going to do when you pull the billet from the forge. While you wait for the billet to come up to heat, go over the movements. Make sure you know where your hammer is. Make sure there's nothing to trip over, etc, etc. When your billet is up to heat, pull it from the forge and quickly make your way to the anvil. Make sure you have your hammer in hand and strike the billet firmly, but not very hard. Start at one end and work your way to the other end in even, deliberate strokes. You want to set a weld at this point, that's it. You can draw the billet out later. If you hit the billet too hard you can make layers slip sideways which is not what you want. I'm not sure how to describe it, but you can hear and feel when a weld sets right. What you're listening for is a sort of "thud". After you've set a few welds, you'll know what I mean.
That's it! Draw your billet out, grind your new welding surfaces clean, and repeat.
-d
. I use borax for flux, just watch out for the flux when you strike the steel; its pretty warm to say the least. For temperature I go for bright yellow with a few sparks coming off. Keep the pieces clean when you layer them to weld, a grill wire brush works well for this.
