5P+ Welding Question

[karmakanic]

Rockyroad,

Here's a hint for a something handy you can learn to do with your torch. As Dave mentioned, when you're cutting metal with a torch, you're not actually melting the metal, you're creating a chemical reaction between the metal and the oxygen. This chemical reation will not start unless the metal is preheated to it's critical temperature. If two pieces of metal are joined togeather, there is a natural temperature difference across the joint. This means you can heat a part of one piece of metal to it's critical point, get your cut started, and the other joined metal will still be below it's critical temperature, and will not be affected by the cutting action. A practical example would be cutting a frozen nut off a bolt without damaging the threads of the bolt. A very handy skill, and guaranteed to wow your buddies.

Dave

 

[bgott]

If you really want to learn how to gas weld, watch an old muffler man. I say old because the kids you see now days use a sawsall and a mig. A good muffler man uses a welding tip to cut. He'll heat up the pipe and when it gets molten he'll cut off the gas and walk the cut around the pipe with just the oxygen.

 

[Anonymous Poster]

Here's a further note on the same thing.......when you try and cut a stack of plates, only the top one will cut (initially) because of what was just mentioned....the joint causes a lack of heat transfer and the oxidation reaction cannot get going. INTERESTINGLY....propane and MAPP (Methylacetylpropadiene) torches will cut across stacks easier than acetylene will, that's why you see so many junkies using them to cut scrap. Messy, but effective. When you are trying to cut a bearing off a shaft or a nut off a bolt, you intentionally make it QUICK, before the heat can transfer and set up the oxidation reaction on the shaft or the bolt itself.

 

[RJohnson]

Rockyroad
Back to original question about amps, your amperage will depend upon two main things; the size of the electrode and the mass of the steel you are welding on. The 5P+ comes in various sizes and each has an amperage range for it:
3/32" 40-70 amps
1/8" 65-130 amps
5/32" 90-175 amps
3/16" 140-225 amps

Your 80 amps will be about right for 1/8" diameter electrodes.

The only "contact" rod I know about is E7018 like the Jetweld LH 70. You can drag the electrode coating against the work peice as the electrode itself sort of melts back up into the covering and has a less visible arc. But you may be able to do this with any rod that has a thick flux covering. The E7014 and E7018 have iron powder added into the coating and it will tend to have a thicker coating than electrodes without iron powder additions. Of course the iron powder is added to increase welding deposition rates and for filling up those places that need the higher deposition rate. Also becasue of iron powder additions you usually have to up the amperage to melt everything into the weld puddle. Good luck and keep practicing.

Randy

 

[Rockyroad]

Thanks for the advice everyone. I went home over the weekend and practiced cutting on an old hunk of leaf spring from an old heavy truck. The stuff if an inch plus thick, depending on the location on the spring. It is thin on the ends, thick in the middle where it evidently broke. Anyways, my friendly junker down the road drops this stuff off for me to play with.

I preheated until the edge got the right color and then hit the oxygen lever. It cut right thru and wasn't half bad for a beginner. I was heating it up too much before and ther were globs of orange steel everywhere. Much better now.

I tried the 5P+ on the same stuff and was able to get some credible looking beads. Nice and smooth. I even practiced cutting the spring into pieces and then welding it back together.

My wife can't see the point to any of this, and wants to know when I am going to do something constructive with it. She really likes my Optrel helmet and figures I look better with it on than without it. They just do not understand.

Anyways, thanks for all the advice. I'm getting better at it and having a whole bunch of fun in the meantime.

My first real project will be a welding table on casters that I can wheel around my barn. I have some heavy channel that my junker buddy gave me that I will use the 4 legs. I will make up a frame, then look around for a piece of heavy plate for the top.