first metal class

started my intro to metal sculpture class last night. great instructor, talked for about 3 hours straight. we covered all the safety stuff, which took most of the time, and then went over how to use an oxy-acetylene rig. the class will mostly focus on MIG welding, but i think i'll be able to get enough brazing practice. plus learning to MIG can't hurt.

this is just meant to be FYI. i can imagine it being useful if one wanted to build their own brazing rig, or even just to better understand how this mysterious contraption works.

i'll start with a breakdown of the parts involved in an oxy-fuel rig:
tanks: one for oxy, one for fuel. each tank has a valve directly attached to it, acting as the main on-off.
regulators: each tank has one attached directly downstream of the tank valve. generally oxy regulator dials are green and fuel are red. controls how much gas pressure flows through the lines. clockwise turning of the screw increases pressure; when screw feels loose, regulator is off.
lines/hoses: same color-coding as regulator dials. connections for fuel are reverse-threaded to avoid confusion.
flashback arrestors: one for each line, located downstream of it right where it attaches to the torch. prevents flashback, which is really bad but that's all i know about it. make sure they're tight.
mixing handle/torch/torch handle: this is the big brass cylinder that one holds while welding/cutting/heating/brazing. gases from the lines mix here. has a valve for each gas to control how much is let in.
tip: secured to the handle by means of a collar. interchangeable for welding different thicknesses of metal and different purposes.

safety check
1. make sure tanks are chained up.
2. make sure regulator screws are loose (off).
3. make sure torch knobs are tight (off).

open acetylene tank valve handle half turn
crack oxy tank valve handle slowly, then open fully
open acetylene torch valve about half turn
open acetylene regulator to recommended psi (refer to chart; based on tip size)
close acetylene torch valve
open oxygen torch valve about half turn
open oxygen regulator to recommended psi (refer to chart; based on tip size; add 1-2 psi usually)
close oxygen torch handle valve

the reason for all this opening and closing is to set the regulator when the lines are open at the torch end, because the recommended pressures are for flow pressure (as opposed to static pressure, when the lines are closed and the gas is contained).

lighting the torch
put on welding gloves and put goggles on head (not over eyes yet).
open acetylene torch valve quarter turn
if there's a gap between tip and flame, close acetylene valve until flame smokes, then open up; gap should disappear.
put goggles over eyes
crack oxygen torch valve slowly with thumb and palm, then open up with fingertips to adjust flame. neutral is best for welding mild steel, but i think it's different for brazing. neutral means the outer blue cone is the same size as the inner blue cone.

turning torch off
close oxygen torch valve
close acetylene torch valve
rub tip on glove or pants or whatever to remove any acetylene buildup

shutting down
turn off acetylene tank valve--tight
turn off oxygen tank valve--tight
bleed each line, acetylene 1st, by opening respective torch valve half turn until regulator reads 0, then close torch valve.
loosen/close both regulator screws (about 2 turns)
remove torch tip
loosely wind hoses around cart handles

does this jive with what others do?

1 comment:

Moz said...

It's more or less what I do, although that depends on how long I'll be away. For lunch breaks I'll just trun the tanks off and not hit the regs or bleed the lines. One advantage of that is that it gives me a regular check for leakage in the hoses (lose pressure over lunch? Something's leaking). I also usually set the pressure static since I'm not too fussy about exact pressures (I build workbikes and usually run hot rather than cool).