brazing safety/technique

from Damon Rinard

Brazing

I collected the following information from various sources on the net
prior to brazing up my first frame. The bulk of it comes from the
framebuilders e-mail list (framebuilders@phred.org).

Safety Advice

1. NEVER transport oxygen or acetylene tanks without the screw-on
cover in place. If the acetylene valve were to break off, there would
be two risks: 1.iminent danger of explosion 2.death by inhaling the
gas. If the oxygen valve were to break off, you would have an unguided
missile that could go crashing through concrete walls and ricochet
back and forth for nearly a half mile before stopping. (Not to mention
what the initial concussion would do to you.)

2. NEVER run your acetylene line pressure above 15 psi. Acetylene
becomes unstable above 15 psi and can ignite explosively simply from
the compression caused by rolling a heavy cart over the hose.

3. Don't bleed your acetylene tank down to nothing before exchanging
it. Doing this will allow acetone to get into your lines, diaphragm,
and regulator. This could cause hoses to break down and the resulting
"sludge" could impair the proper function of the regulator.
Theoretically, it is not possible to drain the acetylene to nothing
because of the way it is released from the tank. There will be a point
at which you will think the tank is down to nothing and half an hour
later -- voila -- you have a healthy flame again. You can do this many
times over and the flame seems to be good after each half hour wait.
The first time it happens, you have drained the tank too low. Try to
exchange your tank before going under 15 to 20 psi.

4. Don't drain your oxygen tank down to nothing. Doing this could
allow the acetylene to seep into the oxygen tank because of the lack
of back pressure. Newer systems use check valves and flashback
arrestors to minimize the possibility of this problem occurring. At
any rate, any minute amount of acetylene in the oxygen tank is
dangerous. Try to exchange your oxygen tank before it goes below 20 or
25 psi.

5. Avoid storing your tanks for long times without exchanging them.
All tanks have an expiration date stamped on the top by the valve. If
you get stuck with an expired tank, you're screwed! If you take them
in before the expiration date, the vendor has to pay for the
hydrostatic pressure testing. Expired tanks could develop a variety of
problems such as moisture build-up or rust inside. I believe the ICC
requires tanks to be re-tested every five years.

6. Remove dented acetylene tanks from service. The spot where the dent
occurs is where the sponge-like core is damaged and the acetylene in
that spot will not be properly in solution and hence will not be
stable.

7. NEVER leave full tanks in an unattended vehicle on a hot day. The
pressure increase from the hot sun beating down on the car could cause
a devastating explosion. (Your welding vendor may have pictures of the
remnants of these explosion posted in their show room.)

8. Always secure tanks being transported from falling down and rolling around.

9. Tanks, by law, are supposed to be chained in place to prevent them
from falling down. Either have them chained against the wall or
secured into a stable welding cart.

10. Always use a striker to start your flame. After using a match, the
head could still be red hot. Throwing that match away could cause a
fire elsewhere in the room. AND, when the room is already somewhat
filled with smoke and fumes AND your vision is cut by tinted lenses,
you may not notice a fire in the room until it is too late.

11. Remember acetylene is alway turned on first and turned off first
during a welding/brazing session.

12. Only open your acetylene valve about 1/2 turn. If there is an
emergency, shut down the acetylene before doing anything else. Opening
the acetylene valve all the way will slow you down drastically when
you want to get the flame turned off. AND, if you use a T wrench on
your acetylene valve, ALWAYS leave the T wrench on the valve. You will
be in trouble if there is an emergency and you're digging in a drawer
for a T wrench to turn off the acetylene.

13. Always keep your torch tips clean. A dirty tip does not dissipate
heat efficiently. Also, incandescent particles could get lodged in the
orifice of a dirty tip and cause problems with the efficient burning
of your gases.

14. Shut the main valves of the tanks, bleed your lines and
regulators, and close the secondary valve at the end of your work day.

Brazing - Advice from Tim Paterek, Author of The Paterek Framebuilding Manual

"I always instruct beginners to keep their flame tangent to the
surface of the tubes so that they are blowing excess heat off into
thin air. You can hover 1/16' above the surface of the steel all day
and never overheat if your excess heat is blowing into thin air. If
you need a sudden blast of heat on your work, then tilt your elbow to
angle the flame toward the joint more. You can easily tilt and swing
the torch tip to control your heat.

I also instruct beginners to aim their flame down the V of the joint
rather than to point toward one tube or the other too much. You can
always tilt when you need more heat on one tube or the other.

Another technique I use is to build webs after laying down a
micro-fillet. These webs stabilize the joint and also act as dams to
build the fillet against - they prevent your fillet from falling on
the floor. There is a particular order in which the webs should be
built and I covered that in my book.

In a nutshell, finish the sides of the joint first to stabilize the
angle. Then build a web on the obtuse side of the joint to counter the
tremendous pulling power the acute side of the joint will have. Then
build the web on the acute side. Then fill in the quarters." - Tim
Paterek