Brazing
is a welding process that allows the joining of similar or dissimilar metals by
using a third metal with a lower melting point as the “glue.” In brazing, a
thin film of filler metal is sucked into the joints by capillary action. In
fact, the joint can be quite weak unless this filler metal is thin. The base
metal (the metals you are attempting to join) is never actually melted as in
conventional welding, but the base metal must reach the proper temperature to
allow molecular bonding with the filler metal. (The filler metal is commonly
bronze.) Brazing in the Product Realization Lab is done with an Oxy-Acetylene
torch. You should read the document entitled “Oxy-Acetylene Welding’ - this
document assumes you are familiar with oxy-acetylene welding. After reading
through this, get a TA to check out your set up and help you the first time
through.
Advantages of
Brazing :
·
It's easy to learn.
·
You can join virtually any dissimilar metals.
·
The bond line can be very neat in appearance.
·
Joint strength is strong enough for most non-heavy-duty use
applications.
Disadvantages
of Brazing :
·
A badly brazed joint looks similar to a good joint, and can
have a VERY low strength.
·
The metal used to bond the two parts may be different in
color than the parts being bonded. This may or may not be a problem.
·
Long-term effects of dissimilar metals in constant contact
may need to be examined for special applications.
·
Since the filler material (typically bronze) melts at a
relatively low temperature, brazed parts may not be put in an environment which
exceeds the melting point of the filler metal.
Materials
Suitable for Brazing in the PRL:
Most
steels
Brass
Copper
Iron
Bronze
Preparation
for Brazing:
1) Assemble all
of the materials needed to make the braze. This includes parts, oxy-acetylene
torch, flux, solder, fixturing, handling tools, and safety equipment.
2) Clean the
parts to remove any oil, rust, or other contaminants. Use a wire brush if
needed to remove any rust.
3) Coat all
surfaces of the parts being brazed with flux.
This will help the solder make a good joint, and will also help protect
the areas of the parts not being brazed by protecting them against oxidation
from the flame.
4) Assemble and
fixture the parts in place - the parts need to be stable for a good braze line.
Ceramic bricks, vise grips, pliers, and clamps are available in a file cabinet
in the welding room for fixturing.
5) If large
surface areas are being bonded together, hammer a small piece of solder into a
very thin sheet and place it between the faces being brazed. This will ensure that solder reaches all of
the surface area. Be sure that the
parts are firmly fixtured to keep the solder in place.
6) Prepare the
nozzle and tanks as described in the oxy-acetylene handout.
Brazing
1) Light the
flame as described in the oxy-acetylene handout
2) Adjust the
flame as described in the oxy-acetylene handout.
3) Apply the
flame to the parts. The goal is to heat
the entire volume of both parts being brazed.
Wash the flame over the surface of the part, and try to avoid overheating
which may melt the surface.
4) Apply solder
to the joint line. Don't apply flame
directly to the solder - let the temperature of the parts melt the solder. Continue heating the parts until the solder
melts and flows into the joint.
5) Add enough
solder to ensure a good bond line. This
takes a little practice.
6) Once you're
done, turn off the flame. Close the
oxygen pin valve first, and then the acetylene valve.
7) Shut down and
clean up as described in the oxy-acetylene handout.
revision history :
Ver 1.0 5/97 Steve Johnson original text
Ver 1.1 6/97 Bryan Cooperrider formatting and revisions