Brazing

1. 1
Brazing

2. 2
Introduction

•Three common processes:
Soldering
Brazing
Braze welding

3. 3
Non-fusion welding Advantages & Disadvantages
•Advantages
Lower temperature
Easy assembly
Weld dissimilar metals
Allows disassembly/realignment
Join metals of different
thicknesses
Joint different types of metal
•Disadvantages
Lower tensile strength
Not efficient method for
thick metal
Not efficient method for
large parts.

4. 4
Four Requirements of Brazing
•Clean metal
•Appropriate filler rod
•Correct flux
•Heat

5. 5
1. Clean Metal
•Molecular bonding requires a clean surface.
•Requires a clean surfacenot a polished surface.
Clean
Polished
•Best method is to grind the surface

6. 6
2. Appropriate Filler Rod
•Filler rods are available for many
non-fusion processes.
•Brazing: (Figure 24-2, pg 314)
Brazing rod are available as bare
rods or flux coated.
•Soldering: (Figure 24-1, pg 314)
Solder can be solid or flux core.
Flux core can be acid or resin.
Can be tin, silver or zinc alloy.

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3. Flux
•Flux must be used with all non-fusion
welding processes.
•Three purposes of flux.
1.Chemically clean the metal
2.Shield from oxidation and
atmospheric contamination
3.Promote wetting
•Flux must be appropriate for the
metal and filler material.
•Flux is available in three (3) forms.
1.Paste
2.Powder
3.Liquid

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4. Heat
•Sufficient heat must be available to raise the base metal
temperature above the melting point of the filler rod.
•The decision on heat source to use is based on the mass of
metal that must be heated, the welding process and the
availability of equipment.

9. 9
Non fusion Heat Sources
Oxyacetylene
Air acetylene
Air propane
Oxypropane
MAPP
Electric soldering iron
Electric soldering gun

10. 10
Tinning
•Tinning is the process of applying
a thin layer of filler rod to the
surface of the metal.
•When soldering sheet metal
joint/seams, both surfaces are
usually tinned before assembling
the joint/seam.
•Makes it easier to get the filler material to fill the joint and bond the
metals together.

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Controlling Heat
•Metals are excellent conductors of heat
Heat applied to joint moves away from the joint.
The greater the mass of metal that must be heated--the greater the
heat requirement.
•Excessive heat will cause the flux to burn.
Contaminates the joint.
Joint must be re cleaned
•Manipulation of the heat source may necessary to heat both
pieces evenly.

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Soldering
•Solder is divided into
two categories;
Soft
Hard
Additional information in
pages 170-172
•A process that uses a metal alloy that melts below 840
o
F.
•May or may not use capillary action.
Capillary action (wicking) is the ability of a substance to draw another
substance into it.
•Soft soldering
Lead or lead replacement solder
Lower tensile strength
Copper pipe and sheet metal
Stained glass
•Hard soldering
Silver based solders
Jewelry

13. 13

14. 14
Brazing
•A process that uses a metal alloy that melts above 840
o
F, but
less than the melting point of the base metal.
•Brazing relies on capillary action to draw the filler metal into the
joint or to keep it in the joint.
The capillary effect is a function of the ability of the liquid to wet a
particular material.
Requires very small gap between metal surfaces, clean surfaces
and flux.

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Brazing Process
1.The joint area is mechanically cleaned and fluxed
Flux can be applied before the joint is assembled, or during the
brazing process.
2.The joint is assembled.
May require clamping.
•A heat source is used to raise the temperature of the base
metal above the melting of the filler metal (>840
o
F).
Must insure the joint is not overheated.
If this occurs the flux will burn and contaminate the joint.
When the joint becomes contaminated it must be recleaned and
refluxed before the welding can continue.
4.The filler metal is added to the joint.
5.The filler metal flows into the joint and adheres to the surfaces.
6.The heat source is removed and the filler metal solidifies,
bonding the surfaces together.

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Brazing Joints
•The strength of a brazed joint is less than a fusion welded joint.
•Joints should be modified to the maximum welded area.
Tensile strength of
brazing rod is
~40,000 psi.
Tensile strength of
steel electrode is
36,000 to 50,000
psi.

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Braze welding
•A process that uses a
metal alloy that melts
above 840
o
F, but less
than the melding point of
the base metal.
•Braze welding is the
same process as brazing
except it does not use
capillary action and a
visible bead is formed.
Process:
1.The joint area is cleaned and fluxed.
2.A heat source is used to raise the
temperature of the base metal to the
melting temperature of the filler
metal.
If excessive heat is added to the
joint, the flux will burn.
When this occurs the process
must start over.
3.The filler metal is added to the joint.
4.The filler metal adheres to both
surfaces forming a bead.
The puddle must be heated until
the key hole collapses.
•The heat source is removed and the
filler metal solidifies, bonding the
surfaces together.

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Braze Welding
Key Hole
•When the brazing rod is
melted in the puddle, it will
bridge across at first--form a
key hole
•Sufficient heat must be added
to cause the key hole to
collapse.
•Failure to collapse the key
hole will result in a joint that
has incomplete penetration.

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Braze Welding
Joints
The five (5) standard joints
can be used for braze
welding. Butt
Lap
Edge
T
Corner

20. 20
Questions?