Brazing & Braze Welding With Oxyacetylene
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Definition
A group of process that use heat to melt a metallic bonding
agent, but not the base metal. The adhesion quality of the
bonding agent binds the parts together when cooled.
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Three Common Processes
 Soldering
 Brazing
 Braze welding
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Non-fusion welding Advantages & Disadvantages
What are the advantages of non fusion welding.
What are some of the disadvantages of fusion welding.
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Four Requirements of Non fusion Welding
1
Clean metal
2
Appropriate filler rod
3
Correct flux
4
Heat
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Non-fusion Requirements
1. Clean Metal
Non-fusion processes bond metal by adhesion.
What is adhesion?
Can you think of one critical condition
that is required for adhesion to be
successful?
Requires a clean surface --not a polished surface.
Clean
Polished
What is the best method to use?
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Non-fusion Requirements
2. Appropriate Filler Material
• Different filler materials are
available for non fusion welding.
• Brazing:
 Brazing rod are available as bare
rods or flux coated.
• Soldering:
 Solder can be solid or flux core.
 Flux core can be acid or rosin.
 Can be tin, silver or zinc alloy.
Is filler material available in other
Yes
forms?
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Non-fusion Requirements
3. Flux
•
Three purposes of flux.
1. Chemically clean the metal
2. Shield from oxidation and
atmospheric contamination
3. Promote wetting
•
Flux must be compatible with the
metal and filler material.
What are the three common forms that
are used for fluxes?
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Non-fusion Requirements
4. Heat
• Sufficient heat (BTU”s) 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.
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Non fusion Heat Sources
 Oxyacetylene
 Air acetylene
 Air propane (LPG)
 Oxypropane
 MAPP
 Electric soldering iron
 Electric soldering gun
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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
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Definition
A nonfusion process that uses a metal alloy that melts below 840 oF.
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Soldering
Relies upon capillary action.
What is capillary action?
What are the requirements for capillary action?
• Solder is divided into
two categories;
 Soft
 Hard
Describe soft soldering?
How is hard soldering different from soft soldering?
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Soldering Process
1. The joint area is cleaned and fluxed.
2. A heat source is used to raise the
temperature of the base metal above the
melting of the filler metal (<840 oF).
3. The filler metal is added to the joint.
 Filler material should melt from the heat of
the metal, not the heat source.
4. The filler metal flows into the joint and
adheres to the surfaces.
5. The heat source is removed and the filler
metal solidifies, bonding the surfaces
together.
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Tinning
Tinning is the process of applying a
thin layer of filler rod to the surface of
the metal.
When would the tinning process be used?
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Brazing
• A process that uses a metal alloy that melts above 840 oF, 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.
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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.
3. A heat source is used to raise the temperature of the base
metal above the melting of the filler metal (>840 oF).
 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 tensile strength of brazing filler material is less than steel.
• The strength of the weld is increased if the joints are modified to
increase the surface 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 oF, 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.
2.
3.
4.
5.
The joint area is cleaned and fluxed.
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.
The filler metal is added to the joint.
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.
Name them.
The five (5) standard welding positions can be used for braze
welding.
Name them.
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Questions?
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