What
is the difference between soldering, brazing and welding?
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Brazing - The AWS defines
brazing as a group of joining processes that produce coalescence
of materials by heating them to the brazing temperature and
by using a filler metal (solder) having a liquidus above 840°F
(450°C), and below the solidus of the base metals.
Soldering - Soldering
has the same definition as brazing except for the fact that
the filler metal used has a liquidus below 840°F (450°C)
and below the solidus of the base metals.
Welding - In welding,
fusion takes place with melting of both the base metal and usually
a filler metal.
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What
does a brazed joint provide?
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Brazing provides:
- Strong joints
- Lower temp/lower
cost
- Maintains integrity
of base metals
- Easily joins
dissimilar metals
- Good joint appearance
- Skill easily
acquired/automated
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How
does brazing work?
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Brazing
creates a metallurgical bond between the filler metal and the
surfaces being joined. Heat is applied to the base metals and
the filler metal is brought into contact with the heated parts.
When the filler metal melts it is drawn through the joint by
capillary action.
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What
types of filler metal forms are there?
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Filler
metals come in wire, strip, powder, or paste form. Availability
in these forms depends on the alloy that is chosen. Preforms
can be made from strip and wire.
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What
is oxidization?
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When
metals are exposed to oxygen, oxides form from oxygen atoms
that attach to the metal. The oxides that form prevent the molten
alloy from metallurgically joining to the metal.
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What
is Flux?
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Flux
is a chemical compound that is applied and shields the joint
surface from air and prevents oxide formation. Although flux
will dissolve and absorb oxides, the metals that are being joined
should be properly cleaned prior to brazing.
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What
are the available flux forms?
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Flux
is available from Lucas-Milhaupt in paste, slurry, liquid and
powder form depending on the type of flux. Paste, slurry, and
liquid fluxes are all water based while dispensable fluxes are
petroleum based. Flux can also be delivered to the joint through
the torch that is being used.
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How
can flux be cleaned off of joint after brazing?
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The
easiest way to clean flux off the brazed joint is to quench
and soak the assembly in hot water. HCl (up to 25%) can be added
to the water for stubborn flux residue. Special cleaners may
also be purchased if needed.
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What
is the shelf life of flux?
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If
stored in the original unopened container, Lucas-Milhaupt flux
is under warranty for twelve months from the date of manufacture.
This does not mean that after twelve months the flux is no longer
useful.
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How
can flux be reconstituted or thinned?
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Water
can be used to thin water-based flux. Usually distilled or de-ionized
water is used for this purpose.
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What
is brazing paste?
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Brazing
paste is a material consisting of metal alloy in a powder form
mixed with a binder. When it is required, flux is added to the
brazing paste to provide protection from oxidization.
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In
what applications is using paste feasible?
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Paste
can be used for torch, induction, and furnace applications.
In these applications flux is usually added to paste formulation.
When using paste in a vacuum or atmosphere furnace flux does
not need to be added to the paste.
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What
is the shelf life of brazing paste?
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Brazing
paste that is in its original unopened container is warranted
for 90 days. Similarly to the flux, this warranty does not mean
that after the 90 days, the paste will not function. Functionality
can only be determined by melting the paste to see if flows
or not. If the alloy flows then it is still functional, conversely
if the alloy balls up then it is not functional.
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What
is the proper clearance for brazing?
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In
general, a joint clearance ranging from 0.002"-0.005," will
produce sound high strength joints when flux brazing. When atmosphere
and vacuum brazing, joint clearance should be 0.000"-0.002."
Care does need to be taken when brazing metals with different
coefficients of thermal expansion. The amount the materials
expand needs to be factored in when determining joint clearance.
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What
types of joint configurations can be used when brazing?
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At
what temperature should the furnace be at when furnace brazing?
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Typically
the furnace will be heated to a temperature 50°F-100°F
above the liquidus of the filler metal being used.
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What
is the strength of a brazed joint?
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The
strength of a brazed joint depends on several different factors.
These being: the base metals being joined; joint clearance;
filler metal used. Joint strength varies with use of different
base metals and filler metals. Joint strength also depends on
the gap between the two metals being joined. When the gap is
increased the joint strength decreases. Often times, under the
correct conditions, the braze joint strength will be equal to
or greater than the strength of the base metals.
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What
is Handy One?
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Handy
one is a flux cored product that simplifies the brazing process.
Handy One is a brazing alloy in strip form rolled around a measured
amount of powdered flux. As the part is heated the flux is released
providing protection from oxidization. It is available in multiple
filler metals and flux combinations to join virtually all common
metals.
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What
alloy is recommended for brazing copper to copper?
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In
most cases, when brazing copper to copper in air conditioning
and refrigeration service, one of our Sil Fos alloys would be
recommended. The phosphorous in the alloys allow the Sil Fos
group to be self fluxing when brazing copper to copper which
eliminates the use of a separate flux.
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Can
stainless steel be brazed in vacuum below a temperature of 1700°
F?
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Stainless
cannot be vacuumed brazed in at a temperature below 1700°
F because of the possibility of chrome-oxide formation which
will prohibit the flow of the filler metal alloy on the stainless
steel. A brazing temperature of at least 1750° F is usually
recommended in vacuum for stainless steel. If the stainless
steel is nickel plated it can be brazed at temperatures lower
than 1700° F.
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What
braze alloy would be appropriate for brazing 300 series steel
that will be subjected to contact with water?
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When brazing
stainless steels that will be exposed to water, an alloy should
be used that contains nickel. Examples of these would be Easy
Flo 3, Braze 505, Braze 630 and Braze 403. The nickel in these
alloys helps prohibit interface corrosion within the steel.
To learn more about interface corrosion please read Technical
Bulletin No. T-9 or contact Lucas-Milhaupt Technical Service.
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