Brazing Of Pipes - Toshiba RAS-07PKVP-E Service Manual

High Wall, Heat Pump Type

2-5. Brazing of Pipes

2-5-1. Materials for Brazing
Silver brazing filler
Silver brazing filler is an alloy mainly composed of
silver and copper. It is used to join iron, copper or
copper alloy, and is relatively expensive though it
excels in solder ability.
Phosphor bronze brazing filler
Phosphor bronze brazing filler is generally used to join
copper or copper alloy.
Low temperature brazing filler
Low temperature brazing filler is generally called
solder, and is an alloy of tin and lead. Since it is weak
in adhesive strength, do not use it for refrigerant pipes.
REQUIREMENT
• Phosphor bronze brazing filler tends to react with
sulfur and produce a fragile compound water
solution, which may cause a gas leakage.
Therefore, use any other type of brazing filler at a
hot spring resort, etc., and coat the surface with a
paint.
• When performing brazing again at time of servicing,
use the same type of brazing filler.
2-5-2. Flux
Reason why flux is necessary
• By removing the oxide film and any foreign matter on
the metal surface, it assists the flow of brazing filler.
• In the brazing process, it prevents the metal surface
from being oxidized.
• By reducing the brazing filler's surface tension, the
brazing filler adheres better to the treated metal.
Characteristics required for flux
• Activated temperature of flux coincides with the
brazing temperature.
• Due to a wide effective temperature range, flux is
hard to carbonize.
• It is easy to remove slag after brazing.
• The corrosive action to the treated metal and brazing
filler is minimum.
• It excels in coating performance and is harmless to
the human body.
As the flux works in a complicated manner as
described above, it is necessary to select an
adequate type of flux according to the type and
shape of treated metal, type of brazing filler and
brazing method, etc.
Types of flux
• Non corrosive flux
Generally, it is a compound of borax and boric acid.
It is effective in case where the brazing temperature
is higher than 800°C.
• Activated flux
Most of fluxes generally used for silver brazing are
this type.
It features an increased oxide film removing
capability due to the addition of compounds such as
potassium fluoride, potassium chloride and sodium
fluoride to the borax-boric acid compound.
Piping materials for brazing and used brazing
filler/flux
Piping material
Copper - Copper
Copper - Iron
Iron - Iron
NOTE
• Do not enter flux into the refrigeration cycle.
• When chlorine contained in the flux remains within
the pipe, the lubricating oil deteriorates.
Therefore, use a flux which does not contain
chlorine.
• When adding water to the flux, use water which
does not contain chlorine (e.g. distilled water or ion-
exchange water).
• Remove the flux after brazing.
2-5-3. Brazing
As brazing work requires sophisticated techniques,
experiences based upon a theoretical knowledge, it
must be performed by a person qualified.
In order to prevent the oxide film from occurring in the
pipe interior during brazing, it is effective to proceed
with brazing while letting dry Nitrogen gas (N2) flow.
Never use gas other than Nitrogen gas.
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Service Manual
Used brazing filler Used flux
Phosphor copper Do not use
Silver Paste flux
Silver Vapour flux
CAUTION