Zanotti un0 060, Workshop Manual

Page: 57 / 248

46
Cooling Circuit
3.2 Operations
Basic steps in brazing
Individual Protection Devices
Goggles, Gloves, Vest
(a)
Ensure fit and clearance: Braz-
ing uses the principle of capillary
action to distribute the molten
filler metal between the surfaces
of the base metals. Therefore,
during the brazing operation,
you should take care to maintain
a clearance between the base
metals to allow capillary action
to work most effectively. This
means, in almost all cases, a
close clearance as 0.25mm -
0.13mm (0.001" - 0.005") is
sufficient. When joining
dissimilar metals, allow for
differences in thermal
expansion.
(b)
Clean metal: Joint parts should be well cleaned before welding operations. Brazing filler metal won’t bond to a rusty
surface, furthermore oil and grease will carbonize when heated, forming a film over which filler metal will not stick
compromising junction strength and seal.
(c)
Flux prior to brazing: Flux is required to prevent oxides from forming while the metal is heated. The flux also serves
the purpose of cleaning any contamination left on the brazing surfaces. Flux can be applied in any number of forms
including flux paste, liquid, powder or pre-made brazing pastes that combine flux with filler metal powder. Flux can
also be applied using brazing rods with a coating of flux, or a flux core. Flux must be chemically compatible with both
base metal and filler metal being used.
(d)
Hold parts in position for
brazing, ensuring correct
alignment during heating and
cooling cycles, so that capillary
action can do its job. Best
practice is to flow nitrogen
inside tubes according aside
Table (approx. 0, 35barg),
avoiding internal oxidation dirt.
Tube Diameter
[mm]
Nitrogen Flowrate
[ l/min ]
6
−
18 3
−
4
20
−
40 4
−
5
> 40
5
−
6
(e)
Brazing: Heat a broad area around the joint by hand held torch. Both metal parts in the assembly should be heated as
uniformly as possible so they reach brazing temperature at the same time. Heated assembly will melt off a portion of
the filler metal, which will instantly be drawn by capillary action throughout the entire joint area.
(f)
Clean junction with a metal brush