The tube should be cut to desired length with
a square cut, preferably in a square-end sawing vise. The cutting
wheel of the type specifically designed for cutting copper tube will
also do a satisfactory job. The tube should be the exact length needed,
so that the tube will enter the cup of the fitting all the way to
the shoulder of the cup. Remove all slivers and burrs left cutting
the tube, by reaming and filing, both inside and outside.
To make a proper brazing joint, the clearance
between the solder cup and the tube should be approximately 0.001"
to 0.010" (0.0254mm to 0.254mm). Maintaining a good fit on
parts to be brazed insures:
应用简易 - 公差过大可能会破坏毛细作用，结果是合金无法流遍连接部位，或者从连接部位冲刷出去。
Ease of Application - Excessively wide tolerances
tend to break capillary force; and, as a result the alloy will either
fail to flow throughout the joint or may flush out of the joint.
耐腐蚀性能 - 连接部位的耐腐蚀性能与连接部件之间间隙有直接的关系。
Corrosion Resistance - There is also a direct
relation between the corrosion resistance of a joint and the clearance
节省 - 要节省地使用铜焊合金，但是，作为必要条件，必须以最少数量应用在恰当的连接部位，使用刚刚能够充满连接部件之间面积的合金量即可。
Economy - If brazing alloys are to be used
economically, they, of necessity, must be applied in the joint proper
and in minimum quantities, using merely enough alloy to fill the
area between the members.
The surfaces to be joined must be clean and
free from oil, grease and heavy oxides. The end of the tube need be
cleaned only for a distance slightly more than it is to enter the
cup. Special wire brushes designed to clean tube ends may be used,
but they should be carefully used so that an excessive amount of metal
will not be removed from the tube. Fine sand cloth or emery cloth
may also be used with the same precautions. The cleaning should not
be done with steel wool, because of the likelihood of leaving small
slivers of the steel or oil in the joint.
The cup of the fitting should be cleaned by
methods similar to those used for the tube end, and care should be
observed in removing residues of the cleaning medium. Attempting to
braze a contaminated or an improperly cleaned surface will result
in an unsatisfactory joint. Brazing alloys will not flow over or bond
to oxides; and oily or greasy surfaces tend to repel fluxes, leaving
bare spots which will oxidize, resulting in voids and inclusions.
Flux should be applied to the tube and solder
cup sparingly and in a fairly thin consistency. Avoid flux on areas
not cleaned. Particularly avoid getting excess flux into the inside
of the tube itself. Flux has three principal functions to perform:
It prevents the oxidation of the metal surfaces
during the heating operation by excluding oxygen.
It absorbs and dissolves residual oxides
that are on the surface and those oxides which may form during
the heating operation.
It assists in the flow of the alloy by presenting
a clean nascent surface for the melted alloy to flow over. In
addition, it is an excellent temperature indicator, especially
if an indicating flux is used.
Immediately after fluxing, the parts to be
brazed should be assembled. If fluxed parts are allowed to stand,
the water in the flux will evaporate, and dried flux is liable to
flake of exposing the metal surfaces to oxidation from the heat. Assemble
the joint by inserting the tube into the cup, hard against the stop.
The assembly should be firmly supported so that it will remain in
alignment during the brazing operation.