Bending springs. They are used by matching the inside diameter
(ID) of the spring with the outside diameter (OD) of the tube
to be bent.
The tubing is then inserted and centered on the
heel of the bend. The bend must be started larger than desired
and gradually worked down to the correct size.
The coiled
spring adds structural strength to the tubing wall during
bending and prevents the tube from crushing or kinking.
Roller Bending Tool.
This tool bends a tube to a desired
radius very efficiently. It consists of a grooved roller with
a degree scale marked on the outside and a slide bar on the
handle to point to the degree mark where the tube is bent. To
use the tool, the straight tubing must be secured in the tool,
and the incidence mark set to indicate zero degree of bend on
the scale. Then, pressure is applied to the slide bar, bending
the tube as shown in Figure 2-6 to the desired degree.
Power Bending
Tool. Tube bending machines are generally used in
depot maintenance
shops.
With such equipment, proper bends can be
made in tubing of
large diameters and hard materials. The production
tube bender is an
example of this type of machine.
Alternate Methods.
Tubing that has a 1/2-inch or large OD is
difficult to bend with hand tools. For this type tubing, power tools
must be used whenever possible, since they have an internal support
to prevent flattening and wrinkling.
However, when power tools are
not available, a filler method using sand, shot, or fusible alloy can
be used.
The steps involved are quite similar regardless of the
filler material used. Because the process using the fusible alloy is
the most complex, and the most accurate, it is presented in detail in
the following paragraphs.
Fusible alloy is a metal alloy with a melting point of
approximately 160F. The material must be melted under hot water at
or near the boiling point to ensure that the molten metal flows
freely. NEVER APPLY A FLAME TO THE TUBING OR TO THE FUSIBLE ALLOY.
EXCESS HEAT DESTROYS THE STRENGTH OF HEAT-TREATED TUBING AND THE
MELTING CHARACTERISTICS OF THE FUSIBLE ALLOY. Boiling water will not
melt fusible alloy after the flame has been applied. Furthermore, if
the tubing is held over a direct flame to remove the alloy, particles
of this metal can stick to the inside of the tube and cause
corrosion.
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AL0907
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