Stainless steels have
higher strength and are more abrasive than many of the ordinary
steels and they work harden more rapidly than conventional
plain carbon steels.
* The smallest radius
formed without cracking is called the 'minimum bend radius'(R).
It increases with the thickness of the material(T).
Flaring: When tubing is flared the edge undergoes considerable
stretching.
The diameter of the flare is limited by the diameter of the
tubing. It is difficult to flare successfully any of the harder
temper conditions of stainless steel, such as 1/4 hard. Flaring
should be done on tubing with a yield strength not exceeding
650 N/mm². Tubing edges should be thoroughly deburred before
flaring.
Bending of Tubing:
Large bend radii, as would be expected, are easier to form
than small radii. Large diameter tubing has a greater differential
in stretch between the inner and outer bend radii and thus
has a greater propensity to thin, or flatten, in bending.
Thin wall tubes tend to wrinkle upon bending. The most difficult
bends are on large diameter, thin wall tubing. All but the
easiest of bends require precautions to avoid collapsing of
the tube. Internal support and often external guidance, or
support, is needed. Internal support can be as simple as sand,
or sealed rubber tubing to avoid collapse. In production operations
an internal mandrel is used.
Some flattening (reduction of the actual tube diameter) will
occur
during bending. This is dependent upon the diameter and wall
thickness of the tubing and the bend radius - the greater
the radius the less the flattening. Flattening for a bend
radius of approximately 2 times the tube diameter, for a 25
to 50 mm diameter tube, is 2.5 to 3 % of the original tube
diameter.
