|
|
Welded and drawn tubing begins as a cold rolled sheet or a
strip which is produced in coils. The metal strips are shaped
to a tube form and passed under a welding head which melts
the edges of the open seam to form a fusion juncture. No filler
material or flux is used and therefore the weld bead is of
the same analysis as the parent metal. As per the method of
welding employed, a weld bead is formed on either on both
the I.D. and the O.D. surfaces. After the cold drawing process
is complete, the weld area can be detected only by etching
or careful microscopic examination. Actually the weld area
is quite homogeneous with the parent metal since the cold
working and intermediate annealing causes the weld area to
recrystallize, thus it becomes equivalent to the parent metal
in ductility, appearance and mechanical properties. Welded
and drawn tubing from cold rolled strip has several advantages |
|
|
|
Cold Drawing consists of pulling the tubing through a die
which is smaller in diameter than the O.D. of the tube. While
it passes through the die, it is usually supported on the
inner surface by a tool which controls the I.D., wall thickness
and the length. The cold drawing process is repeated till
the desired size is attained. Cold drawing reduces ductility
(Pliability) of the alloy. To prevent this, the tubing is
normally annealed between the drawing operations which increases
the ductility and prevents brittleness
|
|
|
 |
| |
| |
The
fine tubes being produced by OST are subjected to Bright Annealing
for relieving the stresses and complete solutionizing of Austenitic
matrix, by putting in thermal energy which allows the stresses
to relax. In this unique process of bright annealing the material
does not get oxidized and hence no scaling. The inert atmosphere
present in the Furnace gives a bright surface and checks any
loss of Chromium, thus the corrosion property remains unaltered.
In OST this function is performed by the latest type of Bright
Annealing Furnaces imported from Japan. |
|
 |
|
