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Hot Finishing
All our hot-finished tubes are produced either through the Assel Mill or the PQF® Mill route. Round steel blooms (billets) of specific lengths are first heated in a rotary hearth Furnace. After heating, these blooms are descaled, end-face centered and passed through a cross-roll Piercing Mill to produce rough hollow blooms. These hollow blooms are then rolled over a mandrel either through a three-roll Assel Mill or through a PQF® Mill to produce hot-finished tubes. If required, these tubes are passed through a hot-sizing mill or a stretch reducing mill to produce tubes of intermediate dimensions. Hot-finished tubes are either delivered "as is" or further cold processed.
The Assel Mill is the ideal process for producing low volume, customized tubes with high dimensional accuracy and excellent concentricity. As a result these tubes are ideal for the manufacture of items such as bearing rings, cages for constant velocity joints (CV cages), automobile parts, etc.
The PQF® Mill, on the other hand, is ideal for producing large volumes of very accurately sized tubes. This process is ideal for producing tubes for the Power Generation industry, OCTG tubes, and other applications where large volumes are required.
Cold Drawing
In the Cold Drawing process, hot-finished tubes are surface treated and
then drawn through the gap between a reducing die and a central plug (or
a mandrel), thereby reducing both the inside and outside diameters and
polishing both internal and external surfaces of the tube to achieve close
final tolerances.
Cold Pilgering
In the Cold Pilgering (Rotorolling) process the hot-finished tube is reduced
by forging and elongating the tube stepwise over a stationary tapered
mandrel. Two rolls, each with a tapering semi-circular groove running
along the circumference embrace the tube from above and below and rock
back and forth over the tube (the pass length), while a stationary tapering
mandrel is held in the center of the tube. At the beginning of the stroke
(pass), the circular section formed between the grooves of the two opposing
rolls corresponds to the diameter of the ingoing tube and to the thickest
section of the mandrel. As the rolls move forward over the tube, the circular
section reduces in area until, at the end of the pass length, the circular
section corresponds exactly to the finished outer diameter of the tube
and the inner mandrel diameter corresponds to the finished inner diameter
of the tube. The tube elongation is achieved by reduction of the outer
diameter as well as the wall thickness of the in-going tubes. The Cold-Pilgered
tube is characterized by very small dimensional variations and a very
high surface quality. Furthermore, the high level of cold working (up
to 70%) results in very high hardness levels and therefore excellent machinability.
Other Processes
Subsequent to the manufacture of tubes, ISMT uses a variety of finishing
processes to produce value-added products such as near-net rings for bearings
and CV cages, swaged and machined axles for trucks/trailers, couplings
for OCTG products and hex-shaped drill rods for mining. Some of the processes
used are:
- Cold-Ring Rolling: We have a number of Bad Deuben machines
that are capable of cold rolling rings to produce near-net shaped annular
components. This process has almost zero wastage and yields a product
with very tight tolerances.
- Machining: ISMT has a variety of in-house machining
facilities and has strategic manufacturing relationships with accredited
vendors allowing us to meet virtually any customer requirements on short
notice.
- Heat treatment: Annealing, Hardening, Normalizing, Spherodizing
- Peeling
- Swaging/Upsetting
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