|
Hot
rolled coils are being produced at Ispat
Industries Ltd. with process
route of EAF – LRF – CCM – HSM.
-
EAF
:
After tapping the last heat , normally 40 ton liquid steel
is being left in the furnace
on which DRI is charged
continuously from the roof through the conveyor belt system. The
DRI feeding rate is in accordance
with the transformer capacity which maintains the bath temperature
around 1560°C . DRI feeding reaches to the peak of 200 t/ hour during
the processing .At the end , DRI feeding rate is being gradually
slowed down . Foamy slag is being practiced to optimize the power
consumption .High FeO in the foamy slag ensures low phosphorous
in the steel. Before
tapping ,sample is taken to check the chemistry of the melt, if
it is “OK” the heat is tapped at around 1600° C to 1620 ° C with
800 to 1000 ppm oxygen level. For tapping furnace is tilted by 10°
and the liquid steel is tapped through eccentric bottom tap hole.
The tapping is done in well
-
LADLE
REFINING FURNACE : The tapped heat comes for final refining
at the ladle furnace wherein
all the ferroalloy additions are done . Refining
normally takes 45 minutes to one hour with continuous purging
of argon gas .The prolong argon purging helps in reducing the inclusion
content in the liquid steel to the minimal level . High purity lime
( approx. 2500 Kg ) is used for slag formation at LRF. Sulphur drops
down to less than 0.01 %.
The chemistry of the steel is finely tuned as per the specification
/ customer’s requirement which is ensured by checking the ladle
heat samples by spectrometer at the express lab. The steel is treated
with calcium just 10 minutes before lifting the ladle to have adequate
fluidity for casting. The ladle is normally lifted at around 1600°C
only after clearance received from express lab.
- CASTING :Casting is done in
continuous casting machine with standard operating practices. Norms
for standard operating practices has been developed set grade wise
covering various casting parameters such as casting speed , mould level
fluctuation, stopper rod percentage, primary and secondary cooling.
- TUNNEL FURNACE : Slabs are
cut into the required length as per the weight requirement
of the customer before entering into the tunnel furnace. Tunnel furnace
mainly does three function ;
- Reheat
the slab to the required mill entry temperature.
- To
maintain uniform temperature through out the cross section and through
out the length of the slab.
-
Acts as a temporary reservoir for any specific requirement
of mill ( Roll change , etc. )
-
HSM
: The descaler is
located just before the
mill It is four
high six stand tandem
mill .
-
Main
features :
-
CVC
rolls.
-
Automatic
gauge control through
hydraulic system
-
Level
– 2 automation
-
Profile
contour and flatness control
system
-
Continuous
width and thickness measurement by Laser and X – Ray through out
the length of the coil.
The high level of automation ensures very close thickness tolerances
on thickness and width. Finishing
and coiling temperatures are maintained exactly as per the norms to
achieve the required mechanical / metallurgical
properties. Circumferencial
and Eye strapping
is done automatically. Normally three samples are collected per
heat for mechanical / metallurgical testing from the sampling station.
Further coil is marked with the hot chalk for it’s identification.
|
