30-01-2013, 11:12 AM
STEEL MELTING SHOP
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INTRUODUCTION :
In Steel Melting Shop of Visakhapatnam Steel Plant, LD Process of steel making has been adopted. The liquid steel obtained from LD process is cast into Blooms through Continuous Casting Machines (Bloom Casters).
For better exploitation of the available facilities and to have efficient administration in the biggest department of VSP, Steel Melting Shop is divided into two major sections.
i) Converter Shop ii) Continuous Casting Shop Each of these shops have been further divided.
CONVERTER SHOP: Bulk Material Handing Section (BMHS) Mixer Shop Converter Bay Scrap Yard Slag Yard Ladle Preparation Bay
CONTINUOUS CASTING SHOP: Tundish preparation Bay (TP Bay) Argon Rinsing Station (ARS) & IRUT & LF Continuous Casting Machines Gas Cutting Machines Bloom Storage Yard.
DESCRIPTION OF FACILITIES:
MIXER SHOP:
It is very difficult to supply the hot metal from Blast Furnace to the converter as per its requirement, unless there is an arrangement for storing the hot metal in SMS. Mixer serves this purpose. There are two mixers in SMS. The Capacity of each mixer is 1300T Hot Metal. In mixer, temperature of hot metal is maintained by burning coke oven gas with air. The Mixer vessel is in cylindrical form with two removable spherical ends. Length of the vessel is 10.67M and diameter is 7.64M. The mixer is installed on a mixer platform and is served by mixer crane (2 no’s of capacity 180T/63T/20T) The main units of the mixer are shell assembly, roller support, tilting mechanism, hand brake mechanism, charging hole cover winch, charging hole platform, spout door opening mechanism, gas & air distribution system, installation of blower, lubrication system, electrical system.
The average life of mixer is about 1.6-1.8 MT (Million Ton), Lining duration is about 30 days. To reduce abnormalities in LD Steel Making, Blast Furnace is supplying Hot Metal to SMS in the following composition and temperature range.
CONVERTER BAY :
Hot metal contains different impurities (C, Si, Mn, S, and P) above safe level which make Pig Iron brittle. But steel is nothing but refined hot metal. Refining is only possible when things are in molten phase. Refining is done by blowing oxygen in the LD converter Charged with Hot Metal, Scrap, Flux, Iron Ore, etc. In this refining process, temperature of liquid steel is kept at 17000 C (average). Different grades of steel is made by adding various Ferro-alloys & additives (FeSi, FeMn, Coke Breeze or Petroleum Coke, Aluminum, etc) in different quantities during taping of liquid steel from converter to steel ladle.
TUNDISH PREPARATION BAY:
Tundish is a refractory lined container having 4 nozzles through which liquid steel is poured in all 4 moulds of a C.C.machine at a time. Pouring of liquid steel from tundish to mould is controlled by stopper-rod mechanism. During casting, Tundish is placed over mould, and below steel ladle. Tundish maintains the constant Ferro-static pressure and it helps in floating of the nonmetallic inclusions at the top layer of liquid steel and thus non-metallic inclusions are prevented from entering into mould.
Casting Powder:
The main purpose of casting powder is to act as a lubricant to prevent the sticking of steel to mould. Casting powder must be added continuously at regular intervals. The meniscus must always be covered enough that it appears dark, but layer thickness should not exceed 30 mm.
Casting powder should meet the following requirement: i) reduce strand friction ii) should protect liquid steel against re-oxidation. iii) Prevent surface heat loss. iv) Promote uniform heat transfer from meniscus to mould in order to avoid longitudinal cracks. v) Rapid and uniform spreading on the bath surface. vi) it should also absorb some oxides in the steel without great change of its viscosity.
Gas Cutting Machines(GCM):
The strand, which continuously comes from the copper mould after getting completely solidified, should be cut as per our requirement, to facilitate easy handling, etc. In order to cut the blooms accurately, a gas cutting machine, using acetylene and oxygen, is used.
Since the bloom travels with certain speed, the machine used for cutting the bloom should travel along with the bloom. For this grippers are used, which grips the bloom and travels along with it, taking the oxy-acetylene flame with it. Each CC machine has been provided with 4 cutting machines to cut the four blooms at a time