Tayo
Rolls Limited is a leading Cast Iron and Steel Roll manufacturer in India. Now,
Tayo has put up manufacturing facility
This note describes the major facilities and process for manufacturing of Forged Roll and Engineering Forgings comprising the Steel melt shop with revamped electric arc furnace (EAF), Ladle furnace (LF), Vacuum degassing unit (VD) with ingot casting facilities, a Forge complex with Heat treatment facilities, Induction Hardening shop (IH) and a Machine shop.
1.0
LAYOUT
1.1
Steel melt Shop Layout
Steel
melt shop is earmarked on the eastern side of the existing plant.
The steel melt shop consists of two parallel bays. Electric Arc furnace,
Ingot annealing furnace, Sponge iron feeding system and Fume extraction system
are located in one bay. Secondary metallurgical units and ingot casting unit are
located in the other bay. Road
bound inter shop transfer cars have been provided for ingot dispatch.
1.2
Forge and Induction Hardening Shop Layout
The Forging shop comprises two bays, one 24m wide main bay with one 13m wide lean to bay. All the Bogie hearth furnaces are
housed primarily in the lean to bay of Forging shop. The Press with Manipulator, all the Hood type furnaces, Quenching and
Auxiliary facilities has been installed in 24 m wide main bay. 2 Nos. EOT cranes of various capacities with a crane rail height of 12
m serve this main forging bay. The Hardening shop comprises of two bays, one 24 m wide main bay and one 13 m wide auxiliary
bay. All the Induction hardening equipment’s, Tempering furnaces and Auxiliary facilities have been installed in the main bay and
the tool room, office room, control room etc is established in the auxiliary bay.
2.0
STEEL MELT SHOP
2.1
Design basis
The
facilities envisaged in the steel melt shop will produce about 50,000 tons of
liquid steel per year after reaching full scale of operation. The liquid steel
are cast into carbon and alloy steel grade forging quality ingots with 100%
bottom pouring practice. Ingots are forged in the Forging shop to produce Forged
rolls and Engineering forgings. Ingots are also being sold directly in the
market.
Expansion
plan for Steel making and Ingot casting facilities at TAYO is based on maximum
utilization of available main equipment, its operating assemblies and related
auxiliaries, such as, Ladle Preparation, Media Supplies and Process Automation
requirements. Special consideration has been envisaged for improvement of steel
quality and yield by installation of Secondary Metallurgical Units.
2.2
ELECTRIC ARC FURNACE
The
existing 25T upgraded Electric Arc Furnace is used to produce liquid steel for
casting into ingots. Input materials for the Electric Arc Furnace is about 30%
Hot metal from the existing Blast furnace, about 40% Direct Reduced Iron and
remaining are scrap and plant returns.
2.3
SECONDARY REFINING
The
liquid steel is tapped slag free as far as practicable into the ladle. The
objective of this treatment is to achieve clean steel chemistry with regard to
hydrogen, nitrogen and oxygen content required for certain grade of steel.
2.4
Selection of Secondary Refining Facility
The
secondary refining treatment is carried out in the 30ton capacity Ladle furnace
(LF) and in the 30ton capacity VD unit. The LF is used for arc heating,
desurphurisation, deoxidation and alloying.
2.4.1
Ladle Furnace (LF)
One
30 ton LF is installed for secondary refining and utilized to hold the heats for
an extended period of time, should it be necessary for reasons,
such as delays in casting. Argon gas is introduced through a porous plug
fitted at the bottom of the ladle for stirring the liquid steel during
treatment.
One
30-ton VD unit is installed in order to produce quality and clean steel in
regard to inclusion rating, gas content, etc.
Small amount of Ferro-alloys for trimming could be added into the melt
under vacuum. Degassing operation
ends by introducing nitrogen/air into the vessel for flooding.
Provision is made for wire feeding, temperature measurement and sampling
after VD treatment.
2.5 Ingot Casting
The entire liquid steel produced from EAF-LF-VD units is cast into Ingots.
Part of the cast ingot are sold to market and balance is hot transferred to
Forge shop for Roll Forge &
Engineering Forge.
Bottom
pouring technique with Hot tops is followed for casting of ingots.
Hot top boxes are removed from the ingot moulds by the stripping crane
and the ingots are stripped for dispatch to Forge shop and to the market as per
requirement.
2.5.1 Ingot Annealing Facility
All
raw materials are brought to the plant by road transport and unloaded and
stacked in respective areas earmarked for Storage of those particular materials.
Scrap and DRI are stored in the covered storage area provided in the steel melt
shop building. Purchased scrap from
the market and plant return scrap are brought by road into the storage area.
This area is served by one existing shop crane.
According
to the production programmed, required Ferro-alloys and other additives are kept
in the area stipulated inside the steel melt shop.
3.0
FORGE SHOP AND HEAT TREATMENT FACILITIES
The Forge Shop is designed for an overall finished product capacity of 8000 tons per year, of which around 3000 tons per year CRM Rolls can be produced of various grades and the rest 5,000 tons per year Forged product can be produced from various low & medium alloy engineering grade steel depending upon the market demand.
Provision
has been made for future ESR project for reducing inclusions, enter segregation
and improved properties of ingots.
3.1
Manufacturing Process
The hot ingots are transferred to reheating bogie hearth furnaces. After heating the ingots for required time they are taken for
forging in 2500 tons Open Die Forging Press to produce components like CRM Rolls, Sugar mill shafts, Wind mill shafts, Double
and Single step down shafts etc according to the job order. All forged ingots require to be annealed /normalized in heat treatment
furnaces prior to machining or further processing. After machining, different process routes are followed for CRM rolls and other
Engineering
grades.
The
CRM rolls are taken to Induction Hardening Shop for necessary heat treatment to
meet the technical specifications.
The
Engineering Forgings are Normalized/ Hardened & Tempered in the heat
treatment furnaces to meet the technical specifications.
3.2
Machining of forged shafts/roll blanks
After
annealing, the Forging ends are cut to desired lengths by Band Saws. All
forgings are identified suitably for subsequent monitoring.
The
Forged Rolls are rough turned in Rough Turning Lathes ensuring specific
tolerance.
Engineering
forgings are either be machined in-house and/ or subcontracted for machining,
depending on customer requirements.
4.0
INDUCTION HARDENING SHOP
Induction
Hardening of CRM rolls is done separately for barrel and journal portion.
4.1
Journal Hardening
The
forged and machined CRM rolls are set for Journal hardening after being
delivered to the Induction Hardening shop from Forge shop. One No. Horizontal
Induction Hardening machine is installed where only the journal portion are
hardened by passing the material through the induction coil followed by forced
air spraying.
4.2
High Temperature Tempering
The
CRM rolls after primary machining and journal hardening are tempered in a High
Temperature Tempering furnace to relieve hardening stresses and achieve the
desired hardness. One 60 tons Horizontal furnace is installed with two bases for
tempering purpose. The furnace is complete with all mechanical and electrical
equipment, refractory, instrumentation and control system.
4.3
Preheating Furnace
After
journal hardening and tempering, CRM rolls are preheated up to 200OC
prior to Induction hardening. One No. 6 tons capacity vertical pit type furnace
is installed for preheating of CRM rolls. This furnace is electrically heated
and complete with all mechanical and electrical equipment, refractory,
instrumentation and control system.
4.4
Barrel Hardening
The
preheated CRM rolls are immediately placed in a vertical Induction Hardening
machine and the barrel portion is passed through the induction coil followed by
water quenching.
The
Forged roll blanks are vertically Induction Hardened by dual Induction Hardening
system of 50 Hz and 250 Hz water cooled copper inductor coils. The rolls are
steadily and vertically lowered from a controlled downward movement facility
through the dual induction coils. Induction hardening is PLC controlled from a
control desk. Hardened depths is 40 mm max. Presently, the Induction Hardening
facility chosen can harden rolls to 10 Ton weight max. of barrel dia. 300 to 840
mm. and lengths to 5.5 M.
4.5
Cryogenic Treatment
Cryogenic/sub-zero
treatment is done after Induction hardening to transform retained austenite into
stable martensite and in this treatment the rolls from ambient temperature are
quenched by spraying liquid nitrogen in order to make the quenching temperature
below martensite finish (Mf)
temperature. Two
Nos. 32 tons capacity Horizontal Cryogenic tank with nitrogen spraying
arrangement is installed to carry out this treatment. Oxygen analyzer is
provided for personnel safety.
The
stressed CRM rolls after Induction hardening and Cryogenic treatment are
tempered in low temperature tempering furnaces. The furnaces are designed
for heating the rolls up to 4500C. The furnaces are complete
with all mechanical and electrical equipment, refractory,
instrumentation and control system.
4.7
Vertical Normalizing/Tempering Furnace
Sometimes
the hardness of CRM rolls after final tempering is not adequate and re hardening
followed by tempering is considered to be necessary to achieve proper hardness.
The rolls are required to be normalized prior to re hardening to relieve the
internal stresses developed in it. In view of the above requirement one No. 12
tons capacity vertical pit type normalizing/tempering furnace has been
installed. This furnace is designed to operate at a maximum temperature of 11000C
and complete with all mechanical and electrical equipment, refractory,
instrumentation and control system.
4.8
Quality Check:
Provision is made for an Inspection table for checking roll dimension accurately before final machining. The hardened and
tempered rolls are checked for cracks and flaws by NDT ultra-sound testing, Vickers/ Equotip for barrel hardness etc. and if
approved for quality, rolls are sent to Roll Machining section. For low hardness or less depth of hardness, mechanical and
structural properties the process of Induction Hardening and heat-treatment are repeated as salvage operation.
5.0
FORGE ROLLS MACHINING SECTION
The Forged, Induction Hardened, Tempered Rolls are finish machined to required dimensions of its barrel, journal and neck by machines installed in finish machine shop.
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6.0 IMAGES
