venkatersan_foseco
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venkatersan_foseco

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Fluid flow can be characterized by velocity,
flow pattern and turbulence intensity. As
shown in Fig 2. the fluid flow in a tundish
is of two types namely active & passive
(Sahai and EMI1).

Active flow consists of the plug and mixed
flow component whereas passive flow
signifies the dead flow.

2.2 Flow Modifiers

The flow pattern in the tundish having
significant influence of the quality and
productivity of the steel produced. Several
devices are generally used in the tundish to
modify steel flow in the tundish to get
optimised performance.

Over the years several designs of flow
modifiers were used in the tundish to
achieve desired results. These were namely
dams, weirs, baffles with multiple holes
etc. The main purpose of using these was
to put barriers in the steel flow path as well
as give directional metal flow upwards
which facilitated inclusion floatation. M.M
Collur,D. B. Love and B.V. Patil2 of
Alleghany Ludlum.Pensilvania, USA did a
detailed study to analyse the effectiveness
of different existing flow modifiers systems
towards inclusion floatation. Michael L.
Lowry and Y. Sahai3, Paul Rasmussen,
Dofasco Inc, Canada4 study and their
subsequent verification during actual
practice in the plant gives a clear idea of
the improvements possible by using these
flow modifiers vis-à-vis having none.

Recent demands of steel industry has
pushed the concept of flow modifiers from
just acting as barriers and directing flow
upwards towards actually suppressing the
energy of incoming steel in the tundish by
custom designed flow controlled pads.
These pads when properly designed for
each plant taking into account its
uniqueness, did gave improved per-
formance over dams. weirs and baffle

Abstract

In this era of ‘Open Economy’ the role of
tundish has been transformed from being a
just mere intermediate vessel for
transferring steel from ladle to mould to a
critical reactor in the continuous casting
process. This has resulted in the need for a
detailed analysis of effectiveness of various
tundish flow modifiers in achieving
optimum flow pattern and improving steel
quality. Kinematic viscocity similarity
between water at room temperature and
liquid steel gives a excellent scope to
understand the flow pattern of steel by
physical modelling. Water Modelling
studies of tundish have shown the need for
developing flow modifier system which
apart from enhancing surface directed flow
will effectively suppress turbulence in the
pouring area and improve laminar flow.
Such a flow pattern not only increases
residence time of steel in the tundish
,thereby facilitating inclusion floatation,
but also reduces transition zone during
mixed grade casting as well as slag
emulsification during ladle change overs.
The flow pattern of steel in the tundish
depends on a host of plant parameters
which makes the tundish of each plant
unique. This uniqueness makes it
imperative to study every plant tundish
separately in order to suggest the optimum
flow modifier system.

1. Introduction

The tundish plays an important role in the
continuous casting process. In this era of
‘Open Economy’ every steel plant is now
facing new challenges of producing quality
steel through cost effective methods. This
new demand has transformed the role of
tundish which was originally considered as
a buffer vessel used to transfer molten
steel from ladle to mould, to a critical
reactor within the continuous casting
operation. In its new role the tundish is
now designed to deliver controlled flow of
metal to mould and facilitate inclusion
floatation.

During the past two decades extensive
work has been done to understand and
improve the fluid flow pattern in the
tundish with the help of both physical and
mathematical modelling. Keeping in view
the changing needs of the steel plant
Foseco India Limited set up their first

tundish water modelling laboratory in USA
in the early nineties. The experience of
developing custom designed tundish flow
modifiers for major US steel plants was
then extended to Europe and India with
two new labs in Germany and India in the
late nineties.

2. Tundish Physical Modelling

2.1 Fluid Flow Characterisation

Prior to widespread adoption of the
continuous casting process two parameters
were considered necessary to characterise
the condition of steel during steel making
and casting. These two parameters were
temperature and composition. However,
recent innovation in post-furnace
steelmaking practice such as ladle
treatments(desulfurisation, allow addition
etc.) and particularly continuous casting
procedures have pressed for the need of
considering a third parameter" Fluid Flow"
to completely characterize steel condition
at any position in the processing sequence.
As shown in Fig.1 interaction between the
three processing parameters determine the
response in terms of both quality and
productivity.

Temperature and composition are linked
through the physical chemistry of
steelmaking process e.g. the solubility of
non-metallic levels in steel and thus the
active oxygen levels in steel are influenced
by temperature. Again the condition of
fluid flow will affect the heat loss and
therefore the temperature.

Fluid flow and composition are strongly
linked with the condition of fluid flow
exerting significant influence on

1. The ability to remove non-metallic
inclusion form metal to slag phase.

2. The degree of re-oxidation due to
atmospheric contact while pouring

3. The success of alloying procedures.

Water Modelling – A tool for Effective
Designing of Turbulence-suppressing
Tundish Impact Pad, TURBOSTOP
Authors: K. G. Venkatesan, S. K. Bera, S. Khurana – Foseco India Limited

TEMPERATURE

COMPOSITION FLUID FLOW

QUALITY PRODUCTIVITY

Fig 1. Three Processing Parameters

Fig 2. Tundish Flow Characterisation

TUNDISH FLOW

ACTIVE FLOW PASSIVE FLOW

MIXED FLOW DEAD FLOWPLUG FLOW

n

Kinematic similarity between model proto-
type and model is ensured if geometric and
dynamic similarities are observed. The
principal forces to be considered in
obtaining dynamic similarity in a
continuous casting system are inertial,
gravitational, viscous, and surface tension
forces. The principal dimensionless groups,
which involve these forces, are given by

.Froude No. = v2/g.L = inertial force/
gravity force

.Reynolds No. = V.L/� = inertial force/
viscous force

.Weber No. = �.V2.L/� = inertial force/
surface tension force

Absolute dynamic similarity that each of
the dimensionless groups listed above have
the same value in both model and actual
system which is impossible to satisfy in a
single model of particular scale.
Reynold No. is satisfied for a full scale only,
which is not practible in all cases. In case of
Weber No. 0.6 scale14 is necessary which in
turn satisfies Froude No also. But
neglecting the influence of surface tension
and considering only the case of
homogeneous flow, Froude No. similarity
can be used which allows any scale factor.

3. Designing of Turbulence
Suppressing Tundish Impact Pad
using Tundish Water Modelling

Tundish Water Modelling in Foseco India
Limited’s Laboratory in Pondicherry is
based on Froude Number similarity
criterion which allows to scale down any
linear dimension e.g. tundish dimensions,
flow modifier dimensions, shroud
dimensions etc by a suitable scale factor (f).
The volumetric flow rate to be used in the
study is calculated using Froude Similarity
Criterion15

Qm = f2.5Qp

Qm = Volumetric flow rate in the tundish
model in the laboratory
Qp = Volumetric flow rate in tundish in
steel plant(actual)
f = Scale Factor
 The water modeling study was carried out
with the following primary objectives

1. Increase in Residence Time to promote
inclusion floatation

2. Reduction of Transition Zone during
Mixed Grade Casting

systems not only w.r.t. steel cleanliness but
also reducing mixed tonnage produced
when two different grades of