1. Physic Behavior of Materials
During Reduction at High
Temperature

2. Introduction
 The behavior of materials from the time
these are charged on is of direct interest in
assessing the blast furnace operation.
 During this process material may
disintegrate by any one or more of the
following;
 Decrepitation
 Low temperature breakdown under
reducing condition

3. Introduction
 Failure under overlying load at high
temperature
 Swelling at high temperature under reducing
condition
 premature softening of materials
 Tests are developed to measure the tendency
of burden materials to degradation

4. Decrepitation
 When iron bearing materials are suddenly
exposed to exhaust gas temperature on charging
,breakdown may occur due to thermal shocks. It
is known as decrepitation.
 In a typical test 500g of 20-40mm size undried
ore is dropped in a furnace previously heated to
400C and retained there for 30 mints under a
flow rate of 5000L of nitrogen per hour.
 The sample is then cooled and the %age of
0.5mm and-5.6 + 0.5 in the product is
determined by sieving.

5. Low Temperature Breakdown Test
 It has been observed that iron bearing
materials do disintegrate at low temperature
under mildly reducing conditions ,it is due to
the presence of micro cracks.
 The test consists of subjecting the charge to
static bed reduction at low temperature in a
rotating furnace for a fixed duration.
 The %age of fines generated is quoted as L .T
.B . T. index

6. Swelling
 Pellets show a maxima in their volume change
with increasing degree of reduction .It is due to
swelling . It also troubles the furnace operation.
 Swelling can be measured for individual particles
but bulk swelling data is of practical use.
 Their apparent volume is measured by
immersion in mercury . then samples are
reduced to different degrees of reduction in a
static bed under following conditions;

7. Swelling
 Temperature 1000C
 Reducing gas 40% CO and 60% N2
 Gas flow 1000 liters/min
 Pre heating under nitrogen
atmosphere
 The %age reduction is ascertained from the
%age weight loss or chemical analysis

8. Hot Compression Test
 The compression strength of burden
materials falls rapidly with increasing
temperature.
 Materials with low hot compression strength
would breakdown under load in the lower
part of the furnace stack and affect the
permeability.
 The hot compression strength can be
measured in a compression testing machine