This document discusses various tests used to evaluate the physical behavior of materials during high-temperature reduction processes in blast furnaces. It describes decrepitation testing which examines how materials breakdown when exposed to exhaust gas temperatures. Low-temperature breakdown testing evaluates disintegration at lower reducing temperatures. Swelling tests measure the change in volume of materials like pellets at different reduction degrees. Finally, hot compression testing assesses the reduction in strength of materials at increased temperatures, important for withstanding loads in the lower furnace.

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-506 + 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 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

9. MUHAMMAD SHAFQAT
MME-10M -11

10. MUHAMMAD SHAFQAT
MME-10M -11