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
Low temperature breakdown under
Failure under overlying load at high
Swelling at high temperature under reducing
premature softening of materials
Tests are developed to measure the tendency
of burden materials to degradation
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
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;
Reducing gas 40% CO and 60% N2
Gas flow 1000 liters/min
Pre heating under nitrogen
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
Materials with low hot compression strength
would breakdown under load in the lower
part of the furnace stack and affect the
The hot compression strength can be
measured in a compression testing machine