WORKING PROPERTIES AND USE OF REFRACTORIES
IN INDUSTRIAL FURNACES
I. D. Kashcheev
Translated from Novye Ogneupory,No.2,pp.3–5,February 2008.
Original article submitted August 21, 2007.
The main reasons are considered that give rise to development of internal stresses in individual refractory
components and a lining. The importance is noted of monitoring thermal expansion of a refractory during
service, and also features of the behavior of monolithic linings on heating.
Refractory materials used in industrial furnaces and
heating installations are subject to various forms of break
down: fusion, deformation, cracks, separation, wear,
chipping, etc. Under real conditions all of the factors listed
operate, and therefore the choice of refractory material
should be made after careful analysis of operating conditions
for the heating unit and operation of the main factors that
affect lining stability, and here consideration should be given
to the production indices of furnaces operating under similar
In the majority of cases in studying the refractory
characteristics of a standard brick specimens are cut from it
for testing. The results obtained in this way determine with
sufficient accuracy such properties as refractoriness, etc.
At the same time these data are unsatisfactory for obtaining
such properties as the magnitude of thermal stresses or
thermal expansion, etc. This is connected with the fact that
after laying individual bricks using a refractory mortar its
physical properties as a whole will be markedly different
from the properties of an individual object.
The amount of thermal expansion is the most important
property of an individual brick. This index is evaluated from
the results of tests by different methods:
measurement of the linear thermal expansion coefficient
(LTEC). The results obtained are provided in the form of
measuring the LTEC in relation to temperature;
determination of the temperature for the start of defor
mation under load. As a result of performing tests the
maximum permissible operating temperature is established
for the refractory material property. Here it should be noted
that the amount of thermal expansion under load is normally
less than linear thermal expansion;
evaluation of the amount of material creep. The ratio of
the amount of deformation with respect to time is deter
mined. In this case the overriding value is not the absolute
amount of deformation, but the difference in deformation
with respect to time;
determination of shrinkage with a reduction in tem-
perature. In operating heating units under real conditions
individual structural elements of a furnace are subjected to
cooling both during furnace warm-up and also during
termination of heating;
measurement of elasticity modulus values. The method
consists of finding the relationship between the magnitude of
load and the level of deformation. The index is taken as an
absolute quantitative property, whereas a change in tempe
rature for the start of deformation under load and material
creep determine the relative level of deformation;
heat resistance testing determines the capacity of a
material to resist internal thermal stresses that arise as a
result of a temperature gradient without failing.
Thermal expansion properties determined for an indivi
dual brick should be used for calculating the behavior of a
refractory lining as a whole.
These laboratory and industrial tests, in the course of
which refractory resistance to a corrosive agent is de
termined, serve as the main choice of refractories. During
furnace operation the lining gradually breaks down. Furnace
lining resistance varies in relation to the type of furnace and
it is an important economic index.
The theoretical possible maximum strength P
crystalline material is determined by the equation
where E is Young’s modulus; g
is solid specific surface
energy; a is lattice parameter. The approximation g
Refractories and Industrial Ceramics Vol. 49, No. 1, 2008
1083-4877/08/4901-0014 © 2008 Springer Science+Business Media, Inc.
GOUVPO UGTU–UPI, Russia.