TITLE OF THE INVENTION
An improved lining pattern and method of installation for use in the walls of
reheating furnaces
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improved lining pattern for use in the walls of
reheating furnaces so as to prevent over-heating of shell thereby reducing heat loss
from the furnace. The invention also relates to an improved method of installation of
refractory in the walls of reheating furnaces.
BACKGROUND AND THE PRIOR ART
Reheating furnaces are used for heating ingots/slabs/blooms/billets for subsequent
rolling into further shapes. In furnace having capacity of 160 T, 8-10 ingots are
placed for further heating. Furnaces are operated at a temperature of 1320°C and
mixed gas of calorific value 1550 kcal/Nm3 is used as fuel. At present, the walls are
lined with traditional firebricks with a 500 mm thick casting with low cement castable
at the top and total 180 T of refractories is utilized for lining the reheating furnace.
Outside shell temperatures of old running furnaces range 120° - 200°C. However, this
type of lining results in frequent damages due to wall erosion by regular hitting with
ingots having bottom bulge as well as due to bulging of walls itself. This results in
poor furnace availability as it is frequently repaired resulting in loss of production.
The additional cost due to repeated repairs is another detrimental factor. Life of
furnaces varies from 9 to 12 months with 3 to 4 intermediate repairs.

OBJECTS OF THE INVENTION
Accordingly, one object of the present invention is to overcome the
disadvantages/problems of the prior art.
Another object of the present invention is to provide an improved lining pattern for
use in the walls of reheating furnaces so as to prevent over-heating of shell thereby
reducing heat loss from the furnace.
Another object of the present invention is to provide an improved quality of
refractory material for lining.
Yet another object of the present invention is to provide a method of installation for
use in the walls of reheating furnaces.
Yet another object of the present invention is to reduce heat loss through the walls of
furnace.
Yet another object of the present invention is to reduce the gas consumption in the
furnace.
Another object of the present invention is to improve the working efficiency of the
furnace.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided an improved lining
pattern for use in the walls of reheating furnaces so as to provide efficient heating of
ingots, said lining pattern comprising :

plurality of layers
wherein
at least one first layer having different thickness of ceramic fibre located in different
regions;
a second layer consisting of light weight brick lining at some places; and
a third layer having an appropriate thickness of high grog fire bricks in some places in
combination with a working layer
wherein said working layer comprising low cement castable lining having 70% of
alumina content.
In non critical areas, thickness of high grog fire bricks have been increased and 70%
Alumina low cement castable has been eliminated.
According to another aspect of the present invention there is provision for installation
of lining pattern as described hereinabove, said composition comprising:
(i) low cement castable with alumina at least up to 70% by weight of the
composition;
(ii) iron oxide in the range of 0.01 - 0.6% by weight of the composition; and
(iii) calcium oxide in the range of 0.1 -1.5% by weight of the composition.
Another to yet another aspect of the present invention there is provided a method for
installation of lining pattern for use in the walls of reheating furnaces, said method
comprising steps of:
(a) Lining at least up to 1500mm of the furnace wall from bottom side
with bricks;
(b) Casting next at least up to 2500mm of the furnace wall using ceramic
fibers, light weight and high grog quality bricks, at least 70% alumina
low cement castable and combinations thereof;

(c) Lining at least up to 400mm of the furnace wall with bricks;
(d) Then casting the remaining height of 600mm of the furnace wall using
ceramic fibres and at least 70% castable.
(e) placing hot ingots in the furnace followed by slow heating using
furnace burner initially drying and heating of the furnace.
The other objects and advantages of the present invention will be apparent from the
description provided hereinbelow with reference to the accompanying figures and
detailed description provided herein below.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates General layout of improved composite lining system.
Figure 2 illustrates Schematic lining system of long walls.
Figure 3 illustrates Schematic lining system of Trackside short wall.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to an improved lining pattern for use in the walls of
reheating furnaces. The pattern comprises plurality of layers which include at least
one first layer having different thickness located in different regions. The second
layer consists of brick lining and third layer comprises ceramic fibre (2), light weight
(3)and high grog quality bricks (4) in combination with a working layer.

Ceramic fiber(2), of different thickness in different regions has been used to protect
the shell from overheating. It is basically a composite lining design in which LCC (5)
has been used in combination with bricks. Lower 1500 mm of the wall consists of
brick lining only. The next about 2500 mm consists of combination of ceramic
fiber(2)„ light weight(3) and high grog(4) quality bricks in combination with working
layer of 400 mm thick LCC(5) was used. In the long walls, above 2500mm as
mentioned above, three layers of bricks have been used and then above that about 600
mm upto top of the furnace, LCC(5) lining was used. Towards Trackside, LCC(5)
lining has been used to the top over lower 1500 mm brick lining. Towards Burner
side, only top 600 mm is made up of LCC and the remaining lower portion is made of
fired fireclay bricks. The working layer comprises low cement castable lining having
70% of alumina content. (Referring figures 1-3)
The specification of LCC used for casting the walls of the furnace is given in Table I.
After lining, the furnace was left open in the air for air curing of castable lining.
Drying and heating of the furnace was initially performed by placing hot ingots in the
furnace followed by slow heating using furnace burner. Initial drying and heating
needs to be very slow as the monolithic wall lining with LCC(5) is very dense and
removal of free moisture from inside the thick wall is very slow. Fast rate of heating
will cause damage/bursting of the lining. So, initial drying and heating needs very
careful attention. After initial heating using hot ingots, the temperature was raised to
300°C @ 20°C/hr and soaked for 12 hours. Temperature was further raised to 600°C
@ 20°C/hr and soaked for 12 hours. Heating of the walls was monitored with the help
of temperature recorder in the control room and simultaneously also with the help of
Infrared non-contact Pyrometer. After that the furnace was put in normal operation.

Experimental Results:
Special 70 % A1203 LCC having high hot strength (HMOR - 60 kg/cm2) was used in
the lining of walls of the furnace. Characteristics of this material are much superior to
the bricks used in the old lining (see Table I & II). Modified lining pattern is a
composite lining design involving castable and bricks (shown in Fig. 1). Sufficient
insulation has been provided adjacent to the metallic shell of the furnace using
ceramic fiber to prevent over heating of the shell, thereby reducing the heat loss
through the walls of the furnace.



The furnace is dismantled and cleaned properly. Bottom bricks are laid first except
top two layers and then walls are made upto a height of 1500mm using bricks.
Specially designed Stainless Steel anchors of 304 quality (SS-304) are used for
application of LCC to take care of mismatch in thermal expansion of refractory lining
and metallic shell and thus prevent development of cracks in the monolithic lining.
After wall lining the remaining two layers are placed in the bottom. After completion
of lining, it is air cured for 24 hour$. Then air injection is given for 24 hours after
closing the furnace. After that bottom is prepared using coke breeze.
Drying and heating of the furnace is done placing hot ingots/hot stock in the furnace
followed by slow heating using burner. After that the furnace is put in normal
operation. There are absolutely no visible cracks anywhere in the lining after heating.
Outside shell temperature, as measured with the help of Infrared pyrometer, ranges
from 90° to 135°C, which is near to the estimated values. Outside shell temperature
of old furnaces ranges from 125° to 200°C. Shell temperature is slightly lower in case

of new lining due to provision of sufficient insulation using ceramic fibre adjacent to
the shell. Thus, there is reduction in heat loss through the walls with modified lining
design.
The overall performance of the modified furnace lining is extremely good as
compared to the performance of the other furnaces with old lining design. In other
pits with old lining design, it takes 12 hours to heat the cold ingots/stock to service
temperature i.e 1320oC. After attaining the desired temperature, a soaking of 6 hours
is given. Thus total heating time is 18 hours. In case of modified reheating furnace, it
takes only 6 hours to raise the temperature to 1320oC . Thus total heating time is 12
hours which includes 6 hours soaking. Hence, there is a reduction of 6 hours in
heating time for cold ingots.
In case of hot ingots/stock, it takes 3-4 hours to raise the temperature to 1320oC for
other reheating furnaces and total heating time is 9-10 hours including 6 hours
soaking where as for modified furnace, total heating time is 7.5 - 8.0 hours including
6 hours soaking. Thus, there is a reduction of 2-3 hours in heating time for hot ingots.
Specific heat saved (Gcal/T) in case of hot cycle is 41% (average)and in case of cold
cycle the saving is 34% (average).
Advantages of the invention:
The main advantages of the present inventions are:
1. The lining pattern of the present invention provides more efficient heating of
ingots/stick in the furnace.

2. Sufficient insulation adjacent to the metallic shell of the furnace using
ceramic fibre thereby preventing over heating of the shell thereby reducing
the heat loss from the furnace.
3. Estimated shell temperature with the modified lining pattern ranges 100° -
150°C. Actual shell temperature with modified lining ranges 90° - 140°C
whereas shell temperature of other furnaces ranges 120° - 200°C which
indicates reduction in heat loss through the walls with modified lining design.
4. Heating time of furnace with modified lining is lower as indicated below:
In case of cold condition, theie is reduction of heating time by 4-6 hrs.
In case of hot condition, there is reduction of heating time by 2 - 3 hours.
5. Significant reduction in gas consumption in furnace with modified lining
design. Specific heat (Gcal/T of ingot rolled) consumption in heating hot
ingots/stock (hot cycle) reduced from 0.345 to 0.202, thus saving 41% and
the same in cold cycle i.e heating cold ingot/stock from cold condition to
working temperature, reduced from 0.923 to 0.609 Gcal/T, thus saving 34%
of gas.
6. Monetary benefit due to saving in gas and improvement in productivity is
approx. 366 lakhs per annum.
7. No. of repairs reduced from 3-4 per annum in case of conventional lining to
no repairs in case of modified lining.
8. Productivity of the new furnace is improved by 15% in comparison to
conventional furnaces.

WE CLAIM
1. An improved lining pattern for use in the walls of reheating furnaces so as to
provide efficient heating of ingots/stock, said liner comprising:
plurality of layers
wherein
at least one first layer having different thickness located in different regions;
a second layer consisting of brick lining; and
a third layer having an appropriate thickness comprising ceramic fibre, light
weight and grog quality bricks in combination with a working layer
wherein said working layer comprising low cement castable lining having
70% of alumina content.
2. Lining pattern as claimed in claim 1 wherein said working layer is 400 mm to
600 mm thick.
3. Lining pattern as claimed in claim 1 wherein thickness of backup insulation
layer is 50 - 280 mm.
4. An improved quality refractory material for the lining pattern as described
hereinabove, said composition comprising :
(i) low cement castable with alumina at least up to 70% by weight of the
composition;
(ii) iron oxide in the range of 0.01 - 0.6% by weight of the composition;
and
(iii) calcium oxide in the range of 0.1 -1.5% by weight of the composition,
(iv) It has got grain size in the range of 0-10mm.
(v) It has got bulk density in the range of 2.75g.cm"3 - 2.8g.cm"3

(vi) It has CCS at 110°C per 24 hours in the range of 700Kg.cm"2 -
800Kg.cm"2 and CCS at 1400°C per 3 hours in the range of
lOOOKg.cm-2 - llOOKg.cm"2
(vii) It has a hot strength ranging from 50-70 Kg.cm"2
(viii) The water required in casting of LCC is in the range of 3.5-4.5%.
5. A method for installation of said lining pattern for use in the walls of
reheating furnaces, said method comprising steps of:
(a) Lining at least up to 1500mm of the furnace wall from bottom side
with bricks;
(b) Casting next at least up to 2500mm of the furnace wall using
ceramic fibers, light weight and high grog quality bricks, at least
70% alumina low cement castable and combinations thereof;
(c) Then lining the next 400mm with bricks over the layer mentioned
in(b),
(d) Casting of remaining 600mm with 70% alumina castable along
with ceramic fibre,
(e) placing hot ingots in the furnace followed by slow heating using
furnace burner initially drying and heating of the furnace.

In the present invention, there is provided an improved lining pattern for use in the walls
of reheating furnaces so as to provide efficient heating of ingots, said lining pattern
comprising plurality of layers wherein at least one first layer having different thickness
of ceramic fibre (2) located in different regions; a second layer consisting of light weight
brick lining(3) at some places; and a third layer having an appropriate thickness of high
grog fire bricks(4) in some places in combination with a working layer wherein said
working layer comprising low cement castable lining having 70% of alumina content.