The present invention relates to an improved oxidation resistance measuring
furnace and in particular improvement in furnace for comparative evaluation of
oxidation resistance of carbon containing refractories.
BACKGROUND ART

In Steel Plant different carbon containing refractories e.g. magnesia carbon,
alumina carbon etc. are used in different metallurgical vessels. In BOF MgO-C
bricks are used as refractory lining material. MgO-C, AI2O3-C, AbCb-MgO-G
bricks are also finding extensive use in EAF, steel ladles. These bricks contain 5
to 20% carbon. Carbon in MgO-C bricks improves slag corrosion resistance and
thermal shock resistance, but the problem with carbon is that it oxidises at high
temperature (above 700°C) in oxidising atmosphere. Therefore different
additives are used to prevent oxidation.
In order to evaluate oxidation resistance different tests are conducted but there is
no standard test method available till date. Generally a 40 or 50 mm cylindrical
sample is taken and fired at 1400°C for 2-3 hours and the depth of decarburized
layer is measured. But due to changes in furnace size, rate of heating, location of
sample inside the furnace, number of samples and their relative positions,
distance from the door etc. the results vary considerably. With lot of precautions
it is presently done with one test sample along with one standard samples for
comparison. Still there is always a chance of error.
OBJECTS OF THE INVENTION
It is therefore th.e basic object of the present invention to develop a furnace for
determination oxidation resistance which will generate accurate and reproducible
comparative result with more number of samples at a time.
Another object of the present invention is to provide an improved oxidation
resistance measuring furnace adapted for uniform exposure to air/gas (furnace
atmosphere) and temperature.
Another object of the present invention is to provide an oxidation resistance
measuring furnace adapted to achieve uniform temperature distribution.
Yet another object of the present invention is to provide an improved oxidation
resistance measuring furnace adapted to test upto six numbers of samples of 40
or 50 mm diameter at a time for comparative evaluation.
Yet further object of the present invention is directed to provide for an improved
oxidation resistance measuring furnace having means for controlled rate of
heating, soaking time, cooling rate and duration of rotation.
Yet further object is directed to provide for an improved oxidation resistance
measuring furnace adapted for creating desired gas atmosphere for different heat
treatment and kinetic studies.
SUMMARY OF THE INVENTION
Thus according to the present invention there is provided a system/furnace for
improved oxidation resistance measuring comprising:
an enclosed chamber for heating having hearth/plate for placing of the test
samples said hearth/plate having at least a portion thereof rotatable under
controlled speed and duration of rotation;
means for controlled heating of the chamber;
releasable closure means for sample placement/replacement on the rotary
hearth/plate ;
means for providing controlled atmosphere/air for oxidation in said chamber; and
means for visual inspection of the oxidation process.
Rotation of hearth;
There is a suitable mechanical arrangement and electrical motor for rotating the
hearth at the rate of approximately 2 to 15 revolutions per minute (rpm). There is
a provision for setting the no. of rotation (count) after which it stops automatically.
Bottom sealing system:
There is a sand sealing arrangement with stainless steel knife system at the
rotary hearth bottom to control air infiltration from the bottom.
Preferably the furnace is of top loading type with an square opening of about
150mm.
There is a cylindrical hole of about 10 mm with opening and closing arrangement
for air circulation. The lid is preferably provided with two handles for easy
opening/closing.
In accordance with a preferred aspect of the present invention, the furnace
chamber is provided a releasable closure means comprising of a top lid for an
opening in the top of the chamber adapted for sample placement and
replacement on and from the rotary plate/hearth. The lid is preferably provided
with two handles for easy opening/closing.
Preferably, the furnace is top loading type with a square opening of about
150mm.
There is a cylindrical hole of about 10mm with opening and closing arrangement
for air circulation.
The said means for providing controlled atmosphere/air for oxidation of said
chamber comprise means for selectively allowing entry and exit to and from
respectively gas or air in and from said chamber for the purpose of oxidation.
Preferably, such means comprise pipelines controlling the gas/air source to the
chamber inside at the top.
Importantly, to achieve uniform heating, the heating element are provided in all
the four side walls of the chamber. Preferably, the furnace is adapted to
accommodate upto six samples of 50 mm diameter for uniform testing.
The means for visual inspection of the oxidation process is preferably by way of
provision of an inspection hole in the top lid.
The details of the invention its objects and advantages are explained hereunder
in greater detail in relation to the non-limiting exemplary illustrations as per the
accompanying drawings wherein:
Figure 1 is a top plan sectional view of the improved oxidation resistance
measuring furnace of the invention.
Fig. 2 is a sectional view of the improved oxidation resistance measuring furnace
in accordance with the present invention.
Reference is first invited to Figure 1, which shows in top plan view, an improved
oxidation resistance measuring furnace in accordance with the present invention.
As shown in said figure, the furnace is basically comprised of the enclosed
chamber (CH) having four side walls (SW) and a bottom (BO) and top (TO) which
are shown in Figure 2. Substantially, in the middle of the chamber there is
provided a rotary plate/hearth (RP) for providing/holding the samples to be
tested.
Reference is now invited to Figure 2, which is a sectional view of the improved
oxidation resistance measuring furnace in accordance with the present invention.
As illustrated in said figure, the said furnace is comprised of the enclosed
chamber (CH) with four side walls (SW) and a bottom (BO) and top (TO). At the
bottom (BO) thereof is provided a cutout portion (CP) through which the rotatable
plate (RP) is operative connected to an arrangement for controlled rotation of the
plate. In order to make the chamber air/gas tight, a sand sealing (SS)
arrangement is provided there between the rotating arrangement (RA) and the
adjacent portions of the cut out portion (CP) of the bottom (BO) of the chamber
(CH). Thus the rotatable plate (RP) can be rotated under desired RPM (speed)
to thereby expose a test sample to uniform heating and conditions in the
chamber. Importantly, in order to facilitate controlled entry of gas/air into the
chamber for the purpose of oxidation, a gas entry pipeline (GP) is provided at the
bottom is operatively linked to the inside of the chamber while a gas outlet
pipeline (GO) at the top is provided communicating with the chamber. Control
means (CM) are provided in the pipelines communicating the gas/air into the
chamber and release of gas/air from the chamber to provide for a controlled entry
and exit of gas/air into and from the chamber respectively.
To facilitate uniform heating of the chamber heating means/heating elements are
uniformly distributed in the chamber preferably in the 4 walls of the chamber.
In order to facilitate placement and replacement of the samples to and from the
rotary plate, a releasable lid (LD) is provided on the top of the chamber. With the
removal of the lid (LD) by using of the handle means (HM) one can introduce
fresh test samples on the rotary plate for testing and there after the lid is closed
to effectuate the oxidation process and finally when the oxidation is completed
the lid is again opened and the oxidised samples taken out for assessment of its
oxidation resistance. Preferably, lid means (LM) is provided with blue glass
inspection hole (IH) to favour inspection of the test sample during the oxidation
process.
It would be apparent from the above details of the improved oxidation resistance
measuring furnace of the invention that the same essentially involves a rotatable
hearth used in a chamber having means for programmed heating. By
programmed heating it is meant to include the rate of heating, soaking
temperature and time as well as the rate of cooling. It is possible to vary the
speed of the rotatable plate/hearth as well as the duration of such rotary motion
of the plate/hearth depending upon the tests desired to be carried out.
By way of use of the above improved furnace, it is thus possible to carry out the
oxidation resistance measuring tests under controlled and simple operating
system. Importantly also, reproducibility characteristics of the improved furnace
are much better than those of conventional furnaces used of such purposes.
The number of test samples, which can be compared with one test sample using
the improved furnace of the invention, can extend up to six in numbers and the
experimental time required for such comparison of different samples can extend
up to one day.
The number of samples that can be compared using the system can extend up to
six and importantly further the furnace provided means for atmosphere control as
well as the control of heating soaking temperature, soaking time and the rate of
cooling.
Thus it is possible by way of the present invention to not only provide for testing
of samples more in numbers under the improved furnace of the invention but
even the time for such testing using the improved furnace would be reduced from
5 days to 1 day thereby effecting save of about 4 days of involvement in carrying
such steps.
There are wide varieties of different antioxidant compounds, which can be used
and includes aluminium, silicon, magnesium, aluminium silicon, aluminium
magnesium, Ca-Si-Mg, AI-Mg-CaB6, AI-Mg-B4C, AI-CaB6, CaB6, glass, boric
compounds and silicates. One or more combination of these compounds can be
used as antioxidant depending upon the type of refractory and area of
application.
The different process parameters related to the pitch/resin quality and quantity
and grain size distribution, pressing pressure/temperature, type of graphite
(amorphous, flake) and their amounts, particle size of graphite, type of carbon
black and its amount and finally impregnation of bricks with pitch.
It is important to note that while so many advantageous features are included in
the improved furnace of the invention it is now possible to test six samples of
approximately 50mm diameter and 50mm height on the rotary hearth plate.
Oxidation is a time-temperature phenomenon. Therefore, the rate of heating,
soaking time and the cooling rate are to be fixed/controlled from experiment to
experiment. Rotation of hearth is essential for uniform oxidation of samples.
Variable rpm will help to find out optimum for uniform oxidation. 4-5 rpm is found
to be acceptable for uniform oxidation purposes.
The gas atmosphere for heat treatment and kinetic studies can be any of the
following such as argon, nitrogen, carbon mono oxide or air. From the location of
the heating element and rotation of the hearth, it is clear that samples are
exposed to uniform temperature and gas/air.
Experimental tests were conducted to determine the efficacy of the oxidation
resistance measuring furnace of the invention and the results achieved are
detailed hereunder:
It is seen from Example-ll, that there is slight variation of weight loss and the
thickness of oxidised layer. This is due to the fact that the distribution of carbon
is not exactly the same in all parts of 550x125x150mm refractory bricks and
therefore results varied slightly are quite acceptable.
Importantly, as illustrated above, the furnace is electrically heated top loading
type, with a part of the hearth circle cross-section adapted to rotate to have
uniform heating and oxidation of test pieces.
Preferably, the heating space is approximately 300mm (width) x 300mm
(breadth) x 200mm (heights). Operating temperature condition operating from
1450°C (max) for 4 hours run and below 1400°C (max) for continuous run. The
heating elements are preferably selected to comprise silicon carbide rods straight
in diameter (solid type) with number of elements ranging from 12 or nearest
equally distributed in all side walls.
The power feed into the furnace can comprise thyrister power driven.
The temperature controller is basically a digital programmer controlled
microprocessor based PID temperatures controller with ramp facility compatible
with different type of thermocouples. The furnace of the invention is thus found to
be capable of:
i) controlling the rate of heating from 3 to 7°C/minute.
ii) Temperature control accuracy: within ± 2°C of set point.
iii) Temperature uniformity inside furnace :
within ± 0.5% at the set temperature above 100°C.
iv) Thermocouples : Pt. - Pt. Rh 13% (R type) or Pt. - Pt. Rh 10% (S type)
Preferably, the constructions of the furnace involve use of welded angle iron
frame floor model with separate control panel. Height of the furnace is about
1200 mm for easy loading of samples from the top. There is a peep hole with
blue glass for observing the samples during firing. There is an arrangement (with
opening and closing system) for sending gas through the lower part of the
furnace.
Working face refractories is made of almost zero shrinkage high alumina backed
by low heat capacity insulation bricks/and ceramic fibre insulation. There is
suitable safety device/blind controller to safe guard against costly heating
elements.
It is thus possibly by way of the present invention to achieve the following:
a. An oxidation resistance measuring furnace wherein atleast a part of the
hearth rotates at different speed ranging from 2 to 15 rpm to thereby achieve
uniform exposure to air/gas (furnace atmosphere) and temperature.
b. SiC heating elements located in all the four side walls provide for uniform
temperature distribution.
c. A top loading type oxidation resistance furnace where up to 6 number of
samples of 40 or 50 mm diameter can be tested at a time for comparative
evaluation.
d. An oxidation resistance furnace where rate of heating, soaking time, cooling
rate and duration of rotation can be controlled.
e. An electrically heated furnace where there is sand sealing arrangement at the
rotating hearth system for closing the entry of air and there is a gas inlet
arrangement for creating desired gas atmosphere for different heat treatment
and kinetic studies.
The above disclosed oxidation resistance measuring furnace of the invention
avoids the problems of conventional systems wherein there is always chances of
error in evaluating oxidation resistance from experiment to experiment and from
furnace to furnace and provide for a system wherein oxidation resistance can be
correctly evaluated and compared with different carbon bearing refractories at a
time.
Reproducible results can be obtained by fixing furnace operating parameters
from experiment to experiment. For more accurate results one standard sample
may be incorporated for comparative evaluation of oxidation resistance from
experiment to experiment. Considerable research time can be saved by
experimenting with more number of smaller diameter samples in one run for the
development of oxidation resistance refractories with addition of different
antioxidant compounds and process parameter. The developed furnace can also
be used for conducting different heat treatment and kinetic studies in different
furnace atmosphere, rate of heating and temperature. The system of the
invention is also economic in that instead of conducting oxidation test by
conventional method for five times, the oxidation test can now be done in the
developed furnace in one experiment thereby saving valuable electrical energy
and laboratory experimentation time.
WE CLAIM :
1. A system/furnace for improved oxidation resistance measuring of carbon containing
refractories comprising:
an enclosed chamber for heating having hearth/plate for placing of the test samples
said hearth/plate having at least a portion thereof rotatable under controlled speed
and duration of rotation;
means for controlled heating of the chamber;
releasable closure means for sample placement/replacement on the rotary
hearth/plate ;
means for providing controlled atmosphere/air for oxidation in said chamber; and
means for visual inspection of the oxidation process.
2. A system/furnace as claimed in claim 1 comprising mechanical arrangement and
electrical motor for rotating the said hearth/plate.
3. A system/furnace as claimed in anyone of claims 1 or 2 wherein said plate/hearth is
adapted for rotation at the rate of approximately 2 to 15 revolutions per minute (rpm).
4. A system/furnace as claimed in anyone of claims 1 to 3 comprising means for setting
the duration of rotation (time).
5. A system/furnace as claimed in anyone of claims 1 to 4 comprising a sand sealing
arrangement with stainless steel knife system at the rotary hearth bottom to control
air infiltration from the bottom.
6. A system/furnace as claimed in anyone of claims 1 to 5 wherein said furnace
chamber is of top loading type with a square opening.
7. A system/furnace as claimed in anyone of claims 1 to 6 wherein the lid is comprised
of handle means for easy opening/closing.
8. A system/furnace as claimed in anyone of claims 1 to 7 wherein the
releasable closure means comprising of a top lid for an opening in the top of
the chamber adapted for sample placement and replacement on and from the
rotary plate/hearth.
9. A system/furnace as claimed in anyone of claims 1 to 8 wherein said means
for providing controlled atmosphere/air for oxidation of said chamber comprise
means for selectively allowing entry and exit to and from respectively gas or
air in and from said chamber for the purpose of oxidation.
10. A system/furnace as claimed in anyone of claims 1 to 9 wherein said means
comprise pipelines controlling the gas/air source to the chamber inside at the
top.
11. A system/furnace as claimed in anyone of claims 1 to 10 comprising means
for uniform heating comprising heating element provided in all the four side
walls of the chamber.
12. A system/furnace as claimed in anyone of claims 1 to 11 wherein said means
for visual inspection of the oxidation process comprise an inspection hole in
the top lid.
13. A system/furnace as claimed in anyone of claims 1 to 12 wherein the bottom
thereof is provided a cutout portion through which the rotatable plate is
operative connected to an arrangement for controlled rotation of the plate.
14. A system/furnace as claimed in anyone of claims 1 to 13 wherein to make the
chamber air/gas tight, a sand sealing arrangement is provided there between
the rotating arrangement and the adjacent portions of the cut out portion of
the bottom of the chamber.
15. A system/furnace as claimed in anyone of claims 1 to 14 comprising means
for controlled entry of gas/air into the chamber for the purpose of oxidation
comprises a gas entry pipeline is provided at the bottom operatively linked to
the inside of the chamber while a gas outlet pipeline at the top provided for
communicating with the chamber.
16. A system/furnace as claimed in claim 15 comprising control means provided
in the pipelines communicating the gas/air into the chamber and release of
gas/air from the chamber to provide for a controlled entry and exit of gas/air
into and from the chamber respectively.
17. A system/furnace as claimed in anyone of claims 1 to 16 wherein said means
for uniform heating of the chamber comprise heating means/heating elements
uniformly distributed in the chamber preferably in the four side walls of the
chamber.
18. A system/furnace as claimed in anyone of claims 1 to 17 wherein said lid
means is provided with blue glass inspection hole to favour inspection of the
test sample during the oxidation process.
19. A system/furnace as claimed in anyone of claims 1 to 18 comprising a
rotatable hearth used in a chamber having means for programmed heating.
20. A system/furnace as claimed in anyone of claims 1 to 19 wherein said
programmed heating means comprise means for controlled rate of heating,
soaking temperature and time as well as the rate of cooling.
21. A system/furnace as claimed in anyone of claims 1 to 20 wherein the gas
atmosphere for heat treatment and kinetic studies comprising gases selected
from argon, nitrogen, carbon mono oxide or air.
22. A system/furnace as claimed in anyone of claims 1 to 21 wherein the heating
space is in the range of 280 to 350 mm (width) preferably 300 mm (width) x
280 to 350 mm preferably 300 mm (breadth) x 170 to 250 mm preferably
200mm (heights).
23. A system/furnace as claimed in anyone of claims 1 to 22 wherein the operating
temperature condition are adapted from temperature from 1450°C (max) for 4
hours run and below 1400°C (max) for continuous run.
24. A system/furnace as claimed in anyone of claims 1 to 23 wherein the heating
elements are preferably selected to comprise silicon carbide rods straight in
diameter (solid type) with number of elements ranging from 12 or nearest equally
distributed in all side walls.
25. A system/furnace as claimed in anyone of claims 1 to 24 wherein the power feed
into the furnace can comprise thyrister power driven.
26. A system/furnace as claimed in anyone of claims 1 to 25 wherein the
temperature controller is basically a digital programmer controlled
microprocessor based PID temperatures controller with ramp facility compatible
with different type of thermocouples.
27. A method for carrying out the evaluation of oxidation resistance of carbon^
containing refractorieSj using system/furnace as claimed in claims 1 to 26
comprising :
i) controlling the rate of heating from 3 to 7°C/minute.
ii) temperature control accuracy : within _i 2°C of set point
iii) temperature uniformity inside furnace :
within ± 0.5% at the set temperature above 100°C.
iv) thermocouples : Pt. - Pt. Rh 13% (R type) or Pt. - Pt. Rh 10% (S type)
28. A system/furnace for improved oxidation resistance measuring and a method for
carrying out the evaluation of oxidation resistance of carbon containing
refractories using such system/furnace substantially such as hereindescribed
with reference to the accompanying figures and examples.

An improved oxidation resistance measuring furnace and in particular
improvement in furnace for comparative evaluation of oxidation resistance of
carbon containing refractories. The system /furnace of the invention basically
comprises of an enclosed chamber for heating having hearth/plate for placing of
the test samples said hearth/plate having at least a portion thereof rotatable
under controlled speed and duration of rotation ; means for controlled heating of
the chamber; releasable closure means for sample placement/replacement on
the rotary hearth/plate ; means for providing controlled atmosphere/air for
oxidation in said chamber ; and means for visual inspection of the oxidation
process.
The furnace provides for determination of oxidation resistance which will
generate accurate and reproducible comparative result with more number of
samples at a time and adapted for uniform exposure to air/gas (furnace
atmosphere) and temperature. The furnace would achieve uniform temperature
distribution. The improved oxidation resistance measuring furnace is adapted to
test upto six numbers of samples of 40 or 50 mm diameter at a time for
comparative evaluation and is directed to provide for an improved oxidation
resistance measuring furnace having means for controlled rate of heating,
soaking time, cooling rate and duration of rotation.The improved oxidation
resistance measuring furnace is further adapted for creating desired gas
atmosphere for different heat treatment and kinetic studies.