FIELD OF THE INVENTION
The present invention relates to a device for testing thermal shock resistance of
ceramic refractory liners in a metal assembly by subjecting the assembly to a
cyclic temperature to elevated temperature. The method further allows
visualization of effect of dissimilar material interface in the form of defects if
generated during the test procedure.
BACKGROUND OF THE INVENTION
The rapidly increasing demand for high performance materials suitable for use
in power plants at high temperature has placed severe limitations on the
high temperature applications of metals and metallic alloys. Ceramic materials
although possess excellent high temperature properties are limited because of
poor thermal shock resistance. The thermal shock resistance of a ceramic
material is defined as its ability to withstand sudden temperature changes
without fracturing. The factors which determine the thermal shock resistance of
such materials are : temperature difference, geometry of the component and
material properties such as thermal expansion, thermal conductivity, Young's
modulus , strength etc. The first two determine the conditions and severity of
the thermal shock while the third group determine the magnitude of the
thermal stresses and the ability of the ceramic body to withstand such stress
factors. During the exposure of a body to thermal stress, all the factors
simultaneously contribute to the defect formation and hence material properties
play an important role in deciding the thermal shock resistance of a body. Most

important three properties which contribute to the thermal shock resistance
property are Thermal expansion coefficient, thermal conductivity and young's
modulus. The ability of the ceramic body to withstand thermal stresses is
dictated by its strength and is dependent on various parameters like grain
size, porosity, second phase , microstructure etc. leading to discrepancy in
calculated and measured values. Typically, the thermal shock resistance
parameter of a component is determined by following the change in one or
combination of the properties such as young's modulus , strength, weibull
modulus etc. The most common method of testing is to subject the component
to high temperature and either air quenching or water quenching and
measuring the parameters in a cyclic manner till it fractures. The thermal
expansion fluctuation of the material during heating and sudden cooling leads
to generation of defects inside the material. The generation of defects ultimately
leads to the failure of the component. The number of such thermal shock cycles
a material can withstand prior to fracture determines its resistance.
There are many methods available in prior art for thermal shock testing of
ceramic materials, which can be broadly classified into two groups : Heating
method and Cooling method. Thermal shock measurement techniques during
heating include hot gas jet method, high power radiation, melt immersion test,
ribbon test method and high power laser heating method. Similarly, thermal
shock resistance measurement technique during cooling include quenching in
water, fluidized beds, cold air jet impinging on hot discs, quenching in contact
with huge brass rods, and indentation method. These methods are well
documented in the published literature.

Wakayama et al ( J Acoustic Emission, 23, 2005, 150) have studied the crack
growth behaviour from a pre-crack in alumina under thermal shock by acoustic
emission technique. In the disc-on-rod test, the central region of the heated
specimen was quenched and the acoustic signals during crack growth were
detected and the temperature distribution in the specimen was measured by the
infra red digital video camera.
In another paper, Panda et al. ( Sci. &Tech. of Adv. Mater., 3, 2002, 327) have
designed a test equipment to generate thermal stress in a test specimen by
heating one surface of it by an oxy-hydrogen flame while cooling the opposite
surface. The in situ crack formation was detected by an acoustic emission
system. The thermal distribution of the system was modeled using finite
element analysis.
In another research paper, Damhof et al. ( J. Eur. Cer. Soc., 2008), the authors
subjected refractory samples to surface contact with molten aluminum followed
by passive cooling in ambient air. The evolution of damage was characterized by
measuring the transit time of ultrasonic longitudinal waves at various sample
locations after each test cycle.
Absi and Glandus ( J Eur. Cer Soc. 24, 2004, 2835) have reported a technique
wherein the sample is uniformly heated at a temperature higher than the boiling
water temperature which is suddenly cooled in periphery by a system of water
jets at room temperature. The water flow is sufficiently high to insure a
permanent contact of the sample periphery with water in liquid state. So, the
surface heat exchanges are significantly greater than those developed during a

thermal shock by immersion and thus make it possible to approach the
conditions of very severe thermal shock. ASTM C 1100-88 (1998) defines the
standard test method for ribbon thermal shock testing of refractory materials
for fireclay and high alumina refractories resulting from specified heating and
cooling cycles.
In US patent 4575257 , the inventors have described a thermal shock chamber
wherein a high temperature air conditioning unit, a low temperature air
conditioning unit and outside air supplying unit are connected with the test area
by means of suitable dampers.
The US patent 592662 describes a method for thermal shock testing of boiler
tubes for investigating crack propagation in thick steel plates. The cylinder is
rotated and is heated from inside to a desired temperature. A cold fluid is
directed onto the surface of the cylinder while it is still being rotated to
experience thermal shock top the cylinder.
US patent 4793716 have described a method to thermal shock testing of
materials. According to the invention, the apparatus consists of a controlled hot
gas stream impinged on the sample. The impinging hot gas stream is
maintained upon the predetermined hot gas stream impingement area of the
sample for a predetermined time imparting a thermal shock to the sample.
US patent 5167451 discloses a thermal shock method for the electronic
components for example in chips and in contact pins. A device is reported for
testing objects for thermal shock in a closed apparatus, wherein the object to be
tested is immersed in a liquid cold bath for cooling followed by passing through a

cold trap or drying chamber. Then the sample is heated by immersing in a liquid
hot bath and then passing through a drying chamber or cold trap and
subsequently repeating the thermal cycle. NGK insulators in Japan through an
US patent 5625154 have reported a method and apparatus for testing ceramic
specimens for simultaneous applications of mechanical and thermal stresses.
The thermal stress is applied by creating a temperature gradient within the
ceramic member, typically by heating a selected portion or portions of the
component. The heating is generated by spot heating such as laser beam
followed by cooling by contact with the surface of another component. Both the
heating and cooling may be intermittent or pulsed. The mechanical stress or the
impact stress is applied once or repeatedly by contacting the surface portion of
the component with a striker component.
US patent 8308352 describes an apparatus for single side thermal shock testing
of specimen comprising of a base and thermal insulation. The base consists of
an internal cavity which is extended through the outer surface of the base. A
specimen supporting surface is recessed within the first outer surface for
supporting a specimen within the base to substantially close the internal cavity.
The most common technique employed however in industry is water quench
method. Though it is a simple technique, the thermal stresses generated by
this technique is very high and in most applications, such thermal shock is
not experienced. Further, the experimental techniques used by various
inventors and authors mainly focused on a small piece or component for
measuring the thermal shock resistance. There are however no reports

available on the thermal shock resistance of a ceramic lined assembly. This is
important because of generation of thermal shock related stress at the interface
of two dissimilar materials : metal and Ceramics. Further, the fixing of ceramics
to the metal casing by the application of cement or with weld plug may affect
the performance of the system. The porosity in the ceramics can also play a
role in thermal shock resistance. These are not documented in the literature
and probably not experimented by any one earlier. This work therefore is s
significant for establishing a new technique for understanding thermal shock
behavior of ceramic lined metal assembly.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to develop a device for testing
thermal shock resistance of ceramic refractory liners in a metal assembly by
subjecting the assembly to a cyclic temperature to elevated temperature.
Another object is to propose a method of testing a ceramic lined assembly in
terms of defect generation on the ceramic product by subjecting the assembly to
thermal shock.
SUMMARY OF THE INVENTION
Accordingly, in a first aspect of the invention, there is provided to a device for
testing thermal shock resistance of ceramic refractory liners in a metal assembly
by subjecting the assembly to a cyclic temperature to elevated temperature.

In a second aspect of the invention there is provided a method of testing a
ceramic lined assembly in terms of defect generation on the ceramic product by
subjecting the assembly to thermal shock.
The method involves generation of high temperature inside the ceramic lined
assembly and cooling at a rate of > 1000 C per hour with forced blowing air.
The device is used to test the refractory assembly and correlate the data with
that was obtained from the component level testing.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS.
Figure 1 depicts the schematic of the thermal shock testing device.
Figure 2 is the schematic of a ceramic lined assembly used for thermal shock
testing.
Figure 3 is a typical thermal cycle followed for the measurement.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is focused on design of a device for testing the thermal
shock resistance of a ceramic/refractory lined assembly. The description of this
invention can be divided into three parts : Development of ceramic assembly,
Design and development of thermal shock test device, and a method of
testing of the ceramic product including the assembly.

A. Development of ceramic/ Refractory assembly
The refractory assembly consists of : a metal casing [4] of material grade SA
387 grade 12 , which is equivalent to the same grade of material used in the
boilers. The casing for example is of 850 mm outer diameter with 10 mm
thickness and rolled in the form of a cylinder. The ceramic tiles are manufactured
using a known patented process and are sintered in a batch kiln at around
1600 C. The final tile configurations are given in figure 2. The tiles [5] having
density in the range of 3.0 - 3.1 g/cc with 3-4 % water absorption property for
maintaining the thermal shock resistance. The tiles are lined to the metal casing
in two configurations : welding with weld plugs and with a high temperature
sustainable cement made from alumina. The tiles are fixed to the inner portion
of the cylinder using the cement and then welded for maintaining integrity
during service. Figure 2 summarizes, tile configuration, weld plug and the tile
assembly inside the cylinder. The ceramic lining can be replaced at any time
depending on the need and a new type of ceramic can be tested using the
same metal casing. The ceramic tiles for example, are of 22 mm thickness
which is developed for replacing ~ 70 mm castables used in cold cyclone
CFBC boilers.
B. Developing a High temperature thermal Shock Resistance Device for
testing
The main aim of the present invention is to test a ceramic lined assembly. The
requirements are a means for holding the lined assembly, means for
generating temperature in a particular duration, an arrangement for fast cooling
and a means for monitoring the temperature during the experiment.

Accordingly, the device comprises a base with refractory lining on the top [3], a
plurality of the wheels [15] for movement of the base; a 18 element heating
assembly [6] thyristor controlled to generate elevated temperature inside the
assembly. The temperature can be achieved by using heating elements and input
power. In one of the example 24kW power input is used to get 500 °C. The
heating element assembly is held by hooking to the roof [1]. The ceramic lined
assembly is wrapped with two layers of mineral wool base insulation [ 7] of 50
mm thick to maintain the surface temperature of < 70 C during the thermal
shock testing. A paperless recorder [17] records the thermal cycle during
testing. The temperature can be programmed using a multi-segment
temperature controller. A heavy duty blower [8] is connected to the base
assembly to blow instant air required during cooling. The boiler has the
capability of cooling down the interior at a rate of 1500 C per hour. Provision
is made to remove the hot air from the chamber through a plurality of
aluminum conduits [12] which are connected to water load. The movement
of the base assembly is performed through multiple channels [13] and two
such assemblies were used for testing one after another.
C. Thermal shock testing of Refractory assembly :
The thermal shock testing of single refractory tile according to prior art is
carried out by air or water quench method by heating the component in a
raising hearth furnace to the peak temperature and after soaking briefly
quenched either in air or in water to complete one cycle. This cycle is
repeated till any major defects appeared in the component.

However, the same tile when assembled in a cylindrical casing can not be
tested by the same manner. This invention is thus focused on the testing
method for such assembly. According to the inventive process, the ceramic lined
assembly [4] is kept on the base assembly [10]. The top head assembly [3] of
the device containing the heating element assembly [6] is brought down
through a pulley arrangement [1,2] and controlled by a remote controller [16]
and placed inside the cylinder. The cylinder is already covered with an insulation
wool [7] from outside. The head assembly [3] completely seals the cylinder, so
that no heat escapes during heating or cooling of the assembly from the top.
The top head assembly [3] is energized and the heating of the cylinder starts
and reaches the peak set temperature. In one of the example 500 C
temperature can be reached in 90 min. from room temperature using a
programmed cycle. Four thermocouples [14] are placed along with the top
assembly which measure temperature of the assembly during testing at four
different places as depicted in Figure 1. The surface temperature can be
manually monitored using a hand held infra red pyrometer. The peak
temperature is maintained for 30 min. in the assembly prior to starting the
blower [8] and passing air through the base assembly to the hot cylinder
without lifting the top assembly [3]. Within 15 min. of blowing air, the
temperature of the assembly is brought down to 125-150 C and the blower (8)
is switched off. The temperature of the assembly again gets raised due to
convection of heat and after 30 min, again the blower (8) is put on to reduce
the temperature of the assembly. This constitute one thermal shock cycle

(Fig. 3). This cycle is repeated upto 100 times in a span of 3 months and
after every 5 cycles the health of the refractory is monitored to notice any
defects arising due to thermal mismatch between metal casing and ceramics
and at the interface of ceramics with cement or ceramics with welding plugs.
The present embodiment can be explained with two suitable examples as
given below :
Example 1:
A special refractory composition was developed and used as liners in the SA
387 Gr. 12 grade alloy steel. This alloy steel is used for fabrication of CFBC
boilers. The refractory tiles with 3 % apparent porosity were lined in the metal
cylinder with high temperature alumina cements supported by stainless steel
weld plugs. The opening of weld plugs were closed with the cement paste. The
refractory lined cylinder was subjected to thermal cycle test of room
temperature to 500 °C - room temperature as described in this invention . It was
observed that the refractory assembly used in this invention could withstand
100 thermal shock cycles with <1 % damage. Number of tiles used in the
assembly were 322 and number of tiles cracked after 100 cycles were 3. The
damaged tiles were analyzed and found that one tile was cracked at the
welding junction and other two tiles were having minor cracks from the
refractory body. However, all the tiles were intact in the metal assembly
without any catastrophic failure. This result confirms the thermal shock
testing of the single component which had passed more than 50 cycles

during stringent air or water quench test at a similar temperature. The result
of this experiment confirmed that the material used for the testing can be
employed as a liner in cold cyclone CFBC boilers which has the maximum
operating temperature of 500 C. The testing of assembly thus is very
significant in order to indirectly predict the life of the component in a
simulated environment.
Example 2
In another experiment, the same alloy cylinder was lined with the
conventional dense wear resistant commercial alumina tiles with the support
of high temperature cement and SS weld plugs. The ceramic lined cylinder was
subjected to thermal shock as per example 1 and it was noted that after 30
cycles, there were 11 % cracks have appeared in the tiles. On analysis of the
damage, it was noted that the majority of the cracks have originated in the tiles
itself. This has confirmed that due to dense structure of tiles, there was little
scope for expansion and contraction of tiles and as a result the cracks were
appeared during thermal shock testing. Therefore, such dense wear resistant
ceramics are only suitable for room temperature applications but are expected
to fail in high temperature thermal shock applications like in CFBC boilers.
Therefore, to impart thermal shock resistance and to maintain good wear
resistance the material property needs to be optimized .

WE CLAIM:
1. A device for testing thermal shock resistance of ceramic refractory liners in a
metal assembly by subjecting assembly to a cyclic temperature to elevated
temperature comprising :
a) a base assembly for holding a test piece;
b) a top assembly with heating elements;
c) a blower arrangement for fast cooling;
d) a control system to monitor heating, cooling, movement of the assembly;
wherein the base assembly is lined with refractory lining to withstand the
testing temperature and enabled to completely seal the bottom portion of the
assembly without any heat loss during testing;
wherein the top assembly with the heating elements to provide uniform
heating throughout the ceramic assembly, wherein the top head assembly is
fixed by a hoist arrangement controlled by a remotely controller.

2. The device as claimed in claim 1, comprising a plurality of thermocouples to
indicate the uniformity in temperature throughout the assembly.
3. The device as claimed in claim 1, wherein high temperature resistant
mineral wool is provided for covering the cylinder assembly from outside to
maintain uniform temperature inside the assembly during testing.
4. The device as claimed in claim 1, wherein the blower is connected to the base
assembly to blow air and rapidly cool the system including removing the hot air
out of the assembly to a dummy water load.

5. The device as claimed in claim 1 comprising a paperless recorder for
recording all the cycles attached to the control panel.
6. The device as claimed in claim 1,wherein the movement of the ceramic
assembly is achieved using a rail track arrangement.
7. A method of testing a ceramic lined assembly in terms of defect generation
on the ceramic product by subjecting the assembly to thermal shock, comprising
the steps of :
placing a ceramic lined cylinder on the base assembly, and lowering by a
pulley means, the top head assembly including a plurality of heating
elements and placing inside the cylinder;

- energizing the top head assembly and heating the cylinder to a peak
temperature of about 500°C;
- maintaining the peak temperature for around 30 minutes;
- starting the blower and passing air through the base assembly to the hot
cylinder to bring down the temperature around 125 - 150°C, and
switching off the blower;
- re-starting the blower after about 30 minutes to reduce the temperature
of the cylinder which had raised meanwhile due to convection of heat;
. repeating the heating cycle for at least 100 times in a span of three
months; and
- determining any defects arising due to thermal mismatch between metal
casing and ceramics and at the interface of ceramics with cement or
ceramics with welding plugs.