FIELD OF THE INVENTION
The present invention relates to a device for testing shrink-fitted cylindrical
components at elevated temperatures. This invention relates to a method in an
universal testing machine, for determining load bearing capability of shrink-fitted
tubular concentric hollow cylinders of fluidized bed heat exchanger at high
temperature in a circulating fluidized bed combustion boiler.
BACKGROUND OF THE INVENTION
Shrink-fitting is a method in which an interference between components is
arrived by a change in relative size after assembly. Shrink-fitting is usually
achieved by heating or cooling one component before assembly and allowing it
to return to the ambient temperature after assembly, employing the occurrence
of thermal expansion to make a load bearing joint.
Shrink fit between two concentric hollow cylinders are commonly used
throughout wide variety of industrial applications to transmit either mechanical or
thermo mechanical loads in the form of axial, radial forces and torque. The
device is to support the horizontal heat transfer sections of Super heater and Re-
heater of Fluidized Bed Heat Exchangers (FBHE) in a Circulating Fluidized Bed
Combustion boilers (CFBC). The interface of the shrink-fitted region is subjected
to a temperature of about 700°C with fluid passing through one of the shrink
fitted components, while the other component is subjected to heat input from
the ash particles of fluidized bed at a temperature ranging in the order of 850°C.
The supporting components of FBHE heat transfer coils in a (CBFC) steam

generator requires stringent vertical load carrying capacity along with a flexible
support arrangement. To determine the load carrying capacity of the shrink-
fitted characteristics of the single instance of the shrink-fitted components is
essential. To determine the load by which an instance of shrink-fitted
components can withstand, there is a need to develop a suitable device.
US 5374808A Patent teaches a method and device for determining bond
separation strength by using induction heating. Induction heating device includes
induction heating gun made by a u-shaped pole piece and housing, with
induction coil wrapped around the pole piece and a capacitor. The heating gun is
mounted on a pull test machine to determine the separation strength of the
bond region.
US 20090113999 Al discloses test methods for testing rotor and stator
assemblies that utilize magnetic bearings prior to installation.
US 4805457A describes pumps and turbines having shafts and impellers or rotors
confined within casings. Specifically, it relates to a vibrational test for
determining the structural integrity of the shaft and impeller or rotor within a
casing without removal of the shaft and the impeller or rotor from the casing.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a method in an universal
testing machine, for determining load bearing capability of shrink-fitted tubular
concentric hollow cylinders of fluidized bed heat exchanger at high temperature
in a circulating fluidized bed combustion boiler in which a maximum load to

which the shrink-fit joint between the boiler dissimilar components can withstand
at the operating temperature of the (FBHE) for a particular value of interference,
is determined.
Another object of the invention is to propose a method in an universal testing
machine, for determining load bearing capability of shrink-fitted tubular
concentric hollow cylinders of fluidized bed heat exchanger at high temperature
in a circulating fluidized bed combustion boiler in which the amount of
interference between the components required to be maintained during the
operation is determined to withstand the thermo-mechanical load of the (FBHE).
A still another object of the invention is to propose a method in an universal
testing machine, for determining load bearing capability of shrink-fitted tubular
concentric hollow cylinders of fluidized bed heat exchanger at high temperature
in a circulating fluidized bed combustion boiler in which the amount of
interference to be maintained at the operating temperature of (FBHE) is
determined as the components are dissimilar in material specification.
SUMMAY OF THE INVENTION
According to the invention, there is provided a method for testing of the shrink-
fit which has been made between hollow concentric components of the (FBHE) in
a (CFBC) boiler. The method determines the load carrying capability of the
shrink-fitted components at the operating temperature of (FBHE). In other
words, the method determines an amount of interference to be present among
the shrink-fitted components, at each instance, in order to sustain the thermo-
mechanical loads experienced during the actual operation of the (FBHE). The

amount of interference is selected such that the contact pressure on either
sleeve or tube remains within the yield limit of both the materials and also shrink
fit is maintained in both the ambient and operating conditions. The method
ensures that the shrink fit is present between the components of (FBHE) at the
operating temperature.
A device has been designed such that the load is primarily transferred on to the
shrink-fitted regions. Shrink fitted components have been modified in length,
while keeping the shrink fitted region as same as the heat transfer coil
requirements. Length of the shrink-fitted components is increased to provide a
gap between the end arrangements such that a temperature applied on the
shrink-fitted region does not affect the end arrangements. End arrangements of
the device has been constructed to match the load applying fixtures of the UTM.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 : Typical location of the shrink fitted components in a Fluidized Bed Heat
Exchanger of Circulating Fluidized Bed Combustion boilers
Figure 2 : Detailed view of the shrink fitted components.
Figure 3 : Zoomed view of radial interference in shrink fitted components
Figure 4 : Detailed view of a device of the invention with shrink-fitted
components, plates on the periphery of components and end arrangement.

Figure 5 : block diagram for loading of the device.
Figure 6 : load and deflection behaviour of the inventive device during testing.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1, shows the typical application of shrink fitted components in the
fluidized bed heat exchanger system of (CFBC) boilers. The fluidized bed heat
exchangers are additional heat transfer surfaces which have been provided to
increase the heat transfer area of super heater, re-heater and evaporative
circuits of circulating Fluidized bed boilers. It also serves the purpose to maintain
the uniform temperature of the combustor in all the operating load conditions of
boiler and efficient burning of coal particles. In fluidized bed heat exchanger, hot
ash from the combustor at a temperature of 850°C is fluidized to transfer the
heat from ash to the heating surfaces. One of the instances (1) of shrink-fitted
components in its predetermined location of heat transfer coils has been shown
in Figure 1. Figure 2 is the enlarged view of the shrink-fitted components in a
(FBHE), with external hollow cylinder (2) and internal hollow cylinder (3) . The
amount of radial interference between the shrink-fitted components is shown in
Figure 3. Shrink-fitted components (2, 3) are arranged in the device as shown in
Figure 4. Shrink fitted components (2, 3) are attached to an end rods (5) by
means of plates (4) over the periphery. Figure 5 shows the loading of the device.

Shrink-fitted components are provided with an extra length to minimize the
effect of heat on the adjacent plates, during hot testing of the device. End rods
(5) are fixed into the loader jaws of a universal testing machine and the device
is heated up to the testing temperature or the operating temperature of the
(FBHE). Heating is localized to the shrink-fitted region of the device by suitable
arrangement. Thermo couples are attached to the shrink fitted region to read the
temperature of the device. Load is applied after achieving the testing
temperature of the shrink-fitted components.
By applying load, the tensile characteristics of the shrink-fitted components can
be recorded. The resulted graph is as shown in Figure 6. Before applying the
load, the shrink-fitted components are heated to the operating temperature of
the (FBHE). The load rate is maintained as 1 ton/min. Observations during
testing are that with load applied the device started expanding. The deflection
was linear to certain point with increase in load. The load and deflection
behaviour has been incorporated in the table below . Shrink-fitted components
has failed at an ultimate load of 3.5 tons.


WE CLAIM :
1. A method in an universal testing machine, for determining load
bearing capability of shrink-fitted tubular concentric hollow cylinders
of fluidized bed heat exchanger at high temperature in a circulating
fluidized bed combustion boiler, the method comprising the steps of :-
providing a device to hold the shrink-fitted hollow cylinder type
components (2, 3), the device consisting of at least two end rods (5)
and a corresponding number of plates (4);
loading of the components (2, 3) on the end rods (5) by means of the
plates over the device periphery;
loading the device fitted with the shrink-fittable components on a
universal testing machine;
heating the device corresponding to the operating temperature of the
FBHE with localization of the heating at the shrink fittable region,
applying load @1 ton/minute on the components to record the tensile
characteristics from linear defection of the region with increase in load;
and
determining from the load and deflection data the amount of
interference withstandable by the components.

2. The method as claimed in claim 1, wherein the components (2, 3)
during testing is formed with extra length than designed.
3. The method as claimed in claim 1, wherein at least one thermocouple
is provided at the shrink-fittable region to record the temperature of
the device.