FIELD OF THE INVENTION:-
The invention relates to a device for endurance testing of a cooling fan impeller
and in particular to a method for endurance testing of traction motor ventilation
fans with variable speeds up to 3000 RPM and variable shock loads/speeds up to
50g @ 10 RPM.
BACKGROUND OF THE INVENTION:-
Presently there are no devices for testing of traction motor fans simulating both
rotation and shock loads. Either they are tested from rotation point of view or
from shock point of view as indicated in the following patent.
An US Patent No. 3495447, dt. Feb 17, 1970 describes "an apparatus designed for
fatigue testing of impellers". The test device is excited under its actual operating
condition to induce rotational and torsional related vibration and dynamic stresses
for accelerated fatigue and other testing. No shock loads can be simulated here.
Another patent US Patent No. 2007/0288181 Al, dt. Dec. 13, 2007 describes "an
apparatus and method for testing of cooling fan by testing vibration values
generated by the cooling fan". These vibration values are recorded by means of
vibration sensors. Shock loads cannot be simulated here.
Due to non availability of endurance testing device for fans with vibration and
shock simulation, it is not possible to validate the design, resulting in early failures
of fans during in-situ operation.
OBJECTS OF THE INVENTION:-
It is therefore, an object of the present invention to propose a device for
endurance testing of traction motor fan and a method for testing which eliminates
the disadvantages of existing state of art.
Another object of the present invention is to propose a device for endurance
testing of traction motor fan and a method for testing which increases the service
life of traction motor ventilation fan.
A further object of the present invention is to propose a device for endurance
testing of traction motor fan and a method for testing which facilitates dual
testing.
SUMMARY OF THE INVENTION:-
A device for endurance testing of cooling fan impeller and a traction motor with
variable speed up to 3000 RPM and variable shock load comprising a steel
structure having a main frame of steel structure and first end of the main frame is
provided with a drive motor with variable speed controller and the second end is
provided with an impeller and a set of base plates disposed on the main frame and
a plurality of springs are housed in between the two base plates and one fan
impeller along with a shaft and a plurality of bearings are mounted on the base
plate and one flexible coupling is mounted with the main shaft of driving motor
and the shaft of the impeller. A mast like steel structure attached on the middle of
the device and disposal at right angle of the device from where a load is applied
on the shaft by means of a cam which is operated by a Gear motor mounted on
the rear side of the device whose speed can be varied to change the frequency of
shock loads and a two element rectangular strain gauge rosette is placed on the
impeller for recording dynamic strain.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:-
FIGURE 1: Model of Fan Test Rig Assembly
FIGURE 2: Side View & Sectional View of Fan Test Rig Assembly
FIGURE 3: Section of Front View Fan Test Rig Assembly
FIGURE 4: Location of Strain Gauge on the Fan Impeller
FIGURE 5: Shows a graph of performance of the fan consisting of air flow rate
developed for various speeds of operation of the test-rig.
FIGURE 6: Shows a graph of performance results of the fan consisting of
pressure developed for various speeds of operation of the test-rig.
DETAILED DESCRIPTION:-
Test Rig for ventilation fan
As shown in fig. 1 to 3, the device for endurance testing is provided with a steel
structure having a main frame (Bi). The first end of the main frame (Bi) is
provided with a drive motor (7) with variable speed controller and the second end
is provided with an impeller (3). A set of base plates (6A, 6B) disposed on the
main frame (Bi). A plurality of springs (11) is housed in between the two base
plates (6A, 6B). One fan impeller (3) along with a shaft (4) and a plurality of
bearings (5) are mounted on the base plate (6B). One flexible coupling (8) is
mounted with the main shaft of driving motor (7) and the shaft (4) of the impeller
(3). A mast like steel structure attached on the middle of the device disposed at
right angle of the device from where a load is applied on the shaft by means of a
cam (15) which is operated by a Gear motor (10) mounted on the rear side of the
device whose speed can be varied to change the frequency of shock loads and
whose magnitude is varied by changing the height and stiffness of the spring (14).
A two element rectangular strain gauge rosette (16) is placed on the impeller (3)
for recording dynamic strain; characterised in that during rotation of the impeller a
vibration imparted on the bearings of the impeller from the adjacent spring
housing and subsequent load application in different time interval on the said
impeller evaluates the possible endurance which is recorded by simulation wherein
a rectangular strain gauge rosette inserted in the impeller for reading/recording
dynamic strain.
As shown in Fig. 4, the V levels coming on the fan impeller during operation of the
test rig are measured using an accelerometer mounted on the bearing housing
closest to the impeller. Strain/stress on the impeller are monitored by bonding a two-
element rectangular strain gauge rosette (16) with strain gauges oriented in the
hoop and radial directions at the critical location on the impeller (on the free surface
of the back plate below the vane joint) and using slip-ring system & dynamic strain
recording instrumentation for reading/recording.
Table 1 gives the results of endurance testing of aluminium impeller after 100 hours
of operation at 1300 RPM, 30g shocks @ 1 RPM, which indicates that the maximum
stresses are within 30 Mpa, while the yield strength of aluminium is 170 Mpa.
Table 1.
Summary of Endurance test results after 100 hours of operation
Evaluation of aerodynamic performance of Impeller
The test rig has facility to evaluate the aerodynamic performance like measurement of flow velocity,
flow rate and pressure.
Endurance test
To evaluate the structural performance of prototype impeller, it is strain gauged at
the critical location and the strains were monitored over a period of time in
operation. To simulate the actual service conditions, the impeller is rotated at
about 1300 RPM (the operating speed in service is 1290 RPM) and intermittent
shock loads of about 70g' were given at about 60 seconds intervals using the cam
and hammer arrangement to simulate the track-joint jolts in actual operation.
Examples / Preferred Embodiments:
Drive motor (7) and variable speed controller that drives the impeller from
100 RPM to 3000 RPM.
The drive motor (7) with a variable speed controller enables the fan to rotate at any
speed up to 3000 RPM.
Drive motor and (10) variable speed controller that drives the cam shaft
to induce variable shock loads.
Another drive motor (10) and variable speed controller with a 150:1 gear box,
enables the cam shaft to be rotated at speeds up to 10 RPM, so that the shock
loads also can be given at 10 per minute.
Spring matrix (11) arrangement below the impeller shaft support system
There is a spring matrix arrangement below the impeller shaft support system to
simulate the field conditions of vibration.

Arrangement for shock loading
A shaft and mass system is arranged for lifting and dropping due to the rotation of
the cam at heights which can be adjusted, depending on the requirement of V
levels. There is a provision for adding compression spring (14) in the shaft and
mass system to further increase the shock load depending on the stiffness of the
chosen spring.
Ducting for the impeller
The impeller is enclosed in a duct so that the aerodynamic performance studies
like flow rate and pressure can also be made for various speeds up to 3000 RPM.
Testing Procedure:-
The method of testing by the device comprises following steps:-
a. impeller 3 is fitted to the shaft 4 through the hub and the whole rotor is
mounted on a platform supported on a spring matrix 11.
b. the protective casing 12 is assembled over the impeller.
c. the controller of the drive motor 7 is switched on and the rotor 4 is rotated
to the required speed typically 1300 RPM as displayed on the monitor, for
traction motor fan impeller.
d. the controller of the gear motor 10 is also switched on and the cam is
rotated at required speed say typically 1RPM by setting 150 RPM as
displayed on the monitor of the controller.
e. strain gauge output is monitored throughout the operation of the fan at
regular intervals.
f. thus the impeller fan is tested as above for the required period of
endurance checking.
g. the *g' levels coming on the fan impeller during operation of the test rig are
measured using an accelerometer mounted on the bearing housing closest
to the impeller.
h. strain/stress on the impeller are monitored by bonding a two-element
rectangular strain gauge rosette 16 with strain gauges oriented in the hoop
and radial directions at the critical location on the impeller (on the free
surface of the back plate below the vane joint) and using slip-ring system
and dynamic strain recording instrumentation for reading/recording.
WE CLAIM:-
1. A device for endurance testing of Traction motor fan with variable speed up
to 3000 RPM and variable shock load comprising:-
— a steel structure having a main frame (Bi);
— first end of the main frame (Bi) is provided with a drive motor (7)
with variable speed controller and the second end is provided
with an impeller (3);
— a set of base plates (6A, 6B) disposed on the main frame (Bi);
— a plurality of springs (11) are housed in between the two base
plates (6A, 6B);
— one fan impeller (3) along with a shaft (4) and a plurality of
bearings (5) are mounted on the base plate (6B);
— one flexible coupling (8) is mounted with the main shaft of
driving motor (7) and the shaft (4) of the impeller (3);
— a mast like steel structure attached on the middle of the device
disposed at right angle of the device from where a load is applied
on the shaft by means of a cam (15) which is operated by a Gear
motor (1) mounted on the rear side of the device whose speed
can be varied to change the frequency of shock loads and whose
magnitude is varied by changing the height and stiffness of the
spring (14);

— a two element rectangular strain gauge rosette (16) is placed on
the impeller (3) for recording dynamic strain;
characterised in that during rotation of the impeller a vibration imparted on
the bearings of the impeller from the adjacent spring housing and
subsequent load application in different time interval on the said impeller
evaluates the possible endurance which is recorded by simulation wherein a
rectangular strain gauge rosette inserted in the impeller for
reading/recording dynamic strain.
2. The method for testing by the device as claimed in claim 1 comprises the
following steps:-
— fitting the impeller (3) to the shaft (4) through the hub and the
whole rotor is mounted on a platform supported on a spring
matrix;
— assembling the protective casing (12) over the impeller;
— switching on the controller of the drive motor (7) and the rotor
(4) starts rotating to the required speed typically 1300 RPM being
displayed on monitor for traction motor fan;
— switching on the controller of the gear motor (10) and the cam
starts rotating at required speed by typically setting 150 RPM as
displayed on the monitor of the controller;
— monitoring the strain gauge output throughout the operation of
the fan at regular intervals;
— testing the impeller fan for a required period of endurance
checking;
— measuring the xg' levels coming on fan impeller during operation
of the test rig using an accelerometer mounted on the bearing
housing closest to impeller;
— monitoring strain/stress on the impeller by bonding a two-
element rectangular strain gauge rosette (10) within strain
gauges oriented in the hoop and radial directions at the critical
location on the impeller and using slip ring system and dynamic
strain recording instrumentation for reading/recording.
3. A device for endurance test of motor fan with variable speed up to 3000
RPM and variable shock load as substantially illustrated and described along
with the accompanying drawings and figures.

A device for endurance testing of cooling fan impeller of a traction motor with
variable speed up to 3000 RPM and variable shock load comprising a steel
structure having a main frame of steel structure and first end of the main frame is
provided with a drive motor with variable speed controller and the second end is
provided with an impeller and a set of base plates disposed on the main frame and
a plurality of springs are housed in between the two base plates and one fan
impeller along with a shaft and a plurality of bearings are mounted on the base
plate and one flexible coupling is mounted with the main shaft of driving motor
and the shaft of the impeller. A mast like steel structure attached on the middle of
the device and disposal at right angle of the device from where a load is applied
on the shaft by means of a cam which is operated by a Gear motor mounted on
the rear side of the device whose speed can be varied to change the frequency of
shock loads and a two element rectangular strain gauge rosette is placed on the
impeller for recording dynamic stain; characterised in that during rotation of the
impeller a vibration imparted on the bearings of the impeller from the adjacent
spring housing and subsequent load application in different time interval and
amplitudes on the said impeller evaluates the possible endurance which is
recorded by simulation wherein a rectangular strain gauge rosette inserted in the
impeller for reading/recording dynamic strain.