FIELD OF THE INVENTION
The present invention generally relates to a non destructive testing method to
identify during joining of fabric belts the presence or absence of air pockets and
disbond by pulse echo velocity technique, which interalia improves quality of the
fabric belt joints. More particularly, the invention relates to a non-destructive
testing process for segregation of defective joints from acceptable joints in fabric
belts of a fabric conveyor belt by pulse echo velocity technique.
BACKGROUND OF THE INVENTION
Fabric conveyor belts are used in bulk material handling in industries, for
example iron ore, coal, sintered product etc., in an iron and steel industry. In
fabric belt, layers of woven fabric are built up with interleaved layers of rubber,
which are bonded together under heat and pressure to form the belt.
US2004206180 describes a method and apparatus for retaining a part in a carrier
during an ultrasonic scan. The part is positioned above a first opening in a lower
chamber while air is drawn out of a second opening in the lower chamber to
apply suction to the lower surface of the part. An ultrasonic transducer is housed
in an upper chamber that dispenses coupling fluid to the top surface of the
object.
EP1008848 discloses process a for making composite wood products in which
curing is monitored ultrasonically, and an apparatus.

According to this prior art invention, curing of the binder used to produce a
lignocellulosic composite material in a press is monitored by inserting a
transmitter probe and a receiver probe into the composite-forming mixture at
parallel points; passing an ultrasonic signal from the transmitter probe through
the composite-forming mixture to the receiver probe; measuring the pulse
velocity of the ultrasonic signal; and comparing the measured pulse velocity to
that of a standard (i.e., velocity of pulse through a composite article in which the
binder is completely cured). When the measured velocity and the velocity of the
standard are equal, the composite article is removed from the press. This
technique is particularly useful for monitoring the commercial production of
composite and engineered wood products.
W09936769 discloses a method of ultrasonic on-line texture characterization.
According to this invention, a sputtering target under test is irradiated with an
ultrasonic pulse. The ultrasonic pulse has a wavelength in the sputtering target
in the range of the average grain size for the target under test. Backscattering
echoes are produced by the interaction of the pulse with grain boundaries in the
target under test. The backscattering echoes are detected and a representative
electrical signal is generated. The number of occurrences of the backscattering
echoes having amplitudes within predetermined ranges are determined. A
histogram of the number of occurrences versus amplitude is plotted. The
histogram for the target under test is compared with reference histograms for
sputtering targets having known crystallographic orientations to determine the
texture of the target under test.

US5473943 teaches an ultrasonic test device for nondestructive testing of a
workpiece moving relative thereto by the pulse echo method, having a fluid
coupling between the ultrasonic oscillator and the surface of the work material.
At least two test heads are provided whose sound beam axes intersect at a point
in the region of the workpiece and a travel path in the form of a chamber is
provided for guiding the fluid medium. To reduce susceptibility to interference
and to achieve high test performance, a separately guided travel path extending
along a determined length of the chamber and forming a duct is associated with
each test head the axes of the travel path being aligned with the respective
sound beam axis.
EP0206296 teaches an appliance for the process-integrated testing of moving
cylindrical stock. According to the invention, the wall thickness of tubes or
sheaths or insulations in cables or conductors can be measured by means of the
ultrasonic pulse echo method in a nondestructive and contact-free manner. In
testing moving stock in a manufacturing line. The technical problem is that
correct positioning of the ultrasonic probes is made difficult by lateral movements
of the product under test and deviations from the ideal cylinder geometry. The
invention incorporates devices which serve to achieve optimum geometrical
positioning of probes, in particular ultrasonic probes, and the product under test
in manufacturing lines producing tubes or cables and conductors with a layer
type structure. In principle, there are two different methods: appropriate
constrained guidance of the product under test if the probes are rigidly mounted
and tracking by the probes if the product under test is freely moving.

GB1421575 discloses a method of and an apparatus for inspecting
inhomogeneities in bodies having plane or slightly curved surfaces in which an
ultrasonic probe transmits pulses obliquely into a test body in a predetermined
direction and an indicating device produces point markings on a plane record
surface, wherein the markings are effected along an axis of indication which in
relation to the record surface follows the direction of the pulses projected on the
body surface, a reference point on the axis of indication follows the movement of
the probe over the body surface and each marking is effected at a distance from
the reference point proportional to the pulse echo travel time. Probe emits pulses
of ultrasound along a direction at a fixed angle to the body surface. A planar
record medium has markers which lie along a line coincident with the pulse
direction. Echo pulses are relayed to conventional receiving apparatus and the
marker energized at the appropriate range. Thus as the probe is moved over the
surface, a composite picture of the inhomogeneity is built up. Several
embodiments are described divided into two types with the recording surface
fixed over the surface of the test body and remote recording surfaces. In the first
type, the probe carries a rigid arm which has markers along its length. These
may be spark gap generators or lightemitting diodes which mark an
appropriately sensitive record medium in response to echo signals derived from
ultrasonic receiver. The light-emitting diodes may be used in conjunction with a
camera. In a modification, the upper surface of the arm has light-emitting diodes
which give a visual representation to the operator of pulse echoes. In a further
embodiment the marking signals are derived from the receiver CRT via optical
fibres which are mounted such that their one ends lie along the CRT trace and
their other ends lie along the arm. In the other embodiments a single marker is
used which is continuously moved along the arm and is responsive to echoes

from the appropriate range to mark the record. The marker is moved along a rod
or is fixed to an endless belt. In a different arrangment, the marker takes the
form of a helical strip on a roller which rotates about an axis parallel to the
indication axis. As the roller rotates, the point of contact with the record sheet is
scanned along the indication axis. In those embodiments using remote
indication, the probe position is resolved electrically or mechanically and the
resultant recording made on a sheet or a CRT which may have a short
persistence screen which is photographed, a long persistence screen or may be
an electronic storage tube. In these embodiments, the movement of the body is
also resolved and taken account of in the recording. In another embodiment, the
probe position and direction are detected by using spark generators on the probe
and an arm attached thereto which extends over the beam axis. Linear
microphones detect the noise generated by the sparks and apparatus determines
the four co-ordinates. These are passed to CRT which shows the indication axis
and the CRT trace follows this axis and records echoes to build up the composite
picture. The apparatus is stated to be useful in flaw detection or medical
diagnosis. By altering the spacing between the markers, the composite picture
can be scaled up or down as required.
US4394345 teaches an ultrasonic transducer apparatus and method for
examining nuclear reactor jet pump beams for cracking. Examination is
conducted in situ. An operator lowers a carriage portion of the apparatus into the
reactor vessel with a pole. Ultrasonic signals are transmitted through suitable
wiring from an external source to the transducer apparatus, which may employ a
pitch-catch or pulse-echo mode of ultrasonic examination to test the beams. The
carriage holds oppositely disposed pairs of ultrasonic transducers and positions

them suitably near the beam to be examined in a proper orientation thereto. The
mode of examination is selected by a switching mechanism. The apparatus
includes a signal generator, receiver, and visual display.
GB111628 teaches an improvent to light projectors. According to this invention, a
headlight is provided with a reflector having surfaces of different contours re
spectively above and below a horizontal plane through the light source, one of
the reflecting-surfaces being adapted to project a relatively concentrated beam
of light for illuminating the distant parts of the roadway and the other reflecting-
surface being adapted to project a relatively divergent beam for illuminating the
nearer portions and sides of the roadway. One of the foci of one surface is
coincident with one of the foci of the other. The reflecting-surfaces may consist
of a paraboloidal surface combined with an elliptical or hyperbolic surface or a
modified elliptical or hyperbolic surface formed by the revolution of a series of
ellipses or hyperbolas having one fixed focus, the second foci of which are
arranged successively along the axis. In some cases, the modified conoidal
surface may be smooth. The two elements of the reflector may be made in one
piece, or may be constructed separately, and are connected together by flanges
along the horizontal plane containing the light source. In modifications, an upper
elliptical or modified elliptical surface is combined with a lower hyperbolic or
modified hyperbolic surface. The modified elliptical or hyperbolic surface is
constructed in such a way that the annular surfaces whose outer foci are near
the light source focus can be placed inside or outside those annular surfaces
whose outer foci are more distant. A screen or mirror may be placed in front of
and above the light source, or the bulb may be correspondingly frosted to
prevent the rays from being projected upwardly. A modified elliptical or

hyperbolic half reflector may be attached to an ordinary headlight having an
ordinary parabolic reflector.
In general, the prior art processes for checking the quality of fabric belt joints,
normally adopt radiographic technique which involve the following drawbacks:-
1. The density difference between the rubber and fabric is very minimum,
which deter the penetration of x / gamma rays, leading to inaccurate
results;
2. Radiation hazard due to use of x-ray or gamma rays is unavoidable; and
3. The processes take huge time for inspection.
Thus, there is no method available in the prior art to check the joint efficiency in
advance to prevent unexpected joint failure.
OBJECTS OF THE INVENTION
It is therefore, an object of the invention to propose a non destructive testing
method to determine the condition of fabric belt joints in conveyor belts to
prevent failure due to defects for example, air voids, disband of the fabric belt
joints.
Another object of the invention is to propose a non destructive testing method to
determine the condition of fabric belt joints in conveyor belts to prevent failure

due to defects for example, air voids, disband of the fabric belt joints, which
ensures quality of the majority portion of the parent material of a fabric belt,
apart from the belt joints.
SUMMARY OF THE INVENTION
Accordingly, there is provided a non destructive testing process for segregation
of detective joints from acceptable joints in fabric belts of fabric conveyor belts
by pulse echo velocity technique, comprising the step of providing a plurality of
different portions of a fabric belt; forming a plurality of specimens from each
portion, said specimens being of a predetermined size; preparing samples of
fabric belt having known size of artificial holes; making initial calibration of a
testing instrument by placing a reference bar with engraved pulse transit time;
balancing the instrument; placing a fabric belt which contains no defects, to
measure the transit time; recording shifting of the transmit time due to presence
of the artificial holes of different diameters; and determining the condition of the
fabric belt joints based on said recorded shifting of the transit time.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The invention can now be described in detail with the help of the figures of the
accompanying drawings in which:
Figure 1 - shows a cross sectional view of a step splice joint in plied belting.
Figure 2 - shows a fabric belt with artificial defects
Figure 3 - shows an ultrasonic testing device

Figure 4 - shows a graphical representation of ultrasonic transit time vs defect
position.
DETAILED DESCRIPTION OF THE INVENTION
Ultrasonic testing through transmission technique is a known and existing
process. The present invention uses this technique to propose a non destructive
testing process for segregation of detective joints from acceptable joints in fabric
belts of fabric conveyor belts by pulse echo velocity technique.
Samples of fabric belts of 100 x 100 x 17 mm was collected from the portion of a
fresh conveyor fabric belt. A conveyor fabric belt is made up of several sections
as shown in the Figure 1. It mainly comprises a top cover, a bottom cover, and a
plurality of carcass interposed between the top and bottom covers. The carcass
can be made up of fabric which is typically cotton, polyester or nylon. The cover
can be made of urethane, PVC, Teflon or synthetic rubber.
Initially the fabric belt in present condition was ultrasonically checked using at
least two transducers which are having the frequency in the range 30-100 kHz.
Another portion of the fabric belt was selected and a plurality of artificial hole
was made of different diameters for example, 1,3 and 5mm at a length of 50mm
each (Figure 2).
For a given frequency and for a part with identical geometry, the only variable
that may affect the transit time of the ultrasonic wave is air void. When the
instrument is balanced with identical components in reference specimen (without

defects), the transmit time difference was noted for the samples having artificial
defects. After this, the same can be used to assess the quality of the fabric belt
joints which will be made at site.
ULTRASONIC (THROUGH TRANSMISSION) PRINCIPLE
This ultrasonic through transmission principle is basically to calculate the time
taken by the pulse to travel throughout the belt thickness. This is also known as
pulse velocity technique through which the quality of the material can be
assessed. There are two transducers having frequency in the range between 30
to 100 kHz each used for this purpose. Both the transducers are placed in top
and bottom portion of the belt after applying the couplant (either grease or
glycerin). The centre axis of both the transducers should be in same line to get
the actual pulse travel time.
Whenever the density of the test component change due to the presence of air
voids/ disbond, it results in change of travel time of pulse. This is reflected in
terms of microsecond on the display of the instrument.
EXPERIMENT
A fresh portion (parent material) of the fabric belt was collected and its size is
100 x lOOx 17mm. The initial calibration was done with a reference bar with
engraved pulse transmit time to check the instrument zero. The couplant was
applied to both the faces of the transducer and pressed firmly to the ends of the
reference bar. SET REF knob was adjusted until the reference bar transit time

was obtained on the display. After the calibration, the same transducers were
pressed against the fabric belt portions firmly on both sides. The transmit time of
the pulse indicated on the display was noted. The same procedure was done on
the other portion of the fabric belts and noted the transit time. The portion of
the fabric belt with same size as mentioned above was taken and the artificial
hole was made of with different diameters at different locations in the belts
(Figure 3).
The size of the hole was 1,3 and 5mm respectively. The transit time was
calculated for these artificial holes using the same procedure as mentioned
above. The reliability and repeatability of these values (transit time) were
ensured by doing the measurement several times at the same place at different
intervals. As seen in the graph (Figure 4), the reduction in transit time was due
to the density reduction in the artificial hole portion.

WE CLAIM
1. A non destructive testing process for segregation of detective joints from
acceptable joints in fabric belts of fabric conveyor belts by pulse echo
velocity technique, comprising:
- providing a plurality of different portions of a fabric belt;
- forming a plurality of specimens from each portion, said specimens
being of a predetermined size;
- preparing samples of fabric belt having known size of artificial holes;
- making initial calibration of a testing instrument by placing a reference
bar with engraved pulse transit time;
- balancing the instrument;
- placing a fabric belt which contains no defects, to measure the transit
time;
- recording shifting of the transmit time due to presence of the artificial
holes of different diameters; and
- determining the condition of the fabric belt joints based on said
recorded shifting of the transit time.

2. The ultrasonic non-destructive process as claimed in claim 1, wherein a
pulse echo velocity method is used.
3. The process as claimed in claim 1 or 2, wherein at least two transducers
with frequency range of 30 to 100 kHz is adapted in the testing device.

ABSTRACT

The invention relates to a non destructive testing process for segregation of
detective joints from acceptable joints in fabric belts of fabric conveyor belts by
pulse echo velocity technique, comprising providing a plurality of different
portions of a fabric belt; forming a plurality of specimens from each portion, said
specimens being of a predetermined size; preparing samples of fabric belt having
known size of artificial holes; making initial calibration of a testing instrument by
placing a reference bar with engraved pulse transit time; balancing the
instrument; placing a fabric belt which contains no defects, to measure the
transit time; recording shifting of the transmit time due to presence of the
artificial holes of different diameters; and determining the condition of the fabric
belt joints based on said recorded shifting of the transit time.