Dettaglio dell'applicazione
Thickness Testing of Reinforced Rubber Conveyor Belts
Application: Measuring the depth of textile and steel reinforcements in rubber conveyor belts, and
measuring the remaining rubber thickness of in-service belts.
Background: A wide variety of rubber conveyor belts for heavy-duty industrial and mining service such as ore and mineral transportation incorporate internal layers of woven fabric or steel cords for strength
reinforcement. Conveyor belt manufacturers need to check the depth of the reinforcement layer across the belt in order to insure that the product meets specification. After installation, belt users need to periodically check the
thickness of the remaining rubber as the belt wears down in order to estimate the remaining service life before replacement. Because large belts can be very expensive, accurate information on remaining rubber thickness is valuable
to users. Panametrics-NDT instruments and transducers have been successfully employed in this test for many years.
Sound energy reflects off the first layer of reinforcement, and in the case of textile or fabric reinforced belts very little sound energy will penetrate deeper. Measurement of total belt thickness is normally possible only in the
case of some steel-reinforced belts where there is sufficiently wide separation between the steel cords to permit sound energy to travel unobstructed the opposite side of the belt. However, the critical dimension for most users is
the amount of rubber over the first reinforcement layer, not total thickness. This is usually a straightforward application for ultrasonic thickness gaging.
Equipment: Rubber thicknesses under approximately 20 mm or 0.750 inch can usually be measured with thickness gage models 35, 35DL, and 37DL PLUS. For greater
thicknesses, the high penetration version of these gages (models 35HP and 35DL-HP) should be used. Thickness measurements can also be made with any of the Epoch series flaw detectors. In the case
of certain very large belts, with rubber thicknesses approaching 50 mm or 2 inches, the Epoch 4 is the preferred instrument.
The transducer selection will depend on the range of rubber thickness to be measured. For rubber layers between approximately 1 mm (0.040") and 6.25 mm (0.250"), a 2.25 MHz delay line transducer (M207-RB)
will usually be recommended. For measurement of rubber between approximately 2.5 mm (0.100") and 25 mm (1"), a 2.25 MHz high penetration contact transducer (M1036) is commonly used. Other transducers are available for
thinner and thicker rubber layers. Consult us for details.
As with any application involving attenuating materials, use of gel couplant or glycerin (Couplant B) is recommended in preference to less viscous fluids. In the case of severely worn in-service belts, any loose rubber or other
debris should be removed from the surface before testing.
Procedure: In the most common situation, using the M1036 transducer to measure the outer rubber layers on belts with textile or fabric reinforcement, start with the gage's M1036 default setup and increase
maximum gain as necessary to measure the thickness range of interest. If necessary for measurement of thin belts, increase initial gain as well. In any of these setups, gain may usually be increased up to the point where the gage
displays a constant false reading when the transducer is uncoupled, which indicates that gain is too high.
typical conveyor belt measurement with M1036
To measure thin rubber layers over textile or fabric reinforcement with the M207 delay line transducer, use the M207 Mode 2 default setup and adjust gain and blanking as necessary based on the echoes from a reference standard.
typical thin rubber layer measurement with M207
Measurement of depth of braided steel cord reinforcements can be more challenging because their irregular contour presents a less optimum reflecting surface. Careful adjustment of instrument gain with the aid of a reference
sample is recommended. Also note that echo polarity will be positive rather than negative because the steel represents a high impedance reflector.
steel cord depth measurement with M1036
Sound velocity in rubber compounds will typically be on the order of 1.650 mm/uS or 0.0650 in/uS. The Panametrics-NDT Applications Lab is always available to assist with gage setups for specific transducers and belt types.
For further information on any of the points discussed here, contact us.
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