Thickness Testing of Reinforced Rubber Conveyor Belts

This application note explores how to measure the depth of textile and steel reinforcements in rubber conveyor belts, as well as measure the remaining rubber thickness of in-service belts during maintenance. 

Background on Conveyor Belt Manufacturing

A wide variety of rubber conveyor belts for heavy-duty industrial and mining services, 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 to confirm that the product meets specification. After installation, belt users need to periodically check the thickness of the remaining rubber as the belt wears down to estimate the remaining service life before replacement. Large belts can be expensive, so accurate information on remaining rubber thickness is valuable to users. Our instruments and transducers have been successfully employed in this test for many years.

Sound energy reflects off the first layer of reinforcement. 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 to 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 gauging.

Ultrasonic Equipment for Measuring Conveyor Belt Rubber Thickness

Conveyor belt rubber thicknesses under approximately 12.5 mm or 0.5 in. can usually be measured with standard thickness gauge models, such as the 39DL PLUS™ gauge or 45MG gauge with Single Element software. For greater thicknesses, use the High Penetration software option for these gauges. Thickness measurements can also be made with any of the EPOCH™ series ultrasonic flaw detectors. In the case of certain very large belts, with rubber thicknesses approaching 50 mm or 2 in., the EPOCH flaw detectors are the preferred instruments.

The transducer selection will depend on the range of rubber thickness to be measured. For rubber layers between approximately 1 mm (0.040 in.) and 6.25 mm (0.250 in.), a 2.25 MHz delay line transducer (M207-RB) is usually recommended. For measurement of rubber between approximately 2.5 mm (0.1 in.) and 25 mm (1 in.), a 2.25 MHz high penetration contact transducer (M1036) is commonly used. Other transducers are available for thinner and thicker rubber layers.

As with any application involving attenuating materials, using gel couplant or glycerin (Couplant B) is recommended in preference to less viscous fluids. For severely worn in-service belts, remove any loose rubber or other debris from the surface before testing.

Ultrasonic Gauging Procedure to Measure Conveyor Belt Thickness

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 gauge'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 gauge displays a constant false reading when the transducer is uncoupled, which indicates that gain is too high.