Standard Test Methods for Rubber (Elastomeric) Conveyor Belting, Flat Type
Theory:
ASTM D378 covers tensile testing of elastomeric conveyor belts which are heavily used in the logistics industry. Conveyor belt tension ratings are specified using a number of different terms including Ultimate Tensile Strength (UTS) and ultimate breaking strength. There are also ratings based on the working ranges that these belts should be run under. This term is usually called the Working Tension, or Maximum Working Tension.
NIBA - The Belting Association defines working tension as "The maximum safe working tension recommended by the belt manufacturer." Assuming a ten to one safety factor is a good rule of thumb, so a belt with UTS of 1,000 PIW (Pounds per Inch of Width) would have a working tension of 100 PIW.
Geometry:
Conveyor belt specimens are cut to a specified width and length. These belts tend to elongate over 100% so the tensile tester must have enough stroke. Usually about 8-12 inches of length is tested. For official specimen geometry, please reference the ASTM standard.
Solution:
The wrap grip design is perfect for this test. The center wrap drum spreads the tensile stress over a larger area which simulates the actual working conditions of a conveyor belt. Please visit the wrap grip product page for more information on these neat fixtures.
Analysis:
Sample calculations for ASTM D378 are relatively simple. UTS is given by the peak load. Elongation data can also be gleaned by measuring the total distance the machine has traveled. Most modern universal testing machines have a position sensor on the crosshead.