FRAS belts undergo multiple tests to cover different flame or belt operational situations, so several tests are used. This section will outline the typical methods used for each classification of belt listed above:
AS4606 – Grade S
Composed of five individual tests to assess the level of performance and requires independent NATA accredited testing with governing body registration and independent verification.
Gallery Fire Test (AS-1334.12) – “Tunnel Test”
In the Gallery Fire test, the potential hazard of a belt being ignited from a continuous external flame source is quantified, as well as the ability of the product to resist spreading the fire to other areas (referred to as fire propagation). This hazard is assessed by using a sample belt length of 2 m supported horizontally on a steel trestle placed in a chamber resembling that of a mine tunnel. This is also why this test has the nickname “tunnel test.”
A continuous flow of air is drawn in through the chamber while the sample is subjected to a controlled flame from a propane burner located under the sample. Upon the flame’s removal, the belt is allowed to continue to burn and glow until cessation of flame, and the total length of undamaged belt is quantified by physical measurement.
Passing this test requires a portion of undamaged belt to be measured after all flames and glowing material have ceased.
Drum Friction Test (AS-1334.11)
This test examines the dangers associated with a stalled belt and a driven rotating drum or pulley resulting in friction heat build-up. A test piece of conveyor belting is mounted and tensioned under an applied load to keep it in a stationary position as it is wrapped halfway around a rotating drum pulley.
The test is continued at specific tensions in the Australian standard until the belt breaks or for two hours whichever occurs first in still or moving air depending on the testing conditions. The presence or absence of flame and glow is noted, and the temperature of the drive drum is measured. Exceeding the maximum permissible temperature, burning, or glowing are all failure conditions for the test.
Small Scale Burn (AS-1334.10) – “Finger Burn”
The “Finger Burn” test, as it is commonly known in the industry, uses a small, finger length sample to check the likelihood of a conveyor belt ignition from a relatively small ignition source in a standard atmosphere. The end of a horizontally oriented belt sample is subjected to a “Bunsen” type flame for a given time period.
Following the removal of the flame and exposure to an air current, the duration of the continued burning present on the belt is noted, as well as any afterflame and afterglow.
For K-Grade, this test is conducted in a slightly different fashion, comprising a vertically held sample being exposed to the Bunsen flame with the burner positioned at an angle.
Passing the test requires belts to meet time thresholds for self-extinguishing.
Electrical Conductivity Test (AS-1334.9) – “Static”
The potential build-up of material and subsequent discharge of static electrical charge on moving conveyors can result in ignition or even explosion in certain environments. Electrical resistance is determined in this test by passing a current at a specified voltage between electrodes placed on a suitably prepared belt surface.
The resistance of the belting between the electrodes is measured after a given time. The internationally recognized acceptance criteria for electrical conductivity is a maximum resistance of 3 × 10⁸ Ohms. Fenner FRAS rubber compounds are formulated to ensure that those products are sufficiently conductive to avoid build-up of static electricity.
Oxygen Index Requirement Test (ISO-4589)
A very common test for rubber and plastic components, this process tests the material for oxygenation levels required in the atmosphere to maintain combustion.
A sample is placed inside a controlled test chamber where oxygen and inert gas levels can be modulated. When a flame is exposed to a sample in the controlled atmosphere, the duration of the burn is measured and quantified as a pass or fail for a given oxygen level. Subsequent samples are then tested across various oxygen levels to gather a range of results of passes and failures. An equation is then applied to these results to determine the material’s Oxygen Index in a percentage value.
This test is useful for quality control purposes as it provides a bench scale method for determining fire-retardant values for materials that don’t readily burn in a standard atmosphere.
