GB/T 3685-2026Conveyor belts—Laboratory scale flammability characteristics—Requirements and test method (English PDF)

3.1 Afterflame

Flame which persists after the ignition source has been removed.

[ISO 13943:2008, definition 4.6].

3.2 Flame, noun

Zone of combustion in the gaseous phase, usually with emission of light.

[ISO 13943:2008, definition 4.133].

4.1 Health and safety

4.1.1 Smoke and flame

The combustion of polymeric materials may produce smoke and toxic gas, which can affect the health of the operators. Therefore, the smoke in the test area shall be removed in time.

4.1.2 Handling, storage and disposal of liquefied petroleum gas containers

All safety regulations for the handling and storage of liquefied petroleum gas (LPG) shall be followed; regulations for the disposal of LPG containers shall also be followed.

If the relevant safety regulations require that the storage temperature of LPG is lower than the test environment temperature, or if there is a certain distance from the test platform, a sufficiently long piping system is required to ensure the temperature required for gas balance in the combustion test. A convenient method is to pass the gas (before the combustion test) through a metal pipe placed in water at 25 °C.

4.2 Principle

Place the test piece cut from the conveyor belt vertically in the flame for a certain period of time, and record the afterflame time of the test piece after removal from the burner.

Then, apply a current of air to the test piece, and record the re-flame.

4.3 Test pieces

4.3.1 General

The test pieces described in 4.3.2 and 4.3.3 shall be cut at least 50 mm from the edge of the belt.

4.3.2 Fabric core conveyor belt

4.3.2.1 Tests on conveyor belts with or without coating

4.3.2.1.1 Prepare 12 test pieces, each (200 mm ± 5 mm) × (25 mm ± 1 mm) as follows:

a) Cut 3 test pieces with coating along the longitudinal direction of the conveyor belt.

b) Cut 3 test pieces with coating along the transverse direction of the conveyor belt.

c) Cut 3 test pieces with coating removed (see 4.3.2.1.2) along the longitudinal direction of the conveyor belt.

d) Cut 3 test pieces with coating removed (see 4.3.2.1.2) along the transverse direction of the conveyor belt.

4.3.2.1.2 Coating can be removed [see c) and d) in 4.3.2.1.1] by stripping, scraping and grinding. If the coating is removed by grinding, special care shall be taken, to ensure that the test piece is not overheated and the fabric core is not damaged.

4.3.2.2 Tests on conveyor belts with intact coating

If the product specification requires the test to be carried out on a conveyor belt with an intact coating, the test requires only 6 test pieces as described in a) and b) of 4.3.2.1.1.

4.3.2.3 Tests on conveyor belts designed without coating

If the product specification requires the conveyor belt to be designed for testing without covering, the test requires only 6 test pieces as described in c) and d) in 4.3.2.1.1.

4.3.3 Steel cord conveyor belt

4.3.3.1 Tests on conveyor belts with intact coating

If the product specification requires a test on the conveyor belt with intact coating, cut 6 test pieces along the longitudinal direction of the belt; the length of the test piece is 200 mm±5mm, and the width is 25 mm as much as possible, depending on the cord diameter and spacing. Each test piece shall be at least 20 mm in width and contain two steel wire cords, which are cut at the midline of adjacent cords.

4.3.3.2 Tests on conveyor belts with coating removed

If the product specification requires a test on the conveyor belt with coating removed, for the test, cut only 6 test pieces as described in 4.3.3.1, and remove the coating by methods such as stripping, scraping and grinding.

4.4 Apparatus

4.4.1 Bunsen burner, whose burner tube insider diameter is (10±0.5) mm, as illustrated

in Figure 1.

4.4.2 Commercial propane gas, as specified in ISO 9162.

4.4.3 Timing device, accurate to 0.2 s or less.

4.4.4 Measuring device, accurate to the millimeter or estimated to the millimeter and calibrated to the appropriate precision.

4.4.5 Test piece holder and fixture location: The height of the rectangular frame of the holder is not less than 500 mm; the distance between the two sides is at least 75 mm;

a suitable fixture is mounted to hold the test pieces; the test piece is at least 20 mm away A location is required as such that the wind speed at the beginning of the test is less than 0.2 m/s, and it is not affected by the operation of mechanical equipment during the test. The oxygen content in the air surrounding the test location shall not decrease as the test proceeds. If the test is carried out in a cabinet with an opened front door, the test piece shall be mounted at least 300 mm from the cabinet wall.

4.6 Conditioning of test pieces

After preparing the test piece as described in 4.3, place the test piece in the standard environment specified in GB/T 30691 for conditioning.

4.7 Procedure

4.7.1 Carry out the test in an environment where the temperature is 10 °C ~ 30 °C and the relative humidity is 15% ~ 80%. The test shall preferably be performed at the same temperature and the same relative humidity for the conditioning, or in the atmosphere applicable at the site of use (if known).

4.7.2 Fix the test piece on the test apparatus described in 4.4.5, ensuring that the test

piece is in a vertical state.

4.7.3 Light the burner and preheat it for 2 minutes; adjust the propane gas flow, so that the total flame height is 150 mm ~ 180 mm, and the inner flame height is about 50 mm.

Place the thermocouple (4.4.6) at the place with the highest flame temperature (just above the inner flame cone, as shown in Figure 1), and check that the measured flame temperature is 1 000 °C ± 20 °C.

If necessary, adjust the burner flame to ensure that the temperature is maintained at 1 000 °C ± 20 °C.

4.7.4 Position the burner at 45° (see Figure 1), and immediately place the flame at the centerline of the test piece, so that the top of the burner tube is 50 mm from the bottom of the test piece.

4.7.5 Remove the burner after 45 s without extinguishing the burner. If other test pieces

are also tested, the burner shall be kept out of the wind. Immediately observe the flame condition and flame duration of the test piece and record the afterflame time.

4.7.6 Within 60 s ± 5 s after removing the burner, apply a current of air (see 4.4.7)

vertically to the test piece for 1 min. Observe and record any recurrence of flame of the test piece and the duration of any such flaming.

4.8 Expression of results

4.8.1 Report the flame condition and flame duration of each test piece (see 4.3) in 4.7.5

and the total flame duration of each group of 6 test pieces (see 4.3).