UL94 flame retardant test

A set of GIF to understand the UL94 flame retardant test

 

UL 94 is the most widely used standard for the plastic materials to evaluate their flame retardant performance. There are 12 grades: HB, V-0, V-1, V-2, 5VA, 5VB, VTM-0, VTM-1, VTM-2, HBF, HF-1, HF-2.

UL 94 is used to evaluate the ability of a material to extinguish after it has been ignited. There are various evaluation methods depending on the burning speed, the burning time,the drip resistance and whether the dripping is burning. Each material to be tested can obtain many values depending on the color or thickness. When a material of a product is selected, its UL rating should meet the thickness requirements of the wall portion of the plastic part. The UL rating must be reported along with the thickness value.

Common UL94 test method

1. Horizontal Burning Test (HB)

HB is the lowest flame retardant rating of the UL 94 standard. The test method is to horizontally clamp one end of the test piece to 45±2 degrees with the horizontal level, take an iron net, fix it horizontally 10±1mm below the test piece, and make the Bunsen burner(flame height about 20mm) into 45 degrees, move to the test. The other end of the sheet is in contact with the sample 6mm and is removed after 30±1 second. When the test piece is burned to the 25mm mark, another timer and remove the Bunsen burner.

 

2. 50W vertical burning test

After the Bunsen burner( flame height of about 20mm) is in contact with the center point below the sample for 10±0.5 seconds, remove the Bunsen burner at a speed of 300mm/s, at least 150mm from the test piece, and record the first spontaneous combustion time. After the spontaneous combustion ceases, the second combustion is performed immediately. After burning for 10±0.5 seconds, the Bunsen burner is removed, and the second spontaneous combustion time and the redness time after the flame is extinguished are recorded.

 

3.500W vertical burning test

plate sample

Keep the Bunsen burner (flame height of 125mm) to 20±5 degrees horizontally and move it to the side of the test piece so that the tip of the flame inner flame (40mm±2mm high) touches one side of the bottom end of the sample and burns for 5±0.5 seconds. Open the Bunsen burner for 5 ± 0.5 seconds, repeat this action five times, remove after the fifth combustion and record the auto-ignition time and the red-hot time after the flame is extinguished.

 

rod specimen

Fix the test piece horizontally with the jig or fixture, and move the Bunsen burner to the bottom of the test piece at 20±5 degrees from the horizontal. The tip of the flame inner flame contacts the bottom point of the sample and burns for 5±0.5 seconds. The lamp was lighted for 5 ± 0.5 seconds, and this action was repeated five times. After the fifth combustion, it was removed and the recording piece was recorded for damage.

 

 UL 94 flame retardant rating criteria

1. UL94 horizontal combustion determination conditions

	Burning Speed	Flame Retardant Rating
Sample thickness 3-13 mm	≤ 40 mm/min	HB
Sample thickness <3 mm	≤ 75 mm/min	HB
The flame is extinguished before the marking line (25 mm/100 mm)	= 0 mm/min	HB

 

2. UL94 vertical combustion determination conditions

Judging condition	V-0	V-1	V-2
Spontaneous combustion time after applying flame（s）	≤ 10	≤ 30	≤ 30
Total spontaneous combustion time(s) (10 times of spontaneous combustion time）	≤ 50	≤ 250	≤ 250
Spontaneous combustion + blazing time after the second flame（s）	≤ 30	≤ 60	≤ 60
Drip igniting cotton	no	no	yes
Burn to the fixture (the sample is completely burned)	no	no	no

 

3. UL94 500w vertical combustion determination conditions

	5 VA	5 VB
Spontaneous combustion + blushing time after 5 tests of any sample（s）	≤ 60	≤ 60
Drip igniting cotton	No	No
Sample hole（<3 mm）	No	Yes