UL 94 Flame Retardant Classification And Testing

UL 94 Flame Retardant Classification And Testing

UL is the abbreviation of Underwriters Laboratories (Underwrites Laboratories Inc.), founded in 1894, is the most authoritative in the United States, the world's largest private organization engaged in safety testing and accreditation of one.

In more than 100 years of development history, its own formed a set of strict organizational management system, standards development and product certification procedures. UL certification is the main purpose of ensuring that the product in terms of safety, performance and quality to meet certain standards, so as to protect the lives and property of consumers.

With the continuous expansion of the Chinese market and the degree of internationalization, more and more Chinese enterprises began to pay attention to product safety issues, and actively apply for UL certification.

1. UL94 Flame Retardant Classification

UL94 is the most widely used international standard for evaluating the flame retardancy of plastic materials, with 12 grades: HB, V-0, V-1, V-2, 5VA, 5VB, VTM-0, VTM-1, VTM-2, HBF, HF-1, HF-2.

Of these, VTM-0, VTM-1 and VTM-2 are applicable to plastic films, and HBF, HF1 and HF2 are applicable to foamed materials.

The equivalent flame retardant grade standard adopted in China is GBT2408 “Test of Plastic Combustion Performance by Horizontal and Vertical Methods”.

The flame retardant grade of plastics increases step by step from HB to V-0: HB<V-2<V-1<V-0<5VB<5VA.

2. UL94 common test methods

UL94 is used to evaluate the ability of a material to extinguish a flame after ignition. There are various evaluation methods based on burning speed, burning time, drop resistance, and whether or not the drop burns.

• UL 94-HB test

HB is the lowest flame retardant grade in UL 94 standard.

The test method is to clamp one end of the test piece horizontally and horizontally into 45±2 degrees, take an iron mesh, fixed horizontally under the test piece 10±1mm, the Bunsen burner (flame height of 20mm or so) into a 45 degree, move to the other end of the test piece to contact with the sample 6mm, and timer for 30±1 seconds and move away, to be burned to the test piece to the mark of 25mm when the test piece to start another timer. If the specimen reaches the 25 mm mark within 30±1 seconds, start another timer and remove the Bunsen burner.

• UL 94-V test

The UL 94-V test is completely different from the HB test, and the material has higher flame retardancy compared to the HB test.

Bunsen burner (flame height of about 20mm) touches the center point below the sample and burns for 10±0.5 seconds, then remove the Bunsen burner at a speed of 300mm/s, at least 150mm away from the specimen, and record the time of spontaneous combustion for the first time. After the spontaneous combustion stops, the second combustion is carried out immediately, and after burning for 10±0.5 seconds, the Bunsen burner is moved away, and the time of the second spontaneous combustion and the time of blazing red after the flame is extinguished are recorded.

• UL 94-5V test

The UL 94-5V test is more stringent than the UL 94-V test and is divided into 2 stages. First, the strip specimen is placed vertically and burned, and then the test is conducted with a flat plate after passing the test.

Stage 1: The test piece with a jig or fixture fixed horizontally, the Bunsen burner to the level of 20 ± 5 degrees to move to the test piece below the tip of the flame, flame contact with the bottom of the sample center point burning 5 ± 0.5 seconds, remove the Bunsen burner 5 ± 0.5 seconds, repeat this action five times in the fifth combustion removed and observed to record the specimen whether there is a hole in the damage.

Stage 2: Bunsen burner (flame height of 125mm or so) to maintain the level of 20 ± 5 degrees to move to the specimen side, so that the flame inside the flame (height of 40mm ± 2mm) of the tip of the flame to contact the bottom side of the sample, after burning 5 ± 0.5 seconds, move away from the Bunsen burner for 5 ± 0.5 seconds, repeat this action for five times, in the fifth combustion after the move away from the flame extinguished and record the time of spontaneous combustion and the time of redness after the flame is extinguished.

In the above experiments, the experimental samples were 130±3mm long, 13.0±0.3mm wide, and 3.0±0.2mm thick, as specified in the national standard.

3. UL94 Rating Judgment Criteria

• HB Rating

HB is the lowest flame retardant rating in the UL94 standard. It is required that for samples 3-13mm thick, the burning speed is less than 40mm/min,for samples less than 3mm thick, the burning speed is less than 75mm/min,or extinguished before the 100mm mark.

• V Rating

V-2: After two 10-second burn tests on the sample, the residual flame & after burning are extinguished within 60 seconds. The dripping particles can ignite cotton.

V-1: After two 10-second burn tests on the sample, the residual flame & after burning are extinguished within 60 seconds. The dripping particles may not ignite the cotton.

V-0: After two 10-second burn tests on the sample, the residual flame & after burning are extinguished within 30 seconds. The droplets must not ignite the cotton.

• 5V Rating

5VB: After five 5-second burn tests on the sample, the residual flame & after burning are extinguished within 60 seconds. Dripping particles must not ignite the cotton. Burn-through is permitted for lumpy samples.

5VA: After five 5-second burn tests on the sample, the flame & after burning are extinguished within 30 seconds. Droplets must not ignite the cotton. No burn-through is allowed for lumpy samples.

4. Three test levels

• 20mm flame, judgment result HB, V-0, V-1 or V-2 grade.

• 125mm flame, judgment result 5V-A or 5V-B grade.

• 20mm flame for thin material, judgment result VTM-0, VTM-1 or VTM-2 grade.

The V rating requires 5 samples, while the HB rating only requires 3. When starting with a V test, if the material exhibits undesirable characteristics in the first two samples, the remaining third sample can be used to switch to an HB test.

When a material is tested and achieves a V-0 rating, it can then be subjected to a 125mm flame test to see if it is possible to achieve a 5VA or 5VB rating. However, the 5V test can only be conducted if the material has passed the V-0 rating.

It should be noted that if the material is very thin, it cannot be tested according to any V rating because the material will "flutter" in the heat of the flame. Such material should be considered a thin material and tested using the VTM (Vertical Test Method) testing procedure. Similarly, the VTM test should only be conducted if the material does not pass or cannot be properly tested according to the V test procedure.

5. UL yellow card parameters interpretation

After the material through UL certification, you can query the yellow card of the material through the number on the UL website. According to the yellow card, you can query the material color, thickness, can achieve what flame retardant grade and other information. The yellow card is shown as follows:

In the electronic and electrical appliances, wire and cable, circuit components industry, many materials need to provide UL yellow card.

UL yellow card contains the following eight important index characteristics: thickness, fire rating, relative temperature index (RTI), hot wire melting rate (HWI), these are physical properties, high current melting rate (HAI), high voltage along the path of the ratio (HVTR), arc resistance impedance (D495) and comparative path index (CTI), these are electrical properties.