UL94 flame retardant grade is the most widely used material flammability standard. It is used to evaluate the ability of materials to extinguish after being ignited. It is a public standard for daily testing whether materials are flame retardant or not. UL94 can be judged by various methods according to the burning speed, burning time, drip resistance and whether the droplet burns after ignition. Many values can be obtained for each tested material according to color or thickness. When the material of a product is selected, its UL grade shall meet the thickness requirements. UL grade shall be reported together with thickness value. It is not enough to report only UL grade without thickness.
As UL94 flame retardant grade is an American Standard, people have a variety of understanding of UL94 flame retardant grade standard after translation. Therefore, many factories have their own set of "V-0" grade, which brings great inconvenience to upstream and downstream enterprises. Here are some common misunderstandings about UL94 flame retardant grade:
Flame retardant grade (from Hb, V-2, V-1 to V-0)
HB: the lowest flame retardant grade in UL94 standard. For samples 3 to 13 mm thick, the combustion rate is required to be less than 40 mm per minute; For samples less than 3 mm thick, the combustion rate is less than 70 mm per minute; Or go out in front of the 100mm mark.
V-2: after two 10 second combustion tests on the sample, the flame goes out within 30 seconds. 30 cm below the cotton wool can be ignited.
V-1: after two 10 second combustion tests on the sample, the flame goes out within 30 seconds. Do not ignite cotton wool below 30cm.
V-0: after two 10 second combustion tests on the sample, the flame goes out within 10 seconds. No combustibles can fall.
Myth 1: the V-0 level can only be reached when the fire goes out
This is the understanding of some factories. There is only one standard for them to judge whether materials are flame retardant: self extinguishing when leaving the fire, that is, "materials cannot be ignited". Once there is combustion, they will be rated as "flame retardant enough". The reason why you can't understand the standard is that you can't understand it completely.
Myth 2: HB grade is not a flame retardant grade, Any material without flame retardant treatment can be marked with HB grade
In fact, Hb grade is the lowest flame retardant grade in UL94 standard, which is usually called "slow burning grade": for samples with a thickness of 3 to 13 mm, the burning speed is required to be less than 70 mm / min, or extinguished before the standard of 100 mm.
Myth 3: the higher the flame retardant grade, the better，V-0 must be better than V-2
Plastics used for different purposes have different requirements for flame retardancy. In reality, people generally hope that the flame retardant level of materials is higher. But in fact, all kinds of flame retardant test methods have limitations, and their conclusions are relative. Therefore, it is not that the higher the flame retardant level, the better.
For example, it is generally considered that UL94V-0 materials are better than V-2 materials. However, some electrical products require materials with arc ignition resistance. At this time, grade V-2 is better than grade V-0. Because the UL94V-2 material will not form electric conduction and coking under the action of electricity, the possibility of ignition is greatly reduced, while the UL94V-0 material is the opposite.
Myth 4: UL yellow card certification only has the natural color of V-0 level, so no matter what color products are made, they can claim to be V-0 level
This is caused by the careless interpretation of UL flame retardant grade standard - although it is possible that natural color materials can reach V-0 grade and other color products can also reach it, this is only possible, not all. Different materials, different flame retardant systems, the influence degree of color is even different.