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What is the difference between an HB and a V0 flame rating (UL 94 testing)?
06-26-2009, 07:30 PM
Post: #1
Question What is the difference between an HB and a V0 flame rating (UL 94 testing)?
HB is a horizontal burn rating. The HB description comes from the specimen orientation during the test. The bar samples are parallel to the work surface. A flame is applied and then removed. The rate of burning is then determined. In order to earn the HB rating, the burn rate must not exceed specified limits. An HB rating does not imply self-extinguishing characteristics. Most plastics, in typical injection molding thicknesses, will meet the HB requirements without the addition of special additives.


V-0 is a vertical burn rating. Other ratings in this class system are V-2 and V-1. The vertical refers to the specimen orientation, which in this case is perpendicular to the work surface. A flame is applied according to a specified protocol and then removed. Burn times and the presence of flaming drips, which can ignite cotton placed under the specimen, determine the specific rating assigned. The vertical ratings do imply self-extinguishing characteristics. Some plastics exhibit self-extinguishing characteristics inherently, while others require the addition of special additives. In this class system V-0 is the most flame retardant (no flaming drips and low burn time), followed by V-1 and finally V-2 (flaming drip ignites the cotton).
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