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Fire behavior of Lexan films
Oxygen limit according to ISO 4589
The purpose of Limiting Oxygen Index (LOI) testing is to measure the relative flammability of a material when exposed to a flame in a controlled environment. The LOI states the minimum concentration of atmospheric oxygen that is required to maintain a flame impingement on the thermoplastic material for 3 minutes or over a length of 50 mm.
The atmosphere in the test cylinder consists of an externally regulated N2/O2 mixture. The vertically supported material sample is set on fire from above with a pilot flame. The ignition flame is removed and the oxygen concentration reduced until the test specimen can no longer feed the flame. The higher the LOI, the lower the flammability of the material.
Image 8:
Image 8:
flammability
Compared to many other polymers, GE films are characterized by their high level of flame resistance. They are therefore also used for numerous applications in electrical engineering and electronics, in vehicle construction and in construction. Flame Retardant (FR) GE films offer increased resistance to flame and ignition.
Flame retardancy according to UL94 – preliminary remark
Standard 94 of the Underwriters' Laboratories (UL94) has established itself as the most authoritative standard for the classification of the flammability of plastics worldwide. According to UL94, the ability of a material to be extinguished after igniting under laboratory conditions is tested. The classification is based on burning rate, extinguishing time, drop (burning/non-burning) or hole formation and afterglow duration. Multiple classifications are possible for each material depending on wall thickness and/or color. When choosing a specific material, the classification that corresponds to the thinnest wall cross-section of the application should always be used as a basis. Information on the UL94 classification is only comparable and meaningful if it states the wall thickness to which it applies.
UL94 ratings* at a glance
HB test body horizontal, burning rate <76 mm/min with wall thicknesses <3 mm or <38 mm/min with wall thicknesses >3 mm.
V-0 test body vertical, self-extinguishing up to 10 s, no burning drops, afterglow max. 30 s.
V-1 test body vertical, self-extinguishing up to 30 s, no burning drops, afterglow max. 60 s.
V-2 test specimen vertical, self-extinguishing up to 30 s after the flame has been removed, flaming droplets permissible, afterglow max. 60 s.
5V- Larger flame, test specimen vertical, self-extinguishing up to 60 s after 5 x 5 s
Flaming, no burning drops, afterglow max. 60 s.
5VA- Like 5VB, but no burn hole permitted - currently the highest UL94 rating.
5VB- Like 5V, but plate-shaped test body horizontal, burn hole permitted after extinguishing.
VTM-0 classification for very thin materials, requirements as V-0, test specimen not rod-shaped but cylindrical.
UL94 HB
Where flame retardancy is required for fire safety reasons, the use of UL94 HB rated materials is typically prohibitive. HB materials are also not recommended for electrotechnical applications other than purely mechanical and/or decorative purposes. Suitable HB materials are also available for connector housings that require high tracking resistance
Disposal.
Often misunderstood: Materials without flame retardant treatment or those not intended for FR applications do not automatically meet the HB criteria.
While HB is the lowest UL94 flammability rating, it can only be achieved through testing.
Figure 9: Testing according to UL94 HB for materials with a wall thickness of up to 3 mm
UL94 V-0, V-1 and V-2
For these ratings, test bars are tested with the same dimensions as for the HB test and with the same sized flame, but held vertically.
In addition to the burning and smoldering time, the decisive factor is whether burning droplets form and whether they ignite the cotton wool underneath the test arrangement, which is only permissible in the case of V-2. Flaming droplets are considered to be one of the main causes of flame propagation in the event of a fire.
Figure 10: Testing according to UL94 V-0, V-1 and V-2
* Dependent on film type and thickness; GE foils can be supplied for all criteria mentioned. classifications
according to this standard are not to be understood as a hazard index for the tested or other materials in the event of an actual fire.
** Please contact our laboratory and application engineering department for further details.
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Discover now our wide-ranged job offers and have a career at Dr. Dietrich Mueller. We are looking for:
Wholesale and Foreign Traders
Graduated in Electrical Engineer.
Inquiries from everyone else about countries:
Tel: 49 4435 971010
Fax: +49 4435 971011
Email: info@mueller-ahlhorn.com
Let us know what product you are search and we will give you the Address of the right sales partner.
Direct request:
Inquiries from Great Britain:
dr Dietrich Mueller UK Limited
Tel: 44 20 80894197
Fax: + 44 20 80894198
Email: info.uk@mueller-ahlhorn.com