When customers ask us about DuPont™ Vespel® the most often asked question is about UL approvals. The properties of Vespel® are ideal for high heat applications. Does DuPont™ Vespel® meet UL ratings for plastics? If so, which DuPont™ Vespel® meets which UL approval?
What Are the Different UL Approvals for Plastics and What do they Mean?
The UL 94 rating is specifically for plastics flammability. Underwriters Laboratories created this standard to give people a consistent standard to be able to communicate and compare different types of plastics and how they react to flame. The system goes from lowest being the least flame retardant, to the highest being the most flame retardant. The rating also gives information about the exact testing method used such as:
- Was the material vertical or horizontal
- How thick
- Were colors added
All of these can vary how a material such as DuPont™ Vespel® will react when exposed to flame. In the selection of materials for high heat applications, electronics, or areas that have potential for fire, UL ratings and their purpose must be fully understood and considered carefully.
One possible example is the Boeing Dreamliner. Although it will likely take years to determine, the materials used in the Boeing 787 Dreamliner are being carefully looked at with an eye toward the UL ratings and whether or not selected materials were used appropriately with regard to their rating.
- UL 94-5VA Surface Burn; Burning stops within 60 seconds, test specimens MAY NOT have a burn-through (no hole). This is the highest (most flame retardant) UL94 rating.
- UL 94-5VB Surface Burn; Burning stop within 60 seconds, test specimens MAY HAVE a burn-through (A hole may be present)
- UL 94 V-0 Vertical Burn; Burning stops within 10 seconds, NO flaming drips are allowed
- UL 94 V-1 Vertical Burn; Burning stops within 60 seconds, NO flaming drips are allowed
- UL 94 V-2 Vertical Burn; Burning stops within 60 seconds, Flaming drips ARE allowed.
- UL 94 H-B Horizontal Burn; Slow horizontal burn test (H-B) are considered self-extinguishing”. This is the lowest (least flame retardant) UL94 rating.
UL Ratings and the Typical Properties of DuPont™ Vespel®
|ASTM or UL test||Property||SP-1||SP-21||SP-22||SP-211||SP-3|
|–||Filler Material||Unfilled||15% Graphite||40% Graphite||10% PTFE, 15% Graphite||15% Moly|
|D792||Density (lb/in³) (g/cm³)||0.051 1.43||0.055 1.51||0.060 1.65||0.056 1.55||0.058 1.60|
|D570||Water Absorption, 24 hrs @ 73°F (%) 48 hrs @ 122°F (%)||0.24 0.72||0.19 0.57||0.14 0.42||0.21 0.49||0.23 0.65|
|D638||Tensile Strength, Ultimate @ 73°F (psi) @ 500°F (psi)||12,500 6,000||9,500 5,500||7,500 3,400||6,500 3,500||8,200 –|
|D638||Tensile Modulus (psi)||–||–||–||–||–|
|D638||Tensile Elongation, Ultimate @ 73°F (%) @ 500°F (%)||7.5 6.0||4.5 6.0||3.0 2.0||3.5 3.0||4.0 –|
|D790||Flexural Strength, Ultimate @ 73°F (psi) @ 500°F (psi)||16,000 9,000||16,000 9,000||13,000 6,500||10,000 5,000||11,000 5,500|
|D790||Flexural Modulus @ 73°F (psi) @ 500°F (psi)||450,000 250,000||550,000 370,000||700,000 400,000||450,000 200,000||475,000 270,000|
|D695||Compressive Strength, 10% strain @ 73°F (psi)||19,300||19,300||16,300||14,800||18,500|
|D695||Compressive Modulus (psi)||350,000||420,000||475,000||300,000||350,000|
|D256||IZOD Notched Impact (ft-lb/in)||0.8||0.8||–||–||0.4|
|D696||Coefficient of Linear Thermal Expansion (x 10-5 in./in./°F)||3.0||2.7||2.1||3.0||2.9|
|D648||Heat Deflection Temp (°F / °C) at 264 psi||680 / 360||680 / 360||–||–||–|
|–||Max Continuous Operating Temp (°F / °C)||500 / 260||500 / 260||500 / 260||500 / 260||500 / 260|
|C177||Thermal Conductivity (BTU-in/ft²-hr-°F) (x 10-4 cal/cm-sec-°C)||2.0 6.9||6.0 20.7||12.0 41.3||5.3 18.3||3.2 11.0|
|D149||Dielectric Strength (V/mil) short time, 1/8″ thick||560||250||–||–||–|
|D150||Dielectric Constant at 1 MHz||3.55||13.2||–||–||–|
|D150||Dissipation Factor at 1 MHz||0.0034||0.0106||–||–||–|
|D257||Volume Resistivity (ohm-cm)at 50% RH||1014 – 1015||1012 – 1013||–||–||–|
How long before the material stops burning (It must stop within 10 seconds for approval) Remember that UL ratings do not tell you the operating temperature of a material. UL ratings only refer the the behavior of a material when it if exposed to a flame source. Material sample are held over an open flame from a Bunsen Burner. After being ignited and allowed to burn the material is removed and testers monitor:When considering use of DuPont™ Vespel® and it’s UL rating there are other important factors to consider:
- If material continues to burn does it drip or run. If it does, the material cannot be UL approved
This article by Homi Ahmadi in Compliance Engineering’s online magazine gives a good description of UL approvals for the electronics industry.
For more in-depth information and the UL-94 ratings and how it relates to plastics beyond DuPont™ Vespel® check out the UL website. http://www.ul.com/global/eng/pages/offerings/industries/chemicals/plastics/testing/flame/
For more information on the DuPont™ Vespel® materials Download our guides or view a brief video on how to machine DuPont™ Vespel®
Sales and Marketing Manager, DuPont™ Vespel®
ThyssenKrupp Materials NA
AIN Plastics Division