Plastic products are increasingly required to meet flame resistance tests in the applications of electrical, electronic and appliance markets.
Plastic products are increasingly sourced globally and are required to meet the internationally accepted global standards. Underwriter Laboratories, originally from USA, has developed flame resistant standards that are accepted by global customers. To market plastic products, converters are required to obtain the recognition of these products from Underwriter Laboratories Inc. To meet the demand of the international plastic processors Underwriter Laboratories have set up facilities all around the World including at Bangalore in India.

Flammability testing is usually the first step toward obtaining plastics recognition. The standard used to establish this recognition is UL 94, "Tests for Flammability of Plastic Materials for Parts in Devices and Appliances", which contains the following tests: HB, V, VTM, and 5V, HBF, HF and Radiant Panel.
HB flame rating would typically be acceptable for portable, attended, intermittent-duty, household use appliance enclosures (i.e. hair dryers) or for decorative parts. The test involves the measurement of the burning rate of a material and is usually applicable to non-flame retardant materials.
V-0, V-1 and V-2 flame ratings would typically be acceptable for portable, unattended, intermittent-duty, household-use appliance enclosures. The test involves the measurement of the ability of the material to extinguish itself and is applicable to flame retardant materials. The criteria for assigning a 94V rating are as follows:

TM test is performed for materials that distort, shrink or are consumed up to the holding clamp in the V test, due to their thinness, and are therefore not suited to a V rating. The criteria for the assignment of VTM-0, -1 or -2 ratings are the same as for V.
Materials used in non-structural applications (i.e. acoustical foam) are tested for HBF, HF-1 or HF-2 ratings.
A 5VA or 5VB rating is required for materials used as an enclosure for products that are of such a size that they are not easily moved, or are attached to conduit systems. This test is conducted on both bar and plaque samples. These materials must also comply with the requirements for a V rating. Materials that do not exhibit burn through of the plaques receive a 5VA rating, whereas burn-through warrants a 5VB rating.

Radiant Panel test is conducted to measure and compare the surface flammability of materials when exposed to a prescribed level of radiant heat energy. Its principle use is for rating materials that may be used in applications having a large surface area, where UL is concerned with the ability of the flame to spread across the surface of the material.

In addition to the flammability tests, infrared analysis, thermogravimetric analysis, differential scanning calorimetry and density may be conducted for the purpose of determining that the original material composition that was tested remains unchanged.
UL94 recognition is not intended for use in judging the acceptance of building materials, furnishings or related contents, and cannot be used to interpret fire resistance in a field situation.

Material that is to be used in electrical insulation and/or mechanical support applications may be required to possess other property characteristics in addition to flammability ratings. These additional property characteristics may be obtained by conducting tests contained in the Standard for "Polymeric Materials - Short Term Property Evaluations", UL 746A. The results of these tests are examined in UL 746C, the standard for "Polymeric Materials - Use in Electrical Equipment Evaluations", to determine the acceptability in a specific application. Many end-product standards reference UL 746C for their plastic requirements.

The first group of tests is the resistance to ignition tests, and is conducted in two or more thicknesses. The remaining tests are tested in one thickness, which is considered representative of all other thicknesses.
Hot Wire Ignition (HWI) is typically required of a material when it is in contact with or in close proximity (typically within 0.8 mm) to uninsulated live parts.
High-Current Arc Ignition (HAI) is applicable if the material is in contact with or in close proximity to uninsulated live parts (typically 0.80 mm for non-arcing parts or 12.5 mm for arcing parts).
High-Voltage Arc Resistance to Ignition (HVAR) is also required by various end-product standards when the material is used in contact with uninsulated live parts.

The second group of tests is the Tracking Tests.
Comparative Tracking Index (CTI), High Voltage Arc Tracking Rate (HVTR) and Inclined-Plane Tracking are typically required of the material when it is used in contact with or in close proximity (within 0.80 mm) to uninsulated live parts and 1) live parts of opposite polarity, or 2) dead metal parts that may be grounded in service or 3) any surface exposed to contact. CTI and/or HVTR are applicable where the voltage potential is 600 volts or less.
Inclined-Plane Tracking is more applicable where the voltage potential is between 601 volts and 35 kV.
A High-Voltage Low-Current Dry Arc Resistance (ASTM D-495) rating is typically required when a material is used in high voltage television applications.

The third group of tests is the insulation tests.
Volume resistivity, surface resistivity and dielectric strength are typically required of materials serving as electrical insulation or enclosures of uninsulated live parts.
The fourth group of tests is the thermal deflection and dimensional change tests.
Heat deflection temperature, Vicat softening point and ball pressure tests are used to determine the temperature at which a material softens under a specified load. However, only one of these tests needs to be conducted for a given material.

In addition, dimensional stability and water absorption tests can also be conducted to determine the material's ability to resist dimensional and weight changes when exposed to moisture. These ratings are typically required of materials when used in applications which could be exposed to water or high humidity.

The last group of tests is the mechanical properties. These tests are typically conducted for one of two reasons. The first reason is when the material is required to maintain the position of a specified part, be it electrical or mechanical. The second is for your customers to have third-party data available to them for material substitution. The five tests in this category are tensile strength, flexural strength, tensile impact, izod impact, and charpy impact. Again, not all of these tests are necessary for each material. Generally, tensile strength and impact tests are performed on thermoplastics and flexural strength and izod impact on thermosets. Charpy impact may be performed on both thermoset and thermoplastic materials.

The last portion of plastics recognition is the assigning of a relative thermal index to the material. The temperature rating of a material is obtained in one of two ways. The first way is to use the temperature rating associated with the generic type of the material. A complete list of materials with generic indices greater than 50 ° C is provided in Table 35.1 of UL 746C and Table 7.1 of UL 746B. All other materials are assigned a 50 ° C rating.

The second way temperature indices are assigned is when the manufacturer requests a higher temperature rating for his material than has been assigned through the generic table. The process for obtaining this higher temperature is called long-term thermal aging, and is outlined in UL 746B.

Underwriter Laboratories Inc. in India can be contacted at their Bangalore office at the following contact details.
B. Nagendra – Manager Business Development / S. V. Srikanth – Executive Technical Support (Industrial)
Telephone : +91 80 41384400 , Customerservice.in@in.ul.com