Thermal Index is an important property for materials that will be used in applications that must withstand significant spans of time at elevated temperatures - for example, outdoor applications and electronic components and housings. There can be more than one Thermal Index for a material, each based on a different physical property. Test Procedure: Critical physical properties, and either multiple temperatures or multiple times a minimum of 4 temperatures or times must first be defined to satisfy the intended purpose of the testing. A control material, with demonstrated end use performance, may be used to enhance the reliability of the data analysis.
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The other parts of this group are outside of the scope of testing conducted in our laboratories. Test can be performed on test specimens which have undergone various pre-conditioning or even some length of thermal aging. Refer to UL A and B for more details. This usually means the test specimens are to be tested are to undergo some length of thermal aging prior to testing.
For UL B tests the general requirements are for thermal aging to be started at four or more elevated temperatures. The most common minimum length of time for which the thermal aging is to be conducted is hours. This does not mean that all long term thermal aging projects can be completed within the minimum hour requirement; the length of time needed for completion is to be agreed upon by all parties involved.
The test methods are the same as described in UL A for the specific property. The preferred test sampling method is the Fixed Time Frame Method. The Screening Test is very helpful in determining which may be the preferred sampling technique.
UL 746 Series