Relative thermal indices

Arrhenius plot A linear Arrhenius plot is extrapolated from the Arrhenius equation to predict the temperature at which failure is to be expected at an arbitrary time that depends on the plastic s heat aging behavior. It is usually 11,000 hours, with a minimum of 5,000 hours. This is the relative thermal index (RTI). 

Relative thermal index Section UL 746B provides a basis for selecting high temperature plastics and provides a long-term... 

RLT reverse laminate theory RTI relative thermal index... 

The relative thermal index is an indicator of a material s long-term resistance to degradation of its electrical, tensile, and impact properties at operating heats. This index is based on tests made to determine the half-life of these properties at elevated heat (i.e., the heat at which the plastic will retain at least one-half of its original properties for the projected life of an electrical appliance or product, up to 100,000 hours), such as summarized in Fig. 10-2. 

The Relative Thermal Index is based on a method developed by Underwriters Laboratories. It is defined as the temperature at which a physical property retains 50 % of its initial value for a period of 60,000 hours. Relative thermal index temperatures (in °C) are given for some common plastics in Table 1. 

Electrical components (connectors, housings, lighting components) Information technology Lighting Computer and business equipment UL, CE Relative thermal index (RTI) Glow wire temperature... 

RTI Relative thermal index (formerly named continuous-use temperature) is the maximum service temperature at which the critical properties of a material will remain within acceptable limits over a long time, as established by UL 746B. There can be up to three independent RTI ratings assigned to a material ... 

Polyamide-imides enjoy exceptional thermal stability with a decomposition onset at 500°C and 10% weight loss at 540 C. Long-term aging at high temperatures (250°C) shows only a 80 to 90% drop in tensile strength after 10,000 h (see Fig. 12.19). The UL relative thermal index (RTl) predicts 100,000 h of useful life at temperatiures as high as 220°C. 

Good thermal stability relative thermal index (RTI) to 125°C]... 

Compared to other engineering plastics, PPS compounds exhibit a superior combination of both elevated-temperature mechanical integrity and long-term resistance to thermal degradation. Table 15.8 compares the elevated-temperature performance of various reinforced engineering plastics as indicated by the heat deflection temperature and UL relative thermal index (RTI). 

Figure 4-13. An example of room-temperature tensile strength retention at 204 C (400°F), based on the UL s relative thermal index (RTI) test.

Relative Thermal Indices. The relative thermal index of a polymeric material is an indication of the material s ability to retain a particular property (physical, electrical, etc.) when exposed to elevated temperatures for an extended period of time. It is a measure of the material s thermal endurance. For each material, a number of relative thermal indices can be established, each index related to a specific thickness of the material (9). 

Relative Thermal Index Based Upon Historical Records. Through experience gained from testing a large volume of complete products and insulating systems over a long period, UL has established relative thermal indices on certain types of plastics. These fundamental temperature indices are applicable to each member of a generic material class. Table 3-1 lists the temperature indices based on past on past field test performance and chemical structure. 

In order to determine the relative thermal index, a control material with a record of good field service at its rated temperature is selected. The control material of the same generic type and the some thickness as the candidate material is preferred. At least four different oven temperatures are selected. The highest temperature is selected so that it will take no more than two months to produce the end-of-life of the material. The next two lower temperatures must produce the anticipated end-of-life of 3 and 6 months, respectively. The lowest temperature selected will take 9-12 months for the anticipated results. 

The long-term, continuous-use temperature resistance ranges from about 120 to 125 °C, as measured by the UL 746B relative thermal index (RTI) test, which places its performance closer to that of the engineermg polymers such as polybutylene terephthalate (PBT), liquid crystal polymers (LCP), and polyethylene terephthalate (PET) than to that of performance polymers such as polyphenylene sulfide (PPS), polyether sulfone (PES), and polyamide imide (PAI). 

Relative thermal index for 3 mm thickness Not stabilized Electrical Mechanical 125 125 65 57-59... 

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