Thermal index

Thermal Properties. Thermal properties include heat-deflection temperature (HDT), specific heat, continuous use temperature, thermal conductivity, coefficient of thermal expansion, and flammability ratings. Heat-deflection temperature is a measure of the minimum temperature that results in a specified deformation of a plastic beam under loads of 1.82 or 0.46 N/mm (264 or 67 psi, respectively). Eor an unreinforced plastic, this is typically ca 20°C below the glass-transition temperature, T, at which the molecular mobility is altered. Sometimes confused with HDT is the UL Thermal Index, which Underwriters Laboratories estabflshed as a safe continuous operation temperature for apparatus made of plastics (37). Typically, UL temperature indexes are significantly lower than HDTs. Specific heat and thermal conductivity relate to insulating properties. The coefficient of thermal expansion is an important component of mold shrinkage and must be considered when designing composite stmctures. 

Underwrilers Laboratories Thermal Index ratings are 105 C for electrical, 90 C for mechanical without impact and 90°C (copolymerVfl5 C (homopolymer) for mechanical with impact. 

High continuous use temperatures with a UL thermal index around 215°C. 

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... 

Thermal index ratings K UL-746B 60,000-h half-life at indicated (9)... 

Heat resistance can be divided into short term such as soldering temperature resistance and long term such as maximum continuous usage temperature, or so called UL (Underwriters Laboratory) thermal index. Types I and II have been granted a 240 C index by UL. This is equivalent to PEEK (polyetheretherketone), and is superior than PES (polyethersulfone), PEI (polyetherimide) and PPS (polyphenylenesulfide). 

Figure 7. Optical Coupling due to Thermal Index Modulation.

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. 

UL. These specifications have a thermal index rating of 266°F (130°C) and a flammability rating of 94 VO. 

UL. The UL specification has a thermal index rating of 155°C (378°F) for most compounds but the glass-reinforced grades and some phenolic alloys carry a 185°C (417°F) rating. The flame retardant rating is at 94 VO in a Vig-in section. 

UL. The thermoset polyester compoimds generally carry a 365°F (180°C) thermal index rating, with a flammability rating of 94 VO in Vie-in sections. 

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. 

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