Temperature continuous use

Acrylonitrile—Butadiene—Styrene. Available only as sheet, ABS has good toughness and high impact resistance. It is readily therm oform able over a wide range of temperatures and can be deeply drawn. ABS has poor solvent resistance and low continuous-use temperature. It is often used in housings for office equipment (see Acrylonitrile polymers). 

Long-term heat-aging tests on Tefzel 280 are in progress. It is expected that its continuous-use temperature will be above 150°C. 

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. 

Over the years many attempts have been made to provide some measure of the maximum service temperature which a material will be able to withstand without thermal degradation rendering it unfit for service. Quite clearly any figure will depend on the time the material is likely to be exposed to elevated temperatures. One assessment that is being increasingly quoted is the UL 746B Relative Temperature Index Test of the Underwriters Laboratories (previously known as the Continuous Use Temperature Rating or Index). 

In the absence of fire retardants the material has a limiting oxygen index of 27.5 and may bum slowly. Only some grades will achieve a UL 94 V-1 rating. The Underwriters Laboratories continuous use temperature index is also somewhat low and similar to the polyarylates with ratings of 135-140°C (electrical) and 105°C (mechanical with impact). Initial marketing has emphasised comparisons with the aliphatic nylons for the reasons given in the previous... 

The polyacetals have a good record of performance in uses involving hot air and hot water. Plumbing components have been used for hot water service in the range 60-80°C and applications in hot air well in excess of 90°C. Recommended maximum continuous use temperatures are given in Table 19.4... 

Table 19.4 Recommended maximum continuous use temperatures for polyacetals...

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

Figure 12-6. Maximum continuous use temperature of some engineering thermoplastics. ...

The UL uses RTIs as a guideline to qualify materials for many of the standard appliances and other electrical products it regulates. This testing is done in a conservative manner qualified by judgments based on long experience with such devices UL does not apply indexes automatically. In general, these RTIs are very conservative and can be used as safe continuous-use temperatures for low-load mechanical products. 

Other terms used in connection with the maximum service temperature are the Underwriters Laboratories index and the maximum continuous use temperature (MCUT) which is usually based on 100,000 hours. One criticism of MCUT (and other similar measures) is that the changes in properties are measured at ambient temperature rather than at the operating temperature (see Section 7.1). 

As electrical insulators, PET and PEN have very similar properties. The major difference between them is the long-term thermal ageing of the respective films and the effect that such ageing has on continuous use at various temperatures. Standard PET films have a continuous-use temperature of 105 °C, as measured... 

Compared with PET, PEN has five times more radiation resistance in air, four times more in O2 and ten times more resistance in vacuum under continuous-use temperature [10]. Cakmak and co-workers calculated the refractive index of PEN this parameter is highest (nc = 1.908) along the chain axis and lowest (nn = 1.36) normal to the naphthalene ring. Biaxially oriented PEN film has a... 

PVC, the cheapest but it is necessary to study the construction carefully to avoid high temperatures exceeding the polymer s continuous use temperature... 

The continuous use temperature is an arbitrary temperature resulting from general experience and observation. It is the maximum temperature that an unstressed part can withstand... 

To give some idea, continuous use temperatures for thermoplastics are in a range from 50°C up to 400°C for exceptional families. 

Figure 3.11. Examples of continuous use temperature in an unstressed state (°C)...

The continuous use temperatures in an unstressed state are generally estimated from 90°C for LDPE up to 110-120°C for HDPE and 130°C for crosslinked polyethylenes if the softening or melting temperatures are higher. For example, the sealing temperature of a given grade of VLDPE is 83°C. 

The continuous use temperatures in an unstressed state are generally estimated from 90°C up to 130°C if softening temperatures are higher. 

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