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    What do we mean by the Heat Resistance of thermoplastics?

    In some applications heat resistance can mean the material’s ability to carry out its intended function at elevated temperatures for short periods.  Otherwise it may imply surviving high temperatures for long periods or coping with very high temperatures for short periods during processing.

    EngineBayBonnet What do we mean by the Heat Resistance of thermoplastics?

    For short term exposure

    The main concern is often the softening. This is when the thermoplastic approaches glass transition temperature (in the case of amorphous thermoplastics) or melt transition temperature (for semi-crystalline thermoplastics). Material datasheets will provide data on ‘Deflection Temperature Under Load’. However, designers are reminded that this applies to a narrow test. This involves specific loads, geometry, heating rates and also acceptable deflection. These may or may not coincide with the service conditions and criteria for failure.  At least the test does give data for two levels of loading.

    For long term ageing

    Designers should be aware of this. ‘Continuous Use Temperature’ usually refers to the temperature at which the mechanical properties decrease by 50%. This is after a period of 5000 or 20,000 hours, which again may or may not cover all scenarios.

    Here is a useful rule of thumb for processors. Raising the processing temperature by 10oC will roughly double the extent of thermal degradation in the same time frame.   Processors may be  tempted to push processing temperatures 5 degrees beyond the recommended limits. In attempting to reduce melt viscosity and make processing easier, they could inflict damage. Although not obvious, this may eventually affect the properties of the product.

    Finally, more information on this topic may be available on the excellent British Plastics Federation website.

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    Coping with weld lines

    In injection moulding, weld lines (knit lines) form when two melt fronts meet. If the melt fronts do not coalesce completely, at best there will be a cosmetic flaw. At worst there will be a mechanical weak-spot, with strengths of the order of 10 - 90 % of the material potential.

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    What determines friction between thermoplastic components?

    Friction is an important property for thermoplastics in bearings and gears but also has a part to play in assembly of plastic parts (snap-fit and interference-fit) and ejection during moulding.

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    Will Styrenic thermoplastics evolve further to meet design demands ?

    Styrenic thermoplastics?

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    Polypropylene: the Workhorse of the Plastics Industry

    Polypropylene. Little did Karl Zeigler or Giulio Natta realise, 60 years ago, when they were developing a catalyst system to produce a useful thermoplastic from the inexpensive monomer, propylene, that their work would have such far reaching consequences.

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    What makes medical grade plastics so special?

    Toughness and transparency are important properties for the constituents of intravenous lines.

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    The Long and the Short of Fibre Reinforcement of Thermoplastics

    Fibre Reinforcement. The advantages of adding glass fibre to thermoplastics to increase stiffness (modulus), strength, heat distortion resistance and dimensional stability are well known.

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    What causes mouldings (and moulders) to be off-colour?

    When mouldings are not the intended colour, the first thing to check is the raw material, particularly the dosing rate, if you are using masterbatch, and the quality of regrind.

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    Transparent ABS can be a clear winner

    Transparent ABS. Mentioning transparency in the context of ABS moulding materials can raise a few eyebrows. This is because ABS is normally taken to be opaque and indeed the vast majority of grades of ABS are opaque.

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    Where are Engineering Thermoplastics Blends going ?

    The timeline of appearance of materials for the plastics industry can be viewed as several overlapping phases.

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    Understanding the difference between SBS & SEBS thermoplastic elastomers?

    The difference between SBS and SEBS thermoplastic elastomers explained.

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