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    See-through Kettles may not be a transparent material selection.

    See-through Kettles may not be a transparent material selection.

    transparent material

    We like our see-through kettles and take them for granted but they have a punishing life cycle.  Over 10 years the kettle could undergo a total of 10,000 cycles. It is filled with cold water, heated up in a few minutes to boiling point and rapidly cooled when emptied.

    You might expect polycarbonate, with a heat distortion temperature of 140oC, to cope with the temperatures involved. However, you also have to think about the time factor and the rapid and repeated temperature swings.   A designer might consult the data sheets and assume that polycarbonate, with a ‘continuous use temperature’ in excess of 100oC would be a safe material to use.   On the other hand, a chemist would see polycarbonate as an ester, subject to attack by water, particularly at elevated temperatures.  A physicist would have concerns about the cyclic expansion and contraction leading to fatigue.  A moulder would be wondering about residual moulding strain leading to environmental stress cracking.

    When the BSH Group were designing their latest kettle, they set a target of 10,000 test cycles and found that most polycarbonates had difficulty in meeting that requirement.  They had to turn to Lexan 1443T, a copolymer of polycarbonate and polysiloxane, from Sabic Innovative Plastics. It survived 12,000 cycles and offered good chemical resistance, outstanding surface finish and the required balance of ductility and melt viscosity.

    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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    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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    Understanding the difference between SBS & SEBS thermoplastic elastomers?

    The difference between SBS and SEBS thermoplastic elastomers explained.

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    Is MFR really much help to moulders these days ?

    Often a moulder has to change material grades. One of the first properties to be consulted on the new data sheet is usually the MFR. This is to establish if the new grade has the same melt viscosity performance.

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    What gives Moulders a Warped View on Life?

    Warping is one of the most frustrating injection moulding faults. This is because it does not always appear immediately, the causes are complex and prevention is difficult.

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