Please note that we only supply polymer in granular form for Injection Moulding or Extrusion applications. We do not supply polymer in rod, sheet or block form.

    Our team are available from 8am-5pm and we always aim to get back to you the same day. If you would rather contact us immediately please join us on live chat or give us a call on 0141 952 1900.

    < Back to home

    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.

    gear train 2 thermoplastic components

    When two surfaces rub together the resisting force is the combination of two effects at the surfaces. First is an adhesion force, caused by attraction between the two surfaces at a molecular level. Secondly there is a deforming force, related to the deformation of the nano-scale ‘peaks’ on the surfaces.  Because these two mechanisms stem from different characteristics of thermoplastics, it is difficult to predict overall friction from first principles. Values of the coefficient of friction have to be acquired from physical tests.

    Despite what you learned at school, the coefficient of friction for thermoplastics is not entirely independent of load and velocity.  You would be correct in thinking that temperature is another variable.  For smooth surfaces and low speeds, the adhesion factor dominates, favouring non-polar materials such as PTFE and HDPE.   At high speeds and rough surfaces, the deforming force is more important, favouring more rigid thermoplastics, either from high crystallinity (polyacetal) or with reinforcing fillers (glass or carbon fibre).  Low levels of additives (PTFE, silicone and molybdenum disulphide) can significantly reduce friction.

    Data for thermoplastics rubbing against steel are fairly readily available but not for two thermoplastics in contact.  In both cases data will be for a limited set of conditions, probably unrelated to the service condition in question.

    Friction between components of the same thermoplastic can be considerably higher than for dissimilar materials, which is why different thermoplastics are used for alternate cogs in gear trains.  If no data is available, selecting HDPE for the alternate gears is normally a safe choice for minimising friction ………….but wear is another story.

    coeff friction a

    For information on all the specified grades that we can offer please contact us today or try our polymer search.

    Search results

    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.

    Read more >

    Will Styrenic thermoplastics evolve further to meet design demands ?

    Styrenic thermoplastics?

    Read more >

    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.

    Read more >

    What makes medical grade plastics so special?

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

    Read more >

    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.

    Read more >

    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.

    Read more >

    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.

    Read more >

    Where are Engineering Thermoplastics Blends going ?

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

    Read more >

    Understanding the difference between SBS & SEBS thermoplastic elastomers?

    The difference between SBS and SEBS thermoplastic elastomers explained.

    Read more >

    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.

    Read more >