Polyamide Compounding Systems

Polyamide (PA) or Nylon based compounds belong to the technical plastics sector, often known as Engineering Plastics due to their main strengths and respective applications: technical components for stringent mechanical and thermal requirements, with good resistance to aggressive chemicals and demanding environments.

Polyamides were developed by DuPont and launched in 1934. First used for textiles and fabrics of all kinds, their applications were soon extended to include injection moulding and extrusion. Further development then focused on application temperatures and reduction of water absorption. Semi-aromatic high-performance polyamides, also known as polyphthalamides (PPA), are heat distortion resistant up to 280°C. The other outstanding properties of PA include high rigidity, good electrical characteristics, and highly attainable flame retardancy.

Compounding requirements for polyamide compounds

These specific characteristics are programmed at the compounding stage, often using a combination of reinforcing agents, fillers, flame retardants and other additives. Compounding polyamides is therefore very demanding and requires customized solutions accordingly. These solutions are given with the BUSS polyamide compounding systems. Specific energy inputs have to be as gentle as possible, large amounts of fillers and flame retardants have to be perfectly distributed, and reinforcement fibres must be added so as to optimize mechanical properties while at the same time maintaining high dwell times in the respective process zones.

Although contradictory in part, all these requirements are well mastered by sophisticated process technology. The BUSS Kneader has proven itself again and again for compounding such highly demanding materials. This is mainly because of its moderate and uniform shear rates, which can be customized, if necessary, to ensure precise temperature control. As a result, just enough energy is dissipated in the melting zone to avoid overstressing the polymer fractions. Thanks to high folding rates, the fillers and flame retardants are optimally distributed over the shortest possible processing length. The reinforcement fibres added, if necessary, downstream are separated and sheathed in order to preserve maximum fibre length. Even with the narrowest process window such as for PPA based materials, with only 30°C temperature margin between melting and incipient breakdown. it is possible to achieve the best characteristics profile also at the highest viscosities.

Special characteristics of PA for parts in motors can be easily produced with BUSS polyamide compounding systems.

The BUSS Kneader’s two-stage system clearly separates the compounding and pressure build-up stages so that each stage can be independently optimized. The hinged housing of the BUSS Kneader ensures fast and easy access for high system availability. Together with broadly based BUSS process expertise, the modular design and therefore adaptable arrangement of the entire compounding line make the BUSS Kneader within the whole polyamide compounding system first choice for complex polyamide production at high quality levels, with maximum investment security.

Typical plant layout for polyamide compounding systems

Typical plant layout for polyamide compounding systems

BUSS polyamide compounding systems offer the following specific benefits

  • High filler loadings
    Filler loadings up to 90% are possible with BUSS technology thanks to 2 or 3 feed openings, separate gravimetric feeding of filler, removal of trapped air by back venting, and excellent conveying efficiency. The moderate shear rates allow perfect handling of the highest viscosities at such high loadings.

  • Intensive mixing at low specific energy input
    BUSS multiple-flight Kneaders of the latest generation achieve better mixing at 15-40% lower overall specific energy input. This is because of an increased number of mixing cycles according to the needs of each individual process section. The energy for melting and mixing is provided almost entirely mechanically and optimally dissipated according to the imparted shear rates.

  • Precise temperature control
    The BUSS Kneader has been well known for precise temperature control since more than 6 decades. This is achieved via controlled energy input due to uniform, moderate shear rates and precise temperature monitoring by thermocouples mounted in pins along the barrel.

  • Degassing of volatiles
    Volatiles are typically removed by a vacuum degassing opening at the end of the barrel or optionally in the discharge unit. Continual highlevel compound surface renewal is achieved with the large number of mixing cycles, striations and foldings created by the BUSS Kneader, thus enabling entrapped air or volatiles to be removed completely.

  • Temperature monitoring at any position
    Temperature control within the limits of the compound can be monitored by replacing mixing pins with thermocouple pins anywhere along the process section. Accuracy is assured since the thermocouples are constantly surrounded by molten compound. This feature enables online quality control.

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  • Laboratory Kneader MX 30