PVC Cable Compounding Systems

Soft PVC cable insulation compounds

Depending on requirements, cable insulation mass by BUSS compunding systems utilizes various different plastics. They include polyolefin, TPE, PPE, EEFE, PVA, and of course soft PVC compounds. PVC has been used for cable insulation since 1932, originally as a replacement for rubber. Due to their relatively high dielectric strength, leading to corresponding induction losses and heating, soft PVC cable insulation compounds are only used at AC voltages of up to 10 kV. Most soft PVC cable mass applications are in this field. Formulations can be adjusted to customize the application temperature range, mechanical characteristics and flexibility of use, flammability and processing.

Here are two examples:

  • Softener formulation adjustment can raise the continuous operating temperature limit to 105°C.
  • Aluminium trihydroxide (ATH) additive can systematically reduce flammability and smoke formation. Regulatory authorities such as the VDE, EN or UL issue standardized property profiles for insulation and coating compounds.

Typical applications

The main application fields of cable insulation mass produced with PVC cable compounding systems by BUSS are power transmission up to the aforesaid 10 kV, domestic installations above all in private housing, and data transmission in general. The automobile industry almost exclusively uses soft PVC compounds.

Cable ends from soft pvc cable insulation compounds as an example for PVC cable compounding systems.

Compounding requirements

PVC cable mass is usually compounded in two stages: hot/cold mixing in the powder phase, followed by compounding and pelletizing on a BUSS Kneader.
Compounding requirements can be summarized as follows. The plasticizers and other constituents like stabilizers, additives, fillers, reinforcements, flame retardants and others. are absorbed in the porous PVC grain and then must be systematically gelled, dispersively and distributively mixed, and agglomerated. This is all in compliance with well defined temperature limits. Custom-tailored property profiles lead to a wide variety of formulations, with efficient production in rather decreasing batch sizes.

The BUSS Kneader can make the most of its strengths profile at uniform, moderate and if necessary, adjustable shear rates. A range of output rates can be achieved on a given BUSS Kneader size according to the requirements of the customer.

In most cases all product variations can be covered with a universal shaft geometry designed to suit the formulations portfolio. Furthermore, the modularity of the entire system (shaft geometry, fittings, forming options, etc.) always enables adjustment to comply with different requirements. This is important for maximum security of investment.

With its low specific energy requirement for the most intensive mixing processes, simple volumetric scale-up, and maximum availability over a wide operating range, the BUSS Kneader within the BUSS PVC Cable Compounding Systems clearly remains first choice for compounding PVC cable mass.

Typical plant layout for PVC cable compounding systems

BUSS PVC cable compounding systems offer the following specific benefits

  • Compounding and pressure build-up optimized in two independent steps
    Mixing on the BUSS Kneader and pressure build-up in the discharge unit are separated to enable the efficient optimization of both steps. This compounding system allows mixing at low pressure and temperature as well as optimized pelletizing, while maintaining temperature control at all times.

  • Wide range of formulations and throughput with one screw configuration
    While processing a wide formulation range with one screw profile is challenging, the BUSS Kneader reciprocating single screw technology is well known for this specific capability, thanks to a process length typically half that of most other systems, moderate and adaptable shear speeds, and great flexibility in screw configuration design.

  • Intensive mixing at low specific energy input
    BUSS multiple-flight compounders 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.

  • Low process temperatures
    The separate execution of compounding in the BUSS Kneader and pressure build-up in the discharge unit allows mixing at low pressure and temperature. The requirements of each individual process section are addressed with ingenious screw designs for optimized temperature profiles.

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

Learn More