Blue cable ends with insulation from silane cross-linked cable compounds which were produced using a BUSS compounder
Application

Silane crosslinked cable compounds (Sioplas®  Process)

Silane cross-linked PE compounds have proven to be cost effective materials worldwide

Polyethylenes (PE) demonstrate excellent insulation properties. A temporary increase in temperature, e.g. due to a load peak in the application as cable insulation can, however, cause full functional failure: the relatively low softening or melting ranges cause thermomechanical failure or even dripping off the insulation.

With the crosslinking of the polyethylene (PEX stands for cross-linked PE), a thermoset material can be made from the thermoplastic material. This can be used at considerably higher operating temperatures, has better mechanical properties, is more stable against organic fluids and often allows thinner wall thicknesses.

Various crosslinking methods are used. The silane crosslinked cable compounds are also described as PEX-b or Sioplas®.

Typical areas of application

Cable section with insulation compound from semi-conducting compounds
Cable end with various cable insulation layers
White raw mixture manufactured from silane cross-linked cable compounds using BUSS compounding technology

The XLPE Sioplas® process was developed by Midland Silicones (now Dow) in 1968. In a two-stage process, a peroxide-activated grafting of the vinyl silane onto the polymer chains is realised during the initial process step. In the second step, the grafted compound is extruded as cable together with a masterbatch using conventional extruders.

The crosslinking process takes place offline in a water or steam atmosphere. Since this process was developed, BUSS Co-Kneaders have been used for the first step and for manufacturing the catalyst masterbatches.

Silane cross-linked cable compounds on a PE basis have proven themselves globally as the most economical for use in cable insulation applications up to voltages of 10 kV and are manufactured in large quantities.

Further insights into our options for cable applications

Benefits

BUSS compounding systems for silane cross-linked cable compounds (Sioplas® Process) offer the following specific benefits

The BUSS Co-Kneader guarantees intense distributive mixing, as the superimposition of rotation and axial movement of the mixing and kneading screw causes flow separations and a large number of shearing surfaces, thereby generating cross-channel mixing.

Thermal sensor pins which can be installed everywhere along the process section enable optimal temperature control because the temperature limits for the respective compound can be monitored precisely. That ensures high precision because the thermal sensor pins are permanently surrounded by molten compound and the influence of housing tempering can be practically neglected. This is an important component of online quality control.

Injection pins, which can be mounted in the BUSS Co-Kneader at any position along the process zone, allow liquid components to be injected directly into the molten polymer at the optimum location for the process. The mixing process begins immediately, without smearing on the barrel wall and enables mixing over the shortest possible process length.

A large number of mixing cycles is achieved with the latest BUSS multiple-flight Co-Kneaders in the compounding machinery. The unique new screw geometries enable maximized splitting and recombining of the compounds, with numerous striations and excellent mixing over a very short process length.

The BUSS Co-Kneader allows precise temperature control due to controlled energy input and uniform, moderate shear rates as well as their temperature monitoring by thermocouples, which are mounted in drilled kneading pins surrounded by polymer at relevant positions along the process section.

Compounding requirements

according to the Sioplas® process

The grafting process requires targeted process management with regard to temperature profile and residence time. The liquid silane peroxide mixture is dosed into the polymer melt via a gravimetric membrane or piston dosage pump and intensively mixed distributively. The silane molecules are bonded to the polymer chains via radical grafting. This process requires specific timing at corresponding temperatures.

In this reactive compounding process, the following properties of the BUSS Co-Kneader within the compounding system are of central significance for the production of silane cross-linked cable compounds: The silane peroxide mixture can be directly injected into the melt pool at the optimum position in terms of process technology. The immediate onset of distributive mixing allows evenly high grafting utilisation and minimizes scorching effects compared to alternative systems.

The silane crosslinking process can be monitored by compound temperature measurements in the process zone at all times. This allows online quality assurance and control.

The pressure build-up step is implemented with a pre-pressure controlled melt pump which feeds underwater granulation for shaping. Therefore, it can be optimized independently. The hinged BUSS Co-Kneader housing ensures quick access and high system availability. All these competences together are why BUSS compounding technology excels in the production process of silane cross-linked cable compounds.

The modular and therefore adaptable structure of the entire compounding system and widely supported BUSS process expertise make the BUSS Co-Kneader the best choice since development of the process for compounding silane cross-linked cable compounds for cable insulation and offer maximum investment security.

Typical plant layout

Typical plant layout for compounding silane cross-linked cable compounds

COMPEO compounder setup for manufacturing silane cross-linked cable compounds

Take a look at our typical plant layout for silane cross-linked cable compounds in our COMPEO showroom.

Get to know our COMPEO compounder series

BUSS Co-Kneaders

worldwide

Our patented Co-Kneaders are used worldwide nowadays, supporting our customers in the production of plastics. With BUSS compounding systems, our customers can master all the demanding requirements for manufacturing silane cross-linked compounds.

World map with an overview of the Co-Kneaders used for cable compounding

Number of Co-Kneaders used for manufacturing cable compounds

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COMPEO series

We present: COMPEO, the state-of-the-art compounder that offers more versatility in its application, higher flexibility in process engineering, and increased added value in compound manufacturing.

XLPE insulation

Peroxidic cross-linked cable compounds are also referred to as PEX. The process was patented during the 1960s and has been used in the cable industry since then.

PVC cable compounds

Depending on the requirements profile, different plastics are used for manufacturing cable insulation with BUSS compounding systems. These include polyolefins, TPE, PPE, EEFE, PVA and naturally flexible PVC cable compounds.