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There are many different polymeric materials used today to manufacture the vast array of electric cables available in the marketplace. It is, therefore, important that users have a basic understanding of the various polymeric materials that are used, to assist them in the selection of the correct cable to suit their particular application.
Almost all the materials used to make cables are compounds, not pure polymers, and they are unique to each manufacturer. As such, their characteristics and performance will not be exactly the same or give exactly the same results in tests.
Important: This guide is simply intended to provide the generic characteristics of the most popular materials; it is not intended to be used for writing detailed contracts or specifications
The most common types of insulation and sheath used are referred to as Thermoplastic; there are, however, a significant number of cables with insulations and sheaths referred to as Thermosetting.
List of Polymeric materials for cables used:
A thermoplastic polymer is one that becomes pliable or mouldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a relatively high molecular weight. The polymer chains associate by intermolecular forces, which weaken rapidly with increased temperature, yielding a viscous liquid. In this state, thermoplastics may be reshaped and are typically used to produce parts by various polymer processing techniques such as injection moulding, compression moulding and extrusion. Different thermoplastics require different temperatures to soften to the point where they will flow and become capable of being extruded or moulded. Most thermoplastics require extrusion and moulding temperatures in the region of 110oC to 180oC. Once cooled, the material reverts to its normal tough character hence the term thermoplastic.
Typical thermoplastic polymers used in cable compounds include PVC, Polyethylene, Nylon and Polyurethane.
Thermoplastics differ from thermosetting polymers, which form irreversible chemical bonds during the curing process. Thermosets do not melt when heated but can decompose and do not reform upon cooling.
Thermosetting compounds are characterised by their retention of physical properties over a wide operating temperature range. The polymers used include EPR, Silicone, PCP and CSP. They are all subject to further processing after extrusion, to promote the cross-linking required for them to attain the enhanced properties exhibited by the finished product.
These materials are also known as elastomeric compounds, or more simply known as rubbers. The polymers used do not have the same strong bond between adjacent polymer chains and thus tend to be softer at room temperature and will tend to flow when subjected to prolonged pressure. To provide resistance to deformation and to enhance chemical and physical properties, these polymers are cross-linked.
Because their properties are permanently fixed following the cross-linking process, these materials are termed thermosets.
Cross-linking, also known as vulcanisation or curing, is a chemical reaction in which adjacent polymer chains are chemically linked together, usually by the application of heat, although irradiation is sometimes used for cables for specialised applications.
The combination of being softer and the fact that after cross-linking, the polymer chains are locked together allows these materials to show elastic properties. When stretched, the polymer chains try to slide over one another, but the cross-links prevent this.
When the tension is released, the polymer returns to its original shape, which gives it elastic or elastomeric characteristics.
In general, the term Rubber and Elastomer can be considered to have the same meaning.
Regardless of being thermoplastic or thermosetting, the most common materials used in the manufacture of cables are compounds, not pure polymers. A typical compound will contain
And in the case of elastomeric and thermosetting compounds
Curing agents &#; added to promote cross-linking
Accelerators &#; added to speed up the cross-linking process
The level of additives incorporated into a compound can vary greatly depending on the polymer and the application. For some elastomeric sheathing compounds, the polymer content may be as low as 30%, whereas, for MV and HV XLPE insulation, the polymer content could be as high as 97%.
Although in common with almost all cable makers, Tratos purchase the specialised insulations that they use to produce their HV and EHV cables, Tratos have developed and compound in-house all of the other insulation and sheathing compounds that they use in the manufacture of their cables, this allows them to optimise the properties required for the particular application or market.
Regardless of the type of polymer, when applied to cables, materials fall into two broad categories of application &#; insulations and sheaths:
The purpose of insulation is simply to:
In considering the function of insulation, you must remember that the conductors in the cable are at different voltages; the voltages are different from one conductor to the next, and different from the general mass of earth.
Definition: Insulating materials incorporated in a cable with the specific function of withstanding voltage. (IEV 461-02-01)
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Definition: The purpose of a sheath is simply to protect the components within the cable from harmful external influences.
Examples of external influences include:
Definition: A non-metallic uniform and continuous layer is applied over an assembly of cores or components to ensure the protection of the cable from external influences. (IEV 461-05-03 Modified)
Tratos have produced a series of information pages containing the basic characteristics of the most popular materials available, including:
Tratos employ engineers and material technologists with years of experience and industry knowledge, who will be only too pleased to answer your questions regarding our cables and the materials that we use to make them
The compounds used in wire and cable products can impact the overall product performance. As part of UL Solutions&#; trusted Plastics Material Recognition Program, our Wire and Cable Material Recognition Program can help drive customer confidence by evaluating materials against applicable standards. Using UL Recognized Components, you may be able to eliminate the need for additional material testing for some certifications, saving you time and money.
Our Wire and Cable Material Recognition Program certifies compounds under the following categories:
For a full list of materials and compounds within each category, please refer to UL Product iQ®.
Our Wire and Cable Material Recognition Program helps industry professionals quickly source or specify wire and cable compounds and materials that meet their compliance needs and project specifications. Use the UL Component Recognition Mark to help communicate performance-related properties to customers or determine if a compound component meets your needs.
Using UL Recognized Components, identifiable through the UL Component Recognition Mark, may help save time and money for the following roles:
Upon successful evaluation through the program, customers can promote the safety and quality of their products to their existing and potential customers. Products evaluated in the Plastics Material Recognition Program are listed in the Product iQ database, which thousands of designers, engineers and suppliers use to find providers of recognized materials and components.
Polymeric materials categorized as QMTT2 are used in wire, cable and flexible lighting products. Among the UL certification tests, we conduct various identification tests to assess if the compound has changed over time.
Thermoplastic materials categorized as QMTT2 are typically intended for outdoor use. Finished products that incorporate these materials include:
Other cable types may also use QMTT2 compounds.
If a QMTT2 Recognized compound is used, certain tests may be omitted during the certification of finished cables. The eliminated tests include:
Compounds categorized as QMTM2 are used to manufacture plenum-rated cables. We analyze the compound composition; we do not conduct any safety or performance testing of the finished cable product.
NFPA 262, the Standard Method of Test for Flame Travel and Smoke of Wires and Cables for Use in Air-Handling Spaces, requires a composition characteristic analysis of the sheath and insulation/buffer layer. If you select a QMTM2-certified material to manufacture a plenum-rated cable, you eliminate the need to perform the composition identification step of the finished cable certification process.
Depending on the material, we perform one or more of the following tests to characterize the compound:
Polymeric materials for use in appliance wiring material (AWM) that has passed the applicable UL 758, the Standard for Appliance Wiring Material (AWM) tests can be recognized as a QMTN2 certified material. If extruded correctly, an AWM using a QMTN2 compound will fulfill the certification requirements in UL 758, the Standard for Appliance Wiring Material.
The use of a QMTN2 compound does not reduce the test program. However, wire manufacturers using a commercially available compound can apply for QMTN2 and AVLV2 files simultaneously. Upon successfully completing the UL Solutions evaluation, you will receive two certifications with one test program.
This program evaluates halogen content in wire and cable construction materials in accordance with UL , the Outline of Investigation for Acid Gas, Acidity and Conductivity of Combusted Materials and Assessment of Halogens. When a cable is constructed with all halogen-free combustible materials, e.g., insulation, fillers and jackets, the cable may be surface marked with the suffix &#;-HF.&#;
This program evaluates the presence of the Restriction of Hazardous Substances Directive (RoHS) restricted substances in all components of a cable. This is in accordance with UL 746R, the Outline of Investigation for Restricted Use Substances in Polymeric Materials, for nonmetallic components, and UL , the Outline for Investigation for Restricted Use in Metallic Components.
These compounds and components are covered under the Recognized component category TEPZ2. UL Certified wire and cables marked &#;-RoHS&#; are manufactured using these Recognized Components. Cable components include:
Contact us to discuss your requirements of FR Polyethylene Cable Compounds Manufacturing. Our experienced sales team can help you identify the options that best suit your needs.