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For the power cable industry, and especially in automotive cables, it is crucial to achieve total insulation of the electrical conductor (copper or aluminium, in most cases), and the spark test is widely used to ensure that every centimetre produced is fully insulated.

  • Delta Tecnic reduces the granule size tenfold to achieve better dilution of the masterbatch in the cable compound.
  • 25% of the company’s sales are in the automotive industry, where satisfactory spark test results are more difficult to achieve.

Insulation of the electrical conductor

The spark test aims to detect any holes in the plastic layer covering the cable conductor, known as insulation and, consequently, a leakage of electrical current. Even if the holes are small, they can cause unwanted effects such as energy leaks and loss of electricity, creating serious problems in an electrical circuit.

In the case of Delta Tecnic, a leading manufacturer of colour masterbatch, 25% of colour masterbatch sales are in the automotive industry, which is precisely the sector that presents the most difficulty in obtaining satisfactory spark test results, due to the use of shorter, high-speed dilution machines. Industry requirements have led Delta Tecnic to achieve excellence in the design and control of its masterbatches with the aim of reducing the faults detected by the spark tester.

Cable insulation: how to minimise spark test failures

The conductor cable, with its respective insulation, passes through the spark tester device, which subjects the cable to a high-voltage electric field to detect any leaks. If an electrical reaction occurs, the device emits a warning signal. In this regard, it is crucial to avoid the presence of large unwanted particles in the cable insulation.

Holes may be caused by the poor dispersion of the products used in the insulation mixture. Plastic insulation is made up of two materials: generally, 98% is a polymeric compound either manufactured by the same cable manufacturer or supplied by companies specialised in compound manufacturing, while the remaining 2% is the colourant provided. Both of these raw materials may contain particles that are poorly dispersed or poorly incorporated into the polymeric mass, resulting in the formation of holes. These holes will result in a failed spark test and, therefore, poor insulation in the electrical conductor.

A poorly manufactured masterbatch can be one of the causes of these holes, due to the presence of excessively large particles in the polymer. It is essential that the masterbatch used in the cable industry achieves the best possible pigment dispersion. Pigment dispersion involves breaking the crystalline units that make up the pigments through a mechanical process using extruders, preventing them from remaining inside the masterbatch.

There is another possible fault, which relates to dilution. During cable manufacturing, the masterbatch used may not be properly diluted in the customer’s compound, and the resulting large unwanted particles can cause holes in the insulation. The concept of dilution implies proper mixing during the extrusion process of the cable insulation layer, where the masterbatch is fully compounded and melted into the polymeric base used.

However, in some cases, customers may face difficulties in diluting masterbatches as the cable industry is increasingly working with faster and shorter extruders that make this process more complex. Therefore, the challenge for the masterbatch manufacturer is to achieve the best dilution possible, which requires an appropriate temperature and mixing process.

Manuel Miret, Area Manager & New Product Developer at Delta Tecnic, states: “At Delta Tecnic, we strive to provide solutions that drive the advancement of the cable industry and improve the quality of cables used in various sectors. Our focus on the optimal dispersion of pigments and the formulation of our masterbatches to achieve a perfect dilution is essential to guarantee the excellence of manufactured cables and optimal results in the spark test during manufacturing.”