Induction pre-heating of wire
Nokian Tyres is not only the largest tyre manufacturer in the Nordic countries, it is also one of the most profitable tyre makers in the world. One reason behind the company’s success has been its unrelenting search for intelligent production processes that maintain quality while simultaneously cutting costs. A perfect example of this approach is the changeover to highfrequency induction heating equipment from EFD Induction for the pre-heating of wire.
Nokian Tyres’ Timo Välimaa (left), and Kari Skarp inspect their new EFD Induction equipment.
The pre-heating of wire is a crucial part of the tyre-manufacturing process. It is, quite literally, the process that holds the tyre together. Obviously, the quality of the preheating process is key to ensuring a safe end-product.
Each side of a tyre contains a steel-wire bead. It is this wire bead which holds the tire onto the wheel. The wire bead of a passenger car tyre consists of a bronze-covered steel wire that is 0.9mm in diameter. This wire is wound into a ring with up to 44 turns.
To ensure the desired adhesion between layers of wire, the steel wire is covered with a thin layer of rubber by means of extrusion before entering the winding process. However, to achieve maximal adhesion during the extruding stage, the wire must first be pre-heated to 90°C.
Previously, Nokian Tyres used a resistance heater to pre-heat the wire. But frequent downtime caused by the resistance heater’s unreliability prompted Nokian Tyres to look for a smarter alternative. (The resistance heater also took up an unacceptably large floor area.)
After reviewing its options, Nokian Tyres decided to move the wire production lines… and to replace inefficient resistance heating with two EFD Induction Sinac 5 SH high- frequency converters. Each converter has a maximum output power of 5 kW and a frequency range of 100-450 kHz. The converters were installed in June 2002 on two winding production lines. Each line features 6 wires that are simultaneously pre-heated and extruded at a speed of 100 meters per minute. Since installation the EFD Induction converters have been working continuously in three-shift production. To date, there have been no interruptions caused by the converters. And unscheduled downtime is zero.