Spectacular energy savings, superior reliability and much faster response than conventional heater bands are some of the advantages offered by a newly developed induction heating system. The heating system uses electromagnetic induction - an old and well-known principle used to heat large industrial furnaces, special machines for injection moulding molten metal, thermoset molds, and some Japanese hot-runner nozzles. However, it is a relatively new concept for heating barrels of plastics molding and extrusion machines.

The system, introduced by Xaloy Inc. from USA turns the steel barrel itself into a resistance heater by generating electrical eddy currents in the metal near the outer surface of the barrel tube. Those eddy currents are induced by electrical current passing through a cable wrapped in a continuous coil around the barrel but not touching it. Although the initial cost is more than heater bands, induction heating reportedly pays for itself in several ways, and also at a faster pace, depending on machine size. Laboratory measurements indicate that the heating efficiency (relative to energy consumed) of typical mica band heaters at 200-300 degree C processing range (common in injection moulding) is likely to be only 40-60%, while that of a ceramic band heater may be 10-15% higher. The remaining energy is wasted by radiation and convection to the surrounding environment. What�s more, a new mica band loses about 10% of its initial efficiency after the first 6 hours of use because it darkens, raising its surface emissivity and consequent radiation losses. At higher barrel temperatures for engineering resins, efficiency drops even more.
In contrast, Xaloy measures induction heating efficiency at about 95%. Radiation losses are minimized by the insulating sleeves, which rise to a temperature of around 60-70 degree C during operation. The low-resistance induction coils remain cool enough to touch.
Xaloy tested the Indx system against band heaters on an 85 ton Toshiba injection press with a barrel having an ID of 36 mm, OD of 90 mm and three heating zones. Each zone used either four mica band heaters consuming a total of 3.2 kW or an induction coil driven by an inverter that delivered 2 kW. A 40 gm part was molded from a range of resins using a 30-sec cycle time. The same zone-temperature set points were used with both heater types. Current draw and barrel temperature were monitored at 1-sec intervals, and melt temperature was sampled at the nozzle to ensure consistent melt quality. Induction heating averaged only 30% as much power consumption as the mica bands.
At present manufacturing volumes, the Indx system initially costs roughly five times as much as conventional heater bands, though that differential could get reduced at a later stage. The higher the machine's throughput and the bigger the barrel, the greater the savings should be. The cost barrier makes medium to large machines using screws of 50 mm or larger - 400 tons or greater clamp capacity; the target market for Indx. The induction barrel heating can pay for itself within 18 months in energy savings alone for a machine with a 70 mm screw operating at high throughput and using electricity at 10�/kwh. Potential savings at a later stage comes from reduced wiring on new machines, less frequent replacement, savings due to fewer number of spare heater bands in inventory, reduced downtime and improved product quality.