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 Technology from Egypt

Injection Barrel heating by Induction

Basic Technical considerations

The traditional band heaters used for barrel heating has what is called a thermal mass, which leads to the barrel temperature rising only when the band heater is hotter than the barrel. The barrel can cool only when the band heater is cooler than the barrel, since band heaters have significant thermal mass (heat retention) ie the heater itself requires time to heat up or cool down.

Induction coils, however, 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, hence adds zero thermal mass to the barrel. So, the only limitation in this respect is the speed of heat conduction through the steel of the barrel wall itself, besides the induction heating acts directly on the steel to a much greater depth, hence less time is required for conduction.

Induction heating takes almost no time to impart maximum heating when power is turned on, or to drop to zero input when power is turned off

The individual heater bands typically heat only 50% to 80% of the barrel circumference, depending on the size and the aligning of their latches and terminals. Hence, in any case, an uneven barrel temperature is present and screw/barrel wear are likely to result.

The heating by Induction results in more uniform heat distribution along the length and around the circumference of the barrel; because the heat develops in the barrel by turning the steel barrel itself throughout its cross section into a resistance heater.

Heating by Induction offers the following advantages :

•  Considerable  reduction in energy consumption

•  High Efficiency of heating.The heating efficiency (relative to energy consumed) of typical band heaters at the processing temperature range from 200 to 300 C common in injection molding is likely to be only 40% to 60% , whereas with induction heating the efficiency reaches over 90%. The radiation losses are minimized by the insulating layer between the Coil/s and the Barrel; the induction coils remain cool enough even to touch.

•  Considerable reduction in Resin Temperature fluctuation. The use of traditional heater bands produces wide swings in barrel temperature, nearly up to five times larger than the fluctuations with induction heating under the same control setup, precisely because external barrel heating with heater bands is too slow in responding to temperature measured deep inside the barrel. Most heater bands are instead pulsed on and off every few seconds to provide constant heat input to the outer diameter of barrel wall. Therefore, they are insensitive to rapid temperature fluctuations near the barrel ID.

Nearly zero thermal mass and deep penetration of induction heaters produces very small swings in barrel temperature even when using the standard temperature controller and temperature sensing from a deep-well thermocouple.

The rapid response of the induction heating to the heat control is able to perfectly synchronize the temperature-control interval with down to 30-sec machine cycle, and the rapid response to the heat control, reduced fluctuation in temperature and the more uniform barrel temperatures lead to potentially improved quality of plastic products.

•  Fast start up. Induction heating provides faster startups by bringing the barrel up to the set temperature min. three times faster than band heaters. During downtime, the insulation layer between the Barrel and the induction Coil/s serve to a big extent in retaining barrel heat.

•  Reliability of the System. Inverters are highly reliable in continuous use, and failures of the induction Coil/s are very rare. While with traditional heating, heater burnout is a common problem among molders, and molders frequently operate unknowingly with failed heater bands; it is difficult and time consuming to identify the failed Band which usually leads to quality problems and hence higher maintenance costs from uneven wear of screws and barrels.

Installation of Retrofits to an existing machine

We undertake  replacing  the traditional  Barrel heating systems on existing Machine by induction heating System,  we only shall require  receiving some needed Machine Data  included on a questionnaire which will be provided by us, to be filled in by the Client after receiving the Inquiry,   

No interference with the machine control whatsoever shall take place on installing a Retrofit for the Induction heating on an older machine, and minimum changes or alterations in the machine board might be necessary, the supply to the induction heating system is usually connected to the outlet provided in the machine control for the conventional heaters

    

INDUCTION Heating  CONTROL ELECTRONICS  FREQUENCY INVERTERS