JEC COMPOSITES MAGAZINE - Issue #75 - August/September 2012 - 47

Electric cartridge heaters versus pressurized water
The design of the electric heating system can be improved with multiple control zones and faster thermocouple response times. Unfortunately, this would raise energy consumption and equipment costs. By enlarging the tool passages by 40%, the pressurized water system would raise the temperature closer to the set point, reduce the variation across the tool and consume less energy. Although not tested in this study, the cooling cycle can be the longer cycle for moulding. The water unit offers cooling through the same channels as the heating fluid and can be quickly cycled. The electric cartridge heaters offer no cooling. Cooling systems do exist to complement electric heating systems, but they require an additional chiller and channels to be added to the mould. Experience with customers has shown that the cooling cycle is of major concern and is the longer cycle by a factor of five for thermoplastic composite moulding applications.

Fig. 11: Total energy consumed to heat and hold molds at temperature

The DSC results confirm the concerns raised by the mould temperature readings during the moulding trials and the part dimensional results. The water-heated mould produced parts that had consistent and acceptable DSC results throughout their length; however, the parts produced from the electricallyheated mould had differing crystallinity percentages throughout any single part.

Conclusions
Oil versus pressurized water Even with 2x the heating capacity (24 kW vs. 12 kW), 2.8x the cooling capacity (116 kW vs. 41 kW) and 1.6x higher rated flow (100 litres/min. vs. 60 litres/min.), the oil unit was unable to reduce the mould heating and cooling times as compared to the water unit. The oil unit also consumed 69% more electricity. The most concerning limitation for the oil unit is the large temperature difference between the TCU and the mould. Electric cartridge heaters versus pressurized water Although the tool was not optimized for the water unit, the unit appears to perform better in every category as compared to electric cartridge heaters. n
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Results
Oil versus pressurized water The tool used showed a larger flow rate for the oil unit, with a rated flow of 100 litres/hour as compared to 60 for the water unit. Temperature differentials for incoming and outgoing fluid for the oil unit averaged 3.75°C. The water unit averaged 2°C. Both numbers are within the range of typical values for tools flowing at optimum rates. Based upon this, it is unlikely that either system’s efficiency in heat transfer would benefit from additional flow. Not charted in the study is the fact that the oil unit averaged a 2.75°C differential across the tool face while the water unit was less than 1°C.

No75 August - September 2012 /

jec composites magazine 47

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JEC COMPOSITES MAGAZINE - Issue #75 - August/September 2012

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