ENERGY MANAGEMENT | TECHNOLOGY


Energy in drying Dryers can also be a key component in a pro- gramme to save energy in the injection moulding operation (see also the feature on drying in Injection World March 2020). “For injection moulders who use resins that require pre-drying, one way to cut operating costs significantly is to switch to new, advanced-technology dryers,” says Frank Kavanagh, Vice President, Global Sales & Marketing, Maguire Products. “Currently tens of thousands of dryers in operation around the world are ten or more years old. The energy savings achieved with new dryers would easily justify the equip- ment investment. The savings are particularly large when the switch is from standard desiccant dryers to Ultra vacuum dryers from Maguire Products. Desiccant dryers — even new ones — are at a disadvantage for two reasons. Firstly, they require far more energy than vacuum dryers to dry resin; and secondly, they consume additional energy to regenerate desiccant.”


He says a vacuum dryer works by heating the


resin to a required temperature, then, in a separate vessel, evacuating air. As air pressure drops, water boils, or volatilises, at lower and lower tempera- tures. Under normal conditions at sea level, with atmospheric pressure at 760 mm (29.92 in) of mercury, water boils at 100˚C (212˚F), but in an Ultra dryer, pressure is reduced to only 635 mm (25.00 in), and the boiling point of water is reduced to 56˚C (133˚F). Under these conditions, residual moisture inside a resin pellet literally boils, becom- ing water vapour. Kavanagh says: “This is a very rapid process — much faster than what happens inside a desiccant dryer. While the energy needed to heat polymer to its required temperature is roughly the same for both vacuum and desiccant dryers, the savings with the Ultra dryer come in the next stage, when the heated resin is actually dried. While the Ultra dryer would run at 19W per pound in the drying cycle, a late-model, energy-efficient desiccant dryer would typically run at 60W per pound of material, and a new desiccant dryer with only standard energy performance could run at 100W per pound. As for a 10- or 15-year old desiccant dryer that a new dryer would replace, the energy use might run as high as 150W per pound. On the basis of energy savings alone, a new Ultra dryer could pay for itself in a matter of months. Over the course of ten years of use, energy cost savings range from US$85,000-125,000.” Kavanagh concludes that the Ultra vacuum dryer consumes 60% less energy than a comparable


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Left: Ultra


vacuum dryers from Maguire Products offer savings in energy usage, says the company


IMAGE: MAGUIRE


desiccant dryer, dries resin in one-sixth of the time, and substantially reduces the heat history to which polymer is exposed. The speed with which the Ultra system removes moisture makes properly dried polymer available for production only 30-40 minutes after a cold start, depending on the polymer. Wittmann has introduced CARD (Compressed


Air Resin Dryer) granulate dryers with energy efficiency in mind. The company says that they offer injection moulders an efficient solution to achieve optimal drying results even with small material throughput rates – as low as 0.16 kg/h. Various functions, such as the Sleep, Rampen, Count Down and Power modes, support the production process and ensure adequate as well as gentle and energy-efficient drying.


Whenever an unintended standstill of a produc- tion cell occurs, the aim of every injection moulder is to resume production as fast as possible. However, the main focus always lies on the injection moulding machine and the automation system. The granulate dryer often tends to be overlooked, which means continued drying of the material with full heating capacity during the downtime and new startup. The consequence is not only that an unnecessary amount of energy is consumed, but also that the plastic material can be damaged. Wittmann says that with CARD compressed air granulate dryers, this is prevented by the Sleep mode. Automatic filling of the drying container proceeds


directly proportional to the machine’s material consumption. While no material is extracted from the dryer, the drying container does not need to be refilled. In this case, the dryer’s control system registers the fact that the material loader used for filling the container has not shown any activity for a certain period of time. This period can be set on the


June 2020 | INJECTION WORLD 53


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